Influence of GGBS–Fly Ash Binder Composition on the Strength of Geopolymer Concrete with Natural and Recycled Concrete Aggregate

Influence of GGBS–Fly Ash Binder Composition on the Strength of Geopolymer Concrete with Natural and Recycled Concrete Aggregate | 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 Influence of GGBS–Fly Ash Binder Composition on the Strength of Geopolymer Concrete with Natural and Recycled Concrete Aggregate Ovijith Goswami, H. M. Raihan, S M Masudur Rahman This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-7894507/v1 This work is licensed under a CC BY 4.0 License Status: Posted Version 1 posted You are reading this latest preprint version Abstract High carbon-emitting Ordinary Portland Cement (OPC) requires sustainable options in construction practices. This study explores the manufacture of high-performance, sustainable geopolymer concrete (GPC) by substituting cement completely with Ground Granulated Blast-furnace Slag (GGBS) and Fly Ash (FA) in proportion with 35% Recycled Concrete Aggregate (RCA). In order to identify the best binder proportion of GGBS:FA for obtaining the desired 25 MPa compressive strength for practical on-site applications, four GPC mixes with different GGBS:FA ratios (100:0, 90:10, 80:20, 70:30) were produced using 10M alkaline activator solutions ( NaOH and Na₂SiO₃ ) as well as cured at atmosphere (ambient) and heat (75°C). Mechanical strengths were studied at 7, 14, 28 days. All the GPC mixes showed better strength compared to the OPC control mix. GPC-2 (90% GGBS: 10% FA) was the optimal mix that attained the best 28-day compressive and flexural strengths of 33.7 MPa as well as 3.60 MPa, respectively, after applying heat curing. Strength development in GPC mixes under heat curing condition consistently outer performed from the GPC mixes under ambient curing condition. The study concludes that the GGBS–FA system, particularly at a 90:10 ratio and when heat-cured, serves as a viable, high-strength alternative to OPC-based concrete and contributes significantly to sustainable construction practices through binder optimization and RCA utilization. Geopolymer concrete GGBS Fly ash Recycled aggregate Compressive strength Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Figure 8 Figure 9 Figure 10 Figure 11 Figure 12 1 Introduction Excessive usage by the construction sector of Ordinary Portland Cement (OPC) represents a great ecological problem. Manufacturing OPC represents the world's most prominent source of greenhouse emissions since it is responsible for 6–8% of global anthropogenic CO2 emissions and is extremely energetically intensive by consuming 15% of global industrial energy (Mohamad et al., 2022 ). On-going quarrying of the raw material equally depletes natural resources as well as devastates ecosystems (Bărbulescu & Hosen, 2025 ).These pressing issues create an urgent need for sustainable alternatives to conventional concrete (Mohamad et al., 2022 ). As these statistics highlight the scale of the problem, the construction industry must have to adopt materials that minimize environmental footprint without compromising structural integrity. Geopolymer Concrete (GPC) provides a potential alternative by replacing the entire OPC with a binder from by-product industrial material in the form of aluminosilicates, i.e., Fly Ash (FA) and Ground Granulated Blast-furnace Slag (GGBS). Current research demonstrates that industrial by-products, when properly utilized, can be not just replacements but rather better alternatives to conventional cementitious systems. Geo-polymerization, the resultant process, avoids the extremely high temperature characteristics in cement production and hence reduce the CO2 emissions by 90%. The GGBS-FA ratio has the highest positive influence; the GGBS content in the form of the high content in calcium provides the chemical accelerant by inducing the reaction in the FA at ambient temperatures and providing early strength gain— a critical property for practical applications (Akcaoglu et al., 2019 ; Ukesh Praveen & Srinivasan, 2017 ). Here, the composition of the binder is a key variable that affects not just early age strength development but also long-term durability and field applicability. For additional progress towards sustainability, in the current research adoption towards Recycled Concrete Aggregate (RCA) is undertaken through the utilization of demolition and building wastes and the conservation of natural aggregates. This creates a "doubly green" composite material (Zhang et al., 2023 ). The RCA utilization aligns with circular economy principles, that means its offering a dual benefit of waste reduction and resource conservation. However, a major obstacle to the on-site application of GPC is the traditional dependence on energy-intensive heat curing to achieve adequate strength (Jindal, 2018 ). Despite the many advantages of GPC, however, the use of high-temperature curing within GPC remains a practical limitation, particularly in areas where facilities for heat curing are lacking. Therefore, this study focuses on solving a key challenge: how to optimize a geopolymer concrete (GPC) system that can reliably sustain at hot and ambient temperature, making it practical and efficient for on-site construction. To address this limitation, the present study proposes a mix design approach that balances binder chemistry, aggregate selection, and curing conditions to achieve reliable performance of GPC under realistic site conditions. Main objectives in the current research work are: 1) evaluate the optimum mix proportion of geo-polymer concrete with different GGBS/Fly ash ratio (as a replacement of cement), alkaline activators, Natural and recycled aggregate under different curing condition and 2) exploring the compressive and flexural strength gain of the mixes of geo-polymer concrete. Scope of the research work is restricted by the target compressive strength in the range 25 MPa in the resultant concrete. Ratios on binder with GGBS:FA ratios 100:0, 90:10, 80:20, and 70:30 are included. Replacement of coarse aggregate by natural and recycled aggregate at 65% and 35% respectively. Water-cement ratio is 0.5. The alkaline activator solution consists of a combination where 10M (Molar) sodium hydroxide ( NaOH ) and sodium silicate (Na₂SiO₃) at a mass ratio of 1:2 were used. All 4×4×4-inch cube specimens are cured under ambient and hot temperature. Compressive and flexural strengths were tested at 7, 14, and 28 days, and the results are compared to a conventional OPC concrete (control mix) which is prepared under identical protocols. By systematically evaluating mix proportions and curing conditions, this study aims to contribute toward the development of GPC systems that are not only sustainable but also feasible for large scale construction. 2 Methodology 2.1 Process Flow Diagram This research focuses on the evaluation of geopolymer concrete made with GGBS and fly ash that act to reduce environmental pollution and mineral deficiency. Materials were first collected and tested for suitability checking, using the ACI 211.1-91 method (American Concrete Institute, 1991), mix proportions were calculated, followed by casting, de-molding, curing (hot water and ambient), compressive and flexure strengths were then tested. Entire working process is stated below in figure 1. 2.2 Material Selection Two types of coarse aggregates were used RCA (Recycled Concrete Aggregate) and NCA (Natural Coarse Aggregate) with a ratio of 35% and 65%. For binders and activators materials the ratio is followed as per table 1. Table 1: Coarse Aggregate, Binder and Activator Ratio S.L. Coarse Aggregates Binders Activators RCA NCA GGBS Fly Ash NaOH NaSiO 3 1 35% 65% 100% 0% 10M 10M 2 90% 10% 3 80% 20% 4 70% 30% Natural Aggregate: Up to ¾ inches size natural coarse aggregate used with a ratio of 65% due to the scarcity of natural aggregate from a local market (Bangla Bazar, Shershah, Bayezid, Chattogram). Recycled Aggregate: Used by maintaining the same size as the alternative of natural aggregate but with a ratio of 35% because of having a bad impact on the environment, purchased from the local market (Bangla Bazar, Shershah, Bayezid, Chattogram). Fine Aggregate: Sylhet sand with a FM of 3.0 (Bangla Bazar, Shershah, Bayezid, Chattogram) Binder: GGBS and Fly ash used as binder materials instead of cement as it binds concrete more easily. GGBS: GGBS (Ground Granular Blast Furnace Slag) is used as a binder in different proportions (as stated table 1) which is obtained from the blast furnace and collected from Mustafa Hakim Cement Company. The GGBS was granular and grounded manually in the laboratory to achieve a finer, more reactive powder suitable for geo-polymerization. While mechanical grinding is ideal, the manual process used here is noted as a potential limitation affecting particle size uniformity. Fly Ash: It is used as a binder in different proportions (as stated table 1). It is available in coal-fired power plants and is very cheap and was collected from the local market and imported from India through importers. Alkaline Activators: A mix of sodium hydroxide (NaOH) and sodium silicate (Na 2 SiO 3 ) was used as the alkaline activator solution. It was collected from Taj Scientific chemical shop, Chattogram. The NaOH concentration was 10M (in terms of molar), meaning 10×40 = 400g of NaOH solids per liter of solution, where 40 is