Early detection of fracture initiation in concrete using distributed fiber optics strain sensing

Detecting microscopic tensile fracture prior to fracture development can allow engineers to take proper remedial work. This study investigates the effectiveness of using Distributed Fiber Optic Strain (DFOS) sensing technique for detecting potential tensile failure in concrete. In the laboratory-scale test, a continuous fiber optic cable was embedded in multiple layers along a 2 m long concrete beam. Flexural testing of the beam was performed with incremental loading to artificially induce gradual fracture propagation. Particle Image Velocimetry (PIV) was implemented using a series of high-resolution photographs to capture the microscopic strain development on the beam surface. The strain profiles obtained by DFOS sensing were compared with the fracture propagation reveled by PIV. The test results show that DFOS sensing captures initial microscopic strain development (invisible to the naked eye) presented by PIV. From the peak strain profile obtained by DFOS sensing, the y-intercepts can be correlated to the change in location of the neutral axis during fracture development in the beam. The deviation of the y-intercept from the linearly increasing trend occurred after microscopic fracture initiation can be considered as an early signature of potential tensile failure of concrete. In conclusion, DFOS sensing can be a proper monitoring technique for early warning detection of fracture in concrete structures.