Durability and Strength Improvement of Ambient-Cured Geopolymer Concrete using Polypropylene Fibers

Durability and Strength Improvement of Ambient-Cured Geopolymer Concrete using Polypropylene Fibers | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Research Article Durability and Strength Improvement of Ambient-Cured Geopolymer Concrete using Polypropylene Fibers Sifiso P. Radebe, Makungu M. Madirisha, Bolanle D. Ikotun, Opeoluwa R. Dada This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-6778704/v1 This work is licensed under a CC BY 4.0 License Status: Published Journal Publication published 29 Jul, 2025 Read the published version in Iranian Journal of Science and Technology, Transactions of Civil Engineering → Version 1 posted 9 You are reading this latest preprint version Abstract This study investigated the effects of polypropylene fiber (PPF) reinforcement on the mechanical and durability properties of ambient-cured geopolymer concrete (GPC) composed of fly ash and ground granulated blast furnace slag (GGBS). While GPC offers a sustainable alternative to Portland cement due to its lower carbon footprint and elimination of heat curing, its inherent brittleness and low tensile strength limit structural applications. To address these challenges, PPF was incorporated at varying dosages (0%, 0.5%, 1%, and 1.5%) to assess its impact on workability, compressive strength, flexural strength, and durability. The results indicate that 1.0% PPF significantly improved flexural strength (3.35 MPa at 90 days) and overall toughness while maintaining compressive strength. However, higher PPF content reduced workability and increased porosity due to fiber agglomeration. Durability assessments showed that PPF reinforcement lowered oxygen permeability and chloride ingress, enhancing resistance to aggressive environments. X-ray diffraction (XRD) analysis confirmed the formation of sodium alumino-silicate hydrate (N-A-S-H) and calcium alumino-silicate hydrate (C-A-S-H) gels, contributing to matrix densification and reduced permeability. These findings suggest that PPF reinforcement enhances durability by refining the pore structure, as evidenced by reduced permeability and water absorption measurements. However, workability decreased at higher PPF contents due to fiber agglomeration. Despite challenges with fiber dispersion at higher dosages, statistical analysis revealed a strong correlation between compressive and flexural strength, underscoring the role of fiber content in mechanical performance. These findings demonstrate that PPF-reinforced GPC has strong potential for sustainable construction applications, particularly in environments requiring enhanced durability. Future research should focus on optimizing fiber dispersion techniques, refining mix designs, and evaluating long-term performance for large-scale implementation. Ambient temperature curing Durability enhancement Geopolymer concrete Polypropylene fiber Sustainable construction Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 1. Introduction The construction industry is undergoing rapid expansion, driven by the increasing demand for infrastructure. However, this growth presents significant environmental challenges, primarily due to the widespread use of Portland cement (PC) in concrete production. PC manufacturing is highly energy-intensive, depletes natural resources, and contributes nearly 8% of global CO₂ emissions, making it a major factor in climate change (Bokkhunthod et al., 2022 ; Sivakrishna et al., 2020 ). As urbanization accelerates, the need for sustainable alternatives to PC becomes increasingly urgent to mitigate the construction sector’s carbon footprint and environmental impact (Sivakrishna et al., 2020 ; Aydın, 2023 ). Geopolymer concrete (GPC) has emerged as a promising alternative, synthesized from aluminosilicate materials such as fly ash and slag. GPC offers several advantages, including lower greenhouse gas emissions, superior thermal stability, and enhanced resistance to chemical attack (Reed et al., 2014 ; Ganesan et al., 2015 ). Additionally, the use of industrial by-products in GPC reduces waste and promotes sustainability (Esparham & Ghalatian, 2022 ). However, despite these benefits, GPC adoption remains limited due to its inherent brittleness, low tensile strength, and poor flexural performance, which can lead to premature cracking and restrict its use in load-bearing applications (Triwulan et al., 2016 ). These mechanical limitations necessitate reinforcement strategies to improve crack resistance and structural integrity (Shaikh, 2019 ; Sarker et al., 2014 ). To address these weaknesses, fiber reinforcement has been identified as an effective strategy for improving mechanical and durability properties. Fibers such as steel, glass, and synthetic fibers are commonly used in PC concrete to enhance ductility and toughness (Shaikh, 2019 ; Korniejenko et al., 2020 ). Among these, polypropylene fibers (PPF) stand out due to their lightweight nature, corrosion resistance, and cost-effectiveness, making them a viable option for improving concrete performance (Ganesan et al., 2015 ; Letsosa et al., 2024 ). While PPF has been extensively studied in PC concrete, research on its integration into GPC, particularly under ambient curing conditions, remains limited. This knowledge gap is significant because ambient curing eliminates the need for high-temperature processing, making GPC more practical and energy-efficient. Addressing this limitation is crucial for advancing GPC’s potential as a viable and sustainable alternative to PC concrete. This study investigated the role of polypropylene fibers in enhancing the mechanical and durability properties of ambient-cured GPC, focusing on optimizing fiber content for strength and environmental resistance. Unlike conventional GPC formulations that often require high-temperature curing, this study focuses on ambient curing, which enhances practicality for real-world construction applications. By systematically examining the effects of varying PPF content on workability, compressive and flexural strength, oxygen permeability, and water sorptivity, this research provides a comprehensive understanding of how polypropylene fibers influence the performance of GPC without altering its fundamental geopolymerization chemistry. 2. Materials and Methods 2.1 Materials The materials used in this study were sourced from reputable suppliers to ensure the production of high-quality geopolymer concrete. Sodium hydroxide pellets (99% purity), procured from MINEMA Chemicals, South Africa, were used to prepare the alkaline solution required for geopolymerization. Polypropylene fiber strands (PPF), supplied by SIKA, South Africa, were incorporated to improve tensile strength and durability. The aggregates used included 20 mm granite stone from Elsana, South Africa and dune sand from Atlantic Sands, South Africa, selected for their optimal particle packing and mechanical performance. Additionally, crusher dust from Hornefels Tygerberg, South Africa was used as a fine aggregate. The binder materials consisted of Class F fly ash and ground granulated blast furnace slag (GGBS), procured from AfriSam, South Africa. Fly ash was chosen for its pozzolanic properties, while GGBS contributed to early strength development. All materials were handled in strict accordance with safety protocols, and personnel used appropriate personal protective equipment (PPE) to ensure safe working conditions throughout the preparation process 2.2 Methods 2.2.1 Aggregate tests Grading A sieve analysis was conducted as described in SANS 3001-AG1 to determine the particle size distribution of fine and coarse aggregates. The test samples were dried at 110°C in a well-ventilated oven and cooled to room temperature. To calculate the fineness modulus, the dried material was successively sieved through sieves of the following apertures: 7.1 mm 5 mm, 2 mm, 1 mm, 0.6 mm, 0.3 mm, 0.15 mm, 0.075 mm and pan, in the order of the largest aperture sieve to the smallest aperture sieve. The following apertures were used to sieve coarse aggregates: 28 mm, 20 mm, 14 mm, 10 mm, 7.1mm and 5 mm. The shape of aggregate particles and variations can influence the concrete's strength and workability as well as water demand. Density The bulk densities of the crusher dust and fine aggregates were measured according to SANS 5845:2006, using both compacted and uncompacted states. Triplicate measurements were taken to ensure accuracy, and the relative density of aggregates was determined following SANS 3001-AG20:2011. These results informed the mix design to optimize strength and durability. 2.2.2 Chemical composition of Fly Ash and GGBS The chemical composition of fly ash and GGBS samples was determined using X-ray fluorescence (XRF) spectrometer. Samples were finely grounded to achieve homogeneity and then compressed into pellets using a Hydraulic Workshop Press WPP T15. XRF analysis was performed using an instrument equipped with optimized parameters for voltage, current, and measurement time, tailored to the elements of interest. Quantitative analysis was conducted through empirical calibration, incorporating corrections for matrix effects to ensure accurate elemental concentration measurements. 2.2.3 Mixing and Curing Process The concrete mixing and curing process adhered to SANS 5861-1:2006 and SANS 5862-3:2006 standards, ensuring precision and consistency throughout the preparation as illustrated in Fig. 1 . Cube and beam molds were treated with a release agent to facilitate smooth demolding. Coarse and fine aggregates, granulated blast furnace slag, fly ash, and polypropylene fibers were accurately weighed using a digital scale and mixed in a 25-litre steel mixing pan. Water and sodium hydroxide solution were then added to prepare the geopolymer concrete. Prior to filling, the molds were thoroughly cleaned and coated with a release agent. The concrete was placed into molds in layers of approximately 5 cm, compacted using a vibrating table, and finished with a trowel to smooth the top surface. The specimens were cured in a cool, moist environment for 24 hours before demolding. Once demolded, the samples were marked for identification and further cured at room temperature for 7,28 and 90 days. This methodical procedure ensured compliance with testing standards and to achieve the desired concrete strength. 2.2.4 Concrete tests Workability The workability of each freshly mixed concrete was assessed by measuring its slump following SANS 5862-1:2006. Workability refers to the concrete’s ease of transportation, placement, compaction, and finishing without segregation of its components. Compressive and Flexural Strength Concrete cubes were prepared from the molds and then cured at room temperature as illustrated in Fig. 2 with accordance to SANS 5861-3:2006 Concrete tests: Part 3 – Making and curing of test specimens, then are crushed after 7 days using a compressive strength testing machine. This procedure was conducted using the relevant South African National Standard (SANS 5863:2006). Compressive strength testing was conducted at 7,28 and 90 days using the Toni Technik (Model 2041) compressive testing machine as illustrated in Fig. 3 . Concrete beams were prepared using the beam molds and then cured at room temperature, following SANS 5861-3:2006 standards for making and curing test specimens. After 7 days, the beams were tested using a flexural machine that applied loads until the beams failed. This testing followed SANS 5864:2006 standards for flexural strength of hardened concrete as depicted in Fig. 3 . The flexural strength testing was conducted at 7, 28, and 90 days to evaluate the strength development over time. Oxygen permeability The oxygen permeability test was conducted following SANS 3001-CO3-1:2015 and SANS 3001-CO3-2:2015. Samples were cored from a concrete cube and subjected to an oven-drying process to eliminate any residual moisture. After drying, the specimens were allowed to cool in a controlled, dry environment to prevent the absorption of ambient moisture. Once cooled, the specimens were placed into an oxygen permeability testing apparatus, which applied a constant pressure of oxygen to the specimens. The test measures the rate at which oxygen permeates through the concrete over a specified period. This measurement is crucial for determining the Oxygen Permeability Index (OPI) of the concrete, which indicates its ability to resist the ingress of oxygen. A lower permeability suggests greater durability, an important factor in assessing the concrete's performance and longevity in various applications. Water sorptivity and porosity The water sorptivity test was conducted following SANS 3001-CO3-1:2015 and SANS 3001-CO3-3:2015 standards. The process involved preparing and drying the concrete specimens, allowing them to cool, before partially submerging them in water. The rate of water absorption was monitored and recorded over time to evaluate the concrete's resistance to water ingress, providing key information on its durability. Chloride conductivity test The chloride conductivity test was performed per SANS 3001-CO3-1:2015 and SANS 3001-CO3-4:2015 standards. Concrete specimens were prepared and immersed in a 3.5% NaCl solution, with a constant voltage of 60V DC applied for 6 hours. The chloride ion penetration was measured to calculate the permeability coefficient, which indicates the concrete's resistance to chloride ion ingress and its durability in chloride-exposed environments. X-ray Diffraction (XRD) Test X-ray diffraction (XRD) analysis was conducted following ASTM standards E937 and E1149, which specify the procedures for X-ray powder diffraction data acquisition and analysis. The sample was compressed into a pellet using a pressing machine at a load of 70 kN. XRD measurements were carried out using an X-ray diffractometer operating at 30 kV and 10 mA, with a Cu Kα radiation source (λ = 1.54060 Å). Data were collected over a scanning range of 5.001° to 64.982° (2θ). The pellets were exposed to X-rays emitted from a copper tube anode, and the diffracted signals were detected using a LYNXEYE detector. The detector was set to an opening angle of 5.812°, with slit sizes of 0.6 mm. 3. Results and Discussion 3.1 Chemical composition of fly ash and GGBS The chemical composition of Class F fly ash and Ground Granulated Blast Furnace Slag (GGBS), as presented in Table 1 , highlights their suitability for geopolymer applications. A key factor in geopolymerisation is the presence of silica (SiO₂) and alumina (Al 2 O 3 ) content which plays a crucial role in forming a dense and durable aluminosilicate network (Cao et al., 2024). However, it is important to note that only the amorphous fraction of SiO₂ is reactive in geopolymerisation. Based on literature estimates, the amorphous silica content in Class F fly ash typically ranges from 50–85% of the total SiO₂ (Davidovits, 2008 ; De Silva et al., 2007 ). Assuming 70% amorphous SiO₂, the estimated reactive portion in 53.83% is approximately 37.7%. Similarly, GGBS contains 37.10% SiO₂, of which 85–95% is typically amorphous due to its rapid quenching during production (Juenger & Siddique, 2015 ). Assuming 90% amorphous SiO₂, the estimated reactive portion is approximately 33.4%. This high amorphous content facilitates dissolution and reaction with alkali activators, forming both aluminosilicate and calcium-silicate-hydrate (C-S-H) phases. The alumina (Al₂O₃) content in fly ash, measured at 33.18%, promotes cross-linking within the geopolymer matrix, strengthening the material and improving its resistance to degradation (Dimas et al., 2009 ). In contrast, the calcium oxide (CaO) content in fly ash is relatively low at 3.63%, indicating its predominantly pozzolanic nature. This low CaO content supports the development of thermally and chemically stable geopolymer structures, distinguishing them from cementitious systems that rely on calcium-based hydration reactions (Farhan et al., 2021 ). Conversely, GGBS has a significant CaO content of 33.20%, which enhances pozzolanic activity and contributes to early strength development in geopolymer systems. Minor oxides such as magnesium oxide (MgO), potassium oxide (K₂O), sodium oxide (Na₂O), titanium dioxide (TiO₂), manganese oxide (Mn₂O₃), and phosphorus pentoxide (P₂O₅) are present in trace amounts in both materials. TiO₂ may provide additional benefits, such as enhanced UV resistance, improving the material’s durability in outdoor applications (Mohammed et al., 2021 ). The redox chemistry of minor oxides, particularly Mn₂O₃ and Fe₂O₃, influences polymerization kinetics and the structural stability of the geopolymer matrix. These oxides act as redox-active species, modifying oxidation states and affecting reactivity and material stability. Additionally, MgO in GGBS, measured at 9.43%, contributes to geopolymer matrix stability by forming Mg-substituted aluminosilicate phases, enhancing sulphate resistance and durability in aggressive environments. The loss on ignition (LOI) is recorded at 0.80% for fly ash and 1.86% for GGBS, indicating high material purity with minimal unburned carbon. A low LOI suggests consistent geopolymerisation reactions, reducing potential interference with the development of the geopolymer matrix (Luhar & Khandelwal, 2015 ). The higher proportion of amorphous silica in fly ash compared to the crystalline forms in GGBS accelerates dissolution, influencing geopolymerisation rates and strength development. Moreover, alkali cations such as Na⁺ and K⁺ also influence the charge balance and network stability within the geopolymer matrix. Potassium ions (K⁺) tend to form larger pore structures than sodium ions (Na⁺), which could affect the permeability and mechanical properties of the geopolymer concrete. The SiO₂/Al₂O₃ ratio for fly ash is approximately 1.93, while that for GGBS is approximately 3.23. Both ratios fall within the optimal range (1.5–3.5) for achieving a well-polymerized aluminosilicate network (Davidovits, 2008 ). This ratio is crucial for promoting effective polymerization, which in turn enhances the mechanical strength, durability, and thermal stability of the geopolymer. Overall, the complementary chemical compositions of Class F fly ash and GGBS suggest that their combined use could optimize geopolymer concrete properties, balancing early strength development with long-term durability. The integration of hybrid geopolymerisation and the influence of alkali and minor oxides underscore the complexity and potential for fine-tuning geopolymer properties to meet specific performance requirements. This analysis confirms the suitability of these materials for producing high-performance geopolymer concrete. Table 1 Chemical composition of class F fly ash and GGBS Oxide/Element % composition Class F fly ash GGBS SiO 2 53.83 37.10 Al 2 O 3 33.18 17.51 Fe 2 O 3 4.16 0.56 CaO 3.63 33.20 MgO 0.93 9.43 K 2 O 0.68 1.61 Na 2 O 0.11 0.34 TiO 2 1.51 0.81 Mn 2 O 3 0.06 1.21 P 2 O 5 0,44 0.01 Cr 2 O 3 0.00 - SrO 0.00 - SO 3 0.80 - S - 1.30 Loss on ignition 0.80 1.86 Sum 99.4 99.9 3.2 Physical properties of aggregates The physical properties of fine and coarse aggregates, as presented in Table 2 , significantly influence the performance of geopolymer concrete. Sieve analysis results indicate that the 20 mm stone aggregates fall within the 13.2 mm–26.5 mm range, ensuring optimal packing and reduced void content, which enhances the concrete matrix density and potentially improves compressive strength (Dimas et al., 2009 ). Likewise, the fine aggregates, ranging from 0.075 mm to 4.75 mm, with a majority in the finer range, contribute to improved packing and mix cohesiveness. The angular and rough-textured nature of the 20 mm aggregates is expected to enhance mechanical interlocking within the matrix, increasing overall strength, while the smoother texture of fine aggregates improves workability and handling without compromising structural integrity. The specific gravity values of approximately 2.65 for the 20 mm stone and 2.60 for the fine aggregates align with those required for producing high-density, high-performance geopolymer concrete (Mohammed et al., 2021 ). Additionally, the absorption capacities of 0.5% for coarse aggregates and 1.0% for fine aggregates indicate minimal water uptake, which supports efficient geopolymerisation while maintaining workability and strength development. These characteristics confirm the suitability of the selected aggregates for producing durable and structurally robust geopolymer concrete. Table 2 Physical properties of fine aggregates and coarse aggregates Aggregate Type Coarse Aggregate Fine Aggregate Size Range (mm) 20 mm 0.075 mm to 4.75 mm Specific Gravity 2.65 2.6 Absorption Capacity (%) 0.5 1 Texture Angular and rough-textured Smoother texture 3.3 Workability The mix design of the geopolymer concrete, as detailed in Supplementary Table 1, maintained a consistent binder-to-aggregate ratio across all samples, ensuring a controlled evaluation of workability. Slump tests, with results presented in Table 3 , assessed the impact of polypropylene fiber content on concrete performance. The control mix (0% fiber) exhibited a slump of 120 mm, indicating moderate workability, which aligns with the typical behavior of geopolymer concrete as reported by Dimas et al. ( 2009 ). This level of workability is ideal for construction scenarios requiring a balance between ease of placement and resistance to segregation. The incorporation of fibers at 0.5% and 1% resulted in improved workability, with slump values rising to 140 mm and 150 mm, respectively. This enhancement highlights the positive influence of fiber dispersion on mix flowability, consistent with findings by Mohammed et al. ( 2021 ). Similarly, Zheng et al. ( 2024 ) reported that optimized ambient-cured geopolymer concrete (GPC) can achieve workability levels comparable to conventional concrete when supplemented with appropriate superplasticizers. Such improvements are advantageous in construction, facilitating easier placement and compaction, especially in complex formwork and heavily reinforced sections. The increased slump values at these fiber dosages indicate an optimal mix where fibers enhance mechanical performance without compromising workability. Conversely, at the highest fiber concentration (1.5%), the slump value dropped significantly to 60 mm, suggesting a marked reduction in workability due to fiber entanglement and increased mix stiffness. This decrease restricts flow, making handling and compaction challenging, potentially leading to defects such as honeycombing. These observations align with Dimas et al. ( 2009 ), who noted that excessive fiber content can negatively affect the fresh properties of fiber-reinforced concrete. From a practical standpoint, these results emphasize the importance of optimizing fiber dosage in geopolymer concrete. The improved workability at 0.5% and 1% fiber content suggests these levels provide a desirable balance between tensile enhancement and ease of handling. However, the substantial workability reduction at 1.5% highlights the need for caution when increasing fiber content. If higher fiber concentrations are required for specific mechanical performance improvements, modifications such as incorporating superplasticizers may be necessary to maintain workability. These findings provide crucial insights into geopolymer concrete mix design, ensuring both mechanical efficiency and practical constructability. Table 3 Slump test results for geopolymer concrete reinforced with fiber Geopolymer concrete with amount fiber in percentage Slump (mm) 0 120 0.5 140 1 150 1.5 60 3.4 Compressive Strength The impact of polypropylene fiber content on the compressive strength of geopolymer concrete over different curing periods; 7, 28, and 90 days is illustrated in Fig. 4 . The results in Supplementary Table 2 highlight the intricate balance between fiber content and the geopolymerisation process, offering insights into optimizing mix designs for construction applications. The control mix (0% fiber) exhibited a compressive strength of 30.00 Mpa at 7 days, which increased to 40.40 Mpa at 28 days and peaked at 46.25 Mpa at 90 days. This steady development is characteristic of geopolymer concrete, as noted by Dimas et al. ( 2009 ), and is attributed to the geopolymerisation process, wherein aluminosilicate precursors react with an alkaline activator to form a stable three-dimensional Si-O-Al network. This dense matrix enhances compressive strength over time, making geopolymer concrete suitable for load-bearing applications, such as beams and columns. Additionally, its lower calcium content compared to Portland cement reduces micro-cracking and shrinkage, improving durability in aggressive environments. At 0.50% fiber content, the 28day compressive strength slightly decreased to 39.66 Mpa, but at 90 days, it remained comparable to the control mix at 47.14 Mpa. This aligns with the findings of Farhan et al. ( 2021 ), who reported that moderate fiber addition enhances workability without significantly compromising strength. Although polypropylene fibers do not directly participate in the geopolymerisation reaction, they act as a reinforcement mechanism, bridging micro-cracks and enhancing energy absorption. This crack control is vital for structural integrity under dynamic loads. From a practical perspective, improved workability at this fiber content ensures better compaction and fiber dispersion, reducing defects in precast elements and complex formwork applications. However, at 1.00% fiber content, a notable reduction in compressive strength was observed across all curing ages, recording 27.31 Mpa at 7 days, 38.63 Mpa at 28 days, and 44.11 Mpa at 90 days. This suggests that excessive fiber content disrupts the geopolymer matrix, leading to fiber entanglement and weak zones within the structure. Mohammed et al. ( 2021 ) similarly reported that high fiber volumes increase stiffness and reduce workability. The high fiber concentration may introduce voids and reduce effective bonding between the binder and aggregates, compromising matrix integrity. In construction, such mixtures pose challenges in placement and compaction, increasing the risk of honeycombing and reduced load-bearing capacity, which is particularly critical for high-rise buildings and infrastructure in seismic zones. At 1.50% fiber content, the compressive strength showed a mixed trend, recording 28.59 Mpa at 7 days, 40.90 Mpa at 28 days, and a slight decline to 41.53 Mpa at 90 days. This unexpected reduction at 90 days suggests that excessive fiber content negatively impacts long-term performance, possibly due to increased void formation and poor fiber-matrix adhesion, as highlighted by Dimas et al. ( 2009 ). The hydrophobic nature of polypropylene fibers may further hinder proper wetting by the geopolymer paste, leading to weak interfacial zones. In practical applications, this can compromise durability, particularly in marine and industrial environments where resistance to chloride and sulfate attacks is essential. Poor interfacial bonding could lead to premature deterioration, raising maintenance costs and reducing service life. These findings indicate that an optimal fiber content range of 0.50–1.00% achieves a balance between improved workability and adequate compressive strength. Maintaining fiber content within this range supports construction efficiency by ensuring uniform stress distribution and minimizing defects. Furthermore, optimizing fiber dosage enhances sustainability by reducing repair needs and prolonging structural lifespan. The inherent ability of geopolymer concrete to incorporate industrial by-products, such as fly ash and slag, further aligns with green construction objectives, significantly lowering CO₂ emissions compared to conventional cement-based systems. Comparing ambient and heat curing effects on geopolymer concrete, heat curing significantly accelerates geopolymerisation, leading to higher early-age compressive strength. Studies show that heat-cured geopolymer concrete can exceed 50 Mpa at 28 days, outperforming ambient-cured concrete, which generally exhibit lower strengths in early curing stages (Zheng et al., 2024 ). The enhanced early strength is attributed to the increased reactivity of alkali-activated materials at elevated temperatures, promoting faster Si-O-Al bond formation. Rabie et al. ( 2022 ) reported that heat curing results in a denser microstructure with reduced porosity and improved durability, making it ideal for environments requiring high strength and chemical resistance. However, rapid setting times in heat-cured geopolymer concrete can pose challenges, particularly in maintaining workability during placement, as noted by Duan et al. ( 2021 ). High fiber content further exacerbates this issue by increasing mix stiffness and reducing flowability, leading to difficulties in achieving a defect-free structure. Consequently, while heat curing enhances strength, careful mix design adjustments, such as using superplasticizers, may be necessary to mitigate workability loss, ensuring both mechanical performance and practical constructability. 3.5 Flexural Strength The flexural strength results illustrated in Fig. 5 highlight the significant impact of polypropylene fiber content on the performance of geopolymer concrete (GPC), underscoring the dynamic interplay between fiber reinforcement and the chemical processes within the geopolymer matrix. For the control mix containing 0% fiber, the average flexural strength progressively increased from 1.50 Mpa at 7 days to 2.28 Mpa at 90 days as illustrated in Supplementary Table 3. This consistent strength development is attributed to the ongoing geopolymerisation process, where aluminosilicate precursors react with alkaline activators to form a robust three-dimensional network (Dimas et al., 2009 ). However, in the absence of fiber reinforcement, the material exhibits limited crack resistance and toughness, rendering it more prone to brittle failure under flexural loads. This finding suggests that unreinforced GPC may be better suited for structural applications primarily experiencing compressive forces, such as columns, where tensile and flexural stresses are minimal. The introduction of 0.5% fiber content improved flexural strengths, reaching 1.67 MPa at 7 days, 2.34 Mpa at 28 days, and 2.52 Mpa at 90 days. This enhancement is attributed to the fiber’s physical interaction with the geopolymer matrix. As demonstrated by Farhan et al. ( 2021 ), polypropylene fibers are chemically inert in alkaline environments and do not interfere with geopolymerisation. Instead, their presence enhances toughness by bridging micro-cracks and distributing stress more evenly, leading to improved post-crack ductility. This property is particularly advantageous for structural elements susceptible to cracking, such as pavements and slabs, where thermal stresses and shrinkage could compromise performance. The mix with 1.0% fiber content exhibited the highest flexural strength, reaching 3.35 Mpa at 90 days, indicating an optimal balance between fiber dispersion and the integrity of the geopolymer matrix. The durability of polypropylene fibers within the alkaline environment plays a crucial role in reinforcing the composite. As noted by Mohammed et al. ( 2021 ), their resistance to degradation enhances mechanical properties, while their ability to bridge cracks improves energy absorption and stress transfer. Consequently, 1.0% fiber-reinforced GPC is particularly suited for infrastructure exposed to harsh conditions, such as marine environments or high-temperature industrial settings. However, increasing the fiber content to 1.5% led to a decline in flexural strength, with values of 1.56 Mpa at 7 days, 2.43 Mpa at 28 days, and 2.81 Mpa at 90 days. This reduction can be attributed to fiber agglomeration and suboptimal wetting by the geopolymer matrix, creating weak interfacial zones that act as stress concentrators. Furthermore, Dimas et al. ( 2009 ), also highlighted that excessive fiber content poses challenges related to effective compaction and densification, increasing the likelihood of voids that compromise overall strength. Therefore, this research finding reinforces the importance of optimizing fiber content to maximize mechanical benefits without inducing defects. These results align with previous studies emphasizing the critical role of fiber reinforcement in enhancing the mechanical properties of geopolymer concrete. Chen et al. (2020) demonstrated that optimal fiber content improves flexural strength while maintaining desirable workability, while Ahlawat et al. ( 2025 ) suggested that fiber fractions around 1.0% yield the best mechanical performance without negatively impacting material density and structural integrity. Comparative analysis between ambient-cured and heat-cured GPC further underscores the significance of this research. Heat curing accelerates the geopolymerisation process, leading to higher early-age compressive and flexural strengths due to the enhancement of the Al-Si network, as demonstrated by Zheng et al. ( 2024 ). Heat-cured GPC often achieves flexural strengths exceeding 4 Mpa at 28 days, significantly outperforming ambient-cured mixes, which exhibit lower early strengths but develop more robust long-term properties due to slower yet continuous geopolymerisation (Rabie et al., 2022 ). 3.6 Durability 3.6.1 Oxygen permeability The assessment of permeability in fiber-reinforced geopolymer concrete (GPC) reveals critical insights into the relationship between polypropylene fiber content and durability characteristics. Table 4 presents the OPI results for samples containing 0%, 0.5%, 1%, and 1.5% fiber content. Table 4 Oxygen Permeability Index (OPI) of Geopolymer Concrete with Different Fiber Contents Fiber content percentage OPI 0% 0.5% 1% 1.5% 9.435 9.502 9.185 9.252 The control sample, with an average permeability index (OPI) of 9.435, served as a baseline, indicating moderate permeability. The inclusion of 0.5% fiber slightly increased the OPI to 9.502, signifying reduced permeability. This improvement can be attributed to enhanced matrix densification and reduced pore connectivity, which are essential for limiting the ingress of water and chlorides that compromise long-term structural integrity. Conversely, the 1.0% fiber sample exhibited a reduced OPI of 9.185, indicating increased permeability. This suggests that inadequate fiber dispersion may have led to micro-channel formation around the fibers, disrupting the geopolymer matrix continuity and facilitating the movement of harmful agents (Chen et al., 2023 ). Similarly, the 1.5% fiber mix recorded an OPI of 9.2525, further reinforcing the observation that excessive fiber content can weaken matrix integrity by promoting void formation (Mohammed et al., 2021 ). Among all tested samples, the 0.5% fiber content demonstrated the highest OPI of 9.502, signifying the lowest permeability. Notably, this value falls within the optimal range for enhancing concrete durability, underscoring its resistance against water, chlorides, and gases—an essential property for maintaining structural longevity, especially in moisture-prone and chemically aggressive environments. These findings align with prior studies emphasizing the role of reduced permeability in improving concrete resilience. Mechtcherine and Schmidt ( 2018 ) emphasized that minimizing permeability is fundamental for long-term durability, while Ganesh et al. (2021) demonstrated that optimized fiber content enhances microstructural properties, mitigating void formation and improving material longevity. The significance of low-permeability GPC is particularly relevant in infrastructure applications exposed to harsh environmental conditions, such as marine and industrial settings. The superior performance of 0.5% fiber-reinforced GPC in restricting the penetration of harmful substances makes it a viable choice for critical structural applications, addressing modern construction demands for enhanced durability and resilience. 3.6.2 Water sorptivity and porosity The calculated sorptivity (g/h⁰·⁵) for geopolymer concrete with 0%, 0.5%, 1%, and 1.5% fiber content at various curing times (0.5–3 hours) is presented in Fig. 6 . Sorptivity, determined from mass gain data (ΔM) using the formula ΔM/t⁰·⁵, measures the material’s capacity to absorb and transmit water through capillary action. The evaluation of initial sorptivity in fiber-reinforced geopolymer concrete (GPC) provides critical insights into the effects of polypropylene fiber content on water absorption characteristics. The control mix, without fiber reinforcement, exhibited an initial sorptivity of 11.19 g/h⁰·⁵ as shown in Supplementary Table 4 within the first 0.5 hours, indicating rapid water uptake. This high sorptivity can be attributed to the early – stage geopolymerisation reactions, where water facilitates the dissolution of aluminosilicate precurs–rs such as metakaolin or fly ash. These observations align with Davidovits ( 2008 ), who emphasized the role of silica and aluminum dissolution in forming a three-dimensional network of N-A-S-H (Sodium Alumino-Silicate Hydrate) gels. As geopolymerisation progresses, the network densifies, leading to a substantial sorptivity reduction to 0.14 g/h⁰·⁵ at 3 hours. This decline reflects the precipitation of N-A-S-H gels, which block capillary pores and reduce connectivity, a phenomenon corroborated by Provis and Bernal ( 2014 ), who documented similar pore-blocking behavior in alkali-activated materials. While the initially high sorptivity suggests poor early-age durability, the long-term decrease reinforces the characteristic behavior of geopolymer concretes, where early water absorption supports ionic mobility for continued geopolymerisation and microstructural refinement. The introduction of 0.5% fibers resulted in an initial sorptivity of 11.75 g/h⁰·⁵, slightly higher than the control mix. This increase can be attributed to capillary action introduced by the fibers, which provide additional pathways for water ingress. Studies by Kwan and Wong ( 2008 ) have demonstrated that fiber incorporation enhances initial water absorption due to the hydrophilic nature of fibers, which introduce hydroxyl groups that facilitate water uptake. Additionally, fibers modify the interfacial transition zones (ITZ) between the fibers and the geopolymer matrix, creating localized areas of increased alkalinity that expedite secondary geopolymerisation reactions. Notably, the study observed that enhanced ion mobility within the ITZ accelerates N-A-S-H gel formation, leading to a quicker reduction in sorptivity over time. After three (3) hours, the sorptivity significantly decreased, indicating that the initial pathways created by fibers were effectively sealed through ongoing geopolymerisation. This observation supports Kwan and Wong’s ( 2008 ) findings that fiber inclusion enhances long-term durability, primarily due to matrix densification. Conversely, higher fiber contents of 1% and 1.5% resulted in the highest initial sorptivity values of 12.03 and 12.44 g/h⁰·⁵ respectively, due to amplified capillary action from the increased volume of fiber interfaces. The enhanced surface area of fibers likely promotes the dissolution of aluminosilicate species, fostering the development of more extensive N-A-S-H networks. However, excessive fiber content may increase pore connectivity, potentially compromising long-term durability if not optimally balanced. This aligns with findings by Addis et al. ( 2022 ), who noted that while higher fiber volumes may initially enhance sorptivity, they can also contribute to fiber agglomeration and micro-void formation, acting as weak points in the matrix. Despite the variations in initial sorptivity, the gradual reduction across all mixes underscores the benefits of ongoing polycondensation reactions, transforming the initially porous matrix into a denser network. The potential formation of C-A-S-H (Calcium Alumino-Silicate Hydrate) gels may further enhance this effect by providing additional pore-blocking mechanisms, like calcium silicate hydrate precipitation that mitigates capillary action. This perspective aligns with the findings of Addis et al. ( 2022 ), emphasizing the need to optimize both fiber content and the geopolymerisation process to enhance durability. While fiber incorporation significantly increases initial sorptivity, particularly at higher contents, it also promotes a more uniform moisture distribution within the geopolymer matrix. This distribution helps mitigate early-age cracking, reinforcing long-term durability by sustaining geopolymerisation reactions. The observed trends align with Kwan and Wong ( 2008 ) and Addis et al. ( 2022 ), highlighting the role of fibers in modifying water transport pathways and improving the microstructural integrity of geopolymer concrete. 4.8.S Chloride conductivity The influence of fiber content on the porosity and conductivity of geopolymer concrete was investigated to assess its impact on durability. Table 5 presents the results, revealing the complex interplay between fiber addition and the concrete microstructure, emphasizing the role of fiber distribution and its chemical interactions with the geopolymer matrix. Notably, chloride conductivity remained consistently low (0.025 mS/cm) across all fiber content samples, indicating that fiber addition did not significantly affect resistance to chloride ion penetration. This stability can be attributed to the chemically robust aluminosilicate network in the geopolymer matrix, which effectively limits ion transport irrespective of fiber content. The aluminosilicate gel, characterized by Si-O-Al and Si-O-Si bonds, forms a dense structure with low ionic diffusivity, thereby maintaining similar conductivity levels across varying fiber contents (Wang et al., 2023 ). Table 5 Chloride conductivity test of geopolymer concrete Sample Conductivity (mS/cm) Porosity 0% fiber control 0.025 0.126 0.5% fiber 0.025 0.262 1% fiber 0.025 0.191 1.5% fiber 0.025 0.152 However, porosity data reveals a more intricate interaction. The control sample (0% fiber) exhibited the lowest porosity (0.126), suggesting a highly compact matrix with minimal unreacted precursors or micro-voids, likely due to an effective geopolymerization process where the dissolution of aluminosilicate sources and subsequent polycondensation yield a tightly cross-linked network. The introduction of 0.5% fiber significantly increased porosity (0.262), potentially due to the formation of microchannels or interfacial voids between fibers and the matrix. This may result from inadequate fiber-matrix interaction or weak bonding, where unreacted silanol (Si-OH) groups hinder optimal cross-linking, preventing the formation of strong Si-O-Si bridges and increasing porosity (Chen et al., 2023 ). Interestingly, porosity reduced to 0.191 at 1% fiber content, suggesting improved fiber dispersion and possible pozzolanic reactions at the fiber-matrix interface. The presence of fibers may have facilitated additional precipitation of aluminosilicate or calcium silicate hydrate (C-S-H) phases, effectively filled micro-voids and enhanced matrix density (Mohammed et al., 2021 ). This reduction in porosity supports the hypothesis that an optimal fiber content can promote secondary geopolymerization reactions, forming additional Si-O-Al bonds that fill voids. At 1.5% fiber content, porosity further decreased to 0.152, indicating a denser matrix, though still higher than the control sample. This suggests that excessive fiber content may introduce interfacial flaws despite improved dispersion. The saturation of reactive sites or limited availability of alkali ions for further geopolymerization might lead to unreacted fibers or fiber agglomeration, creating localized stress points and hindering complete void elimination (Farhan et al., 2021 ). These findings underscore the importance of optimizing fiber content to balance mechanical performance and durability. The interaction between fibers and the geopolymer matrix must account for both physical distribution and chemical compatibility to minimize porosity while maintaining chloride resistance. 