“Structural effect of comb-polymer on the hydration of C3S phase”,

Abstract One of the main topics of the research on cement admixtures is the organic-inorganic interaction at the surface of the cementitious phases to understand the way the polymer acts. The aim of this work is to study the effect of polycarboxylate comb-polymer (PCP), used as dispersing agent, on hydration delay. In order to evaluate the role of the polymer structure on hydration we separated the PCP in two main parts: the backbone (PAA) and the dispersing chain. An active unit that reduces the PCP complexity was “ad hoc” synthesized. It consisted of a single chain based on ethylene oxide polymer(Mw=1000) O-methoxy terminated, at one end and having at the other a carboxylate group able to link the inorganic surface and representing the repetitive unit of the comb-polymer. The hydration delay of C-S-H formation induced by comb-polymer was analyzed by conduction calorimetry and the morphology of the crystalline structure in growth by SEM, specially investigating the relation between structure and hydration time. Because of the several complexities of the cementitious system undergoing hydration reactions we focussed the attention on one of the most important silicate phases of cement, the tricalcium silicate (C3S) and we studied the formation of portlandite crystals. Observing the results we noticed that the hydration delay is ascribable to the comb-shaped structure because ethylene oxide chain can assume conformations able to act as “crown ethers” modifying the salt concentration near the cement surface. Moreover we noticed that organic admixtures can influence portlandite growth better arranging its crystalline structure.