The Effect Of Chloride-ions On Deterioration Of RCC Structures Under Marine Environment

BackgroundPenetration of chloride-ions in cement concrete structures in marine environmental conditions is becoming a serious issue especially when these structures experience dry-wet cycles.Transportation of chloride-ions can cause many problems to the RCC structure,corrosion of steel is regarded as the major problem.Transportation mechanism usually consist of two main mechanism i.e.capillary-suction and diffusion.To better understand the problems,produce in structures regarding the former stated conditions a thorough study is presented based on the already available literature.ObjectivesMain objectives were to determine the depth of convection-zone formed by capillary-suction three types of cement concrete,to present a model by using the second law of Fick to determine the diffusion of chloride-ions in the cement concrete and also by this experiment check the compressive strength of samples using the high percentage of fly ash.Experiment designFour types of samples were prepared ordinary cement concrete,high performance cement concrete and fly ash?FA?cement concrete using 15%and 30%fly ash by weight of cement.Samples were test in sodium chloride?Nacl?solution in dry-wet cyclic immersion conditions.Exposure time was set to 30 and 60 weeks and there types of cyclic arrangements were selected.Chloride-ions profiles were determined by the Rapid-Chloride Test method.FindingsBy the experimental profiles of chloride-ions concentration the depth of convection-zone was found between of 7-13.5mm.Depth of convection-zone has shown the increasing trend when the drying-period was increased and also when the exposure-time was increased.The effects of capillary-absorption on the depth of convection-zone were discussed.By the help of regression analysis of chloride-ions profiles found in the internal part of the cement concrete further than the advection-zone,by the literature and experimental results it is proven that diffusion process is the governing mechanism of chloride-ions transport.With the help of presented model,the results are fitted in MATLAB curve fitting feature by taking the impact of depth of convection-zone into account.Apparent diffusion coefficient of chloride-ions₍?6?was found in curve fitting process then finally,the time dependent chloride-ions coefficient of diffusion D_Cl was obtained by the calculations made upon the tested values of the apparent diffusion coefficient of chloride-ions D_app and the value of time-exponent m.Value of time-exponent“m”was verified by the past researches.The effect Fly ash content in cement concrete was also discussed.Fly ash cement concrete has shown good resistance against penetration of chloride-ions for longer term experiment under dry-wet cycles.