Development of a short time model for predicting chloride ingress into normal and pozzolanic concrete

One of the major origins of corrosion in concrete reinforcing steel is chloride ion penetration. This process deteriorates concrete structures in many parts of the world. Chloride can penetrate into concrete structures mainly through diffusion and absorption. A good percentage of research work has been carried out on diffusion mechanism and the process even though slow is a well understood one. Conversely, few research work has been reported concerning absorption mechanism of chloride ion penetration in concrete. This is a fairly rapid transport process whose mechanism needs to be understudied. For this study, concrete cube specimens containing 100%OPC, 12%BLA and 12%GSA of mix 1:2:4 were prepared. The workability of the various mixes was obtained through slump and compaction factor tests. The hardened cubes, 150 mm³, were thereafter immersed in sodium chloride (NaCl) solution for the specified durations. Compressive strength, absorption and spray tests were carried out on the designed specimens at 28, 56 and 90 days. Numerical models were developed using data obtained from the various tests to predict the depth of chloride penetration into normal and pozzolanic concrete under the condition used in this study. The developed models indicate that absorption has substantial effect on chloride ingress. The models' outputs further propose that the thickness of concrete cover in structures exposed to chloride attack should be greater than the present recommended values in use. However, thickness of concrete cover has practical limits based on the design and analysis, consequently, partial replacement of cement with pozzolans (Bamboo Leaf Ash and Groundnut Shell Ash) should be adopted.