Proprietary and carbon fiber modified overlays in the cathodic protection of reinforced concrete

Steel reinforcement corrosion in chloride contaminated concrete is a costly problem that can be mitigated by cathodic protection. A variety of anode systems are currently available for the cathodic protection of reinforced concrete. One of the most affective anode systems is made of a noble metal oxide coated titanium mesh. The titanium mesh is first mechanically fastened on the concrete and subsequently encapsulated with a shotcrete or concrete overlay. This system is performing extremely well on horizontal surfaces. However, delamination of the encapsulating shotcrete overlay has occasionally been observed on vertical surfaces such as piers, columns, and walls. The present research project was initiated to address this problem The performance of three different cementitious overlays (two proprietary and and one designed in-house) were investigated under impressed current over a period of 31 months. Samples were polarized outdoors or indoors under constant relative humidity. Numerous performance parameters were monitored on the samples that were energized at three different current densities. The worst performance was obtained with the Thorotop HCR overlay for which high circuit resistance and appreciable increases in the driving voltage were observed. The best overlay for cathodic protection was designed to have maximum adhesion using silica fume and miniumum resistivity by the addition of carbon fibres.