Mechanisms of actions of different superplasticizers for high performance concrete

The invention of superplasticizers is one of the most important breakthrough that has led to the development of high performance concrete. Superplasticizers can be used for three different purpose, namely (a) to increase workability without changing the mixture composition, (b) to reduce the amount of mixing water in order to reduce the water-cement ratio and then to increase strength and/or improve durability, and (c) to reduce both water and cement in order to reduce cost in addition to reducing creep, shrinkage and thermal strains caused by heat of cement hydration. Practical examples of these different ways of using superplasticizers are given by referring to the traditional superplasticizers (naphthalene- and melamine-based) and to the recent advances in this area (acrylic polymer-based admixtures). In particular the following topics are examined: composition of superplasticizers, mechanism of action (electrostatic repulsion and steric hindrance), influence of the cement composition (C3A, alkali, S03), mode of addition of superplasticizer, slump loss, blending of superplasticizers.