Underwater Crack Repair

The objective of this research to investigate the use of advanced chemical admixtures for modifying the fluidity and viscosity properties of cement-based grouts or mortars so they can be placed in water flowing into cracks or open voids. Specifically, the materials must be able to withstand washout when
placed directly in front of cracks in concrete dams or voids in embankments. A simplified method of delivery is desirable to either eliminate the need for, or reduce the time for divers repairing crack. This method involved modifying the viscosity of the grout/mortar depending on the head of the water level and allowing the water pressure alone to pull it into the structure. The strength of the materials should be similar to the strength of the concrete to withstand the stresses of thermal movement. If sufficient filler is introduced into the crack, it might completely fill the crack or allow sufficient reduction in leakage so that other, more permanent methods of sealing can be used without draining the reservoir. Experience at Upper Stillwater Dam, Utah have shown that introducing hydrophilic, polyurethane grouts in flowing water was only temporarily effective, and at great cost. Research program DSO-CRACK provided funding in 2005 for the development and testing of underwater, cement-based grouts and mortars for crack sealing or filling applications. Research tasks include: • Design and construction of underwater crack standpipe • Development of underwater mortars/grouts • Test underwater crack repairs with 3 m (10 ft) of water head • Identify methods of preventing plugging of drain holes in concrete dams by the underwater mortar • Complete Final Report • Peer review / Dam Safety Advisory Team (DSAT). The focus of this research program will be on mortars containing both cementitious paste and sand. The materials used in this research were classified as anti-washout or “AWA” mortars. Cement-based grouts without sand may also be used, if desirable for narrower crack widths. This initial research program is focused on low head (3 m [10 ft] of hydraulic head) application due to the high cost of a large scale application. These mortars required more fluidity than expected for higher hydraulic head applications. However, the principals learned from this research are expected to apply to higher head applications as well. However, the fluidity and viscosity of the mortars needed to fill a crack under higher water pressures differ from those of low head applications. The ultimate goal of this research is to be able to develop a mixture suitable for a high head application.