Study On Chloride Ion Transport In Carcked Fly Ash Slag Concrete

Limited by the characteristics of concrete materials,environment and other factors,a large number of concrete structures in service are usually working with cracks.Chloride ion erosion is one of the main causes of steel bar corrosion,which leads to durability failure and seriously shortens the service life of concrete structure.However,due to the diversity of research content and methods,as well as the randomness and complexity of concrete cracks in the test,there is some discreteness in the existing research results.Meanwhile,in order to realize the application of fly ash slag in structural concrete,the chloride ion transport behavior in cracked fly ash slag concrete is studied.The main research contents are as follows:1.A new crack induction method for reinforced concrete specimens was used.Chloride erosion tests were carried out on specimens with different crack widths(0 mm,0.04 mm,0.08 mm,0.12 mm and 0.2 mm)by dry-wet cycle in laboratory.The distribution of chloride ion concentration in different depths around cracks of fly ash slag concrete under different crack widths and different dry-wet cycles was analyzed,and compared with ordinary concrete.The effects of concrete crack width and dry-wet cycle erosion on the distribution and transport of chloride ions in fly ash slag concrete and the corrosion of steel bars were evaluated comprehensively.Research shows that: crack width and erosion time have important effects on the distribution of chloride ion concentration in fly ash slag concrete.With the increase of crack width and erosion time,the chloride ion concentration at the same depth increased.Under most circumstances,the distribution of chloride ion concentration in fly ash slag concrete and ordinary concrete with the same crack width is consistent under the same dry-wet cycle.2.In addition to the study and analysis of chloride ion concentration distribution,the corrosion mechanism of steel reinforcement in cracked concrete was analyzed.Based on this,the corrosion situation and characteristics of steel reinforcement in fly ash slag concrete under different crack widths and different dry-wet cycles were sorted out and analyzed.At the same time,according to the statistics of the distribution of chloride ion concentration in concrete when the reinforcement corrodes and when the reinforcement does not corrode,the recommended range of the critical chloride ion concentration in the powder cinder concrete and ordinary concrete is determined,and the rationality of the recommended value of the critical chloride ion concentration is demonstrated by comparing with the existing research results.3.The diffusion coefficient of chloride ions is one of the best ways to characterize the diffusion of chloride ions in concrete,and the width and characteristics of cracks in concrete are the main factors affecting the diffusion coefficient of chloride ions.Therefore,based on Fick’s second law,the influences of crack width,dry-wet cycle times and concrete type on chloride ion diffusion coefficient were analyzed.The results show that the diffusion coefficient of chloride ions increases obviously with the increase of crack width and dry-wet cycle times.In addition,the chloride ion diffusion coefficient of fly ash slag concrete is generally lower than that of ordinary concrete under the same crack width and dry-wet cycle time,so it is considered that the chloride ion erosion resistance of fly ash slag concrete is slightly better than that of ordinary concrete.4.Four main types of chloride ion diffusion coefficient expressions are compared and verified,including linear expression,quadratic power function expression,cubic power function expression and exponential expression.It is found that the expression of chloride ion diffusion coefficient obtained by quadratic power function form and exponential fitting method generally has a high degree of fitting in this study and has high applicability,which can provide convenience for the research work of chloride ion transport behavior in cracked concrete and the prediction of steel corrosion.