Experimental Investigation on Mechanical and Microstructural Properties of Sulphur-Infiltrated Concrete (SIC)

Experimental Investigation on Mechanical and Microstructural Properties of Sulphur-Infiltrated Concrete (SIC) | 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 Experimental Investigation on Mechanical and Microstructural Properties of Sulphur-Infiltrated Concrete (SIC) Gayatri Harshal Pathak, Shrikant Charhate This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-7393894/v1 This work is licensed under a CC BY 4.0 License Status: Under Review Version 1 posted 12 You are reading this latest preprint version Abstract Sulphur-Infiltrated Concrete (SIC) is an improved method for enhancing the mechanical and durability properties of concrete through sulphur infiltration, with comparison studies also conducted using polypropylene (PP) fiber. This experimental study evaluates the mechanical and microstructural properties of SIC using fiber and sulphur infiltration techniques. The research examines strength using conventional and non-destructive testing methods (Rebound Hammer and UPV), flexural strength, and durability characteristics of SIC specimens compared to regular concrete. Microstructural analysis was performed using Scanning Electron Microscopy with Energy Dispersive X-ray Spectroscopy (SEM-EDX) and Fourier Transform Infrared Spectroscopy (FTIR) to understand the chemical interactions and structural changes. Results show that sulphur infiltration significantly enhances the mechanical properties of concrete. Average strength of regular concrete at 1 day of curing and 1 day of oven drying was 11.13 N/mm², while the sulphur-infiltrated concrete (SIC) achieved strength of 33.43 N/mm², showing an increase of approximately 200.45% whereas the Fiber Reinforced SIC showed 164% increase in strength. Polypropylene fibers were added at 600 g/m³, equal to approximately 0.025% of the total concrete mass by weight. SEM-EDX analysis showed uniform sulphur distribution within the concrete matrix, forming chemical bonds with cement hydration products. FTIR spectroscopy confirmed the formation of new chemical compounds between sulphur and cement paste. The improved performance is due to sulphur's ability to fill micro-voids, improve matrix density, and create additional bonding mechanisms. This research shows the potential of SIC as a sustainable construction material with superior mechanical properties and durability characteristics. Sulphur-Infiltrated Concrete (SIC) PP Fiber Compressive Strength SEM-EDX FTIR Microstructural Analysis Mechanical Properties Sustainable Construction Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 1. Introduction Concrete faces persistent challenges related to durability, permeability, and performance under aggressive environmental conditions. Among various modification methods, sulphur infiltration serves as a promising approach for developing high-performance concrete composites. While sulphur has been used in industry since the early 20th century [ 19 ], its systematic application in concrete enhancement has gained momentum over the past five decades. Sulphur-infiltrated concrete (SIC) involves introducing elemental sulphur into the pore structure of hardened concrete, fundamentally altering its microstructure and performance characteristics. Systematic investigation of this technique was first conducted by Thaulow [ 23 ], who demonstrated the potential of sulphur impregnation to significantly enhance concrete properties. The process involves initial curing for few hours then heating concrete specimens and infiltrating them with molten sulphur, which solidifies within the pore network, creating enhanced composite material [ 21 ]. Early research by Malhotra and colleagues established the foundation for understanding SIC behaviour. Their investigations revealed that sulphur infiltration could substantially increase compressive strength, reduce permeability, and enhance freeze-thaw resistance [ 11 , 12 , 13 , 15 , 16 ]. Later studies examined long-term strength and durability characteristics when exposed to different environmental factors [ 14 ]. Mechanical properties research by Alam and Juruf [ 1 ] and Brown and Baluch [ 5 ] identified factors influencing modulus of rupture, mix design parameters, and creep characteristics. Innovation in impregnation techniques was further explored by Mehta and colleagues [ 17 ], while Yuan and Chen [ 25 ] investigated sulphur-treated concrete applications. Durability considerations have been critical in SIC research. Berry and colleagues conducted pioneering work on sulphur-infiltrated autoclaved concrete [ 3 ] and investigated leaching behaviour in aqueous environments [ 4 ]. Studies examined stability under diverse environmental conditions, whereas Hope and Nashid [ 9 ] and Feldman and Beaudoin [ 8 ] advanced knowledge of composite behaviour and durability characteristics. Chemical research by Lusty et al. [ 10 ] and Mehta and Chen [ 18 ] provided understanding of leaching mechanisms and moisture resistance, along with analytical approaches including infrared spectroscopy [ 6 ]. Despite promising results, challenges exist in practical implementation. Sulphur leaching in alkaline environments [ 4 , 10 ], moisture resistance issues [ 18 ], and energy-intensive infiltration processes have limited widespread adoption. Recent comprehensive reviews by Fediuk et al. [ 7 ] critically examined properties and applications of sulphur-based concrete, highlighting research needs. Contemporary studies by Parmar and Parikh [ 20 ], Vlahovic et al. [ 24 ], and Sokolova et al. [ 22 ] have continued investigating sulphur concrete properties and applications. Advanced nano-material applications in cement composites have also been explored [ 2 ] Previous research on sulphur concrete has primarily focused on sulphur as a binder replacement for cement. However, few studies have explored the post-hardening infiltration method integrated with fiber reinforcement. This research gap necessitates comprehensive investigation of SIC's mechanical and microstructural properties to understand the underlying mechanisms and optimize material composition. The microstructural analysis of SIC is essential for understanding the interaction between sulphur and cement hydration products. Advanced characterization techniques such as SEM-EDX and FTIR provide insights into morphological changes, chemical composition, and bonding mechanisms. This investigation seeks to experimentally determine the mechanical performance and microstructural attributes of SIC with fiber reinforcement. The research objectives include evaluating compressive strength enhancement, analyzing microstructural changes through SEM-EDX and FTIR, determining optimal fiber content, and understanding the mechanisms responsible for property improvements. The significance of this research lies in its potential to develop sustainable, high-performance concrete materials suitable for various construction applications. The utilization of waste sulphur addresses environmental concerns while creating value-added construction materials. The findings will contribute to the understanding of SIC behaviour and provide guidelines for practical implementation. 2. Materials and Experimental Methods 2.1 Materials 2.1.1 Cement Grade 53 Ordinary Portland Cement (OPC) complying with IS 12269 − 2013 was utilized throughout the study. The cement exhibited specific gravity of 3.15, specific surface area of 320 m²/kg, and normal consistency of 30%. Chemical composition analysis revealed SiO₂ content of 21.2%, Al₂O₃ of 5.8%, Fe₂O₃ of 3.1%, CaO of 63.4%, and MgO of 2.3%. 2.1.2 Aggregates Fine aggregate consisted of manufactured sand with specific gravity 2.65, water absorption 1.2%, and fineness modulus 2.8. Coarse aggregates with maximum size 20mm, specific gravity 2.70, water absorption 0.8%, and impact value 18.5%. Both aggregates conformed to IS 383–2016 specifications. 2.1.3 Sulphur Commercial grade sulphur with purity exceeding 99.5% was utilized for infiltration. The sulphur exhibited melting point of 115°C, specific gravity of 2.07, and negligible water solubility. Chemical analysis confirmed minimal impurities including ash content below 0.1%. 2.1.4 Fibers Polypropylene fibers (length 12mm, diameter 18µm, tensile strength 400MPa) were used for experimental work. Fiber properties were verified through manufacturer specifications. 2.1.5 Water Potable water conforming to IS 456–2000 having pH value of 6.5 was utilized for mixing. 2.2 Mix Design and Specimen Preparation 2.2.1 Mix Design/ Proportions Mix design of concrete was done using IS 10262 − 2019 guidelines targeting minimum 30 N/mm 2 strength. The final mix proportions were cement: fine aggregate :coarse aggregate = 1:2.72:3.40 with water-cement ratio of 0.7 as presented in Table 1 . Table 1 Mix Proportions of Control Concrete and Sulphur-Infiltrated Concrete Sample Specimen Type Cement (kg/m 3 ) Sand (kg/m 3 ) Agg.20 mm (kg/m 3 ) Agg.10mm (kg/m 3 ) Water (kg/m 3 ) w/c a/c Sulphur Infiltrated (%) Fibers used (g/m 3 ) OPC (iv) CC 300 847 652 377 210 0.70 4.08 10.24 (max) - OPC (vi) SIC 300 847 652 377 210 0.70 4.08 0 - OPC (v) CC FRC 300 847 652 377 210 0.70 4.08 8.74 (max) 600 OPC (vii) SIC FRC 300 847 652 377 210 0.70 4.08 0 600 *CC-Control Concrete, SIC- Sulphur Infiltrated Concrete, FRC- Fiber Reinforced Concrete 2.2.2 Fiber Content Optimization Polypropylene fibers were added additionally at 600 g/m³, corresponding to approximately 0.025% of the total concrete mass by weight in the mix design used for OPC (v) and OPC (vii). 