Effects of polycarboxylate architecture on flow behaviour of cement paste

Abstract

The effect of polycarboxylate superplasticiser (PCS) architecture in terms of a flexible or rigid backbone and repartition of side-chains along the backbone on the hydrodynamic radius, adsorption properties, flow behaviour and rheological behaviour was systematically evaluated. PCSs with different architectures were found to affect the flow behaviour of cement paste differently, mainly due to difference in PCS surface coverage area on cement particle surfaces. The PCS surface coverage area on cement particle surfaces was determined by the adsorption layer thickness of a single PCS molecule and the adsorption amount. The adsorption layer thickness of a single PCS molecule is correlated with the hydrodynamic radius in solution. The PCS with a rigid structure in the main chain had a more coiled conformation, with an inevitably smaller hydrodynamic radius and thus a thinner adsorption layer. The adsorption amount is closely related to the exposed density of carboxylic groups. A more extended solution conformation facilitates the exposure of carboxylic groups, which is beneficial for the adsorption of PCS onto cement particle surfaces. As a consequence, the thicker the adsorption layer thickness of a single PCS molecule and a larger adsorption amount results in larger PCS surface coverage area on cement particle surfaces, producing better workability of cement paste.