Novel use of fava bean stalk ash in ultra-high-performance geopolymer concrete: A sustainable approach to improving strength and durability

Abstract

Ultra-high-performance geopolymer concrete (UHPGC) provides a sustainable alternative to Portland cement by utilizing industrial and agricultural waste, thereby reducing CO2 emissions in the construction sector. This study investigates the incorporation of thermally treated fava bean stalk ash (FBSA), an agricultural byproduct, as a partial replacement (10 %, 20 %, and 30 %) for the primary binder in UHPGC mixtures composed of either 100 % ground granulated blast furnace slag (GGBFS), 100 % fly ash (FA), or a 50:50 GGBFS–FA blend. Mechanical properties (compressive, tensile, and flexural strength), durability (water permeability, sorptivity, and sulfate resistance), and microstructural characteristics using scanning electron microscopy (SEM) were evaluated. Although FBSA reduced workability, it enhanced strength and durability characteristics. The optimal mix, with 10 % FBSA, achieved a 28-day compressive strength of 188.2 MPa, tensile strength of 20.1 MPa, flexural strength of 29 MPa, and modulus of elasticity of 59.86 GPa. It also showed the lowest water permeability (1.05 × 10−11 cm/s) and sorptivity coefficient (2.11 × 10−4 mm/s0.5). After 180 days of exposure to a 150 g/L sulfate solution. Under thermal exposure at 750 °C, OPGC containing 30 % FBSA retained the highest compressive strength of 35.7 % compared to other blends. The use of FBSA as a partial substitute for GGBFS or FA contributed to enhancing the properties of UHPGC.