the molecular weight of NaOH. Concentration of sodium silicate (Na 2 SiO 3 ) was also 10M. The ratio for Activator and Binders follows as the table 1. Water: Potable lab water is used for the concrete as per code. 2.3 Material Tests Material testing verifies that the materials meet required specifications through various tests. This study includes testing different types of material and specifications of specimens for compressive and flexural tests. Specimens: A total of 54 specimens were prepared, including geopolymer mixes with varying GGBS : fly ash ratios and conventional OPC controls. Specimens were tested for compressive and flexural strength at 7, 14, and 28 days under different curing conditions, as detailed in Table 2. Table 2 : Total Specimen Overview S.L. Mix Type GGBS:Fly Ash Ratio Curing Method Testing Ages (days) Test Types Specimen Dimensions (mm) Quantity 01 Geopolymer Concrete 100:00 Ambient & Heat Curing 7, 14, 28 Compression & Flexural Cube: 100×100×100 Beam:100×100×500 12 02 Geopolymer Concrete 90:10 Ambient & Heat Curing 7, 14, 28 Compression & Flexural Cube: 100×100×100 Beam:100×100×500 12 03 Geopolymer Concrete 80:20 Ambient & Heat Curing 7, 14, 28 Compression & Flexural Cube: 100×100×100 Beam:100×100×500 12 04 Geopolymer Concrete 70:30 Ambient & Heat Curing 7, 14, 28 Compression & Flexural Cube: 100×100×100 Beam:100×100×500 12 05 Controlled OPC Concrete — Water Curing @ Room Temperature 7, 14, 28 Compression & Flexural Cube: 100×100×100 Beam:100×100×500 6 Total: 54 numbers of samples were made for this research. Aggregate tests: Following tests were conducted for both coarse and fine aggregates: Bulk Specific gravity test, Dry unit weight test, Sieve analysis and Slump test (for wet concrete mix). Dry Unit Weight: The unit weight of aggregates, determined by AASHTO, measures the weight of a specific volume of graded aggregates. It is used to monitor aggregates consistency and for mix proportioning. The dry unit weight was obtained for Natural coarse aggregate ad Recycled Concrete aggregates were 1597kg/m 3 and 1024kg/m 3 and for fine aggregate it was 1548 kg/m 3 . Bulk Specific Gravity Test: It refers to the ratio of the weight in air of a unit volume of aggregate to the weight of an equal volume of gas free distilled water at a stated temperature. Specific gravity for NA = 2.486, for RCA = 1.706 and for fine aggregate= 2.26. Sieve analysis: Sieve analysis shows the size distribution of coarse aggregate, taken up to 20 mm in standard sieve size. Fineness modulus indicates the mean particle size and is used to grade the aggregate. Each sieve’s mass was divided by the total dry mass before washing and multiply by 100 to find the percent retained and passing. Calculated to the nearest 0.1%. By the sieve analysis, F.M for NCA and RCA was obtained 3.7 and 5.1. By the sieve analysis, obtained F.M for fine aggregate = 3.09. Slump Test: The mix yielded a slump value of 40 mm (4cm). Strength Testing: The compressive and flexural strength of GRAC (Geo-polymer Recycled Aggregate Concrete) and the control mixture (with natural coarse aggregates) was determined at 7, 14, and 28 days as per standards. 2.4 Alkaline Solution Preparation and Mixing Alkaline solution preparation: To prepare the alkaline activator, a combination of sodium hydroxide (NaOH) and sodium silicate (Na₂SiO₃) was used. The sodium hydroxide solution was prepared to a concentration of 10 Molar (10M) by dissolving 400 grams of NaOH pellets per liter of water. The sodium silicate solution used had a mass ratio of Na₂O to SiO₂ of approximately 0.5 and a specific gravity of 1.4. The two solutions were prepared separately and mixed together just prior to being introduced to the dry components of the mix, with a final mass ratio of sodium silicate to sodium hydroxide solution set at 2:1. Mix proportions: To establish a reliable baseline for comparison, a standard OPC mix was prepared using ACI 211.1-91(American Concrete Institute, 1991). This design guides the aggregate proportions later used in geopolymer mixes by replacing cement with GGBS and fly ash. Lime (CaCO3) addition with 5% of cement ratio during dry mixing of concrete materials. Mix Design of OPC Concrete (Using ACI 211.1-91 Method): To ensure a valid comparison, the Ordinary Portland Cement (OPC) control mix was prepared using the exact same aggregate blend as the geopolymer mixes: a combination of 65% Natural Coarse Aggregate (NCA) and 35% Recycled Concrete Aggregate (RCA). The final mix proportions, derived from the ACI 211.1-91 method and adjusted through trial batches to achieve the target slump of 40 mm, were as follows: Cement (OPC): 320 kg/m³ Water: 160 kg/m³ Fine Aggregate (FA): 715 kg/m³ Coarse Aggregate (CA): 1050 kg/m³ Mix Ratio (Cement : FA : CA : Water): 1 : 2.23 : 3.28 : 0.5 For the geopolymer concrete (GPC) mixes, the total binder quantity of 320 kg/m³ was maintained, replacing the cement with the various GGBS and Fly Ash combinations. Activator ratio = 1:2 (NaOH : Na 2 SiO 3 ) NaOH = 0.5 Litre. (10M) Na 2 SiO 3 = 1.0 Litre. (10M) 2.5 Casting, Demolding and Curing Casting: First, the fine aggregate (FA), coarse aggregates (RCA & NCA) mixed in a manually mixer for 1–2 min, followed by the addition of fly ash and GGBS to the mixer and mixed for a further 2–3 min. Alkali-activated solutions were then progressively poured into the mixer and mixed for another 2–3 min until a uniform consistency was achieved. After mixing, the concrete specimens were cast in 4×4×4 in. cube molds and compacted with a tamping rod. Demolding: All specimens were demolded after 24 hours. Curing: This study examined the effect of curing temperature on slag and fly ash–based geopolymer concrete. Research indicates that elevated curing temperatures (60–90 °C) greatly improve geopolymer strength by accelerating the reaction (geo-polymerization) process, and 70 °C often cited as ideal. Ambient curing is slower but still effective with the right mix design. Curing beyond 100 °C shows little added benefit (strength improvement) and wastes energy (Patil et al., 2014). Two curing methods were tested: Heat Curing: Demolded geopolymer concrete specimens were placed in a laboratory water bath and cured at 75°C for 24 hours. Ambient Curing: Demolded geopolymer concrete specimens were cured at room temperature (27 °C) and 95% relative humidity. To early strength gain without thermal input (heat curing), lime (CaCO3) was added to the mix to promote hydration alongside geo-polymerization. Controlled samples cured under room temperature (27 °C) and 95% relative humidity, without adding any additives. After curing, all specimens were stored in a controlled room at 27°C and 95% relative Humidity, until testing at 7, 14, and 28 days. 3 Results and Discussion 3.1 Compressive Strength Table 3 : Compressive Strengths of Concrete Mixes Mix ID GGBS : Fly Ash Ratio Curing Condition 7-Day Strength (MPa) 14-Day Strength (MPa) 28-Day Strength (MPa) Control N/A (OPC) Ambient 23.5 26.5 29.5 GPC-1 100:0 Ambient 25.8 28.5 31.5 Heat 28.0 30.5 33.2 GPC-2 90:10 Ambient 25.1 27.8 30.8 Heat 28.5 31.0 33.7 GPC-3 80:20 Ambient 23.2 25.9 28.9 Heat 27.3 29.8 32.5 GPC-4 70:30 Ambient 19.9 22.4 25.4 Heat 26.0 28.5 31.2 3.2 Flexural Strength Table 4 : Flexural Strengths of Concrete Mixes Mix ID GGBS : Fly Ash Ratio Curing Condition 7-Day Strength (MPa) 14-Day Strength (MPa) 28-Day Strength (MPa) Control N/A (OPC) Ambient 3.01 3.19 3.37 GPC-1 100:0 Ambient 3.15 3.31 3.48 Heat 3.28 3.42 3.57 GPC-2 90:10 Ambient 3.11 3.27 3.44 Heat 3.31 3.45 3.60 GPC-3 80:20 Ambient 2.99 3.15 3.33 Heat 3.24 3.38 3.53 GPC-4 70:30 Ambient 2.76 2.93 3.12 Heat 3.16 3.31 3.46 3.3 Discussion The results for compressive and flexural strength display the variations in geopolymer concrete with increasing ratios of GGBS and fly ash under ambient and heat curing conditions. All GPC mixes performed better than the control (OPC) mix at every curing age for compressive strength. The highest compressive strength produced at 28 days was seen in GPC-2 (90:10 GGBS:FA), when heat cured, at 33.7 MPa, with close competition by GPC-1 (100:0) with 33.2 MPa. It can generally be inferred that strength suffered a decline as fly ash increased, especially for ambient curing where GPC-4 (70:30) showed the minimum value of 25.4 MPa. A similar trend was shown by flexural strength. Again, under heat curing, GPC-2 gave highest strength on the 28th day, that is, 3.60 MPa, while the control mix gave 3.37 MPa. Just like others, heat curing improved strength for all mixes and especially those whose fly ash content replacement does not exceed 10% gained better than control mix. Both compressive and flexural strength results, thus, suggest that heat curing improves performance, and an optimal mix such as 90% GGBS and 10% fly ash delivers the highest strength results across all testing ages. The superior performance of the geopolymer mixes, particularly GPC-2 (90% GGBS and 10% Fly Ash), can be attributed to the synergistic reaction between the two binder materials. The high calcium content in GGBS acting here as a primary catalyst, which leading to rapid calcium-aluminosilicate-hydrate (C-A-S-H) gel formation alongside primary sodium-aluminosilicate-hydrate (N-A-S-H) gel from the geo-polymerization of fly ash. At here, dual-gel system helps to forming a denser concrete microstructure and high early-age strength development, especially under heat curing, which accelerates these chemical reactions. However, when the fly ash content increases to 20% and 30% (GPC-3 and GPC-4), a strength reduction is also noted here. This is probably because the lower amount of calcium-rich GGBS slows down the rate of reactions, especially under ambient curing conditions, where there isn’t much heat available to speed up reaction time. While fly ash is crucial for the formation of a stable geopolymer network, an optimal balance is necessary. The 90:10 ratio appears to provide this balance, offering enough GGBS to kickstart the reaction and enough fly ash to sustain it, resulting in the highest overall strengths development observed in this study. 