3.7 Phase Composition of geopolymer concrete Quantitative X-ray diffraction (XRD) analysis was performed to characterize the phases of geopolymer concrete (GPC) samples with varying polypropylene fiber content (0%, 0.5%, 1%, and 1.5% by volume). The results, presented in Table 6 , aimed to identify dominant crystalline and amorphous phases and correlate them with the mechanical properties and durability of the concrete. The analysis highlights the significance of optimizing fiber content and its impact on key phases such as quartz (SiO₂), N-A-S-H gel (sodium aluminosilicate hydrate), and mullite (Al₆Si₂O₁₃). Table 6 XRD analysis of reinforced geopolymer concrete with varying polypropylene fiber content Sample ID 2θ (degrees) d-spacing (Å) Intensity (counts) Phase Identification 0% Fiber 26.5 3.36 12500 Quartz (SiO₂) 0% Fiber 32.1 2.79 8500 N-A-S-H gel 0% Fiber 41.5 2.18 5500 Mullite (Al₆Si₂O₁₃) 0.5% Fiber 26.5 3.36 11800 Quartz (SiO₂) 0.5% Fiber 32.1 2.79 9000 N-A-S-H gel 0.5% Fiber 41.5 2.18 6000 Mullite (Al₆Si₂O₁₃) 1% Fiber 26.5 3.36 12200 Quartz (SiO₂) 1% Fiber 32.1 2.79 8800 N-A-S-H gel 1% Fiber 41.5 2.18 5800 Mullite (Al₆Si₂O₁₃) 1.5% Fiber 26.5 3.36 11500 Quartz (SiO₂) 1.5% Fiber 32.1 2.79 8200 N-A-S-H gel 1.5% Fiber 41.5 2.18 5200 Mullite (Al₆Si₂O₁₃) Quartz was consistently present across all samples, attributed to partially unreacted silica particles from precursor materials, serving as a critical filler that enhances the mechanical strength of the geopolymer matrix. This observation aligns with Provis and Bernal ( 2014 ), who emphasized quartz’s role in reinforcing the structural integrity of alkali-activated materials. The presence of N-A-S-H gel, detected at a 2θ angle of 32.1°, is a key indicator of successful geopolymerisation, forming a dense matrix that improves durability. This supports the findings by Davidovits ( 2008 ), who underscored N-A-S-H gel’s fundamental role in developing geopolymer mechanical properties. Variations in N-A-S-H gel intensity across fiber contents suggest that fibers influence the distribution and formation of this amorphous phase, potentially enhancing interfacial bonding with the geopolymer matrix. Kwan and Wong ( 2008 ) similarly noted that fiber reinforcement can improve interfacial interactions, increasing mechanical strength. However, a slight reduction in N-A-S-H gel intensity at higher fiber contents suggests a dilution effect, where excessive fibers may limit reactive site availability, thereby hindering geopolymerisation. This finding is crucial, as it highlights the existence of an optimal fiber content threshold that maximizes N-A-S-H gel formation without compromising reaction efficiency. Mullite, detected at 2θ = 41.5°, is known for its thermal stability and contribution to mechanical strength. Its relatively stable intensity across varying fiber contents indicates that fiber inclusion does not significantly alter the thermal decomposition products of the geopolymer matrix. This stability corroborates Zheng et al. ( 2024 ), who found that the thermal and mechanical properties of geopolymer concrete remain largely unaffected by fiber additions within certain limits. An unidentified phase observed at 2θ = 36.0° exhibited varying intensities, potentially representing intermediate products of incomplete geopolymerisation or residual precursors. Its intensity reduction with increasing fiber content suggests that improved fiber distribution enhances reaction completeness by increasing matrix permeability and facilitating ion transport during curing. This aligns with Addis et al. ( 2022 ), who highlighted the importance of optimizing fiber content to improve reaction kinetics in geopolymerisation. Overall, XRD analysis underscores the critical role of fiber content in modulating the phases of geopolymer concrete. The results demonstrate that optimizing fiber content is essential for balancing N-A-S-H gel formation while maintaining quartz and mullite integrity, directly influencing mechanical performance and durability. These findings reinforce prior research and provide valuable insights into fiber-reinforced geopolymer systems, contributing to the advancement of geopolymer concrete applications in construction. 4.8 Statistical Analysis Comprehensive regression and correlation analyses were performed to assess the relationship between compressive and flexural strengths of geopolymer concrete (GPC) samples with varying polypropylene fiber content (0%, 0.5%, 1%, and 1.5% by volume). These analyses aimed to determine the strength of the correlation between these two mechanical properties and the predictive power of flexural strength for estimating compressive strength. Key parameters evaluated as depicted in Table 7 included the correlation coefficient ( R ), coefficient of determination ( R ²), adjusted R ², standard error of estimate, and p-values for both the correlation and regression models. Table 7 Regression and correlation analysis of compressive and flexural strength Fiber Content (%) R (Correlation) R² Adjusted R² Standard Error of Estimate p-value (Correlation) p-value (Flexural Regression) 0 0.97 0.9 0.87 2.94 < 0.01 0.163 0.5 0.98 1 0.92 2.65 0.96) for all fiber contents, indicating a strong linear relationship between compressive and flexural strengths. These findings align with previous studies that have reported similar correlations in both traditional and geopolymer concretes. Kwan and Wong ( 2008 ) observed a linear correlation between compressive and flexural strengths in geopolymer concrete, attributing this relationship to the integrity of the matrix and its influence on mechanical performance. The high R values suggest that as compressive strength increases, flexural strength tends to rise proportionately, a trend supported by the statistically significant p -values for correlation (typically < 0.05 for most fiber contents). This implies a shared underlying mechanism governing both properties, where factors such as efficient stress transfer at the fiber-matrix interface and the crack-bridging capabilities of fibers contribute significantly to overall strength development (Zheng et al., 2024 ). Particularly notable is the higher correlation observed at 0.5% and 1% fiber contents, suggesting these levels of fiber reinforcement effectively enhance matrix distribution, thereby improving both compressive and flexural performance. This observation resonates with the findings by Ganesh et al. (2021), who demonstrated that moderate fiber content improves interfacial bonding and matrix integrity. Conversely, the slightly lower correlation at 1.5% fiber content may indicate that excessive fibers cause agglomeration or inadequate wetting, which reduces uniformity and diminishes the effectiveness of stress transfer mechanisms. Provis and Bernal ( 2014 ) similarly noted that excessive fiber content can disrupt the geopolymer matrix, compromising mechanical properties. Despite the strong correlations observed, regression analysis reveals that flexural strength is not a statistically significant predictor of compressive strength at any fiber content level, with p-values exceeding 0.05 in all cases. This suggests that while compressive and flexural strengths are closely related, the variability in compressive strength cannot be fully explained by flexural strength alone. Other influencing factors, such as the degree of geopolymerisation, curing conditions, fiber-matrix adhesion, and precursor material properties, play critical roles in determining compressive strength. Kwan and Wong ( 2008 ) emphasized that compressive strength is a multifaceted property influenced by various interactions within the concrete matrix, and these findings reinforce that perspective. The high R² values, approaching 1, indicate that a significant portion of compressive strength variability is influenced by factors beyond flexural strength. Addis et al. ( 2022 ) highlighted that compressive strength is governed by both mechanical and chemical interactions, further supporting the notion that regression models using only flexural strength are insufficient for accurate prediction. The adjusted R² values suggest strong explanatory power, particularly for the 0.5% and 1% fiber mixes, corroborating research by Zheng et al. ( 2024 ) that underscores the importance of model accuracy in predicting mechanical properties. The standard error of the estimate,XXXepressenting the deviation of observed compressive strengths from those predicted by the regression model, varies across different fiber contents. The lowest standard error (2.21 Mpa) at 1% fiber content suggests improved prediction accuracy, reflecting the effectiveness of this fiber concentration in balancing mechanical properties. Ganesh et al. (2021) similarly noted that optimal fiber content is crucial for achieving consistent mechanical performance. In contrast, the higher standard errors at other fiber contents (ranging from 2.65 Mpa to 2.94 Mpa) indicate greater variability, potentially linked to inconsistent fiber distribution. Provis and Bernal ( 2014 ) emphasized the importance of matrix homogeneity in enhancing the mechanical properties of geopolymer concrete, reinforcing the need for careful fiber optimization. The scatter plot illustrated in Fig. 7 visually reinforces the relationship between compressive and flexural strengths across different fiber contents. The positive slope of the trend line further supports the strong correlation between these properties, indicating that improvements in compressive strength generally accompany enhancements in flexural strength. This interdependence is consistent with findings from Kwan and Wong ( 2008 ) and Zheng et al. ( 2024 ), highlighting the need for fiber optimization to achieve maximum performance. Such optimization is critical for ensuring structural integrity and durability, particularly in fiber-reinforced geopolymer concrete applications where both compressive and flexural strengths must be considered. Overall, the findings affirm a strong correlation between compressive and flexural strengths but demonstrate that flexural strength alone is not a reliable predictor of compressive strength in geopolymer concrete. The high correlation coefficients suggest that both strengths are influenced by common factors within the geopolymer matrix, primarily related to fiber-matrix interactions and geopolymerisation quality. However, the lack of statistical significance in the regression analysis highlights that compressive strength is determined by a more complex interplay of factors. Optimizing fiber content, curing conditions, and the composition of the geopolymer matrix is essential for enhancing both compressive and flexural properties, ensuring the practical applicability of geopolymer concrete in load-bearing and flexural-critical applications. 4. Conclusion This study investigated the potential of polypropylene fiber (PPF) as a reinforcement to enhance the mechanical and durability properties of ambient-cured geopolymer concrete (GPC). The results demonstrated that incorporating PPF significantly improved flexural strength, toughness, and durability, with an optimal PPF content of 1.0% achieving a flexural strength of 3.35 Mpa at 90 days without compromising compressive strength. Durability assessments confirmed that PPF reinforcement effectively reduced oxygen permeability and chloride ingress, enhancing the resistance of GPC to aggressive environments. X-ray diffraction (XRD) analysis validated the formation of N-A-S-H and C-A-S-H gels, which contributed to matrix densification and reduced permeability, thus improving long-term performance. Despite these benefits, higher PPF contents led to challenges such as reduced workability and increased porosity due to fiber agglomeration, highlighting the need for careful optimization of fiber content. The findings suggest that PPF-reinforced GPC could serve as a practical and energy-efficient alternative to heat-cured geopolymers, offering a sustainable solution to reduce the carbon footprint of the construction sector. From a practical perspective, the improved durability and mechanical properties of PPF-reinforced GPC make it ideal for structural applications, particularly in environments exposed to chloride and oxygen ingress, such as coastal and industrial infrastructures. However, challenges in fiber dispersion and workability need to be addressed to facilitate large-scale implementation. It is recommended that future work focuses on optimizing fiber dispersion techniques, exploring the use of superplasticizers to maintain workability, and conducting long-term performance assessments under diverse environmental conditions. Additionally, a cost-benefit analysis comparing PPF-reinforced GPC with conventional concrete could help establish its economic feasibility. Overall, the successful integration of PPF into GPC represents a significant step forward in the development of sustainable and durable construction materials, aligning with global efforts to mitigate the environmental impact of concrete production. Abbreviations GPC – Geopolymer Concrete PPF – Polypropylene Fiber GGBS – Ground Granulated Blast Furnace Slag N-A-S-H – Sodium Alumino-Silicate Hydrate C-A-S-H – Calcium Alumino-Silicate Hydrate XRD – X-ray Diffraction XRF – X-ray Fluorescence OPI – Oxygen Permeability Index ITZ – Interfacial Transition Zone PC – Portland Cement SANS – South African National Standards Declarations Acknowledgement The authors gratefully acknowledge the University of South Africa for providing funding, resources, equipment, and laboratory facilities to conduct this research. Author Contributions Radebe S.P.: Conceptualization, methodology, investigation and review of related literature, data curation and analysis and writing of the original draft. Madirisha M.M.: Conceptualization, methodology, writing of original draft, data curation and analysis, writing (review and editing), supervision. Ikotun B.D.: Conceptualization, methodology, writing of original draft, data curation and analysis, writing (review and editing), supervision. Dada O.R : Methodology, writing (review and editing). Conflict of interest: The authors declare no competing interests. Acknowledgement The authors gratefully acknowledge the University of South Africa for providing funding, resources, equipment, and laboratory facilities to conduct this research. References Addis, L. B., Sendekie, Z. B., & Satheesh, N. (2022). Degradation Kinetics and Durability Enhancement Strategies of Cellulosic Fiber‐Reinforced Geopolymers and Cement Composites. Advances in Materials Science and Engineering , 2022 (1), 1981755. Ahlawat, A., Phogat, A., Punia, U., Chhikara, A., Dhingra, A. K., Garg, R. K., … & Chhabra, D. (2025). Innovative Optimization of Mechanical Performance in Carbon Fiber-Reinforced Nylon Composite Using Artificial Neural Networks and Multi-Objective Genetic Algorithms. Journal of Materials Engineering and Performance , 1-14. Alzeebaree, R., Mawlod, A., Amen, D., Younis, K., & Mohammedameen, A. (2021). Fire resistance performance of fiber reinforced geopolymer concrete: review. E3s Web of Conferences, 318, 03003. Aydın, Y. (2023). Neural network predictive models for alkali-activated concrete carbon emission using metaheuristic optimization algorithms. Sustainability, 16(1), 142. Bokkhunthod, N., Thumrongvut, J., Supromwan, J., & Seangatith, S. (2022). Experimental study of cellular lightweight concrete-filled steel tube columns using hydraulic cement. Key Engineering Materials, 922, 147-152. Chen, W., Pan, J., Zhu, B., Ma, X., Zhang, Y., Chen, Y., … & Cai, J. (2023). Improving mechanical properties of 3D printable ‘one-part ‘geopolymer concrete with steel fiber reinforcement. Journal of Building Engineering , 75 , 107077. Davidovits, J. (2008). Geopolymer chemistry and applications. Geopolymer Institute , 1(1), 1-16. De Silva, P., Sagoe-Crenstil, K., & Sirivivatnanon, V. (2007). Kinetics of geopolymerization: Role of Al2O3 and SiO2. Cement and Concrete Research , 37 (4), 512-518. Dimas, A. et al. (2009). Effects of Fiber Reinforcement on Workability and Mechanical Properties of Geopolymer Concrete. Journal of Construction and Building Materials, 40, 175–184. Dimas, D., Giannopoulou, I., & Panias, D. (2009). Polymerization in sodium silicate solutions: a fundamental process in geopolymerization technology. Journal of materials science , 44 (14), 3719-3730. Duan, D., Wu, H., Wei, F., Song, H., Ma, Z., Chen, Z., & Cheng, F. (2021). Preparation, characterization, and rheological analysis of eco-friendly geopolymer grouting cementitious materials based on industrial solid wastes. Journal of Building Engineering , 78 , 107451. Dwijayanti, L., Ekaputri, J., & Bayuaji, R. (2016). Lightweight geopolymer binder with abaca fiber in different curing. Materials Science Forum, 841, 140-147. Esparham, A. and Ghalatian, F. (2022). The features of geopolymer concrete as a novel approach for utilization in green urban structures. Journal of Composites and Compounds, 4(11), 89-96. Farhan, K. Z., Johari, M. A. M., & Demirboğa, R. (2021). Impact of fiber reinforcements on properties of geopolymer composites: A review. Journal of Building Engineering , 44 , 102628. Ganesan, N., Abraham, R., & Raj, S. (2015). Durability characteristics of steel fiber reinforced geopolymer concrete. Construction and Building Materials, 93, 471-476. Ganesh, A. C., & Muthukannan, M. (2021). Development of high performance sustainable optimized fiber reinforced geopolymer concrete and prediction of compressive strength. Journal of Cleaner Production , 282 , 124543. Juenger, M. C., & Siddique, R. (2015). Recent advances in understanding the role of supplementary cementitious materials in concrete. Cement and concrete research , 78 , 71-80. Korniejenko, K., Lin, W., & Šimonová, H. (2020). Mechanical properties of short polymer fiber-reinforced geopolymer composites. Journal of Composites Science, 4(3), 128. Kwan, A. K. H., & Wong, H. S. (2008). Fiber reinforcement in high-performance geopolymer concrete. Journal of Materials in Civil Engineering , 20(11), 730-736. Letsosa C., Dada O., Ikotun B.D (2024). “The effects of different curing conditions on the polypropylene fibre reinforcement concrete” Journal of Physics: Conference Series. 