Corrosion-Induced Deterioration Assessment at Steel-Concrete Interface based on Hoop Strains Measured with Distributed Fiber Optic Sensors

In this study, distributed fiber optic sensors are applied to measure the hoop strain at the interface of a reinforcing bar and its surrounding concrete due to the expansion of steel corrosion products. The measured strain distributions are used to assess the deterioration condition of the steel concrete interface. An optical fiber was spirally winded on a steel bar with a 10-mm spacing. The steel bar was embedded in a concrete beam measuring 140 mm × 70 mm × 70 mm. After cured in lime-saturated water for 28 days, the reinforced concrete beam was immersed in 3.5 wt.% NaCl solution for accelerated corrosion under a current density of 500 μA/cm2. While the steel mass loss was determined from the current density based on the Faraday s law, the hoop strain due to the expansion of corrosion products was simultaneously measured from the distributed fiber optic sensor. The time history of the hoop strain shows three stages. In Stage 1, steel corrosion initiated and generated limited corrosion products that filled surrounding pores in the concrete, resulting in very small hoop strains. In Stage 2, corrosion products encapsulated the bar surface and increased the hoop strain. In Stage 3, concrete cracks appeared due to excessive expansion of the corrosion products, and more oxygen and electrolyte were provided for severe corrosion with a dramatic increase of the hoop strains. The measured hoop strains are used to monitor the corrosion condition of steel bars embedded in the concrete.