Distributed Fibre Optic Strain Sensing to Monitor Deterioration in Reinforced Concrete
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Structural health monitoring (SHM) is an increasingly useful tool for life cycle management of deteriorating infrastructure. Rayleigh backscatter distributed fibre optic strain sensing (FOS) is a promising measurement technology that can provide relevant quantitative data across an entire structure as opposed to the single point data acquisition of conventional strain sensors. Utilizing this FOS technology, an experimental investigation to measure and better understand the effects of deterioration on reinforced concrete behaviour was undertaken. Reinforced concrete tension specimens were instrumented with optical fibres and tested in axial tension to determine if FOS is capable of measuring the effects of tension stiffening and to develop insights into the bond performance of reinforced concrete. It was found that FOS could be used to measure the distributed reinforcement strain, especially before cracking occurs, and these results illustrate how the bond deteriorates with increasing load. In addition, FOS can detect crack locations as well as when cracks develop on only one side of the specimen. The FOS technology was utilized to detect and quantify corrosion levels of the reinforcing steel and to determine how corrosion affects bond performance. An impressed current accelerated corrosion technique was used to corrode additional reinforced concrete tension specimens. Test results showed that reinforced concrete specimens that were corroded to 13% mass loss had a decrease in ultimate capacity of over 30%. This was due to pitting corrosion of the reinforcement that the FOS was able to detect. Additionally, the FOS results showed that as the corrosion levels increase, the bond performance continues to deteriorate. To explore the usefulness of FOS in assessing deteriorated reinforced concrete structures, beams instrumented with optical fibres had the bottom flexural reinforcement corroded and were tested in three point bending. The FOS system was capable of detecting both flexural and shear cracks in the concrete, early signs of corrosion, and bond loss. Test results also showed that just 4.0% mass loss of the bottom reinforcing steel due to corrosion can decrease the ultimate capacity of the beam by 39% due to section loss and debonding of the reinforcing steel.