PHYSICOCHEMICAL PARAMETERS DETERMINING HYDRATION AND PARTICLE INTERACTIONS DURING THE SETTING OF SILICATE CEMENTS

Hydration of tricalcium silicate (Ca3SiO5), the pure phase used as a m odel of the portland cements, is the chemical process leading to the f ormation of hydrates, while setting is a definite time event correspon ding to the change of the paste from the soft to the hard state. Setti ng results from interactions between anhydrous or very partially hydra ted particles. The analysis of these interactions leads to the identif ication of two fundamental steps: the coagulation of cement grains dur ing the first minutes following the mixing and the rigidification of t he coagulated structure which arises simultaneously with the accelerat ion of the calcium silicate hydrates (C-S-H) formation. The chemical e volution of the system, which controls the lime concentration in solut ion, determines the nature of particle interactions and the physical e volution of the suspension or paste: there exists a critical range of lime concentration required to initiate the coagulation of cement part icles and the ability of C-S-H to make rigid the coagulated structure depends on the solubility of these particles.