Monitoring the Corrosion in Columns using Fibre Optic Sensors-Preliminary Investigation

Fibre-Optic Sensors (FOSs) are being introduced for structural-health monitoring (SHM) of bridges and other structures as an attractive alternative to conventional sensors such as electrical strain gauges and vibrating wires. Advantages of the FOS, from a materials point of view, include resilience and durability. The objective of this study was to examine the feasibility of using Osmos fibre optic sensors (FOS) to record the lateral expansion due to corrosion damage in reinforced concrete (RC) columns. Four columns were tested. The columns were 200mm in diameter by 900 mm long. Each column was reinforced longitudinally with 4 15M rebars and 10M stirrups were provided at 200mm o/c. The columns were instrumented with mechanical collars and FOS sensors mounted around the circumference at mid height of the column. The longitudinal rebars in the columns were corroded to 5%, 10% and 15% mass loss using accelerated corrosion technique. During corrosion exposure, the lateral expansion due to corrosion and crack widths were monitored. The readings of the FOS and crack widths showed good correlation. The lateral expansion reached a maximum of 1.1%. Following corrosion exposure, the columns were tested axially to determine the effect of the corrosion on the column’s axial capacity. The reduction in the axial capacity of the column due to corrosion was 28% with a theoretical mass loss of 15%. Introduction Fibre-Optic Sensors (FOSs) are being introduced to various structural engineering applications (bridges and other structures) as an alternative to conventional sensors such as electrical strain gauges and vibrating wires. Fibre-Optic Sensors (FOSs) have been used in civil engineering applications to monitor the structural behaviour on site. Some of these projects include; Esplanade Riel pedestrian bridge and Main Street Bridge in Winnipeg, Manitoba, Canada, and the Portage Creek Bridge in Victoria, British Columbia, Canada (Kim et al. (2010)). Corrosion of steel rebars in concrete reduces their cross sectional area and produces rust that occupies a volume larger than the volume of the steel. As a result, the concrete section cracks. Reinforced concrete columns and piers are subjected to high compressive loads that are resisted by the un-cracked concrete cross section and the full cross section of the reinforcing steel rebar. Therefore, concrete cracking and the reduction in the cross section of the steel rebar caused by corrosion is detrimental to the reinforced concrete columns. Some researchers tried measuring the lateral expansion due to corrosion and correlating it with the mass loss values (Lee et al. (2000) and El Maaddawy et al. (2006)). Most of the previous work focused on restoring the column’s performance using carbon fibre wraps (Lee et al. (2000), Debaiky et al. (2006), Aquino and Hawkins (2007) and El Maaddawy (2008) and Bae and Belarbi (2009)). More experimental work is required using different concrete cover thicknesses and bar diameters to correlate the lateral expansion due to corrosion with the mass loss values. In addition, analysis was proposed to predict the capacity of the corroded unstrengthened and strengthened columns based on some experiments, but more data is required to refine the analysis (Tapan and Aboutaha (2011) and Bae and Belarbi (2009)). The experimental work reported here is a preliminary phase of a larger experimental study that aims to investigate the feasibility of using FOS to measure the expansion due to corrosion in reinforced concrete columns. In addition, the reduced axial capacity of a corroded column is determined experimentally and verified using equations available in the literature.