ABSTRACT
Reinforced concrete marine bridges are susceptible to corrosion. In conventional repairs, a structurally damaged element is often restored with repair patches. Due to the presence of low-level chlorides in the remaining concrete, incipient anodes can develop and lead to the halo effect which is the main reason of short-lived repair. Ultra-high-performance concrete (UHPC) has been promoted as a durable construction material that can provide a barrier to corrosion due to its low permeability, ideally resulting in a durable repair solution with no need for other corrosion control systems. Other material conditions afforded by UHPC such as concrete resistivity, internal moisture availability and oxygen availability will influence the level of galvanic coupling between steel in the dissimilar UHPC repair material and the existing concrete with vestigial low-level chloride concentrations. In this study, the extent of macrocell development between the dissimilar concrete materials was examined to identify possible benefits and challenges of utilizing UHPC asa repair material for reinforced concrete marine bridges.
INTRODUCTION
A major deterioration mechanism of marine concrete structures is the corrosion of reinforcing bars. This mechanism is principally due to steel depassivation by chloride ions (or carbonation of the concrete pore water by carbon dioxide at higher and dryer elevations). In the absence of such aggressive chemical compounds, a passive film of iron oxides on the steel surface resulting from the alkaline concrete pore water protects steel from corrosion1,2. Reinforced concrete in marine environments, especially in marine tidal regions, is susceptible to chloride ingress to the cover depth of the steel reinforcing bars and then subsequent corrosion initiation. Electrochemical reactions continue after corrosion initiation, leading to the accumulation of expansive iron corrosion products that generate tensile stresses in the surrounding concrete of the corroding steel reinforcement. This results in concrete cracking and spalling, which exacerbates the progressive damage, thus affecting the durability of the structure. Other environmental and material factors can affect the rate of steel corrosion including among others, the concrete resistivity, the internal moisture content, concrete porosity, as well as the availability of oxygen3-6.
