Microwave detection of carbonation in mortar using dielectric property characterization

Microwave materials characterization techniques based upon dielectric property measurements are well-suited for detection and evaluation of physical and chemical changes in cement-based materials. In this investigation, microwave dielectric properties of several mortar samples were measured at S-band (2.6-3.95 GHz) and X-band (8.2-12.4 GHz) at two different times nearly one year apart. It was found that during this period, while the samples remained in ambient environment conditions, their masses remained essentially constant over time. However their dielectric properties underwent a relatively substantial change. To investigate the reason(s) behind this phenomenon, both pH indicator test and thermogravimetric analysis were conducted and the results confirmed carbonation in the samples. In this paper, the results of these investigations are presented. Additionally, a first-order dielectric mixing model capable of carbonation depth estimation is described.