Grout Acidification of Ribbon Anode in Impressed Current Cathodic Protection Systems in Concrete

摘要

Impressed current cathodic protection (ICCP) technology has been used for the corrosion protection of chloride contaminated reinforced concrete structures in Australia and globally for the past 30 - 40 years.Mixed Metal Oxide (MMO) Coated Titanium ribbon anode mesh has been the most widely used anode for ICCP systems on bridges and wharves. In recent years, there have been many reports in Australia identifying acidification problems associated with ribbon anode installations, with the problem being most evident in tidal/splash zones of the structures. Based on these reports, issues such as the type of grout encapsulating the anodes and grout cover to the anode were commonly reported as the potential contributing causes of acidification problems.It has been reported that the likely primary cause of acidification is ingress of water to the anode surface. Various methods of preventing water ingress have been specified, however no systematic research work has been performed to verify the long-term performance of such methods for minimising, eliminating or preventing acidification problems in ICCP installations.The primary aim of the present research is to verify a methodology for preventing water ingress to the ribbon anode in water exposure conditions and using accelerated testing to confirm that this method can minimise the acidification problem related to water ingress.The experiments simulate the typical problems of low grout cover and cracking which allows water ingress to the ribbon anode. Following the sealing of the cracks in some samples, accelerated cathodic protection was performed for unrepaired and repaired samples. The objective of the test is to assess the mechanism of grout acidification under these conditions and to verify the effectiveness of the method of anode encapsulation.The results of the present research work confirm that the anode embedment methods currently in use by the industry, often combined with sub-par workmanship, allow water ingress to the ribbon anode, and these are the primary causes of acidification. The results also confirm that the application of a cementitious waterproofing coating, which minimises water ingress to the ribbon anode, can limit or stop the occurrence of grout acidification problems in existing ICCP installations.