Effect of Polycarboxylate-Based Superplasticizer on the Performance of Ultrahigh-Performance Concrete and Potential Interaction with Cement and Pozzolans

Superplasticizers are indispensable admixtures for the design of ultrahigh-performance concrete (UHPC). Their effectiveness is determined by their interactions between the individual constituents, which include a variety of fine powders. In this research, different investigative methods were employed to study the influence of polycarboxylate-based superplasticizers (PCs) on the performance of UHPC. The potential interaction of PC with cement and fine pozzolans was explored. Three PCs, three cements, and three pozzolans typically used in the design of UHPC were selected. Test results showed reduced yield stress and viscosity, and consequently improved workability, along with enhanced compressive strength for PCs with longer side chains compared with PCs with shorter side chains, indicating that they are more efficient in dispersing the system of fine particles in UHPC. It also was found that a larger amount of PC adsorbed onto the surface of cements with higher combined quantities of C3A and C4AF, leaving less PC available to disperse cement grains effectively. Test results also indicated that calcium ion adsorption on the surface of pozzolans may lead to a PC adsorption competition between the cement and fine pozzolans and thus reduce the dispersion efficiency of the PC.