Tricalcium Silicate Hydration Reaction in the Presence of Comb-Shaped Superplasticizers: Boundary Nucleation and Growth Model Applied to Polymer-Modified Pastes

The Boundary Nucleation and Growth Model (BNGM), developed for the analysis of the hydration reaction of tricalcium silicate, has been applied to study the kinetic behavior of pastes containing chemical admixtures. Four comb-shaped polycarboxylate ether (PCE) superplasticizers with well-known molecular structures have been added to tricalcium silicate. The BNGM analysis performed on this series of additives allows insights into the effect of the molecular architecture of the PCEs on the induction time and rate constants. The results show that decreasing the length of the polyethylene oxide side chains of the PCE molecules increases the induction time. Also, the side chain density, which highly influences the adsorption of the polymer to the C3S unreacted grains, is shown to significantly affect the duration of the induction period: in particular, molecules with low side chain density delay the setting of the paste to a greater extent than molecules with denser side chains. Moreover, the chemical admixtures influence the rate constants of the nucleation and growth processes, both reducing them and affecting their temperature dependence.