Using Salt Ponding Test to Evaluate the Chloride Threshold Level in Reinforced Concrete

Reinforced concrete material has been generally used in our daily construction, but corrosion of the steel rebars may decrease the strength and increase the risk of collapse. Taiwan is surrounded by the ocean, the chloride ion would invade reinforced concrete structures by the sea wind. The steel rebar will depassivate and start to corrode when the accumulation of the chloride ion exceeds a critical value. Therefore, understanding the resistance of reinforced concrete from chloride ion intrusion is an important issue. In this study, the specimens are divided into three groups by different water-cement ratio ( 0.45,0.55 and 0.65 ). There are five substitution ratio of pozzolanic material for cement in each group. Salt ponding test is used to prompt the chlorine ion to invade reinforced concrete specimens. Corrosion current density measured by Gecor 8 corrosion current instrument is taken to be the norm of corrosion. The chloride ion content is gauged by acid-soluble method after the end of salt ponding test. The distribution of chloride ion in concrete is simulated by Fick''s Law. Experimental results show that the diffusion coefficient will decrease with the increasing of concrete density. The chloride threshold value increase with the increasing of water-cement ratio. The observation of the surface of steel rebars also points out the specimens with higher water-cement ratio are provided with higher chlorine ion concentration under the same corrosion area.