Atypical adsorption of polycarboxylate superplasticizers on calcium silicate hydrate surface: Converting interaction by solvent effects

Abstract

Although PCE adsorption occurrence is widely perceived to correlate to the anchoring of the carboxyl group on the PCE backbone, the understanding of the details is still insufficient. Here, we investigate the microstructural behavior of PCE adsorption with and without aqueous environments by molecular dynamics simulation and semi-empirical quantum chemistry calculation. We found that the introduction of an aqueous environment can change the mode of adsorption from strictly anchoring to atypical that the chains of PCE can sweep around the C-S-H surface. Two kinds of segments on the C-S-H surface have anchored the PCE, including Ca ions and hydroxyl. The aqueous environment alters the domination segments from Ca ions to hydroxyl. Further electronic analysis proves the weakening of bonding strength between PCE and C-S-H by solvation effects. This weakened interaction promotes the potential well of free energy away from the C-S-H surface and finally caused the atypical adsorption of PCE.