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2015SummerShotcreteEMag

Shotcrete Corner The top of this industrial sump wall is gunned in place using dry-process shotcrete. The shotcrete process provides an excellent natural Shotcrete is gunned at high velocity onto the bond to the substrate without using bonding receiving surface. On initial impact, a larger compounds. In many cases, bonding compounds percentage of aggregate rebounds from the are detrimental to achieving a good bond surface, leaving a thin layer of cement paste at the with shotcrete interface of the new shotcrete and the substrate is a cement-poor, aggregate-rich, improperly things in the field, the more likely you will end hydrated by-product of the shotcrete process and up with a good result. is not the material that you want to have at the point of contact. You cannot wash or blow off the rebound and overspray from areas and mesh where bonding compound has been applied. Using a blowpipe to remove rebound will actually cause more unacceptable material to stick to the adjacent areas where the bonding agent has been applied. Also, because shotcrete is sprayed in place gradually across a repair area and isn’t cast all at once like a concrete pour, the working time of a bonding compound becomes an issue. If shotcrete isn’t placed while the bonding compound is still tacky, the bonding compound becomes a bond On its initial contact, more aggregate rebounds off the receiving surface, breaker. Unless the timing between the application leaving a thin layer of cement paste at the interface between the existing of the bonding compound and the shotcrete is just concrete and the shotcrete. The material begins to build on the cushion of right, some of the repair areas where the bonding plastic material. The velocity of the shotcrete process drives the material compound has been applied may have hardened in place, creating an excellent bond with the existing substrate. by the time the shotcrete is placed. Establishing the “open time” of a bonding agent in place is very difficult to gauge and then coordinate with shotcrete placement. Ted Sofis and his brother, William J. Sofis Jr., are the In summation, when you use bonding Principal Owners of Sofis Company, Inc. After graduating compounds with shotcrete, you increase the risk from Muskingum College, New Concord, OH, with his BA of interfering with the excellent bond produced in 1975, Ted began working full time as a shotcrete naturally with the shotcrete process. Rebound and nozzleman and operator servicing the steel industry. He overspray can easily stick to the fresh bonding began managing Sofis Company, Inc., in 1984 and has compound in areas adjacent to the shotcrete over 40 years of experience in the shotcrete industry. He placement, which will reduce the bond of is Chair of the ASA Publications Committee, a member of subsequently placed shotcrete, creating a high multiple other ASA committees, and an ACI Examiner. Over the years, Sofis probability that sections of the repair will actually Company, Inc., has been involved in bridge, dam, and slope projects using have a bond breaker from the hardened bonding shotcrete and refractory installations in power plants and steel mills. Sofis compound. If I’ve learned anything in my 40 years Company, Inc., is a member of the Pittsburgh Section of the American Society of gunning, it’s that the simpler you can keep of Highway Engineers (ASHE) and ASA. Shotcrete • Summer 2015 31


2015SummerShotcreteEMag
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