Rheology and rebound behaviour of dry-mix shotcrete

Abstract Factors based upon process and concrete technology influence the amount of rebound in the application of shotcrete. One of the important criteria is the consistency of the applied shotcrete, which is affected by grain size distribution of the aggregate and by the quantity and fluidity of the cement paste. The influence of the water–cement ratio, of water reducing, thickening and cohesion improving admixtures on the flow properties of mortar mixtures were investigated. Rheological data on mortar (relative yield stress and relative plastic viscosity) were obtained using a viscometer (Viskomat NT) with a customized measuring profile. In laboratory tests with shotcrete, a correlation between the rheological characteristics and the rebound was established. This result allows a simple, fast assessment to be made of the effect of individual admixtures or additives in minimizing rebound in the laboratory, before conducting any spray experiments (at testing facilities or construction site).