Near-Field Microwave Techniques for Detecting Stress-Induced Cracks in Cement-Based Materials

Concrete columns are subjected to minor to medium damage at plastic hinges during an earthquake event. In such a case, it is desirable to determine the residual strength of steel reinforcement that is still covered with cracked concrete. The mapping of surface cracks on the surface of a concrete column may yield useful information for this purpose. Consequently, near-field microwave nondestructive evaluation (NDE) methods are used to detect flexural cracks and evaluate their width, extent, and spatial distribution on columns. This paper presents the viability of using open-ended rectangular waveguide probes for detecting interior and surface cracks in mortar and concrete samples. The results of scanning cylindrical samples possessing simulated interior and surface-breaking cracks using a microwave reflectometer at several microwave frequencies is presented. In addition, the influence of various parameters on crack detection is discussed