Effect of side chains in block polycarboxylate superplasticizers on early-age properties of cement paste

Abstract

Even though numerous research projects have been carried out on the subject concerning interactions between sequence structure of polycarboxylate superplasticizers (PC) and cement, many questions remain unsolved, such as the influence of PC on early-age microstructural development and PC adsorption behavior. The study first successfully synthesized well-defined block PC with varying side chains length and side chains density using reversible addition–fragmentation chain transfer polymerization. The influence of side chains in block PC on the early-age properties of cement paste was systematically studied by various characterization methods such as paste flow, adsorption properties, calorimetric measurements and amount of hydration products. The results have illustrated that PC with longer side chains and lower side chains density shows higher adsorption amount, thereby a better workability for a given mass ratio of adsorption groups to side chains. Furthermore, the adsorption amount decreases with the increasing side chains length for a fixed length of main chain as well as side chains density. However, there is better initial paste flow and higher paste flow retention capability owing to longer side chains. It is worth noting that PC with longer side chains promotes the cement hydration process thus increasing the hydration products owing to larger surface coverage. All these findings close the gap between side chains in block PC and early-age properties, providing suggestions for the design of PC.