2.2.3 Specimen Preparation Concrete preparation was carried out using a tilting drum mixer. Dry ingredients were mixed for 2 minutes, then water was gradually added over 1 minute, with final mixing for 3 minutes. Fibers were incorporated during the final mixing stage to ensure even distribution. Fresh concrete was cast into 100 mm cube molds for compressive strength assessment and 100×100×500mm beam molds for flexural testing. Compaction process was done by vibrating table to eliminate air voids. Initial curing involved 24-hour moist curing at room temperature before demolding. Subsequently, specimens were water-cured at 27 ± 2°C for 1 day, 7 days and 28 days before sulphur infiltration. 2.3 Sulphur Infiltration Process 2.3.1 Pre-treatment Cured concrete specimens underwent pre-treatment involving surface cleaning and drying at 105°C to 110°C for 24 hours to remove moisture content to avoid formation of polysulphides. This step ensures effective sulphur penetration by eliminating moisture barriers. 2.3.2 Infiltration Procedure Sulphur infiltration was conducted using a existing molten sulphur infiltration chamber. The process involved heating sulphur to 140 ± 5°C in a temperature-controlled chamber. Pre-heated concrete cubes were infiltrated in molten sulphur for 4 hours under atmospheric pressure. The infiltration temperature and duration were optimized through preliminary trials. 2.3.3 Post-infiltration Treatment Following infiltration, specimens were allowed to cool gradually to room temperature over 4 hours. Excess surface sulphur was removed through just wiping out to ensure uniform specimen dimensions. Visual inspection and weight measurements before and after was taken to verify successful infiltration to ensure quality control. 2.4 Testing Procedures 2.4.1 Mechanical Testing Destructive Testing by Compressive Strength Testing Compressive strength assessment was carried out using a 3000kN capacity universal testing machine conforming to IS 516–1959. Cube specimens (100mm) were tested at 1day, 7 days and 28 days of curing for specimens with and without SIC. Also specimens were tested for FRC with and without SIC. Loading rate was maintained at 140 kg/cm²/min. NDT Non-destructive testing (NDT) was performed on the prepared concrete samples using the Rebound Hammer test to assess surface hardness and the Ultrasonic Pulse Velocity (UPV) test to evaluate internal integrity. These test results provided inputs into the compressive strength and uniformity of the concrete without causing any damage. Flexural Strength Testing Evaluation of flexural strength was performed using prismatic concrete beam specimens (100×100×500mm) under two-point loading configuration as per IS 516.The objective of this test was to evaluate the flexural performance of concrete under varying conditions, particularly with and without sulphur infiltration with two curing regimes considered: early-age concrete cured for 1 day and standard 28-day cured concrete specimens. This differentiation was made to assess the influence of sulphur infiltration on the flexural performance of the concrete. 2.4.2 Microstructural Analysis Scanning Electron Microscopy with Energy Dispersive X-ray Spectroscopy (SEM-EDX) SEM-EDX analysis was performed using a scanning electron microscope having EDX detector. Specimen preparation involved cutting small samples from tested specimens, mounting in epoxy resin, and polishing to achieve mirror finish. Samples were carbon-coated before analysis. Imaging was conducted at various magnifications to observe morphological features, sulphur distribution, and fiber-matrix interface. EDX analysis provided elemental composition mapping, particularly focusing on sulphur distribution and concentration within the concrete matrix. Fourier Transform Infrared Spectroscopy (FTIR) FTIR spectral analysis was executed using a FTIR spectrometer. Sample preparation entailed grinding representative samples to fine powder and incorporating with KBr pellets. Spectra were acquired across 4000 − 400 cm⁻¹ with 4 cm⁻¹ resolution. The study focused on detecting characteristic peaks associated with cement hydration products, sulphur compounds, and chemical bonds developed during infiltration. Peak interpretation was conducted using established literature and reference spectral data. 3. Results and Discussion 3.1 Mechanical Properties 3.1.1 Compressive Strength Analysis The strength progression of concrete specimens with and without SIC treatment displayed distinctive behavioural patterns during the curing periods. Control specimens without SIC exhibited a conventional strength gain trajectory, achieving 11.13 N/mm² at 1 day, 17.66 N/mm² at 7 days, and at 28 days it is 22.76 N/mm² of curing as shown in Fig. 1 . This represents a typical strength development pattern with approximately 59% and 105% strength increases from 1 to 7 days and 1 to 28 days, respectively. In contrast, SIC-treated specimens showed significantly enhanced early-age strength development, attaining 33.43 N/mm² at 1 day of curing, which represents a remarkable 200% improvement over the control specimens. However, the SIC specimens demonstrated a temporary strength reduction at 7 days (27.10 N/mm²) before recovering to achieve 35.23 N/mm² at 28 days. The final 28-day compressive strength of SIC specimens was 55% higher than the control specimens, indicating the beneficial long-term effects of sulphur impregnation on concrete strength development. The incorporation of polypropylene fibers in sulphur impregnated concrete (SIC) significantly influenced the compressive strength development compared to non-fiber reinforced SIC specimens. Control specimens without polypropylene fiber reinforcement demonstrated progressive strength gain, achieving 11.56 N/mm² at 1 day, 19.8 N/mm² at 7 days, and 24.16 N/mm² at 28 days of curing, representing strength increases of 71% and 109% from 1 to 7 days and 1 to 28 days, respectively as represented in Fig. 2 . Polypropylene fiber reinforced SIC specimens exhibited substantially enhanced early-age strength, attaining 30.7 N/mm² at 1 day—a remarkable 166% improvement over the control specimens. Similar to the previous SIC behaviour, fiber-reinforced specimens experienced a temporary strength decline at 7 days (21.06 N/mm²) before demonstrating recovery and achieving a final compressive strength of 32.11 N/mm² at 28 days. The ultimate 28-day strength of polypropylene fiber reinforced SIC specimens was 33% higher than the control specimens, indicating that fiber reinforcement enhances both early-age and long-term compressive strength performance while maintaining the characteristic strength development pattern observed in sulphur impregnated concrete systems. The strength enhancement mechanisms in SIC involve multiple factors. Sulphur infiltration fills capillary pores and micro-cracks, creating a denser matrix with reduced void content. The formation of sulphur-cement compound bonds contributes additional binding capacity. Fiber reinforcement provides crack bridging effects and improves load transfer mechanisms. 3.1.2 NDT Surface hardness evaluation was carried out using rebound hammer testing in accordance with IS:13311(2)-1992, employing horizontal testing orientation to determine strength characteristics of concrete specimens. Control specimens without treatment recorded average compressive strengths of 12, 18 and 23 N/mm² at 1, 7 and 28 days, respectively. Specimens treated with SIC showed average compressive strengths of 35 N/mm² at 1 day, 28 N/mm² at 7 days, and 38 N/mm² at 28 days. FRC specimens without SIC treatment shown compressive strengths of 12, 20 and 24 N/mm² at corresponding curing periods. The combined FRC-SIC specimens achieved compressive strengths of 32 N/mm² at 1 day, 22 N/mm² at 7 days and 34 N/mm² at 28 days. Rebound hammer results demonstrated increased surface hardness in SIC-treated specimens and corroborated the strength enhancement patterns identified in compressive testing analysis. Quality assessment of concrete specimens was conducted through UPV testing in compliance with IS 13311:1992 to determine internal structure characteristics. CC specimens registered pulse velocities of 3.26, 3.32, and 3.39 km/sec at 1, 7 and 28 days, respectively, demonstrating continuous improvement in concrete uniformity with curing age. SIC-treated specimens recorded the peak pulse velocities of 4.09 km/sec at 1 day, declining to 3.52 km/sec at 7 days, then increasing to 4.06 km/sec at 28 days. FRC specimens showed pulse velocities of 3.07, 3.82, and 3.87 km/sec at corresponding curing periods. Combined FRC-SIC specimens achieved pulse velocities of 3.86 km/sec at 1 day, 3.62 km/sec at 7 days, and 3.95 km/sec at 28 days as illustrated in Fig. 3 . UPV measurements confirmed improved concrete quality and density in SIC-treated specimens, with all readings exceeding 3.5 km/sec threshold, indicating good quality concrete according to recognized classification criteria. 3.1.3 Flexural Strength Enhancement Flexural strength results demonstrated significant improvements in SIC specimens. the incorporation of sulphur infiltrated concrete (SIC) and fiber reinforced concrete (FRC) exhibited distinct strength development patterns over the curing period. At 1 day of curing, SIC specimens demonstrated significantly higher early-age flexural strength of 3.62 N/mm² compared to control concrete at 1.35 N/mm², while FRC achieved 1.80 N/mm² and FRC-SIC combination reached 3.70 N/mm² as presented in Fig. 4 . After 28 days of curing, the control concrete showed substantial strength development to 3.56 N/mm², whereas SIC concrete experienced a marginal decrease to 3.49 N/mm². The FRC specimens exhibited progressive strength gain reaching 3.40 N/mm² at 28 days, while the FRC-SIC combination maintained relatively stable performance with a slight increase from 3.70 N/mm² to 3.72 N/mm² over the curing period, as illustrated in the flexural strength results versus curing age relationship. 