Rheology and early structural build-up of alkali-activated Baosteel process slag binders

Abstract Alkali-activated binders (AABs), or geopolymers, have emerged as a sustainable alternative for producing cementitious materials from industrial byproducts. Although several aluminosilicate precursors have already been extensively studied, other potential sources remain unexplored. In this context, Baosteel Short Slag Flow (BSSF), a steel-industry byproduct, presents itself as a novel and practically unexplored precursor. However, since the precursor composition strongly influences the rheological behavior and structural build-up of AABs, systematic studies are essential to optimize the workability and performance of these materials for construction applications. Accordingly, the present study addresses this research gap by investigating how varying BSSF contents influence the structural build-up and rheological behavior of AABs. Binary AABs were formulated with varying proportions of BSSF slag and fly ash (FA) ranging from 0% to 100% BSSF in 25% increments. A Portland cement binder (PCB) with equivalent l/b ratio was also evaluated for comparison. Rheological characterization, isothermal calorimetry, compressive strength testing, and SEM analysis were used to assess how precursor composition governs workability, hardening kinetics, mechanical performance, and microstructure. Increasing BSSF slag content influenced viscosity, yield stress, and structural build-up, improving initial workability while accelerating hardening, although this effect may be partly influenced by the higher activator solution fraction at increasing BSSF levels. Compressive strength generally decreased with increasing BSSF content, except for B75, which achieved the highest strength (46.7 MPa). SEM analysis indicated that higher BSSF slag contents modified the binder structure. The findings underscored the potential of BSSF slag as an effective precursor for the development of AABs.