Effect of equipment on spray velocity distribution in shotcrete applications

• The impact velocity fields produced by three shotcrete nozzles are investigated.
• A novel experimental approach using a high-speed imaging system is proposed.
• The effect of equipment on spray features is revealed using normalized parameters.
• The axial velocity profiles at the nozzle outlet follow a Gaussian-type function.
• A mathematical expression of the spray velocity fields investigated is provided.

It is well known that the velocity of particles exiting the nozzle plays a central role on rebound and consolidation in the shotcrete placement process. With this in mind, the impact velocity distribution was investigated using a high-speed imaging system with a full-scale shotcrete spray generated using two dry-mix nozzles and one wet-mix nozzle. The incident velocity was found to be at its maximum in the central region around the spray axis and decrease toward the peripheral regions following a Gaussian-type function. Further analysis using normalized parameters shows that these velocity profiles, which were obtained experimentally, follow a similar function that can be used to compare the effect a given nozzle, or equipment, has on impact velocity distribution. In light of this work, innovative and unique characterization tools are proposed to further support equipment optimization and to improve the understanding of the overall shotcrete process, and especially rebound.