2888(1). Luhar, S., & Khandelwal, U. (2015). A study on water absorption and sorptivity of geopolymer concrete. International Journal of Civil Engineering, 2(8), 1-9. Mechtcherine, V., & Schmidt, M. (2018). The role of permeability in ensuring the durability of concrete structures. Journal of Materials Science , 53(18), 12603-12618. Mohammed, Z. A., Al-Jaberi, L. A., & Shubber, A. N. (2021). Effect of polypropylene fiber on properties of geopolymer concrete based metakolin. Journal of Engineering and Sustainable Development , 25 (2), 58-67. Palomo, A., Maltseva, O., Garcia-Lodeiro, I., & Fernández-Jiménez, A. (2021). Portland versus alkaline cement: continuity or clean break:“a key decision for global sustainability”. Frontiers in Chemistry , 9 , 705475. Primadyas, D. and Nurhuda, I. (2018). The comparison of bond strength between geopolymer concrete and opc concrete for plain reinforcing bars. Matec Web of Conferences, 159, 01017. Provis, J. L., & Bernal, S. A. (2014). Geopolymers and alkali-activated materials. Annual Review of Materials Research , 44, 321-341. Rabie, M., Irshidat, M. R., & Al-Nuaimi, N. (2022). Ambient and heat-cured geopolymer composites: mix design optimization and life cycle assessment. Sustainability , 14 (9), 4942. Reed, M., Lokuge, W., & Karunasena, W. (2014). Fiber-reinforced geopolymer concrete with ambient curing for in situ applications. Journal of Materials Science, 49(12), 4297-4304. SANS 5861-3:2006: Concrete tests: Part 3 – Making and curing of test specimens. SANS 5863:2006: Concrete tests – Compressive strength of hardened concrete SANS. (2006). SANS 5844: 2006 - Testing of aggregate for concrete: Method for the determination of the particle density and water absorption. South African Bureau of Standards. SANS. (2006). SANS 5860: 2006 - Testing of concrete: Method for the determination of the density of concrete. South African Bureau of Standards. SANS. (2006). SANS 5862-1: 2006 - Testing of concrete: Part 1 - Workability. South African Bureau of Standards. SANS. (2006). SANS 5864: 2006 - Testing of concrete: Method for the determination of the flexural strength of hardened concrete. South African Bureau of Standards. SANS. (2008). SANS 201: 2008 - Method for the determination of the grading of aggregates. South African Bureau of Standards. SANS. (2015). SANS 3001-CO3-1: 2015 - Testing of concrete for durability: Part 1 - Determination of density. South African Bureau of Standards. SANS. (2015). SANS 3001-CO3-2: 2015 - Testing of concrete for durability: Part 2 - Determination of the water absorption of hardened concrete. South African Bureau of Standards. Sarker, P., Kelly, S., & Yao, Z. (2014). Effect of fire exposure on cracking, spalling and residual strength of fly ash geopolymer concrete. Materials & Design (1980-2015), 63, 584-592. Shaikh, F. (2019). Effect of cooling on the residual mechanical properties and cracking of plain and fibrous geopolymer concretes at elevated temperatures. Structural Concrete, 20(5), 1583-1595. Sivakrishna, A., Adesina, A., Awoyera, P. O., & Kumar, K. R. (2020). Green concrete: A review of recent developments. Materials Today: Proceedings, 27, 54-58. Triwulan, T., Dwijayanti, L. Y., Ekaputri, J. J., & Bayuaji, R. (2016, February). Lightweight geopolymer binder with abaca fiber in different curing. In Materials Science Forum (Vol. 841, pp. 140-147). Trans Tech Publications Ltd. Wang, D. L., Tang, C. S., Pan, X. H., Liu, B., & Shi, B. (2023). Coupling effect of fiber reinforcement and MICP stabilization on the tensile behavior of calcareous sand. Engineering Geology, 317, 107090. Yazid, M., Faris, M., Abdullah, M., Nabiałek, M., Rahim, S., Salleh, M., … & Jeż, B. (2022). Contribution of interfacial bonding towards geopolymers properties in geopolymers reinforced fibers: a review. Materials, 15(4), 1496. Yu, X., & Cao, C. (2003). Electrochemical study of the corrosion behavior of Ce sealing of anodized 2024 aluminum alloy. Thin Solid Films, 423(2), 252-256. Zheng, Y., Zhang, W., Zheng, L., & Zheng, J. (2024). Mechanical properties of steel fiber-reinforced geopolymer concrete after high temperature exposure. Construction and Building Materials , 439 , 137394. Additional Declarations No competing interests reported. Supplementary Files supplementarydata08.4.2025.docx Cite Share Download PDF Status: Published Journal Publication published 29 Jul, 2025 Read the published version in Iranian Journal of Science and Technology, Transactions of Civil Engineering → Version 1 posted Editorial decision: Revision requested 27 Jun, 2025 Reviews received at journal 23 Jun, 2025 Reviewers agreed at journal 05 Jun, 2025 Reviews received at journal 04 Jun, 2025 Reviewers agreed at journal 03 Jun, 2025 Reviewers invited by journal 03 Jun, 2025 Editor assigned by journal 30 May, 2025 Submission checks completed at journal 30 May, 2025 First submitted to journal 29 May, 2025 You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. We do this by developing innovative software and high quality services for the global research community. Our growing team is made up of researchers and industry professionals working together to solve the most critical problems facing scientific publishing. Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-6778704","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":466455521,"identity":"b8b170d8-dede-41b6-93f9-67166025999c","order_by":0,"name":"Sifiso P. Radebe","email":"data:image/png;base64,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","orcid":"","institution":"University of South Africa","correspondingAuthor":true,"prefix":"","firstName":"Sifiso","middleName":"P.","lastName":"Radebe","suffix":""},{"id":466455522,"identity":"7ba9a46b-0c98-4e2f-b0ce-74fc56ffe60a","order_by":1,"name":"Makungu M. Madirisha","email":"","orcid":"","institution":"University of South Africa","correspondingAuthor":false,"prefix":"","firstName":"Makungu","middleName":"M.","lastName":"Madirisha","suffix":""},{"id":466455523,"identity":"37ecfb0d-8713-4be8-a4bb-3f12eb1b66f8","order_by":2,"name":"Bolanle D. Ikotun","email":"","orcid":"","institution":"University of South Africa","correspondingAuthor":false,"prefix":"","firstName":"Bolanle","middleName":"D.","lastName":"Ikotun","suffix":""},{"id":466455524,"identity":"76c49b44-dfcf-4fb5-b565-6c547e3f66c4","order_by":3,"name":"Opeoluwa R. Dada","email":"","orcid":"","institution":"University of South Africa","correspondingAuthor":false,"prefix":"","firstName":"Opeoluwa","middleName":"R.","lastName":"Dada","suffix":""}],"badges":[],"createdAt":"2025-05-29 17:53:22","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-6778704/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-6778704/v1","draftVersion":[],"editorialEvents":[{"content":"https://doi.org/10.1007/s40996-025-01987-z","type":"published","date":"2025-07-29T16:13:18+00:00"}],"editorialNote":"","failedWorkflow":false,"files":[{"id":84052987,"identity":"c93e3f84-04d8-47ec-9a98-dfba8f7048b8","added_by":"auto","created_at":"2025-06-06 08:48:00","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":810327,"visible":true,"origin":"","legend":"\u003cp\u003eMixing process of fiber-reinforced composite material\u003c/p\u003e","description":"","filename":"1.png","url":"https://assets-eu.researchsquare.com/files/rs-6778704/v1/c91fa2991873b7b0cec46991.png"},{"id":84053882,"identity":"1867146f-542e-449f-afff-1dcaf1e18ebe","added_by":"auto","created_at":"2025-06-06 08:56:00","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":966088,"visible":true,"origin":"","legend":"\u003cp\u003eCuring specimens of beams and cubes at room temperature\u003c/p\u003e","description":"","filename":"2.png","url":"https://assets-eu.researchsquare.com/files/rs-6778704/v1/e501dc045fd661c3adb5fc08.png"},{"id":84052999,"identity":"0b01157d-c2c2-47ef-bfc3-f285d45590c7","added_by":"auto","created_at":"2025-06-06 08:48:00","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":771610,"visible":true,"origin":"","legend":"\u003cp\u003eCompressive and flexural strength testing of a geopolymer concrete sample using a Toni Technik testing machine\u003c/p\u003e","description":"","filename":"3.png","url":"https://assets-eu.researchsquare.com/files/rs-6778704/v1/435be7f4e6a8bf1068a2a2f9.png"},{"id":84052990,"identity":"3951668d-ef89-41f2-b096-ca176bb85038","added_by":"auto","created_at":"2025-06-06 08:48:00","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":70473,"visible":true,"origin":"","legend":"\u003cp\u003eCompressive strength development of geopolymer concrete with varying polypropylene fiber content at 7, 28, and 90 days.\u003c/p\u003e","description":"","filename":"4.png","url":"https://assets-eu.researchsquare.com/files/rs-6778704/v1/d55e1eb0c8ab8155f4f18f1e.png"},{"id":84053884,"identity":"a0b717cf-b489-49c2-8898-645d3c12ee0c","added_by":"auto","created_at":"2025-06-06 08:56:00","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":61623,"visible":true,"origin":"","legend":"\u003cp\u003eFlexural strength development of geopolymer concrete with varying polypropylene fiber content at 7, 28, and 90 days.\u003c/p\u003e","description":"","filename":"5.png","url":"https://assets-eu.researchsquare.com/files/rs-6778704/v1/48143c4303eabc8f04d0f9f6.png"},{"id":84052985,"identity":"4c44642d-c7cc-44da-8fbc-597442c4b52d","added_by":"auto","created_at":"2025-06-06 08:48:00","extension":"png","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":51875,"visible":true,"origin":"","legend":"\u003cp\u003eSorptivity of geopolymer concrete at various fiber contents and curing times\u003c/p\u003e","description":"","filename":"6.png","url":"https://assets-eu.researchsquare.com/files/rs-6778704/v1/801845d9b2d62195c75bea20.png"},{"id":84052997,"identity":"99b9b87b-7d99-4f19-87c8-19507de44c24","added_by":"auto","created_at":"2025-06-06 08:48:00","extension":"png","order_by":7,"title":"Figure 7","display":"","copyAsset":false,"role":"figure","size":33549,"visible":true,"origin":"","legend":"\u003cp\u003eScatter plot compressive strength vs flexural strength of fiber reinforced of geopolymer.\u003c/p\u003e","description":"","filename":"7.png","url":"https://assets-eu.researchsquare.com/files/rs-6778704/v1/13149d41b7cc72f9669d037f.png"},{"id":88268280,"identity":"5882dff2-f9c9-4616-b163-0db132643f66","added_by":"auto","created_at":"2025-08-04 16:50:40","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":4809863,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-6778704/v1/979c99c4-9abb-4ddf-8bf4-53a39919d484.pdf"},{"id":84052988,"identity":"fecd0074-a817-4697-8bbb-438f674d1e49","added_by":"auto","created_at":"2025-06-06 08:48:00","extension":"docx","order_by":0,"title":"","display":"","copyAsset":false,"role":"supplement","size":24904,"visible":true,"origin":"","legend":"","description":"","filename":"supplementarydata08.4.2025.docx","url":"https://assets-eu.researchsquare.com/files/rs-6778704/v1/5801a707a37c7bfd35503f36.docx"}],"financialInterests":"No competing interests reported.","formattedTitle":"Durability and Strength Improvement of Ambient-Cured Geopolymer Concrete using Polypropylene Fibers","fulltext":[{"header":"1. Introduction","content":"\u003cp\u003eThe construction industry is undergoing rapid expansion, driven by the increasing demand for infrastructure. However, this growth presents significant environmental challenges, primarily due to the widespread use of Portland cement (PC) in concrete production. PC manufacturing is highly energy-intensive, depletes natural resources, and contributes nearly 8% of global CO₂ emissions, making it a major factor in climate change (Bokkhunthod et al., \u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e2022\u003c/span\u003e; Sivakrishna et al., \u003cspan citationid=\"CR40\" class=\"CitationRef\"\u003e2020\u003c/span\u003e). As urbanization accelerates, the need for sustainable alternatives to PC becomes increasingly urgent to mitigate the construction sector\u0026rsquo;s carbon footprint and environmental impact (Sivakrishna et al., \u003cspan citationid=\"CR40\" class=\"CitationRef\"\u003e2020\u003c/span\u003e; Aydın, \u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e2023\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eGeopolymer concrete (GPC) has emerged as a promising alternative, synthesized from aluminosilicate materials such as fly ash and slag. GPC offers several advantages, including lower greenhouse gas emissions, superior thermal stability, and enhanced resistance to chemical attack (Reed et al., \u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e2014\u003c/span\u003e; Ganesan et al., \u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e2015\u003c/span\u003e). Additionally, the use of industrial by-products in GPC reduces waste and promotes sustainability (Esparham \u0026amp; Ghalatian, \u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e2022\u003c/span\u003e). However, despite these benefits, GPC adoption remains limited due to its inherent brittleness, low tensile strength, and poor flexural performance, which can lead to premature cracking and restrict its use in load-bearing applications (Triwulan et al., \u003cspan citationid=\"CR41\" class=\"CitationRef\"\u003e2016\u003c/span\u003e). These mechanical limitations necessitate reinforcement strategies to improve crack resistance and structural integrity (Shaikh, \u003cspan citationid=\"CR39\" class=\"CitationRef\"\u003e2019\u003c/span\u003e; Sarker et al., \u003cspan citationid=\"CR38\" class=\"CitationRef\"\u003e2014\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eTo address these weaknesses, fiber reinforcement has been identified as an effective strategy for improving mechanical and durability properties. Fibers such as steel, glass, and synthetic fibers are commonly used in PC concrete to enhance ductility and toughness (Shaikh, \u003cspan citationid=\"CR39\" class=\"CitationRef\"\u003e2019\u003c/span\u003e; Korniejenko et al., \u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e2020\u003c/span\u003e). Among these, polypropylene fibers (PPF) stand out due to their lightweight nature, corrosion resistance, and cost-effectiveness, making them a viable option for improving concrete performance (Ganesan et al., \u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e2015\u003c/span\u003e; Letsosa et al., \u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e2024\u003c/span\u003e). While PPF has been extensively studied in PC concrete, research on its integration into GPC, particularly under ambient curing conditions, remains limited. This knowledge gap is significant because ambient curing eliminates the need for high-temperature processing, making GPC more practical and energy-efficient. Addressing this limitation is crucial for advancing GPC\u0026rsquo;s potential as a viable and sustainable alternative to PC concrete.\u003c/p\u003e \u003cp\u003eThis study investigated the role of polypropylene fibers in enhancing the mechanical and durability properties of ambient-cured GPC, focusing on optimizing fiber content for strength and environmental resistance. Unlike conventional GPC formulations that often require high-temperature curing, this study focuses on ambient curing, which enhances practicality for real-world construction applications. By systematically examining the effects of varying PPF content on workability, compressive and flexural strength, oxygen permeability, and water sorptivity, this research provides a comprehensive understanding of how polypropylene fibers influence the performance of GPC without altering its fundamental geopolymerization chemistry.\u003c/p\u003e"},{"header":"2. Materials and Methods","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e \u003ch2\u003e2.1 Materials\u003c/h2\u003e \u003cp\u003eThe materials used in this study were sourced from reputable suppliers to ensure the production of high-quality geopolymer concrete. Sodium hydroxide pellets (99% purity), procured from MINEMA Chemicals, South Africa, were used to prepare the alkaline solution required for geopolymerization. Polypropylene fiber strands (PPF), supplied by SIKA, South Africa, were incorporated to improve tensile strength and durability. The aggregates used included 20 mm granite stone from Elsana, South Africa and dune sand from Atlantic Sands, South Africa, selected for their optimal particle packing and mechanical performance. Additionally, crusher dust from Hornefels Tygerberg, South Africa was used as a fine aggregate. The binder materials consisted of Class F fly ash and ground granulated blast furnace slag (GGBS), procured from AfriSam, South Africa. Fly ash was chosen for its pozzolanic properties, while GGBS contributed to early strength development. All materials were handled in strict accordance with safety protocols, and personnel used appropriate personal protective equipment (PPE) to ensure safe working conditions throughout the preparation process\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec4\" class=\"Section2\"\u003e \u003ch2\u003e2.2 Methods\u003c/h2\u003e \u003cdiv id=\"Sec5\" class=\"Section3\"\u003e \u003ch2\u003e2.2.1 Aggregate tests\u003c/h2\u003e \u003cp\u003e \u003cb\u003eGrading\u003c/b\u003e \u003c/p\u003e \u003cp\u003eA sieve analysis was conducted as described in SANS 3001-AG1 to determine the particle size distribution of fine and coarse aggregates. The test samples were dried at 110\u0026deg;C in a well-ventilated oven and cooled to room temperature. To calculate the fineness modulus, the dried material was successively sieved through sieves of the following apertures: 7.1 mm 5 mm, 2 mm, 1 mm, 0.6 mm, 0.3 mm, 0.15 mm, 0.075 mm and pan, in the order of the largest aperture sieve to the smallest aperture sieve. The following apertures were used to sieve coarse aggregates: 28 mm, 20 mm, 14 mm, 10 mm, 7.1mm and 5 mm. The shape of aggregate particles and variations can influence the concrete's strength and workability as well as water demand.\u003c/p\u003e \u003cp\u003e \u003cb\u003eDensity\u003c/b\u003e \u003c/p\u003e \u003cp\u003eThe bulk densities of the crusher dust and fine aggregates were measured according to SANS 5845:2006, using both compacted and uncompacted states. Triplicate measurements were taken to ensure accuracy, and the relative density of aggregates was determined following SANS 3001-AG20:2011. These results informed the mix design to optimize strength and durability.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec6\" class=\"Section3\"\u003e \u003ch2\u003e2.2.2 Chemical composition of Fly Ash and GGBS\u003c/h2\u003e \u003cp\u003eThe chemical composition of fly ash and GGBS samples was determined using X-ray fluorescence (XRF) spectrometer. Samples were finely grounded to achieve homogeneity and then compressed into pellets using a Hydraulic Workshop Press WPP T15. XRF analysis was performed using an instrument equipped with optimized parameters for voltage, current, and measurement time, tailored to the elements of interest. Quantitative analysis was conducted through empirical calibration, incorporating corrections for matrix effects to ensure accurate elemental concentration measurements.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec7\" class=\"Section3\"\u003e \u003ch2\u003e2.2.3 Mixing and Curing Process\u003c/h2\u003e \u003cp\u003eThe concrete mixing and curing process adhered to SANS 5861-1:2006 and SANS 5862-3:2006 standards, ensuring precision and consistency throughout the preparation as illustrated in Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e. Cube and beam molds were treated with a release agent to facilitate smooth demolding. Coarse and fine aggregates, granulated blast furnace slag, fly ash, and polypropylene fibers were accurately weighed using a digital scale and mixed in a 25-litre steel mixing pan. Water and sodium hydroxide solution were then added to prepare the geopolymer concrete. Prior to filling, the molds were thoroughly cleaned and coated with a release agent. The concrete was placed into molds in layers of approximately 5 cm, compacted using a vibrating table, and finished with a trowel to smooth the top surface. The specimens were cured in a cool, moist environment for 24 hours before demolding. Once demolded, the samples were marked for identification and further cured at room temperature for 7,28 and 90 days. This methodical procedure ensured compliance with testing standards and to achieve the desired concrete strength.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec8\" class=\"Section3\"\u003e \u003ch2\u003e2.2.4 Concrete tests\u003c/h2\u003e \u003cp\u003e \u003cb\u003eWorkability\u003c/b\u003e \u003c/p\u003e \u003cp\u003eThe workability of each freshly mixed concrete was assessed by measuring its slump following SANS 5862-1:2006. Workability refers to the concrete\u0026rsquo;s ease of transportation, placement, compaction, and finishing without segregation of its components.\u003c/p\u003e \u003cp\u003e \u003cb\u003eCompressive and Flexural Strength\u003c/b\u003e \u003c/p\u003e \u003cp\u003eConcrete cubes were prepared from the molds and then cured at room temperature as illustrated in Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e with accordance to SANS 5861-3:2006 Concrete tests: Part 3 \u0026ndash; Making and curing of test specimens, then are crushed after 7 days using a compressive strength testing machine. This procedure was conducted using the relevant South African National Standard (SANS 5863:2006). Compressive strength testing was conducted at 7,28 and 90 days using the Toni Technik (Model 2041) compressive testing machine as illustrated in Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eConcrete beams were prepared using the beam molds and then cured at room temperature, following SANS 5861-3:2006 standards for making and curing test specimens. After 7 days, the beams were tested using a flexural machine that applied loads until the beams failed. This testing followed SANS 5864:2006 standards for flexural strength of hardened concrete as depicted in Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e. The flexural strength testing was conducted at 7, 28, and 90 days to evaluate the strength development over time.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003e \u003cb\u003eOxygen permeability\u003c/b\u003e \u003c/p\u003e \u003cp\u003eThe oxygen permeability test was conducted following SANS 3001-CO3-1:2015 and SANS 3001-CO3-2:2015. Samples were cored from a concrete cube and subjected to an oven-drying process to eliminate any residual moisture. After drying, the specimens were allowed to cool in a controlled, dry environment to prevent the absorption of ambient moisture. Once cooled, the specimens were placed into an oxygen permeability testing apparatus, which applied a constant pressure of oxygen to the specimens. The test measures the rate at which oxygen permeates through the concrete over a specified period. This measurement is crucial for determining the Oxygen Permeability Index (OPI) of the concrete, which indicates its ability to resist the ingress of oxygen. A lower permeability suggests greater durability, an important factor in assessing the concrete's performance and longevity in various applications.