4 Conclusion and Recommendations: 4.1 Conclusion The project aimed to obtain the best percentage of cement replacement using GGBS and fly ash-based geopolymer concrete, with partial use of recycled concrete aggregates (RCA). The following conclusions were made on the basis of the tests: Compressive Strength: All geopolymer mixes (GPC) were stronger than conventional OPC concrete. GPC-2 (90:10 GGBS:FA) under heat curing had the highest 28-day strength of 33.7 MPa, which was more than that of all other mixtures. Every mix of GPC shows that heat curing always gave higher strength as compared to ambient curing. With increasing fly ash content more than 10%, compressive strength decreased. GPC-4 (70:30) demonstrates the least strength in GPC mixes. 100% GGBS (GPC-1) performed quite well under ambient curing against control (OPC) mix; hence, it can be said that GGBS alone can significantly improve strength. Flexural Strength: Flexural strength also exhibited a similar trend as the compressive strength with GPC-2 (90:10) under heat curing again attaining the maximum strength at 3.60 MPa. Heat curing enhanced flexural strength for all mixes as compared to ambient curing. Mixes with the replacement up to 10% fly ash kept or increased flexural strength, but larger replacements (20-30%) reduced it slightly. Even the worst-performing GPC mix (GPC-4) under heat curing performed better than OPC concrete. Overall: The best compressive and flexural strength performance was achieved with GPC-2 (GGBS:FA; 90:10) under heat curing. Clearly, the findings support that a balanced combination of GGBS and fly ash, especially under heat curing, will perform stronger and more durable concrete than conventional OPC. 4.2 Recommendations for Future Work Future tests are beneficial to assess, in time, the overall strength and durability of GPC with increased percentages and finally 100% RCA replacement. Steam curing has to be studied as an alternative to hot water curing because usually strength decreases after prolonged curing in both ambient and hot water. It is recommended that GGBS be mechanically ground for better uniformity (uniform particle distribution), as manual grinding may not sufficiently enhance its reactivity for effective geopolymerization. This study used a 10M activator as a means; future work could explore using different levels of varying molarity for further strength improvement. In fact, many more trials need to be done with intermediate GGBS to FA ratios, as strength trends do not always follow a linear pattern. Declarations Data availability The datasets generated during the current study are available from the corresponding author on reasonable request. Acknowledgements The authors gratefully acknowledge the support provided by the Laboratory of the Department of Civil Engineering, Southern University Bangladesh. Funding This research received no external funding. Contributions Ovijith Goswami : Original manuscript writing, Analysis, Methodology, Calculation & Validation. H.M. Raihan : Graph, Maniscipt Editing, Data Acquisition. S M Masudur Rahman : Supervising. Ethics declarations Ethics approval and consent to participate This study did not involve human participants or animals. No ethical approval was required for the reported research, and there are no ethical issues associated with the work. Clinical trial number Not applicable. Consent for publication Not applicable. This study does not include any person’s data in any form (including individual details, images, or videos). Competing interests The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper. References American Concrete Institute. (1991, reapproved 2009). Standard practice for selecting proportions for normal, heavyweight, and mass concrete (ACI 211.1-91). American Concrete Institute . Akcaoglu, T., Cubukcuoglu, B., & Awad, A. (2019). A critical review of slag and fly-ash based geopolymer concrete. Computers and Concrete , 24 (5), 453–458. https://doi.org/10.12989/cac.2019.24.5.453 Bărbulescu, A., & Hosen, K. (2025). Cement Industry Pollution and Its Impact on the Environment and Population Health: A Review. Toxics , 13 (7), Article 7. https://doi.org/10.3390/toxics13070587 Jindal, B. B. (2018). Feasibility study of ambient cured geopolymer concrete -A review. Advances in Concrete Construction , 6 (4), 387–405. https://doi.org/10.12989/acc.2018.6.4.387 Mohamad, N., Muthusamy, K., Embong, R., Kusbiantoro, A., & Hashim, M. H. (2022). Environmental impact of cement production and Solutions: A review. Materials Today: Proceedings , 48 , 741–746. https://doi.org/10.1016/j.matpr.2021.02.212 Patil, A. A., Chore, H. S., & Dodeb, P. A. (2014). Effect of curing condition on strength of geopolymer concrete. Advances in Concrete Construction , 2 (1), 29–37. https://doi.org/10.12989/ACC.2014.2.1.029 Ukesh Praveen, P., & Srinivasan, K. (2017). Self-compacting geopolymer concrete-a review. IOP Conference Series: Materials Science and Engineering , 263 (3), 032024. https://doi.org/10.1088/1757-899X/263/3/032024 Zhang, P., Sun, X., Wang, F., & Wang, J. (2023). Mechanical Properties and Durability of Geopolymer Recycled Aggregate Concrete: A Review. Polymers , 15 (3), 615. https://doi.org/10.3390/polym15030615 Additional Declarations No competing interests reported. Cite Share Download PDF Status: Posted Version 1 posted 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. 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2","display":"","copyAsset":false,"role":"figure","size":29707,"visible":true,"origin":"","legend":"\u003cp\u003eTests conducted for aggregates\u003c/p\u003e","description":"","filename":"2.png","url":"https://assets-eu.researchsquare.com/files/rs-7894507/v1/f36b7b9f95e42c5aa23972cd.png"},{"id":95383868,"identity":"7cccde23-d9f9-4c79-9843-ea801911c250","added_by":"auto","created_at":"2025-11-07 12:28:27","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":124237,"visible":true,"origin":"","legend":"\u003cp\u003eCompressive strength at Hot water curing.\u003c/p\u003e","description":"","filename":"3.png","url":"https://assets-eu.researchsquare.com/files/rs-7894507/v1/9b46cadaeeb19d0958d7d9fd.png"},{"id":95526915,"identity":"9e5b0dc4-0c98-4675-966e-75411d01f623","added_by":"auto","created_at":"2025-11-10 10:08:41","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":107944,"visible":true,"origin":"","legend":"\u003cp\u003eCompressive strength at Ambient curing.\u003c/p\u003e","description":"","filename":"4.png","url":"https://assets-eu.researchsquare.com/files/rs-7894507/v1/966cf3ddf41185b5572c44aa.png"},{"id":95383874,"identity":"0ec74e94-8dea-45dd-82fa-617c7a476d65","added_by":"auto","created_at":"2025-11-07 12:28:27","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":56483,"visible":true,"origin":"","legend":"\u003cp\u003eCompare to the design compressive strength, after 7 days.\u003c/p\u003e","description":"","filename":"5.png","url":"https://assets-eu.researchsquare.com/files/rs-7894507/v1/d57d711a0d6529d9c59cc4e1.png"},{"id":95383880,"identity":"ec7196fd-650d-40d8-a76b-941cf6c2e6eb","added_by":"auto","created_at":"2025-11-07 12:28:27","extension":"png","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":58775,"visible":true,"origin":"","legend":"\u003cp\u003eCompare to the design compressive strength, after 14 days.\u003c/p\u003e","description":"","filename":"6.png","url":"https://assets-eu.researchsquare.com/files/rs-7894507/v1/ad8a00b948cd7ff9b9325827.png"},{"id":95383879,"identity":"2baf3401-c9f2-42e3-aa69-77d14609bbec","added_by":"auto","created_at":"2025-11-07 12:28:27","extension":"png","order_by":7,"title":"Figure 7","display":"","copyAsset":false,"role":"figure","size":62545,"visible":true,"origin":"","legend":"\u003cp\u003eCompare to the design compressive strength, after 28 days.\u003c/p\u003e","description":"","filename":"7.png","url":"https://assets-eu.researchsquare.com/files/rs-7894507/v1/ecb5c4ea3f3591dbedc8bbaa.png"},{"id":95526461,"identity":"3bd6a4a2-d04b-4bcf-a004-b06b526914db","added_by":"auto","created_at":"2025-11-10 10:07:00","extension":"png","order_by":8,"title":"Figure 8","display":"","copyAsset":false,"role":"figure","size":103271,"visible":true,"origin":"","legend":"\u003cp\u003eFlexural strength at Hot water curing.\u003c/p\u003e","description":"","filename":"8.png","url":"https://assets-eu.researchsquare.com/files/rs-7894507/v1/4441482a90c41ff4e0ff75e8.png"},{"id":95525655,"identity":"b7902ef1-6003-408e-a4ea-59c87441d71e","added_by":"auto","created_at":"2025-11-10 10:05:31","extension":"png","order_by":9,"title":"Figure 9","display":"","copyAsset":false,"role":"figure","size":82927,"visible":true,"origin":"","legend":"\u003cp\u003eFlexural strength at Ambient curing.