Concrete surface treatment and chloride ions lead to corrosion of steel bars

Waterproof treatment of concrete surface chloride ion erosion tests show that, the waterproof processing can form on the surface of concrete chloride ion good isolation layer, by reducing capillary water absorption effect to prevent chloride ion invasion, significantly reduced the content of chloride ion in concrete. At the same time, the surface treatment of the permeable coating does not affect the internal water loss. When the relative humidity of concrete is reduced to a certain degree, the corrosion rate of the steel bar will obviously decrease.

Also, not in the inhibition of corrosion of reinforcement, according to Stratmann, Fliedmer and Standke research and penetration type silane coating can not only and concrete matrix to produce chemical combination, and reinforced surface can produce some chemical bonding, such as shown in Figure 6.8. If the coating is penetrated to the reinforcing steel surface, its function is to form an oxide layer on the surface, thereby inhibiting the corrosion of the reinforcing steel bar.

De Vries had water cement ratio 0.5 concrete test block a dipping infiltration type waterproof coating. After the the for up to 52 weeks of Yanchi dry wet cycling experiment. The results showed that the infiltration of chloride ions decreased by 20%, and this effect can be maintained for more than 3 years in the outdoor exposure. However, Vries results also found that, for the role of chloride in the corrosion of steel bars have begun to penetrate the waterproof treatment did not significantly inhibit the effect of corrosion.

And Standke Giessler, using a permeable coating system ProtcctosilCLT to the United States, Switzerland, a number of engineering concrete structure are studied by field test, and the reinforcement corrosion detection. The results show that due to water repellent and barrier of chloride ion diffusion and the coating has good inhibition of steel corrosion. Figure 6.9 is a Pennsylvania a garage has been part of the chloride penetration. How dare the current detection results before and after the coating surface protective treatment in 1996. Can be seen, the door after reinforcement corrosion current from the original more than 0.6uA/cm it rapidly declined to negligible of less than 0.1 uA/cm it, and the effect of several years of experience has remained. Figure 3.11 and figure 6.10 are used to deal with the surface treatment technology on a road section of Switzerland and the untreated part of the steel corrosion test results contrast. As can be seen, the concrete reinforcement corrosion current to force untreated smaller figure 6.10 (a), and calculated by the current corrosion weight loss than the untreated small (Figure 6.10 (b). The corrosion potential of figure 6.11 shows that, compared with the active corrosion state of the steel in the untreated concrete, the repeated re passivation of steel bars after silane treatment.

Giessler et al. At the same time, in the high humidity environment, the permeability of the coating on the corrosion of concrete inside the inhibition effect will be more significant, and in the presence of micro cracks can also be faster to maintain an effect.   

Basheer and the half cell potential and corrosion current detection method of 44 weeks Yanchi soaking conditions of rebar in concrete corrosion condition. The results showed that the surface treatment of flat test pieces of the internal steel reinforcement corrosion occurred and untreated trial compared a significant delay. For example, the specimen after surface treatment, the internal reinforcement in Yanchi soaked 20 to 40 weeks will be the beginning of corrosion, and without treatment of the test block in Yanchi soaked 8-12 weeks after began to rust. At the end of the experiment, the specimens were broken and the steel bars were tested for weight loss, and the results were in agreement with the experimental results of the half cell potential and the corrosion current.

Ibrahim, the potential difference is applied to accelerate the time of rebar corrosion and monitoring of concrete cracking, and detection of immersion in chloride salt solution of the reinforced concrete potential and corrosion current density. The results showed that by permeable coating surface treatment of concrete due to reinforcement corrosion cracking hungry time delay, the corrosion degree greatly weakened. Similar results have been obtained from the experimental study of McCarthy et al.

Ren Zhaojun with water to cement ratio of concrete for the 0.6, under dry wet circulation and external environment of chlorine ion, after silane solution inside the concrete reinforcement corrosion penetration were studied. The results as shown in Figure 6.12, from figure 6.12 (a) (b) two half cell potential value can be seen after corrosion of the non steady stage, from the 14 week begin waterproofing OXW specimen potential values tended to be stable, and was significantly lower than that of late potentials continued negative increase without OXN surface waterproofing treatment of specimens. The corrosion current density results shown in Figure 6.12 (c) have similar trends.

After the end of the test, the test pieces cut out to remove the reinforcement to observe, not to water treatment of concrete specimens OXN-0.6 corrosion was significantly greater than the water treatment of concrete specimens OXW-0.6. In addition, the weight loss rate of the corroded reinforcement in the concrete without water treatment is about 3 times of that of the water treatment. This is consistent with the corrosion of steel bars which are reflected by the value of the potential value of the half cell and the corrosion current density of steel bars.

Of rebar in concrete under the condition of dry wet circulation time corrosion to early continued to chloride ion erosion under the condition of corrosion initiation time. Testing continued to chloride ion erosion environment reinforced at about 32 weeks began to appear corrosion (without waterproofing, water cement ratio of 0.6 for the test block). The main reasons are as following: in wet and dry cycles, the intrusion of CL- mainly depends on the capillary absorption of the concrete in direct contact with salt water. The extent of the inward migration of salt depends on the length of the drying and wetting alternation period. Dry and wet alternation of concrete surface not only affects the intrusion of chloride, but also the deeper drying causes the wetting of the future to be more and deeper into chloride. If the concrete surface exposed to chlorine salt solution is not saturated, within a few hours or a few days, chlorine salt solution can is pores inhalation to 5 ~ 15mm depth of concrete. In the experiment, the surface treatment can effectively restrain the corrosion of steel bar under wet and dry cycle. Analysis of the reasons, a waterproofing treatment to in the concrete surface to establish effective chlorine ion isolation layer, in a certain extent hinder the ingress of chloride ion, thereby reducing the reinforcement corrosion caused by chloride ion erosion; on the other hand, waterproof processing in the concrete surface to form a water repellent layer can effectively prevent water entry, concrete pore solution saturation reduce, increase the resistance of the concrete and the electrical conductivity decreases. Therefore, the semi battery resistance value of the non water treatment test piece is obviously negative to the test piece which is larger than the water treatment, the corrosion current density of the reinforcing steel bar is also obviously larger than that of the water treatment.