Performance Comparison of Fly Ash Based Geopolymer Concrete with Ordinary Portland Cement Concrete

Abstract

This research aims to compare the compressive strength of fly ash based geopolymer concrete (GPC) with ordinary Portland cement (OPC) concrete and to evaluate the potential of GPC as a sustainable alternative to OPC concrete. The study was conducted in two phases. In the first phase, GPC was prepared using low calcium (Class F) fly ash activated by a mixture of sodium hydroxide (14M) and sodium silicate, with a ratio of sodium silicate to sodium hydroxide of 2.5. The concrete cubes were cast and cured under oven conditions at 60°C. Simultaneously, OPC concrete cubes were prepared to serve as a benchmark. The compressive strength of the GPC was measured at 7 and 28 days, yielding values of 6.4 MPa and 11.9 MPa, respectively. These results indicated that the GPC did not achieve the targeted strength, showing lower early and final compressive strengths compared to OPC concrete whose 7 days and 28 days compressive strength were 12.67 MPa and 20.68 MPa respectively. To address these issues, a revised mix design was implemented in the second phase of the study. The new GPC mix incorporated 70% fly ash, 10% silica fume, and 20% OPC, with all other materials and methods remaining consistent. This revised mixture was cured under normal room temperature conditions. The compressive strength tests revealed significant improvements, with the 7-day and 28-day strengths recorded at 15.39 MPa and 25.81 MPa, respectively. The enhanced strength is attributed to the inclusion of silica fume and OPC, which facilitated the geo-polymerization process by promoting the dissolution of silicon and aluminum atoms from the fly ash, creating a more alkaline environment, and forming a combination of different gel networks, including NA-S-H, C-A-S-H, and C-S-H. This also eliminated the need for elevated temperature curing for fly ash based geopolymers.
The findings demonstrate that the modified GPC mix not only meets but exceeds the performance of traditional OPC concrete, highlighting its potential as a viable, eco-friendly alternative with a lower carbon footprint. This research underscores the importance of continued exploration in this field to further enhance the properties and applications of geopolymer concrete, contributing to the reduction of CO2 emissions and promoting sustainable construction practices.