Enhancing mechanical properties, durability and multifunctionality of concrete structures via using ultra-high performance concrete layer: A review

As a kind of advanced cement-based composites with superior mechanical properties and remarkable durability, ultra-high performance concrete (UHPC) shows great potential in repairing and strengthening concrete structures in the form of layers. Hence, this paper firstly conducts a systematic review on the static/dynamic mechanical properties, interfacial bond performance between UHPC layer and concrete, durability, and multifunctional/eco-friendly properties (e.g. self-sensing, self-heating, self-healing, self-cleaning, and selfliminescence capability) of UHPC layer repaired/strengthened concrete structures. Carbon polymer reinforced plastic bars reinforced UHPC layer significantly enhances the flexural ultimate load and ductility of reinforced concrete (RC) structures, and two-sided layers are economical and reasonable. Roughing interface and epoxy adhesive treatment are conducive to increasing flexural ultimate load and shear resistance of UHPC layerstrengthened RC beams. The failure mode of RC beams under impact load tends to change from shear to flexure by UHPC layer, and the gap less than 10 mm between UHPC layer and RC beam limits crack development in RC beams under single impact load. Strengthening the column-foot zone by using a UHPC jacket with the size higher than the plastic hinge zone improves their seismic performance of RC columns. The increase of NSC substrate strength, surface moisture, the using of water-based epoxy resin agent, and the proper curing can improve the interfacial bond strength between UHPC layer and RC beam. Meanwhile, it is worthwhile to note that UHPC layer is not beneficial for increasing high-temperature spalling resistance of RC structures, but can be used to develop smart and multifunctional infrastructures.