Effect of alkanolamines on the performance of aluminium sulphate‐based sprayed concrete accelerators

Abstract

Alkali‐free sprayed concrete accelerators (AFA) are liquid admixtures which cause fast setting and hardening of sprayed concrete. They are typically based on aluminium sulphate, acid, alkanolamines, stabilizers and often also on aluminium hydroxide. The accelerating effect is mainly achieved through an intensive ettringite formation. Alkanolamines in the AFA also promote ettringite formation, but certain types can have a retarding effect on the C3S hydration. Therefore, in the present study the effect of alkanolamines in AFA on cement hydration was evaluated by a calorimetric method, varying the type and dosage of the alkanolamines. The application of accelerating additives in the base mix was also investigated.

TEA, and for high dosages also DEIPA, have shown to retard hydration after an initial acceleration. They can therefore be used to control the hydration of clinker phases selectively in combination with other additives. DEA was found to perform very effective and robust, accelerating very early hydration (<6 h), whilst avoiding negative effects on later stages of early hydration (6‐24 h). Furthermore, two effective additives were identified, which enhance the hydration of low carbon cement in combination with AFA.