Rehabilitation of corrosion-damaged reinforced concrete columns using carbon fibre-reinforced polymers (CFRP) wraps

Corrosion of reinforcing steel in concrete structures is a major problem affecting North American infrastructure. The use of de-icing salt causes severe damage to highway bridges and parking facilities. During the past two decades, significant research has been undertaken on the use of Fibre Reinforced Polymers (FRPs) in design, repair, and upgrading of reinforced concrete structures. FRPs have outstanding properties such as high strength and durability, and resistance to electrochemical corrosion. However, the use of FRP wraps and their effectiveness in restoring the integrity of corroded reinforced concrete structures, as well as their impact on the corrosion activity, is still in question.; This thesis focuses on inducing corrosion in the columns using an aggressive environment that simulates natural corrosion and involves two parallel experiments on the use of Carbon Fibre Reinforced Polymer (CFRP) wraps in repair of corrosion-damaged reinforced concrete columns. The main experiment included twelve large-scale circular columns (300mm x 1200mm). Ten columns were cast with 3% NaCl premixed with the mixing water in the outer 75 mm thick ring. The two remaining columns were uncontaminated and used as control specimens. The ten chloride-laden columns were corroded using an aggressive environment created in the laboratory of the Department of Civil Engineering at Queen's University. The experiment incorporated electrochemical chloride extraction (ECE) treatment on four of the columns followed by CFRP wrapping on eight columns. The total duration of the experiment was 44 months from April 1998 to December 2001. The CFRP wraps were proven to reduce the corrosion activity in the column under severe environmental conditions. The strength of the wrapped columns was also very close to that of the control column.; The second experiment involved 52 small-scale reinforced cylinders (150mm x 300mm). The cylinders were corroded using both aggressive environment and impressed current methods for comparison purposes. The introduction of CFRP wraps to the cylinders was made at several stages including a pre-corrosion wrapping to investigate the efficiency of the CFRP wraps when applied on columns with different corrosion levels, a point not studied in the main experiments due to the limited number of columns available. The corrosion rate in cylinders subjected to100 or 200 days of severe exposure dropped significantly directly after wrapping with CFRP sheets. The CFRP wraps were proven to minimize the ingress of chlorides into the concrete compared to unwrapped cylinders.; The research included modelling of the behaviour of FRP-wrapped reinforced concrete columns in axial compression. An incremental technique was used to predict the axial and lateral stresses and strains in the concrete, reinforcing steel, and the FRP wraps. The model was also used to predict the behaviour of wrapped and unwrapped columns with reinforcement corrosion. Finally, the finite element technique was used to model the effect of steel corrosion on circular concrete sections with and without FRP wraps. The model developed was able to predict the behaviour of wrapped and unwrapped columns and the effect of the corrosion on the strength of the columns was accounted for.; The research concluded that the CFRP wraps applied over corrosion-damaged reinforced concrete columns will decrease the corrosion rate of the reinforcement and restore the structural integrity of the column. The application of the wraps will be more effective when applied at earlier stages of the corrosion.