A survey on the macro-cell corrosion in structures and a study on its mechanism

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To clarify the influence of the macro-cell corrosion in structures, investigations on (1) conditions of damaged structures, (2) macro-cell in underground structures, and (3) macro-cell in RC structures, were done.For item (1), the damages in steel structures at port, RC structures and composite structures were surveyed. Also, the possibility of severe macro-cell corrosion in massive RC structures and composite structures were shown.For item (2), experiments about the macro-cell in long underground structures were done. Comparing the influence of macro-cell and that of micro-cell, there was almost no possibility of severe macro-cell in the axial direction of structures.For item (3), the influences of cracks, joints, repair methods and admixtures for concrete were experimentally studied. The results show, (1) Without crack, blast furnace slag powder and silicafume powder were effective against corrosion, however, with cracks, the effects reduced especially with axially directed crack, also the areas of reinforcement exposed to cracks tended to be anodes. (2) Joints and cracks caused macro-cell corrosion and the areas of reinforcement exposed to them were usually to be anodic, however, sometimes they can be cathodic. (3) The repaired areas tended to be cathodic and the joints between repaired and unrepaired part could be anodes and the corrosion rate could be very fast.