The effect of micelles with random pH-sensitive/hydrophobic structure on the workability, hydration process and microstructure of cement paste

Abstract

In this study, the workability, hydration rate and microstructure of cement paste in the presence of the micelles prepared by two different diblock copolymers with random pH sensitive/hydrophobic structure (poly(polylactide methacrylate-co-tert-butyl methacrylate)-b-poly(poly(ethylene glycol) methyl ether methacrylate) (P(PLAMA-co-tBMA)-b-PPEGMA) and poly(ethylene glycol) methyl ether-b-(poly-lactic acid-co-poly(β-amino esters)) (MPEG-b-(PLA-co-PAE)) copolymers, respectively) were investigated. In fresh cement paste, the micelles were efficiently adsorbed on cement particles; although the average zeta potential of cement particles was not significantly changed in the presence of the micelles due to their low concentrations, with a high water to cement ratio, the adsorbed micelles altered the zeta potential of partial cement particles, leading to a better workability of cement paste. In hardened cement paste, the micelles retarded the hydration rate of C₃S at very early hydration age, but accelerated the hydration rate of cement paste at later stages, resulting in a denser cement matrix and increased mechanical property. The most plausible mechanisms are related to the nucleation effect, molecular structure and adsorption performance of the polymeric micelles.