3.2 Microstructural Analysis 3.2.1 SEM-EDX Analysis Results SEM analysis of the control concrete sample revealed a typical porous microstructure with visible voids and gaps between aggregate particles and cement paste Fig. 5 . The morphology showed discrete particles with clear boundaries and interconnected pore networks, characteristic of conventional concrete. In contrast, the sulphur infiltrated concrete (SIC) showed a significantly denser microstructure with decreased porosity and strengthened particle bonding, verifying successful pore filling by sulphur infiltration. EDX analysis confirmed distinct compositional differences between the samples. The control concrete showed negligible sulphur content (0.3 wt%, 0.2 at%), while the SIC demonstrated a substantial increase to 2.9 wt% (1.9 at%) sulphur content - nearly a 10-fold enhancement. The control sample was dominated by oxygen (53.0 wt%), silicon (12.8 wt%), and carbon (12.4 wt%), with calcium at 9.4 wt%, typical of ordinary Portland cement composition. The presence of sodium (2.4 wt%) in the control sample suggests alkali compounds from cement, which were reduced in the SIC sample. This compositional comparison clearly demonstrates successful sulphur infiltration in the SIC samples, correlating with the observed microstructural densification and enhanced compactness compared to the porous structure of control concrete. EDX analysis confirmed dramatic compositional differences, with FRC-SIC showing sulphur content of 19.3 wt% (10.9 at%) compared to only 0.6 wt% (0.3 wt%) in FRC - representing over a 30-fold increase. Other major elements included oxygen (FRC-SIC: 36.2 wt%; FRC: 49.9 wt%), carbon (FRC-SIC: 25.6 wt%; FRC: 16.7 wt%), and calcium (FRC-SIC: 10.4 wt%; FRC: 24.4 wt%). The substantial sulphur infiltration directly correlates with the observed microstructural densification, demonstrating effective pore filling and matrix enhancement in FRC-SIC compared to conventional FRC. 3.2.2 FTIR Spectroscopy Analysis Analysis done after FTIR provided insights into chemical interactions and bond formation in SIC as shown in Fig. 6 (a) and (b). FTIR spectroscopy revealed notable differences between sulphur-infiltrated and control concrete samples. Both samples exhibited characteristic concrete peaks including O-H stretching around 3400 cm⁻¹, carbonate stretching at ~ 1420–1490 cm⁻¹, and Si-O stretching at ~ 1098 cm⁻¹, confirming typical hydration products (C-S-H gel, portlandite, carbonates). However, sulphur infiltration induced several key changes: (i) enhanced peak intensity at 1678 cm⁻¹ indicating modified water bonding, (ii) appearance of additional peaks at 713.67 and 618.19 cm⁻¹ suggesting sulphur-concrete interactions, and (iii) slight shifts in silicate peak positions from 1000.66 cm⁻¹ (control) to 1098.35 cm⁻¹ (sulphur-infiltrated), potentially indicating altered C-S-H gel structure. The retention of major concrete peaks suggests that sulphur infiltration preserves the fundamental concrete matrix while introducing new chemical environments. The FTIR analysis, as shown in Table 2 , reveals distinct peak shifts and new bands in sulphur-infiltrated concrete, indicating chemical interactions between sulphur and concrete components. Table 2 Comparative FTIR Analysis of Control and Sulphur-Infiltrated Concrete Peak Assignment Control Concrete (cm⁻¹) Sulphur-Infiltrated Concrete (cm⁻¹) Attribution O-H stretching ~ 3400 3400.94 Portlandite, C-S-H gel H-O-H bending 1284.68 1678.62 Bound water CO₃²⁻ stretching 1420.45, 1279.32 1490.98, 1417.36 Carbonates Si-O stretching 1000.66 1098.35 C-S-H gel CO₃²⁻ bending 875.77 873.86 Carbonates New peaks Not observed 713.67, 618.19 Sulphur-concrete interactions 3.3 Durability Characteristics 3.3.1 Water Absorption Tests done for water absorption revealed significant improvements in SIC durability. Control concrete specimens showed water absorption of 4.8% by weight, while sulphur infiltration reduced this to 2.1% (56.3% reduction). The reduced absorption is attributed to pore-filling effects of sulphur infiltration. 3.3.2 Chemical Resistance Testing using sulphuric acid exposure showed enhanced performance of SIC. After 90 days exposure to 5% H₂SO₄ solution, control concrete specimens lost 17.6% compressive strength, while SIC specimens lost only 8.9% strength. The improved chemical resistance is attributed to reduced permeability and formation of stable sulphur compounds. 3.4 Economic and Environmental Considerations The economic analysis of SIC production indicates favourable cost-benefit ratios. While initial material costs increase by approximately 15–20% due to sulphur and infiltration processing, the enhanced durability and performance justify the investment. Life-cycle cost analysis demonstrates potential savings of 25–30% resulting from lower maintenance requirements. Environmental benefits include utilization of waste sulphur from petroleum refining, reducing disposal requirements. The enhanced durability of SIC structures extends service life, reducing material consumption and environmental impact over the structure's lifetime. 4. Conclusions Concrete samples with and without sulphur infiltration (Control and SIC) with a w/c ratio of 0.7 were experimentally investigated in this study. Fiber was also included in order to assess its impact on the SIC FRC. The objective was to observe the influence of molten sulphur on compressive strength, flexural strength and the microstructural properties. The findings of this study are as follows: Sulphur-infiltrated concrete (SIC) demonstrated substantial enhancement in early-age (1 day curing and 1 day oven drying) compressive strength compared to control specimens, with up to 200% increase at 1 day and 55% improvement at 28 days. The incorporation of polypropylene fibers in SIC did not result in further strength enhancement beyond that achieved by SIC alone, suggesting that the benefits of sulphur infiltration had the greatest influence on mechanical behaviour. Non-destructive testing using rebound hammer and ultrasonic pulse velocity confirmed the superior surface hardness and internal density of SIC specimens, validating the observed improvements in compressive strength and material integrity. SEM-EDX examination showed a denser microstructure and substantially increased sulphur content in SIC specimens compared to control and FRC, verifying efficient sulphur penetration and its impact on pore refinement and matrix densification. FTIR spectroscopy identified new absorption bands and peak shifts in SIC, indicating chemical interactions between sulphur and cementitious phases, while durability tests confirmed reduced water absorption and improved chemical resistance, supporting the long-term performance advantages of sulphur infiltration. The findings of this study contribute significantly to the understanding of SIC behaviour and provide a foundation for practical implementation in construction applications. The combination of mechanical testing and advanced microstructural analysis has elucidated the mechanisms responsible for property improvements, enabling optimization of SIC formulations for specific applications. Declarations Funding This research received no external funding. Conflict of Interest On behalf of all authors, the corresponding author states that there is no conflict of interest. Clinical trial registration Clinical trial number: Not applicable. Ethics Not applicable. Consent to Participate Not applicable. Consent for Publish Not applicable. Author Contribution The first author carried out all the experimental work, data analysis, and manuscript preparation. The corresponding author supervised the research work, provided guidance throughout the study, and assisted in reviewing and editing the manuscript. Data availability The datasets generated and/or analyzed during the current study are available from the corresponding author on reasonable request. 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Pathak","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAA9klEQVRIiWNgGAWjYPACCcZ++ccHHwBZPHxEaTgA1DKzIS3ZAKSFjUgtDIwbGnLUJEAcglrk3c8Yfv64x0J2A8MZtsqvOXYybAzMDx/dwKPF8EyOscSBZxLG2xl7j92W3ZYMdBibsXEOPi0NOQYSBw5IJO5s5ku7LbmNGaiFh00ar5b+N8Y/QFo2HOMxK5bcVk9Yi7xEjhnYlg1neMwYP247TFiLgcSzMoszBySMZ85gS5Zm3Hach42ZgF/k+5M336g4UCfbL8F88OPPbdX2/OzNDx/jteUAhwGcw8wDJvEoB9vSwP4AzmH8QUD1KBgFo2AUjEwAACAVTAI3G6+zAAAAAElFTkSuQmCC","orcid":"","institution":"Amity University","correspondingAuthor":true,"prefix":"","firstName":"Gayatri","middleName":"Harshal","lastName":"Pathak","suffix":""},{"id":514818932,"identity":"4aa9fd84-b999-4a68-84ce-ba6d95249d89","order_by":1,"name":"Shrikant Charhate","email":"","orcid":"","institution":"Amity University","correspondingAuthor":false,"prefix":"","firstName":"Shrikant","middleName":"","lastName":"Charhate","suffix":""}],"badges":[],"createdAt":"2025-08-17 18:08:08","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-7393894/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-7393894/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":91416322,"identity":"dd031faa-a97e-48d8-81d6-c436ad3ca39f","added_by":"auto","created_at":"2025-09-16 09:30:48","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":27107,"visible":true,"origin":"","legend":"\u003cp\u003eComparison of Compressive Strength of Control Concrete and Sulphur Infiltrated Concrete\u003c/p\u003e","description":"","filename":"1.png","url":"https://assets-eu.researchsquare.com/files/rs-7393894/v1/bcf48e8e7e6f9202e5e0fecc.png"},{"id":91416323,"identity":"85b0b6c7-3d71-4774-9790-85bc4d99e836","added_by":"auto","created_at":"2025-09-16 09:30:48","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":34989,"visible":true,"origin":"","legend":"\u003cp\u003eCompressive Strength of Polypropylene Fiber Reinforced Concrete with and without Sulphur