The role of coal gasification slag in cement paste with and without polycarboxylate superplasticizer and its rheology

Coal gasification slag (CGS) is the main by-product of coal gasification technology, and the utilization of CGS as mineral admixture is environmentally sound. In this paper, the effect and mechanisms of CGS on the workability (i.e., fluidity and rheological behaviors) of ordinary Portland cement (OPC) paste with and without polycarboxylate superplasticizer (PCE) were studied. The zeta potential and surface free energies of OPC and CGS were tested to calculate the electrostatic force and Van der Waals force variations due to the addition of CGS particles. The results revealed that CGS mainly decreases the van der Waals attraction force between binder particles, enhancing the fluidity and reducing cement pastes’ yield stress and plastic viscosity. When blended with PCE, the dissolution of CGS mainly increased the ionic concentrations of Si(OH)x(4-x), which promoted the aggregation of PCE and decreased its adsorption, thus decreasing the fluidity and increasing the rheological parameters.