Investigation of spray pattern in shotcrete applications

Impact kinetic energy is well known to play a central and key role on rebound and consolidation mechanisms controlling the shotcrete placement process. While the impact velocity of the traveling particles at their exit of the nozzle has received some attention recently, the mass flow distribution of the sprayed material as it impacts the receiving surface remains unexplored despite its obvious importance on rebound. In this context, a novel apparatus that collects the sprayed material traveling out of the nozzle was developed; material spatial distribution and composition are brought forward. The incident mass flow of material was found to be denser in the central region around the spray axis and decrease toward the peripheral regions following a Gaussian-type function. Additionally, a cement-rich layer formed in the spray's peripheral zones is also revealed and its origins are discussed. In light of this work, an innovative and unique analytical characterization tool is proposed to further investigate the spraying process and to improve the understanding of shotcrete, and especially material losses through rebound. (C) 2015 Elsevier Ltd. All rights reserved.