\u003c/p\u003e \u003cp\u003e \u003cb\u003eWater sorptivity and porosity\u003c/b\u003e \u003c/p\u003e \u003cp\u003eThe water sorptivity test was conducted following SANS 3001-CO3-1:2015 and SANS 3001-CO3-3:2015 standards. The process involved preparing and drying the concrete specimens, allowing them to cool, before partially submerging them in water. The rate of water absorption was monitored and recorded over time to evaluate the concrete's resistance to water ingress, providing key information on its durability.\u003c/p\u003e \u003cp\u003e \u003cb\u003eChloride conductivity test\u003c/b\u003e \u003c/p\u003e \u003cp\u003eThe chloride conductivity test was performed per SANS 3001-CO3-1:2015 and SANS 3001-CO3-4:2015 standards. Concrete specimens were prepared and immersed in a 3.5% NaCl solution, with a constant voltage of 60V DC applied for 6 hours. The chloride ion penetration was measured to calculate the permeability coefficient, which indicates the concrete's resistance to chloride ion ingress and its durability in chloride-exposed environments.\u003c/p\u003e \u003cp\u003e \u003cb\u003eX-ray Diffraction (XRD) Test\u003c/b\u003e \u003c/p\u003e \u003cp\u003eX-ray diffraction (XRD) analysis was conducted following ASTM standards E937 and E1149, which specify the procedures for X-ray powder diffraction data acquisition and analysis. The sample was compressed into a pellet using a pressing machine at a load of 70 kN. XRD measurements were carried out using an X-ray diffractometer operating at 30 kV and 10 mA, with a Cu Kα radiation source (λ\u0026thinsp;=\u0026thinsp;1.54060 \u0026Aring;). Data were collected over a scanning range of 5.001\u0026deg; to 64.982\u0026deg; (2θ). The pellets were exposed to X-rays emitted from a copper tube anode, and the diffracted signals were detected using a LYNXEYE detector. The detector was set to an opening angle of 5.812\u0026deg;, with slit sizes of 0.6 mm.\u003c/p\u003e \u003c/div\u003e \u003c/div\u003e"},{"header":"3. Results and Discussion","content":"\u003cdiv id=\"Sec10\" class=\"Section2\"\u003e \u003ch2\u003e3.1 Chemical composition of fly ash and GGBS\u003c/h2\u003e \u003cp\u003eThe chemical composition of Class F fly ash and Ground Granulated Blast Furnace Slag (GGBS), as presented in Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e, highlights their suitability for geopolymer applications. A key factor in geopolymerisation is the presence of silica (SiO₂) and alumina (Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e) content which plays a crucial role in forming a dense and durable aluminosilicate network (Cao et al., 2024). However, it is important to note that only the amorphous fraction of SiO₂ is reactive in geopolymerisation. Based on literature estimates, the amorphous silica content in Class F fly ash typically ranges from 50\u0026ndash;85% of the total SiO₂ (Davidovits, \u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e2008\u003c/span\u003e; De Silva et al., \u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e2007\u003c/span\u003e). Assuming 70% amorphous SiO₂, the estimated reactive portion in 53.83% is approximately 37.7%.\u003c/p\u003e \u003cp\u003eSimilarly, GGBS contains 37.10% SiO₂, of which 85\u0026ndash;95% is typically amorphous due to its rapid quenching during production (Juenger \u0026amp; Siddique, \u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e2015\u003c/span\u003e). Assuming 90% amorphous SiO₂, the estimated reactive portion is approximately 33.4%. This high amorphous content facilitates dissolution and reaction with alkali activators, forming both aluminosilicate and calcium-silicate-hydrate (C-S-H) phases.\u003c/p\u003e \u003cp\u003eThe alumina (Al₂O₃) content in fly ash, measured at 33.18%, promotes cross-linking within the geopolymer matrix, strengthening the material and improving its resistance to degradation (Dimas et al., \u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e2009\u003c/span\u003e). In contrast, the calcium oxide (CaO) content in fly ash is relatively low at 3.63%, indicating its predominantly pozzolanic nature. This low CaO content supports the development of thermally and chemically stable geopolymer structures, distinguishing them from cementitious systems that rely on calcium-based hydration reactions (Farhan et al., \u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e2021\u003c/span\u003e). Conversely, GGBS has a significant CaO content of 33.20%, which enhances pozzolanic activity and contributes to early strength development in geopolymer systems.\u003c/p\u003e \u003cp\u003eMinor oxides such as magnesium oxide (MgO), potassium oxide (K₂O), sodium oxide (Na₂O), titanium dioxide (TiO₂), manganese oxide (Mn₂O₃), and phosphorus pentoxide (P₂O₅) are present in trace amounts in both materials. TiO₂ may provide additional benefits, such as enhanced UV resistance, improving the material\u0026rsquo;s durability in outdoor applications (Mohammed et al., \u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e2021\u003c/span\u003e). The redox chemistry of minor oxides, particularly Mn₂O₃ and Fe₂O₃, influences polymerization kinetics and the structural stability of the geopolymer matrix. These oxides act as redox-active species, modifying oxidation states and affecting reactivity and material stability. Additionally, MgO in GGBS, measured at 9.43%, contributes to geopolymer matrix stability by forming Mg-substituted aluminosilicate phases, enhancing sulphate resistance and durability in aggressive environments.\u003c/p\u003e \u003cp\u003eThe loss on ignition (LOI) is recorded at 0.80% for fly ash and 1.86% for GGBS, indicating high material purity with minimal unburned carbon. A low LOI suggests consistent geopolymerisation reactions, reducing potential interference with the development of the geopolymer matrix (Luhar \u0026amp; Khandelwal, \u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e2015\u003c/span\u003e). The higher proportion of amorphous silica in fly ash compared to the crystalline forms in GGBS accelerates dissolution, influencing geopolymerisation rates and strength development. Moreover, alkali cations such as Na⁺ and K⁺ also influence the charge balance and network stability within the geopolymer matrix. Potassium ions (K⁺) tend to form larger pore structures than sodium ions (Na⁺), which could affect the permeability and mechanical properties of the geopolymer concrete. The SiO₂/Al₂O₃ ratio for fly ash is approximately 1.93, while that for GGBS is approximately 3.23. Both ratios fall within the optimal range (1.5\u0026ndash;3.5) for achieving a well-polymerized aluminosilicate network (Davidovits, \u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e2008\u003c/span\u003e). This ratio is crucial for promoting effective polymerization, which in turn enhances the mechanical strength, durability, and thermal stability of the geopolymer.\u003c/p\u003e \u003cp\u003eOverall, the complementary chemical compositions of Class F fly ash and GGBS suggest that their combined use could optimize geopolymer concrete properties, balancing early strength development with long-term durability. The integration of hybrid geopolymerisation and the influence of alkali and minor oxides underscore the complexity and potential for fine-tuning geopolymer properties to meet specific performance requirements. This analysis confirms the suitability of these materials for producing high-performance geopolymer concrete.\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab1\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 1\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eChemical composition of class F fly ash and GGBS\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"3\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eOxide/Element\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colspan=\"2\" nameend=\"c3\" namest=\"c2\"\u003e \u003cp\u003e% composition\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eClass F fly ash\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eGGBS\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eSiO\u003csub\u003e2\u003c/sub\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e53.83\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e37.10\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eAl\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e33.18\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e17.51\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eFe\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e4.16\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e0.56\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eCaO\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e3.63\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e33.20\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eMgO\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e0.93\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e9.43\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eK\u003csub\u003e2\u003c/sub\u003eO\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e0.68\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e1.61\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eNa\u003csub\u003e2\u003c/sub\u003eO\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e0.11\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e0.34\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eTiO\u003csub\u003e2\u003c/sub\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e1.51\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e0.81\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eMn\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e0.06\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e1.21\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eP\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e5\u003c/sub\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e0,44\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e0.01\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eCr\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e0.00\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e-\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eSrO\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e0.00\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e-\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eSO\u003csub\u003e3\u003c/sub\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e0.80\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e-\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eS\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e-\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e1.30\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eLoss on ignition\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e0.80\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e1.86\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003eSum\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e\u003cb\u003e99.4\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e\u003cb\u003e99.9\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec11\" class=\"Section2\"\u003e \u003ch2\u003e3.2 Physical properties of aggregates\u003c/h2\u003e \u003cp\u003eThe physical properties of fine and coarse aggregates, as presented in Table\u0026nbsp;\u003cspan refid=\"Tab2\" class=\"InternalRef\"\u003e2\u003c/span\u003e, significantly influence the performance of geopolymer concrete. Sieve analysis results indicate that the 20 mm stone aggregates fall within the 13.2 mm\u0026ndash;26.5 mm range, ensuring optimal packing and reduced void content, which enhances the concrete matrix density and potentially improves compressive strength (Dimas et al., \u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e2009\u003c/span\u003e). Likewise, the fine aggregates, ranging from 0.075 mm to 4.75 mm, with a majority in the finer range, contribute to improved packing and mix cohesiveness. The angular and rough-textured nature of the 20 mm aggregates is expected to enhance mechanical interlocking within the matrix, increasing overall strength, while the smoother texture of fine aggregates improves workability and handling without compromising structural integrity.\u003c/p\u003e \u003cp\u003eThe specific gravity values of approximately 2.65 for the 20 mm stone and 2.60 for the fine aggregates align with those required for producing high-density, high-performance geopolymer concrete (Mohammed et al., \u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e2021\u003c/span\u003e). Additionally, the absorption capacities of 0.5% for coarse aggregates and 1.0% for fine aggregates indicate minimal water uptake, which supports efficient geopolymerisation while maintaining workability and strength development. These characteristics confirm the suitability of the selected aggregates for producing durable and structurally robust geopolymer concrete.\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab2\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 2\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003ePhysical properties of fine aggregates and coarse aggregates\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"3\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eAggregate Type\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eCoarse Aggregate\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eFine Aggregate\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eSize Range (mm)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e20 mm\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e0.075 mm to 4.75 mm\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eSpecific Gravity\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e2.65\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e2.6\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eAbsorption Capacity (%)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e0.5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e1\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eTexture\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eAngular and rough-textured\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eSmoother texture\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec12\" class=\"Section2\"\u003e \u003ch2\u003e3.3 Workability\u003c/h2\u003e \u003cp\u003eThe mix design of the geopolymer concrete, as detailed in Supplementary Table\u0026nbsp;1, maintained a consistent binder-to-aggregate ratio across all samples, ensuring a controlled evaluation of workability. Slump tests, with results presented in Table\u0026nbsp;\u003cspan refid=\"Tab3\" class=\"InternalRef\"\u003e3\u003c/span\u003e, assessed the impact of polypropylene fiber content on concrete performance. The control mix (0% fiber) exhibited a slump of 120 mm, indicating moderate workability, which aligns with the typical behavior of geopolymer concrete as reported by Dimas et al. (\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e2009\u003c/span\u003e). This level of workability is ideal for construction scenarios requiring a balance between ease of placement and resistance to segregation.\u003c/p\u003e \u003cp\u003eThe incorporation of fibers at 0.5% and 1% resulted in improved workability, with slump values rising to 140 mm and 150 mm, respectively. This enhancement highlights the positive influence of fiber dispersion on mix flowability, consistent with findings by Mohammed et al. (\u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e2021\u003c/span\u003e). Similarly, Zheng et al. (\u003cspan citationid=\"CR45\" class=\"CitationRef\"\u003e2024\u003c/span\u003e) reported that optimized ambient-cured geopolymer concrete (GPC) can achieve workability levels comparable to conventional concrete when supplemented with appropriate superplasticizers. Such improvements are advantageous in construction, facilitating easier placement and compaction, especially in complex formwork and heavily reinforced sections. The increased slump values at these fiber dosages indicate an optimal mix where fibers enhance mechanical performance without compromising workability.\u003c/p\u003e \u003cp\u003eConversely, at the highest fiber concentration (1.5%), the slump value dropped significantly to 60 mm, suggesting a marked reduction in workability due to fiber entanglement and increased mix stiffness. This decrease restricts flow, making handling and compaction challenging, potentially leading to defects such as honeycombing. These observations align with Dimas et al. (\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e2009\u003c/span\u003e), who noted that excessive fiber content can negatively affect the fresh properties of fiber-reinforced concrete.\u003c/p\u003e \u003cp\u003eFrom a practical standpoint, these results emphasize the importance of optimizing fiber dosage in geopolymer concrete. The improved workability at 0.5% and 1% fiber content suggests these levels provide a desirable balance between tensile enhancement and ease of handling. However, the substantial workability reduction at 1.5% highlights the need for caution when increasing fiber content. If higher fiber concentrations are required for specific mechanical performance improvements, modifications such as incorporating superplasticizers may be necessary to maintain workability. These findings provide crucial insights into geopolymer concrete mix design, ensuring both mechanical efficiency and practical constructability.\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab3\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 3\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eSlump test results for geopolymer concrete reinforced with fiber\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"2\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eGeopolymer concrete with amount fiber in percentage\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eSlump (mm)\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e120\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e0.5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e140\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e150\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e1.5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e60\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec13\" class=\"Section2\"\u003e \u003ch2\u003e3.4 Compressive Strength\u003c/h2\u003e \u003cp\u003eThe impact of polypropylene fiber content on the compressive strength of geopolymer concrete over different curing periods; 7, 28, and 90 days is illustrated in Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e. The results in Supplementary Table\u0026nbsp;2 highlight the intricate balance between fiber content and the geopolymerisation process, offering insights into optimizing mix designs for construction applications. The control mix (0% fiber) exhibited a compressive strength of 30.00 Mpa at 7 days, which increased to 40.40 Mpa at 28 days and peaked at 46.25 Mpa at 90 days. This steady development is characteristic of geopolymer concrete, as noted by Dimas et al. (\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e2009\u003c/span\u003e), and is attributed to the geopolymerisation process, wherein aluminosilicate precursors react with an alkaline activator to form a stable three-dimensional Si-O-Al network. This dense matrix enhances compressive strength over time, making geopolymer concrete suitable for load-bearing applications, such as beams and columns. Additionally, its lower calcium content compared to Portland cement reduces micro-cracking and shrinkage, improving durability in aggressive environments.\u003c/p\u003e \u003cp\u003eAt 0.50% fiber content, the 28day compressive strength slightly decreased to 39.66 Mpa, but at 90 days, it remained comparable to the control mix at 47.14 Mpa. This aligns with the findings of Farhan et al. (\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e2021\u003c/span\u003e), who reported that moderate fiber addition enhances workability without significantly compromising strength. Although polypropylene fibers do not directly participate in the geopolymerisation reaction, they act as a reinforcement mechanism, bridging micro-cracks and enhancing energy absorption. This crack control is vital for structural integrity under dynamic loads. From a practical perspective, improved workability at this fiber content ensures better compaction and fiber dispersion, reducing defects in precast elements and complex formwork applications.\u003c/p\u003e \u003cp\u003eHowever, at 1.00% fiber content, a notable reduction in compressive strength was observed across all curing ages, recording 27.31 Mpa at 7 days, 38.63 Mpa at 28 days, and 44.11 Mpa at 90 days. This suggests that excessive fiber content disrupts the geopolymer matrix, leading to fiber entanglement and weak zones within the structure. Mohammed et al. (\u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e2021\u003c/span\u003e) similarly reported that high fiber volumes increase stiffness and reduce workability. The high fiber concentration may introduce voids and reduce effective bonding between the binder and aggregates, compromising matrix integrity. In construction, such mixtures pose challenges in placement and compaction, increasing the risk of honeycombing and reduced load-bearing capacity, which is particularly critical for high-rise buildings and infrastructure in seismic zones.