Development of Geopolymer Concrete Using Hazardous Thermal Power and Steel Industrial Waste: Age-Dependent Tensile Behavior, Microstructure, and Predictive Models

Fly ash (FA) is a hazardous industrial by-product of coal combustion that contains toxic metals and fine particles, posing serious environmental and health risks. Its utilization in geopolymer concrete (GPC) provides a sustainable alternative to ordinary portland cement concrete (OPCC), reducing the need for traditional cement. However, FA-GPC requires heat curing, which limits its practical use. The incorporation of ground granulated blast furnace slag (GGBFS) into FA-GPC addresses this limitation by facilitating the curing at ambient temperature. This study examines the age-dependent splitting tensile strength (fspt) and flexural tensile strength (fr) of GPC, incorporating varying proportions of FA and GGBFS ranging from 0% to 80%, with testing conducted up to 180 days. For comparison, an OPCC mix with the same binder content was prepared to evaluate the strength evolution in both concretes. The results showed continuous strength development in all GPC mixes, with GGBFS significantly improving both early and long-term tensile performance. GPC mixes with balanced FA and GGBFS content outperformed OPCC. Microstructural analysis confirmed that increased GGBFS content enhances matrix densification through the formation of additional calcium-alumino-silicate-hydrate gel alongside sodium aluminosilicate hydrate gel, leading to superior tensile properties. Furthermore, predictive models were developed to estimate fspt and fr of GPC based on age and GGBFS content. Overall, this study enhances understanding of the tensile and microstructural behavior of FA-GGBFS GPC, contributing to the advancement of sustainable concrete for construction applications.