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

   Figure 6.7 is the experimental results of steel corrosion accelerated carbonation and wet and dry cycles. Water cement ratio of 0.4 and 0.6 of concrete was used in the experiment. Accelerated carbonation test was carried out using the standard method of "test method for long term performance and durability of ordinary concrete" (GBJ82-85).

      In the testing process, the laboratory under the condition of the water cement ratio of 0.4, without waterproofing treatment trial EN-0.4 calomel half cell bit less than - 120mV. According to ASTM criterion, the corrosion risk is 10%, the corrosion current measured value is less than 0.1Ua/cm it. According to the correlation between the linear polarization measurements and corrosion condition of reinforcing steel bar, try EN-0.4 reinforced in the detection process in a passive state. And also several accelerated carbonation conditions, especially not the waterproof processing of the test block, half cell potential absolute value and the corrosion current obviously than EN-0.4 for protective layer of reinforced concrete top has completely carbonized and waterproof treatment of the specimen TBW-0.4. Under the condition of dry wet circulation of half cell potential value and the reinforcement corrosion current density value and try EN-0.4 little difference and reinforced in the passive state. Without the solution of silane surface waterproofing treatment, the top of reinforced protection layer complete carbonization of the concrete test piece TBN-0.4, the values of the half cell potential absolute value and the corrosion current density were greater than TRW-0.4 waterproof processing; increase with time, try a TBN-0.4 semi battery bit value negative to increase, corrosion current density also increases, which means that steel bar corrosion trend. During the 20 weeks of dry and wet conditions, the protective layer of reinforced concrete on the top of the concrete has been completely carbonated, and the water cement ratio of 0.6 has not been waterproof treatment time TBN-0.6 copper / copper sulfate half cell potential value reached -104mV. The corrosion current density of steel is more than 0.101Ua/cm - this time, specimen TBN-0.6 in bold may at the beginning corrosion state.

        Due to the carbonation of concrete protective layer alkalinity decreased and may cause shrinkage, and aggregate to cement mortar shrinkage limit may lead to micro cracks produced, so will make the hidden danger of steel corrosion increased. Experimental results show that the corrosion of reinforcing steel in wet dry cycle concrete is more serious than that in general. Dry and wet cycling makes the oxygen and water more easily into the concrete, and promotes the occurrence and development of the corrosion of steel bar.