\u003c/p\u003e","description":"","filename":"9.png","url":"https://assets-eu.researchsquare.com/files/rs-7894507/v1/bdfe8849bfcd5138bad44dde.png"},{"id":95383876,"identity":"810f582e-85ca-4ab5-afcb-b5c92cc80e47","added_by":"auto","created_at":"2025-11-07 12:28:27","extension":"png","order_by":10,"title":"Figure 10","display":"","copyAsset":false,"role":"figure","size":67517,"visible":true,"origin":"","legend":"\u003cp\u003eCompare to the design flexural strength, after 7 days.\u003c/p\u003e","description":"","filename":"10.png","url":"https://assets-eu.researchsquare.com/files/rs-7894507/v1/3eeb416bce47305b50509ad1.png"},{"id":95525354,"identity":"1fdb6d6e-9341-4309-a835-7a240d856fef","added_by":"auto","created_at":"2025-11-10 10:04:52","extension":"png","order_by":11,"title":"Figure 11","display":"","copyAsset":false,"role":"figure","size":66643,"visible":true,"origin":"","legend":"\u003cp\u003eCompare to the design flexural strength, after 14 days.\u003c/p\u003e","description":"","filename":"11.png","url":"https://assets-eu.researchsquare.com/files/rs-7894507/v1/05e6e9b5b6f8f162f6fd1b60.png"},{"id":95383882,"identity":"08875872-e30f-4dd0-b6eb-37e40e8148b9","added_by":"auto","created_at":"2025-11-07 12:28:27","extension":"png","order_by":12,"title":"Figure 12","display":"","copyAsset":false,"role":"figure","size":72633,"visible":true,"origin":"","legend":"\u003cp\u003eCompare to the design flexural strength, after 28 days.\u003c/p\u003e","description":"","filename":"12.png","url":"https://assets-eu.researchsquare.com/files/rs-7894507/v1/c2001f1de8ed04d172c62ecd.png"},{"id":101858566,"identity":"2911afc4-1321-4efc-a879-2e9ceff643ca","added_by":"auto","created_at":"2026-02-04 11:12:46","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":1524921,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-7894507/v1/bcc1ce50-79ed-4954-a1be-785fecdaf3fd.pdf"}],"financialInterests":"No competing interests reported.","formattedTitle":"Influence of GGBS–Fly Ash Binder Composition on the Strength of Geopolymer Concrete with Natural and Recycled Concrete Aggregate","fulltext":[{"header":"1 Introduction","content":"\u003cp\u003eExcessive usage by the construction sector of Ordinary Portland Cement (OPC) represents a great ecological problem. Manufacturing OPC represents the world's most prominent source of greenhouse emissions since it is responsible for 6\u0026ndash;8% of global anthropogenic CO2 emissions and is extremely energetically intensive by consuming 15% of global industrial energy (Mohamad et al., \u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e2022\u003c/span\u003e). On-going quarrying of the raw material equally depletes natural resources as well as devastates ecosystems (Bărbulescu \u0026amp; Hosen, \u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e2025\u003c/span\u003e).These pressing issues create an urgent need for sustainable alternatives to conventional concrete (Mohamad et al., \u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e2022\u003c/span\u003e). As these statistics highlight the scale of the problem, the construction industry must have to adopt materials that minimize environmental footprint without compromising structural integrity. Geopolymer Concrete (GPC) provides a potential alternative by replacing the entire OPC with a binder from by-product industrial material in the form of aluminosilicates, i.e., Fly Ash (FA) and Ground Granulated Blast-furnace Slag (GGBS). Current research demonstrates that industrial by-products, when properly utilized, can be not just replacements but rather better alternatives to conventional cementitious systems. Geo-polymerization, the resultant process, avoids the extremely high temperature characteristics in cement production and hence reduce the CO2 emissions by 90%. The GGBS-FA ratio has the highest positive influence; the GGBS content in the form of the high content in calcium provides the chemical accelerant by inducing the reaction in the FA at ambient temperatures and providing early strength gain\u0026mdash; a critical property for practical applications (Akcaoglu et al., \u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2019\u003c/span\u003e; Ukesh Praveen \u0026amp; Srinivasan, \u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e2017\u003c/span\u003e). Here, the composition of the binder is a key variable that affects not just early age strength development but also long-term durability and field applicability. For additional progress towards sustainability, in the current research adoption towards Recycled Concrete Aggregate (RCA) is undertaken through the utilization of demolition and building wastes and the conservation of natural aggregates. This creates a \"doubly green\" composite material (Zhang et al., \u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e2023\u003c/span\u003e). The RCA utilization aligns with circular economy principles, that means its offering a dual benefit of waste reduction and resource conservation. However, a major obstacle to the on-site application of GPC is the traditional dependence on energy-intensive heat curing to achieve adequate strength (Jindal, \u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e2018\u003c/span\u003e). Despite the many advantages of GPC, however, the use of high-temperature curing within GPC remains a practical limitation, particularly in areas where facilities for heat curing are lacking. Therefore, this study focuses on solving a key challenge: how to optimize a geopolymer concrete (GPC) system that can reliably sustain at hot and ambient temperature, making it practical and efficient for on-site construction. To address this limitation, the present study proposes a mix design approach that balances binder chemistry, aggregate selection, and curing conditions to achieve reliable performance of GPC under realistic site conditions.\u003c/p\u003e\u003cp\u003eMain objectives in the current research work are: 1) evaluate the optimum mix proportion of geo-polymer concrete with different GGBS/Fly ash ratio (as a replacement of cement), alkaline activators, Natural and recycled aggregate under different curing condition and 2) exploring the compressive and flexural strength gain of the mixes of geo-polymer concrete. Scope of the research work is restricted by the target compressive strength in the range 25 MPa in the resultant concrete. Ratios on binder with GGBS:FA ratios 100:0, 90:10, 80:20, and 70:30 are included. Replacement of coarse aggregate by natural and recycled aggregate at 65% and 35% respectively. Water-cement ratio is 0.5. The alkaline activator solution consists of a combination where 10M (Molar) sodium hydroxide (\u003cem\u003eNaOH\u003c/em\u003e) and sodium silicate (Na₂SiO₃) at a mass ratio of 1:2 were used. All 4\u0026times;4\u0026times;4-inch cube specimens are cured under ambient and hot temperature. Compressive and flexural strengths were tested at 7, 14, and 28 days, and the results are compared to a conventional OPC concrete (control mix) which is prepared under identical protocols. By systematically evaluating mix proportions and curing conditions, this study aims to contribute toward the development of GPC systems that are not only sustainable but also feasible for large scale construction.\u003c/p\u003e"},{"header":"2 Methodology","content":"\u003cp\u003e\u003cstrong\u003e2.1 Process Flow Diagram\u0026nbsp;\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThis research focuses on the evaluation of geopolymer concrete made with GGBS and fly ash that act to reduce environmental pollution and mineral deficiency. Materials were first collected and tested for suitability checking, using the ACI 211.1-91 method (American Concrete Institute, 1991), mix proportions were calculated, followed by casting, de-molding, curing (hot water and ambient), compressive and flexure strengths were then tested. Entire working process is stated below in figure 1.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003e2.2 Material Selection\u003c/strong\u003e\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eTwo types of coarse aggregates were used RCA (Recycled Concrete Aggregate) and NCA (Natural Coarse Aggregate) with a ratio of 35% and 65%. For binders and activators materials the ratio is followed as per table 1.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eTable 1: Coarse Aggregate, Binder and Activator Ratio\u003c/p\u003e\n\u003cdiv align=\"\"\u003e\n \u003ctable border=\"1\" cellspacing=\"0\" cellpadding=\"0\"\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd rowspan=\"2\" style=\"width: 62px;\"\u003e\n \u003cp\u003eS.L.