Materials Performance

NOV 2014

Materials Performance is the world's most widely circulated magazine dedicated to corrosion prevention and control. MP provides information about the latest corrosion control technologies and practical applications for every industry and environment.

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35 NACE INTERNATIONAL: VOL. 53, NO. 11 MATERIALS PERFORMANCE NOVEMBER 2014 Cost Effective Cathodic Protection System for Concrete Structures Computer Modeling To confirm the CP current distribu- tion, computer modeling was performed for the semi-conductive layered MMO tita- nium tape anode and the conventional slotted ribbon mesh anode systems. For the analysis, 300-mm anode spacing and 50,000 Ω-cm c on cret e re si stiv ity were used. The results, shown in Figure 4, indi- cat e that th e semi-c onductive l ayered MMO titanium tape anode system can dis- tribute CP current more uniformly to the rebar than the slotted ribbon mesh anode system. Field Trials Two structures were used for the field t r i a l s . T h e f i r st st r u c tu re i s a p o st - tensioned bridge deck in Denmark, and the second is a reinforced concrete bridge abutment in Australia. Bridge in Denmark The Danish bridge is located ~100 m above seawater and is frequently exposed to strong winds. The deck surface is dry most of the time. In addition, the deck structure contains a large amount of steel components, and most trial CP systems could not provide adequate protection due to their high anode circuit resistance and high CP current requirement. The trial system was installed in an area 2-m wide by 17-m long. After the deck soffit was prepared with a high-pressure water jet, 20-mm w i d e MMO tit anium t ap e anodes were installed at 400 mm spacing (Figures 5[a] and [b]). The anode and con- ductor tapes were installed on a layer of silicone adhesive, which acts as a dielectric shield and eliminates current discharge from the bare titanium face of the anode. After the tape anode system was installed, a 5-mm thick semi-conductive layer of m o r t a r w a s a p p l i e d by h a n d t r o w e l . Unfortunately, shrinkage cracks occurred in the semi-conductive layer in a short period of time. However, the CP current distribution from the uniformly spaced tape anodes was not expected to be influ- enced by the cracks. Therefore, the system was energized for testing. FIGURE 6 (a) The anode setup for the trial in Australia. (b) MMO titanium tape anode installation. (a) (a) (b) (b) FIGURE 5 (a) Anode layout on the deck sofft in Denmark. (b) Installed MMO titanium tape anodes. Bridge in Australia T h e A u s t r a l i a n t r i a l s y s t e m w a s installed on a 5-m long by 1-m wide test area of a road bridge abutment. The loca- tion is in the atmospheric zone above the high water mark and splash zones. The trial system was designed to determine the effectiveness and CP current distribution at 200 mm and 400 mm anode spacing (Figures 6[a] and [b]). Four reference elec- trodes were installed at locations designed to provide test data closest to and furthest

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