Evaluation of the Chloride Diffusion and the Corrosion of Reinforced Concrete with Salt Ponding Test

　　Due to the climate and geographic location, coastal reinforced concrete buildings in Taiwan are attacked by chloride ion and exposed to corrosive environments. When the chloride content on the surface of rebar reaches the limit, the passive film would be destroyed so that the rebar could be corroded. This result would reduce the strength and stiffness of structure and significantly shorten service life of buildings. Therefore, the issue of chloride-induced corrosion becomes important in this age. 　　In this study, chloride ions are accumulated on the surface of rebar and diffuse into the reinforced concrete through salt ponding test. Moreover, parts of cement of the specimens are replaced by slag and fly ash to clarify the influence of the density with different pozzolanic materials. In this study, the value of chloride threshold, which makes rebar start to corrode, is determined by measuring the corrosion current density, and the studied influenced factors are diffusion coefficient, total ingressive chloride amount, chloride binding capacity on density of concrete and corrosion current density on corrosion of rebar. 　　The results show that diffusion coefficients increase with the increase of water-binder ratio. At early age, the diffusion coefficient is decreased effectively by adding slag. On the other hand, adding fly ash makes higher diffusion coefficient because of the lower permeability. Also, it is discovered that the main factor influencing the initial time of corrosion is the density of concrete. The higher density takes more time corroding. The secondary factor is the pH value. The lower pH value makes the rebar corrode faster. 　　From the experimental results, the chloride threshold value is better defined as 0.1μA/cm2 of corrosion current density instead of 0.5μA/cm2. Additionally, it is noted that the chloride threshold value defined by [Cl-]/[OH-] is of accurate range as 1.351~1.807% of binder mass, while the chloride threshold values defined by total chloride content and free chloride content are of wider ranges as 0.604~1.833% and 0.517~1.588% of binder mass.