Toward the viscosity reducing of cement paste: Optimization of the molecular weight of polycarboxylate superplasticizers

Abstract The influence of polycarboxylate superplasticizers (PCEs) on rheology was investigated for viscosity reducing of cement pastes. Five types of PCEs of varied molecular weight were employed. For pastes with same w/c and consistent spread value, yield stress was almost the same, while residual viscosity decreased with the increase of molecular weight of PCE. It was suggested that it was probably the “bridging effect” causing more adsorption amount required to achieve similar yield stress for PCE of larger molecular weight. The large adsorption layer thickness was beneficial for improving packing density, which enlarged the average particle separating distance, and finally resulted in a significant decrease in residual viscosity of cement pastes. Considering that packing density improvement was pronounced for viscosity reducing of cement paste, development of PCE with high surface coverage of the long side chain should be the necessary and sufficient condition for the lowering of apparent viscosity of cement paste.