Evaluating the performance and environmental impact of low calcium fly ash-based geopolymer in comparison to OPC-based concrete

The current paper explores the performance, microstructure and environmental consequences of low-calcium fly ash-based geopolymer concrete compared to OPC-based concrete. The performance of the concrete is assessed based on strength, permeability, sulfate resistance, and acid attack. Two geopolymer mixes were designed by adjusting the binder dosage. The geopolymer concrete mixes achieved 11-16% higher strength than OPC-based concrete. However, increasing the binder dosage from 30 to 40% led to 5% reduction in strength at later ages. Geopolymer concrete demonstrated superior resistance to sulfate and acid attacks, as well as lower penetration depth and permeability coefficient compared to OPC-based concrete. Microstructural analysis was conducted using XRD and SEM techniques, identifying sodium aluminosilicate gel as the product formed during the polymerization process. The environmental impact was evaluated through a life cycle assessment using a cradle-to-gate approach. Geopolymer concrete requires 25-33% less energy and emits 14-28% less kg-CO₂ eq. than OPC-based concrete. The production of OPC-based concrete had the greatest negative environmental impact, except in the categories of metal depletion (MDP) and ionizing radiation (IRP_HE). In geopolymer concrete, the use of alkaline activators accounted for higher energy consumption and accounted for 73-75% kg-CO₂ eq. emissions. Overall, fly ash-based geopolymer concrete showed higher strength and excellent resistance to acid and sulfate attacks, along with a lower carbon footprint and energy consumption.