\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd colspan=\"2\" style=\"width: 171px;\"\u003e\n \u003cp\u003eCoarse Aggregates\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd colspan=\"2\" style=\"width: 171px;\"\u003e\n \u003cp\u003eBinders\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd colspan=\"2\" style=\"width: 171px;\"\u003e\n \u003cp\u003eActivators\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 86px;\"\u003e\n \u003cp\u003eRCA\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 86px;\"\u003e\n \u003cp\u003eNCA\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 86px;\"\u003e\n \u003cp\u003eGGBS\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 86px;\"\u003e\n \u003cp\u003eFly Ash\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 86px;\"\u003e\n \u003cp\u003eNaOH\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 86px;\"\u003e\n \u003cp\u003eNaSiO\u003csub\u003e3\u003c/sub\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 62px;\"\u003e\n \u003cp\u003e1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd rowspan=\"4\" style=\"width: 86px;\"\u003e\n \u003cp\u003e35%\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd rowspan=\"4\" style=\"width: 86px;\"\u003e\n \u003cp\u003e65%\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 86px;\"\u003e\n \u003cp\u003e100%\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 86px;\"\u003e\n \u003cp\u003e0%\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd rowspan=\"4\" style=\"width: 86px;\"\u003e\n \u003cp\u003e10M\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd rowspan=\"4\" style=\"width: 86px;\"\u003e\n \u003cp\u003e10M\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 62px;\"\u003e\n \u003cp\u003e2\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 86px;\"\u003e\n \u003cp\u003e90%\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 86px;\"\u003e\n \u003cp\u003e10%\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 62px;\"\u003e\n \u003cp\u003e3\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 86px;\"\u003e\n \u003cp\u003e80%\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 86px;\"\u003e\n \u003cp\u003e20%\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 62px;\"\u003e\n \u003cp\u003e4\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 86px;\"\u003e\n \u003cp\u003e70%\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 86px;\"\u003e\n \u003cp\u003e30%\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n \u003c/table\u003e\n\u003c/div\u003e\n\u003cp\u003e\u003cem\u003eNatural Aggregate:\u003c/em\u003e Up to \u0026frac34; inches size natural coarse aggregate used with a ratio of 65% due to the scarcity of natural aggregate from a local market (Bangla Bazar, Shershah, Bayezid, Chattogram).\u003c/p\u003e\n\u003cp\u003e\u003cem\u003eRecycled Aggregate:\u003c/em\u003e Used by maintaining the same size as the alternative of natural aggregate but with a ratio of 35% because of having a bad impact on the environment, purchased from the local market (Bangla Bazar, Shershah, Bayezid, Chattogram).\u003c/p\u003e\n\u003cp\u003e\u003cem\u003eFine Aggregate:\u003c/em\u003e Sylhet sand with a FM of 3.0 (Bangla Bazar, Shershah, Bayezid, Chattogram)\u003c/p\u003e\n\u003cp\u003e\u003cem\u003eBinder:\u003c/em\u003e GGBS and Fly ash used as binder materials instead of cement as it binds concrete more easily.\u003c/p\u003e\n\u003cp\u003e\u003cem\u003eGGBS:\u003c/em\u003e GGBS (Ground Granular Blast Furnace Slag) is used as a binder in different proportions (as stated table 1) which is obtained from the blast furnace and collected from Mustafa Hakim Cement Company. The GGBS was granular and grounded manually in the laboratory to achieve a finer, more reactive powder suitable for geo-polymerization. While mechanical grinding is ideal, the manual process used here is noted as a potential limitation affecting particle size uniformity.\u003c/p\u003e\n\u003cp\u003e\u003cem\u003eFly Ash:\u003c/em\u003e It is used as a binder in different proportions (as stated table 1). It is available in coal-fired power plants and is very cheap and was collected from the local market and imported from India through importers.\u003c/p\u003e\n\u003cp\u003e\u003cem\u003eAlkaline Activators:\u003c/em\u003e A mix of sodium hydroxide (NaOH) and sodium silicate (Na\u003csub\u003e2\u003c/sub\u003eSiO\u003csub\u003e3\u003c/sub\u003e) was used as the alkaline activator solution. It was collected from Taj Scientific chemical shop, Chattogram. The NaOH concentration was 10M (in terms of molar), meaning 10\u0026times;40 = 400g of NaOH solids per liter of solution, where 40 is the molecular weight of NaOH. Concentration of sodium silicate (Na\u003csub\u003e2\u003c/sub\u003eSiO\u003csub\u003e3\u003c/sub\u003e) was also 10M.\u003c/p\u003e\n\u003cp\u003eThe ratio for Activator and Binders follows as the table 1.\u003c/p\u003e\n\u003cp\u003e\u003cem\u003eWater:\u003c/em\u003e Potable lab water is used for the concrete as per code.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003e2.3 Material Tests\u0026nbsp;\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eMaterial testing verifies that the materials meet required specifications through various tests. This study includes testing different types of material and specifications of specimens for compressive and flexural\u0026nbsp;tests.\u003c/p\u003e\n\u003cp\u003e\u003cem\u003eSpecimens:\u003c/em\u003e A total of 54 specimens were prepared, including geopolymer mixes with varying GGBS : fly ash ratios and conventional OPC controls. Specimens were tested for compressive and flexural strength at 7, 14, and 28 days under different curing conditions, as detailed in Table 2.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eTable 2 : Total Specimen Overview\u003c/p\u003e\n\u003cdiv align=\"\"\u003e\n \u003ctable border=\"1\" cellspacing=\"0\" cellpadding=\"0\" width=\"610\"\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd\u003e\n \u003cp\u003eS.L.\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003eMix Type\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003eGGBS:Fly Ash Ratio\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003eCuring Method\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003eTesting Ages (days)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003eTest Types\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003eSpecimen Dimensions (mm)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003eQuantity\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd\u003e\n \u003cp\u003e01\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003eGeopolymer Concrete\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e100:00\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003eAmbient \u0026amp; Heat Curing\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e7, 14, 28\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003eCompression \u0026amp; Flexural\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003eCube: 100\u0026times;100\u0026times;100\u003c/p\u003e\n \u003cp\u003eBeam:100\u0026times;100\u0026times;500\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e12\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd\u003e\n \u003cp\u003e02\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003eGeopolymer Concrete\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e90:10\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003eAmbient \u0026amp; Heat Curing\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e7, 14, 28\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003eCompression \u0026amp; Flexural\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003eCube: 100\u0026times;100\u0026times;100\u003c/p\u003e\n \u003cp\u003eBeam:100\u0026times;100\u0026times;500\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e12\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd\u003e\n \u003cp\u003e03\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003eGeopolymer Concrete\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e80:20\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003eAmbient \u0026amp; Heat Curing\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e7, 14, 28\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003eCompression \u0026amp; Flexural\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003eCube: 100\u0026times;100\u0026times;100\u003c/p\u003e\n \u003cp\u003eBeam:100\u0026times;100\u0026times;500\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e12\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd\u003e\n \u003cp\u003e04\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003eGeopolymer Concrete\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e70:30\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003eAmbient \u0026amp; Heat Curing\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e7, 14, 28\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003eCompression \u0026amp; Flexural\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003eCube: 100\u0026times;100\u0026times;100\u003c/p\u003e\n \u003cp\u003eBeam:100\u0026times;100\u0026times;500\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e12\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd\u003e\n \u003cp\u003e05\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003eControlled OPC Concrete\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e\u0026mdash;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003eWater Curing @ Room Temperature\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e7, 14, 28\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003eCompression \u0026amp; Flexural\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003eCube: 100\u0026times;100\u0026times;100\u003c/p\u003e\n \u003cp\u003eBeam:100\u0026times;100\u0026times;500\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e6\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd colspan=\"8\"\u003e\n \u003cp\u003eTotal: 54 numbers of samples were made for this research.\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n \u003c/table\u003e\n\u003c/div\u003e\n\u003cp\u003e\u003cem\u003eAggregate tests:\u003c/em\u003e Following tests were conducted for both coarse and fine aggregates: Bulk Specific gravity test, Dry unit weight test, Sieve analysis and Slump test (for wet concrete mix).