Abstract

Geopolymer concrete (GPC), an eco-friendly alternative to traditional Portland cement concrete, is produced using industrial by-products such as fly ash and ground granulated blast furnace slag (GGBS). Both fly ash and GGBS by-products of coal combustion are rich in silicon dioxide (SiO₂), aluminium oxide, and iron oxide, which contribute to enhanced long-term strength and durability. The inclusion of these materials promotes the formation of calcium silicate hydrate (C–S–H) gel, complementing the geopolymeric gel and improving the concrete’s overall performance. In this study, GPC was produced using a 70:30 blend of fly ash and GGBS and partially replaced with recycled concrete aggregates (RCA) in a 70:30 ratio with natural aggregates. An alkali activator solution was used, comprising sodium hydroxide (NaOH) and sodium silicate (Na₂SiO₃) in a 1:2.5 ratio, with a NaOH molarity of 12M and an alkaline activator-to-binder ratio (AA/B) of 0.45. Curing conditions included oven curing, accelerated curing (using boiling water), and open-air curing, and the results were compared with conventional cement concrete. Accelerated curing enabled the GPC to attain up to 50% of its compressive strength within the first 24 hours, comparable to oven curing and approximately 50% higher than that of cement concrete. In contrast, open-air curing resulted in only 2 MPa strength gain in the same duration. Furthermore, the flexural and split tensile strengths were significantly higher in GPC subjected to accelerated curing. Scanning electron microscopy (SEM) and energy dispersive X-ray (EDX) analysis confirmed enhanced geopolymerization due to the thermal energy supplied by the boiling water during accelerated curing. This enhanced geopolymerization contributed to notable improvements in compressive, tensile, and flexural strength, suggesting potential for superior long-term performance.

Keywords

Geopolymer concrete, Fly ash, Ground granulated blast furnace slag (GGBS), Recycled concrete aggregate (RCA), Alkali activation, Accelerated curing, Mechanical properties enhancement.

References

[1] Singh B, Ishwarya G, Gupta M, Bhattacharyya SK. Geopolymer concrete: a review of some recent developments. Construction and Building Materials. 2015; 85:78-90.

[2] https://cea.nic.in/wp-content/uploads/2020/04/flyash_201819-firsthalf.pdf. Accessed 20 June 2025.

[3] Davidovits J. 30 years of successes and failures in geopolymer applications. Market trends and potential breakthroughs. In geopolymer conference 2002 (pp. 1-16).

[4] Barbhuiya S, Das BB, Adak D, Kapoor K, Tabish M. Low carbon concrete: advancements, challenges and future directions in sustainable construction. Discover Concrete and Cement. 2025; 1(1):1-24.

[5] Sahoo S. A review of activation methods in fly ash and the comparison in context of concrete strength. Journal of Basic and Applied Engineering Research. 2016; 3(10):883-7.

[6] Nagajothi S, Elavenil S. Effect of GGBS addition on reactivity and microstructure properties of ambient cured fly ash based geopolymer concrete. Silicon. 2021; 13(2):507-16.

[7] Xiao L, Zhang C, Zhang H, Jiang Z. Internal curing effects of slag on properties and microstructure of ambient-cured fly ash-based geopolymer mortar. Buildings. 2024; 14(12):1-14.

[8] Chen WZ, Jiao CJ, Zhang XC, Yang Y, Chen XF. Study on the microstructure of recycled aggregate concrete strengthened by the nano-SiO2 soaking method. Structures. 2023; 58:105388.

[9] Khan MU, Dominic M. Sustainability of concrete using recycled aggregate: a review. Sustainability, Agri, Food and Environmental Research-Discontinued. 2022; 10:1-10.

[10] Thomas BS, Yang J, Bahurudeen A, Chinnu SN, Abdalla JA, Hawileh RA, et al. Geopolymer concrete incorporating recycled aggregates: a comprehensive review. Cleaner Materials. 2022; 3:1-20.

