Humectant Use in the Cathodic Protection of Reinforced Concrete

Use of humectants to improve the thermal-sprayed zinc anode performance during the cathodic protection (CP)of reinforced concrete was examined. A humectant is a hygroscopic material. It is applied onto the surface of the zinc anode to keep the concrete-anode interface moist and a good conductor. The thermodynamics of humectants are discussed. Laboratory results are presented on the effects of using lithium bromide (LiBr)and lithium nitrate (LiNO3)as humectants in galvanic cathodic protection (GCP)and impressed current cathodic protection (ICCP)systems, in high and low relative humidities, and on new and previously electrochemically aged CP systems. LiNO3 and LiBr promoted more effective CP performance. Both improved the performance of aged slabs, suggesting that application of humectants onto existing CP systems would be beneficial. Microscopy showed that humectant-treated slabs develop the same cement-reaction zone, zinc anode structures as untreated slabs. Microscopy of LiBr-treated slabs revealed that the highest concentration of bromide was in the reaction zone. In GCP tests, LiBr was more effective than LiNO3. In accelerated ICCP tests, LiNO3 was more effective than LiBr. It was surmised that bromide could be oxidized in the high-voltage, accelerated ICCP tests. At the lower impressed currents of most installed ICCP systems, LiBr may perform as well as or better than LiNO3.