Infiltration\u003c/p\u003e","description":"","filename":"2.png","url":"https://assets-eu.researchsquare.com/files/rs-7393894/v1/7ff3b2d98d4d9dbaa5d7488a.png"},{"id":91416324,"identity":"7475eb3b-fc32-4803-b59d-6b267e1086fa","added_by":"auto","created_at":"2025-09-16 09:30:48","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":45151,"visible":true,"origin":"","legend":"\u003cp\u003eUltrasonic pulse velocity development of concrete specimens with different treatments across curing ages\u003c/p\u003e","description":"","filename":"3.png","url":"https://assets-eu.researchsquare.com/files/rs-7393894/v1/2d8307238c1e64a204906f77.png"},{"id":91416326,"identity":"00ea64f2-841b-4fac-873e-f489906682f5","added_by":"auto","created_at":"2025-09-16 09:30:48","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":45546,"visible":true,"origin":"","legend":"\u003cp\u003eFlexural Strength Results of concrete specimens\u003c/p\u003e","description":"","filename":"4.png","url":"https://assets-eu.researchsquare.com/files/rs-7393894/v1/f5e6cfb66d0581244d2196d2.png"},{"id":91417503,"identity":"62fcd661-77ff-4d62-8d05-83d58b075980","added_by":"auto","created_at":"2025-09-16 09:38:48","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":275768,"visible":true,"origin":"","legend":"\u003cp\u003eSEM-EDX Analysis of Concrete Samples: Microstructural and Compositional Comparison\u003c/p\u003e","description":"","filename":"5.png","url":"https://assets-eu.researchsquare.com/files/rs-7393894/v1/7e9c373e51b10f831d7717f3.png"},{"id":91416325,"identity":"0b1306c5-4513-4f65-9131-ffce235574ef","added_by":"auto","created_at":"2025-09-16 09:30:48","extension":"png","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":75505,"visible":true,"origin":"","legend":"\u003cp\u003eFTIR spectra of (a) sulphur-infiltrated concrete and (b) control concrete showing characteristic peaks with wavenumber assignments.\u003c/p\u003e","description":"","filename":"6.png","url":"https://assets-eu.researchsquare.com/files/rs-7393894/v1/59df26fd5cd468b4758b8e40.png"},{"id":91419337,"identity":"4bf43619-0d3b-4fc0-b295-2d29f16a2342","added_by":"auto","created_at":"2025-09-16 09:54:49","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":1491346,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-7393894/v1/df045839-8694-43ca-a90d-368482d11c36.pdf"}],"financialInterests":"No competing interests reported.","formattedTitle":"Experimental Investigation on Mechanical and Microstructural Properties of Sulphur-Infiltrated Concrete (SIC)","fulltext":[{"header":"1. Introduction","content":"\u003cp\u003eConcrete faces persistent challenges related to durability, permeability, and performance under aggressive environmental conditions. Among various modification methods, sulphur infiltration serves as a promising approach for developing high-performance concrete composites. While sulphur has been used in industry since the early 20th century [\u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e], its systematic application in concrete enhancement has gained momentum over the past five decades.\u003c/p\u003e\u003cp\u003eSulphur-infiltrated concrete (SIC) involves introducing elemental sulphur into the pore structure of hardened concrete, fundamentally altering its microstructure and performance characteristics. Systematic investigation of this technique was first conducted by Thaulow [\u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e], who demonstrated the potential of sulphur impregnation to significantly enhance concrete properties. The process involves initial curing for few hours then heating concrete specimens and infiltrating them with molten sulphur, which solidifies within the pore network, creating enhanced composite material [\u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e].\u003c/p\u003e\u003cp\u003eEarly research by Malhotra and colleagues established the foundation for understanding SIC behaviour. Their investigations revealed that sulphur infiltration could substantially increase compressive strength, reduce permeability, and enhance freeze-thaw resistance [\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e, \u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e, \u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e, \u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e, \u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e]. Later studies examined long-term strength and durability characteristics when exposed to different environmental factors [\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e]. Mechanical properties research by Alam and Juruf [\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e] and Brown and Baluch [\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e] identified factors influencing modulus of rupture, mix design parameters, and creep characteristics. Innovation in impregnation techniques was further explored by Mehta and colleagues [\u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e], while Yuan and Chen [\u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e25\u003c/span\u003e] investigated sulphur-treated concrete applications.\u003c/p\u003e\u003cp\u003eDurability considerations have been critical in SIC research. Berry and colleagues conducted pioneering work on sulphur-infiltrated autoclaved concrete [\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e] and investigated leaching behaviour in aqueous environments [\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e]. Studies examined stability under diverse environmental conditions, whereas Hope and Nashid [\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e] and Feldman and Beaudoin [\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e] advanced knowledge of composite behaviour and durability characteristics. Chemical research by Lusty et al. [\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e] and Mehta and Chen [\u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e] provided understanding of leaching mechanisms and moisture resistance, along with analytical approaches including infrared spectroscopy [\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e].\u003c/p\u003e\u003cp\u003eDespite promising results, challenges exist in practical implementation. Sulphur leaching in alkaline environments [\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e, \u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e], moisture resistance issues [\u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e], and energy-intensive infiltration processes have limited widespread adoption. Recent comprehensive reviews by Fediuk et al. [\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e] critically examined properties and applications of sulphur-based concrete, highlighting research needs. Contemporary studies by Parmar and Parikh [\u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e], Vlahovic et al. [\u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e], and Sokolova et al. [\u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e] have continued investigating sulphur concrete properties and applications. Advanced nano-material applications in cement composites have also been explored [\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e]\u003c/p\u003e\u003cp\u003ePrevious research on sulphur concrete has primarily focused on sulphur as a binder replacement for cement. However, few studies have explored the post-hardening infiltration method integrated with fiber reinforcement. This research gap necessitates comprehensive investigation of SIC's mechanical and microstructural properties to understand the underlying mechanisms and optimize material composition.\u003c/p\u003e\u003cp\u003eThe microstructural analysis of SIC is essential for understanding the interaction between sulphur and cement hydration products. Advanced characterization techniques such as SEM-EDX and FTIR provide insights into morphological changes, chemical composition, and bonding mechanisms.\u003c/p\u003e\u003cp\u003eThis investigation seeks to experimentally determine the mechanical performance and microstructural attributes of SIC with fiber reinforcement. The research objectives include evaluating compressive strength enhancement, analyzing microstructural changes through SEM-EDX and FTIR, determining optimal fiber content, and understanding the mechanisms responsible for property improvements. The significance of this research lies in its potential to develop sustainable, high-performance concrete materials suitable for various construction applications. The utilization of waste sulphur addresses environmental concerns while creating value-added construction materials. The findings will contribute to the understanding of SIC behaviour and provide guidelines for practical implementation.\u003c/p\u003e"},{"header":"2. Materials and Experimental Methods","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e\u003ch2\u003e2.1 Materials\u003c/h2\u003e\u003cdiv id=\"Sec4\" class=\"Section3\"\u003e\u003ch2\u003e2.1.1 Cement\u003c/h2\u003e\u003cp\u003eGrade 53 Ordinary Portland Cement (OPC) complying with IS 12269\u0026thinsp;\u0026minus;\u0026thinsp;2013 was utilized throughout the study. The cement exhibited specific gravity of 3.15, specific surface area of 320 m\u0026sup2;/kg, and normal consistency of 30%. Chemical composition analysis revealed SiO₂ content of 21.2%, Al₂O₃ of 5.8%, Fe₂O₃ of 3.1%, CaO of 63.4%, and MgO of 2.3%.\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec5\" class=\"Section3\"\u003e\u003ch2\u003e2.1.2 Aggregates\u003c/h2\u003e\u003cp\u003eFine aggregate consisted of manufactured sand with specific gravity 2.65, water absorption 1.2%, and fineness modulus 2.8. Coarse aggregates with maximum size 20mm, specific gravity 2.70, water absorption 0.8%, and impact value 18.5%. Both aggregates conformed to IS 383\u0026ndash;2016 specifications.