Study On The Durability And Deterioration Of Concrete Under Salt Freezing Environment

In order to alleviate the inconvenience caused by snow and ice,deicing salt is widely applied in roads and bridges to reduce the freezing point of snow and ice for melting.However,salt solution and freezing-thawing cycles can cause freezing-thawing damage and erosion on concrete infrastructure such as roads,and can also contaminate soil,vegetation and groundwater.Different deicing salts have different impacts on environment and concrete.In order to reduce the influence caused by deicing salts on concrete roads and bridges,it is of great significance to study on the durability and change law of concrete under the different salt-freezing conditions.In this thesis,freezing-thawing cycle tests of concrete in different solutions?pure water,5%NaCl,5%CaCl₂ and 5%CH₃COOK?were conducted to study the relation between various factors,including conrete strength,solutions and cycling times,and freezing-resistance durability of concrete.The Multiscalevoxel-450 industrial CT was used to analyze the changes of internal pore of C30 grade concrete in different salt-freezing environments,and the impacts caused by different salt-freezing environments on the damage and deterioration of concrete was discussed.Drawing the following conclusions:?1?Under freeze-thaw cycles of water and salt solution,peeling erosion constantly appears on the concrete surfaces.With the increase of freeze-thaw cycles,mass loss increases,while the relative dynamic elastic modulus and compressive strength decrease gradually.Generally,the frost resistance of concrete with lower water-cement ratio and higher strength is better than that of concrete with higher water-cement ratio and lower strength.?2?According to the comparison of the four solutions,it can be found that the freeze-thaw damage of concrete is most serious in NaCl solution.The damage level caused by CH₃COOK solution on concrete is similar to that of pure water.The result of comparison of frost resistance in different freeze-thawing solutions shows:CH₃COOK?pure water>CaCl₂>NaCl?">"means superior?.?3?Industrial CT was used to analyze the internal pore of C30 grade concrete after 50freezing-thawing cycles under different freezing-thawing environments.From comparison,it is found that the increase of porosity under various solution environments shows:NaCl>CaCl₂>CH₃COOK>pure water.In the first 25 freeze-thaw cycles,the growth of internal pores in C30 grade concrete for the all four solutions is dominated by the pore whose volume is less than 0.1mm³.After 50 freeze-thaw cycles,the deterioration of concrete in water environment is similar to the result in 25 freeze-thaw cycles,while the proportion of pore volume?<0.1mm³?in concrete under the freezing-thawing of NaCl solution and CH₃COOK solution begins to decrease,and the proportion of pore volume?0.1-0.5mm³?gradually increases,which shows a trend of pore evolution.The deterioration of concrete in CaCl₂ solution mainly occurs in pores with the size of 0.1-0.5mm³ and 0.5-1mm³,and the future development will be mainly in the growth of small and medium pores.