The influence of alkali-free and alkaline shotcrete accelerators within cement systems I.: Characterization of the setting behavior

The influence of alkali-free and alkaline accelerators on the setting behavior of cementitious mixtures is investigated. The aluminium sulfate present in the alkali-free accelerators promotes the crystallization of ettringite prisms (2-7 mum) between the clinkers, thus connecting them in a compact mass and accelerating the setting. The very rapid setting promoted by the addition of the alkali KAl(OH)(4)-rich admixture is mainly the result of the precipitation of CH plates and amorphous KCASSH hydrates. In this case, the crystallization of elongated ettringite rods contributes to a smaller extent to the setting. (C) 2001 Elsevier Science Ltd. All rights reserved.