Experimental study on repairing damaged underwater structures with NUC and steel bar implantation

Non-dispersible underwater concrete (NUC) is increasingly used in new water conservancy projects. However, existing research has not yet established a standardized repair system integrating material optimization, construction technology, and performance evaluation for NUC-based repair of damaged underwater concrete structures, which limits its reliable application in practical repair projects. This study innovatively clarifies the synergistic mechanism of water-cement ratio and steel bar implantation on NUC repair performance, and provides a technical basis for the standardized repair of damaged underwater structures. To address the aforementioned issues, we first analyzed the splitting tensile strength and flowability of NUC with different water-cement ratios (0.4, 0.45, and 0.5) through laboratory experiments. Subsequently, the optimal mix proportion was adopted to repair damaged underwater concrete structures, and the corresponding bonding splitting tensile strength was tested. The results indicated that the water-cement ratio significantly affects the flowability and splitting tensile strength of NUC. When using NUC with a water-cement ratio of 0.45 to repair defective underwater structures, steel bar implantation can effectively improve the coordinated deformation between new and old concrete. Additionally, the water-to-air strength ratios of splitting tensile strength for reinforced and unreinforced specimens were 0.88 and 0.81, respectively. Reinforced concrete mainly exhibited plastic failure during splitting, and numerical simulation results revealed that splitting cracks were concentrated at the position of 4/5 of the anchorage end starting point. Finally, a NUC mix proportion suitable for repairing damaged underwater structures was proposed, which ensures sufficient mortar flowability during construction and meets the design requirements for structural strength.