Electrokinetic properties which control the coagulation of silicate cement suspensions during early age hydration

The coagulation of cement particles during early age hydration has been previously identified as the first step of the setting and hardening of cement pastes. By hydrating Ca(3)SiO(5) and a silicate-rich clinker under controlled conditions, a correlation between the coagulation of the suspensions and the electrokinetic properties of particles is established. The zeta potential, and hence the surface charge, of particles in suspension depends on the calcium content of the medium. At low concentrations of Ca(2+), the zeta potential of Ca(3)SiO(5) particles, calcium silicate hydrate (C-S-H), and clinker is negative(< -30 mV) and the suspensions are well dispersed. A strong coagulation occurs at intermediate concentrations (1 to 10 mmol/L of Ca(2+)) as the zeta potential becomes weaker under these conditions. The mean diameter of the aggregates decreases at high Ca(2+) concentrations, where the zeta potential of the particles is high and positive. (C) 1998 Academic Press.