\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec6\" class=\"Section3\"\u003e\u003ch2\u003e2.1.3 Sulphur\u003c/h2\u003e\u003cp\u003eCommercial grade sulphur with purity exceeding 99.5% was utilized for infiltration. The sulphur exhibited melting point of 115\u0026deg;C, specific gravity of 2.07, and negligible water solubility. Chemical analysis confirmed minimal impurities including ash content below 0.1%.\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec7\" class=\"Section3\"\u003e\u003ch2\u003e2.1.4 Fibers\u003c/h2\u003e\u003cp\u003ePolypropylene fibers (length 12mm, diameter 18\u0026micro;m, tensile strength 400MPa) were used for experimental work. Fiber properties were verified through manufacturer specifications.\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec8\" class=\"Section3\"\u003e\u003ch2\u003e2.1.5 Water\u003c/h2\u003e\u003cp\u003ePotable water conforming to IS 456\u0026ndash;2000 having pH value of 6.5 was utilized for mixing.\u003c/p\u003e\u003c/div\u003e\u003c/div\u003e\u003cdiv id=\"Sec9\" class=\"Section2\"\u003e\u003ch2\u003e2.2 Mix Design and Specimen Preparation\u003c/h2\u003e\u003cdiv id=\"Sec10\" class=\"Section3\"\u003e\u003ch2\u003e2.2.1 Mix Design/ Proportions\u003c/h2\u003e\u003cp\u003eMix design of concrete was done using IS 10262\u0026thinsp;\u0026minus;\u0026thinsp;2019 guidelines targeting minimum 30 N/mm\u003csup\u003e2\u003c/sup\u003e strength. The final mix proportions were cement: fine aggregate :coarse aggregate\u0026thinsp;=\u0026thinsp;1:2.72:3.40 with water-cement ratio of 0.7 as presented in Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e.\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\u003eMix Proportions of Control Concrete and Sulphur-Infiltrated Concrete\u003c/p\u003e\u003c/div\u003e\u003c/caption\u003e\u003ccolgroup cols=\"11\"\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=\"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=\"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\u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c8\" colnum=\"8\"\u003e\u003c/div\u003e\u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c9\" colnum=\"9\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c10\" colnum=\"10\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c11\" colnum=\"11\"\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\u003eSpecimen Type\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c3\"\u003e\u003cp\u003eCement (kg/m\u003csup\u003e3\u003c/sup\u003e)\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c4\"\u003e\u003cp\u003eSand (kg/m\u003csup\u003e3\u003c/sup\u003e)\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c5\"\u003e\u003cp\u003eAgg.20 mm (kg/m\u003csup\u003e3\u003c/sup\u003e)\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c6\"\u003e\u003cp\u003eAgg.10mm (kg/m\u003csup\u003e3\u003c/sup\u003e)\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c7\"\u003e\u003cp\u003eWater (kg/m\u003csup\u003e3\u003c/sup\u003e)\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c8\"\u003e\u003cp\u003ew/c\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c9\"\u003e\u003cp\u003ea/c\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c10\"\u003e\u003cp\u003eSulphur Infiltrated (%)\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c11\"\u003e\u003cp\u003eFibers used (g/m\u003csup\u003e3\u003c/sup\u003e)\u003c/p\u003e\u003c/th\u003e\u003c/tr\u003e\u003c/thead\u003e\u003ctbody\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e\u003cb\u003eOPC (iv)\u003c/b\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e\u003cb\u003eCC\u003c/b\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e300\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e847\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e\u003cp\u003e652\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e\u003cp\u003e377\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e\u003cp\u003e210\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c8\"\u003e\u003cp\u003e0.70\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c9\"\u003e\u003cp\u003e4.08\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c10\"\u003e\u003cp\u003e10.24 (max)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c11\"\u003e\u003cp\u003e-\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e\u003cb\u003eOPC (vi)\u003c/b\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e\u003cb\u003eSIC\u003c/b\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e300\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e847\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e\u003cp\u003e652\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e\u003cp\u003e377\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e\u003cp\u003e210\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c8\"\u003e\u003cp\u003e0.70\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c9\"\u003e\u003cp\u003e4.08\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c10\"\u003e\u003cp\u003e0\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c11\"\u003e\u003cp\u003e-\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e\u003cb\u003eOPC (v)\u003c/b\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e\u003cb\u003eCC FRC\u003c/b\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e300\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e847\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e\u003cp\u003e652\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e\u003cp\u003e377\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e\u003cp\u003e210\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c8\"\u003e\u003cp\u003e0.70\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c9\"\u003e\u003cp\u003e4.08\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c10\"\u003e\u003cp\u003e8.74 (max)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c11\"\u003e\u003cp\u003e600\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e\u003cb\u003eOPC (vii)\u003c/b\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e\u003cb\u003eSIC FRC\u003c/b\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e300\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e847\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e\u003cp\u003e652\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e\u003cp\u003e377\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e\u003cp\u003e210\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c8\"\u003e\u003cp\u003e0.70\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c9\"\u003e\u003cp\u003e4.08\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c10\"\u003e\u003cp\u003e0\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c11\"\u003e\u003cp\u003e600\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003c/tbody\u003e\u003c/colgroup\u003e\u003ctfoot\u003e\u003ctr\u003e\u003ctd colspan=\"11\"\u003e*CC-Control Concrete, SIC- Sulphur Infiltrated Concrete, FRC- Fiber Reinforced Concrete\u003c/td\u003e\u003c/tr\u003e\u003c/tfoot\u003e\u003c/table\u003e\u003c/div\u003e\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec11\" class=\"Section3\"\u003e\u003ch2\u003e2.2.2 Fiber Content Optimization\u003c/h2\u003e\u003cp\u003ePolypropylene fibers were added additionally at 600 g/m\u0026sup3;, corresponding to approximately 0.025% of the total concrete mass by weight in the mix design used for OPC (v) and OPC (vii).\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec12\" class=\"Section3\"\u003e\u003ch2\u003e2.2.3 Specimen Preparation\u003c/h2\u003e\u003cp\u003eConcrete preparation was carried out using a tilting drum mixer. Dry ingredients were mixed for 2 minutes, then water was gradually added over 1 minute, with final mixing for 3 minutes. Fibers were incorporated during the final mixing stage to ensure even distribution. Fresh concrete was cast into 100 mm cube molds for compressive strength assessment and 100\u0026times;100\u0026times;500mm beam molds for flexural testing.\u003c/p\u003e\u003cp\u003eCompaction process was done by vibrating table to eliminate air voids. Initial curing involved 24-hour moist curing at room temperature before demolding. Subsequently, specimens were water-cured at 27\u0026thinsp;\u0026plusmn;\u0026thinsp;2\u0026deg;C for 1 day, 7 days and 28 days before sulphur infiltration.\u003c/p\u003e\u003c/div\u003e\u003c/div\u003e\u003cdiv id=\"Sec13\" class=\"Section2\"\u003e\u003ch2\u003e2.3 Sulphur Infiltration Process\u003c/h2\u003e\u003cdiv id=\"Sec14\" class=\"Section3\"\u003e\u003ch2\u003e2.3.1 Pre-treatment\u003c/h2\u003e\u003cp\u003eCured concrete specimens underwent pre-treatment involving surface cleaning and drying at 105\u0026deg;C to 110\u0026deg;C for 24 hours to remove moisture content to avoid formation of polysulphides. This step ensures effective sulphur penetration by eliminating moisture barriers.\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec15\" class=\"Section3\"\u003e\u003ch2\u003e2.3.2 Infiltration Procedure\u003c/h2\u003e\u003cp\u003eSulphur infiltration was conducted using a existing molten sulphur infiltration chamber. The process involved heating sulphur to 140\u0026thinsp;\u0026plusmn;\u0026thinsp;5\u0026deg;C in a temperature-controlled chamber. Pre-heated concrete cubes were infiltrated in molten sulphur for 4 hours under atmospheric pressure. The infiltration temperature and duration were optimized through preliminary trials.\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec16\" class=\"Section3\"\u003e\u003ch2\u003e2.3.3 Post-infiltration Treatment\u003c/h2\u003e\u003cp\u003eFollowing infiltration, specimens were allowed to cool gradually to room temperature over 4 hours. Excess surface sulphur was removed through just wiping out to ensure uniform specimen dimensions. Visual inspection and weight measurements before and after was taken to verify successful infiltration to ensure quality control.