DETERIORATION AND PREVENTIVE EFFECTS OF FINISHING MATERIALS AGAINST CARBONATION AND CORROSION OF REINFORCING BARS IN CONCRETE BASED ON THIRTY YEAR OUTDOOR EXPOSURE TEST USING MODEL BUILDING

Abstract

　The durability of Reinforced concrete (RC) buildings are basically determined by the presence or absence of steel corrosion. In order to prevent corrosion of steel in concrete, degradation factors such as carbon dioxide (CO₂) and chloride ions need to be prevented from penetrating into concrete. In many RC buildings, finishes are applied to concrete surfaces, which prevent the penetration of degradation factors. While many studies have been reported on the preventive effects of finishing materials based on accelerated testing, little is based on the long-term exposure to the outdoor conditions. In this study, a model building made from concrete block specimens whose surfaces were coated with various finishing materials was constructed for the outdoor exposure test. After 30 years of outdoor exposure, the deterioration of finishes and their carbonation and corrosion inhibition effects were investigated.

　The follow conclusions could be drawn based on this study:

(1) As for the degradation status of finish materials, all finish materials undergo some kind of degradation after a long period of outdoor exposure. In the case of dirt and chalking, rainwater and other influences may improve the judgment of the deterioration status.

(2) As for the carbonation depth, those with multiple layers of finishes, such as multi-layer type, those with low moisture permeability, such as waterproofing materials, and those with thick finishes are more effective in inhibiting carbonation. On the other hand, those with water repellency or air permeability will accelerate the carbonation.

(3) Carbonation rate was less than 0.5 for coating materials, such as No.1, 4, 5, 7, 10, 16, 17, 21 and No.22. Because of the large variation, it was not possible to confirm the change in the carbonation protection effect of the finishing materials over time.

(4) The corrosion depth was smaller in those with multiple layers of finishes, those with low moisture permeability, and those with thick finishes, as well as the carbonation depth.

(5) The corrosion progress of concrete, containing chlorides, is inhibited by the use of finishing materials that inhibit the penetration of oxygen and moisture.

(6) The relationship between the corrosion depth and the carbonation depth is that the carbonation progresses first and then the corrosion progresses.