Mechanical and fracture properties of slag/steel slag-based geopolymer fully recycled aggregate concrete

Abstract

Blast furnace /steel slag-based geopolymer and recycled aggregate (RA) as green alternatives to cement and natural aggregate (NA), respectively, are attracting increasing attention. This study investigated the influence of four different aggregate systems (i.e., full-NA, full-recycled coarse aggregate, full-recycled fine aggregate, and full-RA) and three different replacement ratios of steel slag (i.e., 0%, 25%, and 50% of the precursor) on the mechanical properties (compressive and splitting tensile strength) and fracture properties (fracture energy and fracture toughness) of one-part slag/steel slag-based geopolymer concrete, aiming to promote its utilization in structural engineering. The experimental results indicate that substituting ordinary Portland cement with slag-based one-part geopolymer significantly enhanced the compressive and splitting tensile strength of geopolymer natural aggregate concrete (GNAC), although it leaded to a decrease in fracture properties. The incorporation of RA in GNAC resulted in deteriorated properties, with the 28-day compressive strength being reduced by up to 5%− 19.4% and fracture energy being reduced by up to 16.8%− 43.8%. Moreover, incorporating an appropriate amount of steel slag (approximately 25%) in geopolymer fully recycled aggregate concrete (GFRAC) had minimal impact on mechanical properties, while it enhanced the fracture energy values by up to approximately 16.6%. Nevertheless, a higher content of steel slag adversely affected the relevant properties due to its lower cementitious activity compared to slag. To mitigate the drawbacks associated with steel slag, less than 25% of steel slag content is recommended considering the mechanical and fracture properties of GFRAC.