\u003c/p\u003e \u003cp\u003eAt 1.50% fiber content, the compressive strength showed a mixed trend, recording 28.59 Mpa at 7 days, 40.90 Mpa at 28 days, and a slight decline to 41.53 Mpa at 90 days. This unexpected reduction at 90 days suggests that excessive fiber content negatively impacts long-term performance, possibly due to increased void formation and poor fiber-matrix adhesion, as highlighted by Dimas et al. (\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e2009\u003c/span\u003e). The hydrophobic nature of polypropylene fibers may further hinder proper wetting by the geopolymer paste, leading to weak interfacial zones. In practical applications, this can compromise durability, particularly in marine and industrial environments where resistance to chloride and sulfate attacks is essential. Poor interfacial bonding could lead to premature deterioration, raising maintenance costs and reducing service life.\u003c/p\u003e \u003cp\u003eThese findings indicate that an optimal fiber content range of 0.50\u0026ndash;1.00% achieves a balance between improved workability and adequate compressive strength. Maintaining fiber content within this range supports construction efficiency by ensuring uniform stress distribution and minimizing defects. Furthermore, optimizing fiber dosage enhances sustainability by reducing repair needs and prolonging structural lifespan. The inherent ability of geopolymer concrete to incorporate industrial by-products, such as fly ash and slag, further aligns with green construction objectives, significantly lowering CO₂ emissions compared to conventional cement-based systems.\u003c/p\u003e \u003cp\u003eComparing ambient and heat curing effects on geopolymer concrete, heat curing significantly accelerates geopolymerisation, leading to higher early-age compressive strength. Studies show that heat-cured geopolymer concrete can exceed 50 Mpa at 28 days, outperforming ambient-cured concrete, which generally exhibit lower strengths in early curing stages (Zheng et al., \u003cspan citationid=\"CR45\" class=\"CitationRef\"\u003e2024\u003c/span\u003e). The enhanced early strength is attributed to the increased reactivity of alkali-activated materials at elevated temperatures, promoting faster Si-O-Al bond formation. Rabie et al. (\u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e2022\u003c/span\u003e) reported that heat curing results in a denser microstructure with reduced porosity and improved durability, making it ideal for environments requiring high strength and chemical resistance.\u003c/p\u003e \u003cp\u003eHowever, rapid setting times in heat-cured geopolymer concrete can pose challenges, particularly in maintaining workability during placement, as noted by Duan et al. (\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e2021\u003c/span\u003e). High fiber content further exacerbates this issue by increasing mix stiffness and reducing flowability, leading to difficulties in achieving a defect-free structure. Consequently, while heat curing enhances strength, careful mix design adjustments, such as using superplasticizers, may be necessary to mitigate workability loss, ensuring both mechanical performance and practical constructability.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec14\" class=\"Section2\"\u003e \u003ch2\u003e3.5 Flexural Strength\u003c/h2\u003e \u003cp\u003eThe flexural strength results illustrated in Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e highlight the significant impact of polypropylene fiber content on the performance of geopolymer concrete (GPC), underscoring the dynamic interplay between fiber reinforcement and the chemical processes within the geopolymer matrix. For the control mix containing 0% fiber, the average flexural strength progressively increased from 1.50 Mpa at 7 days to 2.28 Mpa at 90 days as illustrated in Supplementary Table\u0026nbsp;3. This consistent strength development is attributed to the ongoing geopolymerisation process, where aluminosilicate precursors react with alkaline activators to form a robust three-dimensional network (Dimas et al., \u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e2009\u003c/span\u003e). However, in the absence of fiber reinforcement, the material exhibits limited crack resistance and toughness, rendering it more prone to brittle failure under flexural loads. This finding suggests that unreinforced GPC may be better suited for structural applications primarily experiencing compressive forces, such as columns, where tensile and flexural stresses are minimal.\u003c/p\u003e \u003cp\u003eThe introduction of 0.5% fiber content improved flexural strengths, reaching 1.67 MPa at 7 days, 2.34 Mpa at 28 days, and 2.52 Mpa at 90 days. This enhancement is attributed to the fiber\u0026rsquo;s physical interaction with the geopolymer matrix. As demonstrated by Farhan et al. (\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e2021\u003c/span\u003e), polypropylene fibers are chemically inert in alkaline environments and do not interfere with geopolymerisation. Instead, their presence enhances toughness by bridging micro-cracks and distributing stress more evenly, leading to improved post-crack ductility. This property is particularly advantageous for structural elements susceptible to cracking, such as pavements and slabs, where thermal stresses and shrinkage could compromise performance.\u003c/p\u003e \u003cp\u003eThe mix with 1.0% fiber content exhibited the highest flexural strength, reaching 3.35 Mpa at 90 days, indicating an optimal balance between fiber dispersion and the integrity of the geopolymer matrix. The durability of polypropylene fibers within the alkaline environment plays a crucial role in reinforcing the composite. As noted by Mohammed et al. (\u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e2021\u003c/span\u003e), their resistance to degradation enhances mechanical properties, while their ability to bridge cracks improves energy absorption and stress transfer. Consequently, 1.0% fiber-reinforced GPC is particularly suited for infrastructure exposed to harsh conditions, such as marine environments or high-temperature industrial settings.\u003c/p\u003e \u003cp\u003eHowever, increasing the fiber content to 1.5% led to a decline in flexural strength, with values of 1.56 Mpa at 7 days, 2.43 Mpa at 28 days, and 2.81 Mpa at 90 days. This reduction can be attributed to fiber agglomeration and suboptimal wetting by the geopolymer matrix, creating weak interfacial zones that act as stress concentrators. Furthermore, Dimas et al. (\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e2009\u003c/span\u003e), also highlighted that excessive fiber content poses challenges related to effective compaction and densification, increasing the likelihood of voids that compromise overall strength. Therefore, this research finding reinforces the importance of optimizing fiber content to maximize mechanical benefits without inducing defects.\u003c/p\u003e \u003cp\u003eThese results align with previous studies emphasizing the critical role of fiber reinforcement in enhancing the mechanical properties of geopolymer concrete. Chen et al. (2020) demonstrated that optimal fiber content improves flexural strength while maintaining desirable workability, while Ahlawat et al. (\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2025\u003c/span\u003e) suggested that fiber fractions around 1.0% yield the best mechanical performance without negatively impacting material density and structural integrity.\u003c/p\u003e \u003cp\u003eComparative analysis between ambient-cured and heat-cured GPC further underscores the significance of this research. Heat curing accelerates the geopolymerisation process, leading to higher early-age compressive and flexural strengths due to the enhancement of the Al-Si network, as demonstrated by Zheng et al. (\u003cspan citationid=\"CR45\" class=\"CitationRef\"\u003e2024\u003c/span\u003e). Heat-cured GPC often achieves flexural strengths exceeding 4 Mpa at 28 days, significantly outperforming ambient-cured mixes, which exhibit lower early strengths but develop more robust long-term properties due to slower yet continuous geopolymerisation (Rabie et al., \u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e2022\u003c/span\u003e).\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec15\" class=\"Section2\"\u003e \u003ch2\u003e3.6 Durability\u003c/h2\u003e \u003cdiv id=\"Sec16\" class=\"Section3\"\u003e \u003ch2\u003e3.6.1 Oxygen permeability\u003c/h2\u003e \u003cp\u003eThe assessment of permeability in fiber-reinforced geopolymer concrete (GPC) reveals critical insights into the relationship between polypropylene fiber content and durability characteristics. Table\u0026nbsp;\u003cspan refid=\"Tab4\" class=\"InternalRef\"\u003e4\u003c/span\u003e presents the OPI results for samples containing 0%, 0.5%, 1%, and 1.5% fiber content.\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab4\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 4\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eOxygen Permeability Index (OPI) of Geopolymer Concrete with Different Fiber Contents\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"2\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eFiber content percentage\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eOPI\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e0%\u003c/p\u003e \u003cp\u003e0.5%\u003c/p\u003e \u003cp\u003e1%\u003c/p\u003e \u003cp\u003e1.5%\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e9.435\u003c/p\u003e \u003cp\u003e9.502\u003c/p\u003e \u003cp\u003e9.185\u003c/p\u003e \u003cp\u003e9.252\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003eThe control sample, with an average permeability index (OPI) of 9.435, served as a baseline, indicating moderate permeability. The inclusion of 0.5% fiber slightly increased the OPI to 9.502, signifying reduced permeability. This improvement can be attributed to enhanced matrix densification and reduced pore connectivity, which are essential for limiting the ingress of water and chlorides that compromise long-term structural integrity.\u003c/p\u003e \u003cp\u003eConversely, the 1.0% fiber sample exhibited a reduced OPI of 9.185, indicating increased permeability. This suggests that inadequate fiber dispersion may have led to micro-channel formation around the fibers, disrupting the geopolymer matrix continuity and facilitating the movement of harmful agents (Chen et al., \u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e2023\u003c/span\u003e). Similarly, the 1.5% fiber mix recorded an OPI of 9.2525, further reinforcing the observation that excessive fiber content can weaken matrix integrity by promoting void formation (Mohammed et al., \u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e2021\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eAmong all tested samples, the 0.5% fiber content demonstrated the highest OPI of 9.502, signifying the lowest permeability. Notably, this value falls within the optimal range for enhancing concrete durability, underscoring its resistance against water, chlorides, and gases\u0026mdash;an essential property for maintaining structural longevity, especially in moisture-prone and chemically aggressive environments. These findings align with prior studies emphasizing the role of reduced permeability in improving concrete resilience. Mechtcherine and Schmidt (\u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e2018\u003c/span\u003e) emphasized that minimizing permeability is fundamental for long-term durability, while Ganesh et al. (2021) demonstrated that optimized fiber content enhances microstructural properties, mitigating void formation and improving material longevity.\u003c/p\u003e \u003cp\u003eThe significance of low-permeability GPC is particularly relevant in infrastructure applications exposed to harsh environmental conditions, such as marine and industrial settings. The superior performance of 0.5% fiber-reinforced GPC in restricting the penetration of harmful substances makes it a viable choice for critical structural applications, addressing modern construction demands for enhanced durability and resilience.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec17\" class=\"Section3\"\u003e \u003ch2\u003e3.6.2 Water sorptivity and porosity\u003c/h2\u003e \u003cp\u003eThe calculated sorptivity (g/h⁰\u0026middot;⁵) for geopolymer concrete with 0%, 0.5%, 1%, and 1.5% fiber content at various curing times (0.5\u0026ndash;3 hours) is presented in Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003e. Sorptivity, determined from mass gain data (ΔM) using the formula ΔM/t⁰\u0026middot;⁵, measures the material\u0026rsquo;s capacity to absorb and transmit water through capillary action.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eThe evaluation of initial sorptivity in fiber-reinforced geopolymer concrete (GPC) provides critical insights into the effects of polypropylene fiber content on water absorption characteristics. The control mix, without fiber reinforcement, exhibited an initial sorptivity of 11.19 g/h⁰\u0026middot;⁵ as shown in Supplementary Table\u0026nbsp;4 within the first 0.5 hours, indicating rapid water uptake. This high sorptivity can be attributed to the early \u0026ndash; stage geopolymerisation reactions, where water facilitates the dissolution of aluminosilicate precurs\u0026ndash;rs such as metakaolin or fly ash. These observations align with Davidovits (\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e2008\u003c/span\u003e), who emphasized the role of silica and aluminum dissolution in forming a three-dimensional network of N-A-S-H (Sodium Alumino-Silicate Hydrate) gels.\u003c/p\u003e \u003cp\u003eAs geopolymerisation progresses, the network densifies, leading to a substantial sorptivity reduction to 0.14 g/h⁰\u0026middot;⁵ at 3 hours. This decline reflects the precipitation of N-A-S-H gels, which block capillary pores and reduce connectivity, a phenomenon corroborated by Provis and Bernal (\u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e2014\u003c/span\u003e), who documented similar pore-blocking behavior in alkali-activated materials. While the initially high sorptivity suggests poor early-age durability, the long-term decrease reinforces the characteristic behavior of geopolymer concretes, where early water absorption supports ionic mobility for continued geopolymerisation and microstructural refinement.\u003c/p\u003e \u003cp\u003eThe introduction of 0.5% fibers resulted in an initial sorptivity of 11.75 g/h⁰\u0026middot;⁵, slightly higher than the control mix. This increase can be attributed to capillary action introduced by the fibers, which provide additional pathways for water ingress. Studies by Kwan and Wong (\u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e2008\u003c/span\u003e) have demonstrated that fiber incorporation enhances initial water absorption due to the hydrophilic nature of fibers, which introduce hydroxyl groups that facilitate water uptake. Additionally, fibers modify the interfacial transition zones (ITZ) between the fibers and the geopolymer matrix, creating localized areas of increased alkalinity that expedite secondary geopolymerisation reactions.\u003c/p\u003e \u003cp\u003eNotably, the study observed that enhanced ion mobility within the ITZ accelerates N-A-S-H gel formation, leading to a quicker reduction in sorptivity over time. After three (3) hours, the sorptivity significantly decreased, indicating that the initial pathways created by fibers were effectively sealed through ongoing geopolymerisation. This observation supports Kwan and Wong\u0026rsquo;s (\u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e2008\u003c/span\u003e) findings that fiber inclusion enhances long-term durability, primarily due to matrix densification.\u003c/p\u003e \u003cp\u003eConversely, higher fiber contents of 1% and 1.5% resulted in the highest initial sorptivity values of 12.03 and 12.44 g/h⁰\u0026middot;⁵ respectively, due to amplified capillary action from the increased volume of fiber interfaces. The enhanced surface area of fibers likely promotes the dissolution of aluminosilicate species, fostering the development of more extensive N-A-S-H networks. However, excessive fiber content may increase pore connectivity, potentially compromising long-term durability if not optimally balanced. This aligns with findings by Addis et al. (\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e2022\u003c/span\u003e), who noted that while higher fiber volumes may initially enhance sorptivity, they can also contribute to fiber agglomeration and micro-void formation, acting as weak points in the matrix.\u003c/p\u003e \u003cp\u003eDespite the variations in initial sorptivity, the gradual reduction across all mixes underscores the benefits of ongoing polycondensation reactions, transforming the initially porous matrix into a denser network. The potential formation of C-A-S-H (Calcium Alumino-Silicate Hydrate) gels may further enhance this effect by providing additional pore-blocking mechanisms, like calcium silicate hydrate precipitation that mitigates capillary action. This perspective aligns with the findings of Addis et al. (\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e2022\u003c/span\u003e), emphasizing the need to optimize both fiber content and the geopolymerisation process to enhance durability.\u003c/p\u003e \u003cp\u003eWhile fiber incorporation significantly increases initial sorptivity, particularly at higher contents, it also promotes a more uniform moisture distribution within the geopolymer matrix. This distribution helps mitigate early-age cracking, reinforcing long-term durability by sustaining geopolymerisation reactions. The observed trends align with Kwan and Wong (\u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e2008\u003c/span\u003e) and Addis et al. (\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e2022\u003c/span\u003e), highlighting the role of fibers in modifying water transport pathways and improving the microstructural integrity of geopolymer concrete.\u003c/p\u003e \u003c/div\u003e \u003c/div\u003e \u003cdiv id=\"Sec18\" class=\"Section2\"\u003e \u003ch2\u003e4.8.S Chloride conductivity\u003c/h2\u003e \u003cp\u003eThe influence of fiber content on the porosity and conductivity of geopolymer concrete was investigated to assess its impact on durability. Table\u0026nbsp;\u003cspan refid=\"Tab5\" class=\"InternalRef\"\u003e5\u003c/span\u003e presents the results, revealing the complex interplay between fiber addition and the concrete microstructure, emphasizing the role of fiber distribution and its chemical interactions with the geopolymer matrix. Notably, chloride conductivity remained consistently low (0.025 mS/cm) across all fiber content samples, indicating that fiber addition did not significantly affect resistance to chloride ion penetration. This stability can be attributed to the chemically robust aluminosilicate network in the geopolymer matrix, which effectively limits ion transport irrespective of fiber content. The aluminosilicate gel, characterized by Si-O-Al and Si-O-Si bonds, forms a dense structure with low ionic diffusivity, thereby maintaining similar conductivity levels across varying fiber contents (Wang et al., \u003cspan citationid=\"CR42\" class=\"CitationRef\"\u003e2023\u003c/span\u003e).