Influence Of Carbonation On Frost-Resistant Durability Of Concrete

This study was based on the characteristics of the service area of the concrete in the natural environment in Beijing, that the deterioration of concrete structures in Beijing mainly experienced carbide and freeze-thaw cycles. Concrete structures are generally poured in the spring or summer, experienced carbonation in the spring and summer and freeze-thaw cycles in the winter. The freeze-thaw cycles was performed after the carbonation in experiments. In the winter, deicing salt was used to reduce the impact of snow on the road safety, and part of theconcrete facility experiencedthe freeze-thaw cycles under the saline condition.The paper studied four types of concrete, which are the ordinary concrete, the concrete mixed with fly ash, the air entrained concrete and the concrete mixed with fly ash and air-entraining agent, the data of macroeconomic indicators and microscopic parameters were measured after multiple concrete deterioration, the impact of carbonation on the performance of concrete frost was comparatively analyzed. The research showed that the carbonation can slow the damage rate of freeze-thaw cycles on concrete and improve the frost resistance durability of concrete. The durability prediction model was established based on the damage coefficient, the water-cement ratio, the fly ash content, the gas content, the time of carbonation, the condition and time of the freeze-thaw cycles.Through this research data validation, it was showed that the model was applicable to the prediction of the dynamic elastic modulus in which the concrete was carbonatedand experienced freeze-thaw cycles again. Through predicting the microscopic structure inside the concrete, adding fly ash will make the pore size less than 8nm increase and the pore sizewithin 275nm~2000nmslightly decrease; adding air-entraining agent will make the pore sizewithin 275nm~2000nmincrease by a great margin and other pore size change little. After carbonation, the pore sizewithin 8~40nmincreased by a greater margin and the pore sizewithin 40~80nmdecreased by a greater margin. In the condition with the same time of freeze-thaw cycles, the pore size inside the carbonated concrete changed little.Usinthe grey relation theory to analysis the internal microscopic parameters of co ncrete and the correlation of change trend of concrete dynamic elastic modulus, we ca n reach that the tendency of fractal dimension, median pore diameter(area) and porosi ty is most close to the tendency of the dynamic elasticity modulus. With fractal dimen sion, the median pore diameter(area) and porosity and dynamic elastic modulus, the c alculation model is established. Through this measured data validation, the model app lies to estimation the dynamic elasticity modulus of concrete specimen through micro scopic parameter.This study has a certain guiding significance to evaluate the durability of concrete in the field of transportation infrastructure. This study has a certain theoretical valu e in predicting the dynamic elastic modulus of concrete through microscopic structure...