Optimized mix design and fire resistance of geopolymer recycled aggregate concrete under elevated temperatures

This study investigates the performance of fly ash-based geopolymer recycled aggregate concrete (GRAC) as a sustainable alternative to Ordinary Portland Cement (OPC) concrete, focusing on its compressive strength and behavior under high-temperature exposure (150 °C, 300 °C, 600 °C, and 900 °C). The research emphasizes the use of 100 % recycled concrete aggregates as a replacement for natural aggregates, with samples cured at ambient conditions and at 60 °C in an oven. Key factors, including water content and curing conditions, were evaluated to determine their influence on compressive strength and thermal stability. Results indicate that water content is the primary factor governing compressive strength, while recycled aggregates contribute to a secondary but notable effect. GRAC maintained up to 65 % of its initial strength after exposure to 600 °C, though strength degradation and severe cracking occurred at 900 °C. Oven-cured samples showed fewer surface cracks but experienced slightly higher mass loss than room-cured counterparts. This study highlights the potential of GRAC as an environmentally friendly material capable of withstanding moderate thermal conditions, providing significant contributions to green construction practices and the reuse of construction and demolition waste.