Effect of Particle Density on Its Rebound in Dry-Mix Shotcrete

When concrete is sprayed during shotcreting, inevitably some material is lost due to rebound. The relative losses for coarse aggregates and fibers are higher than that for the rest, and therefore the composition of the material in-place is deficient in these phases. In order to compensate for such loss and indeed to minimize it, one must identify the parameters affecting rebound and comprehend the underlying mechanisms. Recent work has established a theory of rebound for coarse aggregates. However, fibers differ from aggregates in their material and geometric properties and the effect of these must be understood in order to extend the existing theory of rebound to fibers. This is a study on the influence of particle density upon the rebound of a projectile impinging via the dry-mix process onto fresh shotcrete. The empirical model developed in this study postulates that a lower aggregate density favors lower rebound and this prediction was verified using two kinds of lightweight aggregates in dry-mix shotcrete.