Measurement of chloride ion concentration in concrete structures using terahertz time domain spectroscopy (THz-TDS)

We have employed terahertz time domain spectroscopy (THz-TDS) to investigate the chloride ion (Cl−) concentration in concrete structures. Cement paste and mortar samples with different Cl− concentrations were prepared and their absorption coefficients were measured in the sub-terahertz frequency range. In both cases, the absorption coefficient increases with the increase in Cl− concentration and a good linear relationship between them is observed. Our results demonstrate that the THz-TDS could be a valuable tool to monitor and inspect the Cl− concentration in concrete structures.