An Experimental Study On The Coupling Effect Of Freeze-thaw And Chloride Ion Erosion In Concrete

The problem of premature structural failure due to insufficient durability has brought huge economic losses and waste of resources.Therefore,while focusing on improving the bearing capacity of concrete,it is of great significance to study the deterioration mechanism of concrete to the implementation of sustainable development concept.The coupling effect of freezing and thawing and chloride ion erosion in high latitude offshore environment will accelerate the deterioration of concrete structure,and studies have shown that the chloride ion content in the fast chloride salt freeze-thaw test is significantly increased.In this paper,the mechanism of some unexplained phenomena in the rapid chloride salt freeze-thaw cycles experiment is speculated,and a test is designed to analyze and verify the chloride ion transport mode in concrete during the freeze-thaw cycle.Before conducting the experimental research,the limitations and shortcomings of the current theory to explain the phenomenon that chloride ion erosion was discovered in the rapid chloride salt freeze-thaw cycles experiment were analyzed based on the previous experimental research results.Therefore,according to the quantitative change and phase transformation of concrete pore solution during freeze-thaw cycle,this paper attempts to propose a hypothesis of rapid erosion of chloride ions with phase change of pore solution.In order to verify the hypothesis,a new test method was designed: the salt freezing process was split,that is,the freeze-thaw cycle process of concrete in chloride ion solution and the external chloride salt diffusion erosion were separated alternately,so that to the extent,the chloride ions eroding with phase transition of pore solution are distinguished from the chloride ions eroding by diffusion.And then the control variable method is used to qualitatively and quantitatively analyze the migration mode of chloride ions by setting the control group.Based on the distribution of chloride ion content with intrusion depth,the influence of freeze-thaw damage on the adsorption capacity of concrete for chloride ions and the significance of chloride ion transport rate were analyzed.At the same time,the effects of the curing time of the fly ash concrete on its antifreeze performance and resistance to chloride ion erosion were confirmed.Then according to the chloride ion diffusion coefficient of the concrete test block under different freezing and thawing cycles,the growth function of the chloride ion diffusion coefficient with the number of freeze-thaw cycles is constructed based on Fick's second law.So that chloride ion diffusion concentration for a given number of freeze-thaw cycles can be calculated by solving the partial differential equation,which can used to correct the effect of the number of freezethaw cycles on the diffusion rate of chloride ions.By comparing and analyzing the distribution law of chloride ion content in each group of concrete test blocks,it is confirmed that there is indeed a phenomenon that chloride ions collide rapidly with the freeze-thaw phase transition of pore solution,which occurs from the surface to the interior with the increase of internal water saturation of concrete.