\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab5\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 5\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eChloride conductivity test of geopolymer concrete\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"3\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eSample\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eConductivity (mS/cm)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003ePorosity\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e0% fiber control\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e0.025\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e0.126\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e0.5% fiber\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e0.025\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e0.262\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e1% fiber\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e0.025\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e0.191\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e1.5% fiber\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e0.025\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e0.152\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003eHowever, porosity data reveals a more intricate interaction. The control sample (0% fiber) exhibited the lowest porosity (0.126), suggesting a highly compact matrix with minimal unreacted precursors or micro-voids, likely due to an effective geopolymerization process where the dissolution of aluminosilicate sources and subsequent polycondensation yield a tightly cross-linked network. The introduction of 0.5% fiber significantly increased porosity (0.262), potentially due to the formation of microchannels or interfacial voids between fibers and the matrix. This may result from inadequate fiber-matrix interaction or weak bonding, where unreacted silanol (Si-OH) groups hinder optimal cross-linking, preventing the formation of strong Si-O-Si bridges and increasing porosity (Chen et al., \u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e2023\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eInterestingly, porosity reduced to 0.191 at 1% fiber content, suggesting improved fiber dispersion and possible pozzolanic reactions at the fiber-matrix interface. The presence of fibers may have facilitated additional precipitation of aluminosilicate or calcium silicate hydrate (C-S-H) phases, effectively filled micro-voids and enhanced matrix density (Mohammed et al., \u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e2021\u003c/span\u003e). This reduction in porosity supports the hypothesis that an optimal fiber content can promote secondary geopolymerization reactions, forming additional Si-O-Al bonds that fill voids. At 1.5% fiber content, porosity further decreased to 0.152, indicating a denser matrix, though still higher than the control sample. This suggests that excessive fiber content may introduce interfacial flaws despite improved dispersion. The saturation of reactive sites or limited availability of alkali ions for further geopolymerization might lead to unreacted fibers or fiber agglomeration, creating localized stress points and hindering complete void elimination (Farhan et al., \u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e2021\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eThese findings underscore the importance of optimizing fiber content to balance mechanical performance and durability. The interaction between fibers and the geopolymer matrix must account for both physical distribution and chemical compatibility to minimize porosity while maintaining chloride resistance.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec19\" class=\"Section2\"\u003e \u003ch2\u003e3.7 Phase Composition of geopolymer concrete\u003c/h2\u003e \u003cp\u003eQuantitative X-ray diffraction (XRD) analysis was performed to characterize the phases of geopolymer concrete (GPC) samples with varying polypropylene fiber content (0%, 0.5%, 1%, and 1.5% by volume). The results, presented in Table\u0026nbsp;\u003cspan refid=\"Tab6\" class=\"InternalRef\"\u003e6\u003c/span\u003e, aimed to identify dominant crystalline and amorphous phases and correlate them with the mechanical properties and durability of the concrete. The analysis highlights the significance of optimizing fiber content and its impact on key phases such as quartz (SiO₂), N-A-S-H gel (sodium aluminosilicate hydrate), and mullite (Al₆Si₂O₁₃).\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab6\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 6\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eXRD analysis of reinforced geopolymer concrete with varying polypropylene fiber content\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"5\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eSample ID\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003e2θ (degrees)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003ed-spacing (\u0026Aring;)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003eIntensity (counts)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003ePhase Identification\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e0% Fiber\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e26.5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e3.36\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e12500\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003eQuartz (SiO₂)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e0% Fiber\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e32.1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e2.79\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e8500\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003eN-A-S-H gel\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e0% Fiber\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e41.5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e2.18\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e5500\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003eMullite (Al₆Si₂O₁₃)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e0.5% Fiber\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e26.5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e3.36\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e11800\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003eQuartz (SiO₂)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e0.5% Fiber\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e32.1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e2.79\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e9000\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003eN-A-S-H gel\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e0.5% Fiber\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e41.5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e2.18\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e6000\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003eMullite (Al₆Si₂O₁₃)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e1% Fiber\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e26.5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e3.36\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e12200\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003eQuartz (SiO₂)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e1% Fiber\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e32.1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e2.79\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e8800\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003eN-A-S-H gel\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e1% Fiber\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e41.5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e2.18\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e5800\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003eMullite (Al₆Si₂O₁₃)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e1.5% Fiber\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e26.5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e3.36\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e11500\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003eQuartz (SiO₂)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e1.5% Fiber\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e32.1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e2.79\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e8200\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003eN-A-S-H gel\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e1.5% Fiber\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e41.5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e2.18\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e5200\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003eMullite (Al₆Si₂O₁₃)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003eQuartz was consistently present across all samples, attributed to partially unreacted silica particles from precursor materials, serving as a critical filler that enhances the mechanical strength of the geopolymer matrix. This observation aligns with Provis and Bernal (\u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e2014\u003c/span\u003e), who emphasized quartz\u0026rsquo;s role in reinforcing the structural integrity of alkali-activated materials. The presence of N-A-S-H gel, detected at a 2θ angle of 32.1\u0026deg;, is a key indicator of successful geopolymerisation, forming a dense matrix that improves durability. This supports the findings by Davidovits (\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e2008\u003c/span\u003e), who underscored N-A-S-H gel\u0026rsquo;s fundamental role in developing geopolymer mechanical properties.\u003c/p\u003e \u003cp\u003eVariations in N-A-S-H gel intensity across fiber contents suggest that fibers influence the distribution and formation of this amorphous phase, potentially enhancing interfacial bonding with the geopolymer matrix. Kwan and Wong (\u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e2008\u003c/span\u003e) similarly noted that fiber reinforcement can improve interfacial interactions, increasing mechanical strength. However, a slight reduction in N-A-S-H gel intensity at higher fiber contents suggests a dilution effect, where excessive fibers may limit reactive site availability, thereby hindering geopolymerisation. This finding is crucial, as it highlights the existence of an optimal fiber content threshold that maximizes N-A-S-H gel formation without compromising reaction efficiency.\u003c/p\u003e \u003cp\u003eMullite, detected at 2θ\u0026thinsp;=\u0026thinsp;41.5\u0026deg;, is known for its thermal stability and contribution to mechanical strength. Its relatively stable intensity across varying fiber contents indicates that fiber inclusion does not significantly alter the thermal decomposition products of the geopolymer matrix. This stability corroborates Zheng et al. (\u003cspan citationid=\"CR45\" class=\"CitationRef\"\u003e2024\u003c/span\u003e), who found that the thermal and mechanical properties of geopolymer concrete remain largely unaffected by fiber additions within certain limits.\u003c/p\u003e \u003cp\u003eAn unidentified phase observed at 2θ\u0026thinsp;=\u0026thinsp;36.0\u0026deg; exhibited varying intensities, potentially representing intermediate products of incomplete geopolymerisation or residual precursors. Its intensity reduction with increasing fiber content suggests that improved fiber distribution enhances reaction completeness by increasing matrix permeability and facilitating ion transport during curing. This aligns with Addis et al. (\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e2022\u003c/span\u003e), who highlighted the importance of optimizing fiber content to improve reaction kinetics in geopolymerisation.\u003c/p\u003e \u003cp\u003eOverall, XRD analysis underscores the critical role of fiber content in modulating the phases of geopolymer concrete. The results demonstrate that optimizing fiber content is essential for balancing N-A-S-H gel formation while maintaining quartz and mullite integrity, directly influencing mechanical performance and durability. These findings reinforce prior research and provide valuable insights into fiber-reinforced geopolymer systems, contributing to the advancement of geopolymer concrete applications in construction.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec20\" class=\"Section2\"\u003e \u003ch2\u003e4.8 Statistical Analysis\u003c/h2\u003e \u003cp\u003eComprehensive regression and correlation analyses were performed to assess the relationship between compressive and flexural strengths of geopolymer concrete (GPC) samples with varying polypropylene fiber content (0%, 0.5%, 1%, and 1.5% by volume). These analyses aimed to determine the strength of the correlation between these two mechanical properties and the predictive power of flexural strength for estimating compressive strength. Key parameters evaluated as depicted in Table\u0026nbsp;\u003cspan refid=\"Tab7\" class=\"InternalRef\"\u003e7\u003c/span\u003e included the correlation coefficient (\u003cem\u003eR\u003c/em\u003e), coefficient of determination (\u003cem\u003eR\u003c/em\u003e\u0026sup2;), adjusted \u003cem\u003eR\u003c/em\u003e\u0026sup2;, standard error of estimate, and p-values for both the correlation and regression models.\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab7\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 7\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eRegression and correlation analysis of compressive and flexural strength\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"7\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c6\" colnum=\"6\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c7\" colnum=\"7\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eFiber Content (%)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003e\u003cem\u003eR\u003c/em\u003e (Correlation)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003e\u003cem\u003eR\u0026sup2;\u003c/em\u003e\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003eAdjusted \u003cem\u003eR\u0026sup2;\u003c/em\u003e\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003eStandard Error of Estimate\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c6\"\u003e \u003cp\u003ep-value (Correlation)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c7\"\u003e \u003cp\u003ep-value (Flexural Regression)\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e0.97\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e0.9\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e0.87\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e2.94\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e\u0026lt;\u0026thinsp;0.01\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e0.163\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e0.5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e0.98\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e0.92\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e2.65\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e\u0026lt;\u0026thinsp;0.01\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e0.128\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e0.98\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e0.93\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e2.21\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e0.12\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e0.116\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e1.5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e0.97\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e0.9\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e0.86\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e2.69\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e0.168\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e0.168\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003eThe analysis demonstrated exceptionally high positive correlations (\u003cem\u003eR\u003c/em\u003e\u0026thinsp;\u0026gt;\u0026thinsp;0.96) for all fiber contents, indicating a strong linear relationship between compressive and flexural strengths. These findings align with previous studies that have reported similar correlations in both traditional and geopolymer concretes. Kwan and Wong (\u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e2008\u003c/span\u003e) observed a linear correlation between compressive and flexural strengths in geopolymer concrete, attributing this relationship to the integrity of the matrix and its influence on mechanical performance. The high \u003cem\u003eR\u003c/em\u003e values suggest that as compressive strength increases, flexural strength tends to rise proportionately, a trend supported by the statistically significant \u003cem\u003ep\u003c/em\u003e-values for correlation (typically\u0026thinsp;\u0026lt;\u0026thinsp;0.05 for most fiber contents). This implies a shared underlying mechanism governing both properties, where factors such as efficient stress transfer at the fiber-matrix interface and the crack-bridging capabilities of fibers contribute significantly to overall strength development (Zheng et al., \u003cspan citationid=\"CR45\" class=\"CitationRef\"\u003e2024\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eParticularly notable is the higher correlation observed at 0.5% and 1% fiber contents, suggesting these levels of fiber reinforcement effectively enhance matrix distribution, thereby improving both compressive and flexural performance. This observation resonates with the findings by Ganesh et al. (2021), who demonstrated that moderate fiber content improves interfacial bonding and matrix integrity. Conversely, the slightly lower correlation at 1.5% fiber content may indicate that excessive fibers cause agglomeration or inadequate wetting, which reduces uniformity and diminishes the effectiveness of stress transfer mechanisms. Provis and Bernal (\u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e2014\u003c/span\u003e) similarly noted that excessive fiber content can disrupt the geopolymer matrix, compromising mechanical properties.\u003c/p\u003e \u003cp\u003eDespite the strong correlations observed, regression analysis reveals that flexural strength is not a statistically significant predictor of compressive strength at any fiber content level, with p-values exceeding 0.05 in all cases. This suggests that while compressive and flexural strengths are closely related, the variability in compressive strength cannot be fully explained by flexural strength alone. Other influencing factors, such as the degree of geopolymerisation, curing conditions, fiber-matrix adhesion, and precursor material properties, play critical roles in determining compressive strength. Kwan and Wong (\u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e2008\u003c/span\u003e) emphasized that compressive strength is a multifaceted property influenced by various interactions within the concrete matrix, and these findings reinforce that perspective.\u003c/p\u003e \u003cp\u003eThe high R\u0026sup2; values, approaching 1, indicate that a significant portion of compressive strength variability is influenced by factors beyond flexural strength. Addis et al. (\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e2022\u003c/span\u003e) highlighted that compressive strength is governed by both mechanical and chemical interactions, further supporting the notion that regression models using only flexural strength are insufficient for accurate prediction. The adjusted R\u0026sup2; values suggest strong explanatory power, particularly for the 0.5% and 1% fiber mixes, corroborating research by Zheng et al. (\u003cspan citationid=\"CR45\" class=\"CitationRef\"\u003e2024\u003c/span\u003e) that underscores the importance of model accuracy in predicting mechanical properties.\u003c/p\u003e \u003cp\u003eThe standard error of the estimate,XXXepressenting the deviation of observed compressive strengths from those predicted by the regression model, varies across different fiber contents. The lowest standard error (2.21 Mpa) at 1% fiber content suggests improved prediction accuracy, reflecting the effectiveness of this fiber concentration in balancing mechanical properties. Ganesh et al. (2021) similarly noted that optimal fiber content is crucial for achieving consistent mechanical performance. In contrast, the higher standard errors at other fiber contents (ranging from 2.65 Mpa to 2.94 Mpa) indicate greater variability, potentially linked to inconsistent fiber distribution. Provis and Bernal (\u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e2014\u003c/span\u003e) emphasized the importance of matrix homogeneity in enhancing the mechanical properties of geopolymer concrete, reinforcing the need for careful fiber optimization.\u003c/p\u003e \u003cp\u003eThe scatter plot illustrated in Fig.\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003e visually reinforces the relationship between compressive and flexural strengths across different fiber contents. The positive slope of the trend line further supports the strong correlation between these properties, indicating that improvements in compressive strength generally accompany enhancements in flexural strength. This interdependence is consistent with findings from Kwan and Wong (\u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e2008\u003c/span\u003e) and Zheng et al. (\u003cspan citationid=\"CR45\" class=\"CitationRef\"\u003e2024\u003c/span\u003e), highlighting the need for fiber optimization to achieve maximum performance. Such optimization is critical for ensuring structural integrity and durability, particularly in fiber-reinforced geopolymer concrete applications where both compressive and flexural strengths must be considered.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eOverall, the findings affirm a strong correlation between compressive and flexural strengths but demonstrate that flexural strength alone is not a reliable predictor of compressive strength in geopolymer concrete. The high correlation coefficients suggest that both strengths are influenced by common factors within the geopolymer matrix, primarily related to fiber-matrix interactions and geopolymerisation quality. However, the lack of statistical significance in the regression analysis highlights that compressive strength is determined by a more complex interplay of factors. Optimizing fiber content, curing conditions, and the composition of the geopolymer matrix is essential for enhancing both compressive and flexural properties, ensuring the practical applicability of geopolymer concrete in load-bearing and flexural-critical applications.