Corrosion of steel in reinforced concrete structures is a multi-billion-dollar problem worldwide. While the corrosion of steel is rarely responsible for major structural problems, the serviceability of the structure will be significantly affected by reinforcement corrosion with time. The problem of steel corrosion in Canada is very prominent in parking garages and highway bridges where snow contaminated with de-icing salt is frequently splashed during winter and spring months.
Environmental conditions play a vital role in the formation of corrosion cells in reinforced concrete elements. Moisture, oxygen, and. chlorides must be found in the concrete at the steel level to cause the corrosion of the steel. Only a certain mixture of these elements will ensure the continuation of corrosion activity. Submerged or very dry concrete will not corrode due to oxygen and moisture starvation, respectively. Also, the absence of chloride ions will allow the formation of a dense protective oxide film around the steel bar and prevent further corrosion. In bridge columns, the ideal mixture of these influential elements is usually found around the middle third of the column height on the side of the column facing the oncoming traffic; it is this zone that is splashed the most with contaminated snow.
The typical retrofitting technique used to preserve deteriorated columns is surface patching. This procedure includes the removal of the cracked concrete cover, cleaning of the corroded steel and, in some situations, epoxy coating of the cleaned rebar. Low-shrinkage mortar or concrete is then used to patch the repaired area. This technique, while inexpensive and well practiced, does not prevent future corrosion from taking place. Macro-cell corrosion and formation of an incipient anode after patching are very common problems that lead to further corrosion deterioration in a few years. Therefore, a long-term treatment must prevent the aggressive chlorides from penetrating the concrete. Also, sealing the concrete from moisture or air ingress will successfully minimize the corrosion activity by suffocating the cathodic part of the corrosion cell.
Wrapping reinforced concrete columns with fibre reinforced polymer (FRP) sheets, especially those containing carbon fibres (CFRP), has been praised by several researchers in the last few years. The wrapping methodology using FRP sheets has mainly been used as a seismic retrofitting and upgrading technique. FRPs are expected to have a significant impact on the concrete industry mainly for their high strength/weight ratio and non-metallic nature. When compared to other methods of retrofitting, such as steel or concrete jacketing, applying FRP wraps on concrete columns is a fast and simple procedure, with less labour and time needed to apply the wraps. In highway bridge columns, this means fewer traffic disruption |
