Concrete surface treatment and reinforcement corrosion caused by carbonation - under the influence of atmospheric conditions

      Carbonation is one of the important environmental factors that lead to corrosion of steel bars in concrete. In front of it has been talked about, concrete carbonation caused by steel corrosion without obvious anode and cathode, steel corrosion is relatively uniform. Carbonation is closely related to the permeability of concrete, and the surface treatment of silane penetration coating will not affect the permeability of concrete.

       The theoretical evaluation of the effect of water treatment is not easy to be carried out because of the complexity of the atmospheric environmental conditions of the outdoor concrete structure. Mattila developed a set of equipment can be automatic, continuous, multi-channel on-site monitoring of steel corrosion in concrete. The results show that the corrosion of steel in concrete can be reduced by about 80% after waterproof treatment. ,

       A series of experiments on the effect of water treatment on the corrosion of reinforcing steel bar by Ren Zhaojun. Test for water treatment, in a flat bottomed vessel into the support the test pieces of small block. The test piece is placed on the block, preparatory treatment of concrete surface is facing down, slowly into the container in a silane solution, until the liquid level higher concrete at the bottom of the 5 + 1mm (see Figure 6.5), the mixed concrete surface immersed in silane solution and maintain 1H capillary absorption. After treatment, the test piece was placed in the test chamber for 1 weeks, so that the water proofing agent and the concrete were fully reacted.

       Concrete with water binder ratio of 0.6 was used in the experiment. Figure 6.6 is the result of the test of the half cell potential and corrosion current of the concrete under atmospheric conditions, which are waterproof and without water treatment.

       As can be seen from figure 6.6, in the 16 weeks before, the two sets of test pieces of the potential value of the battery will be decreased with the time increased. There are two main reasons for this trend; one is due to early detection, concrete rigid from standard curing room out, internal water content is relatively high resistance value is relatively small, electrical conductivity is relatively high. Therefore, the measured the half cell potential negative values to larger, but this can not reflect the at this point the corrosion of rebar in concrete conditions; the second is due to reinforcement embedded in the concrete before the polished, before the exposed to harmful medium erosion and no passive film formation, in the laboratory, along with the age growth, steel bar in the concrete of high alkali environment passivation film gradually consolidate. Therefore, the measured value of the half cell potential decreases with the time increasing, and the corrosion current decreases with the increase of time. Since then, under the conditions of natural drying in the laboratory, the water in the concrete is constantly evaporating into the atmosphere, the resistance value of the concrete increases slowly, and the electrical conductivity value decreases. And 16 weeks later, the relative humidity of the concrete inside and the environment to achieve a balance, at this time, the potential value of the test piece can reflect the corrosion of steel in concrete.

      After 16 weeks of molding, the half cell potential of the two groups had a negative trend with the increase of time. The corrosion current density of reinforcing steel also increases with the increase of time. At the end of the experiment, not waterproof processing test EN-0.6 copper / copper sulfate half cell potential value to -115mV and calomel half cell potential value to -48mV and its absolute value were greater than for waterproofing treatment trial EW-0.5.EN-0.6 corrosion of reinforcement touch current density to achieve 0.08luA/cm it, for waterproofing test EW-0.6.