Detection of chlorides in concrete using low radio frequencies

An experimental program was conducted to study the effect of chloride contamination of portland cement concrete (PCC) on its complex permittivity over low radio frequencies (RF) range (0.1-40.1 MHz). Two types of aggregate (quartzite and limestone) were used to prepare the PCC mixes at a water to cement ratio (w/c) of 0.45. Two methods were used to induce chlorides into PCC: partial immersion in NaCl solution (6% by weight) and the addition of NaCl to the PCC mixing water. For the NaCl addition to the mixing water, three levels of chloride content were used. Dielectric measurements were taken for PCC specimens during the 28-day curing period and continued for six months. Powder PCC samples were collected periodically to estimate the chloride content in the PCC specimens. Results showed that complex permittivity of PCC specimens (immersed in NaCl solution) quantitatively increased as the chloride content increased, until quantitatively 75% of the chloride content estimated theoretical saturation volume. Aggregate type and frequency also show a significant effect on the measured dielectric constant.