StructuralQ We are considering sealing off the openings of some existing water tunnels by constructing reinforced concrete walls within the openings. One wall, for instance, is 9.25 ft wide by 12 ft high (3 x 4 m) and is to be 22 in. (559 mm) thick. Other walls will be in the range of 18 to 26 in. (457 to 660 mm) thick. What are the limits as to the maximum thickness/size wall that shotcrete can be used to construct? Also, I noticed that in the latest revision of ACI 506R-05 that the previous recommended limits on the reinforcing bar size have been removed. I believe in the past, the reinforcing bars were limited to the smaller-size bars to reduce the development of sand pockets behind the bars. Is there a recommended limit on the size bars that can be used? Perhaps it was in the ACI standard but I just overlooked it.
Experienced shotcrete contractors with qualified crews have often shot structural concrete sections 24 to 30 in. (610 to 762 mm) thick with reinforcing bars up to No. 11 in size. There is no real limit to how thick you can build a shotcrete “wall.” Though earlier versions of ACI 506R, “Guide to Shotcrete,” did recommend limiting reinforcing bars sizes, modern equipment, concrete mixtures, and shooting techniques have proven that large-diameter steel reinforcing bars can be properly encased on a routine basis by experienced shotcrete crews. Thus, ACI 506R was updated to reflect the successful industry practice.
