Development of Ambient‐Cured Geopolymer Concrete: Investigating Bottom Ash as a Sustainable Alternative to Natural River Sand

Portland cement production is a major contributor to global CO 2 emissions, and the scarcity of natural river sand limits conventional concrete production. Despite increasing interest in geopolymer concrete (GPC), studies on sustainable, low‐temperature cured GPC using industrial by‐products as fine aggregate replacements are limited. This study introduces a novel approach by utilizing coal bottom ash (BA) as a partial fine aggregate substitute in ambient‐cured fly ash–based GPC, addressing both environmental concerns and resource scarcity. Concrete mixes containing 0%, 5%, 10%, and 15% BA were prepared and evaluated for workability, compressive and flexural strength, water absorption, microstructural characteristics, embodied energy, and CO 2 emissions. The 28‐day compressive (30.39 MPa) and flexural strength (3.18 MPa) were highest at 5% BA, attributed to microfiller effects and matrix densification, while water absorption remained within ASTM limits. Microstructural analysis confirmed additional N‐A‐S‐H and C‐(A)‐S‐H gel formation, and incorporation of BA reduced embodied energy and CO 2 emissions by 57.7% and 93.2%, respectively, demonstrating significant mechanical and environmental advantages. These findings highlight the potential of BA as a sustainable fine aggregate in ambient‐cured GPC, providing a novel, low‐carbon solution for the construction industry.