Evaluating the Impact of Binder‐Accelerator Combinations on Setting Behaviour in Low‐carbon Shotcrete

Abstract

In shotcrete, liquid accelerators interact with cementitious binders to achieve a fast setting and hardening. However, the increasing use of low‐carbon cements with high clinker substitution rates can disturb the balance of the binder‐accelerator combination and limit their application in shotcrete. The characterization of that interaction is thus crucial to evaluate the performance of accelerators or specific accelerator‐binder combinations. Typical test procedures (e.g. Vicat test) are based on the resistance of cement paste against the penetration with a defined needle. An alternative approach was applied here, using a rheometer, which determines time‐dependent rheology changes of binder‐accelerator combinations. 'Various binder‐accelerator combinations were tested by using the “Viskomat NT” rheometer. To avoid complete setting of the accelerated binder pastes in the rheometer, rather low, diluted accelerator dosages (max. 1 %) had to be used. The results of rheometer measurements were compared to common test procedures for setting with typical accelerator dosages. It was found that the rheometer measurements are a reliable procedure for determining the accelerator‐binder interaction at early ages.