\u003c/p\u003e\u003c/div\u003e\u003c/div\u003e\u003cdiv id=\"Sec17\" class=\"Section2\"\u003e\u003ch2\u003e2.4 Testing Procedures\u003c/h2\u003e\u003cdiv id=\"Sec18\" class=\"Section3\"\u003e\u003ch2\u003e2.4.1 Mechanical Testing\u003c/h2\u003e\u003cp\u003e\u003cb\u003eDestructive Testing by Compressive Strength Testing\u003c/b\u003e\u003c/p\u003e\u003cp\u003eCompressive strength assessment was carried out using a 3000kN capacity universal testing machine conforming to IS 516\u0026ndash;1959. Cube specimens (100mm) were tested at 1day, 7 days and 28 days of curing for specimens with and without SIC. Also specimens were tested for FRC with and without SIC. Loading rate was maintained at 140 kg/cm\u0026sup2;/min.\u003c/p\u003e\u003cp\u003e\u003cb\u003eNDT\u003c/b\u003e\u003c/p\u003e\u003cp\u003eNon-destructive testing (NDT) was performed on the prepared concrete samples using the Rebound Hammer test to assess surface hardness and the Ultrasonic Pulse Velocity (UPV) test to evaluate internal integrity. These test results provided inputs into the compressive strength and uniformity of the concrete without causing any damage.\u003c/p\u003e\u003cp\u003e\u003cb\u003eFlexural Strength Testing\u003c/b\u003e\u003c/p\u003e\u003cp\u003eEvaluation of flexural strength was performed using prismatic concrete beam specimens (100\u0026times;100\u0026times;500mm) under two-point loading configuration as per IS 516.The objective of this test was to evaluate the flexural performance of concrete under varying conditions, particularly with and without sulphur infiltration with two curing regimes considered: early-age concrete cured for 1 day and standard 28-day cured concrete specimens. This differentiation was made to assess the influence of sulphur infiltration on the flexural performance of the concrete.\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec19\" class=\"Section3\"\u003e\u003ch2\u003e2.4.2 Microstructural Analysis\u003c/h2\u003e\u003cp\u003e\u003cb\u003eScanning Electron Microscopy with Energy Dispersive X-ray Spectroscopy (SEM-EDX)\u003c/b\u003e\u003c/p\u003e\u003cp\u003eSEM-EDX analysis was performed using a scanning electron microscope having EDX detector. Specimen preparation involved cutting small samples from tested specimens, mounting in epoxy resin, and polishing to achieve mirror finish. Samples were carbon-coated before analysis.\u003c/p\u003e\u003cp\u003eImaging was conducted at various magnifications to observe morphological features, sulphur distribution, and fiber-matrix interface. EDX analysis provided elemental composition mapping, particularly focusing on sulphur distribution and concentration within the concrete matrix.\u003c/p\u003e\u003cp\u003e\u003cb\u003eFourier Transform Infrared Spectroscopy (FTIR)\u003c/b\u003e\u003c/p\u003e\u003cp\u003eFTIR spectral analysis was executed using a FTIR spectrometer. Sample preparation entailed grinding representative samples to fine powder and incorporating with KBr pellets. Spectra were acquired across 4000\u0026thinsp;\u0026minus;\u0026thinsp;400 cm⁻\u0026sup1; with 4 cm⁻\u0026sup1; resolution.\u003c/p\u003e\u003cp\u003eThe study focused on detecting characteristic peaks associated with cement hydration products, sulphur compounds, and chemical bonds developed during infiltration. Peak interpretation was conducted using established literature and reference spectral data.\u003c/p\u003e\u003c/div\u003e\u003c/div\u003e"},{"header":"3. Results and Discussion","content":"\u003cdiv id=\"Sec21\" class=\"Section2\"\u003e\u003ch2\u003e3.1 Mechanical Properties\u003c/h2\u003e\u003cdiv id=\"Sec22\" class=\"Section3\"\u003e\u003ch2\u003e3.1.1 Compressive Strength Analysis\u003c/h2\u003e\u003cp\u003eThe strength progression of concrete specimens with and without SIC treatment displayed distinctive behavioural patterns during the curing periods. Control specimens without SIC exhibited a conventional strength gain trajectory, achieving 11.13 N/mm\u0026sup2; at 1 day, 17.66 N/mm\u0026sup2; at 7 days, and at 28 days it is 22.76 N/mm\u0026sup2; of curing as shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e. This represents a typical strength development pattern with approximately 59% and 105% strength increases from 1 to 7 days and 1 to 28 days, respectively. In contrast, SIC-treated specimens showed significantly enhanced early-age strength development, attaining 33.43 N/mm\u0026sup2; at 1 day of curing, which represents a remarkable 200% improvement over the control specimens. However, the SIC specimens demonstrated a temporary strength reduction at 7 days (27.10 N/mm\u0026sup2;) before recovering to achieve 35.23 N/mm\u0026sup2; at 28 days. The final 28-day compressive strength of SIC specimens was 55% higher than the control specimens, indicating the beneficial long-term effects of sulphur impregnation on concrete strength development.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003eThe incorporation of polypropylene fibers in sulphur impregnated concrete (SIC) significantly influenced the compressive strength development compared to non-fiber reinforced SIC specimens. Control specimens without polypropylene fiber reinforcement demonstrated progressive strength gain, achieving 11.56 N/mm\u0026sup2; at 1 day, 19.8 N/mm\u0026sup2; at 7 days, and 24.16 N/mm\u0026sup2; at 28 days of curing, representing strength increases of 71% and 109% from 1 to 7 days and 1 to 28 days, respectively as represented in Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e. Polypropylene fiber reinforced SIC specimens exhibited substantially enhanced early-age strength, attaining 30.7 N/mm\u0026sup2; at 1 day\u0026mdash;a remarkable 166% improvement over the control specimens. Similar to the previous SIC behaviour, fiber-reinforced specimens experienced a temporary strength decline at 7 days (21.06 N/mm\u0026sup2;) before demonstrating recovery and achieving a final compressive strength of 32.11 N/mm\u0026sup2; at 28 days. The ultimate 28-day strength of polypropylene fiber reinforced SIC specimens was 33% higher than the control specimens, indicating that fiber reinforcement enhances both early-age and long-term compressive strength performance while maintaining the characteristic strength development pattern observed in sulphur impregnated concrete systems.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003eThe strength enhancement mechanisms in SIC involve multiple factors. Sulphur infiltration fills capillary pores and micro-cracks, creating a denser matrix with reduced void content. The formation of sulphur-cement compound bonds contributes additional binding capacity. Fiber reinforcement provides crack bridging effects and improves load transfer mechanisms.\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec23\" class=\"Section3\"\u003e\u003ch2\u003e3.1.2 NDT\u003c/h2\u003e\u003cp\u003eSurface hardness evaluation was carried out using rebound hammer testing in accordance with IS:13311(2)-1992, employing horizontal testing orientation to determine strength characteristics of concrete specimens. Control specimens without treatment recorded average compressive strengths of 12, 18 and 23 N/mm\u0026sup2; at 1, 7 and 28 days, respectively. Specimens treated with SIC showed average compressive strengths of 35 N/mm\u0026sup2; at 1 day, 28 N/mm\u0026sup2; at 7 days, and 38 N/mm\u0026sup2; at 28 days. FRC specimens without SIC treatment shown compressive strengths of 12, 20 and 24 N/mm\u0026sup2; at corresponding curing periods. The combined FRC-SIC specimens achieved compressive strengths of 32 N/mm\u0026sup2; at 1 day, 22 N/mm\u0026sup2; at 7 days and 34 N/mm\u0026sup2; at 28 days. Rebound hammer results demonstrated increased surface hardness in SIC-treated specimens and corroborated the strength enhancement patterns identified in compressive testing analysis.\u003c/p\u003e\u003cp\u003eQuality assessment of concrete specimens was conducted through UPV testing in compliance with IS 13311:1992 to determine internal structure characteristics. CC specimens registered pulse velocities of 3.26, 3.32, and 3.39 km/sec at 1, 7 and 28 days, respectively, demonstrating continuous improvement in concrete uniformity with curing age. SIC-treated specimens recorded the peak pulse velocities of 4.09 km/sec at 1 day, declining to 3.52 km/sec at 7 days, then increasing to 4.06 km/sec at 28 days. FRC specimens showed pulse velocities of 3.07, 3.82, and 3.87 km/sec at corresponding curing periods. Combined FRC-SIC specimens achieved pulse velocities of 3.86 km/sec at 1 day, 3.62 km/sec at 7 days, and 3.95 km/sec at 28 days as illustrated in Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e. UPV measurements confirmed improved concrete quality and density in SIC-treated specimens, with all readings exceeding 3.5 km/sec threshold, indicating good quality concrete according to recognized classification criteria.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec24\" class=\"Section3\"\u003e\u003ch2\u003e3.1.3 Flexural Strength Enhancement\u003c/h2\u003e\u003cp\u003eFlexural strength results demonstrated significant improvements in SIC specimens. the incorporation of sulphur infiltrated concrete (SIC) and fiber reinforced concrete (FRC) exhibited distinct strength development patterns over the curing period. At 1 day of curing, SIC specimens demonstrated significantly higher early-age flexural strength of 3.62 N/mm\u0026sup2; compared to control concrete at 1.35 N/mm\u0026sup2;, while FRC achieved 1.80 N/mm\u0026sup2; and FRC-SIC combination reached 3.70 N/mm\u0026sup2; as presented in Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e. After 28 days of curing, the control concrete showed substantial strength development to 3.56 N/mm\u0026sup2;, whereas SIC concrete experienced a marginal decrease to 3.49 N/mm\u0026sup2;. The FRC specimens exhibited progressive strength gain reaching 3.40 N/mm\u0026sup2; at 28 days, while the FRC-SIC combination maintained relatively stable performance with a slight increase from 3.70 N/mm\u0026sup2; to 3.72 N/mm\u0026sup2; over the curing period, as illustrated in the flexural strength results versus curing age relationship.