Chemical admixture-cement interactions: Phenomenology and physico-chemical concepts

Chemical admixtures are often used to alter the course of cement hydration reactions and the properties of fresh or hardened concrete. The admixtures, in most cases organic compounds, can perform such functions through various types of physico-chemical interactions with the hydrating cement phases. To understand the consequences of admixture-cement interactions, and to optimize the functional properties of admixtures, appropriate descriptions of their mode of action must be developed. An overview of the latter is attempted here, drawing mainly from: (1) the chemistry and phenomenology of cement hydration; (2) a review of the various types of molecular processes in which admixture molecules can be involved at the solid-solution interface; (3) selected experimental data on the influence of water reducers and superplasticizers which illustrate some basic features of admixture-cement interactions. (C) 1998 Elsevier Science Ltd. All rights reserved.