[11] Hassan A, Arif M, Shariq MJ. Effect of curing condition on the mechanical properties of fly ash-based geopolymer concrete. SN Applied Sciences. 2019; 1(12):1-9.

[12] Marsh AT, Velenturf AP, Bernal SA. Circular Economy strategies for concrete: implementation and integration. Journal of Cleaner Production. 2022; 362:1-17.

[13] Jalilifar H, Sajedi F. Micro-structural analysis of recycled concretes made with recycled coarse concrete aggregates. Construction and Building Materials. 2021; 267:121041.

[14] Manzoor T, Bhat JA, Shah AH. Performance of geopolymer concrete at elevated temperature- a critical review. Construction and Building Materials. 2024; 420:135578.

[15] Nagajothi S, Elavenil S, Angalaeswari S, Natrayan L, Mammo WD. Durability studies on fly ash based geopolymer concrete incorporated with slag and alkali solutions. Advances in Civil Engineering. 2022; 2022(1):1-13.

[16] Amran M, Al-fakih A, Chu SH, Fediuk R, Haruna S, Azevedo A, et al. Long-term durability properties of geopolymer concrete: an in-depth review. Case Studies in Construction Materials. 2021; 15:1-26.

[17] Satpute MB, Wakchaure MR, Patankar SV. Effect of duration and temperature of curing on compressive strength of geopolymer concrete. International Journal of Engineering and Innovative Technology. 2012; 1(5):152-5.

[18] Walkley B. Geopolymers. In Encyclopedia of engineering geology 2018 (pp. 406-7). Springer, Cham.

[19] Parashar AK, Sharma P, Sharma N. Effect on the strength of GGBS and fly ash based geopolymer concrete. Materials Today: Proceedings. 2022; 62:4130-3.

[20] Rathore SS, Meesala CR. Influence of recycled coarse aggregate on properties of fly ash and slag-based geopolymer concrete cured under oven and ambient temperature. World Journal of Engineering. 2025; 22(3):495-513.

[21] Ruan S, Al-mansour A, Zeng Q, Zhou X. Alkali-activated concrete via oven and microwave radiation curing. Handbook of Advances in Alkali-Activated Concrete. 2022: 125-55.

[22] Giasuddin HM, Sanjayan JG, Ranjith PG. Strength of geopolymer cured in saline water in ambient conditions. Fuel. 2013; 107:34-9.

[23] Ilcan H, Sahin O, Unsal Z, Ozcelikci E, Kul A, Demiral NC, et al. Effect of industrial waste-based precursors on the fresh, hardened and environmental performance of construction and demolition wastes-based geopolymers. Construction and Building Materials. 2023; 394:132265.

[24] Öztürk O. Engineering performance of reinforced lightweight geopolymer concrete beams produced by ambient curing. Structural Concrete. 2022; 23(4):2076-87.

[25] Islam MM, Li J, Wu YF, Roychand R, Saberian M. Design and strength optimization method for the production of structural lightweight concrete: an experimental investigation for the complete replacement of conventional coarse aggregates by waste rubber particles. Resources, Conservation and Recycling. 2022; 184:106390.

[26] Rawat R, Pasla D. Evaluating the corrosion resistance and LCA of lightweight geopolymer concrete integrating sintered fly ash aggregate as coarse aggregate. Construction and Building Materials. 2024; 449:138370.

[27] Kanagaraj B, Kiran T, N A, Jabri AK, S J. Development and strength assessment of eco-friendly geopolymer concrete made with natural and recycled aggregates. Construction Innovation. 2023; 23(3):524-45.

[28] Balapanov B, Montayev S, Aygün BF, Uysal M. Accelerated microwave curing of hybrid geopolymers with nano-silica for enhanced physico-mechanical properties. Journal of Sustainable Construction Materials and Technologies. 2024; 9(4):346-54.

[29] Swathi B, Vidjeapriya R. Influence of precursor materials and molar ratios on normal, high, and ultra-high performance geopolymer concrete–a state of art review. Construction and Building Materials. 2023; 392:132006.

