Dear reader in our last part of this topic we have learnt that rebound of coarse particles produce rich shotcrete which results little increase in shrinkage. The rebound percentage is not uniform throughout the shotcrete projection.
Many factors influence the rebound percentage, of these; most important factor is thickness of section to be produced by shotcrete. A thin layer of shotcrete suffers more loss than thicker section.
The probable cause of more initial loss is the highest percentage of rebound is occurred at the beginning of shotcreting when the material is impacting on hard backup surface.
The loss is generally diminished as the progress of shotcreting. This is due to impacting of materials on plastic cushion provided by shotcrete which is built up gradually.
The typical values of rebound of materials are:
The degree of rebound with previously discussed plastic shrinkage; another economic consideration is waste of materials. Not only loss incorporated in rebound but also materials are accumulated in critical locations where subsequent layers of shotcrete produce a greater section than expected.
Dear reader we will learn about accumulation of steel fiber in shotcreting in our next post.