We use up about one-quarter of our shotcrete materials in wast from rebound and not enough sticks to the wall. What are we doing wrong?
It may be that you are doing nothing wrong. According to the American Concrete Institute Recommended Practice for shotcreting (ACI 506) the approximate range of rebound for walls is 15 to 30 percent of the total mix. On floors and slabs it is only 5 to 15 percent, but on overhead work it ranges from 25 to 50 percent Rebound is large when the work begins but decreases after a cushion of plastic shotcrete begins to build up. among the many factors that affect rebound is the skill of the nozzleman; he must know what distance to maintain between the nozzle and the work and what angles of impingement are best for various percentages of reinforcement. Air pressures, mix proportions, and aggregate gradings all have their effects. Any or all of these should be investigated if the rebound is highter than the amounts given by ACI 506.