[30] Rajashekar S, Sreenivas BS, Shanker K. Fresh and hardened behaviour of geopolymer activated with water glass. In IOP conference series: earth and environmental science 2023 (pp. 1-8). IOP Publishing.

[31] Tokdemir M, Ramyar K, Gultekin A. High-temperature resistance of industrial waste-based lightweight geopolymer mortars produced using microwave technology. Arabian Journal for Science and Engineering. 2024:1-20.

[32] Singh RP, Vanapalli KR, Cheela VR, Peddireddy SR, Sharma HB, Mohanty B. Fly ash, GGBS, and silica fume based geopolymer concrete with recycled aggregates: properties and environmental impacts. Construction and Building Materials. 2023; 378:131168.

[33] Thapa S, Debnath S, Kulkarni S, Solanki H, Nath S. Mechanical properties of geopolymer concrete incorporating supplementary cementitious materials as binding agents. Discover Civil Engineering. 2024; 1(1):1-12.

[34] Bureau of Indian Standards. IS 516-1959: method of tests for strength of concrete. 1959.

[35] IS: 3812 (part-1). Pulverized fuel ash–specification. part 1: for use as pozzolana in cement, cement mortar and concrete (second revision). 2003.

[36] Lăzărescu AV, Szilagyi H, Baeră C, Ioani A. The effect of alkaline activator ratio on the compressive strength of fly ash-based geopolymer paste. In IOP conference series: materials science and engineering 2017 (pp. 1-6). IOP Publishing.

[37] Rajamane NP, Nataraja MC, Lakshmanan N. An introduction to geopolymer concrete. Indian Concrete Journal. 2011; 85(11):25-8.

[38] Anuradha R, Sreevidya V, Venkatasubramani R, Rangan BV. Modified guidelines for geopolymer concrete mix design using Indian standard. Asian Journal of Civil Engineering. 2012:353-64.

[39] Mallikarjuna RG, Gunneswara RTD. Final setting time and compressive strength of fly ash and GGBS-based geopolymer paste and mortar. Arabian Journal for Science and Engineering. 2015; 40(11):3067-74.

[40] Jithendra C, Elavenil S. Role of superplasticizer on GGBS based geopolymer concrete under ambient curing. Materials Today: Proceedings. 2019; 18:148-54.

[41] Bureau of Indian Standard. Concrete mix proportioning-guidelines. 2019.

[42] Xie J, Wang J, Rao R, Wang C, Fang C. Effects of combined usage of GGBS and fly ash on workability and mechanical properties of alkali activated geopolymer concrete with recycled aggregate. Composites Part B: Engineering. 2019; 164:179-90.

[43] Nurruddin MF, Sani H, Mohammed BS, Shaaban I. Methods of curing geopolymer concrete: a review. International Journal of Advanced and Applied Sciences. 2018; 5(1):31-6.

[44] IS:9013-1978 Reaffirmed 2008. Indian standard method of making, curing and determining comopressive strength of accelerated cured concrete test specimens. Bureau of Indian Standards, New Delhi, India. 1978.

[45] Bureau of Indian Standards, IS 5816:1999 – Splitting tensile strength of concrete- method of test. New Delhi, India: BIS, 1999.

[46] Manjunatha GS, Radhakrishna VK, Venugopala K. Strength and durability performance of open air cured alkali activated concrete. Journal of Civil Engineering Technology and Research. 2024; 2(1):147-57.https://scholar.google.com/scholar?hl=en&as_sdt=0%2C5&q=Strength+and+Durability+Performance+of+Open-Air+Cured+Alkali+Activated+Concrete&btnG=

[47] Yazdi MA, Liebscher M, Hempel S, Yang J, Mechtcherine V. Correlation of microstructural and mechanical properties of geopolymers produced from fly ash and slag at room temperature. Construction and Building materials. 2018; 191:330-41.

[48] Jawahar JG, Mounika G. Strength properties of fly ash and GGBS based geopolymer concrete. Asian Journal of Civil Engineering (BHRC). 2016; 17(1):127-35.

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