Effect of Glass Fiber on the Properties of Geopolymer Concrete

Abstract

Geopolymer concrete is produced by the reaction of alumino-silicate materials such as fly ash with alkaline activator solutions like sodium hydroxide (NaOH) and sodium silicate (Na?SiO?). The present study focuses on the strength and durability performance of fly ash-based geopolymer concrete with the addition of glass fibers.In this study, the alkaline solution to fly ash ratio was maintained at 0.5 and the sodium hydroxide solution concentration was taken as 10M. Glass fibers were added in different proportions to determine the optimum dosage. The compressive, split tensile, and flexural strengths of geopolymer concrete with glass fiber were evaluated as per relevant IS codes. The results showed that the compressive strength increased from 34.02 MPa to 38.08 MPa and the split tensile strength increased from 2.48 MPa to 3.1 MPa with the addition of glass fibers. Similarly, the flexural strength also improved compared to conventional geopolymer concrete. The study concluded that 1% glass fiber is the optimum dosage for enhancing the mechanical properties of geopolymer concrete.

Introduction

Geopolymer concrete (GPC) is an inorganic polymer material formed by the reaction of aluminosilicate sources (e.g., fly ash, GGBS, metakaolin) with alkaline activators (sodium hydroxide or potassium hydroxide combined with sodium silicate). Unlike conventional Portland cement, geopolymers are synthesized at relatively low temperatures and offer non-combustibility, high heat resistance, acid resistance, and environmental benefits by utilizing industrial by-products. The geopolymerization process involves dissolution of aluminosilicates in alkaline solutions followed by polycondensation into a three-dimensional polymeric network.

Mechanical properties such as compressive strength depend on factors including Si/Al ratio, CaO and K?O content, type of activator, and curing conditions. Research has shown that heat curing (e.g., 70°C for 24 hours) and combined sodium hydroxide-sodium silicate activators improve strength, with typical compressive strengths ranging from 46–70 MPa. GPC behaves similarly to conventional concrete in structural applications, demonstrating effective binding of aggregates and comparable performance in reinforced beams and columns. It also exhibits superior durability, including resistance to sulphate attack, acid exposure, fire, and corrosion of embedded steel.

The study details the preparation of low-calcium fly ash-based GPC reinforced with alkali-resistant glass fibers. Materials include Class C fly ash, OPC (for comparison), fine and coarse aggregates, sodium silicate and sodium hydroxide as activators, water, and glass fibers. Mixture proportions are designed following Rangan’s guidelines, with an alkaline liquid to fly ash ratio of 0.5. The manufacturing process involves preparing the alkaline solution in advance, mixing it with aggregates and fly ash, and adding glass fibers in varying percentages (0.5–2%) to optimize compressive, tensile, and flexural strength as well as durability properties.

Overall, geopolymer concrete offers a sustainable, high-performance alternative to Portland cement concrete, though standardized mix design procedures are still evolving.

Conclusion

The results of the study show that the alkaline solution to fly ash ratio and the concentration of sodium hydroxide significantly influence the compressive strength development of geopolymer concrete. An alkaline solution to fly ash ratio of 0.5 with 10M NaOH produced higher compressive strength when glass fibers were added. The curing condition also played an important role in the strength development of geopolymer concrete. The compressive strength of glass fiber reinforced geopolymer concrete ranged from 34.02 MPa to 38.08 MPa at 28 days, and the addition of 1% glass fiber increased the compressive strength by about 10% compared to conventional geopolymer concrete. Similarly, the split tensile strength varied from 2.48 MPa to 3.1 MPa, showing an increase of about 10%, while the flexural strength ranged from 3.27 MPa to 7.06 MPa, with an improvement of about 20% for 1% glass fiber addition. The results indicate that 1% glass fiber is the optimum dosage for improving the mechanical properties of geopolymer concrete. The water absorption of geopolymer concrete was found to be between 2.4% and 4.2%, and it slightly increased with the addition of glass fibers. However, the weight loss due to sulphate attack decreased with the increase in glass fiber content up to 1.5%, indicating improved durability. Overall, geopolymer concrete with 1% glass fiber reinforcement showed better strength and durability and can be effectively used in aggressive environmental conditions. Moreover, the use of Class C fly ash in geopolymer concrete helps reduce the consumption of Portland cement and indirectly lowers the emission of greenhouse gases such as CO?, making it an environmentally friendly construction material.

References

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Copyright

Copyright © 2026 Vaidehi V, Shanthi V, Vinothini K, Tamilmozhi R. 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.