Sustainable Cement-Free Concrete Development for Eco-Friendly Construction: A Study on Fly Ash-Based Geopolymer Concrete

Abstract

The present paper offers a technical in-depth research on the manufacturing, production, and performance assessment of Fly Ash-Based Geopolymer Concrete (GPC) as a green substitute for Ordinary Portland Cement (OPC) concrete. The study aims at resolving environmental issues related to the production of cement, namely its CO? footprint, and suggests GPC as a green building material possessing better mechanical, chemical, and durability properties. The research delineates the preparation process, source material choice, alkaline activator mix, and curing regimens, followed by experimental tests like compressive strength, slump, sulphate attack, and acid resistance tests. The outcomes suggest remarkable benefits in terms of early strength gain, sustainability in harsh environments, and cost-effectiveness, favoring the implementation of GPC on a large-scale infrastructure.

Introduction

Global cement production is projected to reach 3.7–4.4 billion tonnes by 2050, making it a major source of CO? emissions, second only to transportation. Traditional Ordinary Portland Cement (OPC) emits roughly 1 tonne of CO? per tonne produced, contributing heavily to environmental pollution. Geopolymer concrete (GPC), developed by Davidovits in 1988, offers a sustainable alternative by using aluminosilicate-rich industrial by-products such as fly ash, activated by alkaline solutions to form a polymeric binder without calcium silicate hydrate (CSH), the typical binder in OPC.

Fly ash, a by-product of coal combustion rich in silica and alumina, is highly pozzolanic and used as the main binder in this study's Class F low-calcium fly ash-based geopolymer concrete. This reduces waste, energy use, and CO? emissions in production. The study covers materials, mix design, preparation, curing, and testing for workability, strength, and durability.

Key materials include Class F fly ash, crushed granite and river sand aggregates, sodium hydroxide (NaOH), and sodium silicate (Na?SiO?) as alkaline activators, plus superplasticizers to improve flow. The alkaline solution is prepared by dissolving NaOH pellets into water and mixing with sodium silicate, then combined with dry aggregates and fly ash.

After casting, specimens are heat-cured at 80°C for 24 hours, then ambient cured and tested for compressive strength and durability at multiple intervals. Results show GPC achieves compressive strength around 40 MPa at 28 days, comparable to OPC concrete, with superior resistance to sulphate and acid attacks due to its stable aluminosilicate gel matrix.

Economically, GPC reduces binder costs, energy usage, and CO? emissions by 10–30% compared to OPC and may qualify for carbon credits. Overall, GPC offers high strength, thermal and chemical durability, and eco-friendliness but faces challenges including complex mix design, safety concerns handling alkaline activators, variability in raw materials, lack of standardized codes, need for heat curing, and limited large-scale application data.

Conclusion

Fly ash–based Geopolymer Concrete (GPC) proves to be a sustainable and high-performance alternative to Ordinary Portland Cement (OPC) concrete. Experimental results confirm that GPC achieves high compressive strength (~40 MPa at 28 days) with rapid early strength gain due to the formation of a dense aluminosilicate gel network. It demonstrates excellent durability against sulphate and acid attack, superior thermal stability, and a significant reduction in CO? emissions (~80%), making it an eco-friendly material. Although challenges such as complex activator handling, heat curing requirements, and lack of standard design codes remain, the overall performance highlights GPC as a technically viable and economically feasible material for future construction practices.

References

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Copyright

Copyright © 2025 Aashu ., Prabhat Kumar, Sachin Kumar, Divya , Shubhankar Yadav. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.