The influence of the molecular structure of PCEs on the interaction with expandable clays

The dispersing efficiency of superplasticizers, especially PCE polycarboxylates, can be greatly affected by the presence of clay-bearing aggregates in concrete mixtures. Particularly, expandable clays are the most detrimental, due to their ability to sequester large amounts of PCEs through adsorption and intercalation mechanisms. Thereby, PCE molecules are no longer available to effectively disperse the cement particles and the flowability of concrete mixtures is correspondingly reduced. In recent years, many studies have been done to investigate the mechanism of PCE/clay interactions, with the aim of mitigating the effects of clay-bearing aggregates. In the present work, different PCE polymers were synthesized and characterized in terms of molecular weight distribution and molecular structure. Their interactions with expandable clays were investigated by X-Ray Powder Diffraction (XRPD) and Total Organic Carbon (TOC). The effect of expandable clays on the flowability of cement pastes containing different polymers was studied by mini-slump test. The results of the present study show that polymers with different molecular structure exhibit different interactions with swelling clays, highlighted by different XRPD patterns and d-spacing values, and that the molecular structure of PCEs is a fundamental parameter in determining such interactions. Moreover, through the appropriate tuning of structural molecular parameters, it is possible to formulate PCE-based superplasticizers more tolerant to swelling clays.