Correlations of the dispersing capability of NSF and PCE types of superplasticizer and their impacts on cement hydration with the adsorption in fresh cement pastes

Comparative study of NSF and PCE superplasticizers was carried out aiming at correlating the adsorption in fresh cement pastes (fcps) with their dispersing capability and the impacts on cement hydration. Results show that the adsorption of NSF follows a typical Langmuir monolayer adsorption model while PCE exhibits a multi-layer adsorption. The fluidity of fcps containing NSF and the retardation effect of NSF on hydration are directly proportional to the surface coverage of NSF on cement grains. As full coverage is achieved, the fluidity enhancement and the retardation effect reach maximum by addition of NSF. By contrast, the fluidity of fcps with PCE is related to the coverage of the first adsorbed layer and the secondary adsorbed layer does not contribute to the enhancement of fluidity. Both the adsorbed PCE and the PCE remaining in aqueous phase participate in retarding cement hydration because of the complexation effect of COO− with Ca2 +.