\u003c/p\u003e\n\u003cp\u003e\u003cem\u003eDry Unit Weight:\u003c/em\u003e The unit weight of aggregates, determined by AASHTO, measures the weight of a specific volume of graded aggregates. It is used to monitor aggregates consistency and for mix proportioning. The dry unit weight was obtained for Natural coarse aggregate ad Recycled Concrete aggregates were 1597kg/m\u003csup\u003e3\u003c/sup\u003e and 1024kg/m\u003csup\u003e3\u003c/sup\u003e and for fine aggregate it was 1548 kg/m\u003csup\u003e3\u003c/sup\u003e.\u003c/p\u003e\n\u003cp\u003e\u003cem\u003eBulk Specific Gravity Test:\u003c/em\u003e It refers to the ratio of the weight in air of a unit volume of aggregate to the weight of an equal volume of gas free distilled water at a stated temperature. Specific gravity for NA = 2.486, for RCA = 1.706 and for fine aggregate= 2.26.\u003c/p\u003e\n\u003cp\u003e\u003cem\u003eSieve analysis:\u003c/em\u003e Sieve analysis shows the size distribution of coarse aggregate, taken up to 20 mm in standard sieve size. Fineness modulus indicates the mean particle size and is used to grade the aggregate. Each sieve\u0026rsquo;s mass was divided by the total dry mass before washing and multiply by 100 to find the percent retained and passing. Calculated to the nearest 0.1%. By the sieve analysis, F.M for NCA and RCA was obtained 3.7 and 5.1. By the sieve analysis, obtained F.M for fine aggregate = 3.09.\u003c/p\u003e\n\u003cp\u003e\u003cem\u003eSlump Test:\u003c/em\u003e The mix yielded a slump value of 40 mm (4cm).\u003c/p\u003e\n\u003cp\u003e\u003cem\u003eStrength Testing:\u003c/em\u003e The compressive and flexural strength of GRAC (Geo-polymer Recycled Aggregate Concrete) and the control mixture (with natural coarse aggregates) was determined at 7, 14, and 28 days as per standards.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003e2.4 Alkaline Solution Preparation and Mixing\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003e\u003cem\u003eAlkaline solution preparation:\u003c/em\u003e To prepare the alkaline activator, a combination of sodium hydroxide (NaOH) and sodium silicate (Na₂SiO₃) was used. The sodium hydroxide solution was prepared to a concentration of 10 Molar (10M) by dissolving 400 grams of NaOH pellets per liter of water. The sodium silicate solution used had a mass ratio of Na₂O to SiO₂ of approximately 0.5 and a specific gravity of 1.4. The two solutions were prepared separately and mixed together just prior to being introduced to the dry components of the mix, with a final mass ratio of sodium silicate to sodium hydroxide solution set at 2:1.\u003c/p\u003e\n\u003cp\u003e\u003cem\u003eMix proportions:\u003c/em\u003e To establish a reliable baseline for comparison, a standard OPC mix was prepared using ACI 211.1-91(American Concrete Institute, 1991). This design guides the aggregate proportions later used in geopolymer mixes by replacing cement with GGBS and fly ash. Lime (CaCO3) addition with 5% of cement ratio during dry mixing of concrete materials.\u003c/p\u003e\n\u003cp\u003eMix Design of OPC Concrete (Using ACI 211.1-91 Method):\u003c/p\u003e\n\u003cp\u003eTo ensure a valid comparison, the Ordinary Portland Cement (OPC) control mix was prepared using the exact same aggregate blend as the geopolymer mixes: a combination of 65% Natural Coarse Aggregate (NCA) and 35% Recycled Concrete Aggregate (RCA).\u003c/p\u003e\n\u003cp\u003eThe final mix proportions, derived from the ACI 211.1-91 method and adjusted through trial batches to achieve the target slump of 40 mm, were as follows:\u003c/p\u003e\n\u003cul type=\"disc\"\u003e\n \u003cli\u003eCement (OPC): 320 kg/m\u0026sup3;\u003c/li\u003e\n \u003cli\u003eWater: 160 kg/m\u0026sup3;\u003c/li\u003e\n \u003cli\u003eFine Aggregate (FA): 715 kg/m\u0026sup3;\u003c/li\u003e\n \u003cli\u003eCoarse Aggregate (CA): 1050 kg/m\u0026sup3;\u003c/li\u003e\n \u003cli\u003eMix Ratio (Cement : FA : CA : Water): 1 : 2.23 : 3.28 : 0.5\u003c/li\u003e\n\u003c/ul\u003e\n\u003cp\u003eFor the geopolymer concrete (GPC) mixes, the total binder quantity of 320 kg/m\u0026sup3; was maintained, replacing the cement with the various GGBS and Fly Ash combinations.\u003c/p\u003e\n\u003cp\u003eActivator ratio = 1:2 (NaOH : Na\u003csub\u003e2\u003c/sub\u003eSiO\u003csub\u003e3\u003c/sub\u003e)\u003c/p\u003e\n\u003cp\u003eNaOH = 0.5 Litre. (10M)\u003c/p\u003e\n\u003cp\u003eNa\u003csub\u003e2\u003c/sub\u003eSiO\u003csub\u003e3\u003c/sub\u003e = 1.0 Litre. (10M)\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003e2.5 Casting, Demolding and Curing\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003e\u003cem\u003eCasting:\u003c/em\u003e First, the fine aggregate (FA), coarse aggregates (RCA \u0026amp; NCA) mixed in a manually mixer for 1\u0026ndash;2 min, followed by the addition of fly ash and GGBS to the mixer and mixed for a further 2\u0026ndash;3 min. Alkali-activated solutions were then progressively poured into the mixer and mixed for another 2\u0026ndash;3 min until a uniform consistency was achieved. After mixing, the concrete specimens were cast in 4\u0026times;4\u0026times;4 in. cube molds and compacted with a tamping rod.\u003c/p\u003e\n\u003cp\u003e\u003cem\u003eDemolding:\u0026nbsp;\u003c/em\u003eAll specimens were demolded after 24 hours.\u003c/p\u003e\n\u003cp\u003e\u003cem\u003eCuring:\u003c/em\u003e This study examined the effect of curing temperature on slag and fly ash\u0026ndash;based geopolymer concrete. Research indicates that elevated curing temperatures (60\u0026ndash;90 \u0026deg;C) greatly improve geopolymer strength by accelerating the reaction (geo-polymerization) process, and 70 \u0026deg;C often cited as ideal. Ambient curing is slower but still effective with the right mix design. Curing beyond 100 \u0026deg;C shows little added benefit (strength improvement) and wastes energy (Patil et al., 2014).\u003c/p\u003e\n\u003cp\u003eTwo curing methods were tested:\u003c/p\u003e\n\u003col start=\"1\" type=\"1\"\u003e\n \u003cli\u003eHeat Curing: Demolded geopolymer concrete specimens were placed in a laboratory water bath and cured at 75\u0026deg;C for 24 hours.\u003c/li\u003e\n \u003cli\u003eAmbient Curing: Demolded geopolymer concrete specimens were cured at room temperature (27 \u0026deg;C) and 95% relative humidity. To early strength gain without thermal input (heat curing), lime (CaCO3) was added to the mix to promote hydration alongside geo-polymerization.\u0026nbsp;\u003c/li\u003e\n\u003c/ol\u003e\n\u003cp\u003eControlled samples cured under room temperature (27 \u0026deg;C) and 95% relative humidity, without adding any additives. After curing, all specimens were stored in a controlled room at 27\u0026deg;C and 95% relative Humidity, until testing at 7, 14, and 28 days.\u003c/p\u003e"},{"header":"3 Results and Discussion","content":"\u003cp\u003e\u003cstrong\u003e3.1 Compressive Strength\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eTable 3 : Compressive Strengths of Concrete Mixes\u003c/p\u003e\n\u003cdiv align=\"\"\u003e\n \u003ctable border=\"1\" cellspacing=\"0\" cellpadding=\"0\" width=\"578\"\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd\u003e\n \u003cp\u003eMix ID\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003eGGBS : Fly Ash Ratio\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003eCuring Condition\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e7-Day Strength (MPa)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e14-Day Strength (MPa)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e28-Day Strength (MPa)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd\u003e\n \u003cp\u003eControl\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003eN/A (OPC)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003eAmbient\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e23.5\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e26.5\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e29.5\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd rowspan=\"2\"\u003e\n \u003cp\u003eGPC-1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd rowspan=\"2\"\u003e\n \u003cp\u003e100:0\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003eAmbient\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e25.8\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e28.5\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e31.5\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd\u003e\n \u003cp\u003eHeat\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e28.0\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e30.5\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e33.2\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd rowspan=\"2\"\u003e\n \u003cp\u003eGPC-2\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd rowspan=\"2\"\u003e\n \u003cp\u003e90:10\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003eAmbient\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e25.1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e27.8\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e30.8\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd\u003e\n \u003cp\u003eHeat\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e28.5\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e31.0\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e33.7\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd rowspan=\"2\"\u003e\n \u003cp\u003eGPC-3\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd rowspan=\"2\"\u003e\n \u003cp\u003e80:20\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003eAmbient\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e23.2\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e25.9\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e28.9\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd\u003e\n \u003cp\u003eHeat\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e27.3\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e29.8\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e32.5\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd rowspan=\"2\"\u003e\n \u003cp\u003eGPC-4\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd rowspan=\"2\"\u003e\n \u003cp\u003e70:30\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003eAmbient\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e19.9\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e22.4\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e25.4\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd\u003e\n \u003cp\u003eHeat\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e26.0\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e28.5\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e31.2\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n \u003c/table\u003e\n\u003c/div\u003e\n\u003cp\u003e\u003cstrong\u003e3.2 Flexural Strength\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eTable 4 : Flexural Strengths of Concrete Mixes\u003c/p\u003e\n\u003cdiv align=\"\"\u003e\n \u003ctable border=\"1\" cellspacing=\"0\" cellpadding=\"0\" width=\"579\"\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd\u003e\n \u003cp\u003eMix ID\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003eGGBS : Fly Ash Ratio\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003eCuring Condition\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e7-Day Strength (MPa)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e14-Day Strength (MPa)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e28-Day Strength (MPa)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd\u003e\n \u003cp\u003eControl\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003eN/A (OPC)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003eAmbient\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e3.01\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e3.19\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e3.37\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd rowspan=\"2\"\u003e\n \u003cp\u003eGPC-1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd rowspan=\"2\"\u003e\n \u003cp\u003e100:0\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003eAmbient\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e3.15\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e3.31\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e3.48\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd\u003e\n \u003cp\u003eHeat\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e3.28\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e3.42\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e3.57\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd rowspan=\"2\"\u003e\n \u003cp\u003eGPC-2\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd rowspan=\"2\"\u003e\n \u003cp\u003e90:10\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003eAmbient\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e3.11\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e3.27\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e3.44\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd\u003e\n \u003cp\u003eHeat\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e3.31\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e3.45\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e3.60\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd rowspan=\"2\"\u003e\n \u003cp\u003eGPC-3\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd rowspan=\"2\"\u003e\n \u003cp\u003e80:20\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003eAmbient\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e2.99\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e3.15\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e3.33\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd\u003e\n \u003cp\u003eHeat\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e3.24\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e3.38\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e3.53\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd rowspan=\"2\"\u003e\n \u003cp\u003eGPC-4\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd rowspan=\"2\"\u003e\n \u003cp\u003e70:30\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003eAmbient\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e2.76\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e2.93\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e3.12\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd\u003e\n \u003cp\u003eHeat\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e3.16\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e3.31\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e3.46\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n \u003c/table\u003e\n\u003c/div\u003e\u003cp\u003e\u003cstrong\u003e3.3 Discussion\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe results for compressive and flexural strength display the variations in geopolymer concrete with increasing ratios of GGBS and fly ash under ambient and heat curing conditions.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eAll GPC mixes performed better than the control (OPC) mix at every curing age for compressive strength. The highest compressive strength produced at 28 days was seen in GPC-2 (90:10 GGBS:FA), when heat cured, at 33.7 MPa, with close competition by GPC-1 (100:0) with 33.2 MPa. It can generally be inferred that strength suffered a decline as fly ash increased, especially for ambient curing where GPC-4 (70:30) showed the minimum value of 25.4 MPa.\u003c/p\u003e\n\u003cp\u003eA similar trend was shown by flexural strength. Again, under heat curing, GPC-2 gave highest strength on the 28th day, that is, 3.60 MPa, while the control mix gave 3.37 MPa. Just like others, heat curing improved strength for all mixes and especially those whose fly ash content replacement does not exceed 10% gained better than control mix. Both compressive and flexural strength results, thus, suggest that heat curing improves performance, and an optimal mix such as 90% GGBS and 10% fly ash delivers the highest strength results across all testing ages.\u003c/p\u003e\n\u003cp\u003eThe superior performance of the geopolymer mixes, particularly GPC-2 (90% GGBS and 10% Fly Ash), can be attributed to the synergistic reaction between the two binder materials. The high calcium content in GGBS acting here as a primary catalyst, which leading to rapid calcium-aluminosilicate-hydrate (C-A-S-H) gel formation alongside primary sodium-aluminosilicate-hydrate (N-A-S-H) gel from the geo-polymerization of fly ash. At here, dual-gel system helps to forming a denser concrete microstructure and high early-age strength development, especially under heat curing, which accelerates these chemical reactions.\u003c/p\u003e\n\u003cp\u003eHowever, when the fly ash content increases to 20% and 30% (GPC-3 and GPC-4), a strength reduction is also noted here. This is probably because the lower amount of calcium-rich GGBS slows down the rate of reactions, especially under ambient curing conditions, where there isn\u0026rsquo;t much heat available to speed up reaction time. While fly ash is crucial for the formation of a stable geopolymer network, an optimal balance is necessary. The 90:10 ratio appears to provide this balance, offering enough GGBS to kickstart the reaction and enough fly ash to sustain it, resulting in the highest overall strengths development observed in this study.\u003c/p\u003e"},{"header":"4 Conclusion and Recommendations:","content":"\u003cp\u003e\u003cstrong\u003e4.1 Conclusion\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe project aimed to obtain the best percentage of cement replacement using GGBS and fly ash-based geopolymer concrete, with partial use of recycled concrete aggregates (RCA). The following conclusions were made on the basis of the tests:\u003c/p\u003e\n\u003cp\u003e\u003cem\u003eCompressive Strength:\u0026nbsp;\u003c/em\u003e\u003c/p\u003e\n\u003cul class=\"decimal_type\"\u003e\n \u003cli\u003eAll geopolymer mixes (GPC) were stronger than conventional OPC concrete.\u0026nbsp;\u003c/li\u003e\n \u003cli\u003eGPC-2 (90:10 GGBS:FA) under heat curing had the highest 28-day strength of 33.7 MPa, which was more than that of all other mixtures.\u0026nbsp;\u003c/li\u003e\n \u003cli\u003eEvery mix of GPC shows that heat curing always gave higher strength as compared to ambient curing.\u0026nbsp;\u003c/li\u003e\n \u003cli\u003eWith increasing fly ash content more than 10%, compressive strength decreased. GPC-4 (70:30) demonstrates the least strength in GPC mixes.\u0026nbsp;\u003c/li\u003e\n \u003cli\u003e100% GGBS (GPC-1) performed quite well under ambient curing against control (OPC) mix; hence, it can be said that GGBS alone can significantly improve strength.