ABSTRACT
This chapter discusses the five distinct types which together make up more than 80% of the total quantities used in concrete – plasticisers, superplasticisers, accelerators, retarders and air-entraining agents – and briefly mention others. Admixtures are chemicals that are added to concrete during mixing and significantly change its fresh, early age or hardened state to economic or physical advantage. As the name implies superplasticisers are more powerful than plasticisers and they are used to achieve increases in fluidity and workability of a much greater magnitude than those obtainable with plasticisers. The mode of action of superplasticisers is similar to that of plasticizers, i.e. they cause a combination of mutual repulsion and steric hindrance between the cement particles. The limited range and effectiveness of a lignosulphonate-based plasticiser and the greater efficiency of a Polycarboxylate ethers superplasticiser compared to a Sulphonated naphthalene formaldehyde condensates -based material are apparent.