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003c/div\u003e\u003c/div\u003e\u003cdiv id=\"Sec25\" class=\"Section2\"\u003e\u003ch2\u003e3.2 Microstructural Analysis\u003c/h2\u003e\u003cdiv id=\"Sec26\" class=\"Section3\"\u003e\u003ch2\u003e3.2.1 SEM-EDX Analysis Results\u003c/h2\u003e\u003cp\u003eSEM analysis of the control concrete sample revealed a typical porous microstructure with visible voids and gaps between aggregate particles and cement paste Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e. The morphology showed discrete particles with clear boundaries and interconnected pore networks, characteristic of conventional concrete. In contrast, the sulphur infiltrated concrete (SIC) showed a significantly denser microstructure with decreased porosity and strengthened particle bonding, verifying successful pore filling by sulphur infiltration. EDX analysis confirmed distinct compositional differences between the samples. The control concrete showed negligible sulphur content (0.3 wt%, 0.2 at%), while the SIC demonstrated a substantial increase to 2.9 wt% (1.9 at%) sulphur content - nearly a 10-fold enhancement. The control sample was dominated by oxygen (53.0 wt%), silicon (12.8 wt%), and carbon (12.4 wt%), with calcium at 9.4 wt%, typical of ordinary Portland cement composition. The presence of sodium (2.4 wt%) in the control sample suggests alkali compounds from cement, which were reduced in the SIC sample. This compositional comparison clearly demonstrates successful sulphur infiltration in the SIC samples, correlating with the observed microstructural densification and enhanced compactness compared to the porous structure of control concrete.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003eEDX analysis confirmed dramatic compositional differences, with FRC-SIC showing sulphur content of 19.3 wt% (10.9 at%) compared to only 0.6 wt% (0.3 wt%) in FRC - representing over a 30-fold increase. Other major elements included oxygen (FRC-SIC: 36.2 wt%; FRC: 49.9 wt%), carbon (FRC-SIC: 25.6 wt%; FRC: 16.7 wt%), and calcium (FRC-SIC: 10.4 wt%; FRC: 24.4 wt%). The substantial sulphur infiltration directly correlates with the observed microstructural densification, demonstrating effective pore filling and matrix enhancement in FRC-SIC compared to conventional FRC.\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec27\" class=\"Section3\"\u003e\u003ch2\u003e3.2.2 FTIR Spectroscopy Analysis\u003c/h2\u003e\u003cp\u003eAnalysis done after FTIR provided insights into chemical interactions and bond formation in SIC as shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003e (a) and (b). FTIR spectroscopy revealed notable differences between sulphur-infiltrated and control concrete samples. Both samples exhibited characteristic concrete peaks including O-H stretching around 3400 cm⁻\u0026sup1;, carbonate stretching at ~\u0026thinsp;1420\u0026ndash;1490 cm⁻\u0026sup1;, and Si-O stretching at ~\u0026thinsp;1098 cm⁻\u0026sup1;, confirming typical hydration products (C-S-H gel, portlandite, carbonates). However, sulphur infiltration induced several key changes: (i) enhanced peak intensity at 1678 cm⁻\u0026sup1; indicating modified water bonding, (ii) appearance of additional peaks at 713.67 and 618.19 cm⁻\u0026sup1; suggesting sulphur-concrete interactions, and (iii) slight shifts in silicate peak positions from 1000.66 cm⁻\u0026sup1; (control) to 1098.35 cm⁻\u0026sup1; (sulphur-infiltrated), potentially indicating altered C-S-H gel structure. The retention of major concrete peaks suggests that sulphur infiltration preserves the fundamental concrete matrix while introducing new chemical environments.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003eThe FTIR analysis, as shown in Table\u0026nbsp;\u003cspan refid=\"Tab2\" class=\"InternalRef\"\u003e2\u003c/span\u003e, reveals distinct peak shifts and new bands in sulphur-infiltrated concrete, indicating chemical interactions between sulphur and concrete components.\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\u003eComparative FTIR Analysis of Control and Sulphur-Infiltrated Concrete\u003c/p\u003e\u003c/div\u003e\u003c/caption\u003e\u003ccolgroup cols=\"4\"\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=\"char\" char=\".\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e\u003cthead\u003e\u003ctr\u003e\u003cth align=\"left\" colname=\"c1\"\u003e\u003cp\u003ePeak Assignment\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c2\"\u003e\u003cp\u003eControl Concrete (cm⁻\u0026sup1;)\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c3\"\u003e\u003cp\u003eSulphur-Infiltrated Concrete (cm⁻\u0026sup1;)\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c4\"\u003e\u003cp\u003eAttribution\u003c/p\u003e\u003c/th\u003e\u003c/tr\u003e\u003c/thead\u003e\u003ctbody\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eO-H stretching\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e~\u0026thinsp;3400\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e3400.94\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003ePortlandite, C-S-H gel\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eH-O-H bending\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e1284.68\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e1678.62\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003eBound water\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eCO₃\u0026sup2;⁻ stretching\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e1420.45, 1279.32\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e1490.98, 1417.36\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003eCarbonates\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eSi-O stretching\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e1000.66\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e1098.35\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003eC-S-H gel\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eCO₃\u0026sup2;⁻ bending\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e875.77\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e873.86\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003eCarbonates\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eNew peaks\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eNot observed\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e713.67, 618.19\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003eSulphur-concrete interactions\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\u003c/div\u003e\u003cdiv id=\"Sec28\" class=\"Section2\"\u003e\u003ch2\u003e3.3 Durability Characteristics\u003c/h2\u003e\u003cdiv id=\"Sec29\" class=\"Section3\"\u003e\u003ch2\u003e3.3.1 Water Absorption\u003c/h2\u003e\u003cp\u003eTests done for water absorption revealed significant improvements in SIC durability. Control concrete specimens showed water absorption of 4.8% by weight, while sulphur infiltration reduced this to 2.1% (56.3% reduction). The reduced absorption is attributed to pore-filling effects of sulphur infiltration.\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec30\" class=\"Section3\"\u003e\u003ch2\u003e3.3.2 Chemical Resistance\u003c/h2\u003e\u003cp\u003eTesting using sulphuric acid exposure showed enhanced performance of SIC. After 90 days exposure to 5% H₂SO₄ solution, control concrete specimens lost 17.6% compressive strength, while SIC specimens lost only 8.9% strength. The improved chemical resistance is attributed to reduced permeability and formation of stable sulphur compounds.\u003c/p\u003e\u003c/div\u003e\u003c/div\u003e\u003cdiv id=\"Sec31\" class=\"Section2\"\u003e\u003ch2\u003e3.4 Economic and Environmental Considerations\u003c/h2\u003e\u003cp\u003eThe economic analysis of SIC production indicates favourable cost-benefit ratios. While initial material costs increase by approximately 15\u0026ndash;20% due to sulphur and infiltration processing, the enhanced durability and performance justify the investment. Life-cycle cost analysis demonstrates potential savings of 25\u0026ndash;30% resulting from lower maintenance requirements. Environmental benefits include utilization of waste sulphur from petroleum refining, reducing disposal requirements. The enhanced durability of SIC structures extends service life, reducing material consumption and environmental impact over the structure's lifetime.\u003c/p\u003e\u003c/div\u003e"},{"header":"4. Conclusions","content":"\u003cp\u003eConcrete samples with and without sulphur infiltration (Control and SIC) with a w/c ratio of 0.7 were experimentally investigated in this study. Fiber was also included in order to assess its impact on the SIC FRC. The objective was to observe the influence of molten sulphur on compressive strength, flexural strength and the microstructural properties. The findings of this study are as follows:\u003c/p\u003e\u003cp\u003e\u003col\u003e\u003cspan\u003e\u003cli\u003e\u003cp\u003eSulphur-infiltrated concrete (SIC) demonstrated substantial enhancement in early-age (1 day curing and 1 day oven drying) compressive strength compared to control specimens, with up to 200% increase at 1 day and 55% improvement at 28 days.\u003c/p\u003e\u003c/li\u003e\u003c/span\u003e\u003cspan\u003e\u003cli\u003e\u003cp\u003eThe incorporation of polypropylene fibers in SIC did not result in further strength enhancement beyond that achieved by SIC alone, suggesting that the benefits of sulphur infiltration had the greatest influence on mechanical behaviour.