Ettringite growth in presence of superplasticizer

This work concerns the influence of two different types of dispersing polymers on the ettringite growing over a model substrate obtained from Al2(SO4)3/Ca(OH)2 mixture. Specifically the work concerns the influence of a comb-polymer (PC) super-plasticizer and of one linear carboxy terminated ethylene oxide polymer (PEO-SA). The last polymer may be considered the elementary unit of the former PC, having a negative site (carboxylic group) linked to polyethylene oxide chain (MW 1000) similar to the PC’s side branch. XRD diffraction confirms ettringite formation over the substrate. SEM and TG/DTG analysis put in evidence the morphology modifications induced by the polymer. At initial hydration time we compared the crystal morphology of mixtures with and without polymer. It changes from long and thin to short and thick needles in presence of PEO-SA while with the PC, the crystals remain short but more thin. The modifications depend on polymer structure and on reaction time. The influence of the carboxylated comb polymer (PC) backbone is evidenced.