Influence of Surfactant Chemical Admixtures on the Stability and Rheological Properties of Calcium Carbonate and Cement Pastes

摘要

The influence of various types of surfactants on the rheological properties and on the rates of bleeding and sedimentation of limestone and cement pastes has been examined as function of surfactant concentration. The surfactants selected include both low foaming and foaming compounds to enable a distinction of the effects inherent to the surfactants, from those due to air entrained in the pastes. Over the range of concentration examined, the rheological characterization performed shortly after mixing showed little change in the paste rheology due to the presence of the surfactants, in the absence of entrained air. As expected, with entrained air, the rheological parameters are all moderately altered. On the other hand,the stability of the CaCO3 pastes, evaluated through their bleeding and sedimentation kinetics, is markedly affected by the surfactants. At short times (<1hr), the stability is only marginally changed; at longer times, the paste stability is substantially decreased through cooperative bleeding and sedimentation behavior. Similar effects were observed in lime-saturated CaCO3 pastes, though less pronounced due to the higher stability of these pastes. In relatively stable cement pastes, the bleeding and sedimentation were initially similar to the limestone pastes, but no cooperative destabilization was observed, with or without surfactants.The influence of the surfactants on bleeding and sedimentation kinetics was attributed to the formation of channels in the pastes, a process facilitated by the surfactants. The variations observed with surfactant molecular and solution properties and concentration are discussed; a plausible mechanism is suggested to explain surfactant-induced effects.