Detection of Chlorides in Concrete Using Low Radio Frequencies

Chloride intrusion into reinforced portland cement concrete (PCC) is of special interest to researchers due to chloride's action as a catalyst and accelerator of PCC reinforcing-steel corrosion. The authors conducted experiments to study the effect of chloride contamination of PCC on its complex permittivity over low radio frequencies (RF) range (0.1-40.1 MHz). Quartzite and limestone were the aggregates used to prepare the PCC mixes at a water-to-cement ratio (w/c) of 0.45. Partial immersion in NaCl solution and the addition of NaCl to the PCC mixing water were the two methods used to induce chlorides into PCC. For the NaCl addition to the mixing water, three levels of chloride contents were used. Dielectric measurements were recorded for PCC specimens during the 28-day curing period and continued for 6 months. Powder PCC samples were gathered occasionally to estimate the chloride content in the PCC specimens. Findings indicate that complex permittivity of PCC specimens increased quantitatively as the chloride content increased, until quantitatively 75 percent of the chloride content estimated theoretical saturation volume. Aggregate type and frequency also significantly impacted on the measured dielectric constant.