\u003c/p\u003e\u003c/li\u003e\u003c/span\u003e\u003cspan\u003e\u003cli\u003e\u003cp\u003eNon-destructive testing using rebound hammer and ultrasonic pulse velocity confirmed the superior surface hardness and internal density of SIC specimens, validating the observed improvements in compressive strength and material integrity.\u003c/p\u003e\u003c/li\u003e\u003c/span\u003e\u003cspan\u003e\u003cli\u003e\u003cp\u003eSEM-EDX examination showed a denser microstructure and substantially increased sulphur content in SIC specimens compared to control and FRC, verifying efficient sulphur penetration and its impact on pore refinement and matrix densification.\u003c/p\u003e\u003c/li\u003e\u003c/span\u003e\u003cspan\u003e\u003cli\u003e\u003cp\u003eFTIR spectroscopy identified new absorption bands and peak shifts in SIC, indicating chemical interactions between sulphur and cementitious phases, while durability tests confirmed reduced water absorption and improved chemical resistance, supporting the long-term performance advantages of sulphur infiltration.\u003c/p\u003e\u003c/li\u003e\u003c/span\u003e\u003c/ol\u003e\u003c/p\u003e\u003cp\u003eThe findings of this study contribute significantly to the understanding of SIC behaviour and provide a foundation for practical implementation in construction applications. The combination of mechanical testing and advanced microstructural analysis has elucidated the mechanisms responsible for property improvements, enabling optimization of SIC formulations for specific applications.\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eFunding\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThis research received no external funding.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eConflict of Interest\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eOn behalf of all authors, the corresponding author states that there is no conflict of interest.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eClinical trial registration\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eClinical trial number: Not applicable.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eEthics \u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eNot applicable.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eConsent to Participate\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eNot applicable.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eConsent for Publish\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eNot applicable.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAuthor Contribution\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe first author carried out all the experimental work, data analysis, and manuscript preparation. The corresponding author supervised the research work, provided guidance throughout the study, and assisted in reviewing and editing the manuscript.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eData availability\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe datasets generated and/or analyzed during the current study are available from the corresponding author on reasonable request.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\u003cli\u003e\u003cspan\u003eAlam MS, Juruf RS. Factors influencing the modulus of rupture of Sulphur-Infiltrated Concrete. Cem Concr Res. 1983;13(2):161\u0026ndash;70. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1016/0008-8846(83)90098-4\u003c/span\u003e\u003cspan address=\"10.1016/0008-8846(83)90098-4\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eShruthi BK, Shrikant C, A Review on Nano Materials for Cement Composites (June 26., 2020). Proceedings of the International Conference on Recent Advances in Computational Techniques (IC-RACT) 2020. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttp://dx.doi.org/10.2139/ssrn.3697550\u003c/span\u003e\u003cspan address=\"10.2139/ssrn.3697550\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eBerry EE, Hope BB. Preparation and properties of sulphur-infiltrated autoclaved concrete. 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(1980) Sulphur-treated concrete slabs \u003cem\u003eIn: Dhir RK\u003c/em\u003e, \u003cem\u003eMunday JGL (eds)\u003c/em\u003e Advances in Concrete Slab Technology Pergamon, Oxford, 75\u0026ndash;83 \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1016/B978-0-08-023256-0.50017-6\u003c/span\u003e\u003cspan address=\"10.1016/B978-0-08-023256-0.50017-6\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e.\u003c/span\u003e\u003c/li\u003e\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":"discover-civil-engineering","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"","sideBox":"Learn more about [Discover Civil Engineering](https://www.springer.com/journal/44290)","snPcode":"44290","submissionUrl":"https://submission.nature.com/new-submission/44290","title":"Discover Civil Engineering","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"stoa","reportingPortfolio":"Discover Series","inReviewEnabled":true,"inReviewRevisionsEnabled":true},"keywords":"Sulphur-Infiltrated Concrete (SIC), PP Fiber, Compressive Strength, SEM-EDX, FTIR, Microstructural Analysis, Mechanical Properties, Sustainable Construction","lastPublishedDoi":"10.21203/rs.3.rs-7393894/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-7393894/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eSulphur-Infiltrated Concrete (SIC) is an improved method for enhancing the mechanical and durability properties of concrete through sulphur infiltration, with comparison studies also conducted using polypropylene (PP) fiber. This experimental study evaluates the mechanical and microstructural properties of SIC using fiber and sulphur infiltration techniques. The research examines strength using conventional and non-destructive testing methods (Rebound Hammer and UPV), flexural strength, and durability characteristics of SIC specimens compared to regular concrete. Microstructural analysis was performed using Scanning Electron Microscopy with Energy Dispersive X-ray Spectroscopy (SEM-EDX) and Fourier Transform Infrared Spectroscopy (FTIR) to understand the chemical interactions and structural changes. Results show that sulphur infiltration significantly enhances the mechanical properties of concrete. Average strength of regular concrete at 1 day of curing and 1 day of oven drying was 11.13 N/mm\u0026sup2;, while the sulphur-infiltrated concrete (SIC) achieved strength of 33.43 N/mm\u0026sup2;, showing an increase of approximately 200.45% whereas the Fiber Reinforced SIC showed 164% increase in strength. Polypropylene fibers were added at 600 g/m\u0026sup3;, equal to approximately 0.025% of the total concrete mass by weight. SEM-EDX analysis showed uniform sulphur distribution within the concrete matrix, forming chemical bonds with cement hydration products. FTIR spectroscopy confirmed the formation of new chemical compounds between sulphur and cement paste. The improved performance is due to sulphur's ability to fill micro-voids, improve matrix density, and create additional bonding mechanisms. This research shows the potential of SIC as a sustainable construction material with superior mechanical properties and durability characteristics.\u003c/p\u003e","manuscriptTitle":"Experimental Investigation on Mechanical and Microstructural Properties of Sulphur-Infiltrated Concrete (SIC)","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2025-09-16 09:30:43","doi":"10.21203/rs.3.rs-7393894/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"decision","content":"Revision requested","date":"2025-09-23T11:02:59+00:00","index":"","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2025-09-18T19:21:37+00:00","index":"hide","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2025-09-14T12:54:35+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"330766349522185281707962891010263256628","date":"2025-09-11T14:04:09+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"52723092347001238675480846907939973636","date":"2025-09-08T23:20:45+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"262040376588351355849671913216975832095","date":"2025-09-08T14:12:38+00:00","index":"hide","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2025-09-08T14:04:52+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"191425959907295800921184990453894557804","date":"2025-09-08T13:58:32+00:00","index":"hide","fulltext":""},{"type":"reviewersInvited","content":"","date":"2025-09-08T13:15:32+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2025-09-01T11:12:24+00:00","index":"","fulltext":""},{"type":"checksComplete","content":"","date":"2025-08-30T04:38:43+00:00","index":"","fulltext":""},{"type":"submitted","content":"Discover Civil Engineering","date":"2025-08-30T04:36:11+00:00","index":"","fulltext":""}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"discover-civil-engineering","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"","sideBox":"Learn more about [Discover Civil Engineering](https://www.springer.com/journal/44290)","snPcode":"44290","submissionUrl":"https://submission.nature.com/new-submission/44290","title":"Discover Civil Engineering","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"stoa","reportingPortfolio":"Discover Series","inReviewEnabled":true,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"7996bc9c-2571-441c-939f-f3b7fc75232e","owner":[],"postedDate":"September 16th, 2025","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"under-review","subjectAreas":[],"tags":[],"updatedAt":"2025-11-14T05:38:08+00:00","versionOfRecord":[],"versionCreatedAt":"2025-09-16 09:30:43","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-7393894","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-7393894","identity":"rs-7393894","version":["v1"]},"buildId":"8U1c8b4HqxoKbykW_rLl7","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}