Influence of Surface Preparation on Long-Term Bonding of Shotcrete

Bonding tests were performed to evaluate the capacity of different shotcrete mixes to provide a good and durable joint with concrete surfaces prepared for repair in various ways. A total of 21 slabs made of ordinary or conventional concrete were covered with a 75- to 100-mm layer of shotcrete. The concrete surfaces to be covered with shotcrete were prepared in different ways: sandblasting, chipping with jackhammers, grinding, or hydrodemolition. Both dry-mix and wet-mix shotcretes were used. Pullout tests, performed after 2 and 6 months, were used to evaluate the strength and durability of the bonding. The results indicate that the type of surface preparation has a strong influence on the strength and durability of the bonding, and that hydrodemolition is probably the best type of surface preparation. The shotcrete mix composition, however, was found to have relatively little influence on bonding durability.