Performance of reinforced concrete beams retrofitted with fiber-reinforced shotcrete at early age
Creators: name: Holland, Reid
Publisher: name: No Publisher Supplied
Year: 2019

description: Similar to how a lot of our country’s land has already been developed, a lot of our necessary structures have already been built. Our infrastructure relies on old bridges, buildings, dams, etc. which produce a massive economic strain in the form of repair and maintenance. Tearing down an old structure to create a new one is not nearly as economical as its improvement or repair. These economic factors force our hands as engineers to produce new technologies to increase economic efficiency, one of them being shotcrete. In recent years, shotcrete has gained a lot of traction in its usefulness for repairing and retrofitting due to its ease of application and bond strength to the applied substrate. In this study, the effects of shotcrete on the repair of reinforced concrete beams is examined using fiber reinforced shotcrete (FRS) with and without a steel or basalt mesh for a total of 3 different shotcrete layer types. Each mix is tested at two different curing times after the shotcrete is applied, 3 days and 7 days. The effectiveness of fiber reinforced shotcrete is monitored using synthetic macro fibers (1.5") in a shotcrete laminate versus the same fibers in self-consolidating concrete (FR-SCC). The shotcrete proved to have a higher ultimate strength, lower crack width, and higher deflection compared to a concrete beam compared to the FR-SCC laminates and Full Class A beams.In order to simulate the already deteriorated reinforced concrete beam in a controlled lab environment the beams, stirrups were exposed at the bottom where the shotcrete is applied. Included in the shotcrete layer is a steel mesh or basalt mesh with 1 square inch openings to produce a shotcrete laminate, while also studying an FR-SH layer with no mesh. Of the two meshes used, steel proved to be the most beneficial for ultimate load, while basalt was more beneficial for deflection. Having no mesh also proved to be a viable design option, however, provides no benefit over the two except for early age ductility.Curing methodology is also studied in order to better gage optimal curing regimes. The three methods examined were wet burlap, curing compound, and dry curing where dry curing involves only wrapping the concrete member in plastic. Of the three, the most consistent performer was wet burlap. Curing compound proved to be more erratic, though overall similar to wet burlap and dry curing proved to have good early properties, however is not considered sufficient for later stages.In addition to beam testing, a comparison between the hardened properties of shotcrete were compared under different methods. Cylinders were shot directly by the nozzleman during casting and cast by hand using the same mix before being shot in both 4"x8" and 6"x12" cylinders. These were compared with cored samples to see which results more closely relate to the cylinders to help produce an easier method of testing the shotcrete’s properties. Overall, only compression and tensile strengths were relatable due to constraints of how the cylinders can be tested. Cored samples cannot be tested using the same methodology and would have to be developed. For compression strength, the 4"x8" cylinders cast by hand produced results very similar to the cored samples. For tensile strength, the 4"x8" cylinders shot by the nozzleman were very similar. Both have potential to be used as a substitute to cores.