Effect of hydrophobic units of polycarboxylate superplasticizer on the flow behavior of cement paste

Abstract

For the tuning of conformation of polycarboxylate (PCE) superplasticizers, hydrophobic groups of different stiffness were incorporated, including styrene (St), methyl methacrylate (MMA), ethyl acrylate (EA), and n-butyl acrylate (n-BA) units. The effect of these hydrophobic groups on the dispersing performance, adsorption process and, rheology of cement paste were investigated. Investigation on the solution conformation and adsorption layer thickness indicated the action mechanism of these groups. High backbone stiffness resulted in a lower extent of conformation condensation from pure aqueous solution to pore solution, and therefore more carboxylic groups could be accessible for adsorption. However, the conformation change after adsorption might also be limited and the size of single molecule after adsorption should be small. Hydrophobic groups always resulted in a coiled PCE conformation in salt solution, which indicated a lower adsorption affinity and thinner adsorption layer for these PCE molecules.</p