\u003c/li\u003e\n\u003c/ul\u003e\n\u003cp\u003e\u003cem\u003eFlexural Strength:\u0026nbsp;\u003c/em\u003e\u003c/p\u003e\n\u003cul\u003e\n \u003cli\u003eFlexural strength also exhibited a similar trend as the compressive strength with GPC-2 (90:10) under heat curing again attaining the maximum strength at 3.60 MPa.\u0026nbsp;\u003c/li\u003e\n \u003cli\u003eHeat curing enhanced flexural strength for all mixes as compared to ambient curing.\u0026nbsp;\u003c/li\u003e\n \u003cli\u003eMixes with the replacement up to 10% fly ash kept or increased flexural strength, but larger replacements (20-30%) reduced it slightly.\u0026nbsp;\u003c/li\u003e\n \u003cli\u003eEven the worst-performing GPC mix (GPC-4) under heat curing performed better than OPC concrete.\u003c/li\u003e\n\u003c/ul\u003e\n\u003cp\u003e\u003cem\u003eOverall:\u0026nbsp;\u003c/em\u003e\u003c/p\u003e\n\u003cul\u003e\n \u003cli\u003eThe best compressive and flexural strength performance was achieved with GPC-2 (GGBS:FA; 90:10) under heat curing. Clearly, the findings support that a balanced combination of GGBS and fly ash, especially under heat curing, will perform stronger and more durable concrete than conventional OPC.\u003c/li\u003e\n\u003c/ul\u003e\n\u003cp\u003e\u003cstrong\u003e4.2 Recommendations for Future Work\u0026nbsp;\u003c/strong\u003e\u003c/p\u003e\n\u003cul\u003e\n \u003cli\u003eFuture tests are beneficial to assess, in time, the overall strength and durability of GPC with increased percentages and finally 100% RCA replacement.\u0026nbsp;\u003c/li\u003e\n \u003cli\u003eSteam curing has to be studied as an alternative to hot water curing because usually strength decreases after prolonged curing in both ambient and hot water.\u0026nbsp;\u003c/li\u003e\n \u003cli\u003eIt is recommended that GGBS be mechanically ground for better uniformity (uniform particle distribution), as manual grinding may not sufficiently enhance its reactivity for effective geopolymerization.\u0026nbsp;\u003c/li\u003e\n \u003cli\u003eThis study used a 10M activator as a means; future work could explore using different levels of varying molarity for further strength improvement.\u0026nbsp;\u003c/li\u003e\n \u003cli\u003eIn fact, many more trials need to be done with intermediate GGBS to FA ratios, as strength trends do not always follow a linear pattern.\u003c/li\u003e\n\u003c/ul\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eData availability\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe datasets generated during the current study are available from the corresponding author on reasonable request.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAcknowledgements\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe authors gratefully acknowledge the support provided by the Laboratory of the Department of Civil Engineering, Southern University Bangladesh.\u003c/p\u003e\n\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\u003eContributions\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eOvijith Goswami : Original manuscript writing, Analysis, Methodology, Calculation \u0026amp; Validation.\u003c/p\u003e\n\u003cp\u003eH.M. Raihan : Graph, Maniscipt Editing, Data Acquisition.\u003c/p\u003e\n\u003cp\u003eS M Masudur Rahman : Supervising.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eEthics declarations\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eEthics approval and consent to participate\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThis study did not involve human participants or animals. No ethical approval was required for the reported research, and there are no ethical issues associated with the work.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eClinical trial number\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eNot applicable.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eConsent for publication\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eNot applicable. This study does not include any person\u0026rsquo;s data in any form (including individual details, images, or videos).\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eCompeting interests\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.\u0026nbsp;\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n \u003cli\u003e American Concrete Institute. (1991, reapproved 2009). Standard practice for selecting proportions for normal, heavyweight, and mass concrete (ACI 211.1-91). \u003cem\u003eAmerican Concrete Institute\u003c/em\u003e.\u003c/li\u003e\n \u003cli\u003eAkcaoglu, T., Cubukcuoglu, B., \u0026amp; Awad, A. (2019). A critical review of slag and fly-ash based geopolymer concrete. \u003cem\u003eComputers and Concrete\u003c/em\u003e, \u003cem\u003e24\u003c/em\u003e(5), 453\u0026ndash;458. https://doi.org/10.12989/cac.2019.24.5.453\u003c/li\u003e\n \u003cli\u003eBărbulescu, A., \u0026amp; Hosen, K. (2025). Cement Industry Pollution and Its Impact on the Environment and Population Health: A Review. \u003cem\u003eToxics\u003c/em\u003e, \u003cem\u003e13\u003c/em\u003e(7), Article 7. https://doi.org/10.3390/toxics13070587\u003c/li\u003e\n \u003cli\u003eJindal, B. B. (2018). Feasibility study of ambient cured geopolymer concrete -A review. \u003cem\u003eAdvances in Concrete Construction\u003c/em\u003e, \u003cem\u003e6\u003c/em\u003e(4), 387\u0026ndash;405. https://doi.org/10.12989/acc.2018.6.4.387\u003c/li\u003e\n \u003cli\u003eMohamad, N., Muthusamy, K., Embong, R., Kusbiantoro, A., \u0026amp; Hashim, M. H. (2022). Environmental impact of cement production and Solutions: A review. \u003cem\u003eMaterials Today: Proceedings\u003c/em\u003e, \u003cem\u003e48\u003c/em\u003e, 741\u0026ndash;746. https://doi.org/10.1016/j.matpr.2021.02.212\u003c/li\u003e\n \u003cli\u003ePatil, A. A., Chore, H. S., \u0026amp; Dodeb, P. A. (2014). Effect of curing condition on strength of geopolymer concrete. \u003cem\u003eAdvances in Concrete Construction\u003c/em\u003e, \u003cem\u003e2\u003c/em\u003e(1), 29\u0026ndash;37. https://doi.org/10.12989/ACC.2014.2.1.029\u003c/li\u003e\n \u003cli\u003eUkesh Praveen, P., \u0026amp; Srinivasan, K. (2017). Self-compacting geopolymer concrete-a review. \u003cem\u003eIOP Conference Series: Materials Science and Engineering\u003c/em\u003e, \u003cem\u003e263\u003c/em\u003e(3), 032024. https://doi.org/10.1088/1757-899X/263/3/032024\u003c/li\u003e\n \u003cli\u003eZhang, P., Sun, X., Wang, F., \u0026amp; Wang, J. (2023). Mechanical Properties and Durability of Geopolymer Recycled Aggregate Concrete: A Review. \u003cem\u003ePolymers\u003c/em\u003e, \u003cem\u003e15\u003c/em\u003e(3), 615. https://doi.org/10.3390/polym15030615\u003c/li\u003e\n\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":true,"highlight":"","institution":"","isAcceptedByJournal":false,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true},"keywords":"Geopolymer concrete, GGBS, Fly ash, Recycled aggregate, Compressive strength","lastPublishedDoi":"10.21203/rs.3.rs-7894507/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-7894507/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eHigh carbon-emitting Ordinary Portland Cement (OPC) requires sustainable options in construction practices. This study explores the manufacture of high-performance, sustainable geopolymer concrete (GPC) by substituting cement completely with Ground Granulated Blast-furnace Slag (GGBS) and Fly Ash (FA) in proportion with 35% Recycled Concrete Aggregate (RCA). In order to identify the best binder proportion of GGBS:FA for obtaining the desired 25 MPa compressive strength for practical on-site applications, four GPC mixes with different GGBS:FA ratios (100:0, 90:10, 80:20, 70:30) were produced using 10M alkaline activator solutions (\u003cem\u003eNaOH\u003c/em\u003e and \u003cem\u003eNa₂SiO₃\u003c/em\u003e) as well as cured at atmosphere (ambient) and heat (75\u0026deg;C). Mechanical strengths were studied at 7, 14, 28 days. All the GPC mixes showed better strength compared to the OPC control mix. GPC-2 (90% GGBS: 10% FA) was the optimal mix that attained the best 28-day compressive and flexural strengths of 33.7 MPa as well as 3.60 MPa, respectively, after applying heat curing. Strength development in GPC mixes under heat curing condition consistently outer performed from the GPC mixes under ambient curing condition. The study concludes that the GGBS\u0026ndash;FA system, particularly at a 90:10 ratio and when heat-cured, serves as a viable, high-strength alternative to OPC-based concrete and contributes significantly to sustainable construction practices through binder optimization and RCA utilization.\u003c/p\u003e","manuscriptTitle":"Influence of GGBS–Fly Ash Binder Composition on the Strength of Geopolymer Concrete with Natural and Recycled Concrete Aggregate","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2025-11-07 12:28:22","doi":"10.21203/rs.3.rs-7894507/v1","editorialEvents":[{"type":"communityComments","content":0}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"e47f42a0-81f5-4893-bbca-df97edb55f97","owner":[],"postedDate":"November 7th, 2025","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"posted","subjectAreas":[],"tags":[],"updatedAt":"2026-02-04T11:12:03+00:00","versionOfRecord":[],"versionCreatedAt":"2025-11-07 12:28:22","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-7894507","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-7894507","identity":"rs-7894507","version":["v1"]},"buildId":"XKTyCvWXoU3ODBz1xrDgd","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}