Durability Performance of Sustainable Fly Ash-Based Geopolymer Concrete Incorporating Waste Glass

The cement and concrete industries contribute significantly to environmental degradation through high CO₂ emissions and extensive resource consumption. Cement manufacturing accounts for nearly 8% of global CO₂ emissions, primarily from limestone calcination, while raw material extraction leads to resource depletion and ecological disruption. Increasing attention is being directed toward the use of recycled glass as an eco-friendly substitute in geopolymer concrete, offering a sustainable solution to existing challenges. This study investigates the effectiveness of replacing fly ash with waste glass powder (WGP) at 0%, 10%, 20%, and 30%, and substituting natural sand with waste glass sand (WGS) at 0%, 15%, 30%, and 50%. A dual substitution strategy was also examined using 10% replacement for both fly ash and sand. The modified geopolymer concrete was evaluated for workability, compressive strength, water absorption, water permeability, sulfate resistance, and elevated temperature resistance. Microstructural and chemical characterization was conducted using scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDX). Results showed significant improvements in mechanical properties and durability. At 30% WGP replacement, compressive strength increased by 22% from 37.0 MPa to 45.2 MPa at 28 days, due to enhanced pozzolanic activity. Similarly, 30% WGS improved packing density and workability, resulting in a 29% increase in strength from 35.5 MPa to 45.8 MPa. SEM and EDX analyses confirmed that waste glass incorporation led to a denser and more cohesive matrix, reducing micro voids and enhancing long-term durability indicators such as water resistance, sulfate attack resilience, and thermal stability.