Improved interdigital sensors for structural health monitoring of composite retrofit systems

In this article, an improved sensor performance based on detecting the dielectric variations in composite—concrete interface and linking these variations to bond deterioration is presented. The use of composites in retrofitting concrete structures is becoming a standard technique worldwide. The bond between the composite system and the concrete element surface is essential to ensure achieving the designed performance. However, there is little research on the development of an economic structural health monitoring technique for monitoring bond quality in large structures, such as buildings and bridges. The improved sensing technique utilizes an Interdigital Capacitance Sensor design to increase the signal-to-noise ratio and to detect shallow—depth bond deteriorations. An analytical modeling technique was used to analyze the influence of the different sensor parameters, especially the dependency of the capacitance signals on the sensor geometrical dimensions. Two-dimensional finite element (FE) simulations were also used to assess different related design parameters and to verify the experimental results. A concrete slab retrofitted with composites containing pre-induced air voids to simulate bond deteriorations defects were constructed and inspected in a laboratory setting. Good agreements were found between experimental capacitance signal response parameters and those predicated from the FE simulations of the slab specimen.