The effect of replacing fly ash with GGBFS on the fracture parameters of geopolymer concrete

Abstract

Given the abundance, reduced cost, and environmental advantages associated with the utilization of ground granulated blast furnace slag (GGBFS) as a substitute for fly ash, this investigation examines the influence of GGBFS replacement levels of 5, 10, 15, 20, 25, and 30 % on the fracture behavior of lightweight fly ash-based geopolymer concrete (LWFCGC). Concrete specimens were produced using different proportions of GGBFS and fly ash and cured at 80 °C. Subsequently, they were subjected to compressive, tensile, and three-point bending tests. The results indicate that replacing fly ash with GGBFS significantly influences the mechanical properties of geopolymer concrete. Generally, increasing the GGBFS replacement percentage up to 20 % led to higher compressive strength and reduced porosity. However, increasing the GGBFS from 20 % to 30 % led to lower compressive strength. Increasing the replacement percentage from 0 % to 30 % resulted in an increase in fracture toughness from 16.73 to 27.49 MPa√mm and fracture energy from 54.9 to 156.06 N/m. In conclusion, this study shows that GGBFS can be a suitable substitute for fly ash in geopolymer concrete to some extent. By carefully selecting the ratio of GGBFS to fly ash, geopolymer concrete with desirable mechanical properties, fracture parameters, and durability can be achieved. © 2025 Elsevier B.V.