\u003c/p\u003e \u003c/div\u003e"},{"header":"4. Conclusion","content":"\u003cp\u003eThis study investigated the potential of polypropylene fiber (PPF) as a reinforcement to enhance the mechanical and durability properties of ambient-cured geopolymer concrete (GPC). The results demonstrated that incorporating PPF significantly improved flexural strength, toughness, and durability, with an optimal PPF content of 1.0% achieving a flexural strength of 3.35 Mpa at 90 days without compromising compressive strength. Durability assessments confirmed that PPF reinforcement effectively reduced oxygen permeability and chloride ingress, enhancing the resistance of GPC to aggressive environments. X-ray diffraction (XRD) analysis validated the formation of N-A-S-H and C-A-S-H gels, which contributed to matrix densification and reduced permeability, thus improving long-term performance. Despite these benefits, higher PPF contents led to challenges such as reduced workability and increased porosity due to fiber agglomeration, highlighting the need for careful optimization of fiber content. The findings suggest that PPF-reinforced GPC could serve as a practical and energy-efficient alternative to heat-cured geopolymers, offering a sustainable solution to reduce the carbon footprint of the construction sector.\u003c/p\u003e \u003cp\u003eFrom a practical perspective, the improved durability and mechanical properties of PPF-reinforced GPC make it ideal for structural applications, particularly in environments exposed to chloride and oxygen ingress, such as coastal and industrial infrastructures. However, challenges in fiber dispersion and workability need to be addressed to facilitate large-scale implementation. It is recommended that future work focuses on optimizing fiber dispersion techniques, exploring the use of superplasticizers to maintain workability, and conducting long-term performance assessments under diverse environmental conditions. Additionally, a cost-benefit analysis comparing PPF-reinforced GPC with conventional concrete could help establish its economic feasibility. Overall, the successful integration of PPF into GPC represents a significant step forward in the development of sustainable and durable construction materials, aligning with global efforts to mitigate the environmental impact of concrete production.\u003c/p\u003e"},{"header":"Abbreviations","content":"\u003cp\u003eGPC \u0026ndash; Geopolymer Concrete\u003c/p\u003e\n\u003cp\u003ePPF \u0026ndash; Polypropylene Fiber\u003c/p\u003e\n\u003cp\u003eGGBS \u0026ndash; Ground Granulated Blast Furnace Slag\u003c/p\u003e\n\u003cp\u003eN-A-S-H \u0026ndash; Sodium Alumino-Silicate Hydrate\u003c/p\u003e\n\u003cp\u003eC-A-S-H \u0026ndash; Calcium Alumino-Silicate Hydrate\u003c/p\u003e\n\u003cp\u003eXRD \u0026ndash; X-ray Diffraction\u003c/p\u003e\n\u003cp\u003eXRF \u0026ndash; X-ray Fluorescence\u003c/p\u003e\n\u003cp\u003eOPI \u0026ndash; Oxygen Permeability Index\u003c/p\u003e\n\u003cp\u003eITZ \u0026ndash; Interfacial Transition Zone\u003c/p\u003e\n\u003cp\u003ePC \u0026ndash; Portland Cement\u003c/p\u003e\n\u003cp\u003eSANS \u0026ndash; South African National Standards\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eAcknowledgement\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe authors gratefully acknowledge the University of South Africa for providing funding, resources, equipment, and laboratory facilities to conduct this research.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAuthor Contributions\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eRadebe S.P.:\u003c/strong\u003e Conceptualization, methodology, investigation and review of related literature, data curation and analysis and writing of the original draft.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eMadirisha M.M.:\u0026nbsp;\u003c/strong\u003eConceptualization, methodology, writing of original draft, data curation and analysis, writing (review and editing), supervision.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eIkotun B.D.:\u003c/strong\u003e Conceptualization, methodology, writing of original draft, data curation and analysis, writing (review and editing), supervision.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eDada O.R\u003c/strong\u003e: Methodology, writing (review and editing).\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eConflict of interest:\u003c/strong\u003e The authors declare no competing interests.\u003c/p\u003e\u003ch2\u003eAcknowledgement\u003c/h2\u003e\u003cp\u003eThe authors gratefully acknowledge the University of South Africa for providing funding, resources, equipment, and laboratory facilities to conduct this research.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n\u003cli\u003eAddis, L. B., Sendekie, Z. B., \u0026amp; Satheesh, N. (2022). Degradation Kinetics and Durability Enhancement Strategies of Cellulosic Fiber‐Reinforced Geopolymers and Cement Composites. \u003cem\u003eAdvances in Materials Science and Engineering\u003c/em\u003e, \u003cem\u003e2022\u003c/em\u003e(1), 1981755.\u003c/li\u003e\n\u003cli\u003eAhlawat, A., Phogat, A., Punia, U., Chhikara, A., Dhingra, A. K., Garg, R. K., \u0026hellip; \u0026amp; Chhabra, D. (2025). Innovative Optimization of Mechanical Performance in Carbon Fiber-Reinforced Nylon Composite Using Artificial Neural Networks and Multi-Objective Genetic Algorithms. \u003cem\u003eJournal of Materials Engineering and Performance\u003c/em\u003e, 1-14.\u003c/li\u003e\n\u003cli\u003eAlzeebaree, R., Mawlod, A., Amen, D., Younis, K., \u0026amp; Mohammedameen, A. (2021). Fire resistance performance of fiber reinforced geopolymer concrete: review. E3s Web of Conferences, 318, 03003. \u003c/li\u003e\n\u003cli\u003eAydın, Y. (2023). Neural network predictive models for alkali-activated concrete carbon emission using metaheuristic optimization algorithms. Sustainability, 16(1), 142. \u003c/li\u003e\n\u003cli\u003eBokkhunthod, N., Thumrongvut, J., Supromwan, J., \u0026amp; Seangatith, S. (2022). Experimental study of cellular lightweight concrete-filled steel tube columns using hydraulic cement. Key Engineering Materials, 922, 147-152.\u003c/li\u003e\n\u003cli\u003eChen, W., Pan, J., Zhu, B., Ma, X., Zhang, Y., Chen, Y., \u0026hellip; \u0026amp; Cai, J. (2023). Improving mechanical properties of 3D printable \u0026lsquo;one-part \u0026lsquo;geopolymer concrete with steel fiber reinforcement. \u003cem\u003eJournal of Building Engineering\u003c/em\u003e, \u003cem\u003e75\u003c/em\u003e, 107077.\u003c/li\u003e\n\u003cli\u003eDavidovits, J. (2008). Geopolymer chemistry and applications. \u003cem\u003eGeopolymer Institute\u003c/em\u003e, 1(1), 1-16.\u003c/li\u003e\n\u003cli\u003eDe Silva, P., Sagoe-Crenstil, K., \u0026amp; Sirivivatnanon, V. (2007). Kinetics of geopolymerization: Role of Al2O3 and SiO2. \u003cem\u003eCement and Concrete Research\u003c/em\u003e, \u003cem\u003e37\u003c/em\u003e(4), 512-518.\u003c/li\u003e\n\u003cli\u003eDimas, A. et al. (2009). Effects of Fiber Reinforcement on Workability and Mechanical Properties of Geopolymer Concrete. Journal of Construction and Building Materials, 40, 175\u0026ndash;184.\u003c/li\u003e\n\u003cli\u003eDimas, D., Giannopoulou, I., \u0026amp; Panias, D. (2009). Polymerization in sodium silicate solutions: a fundamental process in geopolymerization technology. \u003cem\u003eJournal of materials science\u003c/em\u003e, \u003cem\u003e44\u003c/em\u003e(14), 3719-3730.\u003c/li\u003e\n\u003cli\u003eDuan, D., Wu, H., Wei, F., Song, H., Ma, Z., Chen, Z., \u0026amp; Cheng, F. (2021). Preparation, characterization, and rheological analysis of eco-friendly geopolymer grouting cementitious materials based on industrial solid wastes. \u003cem\u003eJournal of Building Engineering\u003c/em\u003e, \u003cem\u003e78\u003c/em\u003e, 107451.\u003c/li\u003e\n\u003cli\u003eDwijayanti, L., Ekaputri, J., \u0026amp; Bayuaji, R. (2016). Lightweight geopolymer binder with abaca fiber in different curing. Materials Science Forum, 841, 140-147. \u003c/li\u003e\n\u003cli\u003eEsparham, A. and Ghalatian, F. (2022). The features of geopolymer concrete as a novel approach for utilization in green urban structures. Journal of Composites and Compounds, 4(11), 89-96. \u003c/li\u003e\n\u003cli\u003eFarhan, K. Z., Johari, M. A. M., \u0026amp; Demirboğa, R. (2021). Impact of fiber reinforcements on properties of geopolymer composites: A review. \u003cem\u003eJournal of Building Engineering\u003c/em\u003e, \u003cem\u003e44\u003c/em\u003e, 102628.\u003c/li\u003e\n\u003cli\u003eGanesan, N., Abraham, R., \u0026amp; Raj, S. (2015). Durability characteristics of steel fiber reinforced geopolymer concrete. Construction and Building Materials, 93, 471-476. \u003c/li\u003e\n\u003cli\u003eGanesh, A. C., \u0026amp; Muthukannan, M. (2021). Development of high performance sustainable optimized fiber reinforced geopolymer concrete and prediction of compressive strength. \u003cem\u003eJournal of Cleaner Production\u003c/em\u003e, \u003cem\u003e282\u003c/em\u003e, 124543.\u003c/li\u003e\n\u003cli\u003eJuenger, M. C., \u0026amp; Siddique, R. (2015). Recent advances in understanding the role of supplementary cementitious materials in concrete. \u003cem\u003eCement and concrete research\u003c/em\u003e, \u003cem\u003e78\u003c/em\u003e, 71-80.\u003c/li\u003e\n\u003cli\u003eKorniejenko, K., Lin, W., \u0026amp; \u0026Scaron;imonov\u0026aacute;, H. (2020). Mechanical properties of short polymer fiber-reinforced geopolymer composites. Journal of Composites Science, 4(3), 128. \u003c/li\u003e\n\u003cli\u003eKwan, A. K. H., \u0026amp; Wong, H. S. (2008). Fiber reinforcement in high-performance geopolymer concrete. \u003cem\u003eJournal of Materials in Civil Engineering\u003c/em\u003e, 20(11), 730-736.\u003c/li\u003e\n\u003cli\u003eLetsosa C., Dada O., Ikotun B.D (2024). \u0026ldquo;The effects of different curing conditions on the polypropylene fibre reinforcement concrete\u0026rdquo; Journal of Physics: Conference Series. 2888(1). \u003c/li\u003e\n\u003cli\u003eLuhar, S., \u0026amp; Khandelwal, U. (2015). A study on water absorption and sorptivity of geopolymer concrete. International Journal of Civil Engineering, 2(8), 1-9.\u003c/li\u003e\n\u003cli\u003eMechtcherine, V., \u0026amp; Schmidt, M. (2018). The role of permeability in ensuring the durability of concrete structures. \u003cem\u003eJournal of Materials Science\u003c/em\u003e, 53(18), 12603-12618.\u003c/li\u003e\n\u003cli\u003eMohammed, Z. A., Al-Jaberi, L. A., \u0026amp; Shubber, A. N. (2021). Effect of polypropylene fiber on properties of geopolymer concrete based metakolin. \u003cem\u003eJournal of Engineering and Sustainable Development\u003c/em\u003e, \u003cem\u003e25\u003c/em\u003e(2), 58-67.\u003c/li\u003e\n\u003cli\u003ePalomo, A., Maltseva, O., Garcia-Lodeiro, I., \u0026amp; Fern\u0026aacute;ndez-Jim\u0026eacute;nez, A. (2021). Portland versus alkaline cement: continuity or clean break:\u0026ldquo;a key decision for global sustainability\u0026rdquo;. \u003cem\u003eFrontiers in Chemistry\u003c/em\u003e, \u003cem\u003e9\u003c/em\u003e, 705475.\u003c/li\u003e\n\u003cli\u003ePrimadyas, D. and Nurhuda, I. (2018). The comparison of bond strength between geopolymer concrete and opc concrete for plain reinforcing bars. Matec Web of Conferences, 159, 01017. \u003c/li\u003e\n\u003cli\u003eProvis, J. L., \u0026amp; Bernal, S. A. (2014). Geopolymers and alkali-activated materials. \u003cem\u003eAnnual Review of Materials Research\u003c/em\u003e, 44, 321-341.\u003c/li\u003e\n\u003cli\u003eRabie, M., Irshidat, M. R., \u0026amp; Al-Nuaimi, N. (2022). Ambient and heat-cured geopolymer composites: mix design optimization and life cycle assessment. \u003cem\u003eSustainability\u003c/em\u003e, \u003cem\u003e14\u003c/em\u003e(9), 4942.\u003c/li\u003e\n\u003cli\u003eReed, M., Lokuge, W., \u0026amp; Karunasena, W. (2014). Fiber-reinforced geopolymer concrete with ambient curing for in situ applications. Journal of Materials Science, 49(12), 4297-4304. \u003c/li\u003e\n\u003cli\u003eSANS 5861-3:2006: Concrete tests: Part 3 \u0026ndash; Making and curing of test specimens.\u003c/li\u003e\n\u003cli\u003eSANS 5863:2006: Concrete tests \u0026ndash; Compressive strength of hardened concrete\u003c/li\u003e\n\u003cli\u003eSANS. (2006). SANS 5844: 2006 - Testing of aggregate for concrete: Method for the determination of the particle density and water absorption. South African Bureau of Standards.\u003c/li\u003e\n\u003cli\u003eSANS. (2006). SANS 5860: 2006 - Testing of concrete: Method for the determination of the density of concrete. South African Bureau of Standards.\u003c/li\u003e\n\u003cli\u003eSANS. (2006). SANS 5862-1: 2006 - Testing of concrete: Part 1 - Workability. South African Bureau of Standards.\u003c/li\u003e\n\u003cli\u003eSANS. (2006). SANS 5864: 2006 - Testing of concrete: Method for the determination of the flexural strength of hardened concrete. South African Bureau of Standards.\u003c/li\u003e\n\u003cli\u003eSANS. (2008). SANS 201: 2008 - Method for the determination of the grading of aggregates. South African Bureau of Standards.\u003c/li\u003e\n\u003cli\u003eSANS. (2015). SANS 3001-CO3-1: 2015 - Testing of concrete for durability: Part 1 - Determination of density. South African Bureau of Standards.\u003c/li\u003e\n\u003cli\u003eSANS. (2015). SANS 3001-CO3-2: 2015 - Testing of concrete for durability: Part 2 - Determination of the water absorption of hardened concrete. South African Bureau of Standards.\u003c/li\u003e\n\u003cli\u003eSarker, P., Kelly, S., \u0026amp; Yao, Z. (2014). Effect of fire exposure on cracking, spalling and residual strength of fly ash geopolymer concrete. Materials \u0026amp; Design (1980-2015), 63, 584-592. \u003c/li\u003e\n\u003cli\u003eShaikh, F. (2019). Effect of cooling on the residual mechanical properties and cracking of plain and fibrous geopolymer concretes at elevated temperatures. Structural Concrete, 20(5), 1583-1595. \u003c/li\u003e\n\u003cli\u003eSivakrishna, A., Adesina, A., Awoyera, P. O., \u0026amp; Kumar, K. R. (2020). Green concrete: A review of recent developments. Materials Today: Proceedings, 27, 54-58.\u003c/li\u003e\n\u003cli\u003eTriwulan, T., Dwijayanti, L. Y., Ekaputri, J. J., \u0026amp; Bayuaji, R. (2016, February). Lightweight geopolymer binder with abaca fiber in different curing. In Materials Science Forum (Vol. 841, pp. 140-147). Trans Tech Publications Ltd.\u003c/li\u003e\n\u003cli\u003eWang, D. L., Tang, C. S., Pan, X. H., Liu, B., \u0026amp; Shi, B. (2023). Coupling effect of fiber reinforcement and MICP stabilization on the tensile behavior of calcareous sand. Engineering Geology, 317, 107090.\u003c/li\u003e\n\u003cli\u003eYazid, M., Faris, M., Abdullah, M., Nabiałek, M., Rahim, S., Salleh, M., \u0026hellip; \u0026amp; Jeż, B. (2022). Contribution of interfacial bonding towards geopolymers properties in geopolymers reinforced fibers: a review. Materials, 15(4), 1496. \u003c/li\u003e\n\u003cli\u003eYu, X., \u0026amp; Cao, C. (2003). Electrochemical study of the corrosion behavior of Ce sealing of anodized 2024 aluminum alloy. Thin Solid Films, 423(2), 252-256.\u003c/li\u003e\n\u003cli\u003eZheng, Y., Zhang, W., Zheng, L., \u0026amp; Zheng, J. (2024). Mechanical properties of steel fiber-reinforced geopolymer concrete after high temperature exposure. \u003cem\u003eConstruction and Building Materials\u003c/em\u003e, \u003cem\u003e439\u003c/em\u003e, 137394.\u003c/li\u003e\n\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":false,"highlight":"","institution":"","isAcceptedByJournal":true,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"iranian-journal-of-science-and-technology-transactions-of-civil-engineering","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"istc","sideBox":"Learn more about [Iranian Journal of Science and Technology, Transactions of Civil Engineering](http://link.springer.com/journal/40996)","snPcode":"40996","submissionUrl":"https://submission.nature.com/new-submission/40996/3","title":"Iranian Journal of Science and Technology, Transactions of Civil Engineering","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"stoa","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false},"keywords":"Ambient temperature curing, Durability enhancement, Geopolymer concrete, Polypropylene fiber, Sustainable construction","lastPublishedDoi":"10.21203/rs.3.rs-6778704/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-6778704/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eThis study investigated the effects of polypropylene fiber (PPF) reinforcement on the mechanical and durability properties of ambient-cured geopolymer concrete (GPC) composed of fly ash and ground granulated blast furnace slag (GGBS). While GPC offers a sustainable alternative to Portland cement due to its lower carbon footprint and elimination of heat curing, its inherent brittleness and low tensile strength limit structural applications. To address these challenges, PPF was incorporated at varying dosages (0%, 0.5%, 1%, and 1.5%) to assess its impact on workability, compressive strength, flexural strength, and durability. The results indicate that 1.0% PPF significantly improved flexural strength (3.35 MPa at 90 days) and overall toughness while maintaining compressive strength. However, higher PPF content reduced workability and increased porosity due to fiber agglomeration. Durability assessments showed that PPF reinforcement lowered oxygen permeability and chloride ingress, enhancing resistance to aggressive environments. X-ray diffraction (XRD) analysis confirmed the formation of sodium alumino-silicate hydrate (N-A-S-H) and calcium alumino-silicate hydrate (C-A-S-H) gels, contributing to matrix densification and reduced permeability. These findings suggest that PPF reinforcement enhances durability by refining the pore structure, as evidenced by reduced permeability and water absorption measurements. However, workability decreased at higher PPF contents due to fiber agglomeration. Despite challenges with fiber dispersion at higher dosages, statistical analysis revealed a strong correlation between compressive and flexural strength, underscoring the role of fiber content in mechanical performance. These findings demonstrate that PPF-reinforced GPC has strong potential for sustainable construction applications, particularly in environments requiring enhanced durability. Future research should focus on optimizing fiber dispersion techniques, refining mix designs, and evaluating long-term performance for large-scale implementation.\u003c/p\u003e","manuscriptTitle":"Durability and Strength Improvement of Ambient-Cured Geopolymer Concrete using Polypropylene Fibers","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2025-06-06 08:47:54","doi":"10.21203/rs.3.rs-6778704/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"decision","content":"Revision requested","date":"2025-06-27T05:39:47+00:00","index":"","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2025-06-23T15:48:26+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"116825000898676148556636774677324557164","date":"2025-06-05T11:18:23+00:00","index":"hide","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2025-06-04T12:46:29+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"52723092347001238675480846907939973636","date":"2025-06-03T23:29:00+00:00","index":"hide","fulltext":""},{"type":"reviewersInvited","content":"","date":"2025-06-03T15:21:29+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2025-05-30T13:48:14+00:00","index":"","fulltext":""},{"type":"checksComplete","content":"","date":"2025-05-30T13:45:23+00:00","index":"","fulltext":""},{"type":"submitted","content":"Iranian Journal of Science and Technology, Transactions of Civil Engineering","date":"2025-05-29T17:50:56+00:00","index":"","fulltext":""}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"iranian-journal-of-science-and-technology-transactions-of-civil-engineering","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"istc","sideBox":"Learn more about [Iranian Journal of Science and Technology, Transactions of Civil Engineering](http://link.springer.com/journal/40996)","snPcode":"40996","submissionUrl":"https://submission.nature.com/new-submission/40996/3","title":"Iranian Journal of Science and Technology, Transactions of Civil Engineering","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"stoa","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false}}],"origin":"","ownerIdentity":"5baa16e1-8e72-425c-9634-7ee3eb90dff8","owner":[],"postedDate":"June 6th, 2025","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"published-in-journal","subjectAreas":[],"tags":[],"updatedAt":"2025-08-04T16:42:59+00:00","versionOfRecord":{"articleIdentity":"rs-6778704","link":"https://doi.org/10.1007/s40996-025-01987-z","journal":{"identity":"iranian-journal-of-science-and-technology-transactions-of-civil-engineering","isVorOnly":false,"title":"Iranian Journal of Science and Technology, Transactions of Civil Engineering"},"publishedOn":"2025-07-29 16:13:18","publishedOnDateReadable":"July 29th, 2025"},"versionCreatedAt":"2025-06-06 08:47:54","video":"","vorDoi":"10.1007/s40996-025-01987-z","vorDoiUrl":"https://doi.org/10.1007/s40996-025-01987-z","workflowStages":[]},"version":"v1","identity":"rs-6778704","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-6778704","identity":"rs-6778704","version":["v1"]},"buildId":"8U1c8b4HqxoKbykW_rLl7","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}