Fiber optic sensing of concrete cracking and rebar deformation using several types of cable

Distributed fiber optic sensing (DFOS) is increasingly being applied in civil engineering. One recently emerging type of DFOS, Optical Frequency Domain Reflectometry (OFDR), offers improved accuracy and resolution. This paper presents an experimental study that investigates the ability of OFDR, implemented using several types of fiber optic cable, to detect concrete cracking and large strain steel deformation. More specifically, the experimental investigation involved six reinforced concrete specimens with different types of optical fiber embedded in both the concrete and rebar. OFDR successfully detected continuous rebar deformation and bond stress through the post yielding range, as well as strain localization indicative of concrete cracking. The type of optical fiber is shown to have a substantial influence on the measured strain response after the onset of nonlinear behavior (i.e., cracking and yielding) and into the large deformation regime where measurement survivability becomes an issue. The higher performing fibers reveal unprecedented detail regarding the interaction between concrete and rebar and demonstrate potential for application in RC structures. Based on these findings, the paper gives practical recommendations for cables with different size and structure.