Interaction between cement and chemical admixture from the point of cement hydration, absorption behaviour of admixture, and paste rheology

Chemical admixtures can improve the properties of concrete. High performance concrete with high strength, superior fluidity, and self-compactibility can be realized mainly because of chemical admixtures. Rheological properties of fresh concrete can be strongly affected by the combination of cement and chemical admixture, method of admixture addition, or the water-cement ratio. Problems in fluidity, such as stiffening and large slump-loss, occasionally happen under a particular combination of cement and admixture. These phenomena are generally called incompatibilities between cement and chemical admixtures. In this study, the interaction between cement and the chemical admixture types lignin sulfonate, naphthalene sulfonate, melamine sulfonate, amino sulfonate, and polycarboxylate, together with the working factors and mechanisms, are discussed from the viewpoint of cement hydration. Although the polycarboxylate type superplasticizer was considered to have better compatibility in combination with different kinds of cement, the authors show that its compatibility is affected by the amount of alkaline sulfates in cement. (C) 1999 Elsevier Science Ltd. All rights reserved.