Rheology, mechanical properties, and hydration of synergistically activated coal gasification slag with three typical solid wastes

The utilization of multiple solid-waste-activated slags to prepare clinker-free binders has garnered considerable interest due to their environmental friendliness and low cost. In this study, a novel binder was developed by incorporating multiple solid wastes, namely red mud (RM), carbide slag (CS), phosphogypsum (PG), and coal gasification slag (CGS). RM, CS, and PG were used as activators to synergistically activate two kinds of ultra-fine CGS precursors with median particle sizes of 5.2 mu m and 6.1 mu m, respectively. The effects of parameters including precursor fineness and activator dosage were systematically investigated. The hydration products were then characterized to elucidate the activation mechanism. The results showed that the rheology of the pastes fitted well with Herschel-Bulkley model, exhibiting shear thinning behavior regardless of the proportion of the activators. The low CGS fineness and high PG dosage reduced viscosity, yield stress, and shear stress of the pastes. Fine CGS particles were found to shorten the hydration dormancy period and accelerate the appearance of the second exothermic peak, thus promoting strength development. CGS with small particles facilitated the formation of ettringite but restricted hydrotalcite generation. This study reported a binder utilizing full solid wastes and confirmed its feasibility as a sustainable alternative in construction applications.