STUDY ON DURABILITY EVALUATION OF RC BUILDINGS CONSIDERING PROGRESS OF REBAR CORROSION AFTER CARBONATION (PART 1): EXPERIMENTAL RESULTS OF SPECIMENS WITH DIFFERENT CONCRETE COVER THICKNESS USING BLAST FURNACE SLAG CEMENT TYPE B

<p> In recent years, many reinforced concrete buildings have passed 50 years after construction, and it is necessary to determine whether to continue using them or dismantle them in the future. The durability of reinforced concrete buildings is evaluated by the depth of carbonation of concrete, which is a factor that causes rebar corrosion, from design to maintenance. However, in indoor members to which water is not supplied, there is a survey result that even if carbonation of concrete progresses, rebar corrosion does not progress. The purpose of this study is to propose a new durability evaluation method for reinforced concrete buildings considering the progress of rebar corrosion after carbonation of concrete. In this report, the carbonated concrete specimens with different concrete cover thickness of 10 to 30 mm ware exposed to several different humidity environments for 2 to 3.5 years and measured rebar corrosion rate after carbonation electrochemically. From the experimental results, the relationship between the water content of concrete and the corrosion rate of rebar was examined. In addition, the calculation results of the prediction of durability of reinforced concrete structures considering the progress of rebar corrosion after carbonation ware shown. The results obtained in this study are summarized below.</p><p> 1. The water content of concrete was indicated by the degree of saturation of concrete, and the relationship between the saturation of concrete and rebar corrosion rate was discussed.</p><p> 2. The rebar corrosion rate after carbonation was measured electrochemically.</p><p> 3. When the concrete cover thickness is 10 mm, if the saturation of concrete is lower than 50%, it is evaluated as equivalent to the rebar corrosion rate after carbonation of the passive state. If it is higher than 50%, the rebar corrosion rate become high. When it is just 50%, the corrosion rate of rebar after carbonation become the maximum. It is considered that the content of water and oxygen in the pores of the concrete at the position of the rebar has an effect.</p><p> 4. When the concrete cover thickness is 20 or 30 mm, the corrosion rate of the rebar after carbonation tends to increase as the water content of the concrete increased, but it is determined that the corrosion rate is generally low.</p><p> 5. Based on the results of this experiment, the lifetime of reinforced concrete structures due to the progress of rebar corrosion after carbonation was calculated. When the saturation of concrete exceeds 50%, it is about 9 to 22 years. When the saturation of concrete is less than 50%, it is about 120 to 190 years.</p><p> 6. The lifetime was calculated considering both the progress of concrete carbonation and rebar corrosion. As a result, regardless of the exposure environment, when the concrete cover thickness is 10 mm, it is over 90 years and when the concrete cover thickness is 20 mm and 30mm, it is over 200 years.</p><p> 7. The reasonable durability evaluation method for reinforced concrete buildings considering both the progress of concrete carbonation and rebar corrosion in the exposed environment was presented.</p>