Ultra-high-performance concrete (UHPC) has been introduced for reinforced concrete structures due to its enhanced mechanical performance, including high compressive strength and tensile capacity. In certain applications, such as closure joints, connections, and concrete repairs, reinforcing steel may be embedded in dissimilar concrete elements partially incorporating UHPC. Superficially, UHPC can be considered to provide enhanced corrosion durability in marine environments due to its low permeability which would mitigate chloride-induced corrosion of rebar in the bulk material. However, the chloride intrusion through cold joints can be faster than that in bulk concrete and may jeopardize the durability of structures. This research examines the possibility of enhanced chloride transport at the cold joint incorporating UHPC. The effectiveness of the bond on chloride penetration at the concrete interface with various levels of moisture availability for the substrate at the time of UHPC repair was examined. To this effect, the substrate concrete was conditioned to different moisture content including 0%, 75%, and 100% relative humidity, and soaked prior to UHPC repair concrete casting. Chloride penetration was accelerated by an impressed current source and assessed by silver nitrate solution sprayed on the cold joint. Moreover, the tensile bond strength between substrate concrete and UHPC was measured using the splitting tensile test.

Ultra high-performance concrete (UHPC) application, to enhance the mechanical strength of axially loaded reinforced concrete bridge substructure elements, was proposed and investigated in an earlier study. The results recommended that depending on the UHPC shell thickness, this method may cause shifting of the critical section to undesired locations, due to over-strengthening of the repaired section, and this should be a design consideration. This paper proposes a new simplified analytical approach to calculate the bending moment capacity of the repaired circular section. This method relies on hand calculations and only requires basic material properties (compressive and tensile strengths). The results from the simplified approach are validated with a well-established numerical sectional analysis method. The proposed approach may be considered simple and more straightforward for professional engineers.