| Ultra High Performance Concrete(UHPC), a new kind of cement-based materials with high strength, high ductility, and low porosity developed in recent 20 years, has been recognized as a composite with wide development prospect and application value in the future for its advantages. With the widespread use of UHPC, the research on its repair technology has now been seriously undertaken.The most common method to repair concrete could be generally divided into the following several steps: first roughening the old concrete substrate surface, then coating the treated surface with layers of bonding agent, and finally placing the new repair materials on the saturated-surface-dry substrate before making proper curing.In the process of repairing, the fresh-old concrete bonding interface, subjected to the effects of shrinkage and mechanical loading, tends to be damaged first and presents a weak link in the repaired structure. Therefore, the performance of the bond interface becomes the key to successful repair. The addition of discontinuously scattered steel fiber to UHPC is known to significantly increase the ductility of UHPC.Consequently, in accordance with the high-strength property of fiber-reinforced UHPC, the selection of the proper repair method is of primary importance in maintaining the integrity and performance of steel fibers.This thesis concentrates on the repair technology of UHPC by using high pressure water jet to artificially chisel the UHPC and introducing polymer-modified UHPC as the repair material. The proper repair method and material of UHPC is thus investigated. The main research contents could be concluded as follows:1) By artificially chiseling fiber-reinforced UHPC with high pressure water jet,the appropriate parameters for artificial chiseling are obtained in accordance with the needs for sound repair and the property of the old concrete substrate. The various parameters of high pressure water jet adjusted in our experiments include the working pressure, blade height and aperture, segment walking velocity, and cutting routes and gaps;2) The feasibility of using UHPC with different polymer-cement ratios as repair material is explored. By measuring the flexural and compressive strength of UHPC as well as considering the maneuverability, the optimal polymer-cement ratio is selected.Three modified polymers are chosen in our experiments, styrene-butadiene rubber latex, redispersible latex powder and epoxy emulsion;3) The well-performed polymer modified UHPC is selected as the repair material.After a 72-hour hot curing and 28-day standard curing, the proper repair material and method is determined by measuring the flexural strength of different specimens. The feasible technological process for repairing UHPC is hence formed. |
