A crucial step in cement superplasticizer compatibility

The rheology of cementitious system containing superplasticizer is the consequence of a physical process due to the electrostatic repulsion between particles, but also of a chemical process linked to the nature of the phases that are formed. Ettringite crystallization play as a key role in this matter and the nature of the sulfate phase added to control cement setting is as important as its dosage. Alkali sulfates, which provide only SO42- ions, do not promote the formation of ettringite for which the presence of large amounts of Ca2+ is necessary. The adsorption of superplasticizer molecules on hydrated cement grains slows down the dissolution rates of the constituents and modifies the nature of the compounds formed. It could result in a modification of the ettringite morphology. (C) 2002 Elsevier Science Ltd. All rights reserved.