The Research Of Durability Properties Of Deck Paving Concrete Based On The Freeze-thaw Cycle And Chlorine Salt Erosion Coupling Conditions

Due to the advantages of high strength,good stability and high economic benefits,cement concrete has been widely used in the transportation industry,especially in the field of bridge deck pavement in china.However,in order to eliminate the ice surface in the cold area of North China,it is widely accepted that the deicing salt is spread,which results in a great damage to the durability of pavement concrete.Based on the meteorological data statistics and combined with the road salt concentration,we determined the experimental conditions.Three kinds of concrete was prepared,that is SAC,JS and P.O respectively,which was put in the Na Cl solution under four concentration(0,2%,3.5%,5%)then went through fast freeze-thaw test,from which we analysis the concrete damage rule of development under different freeze-thaw conditions.Comparing with flux method and chloride ion diffusion coefficient method,we find out the the correlation and analyze the chloride ion resistance of different concrete further.By means of pore structure test and SEM observation,we analysis the internal damage mechanism of different concrete in salt freezing environment.The experimental results show that:(1)With the increase number of freeze-thaw cycles,the compressive strength and relative dynamic elastic modulus of concrete decreased gradually.Compared with the salt freezing,the mass did not change obviously in waterfreezing.The frost damage of the salt water is faster than that of the water,and the damage is more serious.The damage degree of the salt concentration to the concrete is 3.5%,5%,and 2%,respectively.And the frost resistance of the two kinds of environments are P.O > JS > SAC,this has a close relationship between rubber powder of high performance and silica fume of fine aggregate effect and volcano ash effect.Compared with the water freezing damage,the concrete in the salt frost shows obvious pulp falling off,accompanied with white crystal precipitation.(2)With the increase of age,the electric flux and chloride diffusion coefficient of concrete decrease gradually,linear correlation between them is obtained,and the coefficient is 0.64925.The electric flux and chloride diffusion coefficient of concrete with higher strength are lower,which shows that the strength is high,the internal density is high,and the resistance to chloride ion permeability is better.Both in 28 d and 56 d,the penetration of concrete results were SAC > JS > P.O,which shows that the second hydration effect of silica fume is more advantageous to the improvement of permeability than the physical filling and high adhesion of robber power.Compared with 28 d strength,the strength of P.O increased by 14% in the edge of 56 d,while SAC and JS only increased by 3%~4%,which was related to the different hydration degree in different types of concrete.(3)The effects of pore structure on the performance of concrete are directly affected by silica fume and rubber powder,also silica fume effects different cementitious materials differently.under the same water cement ratio,the development rules of the bubble number,the average bubble radius and the bubble spacing coefficient of different types of concrete are consistent,which does not agree with the gas content and the bubble size distribution.Compared with the compressive strength and durability index of the three kinds of concrete,P.O has obvious advantages,which is directly related to the two hydration effect of silica fume.At the same time,the durability index increases with the decrease of the bubble partition coefficient and the increase of the number of bubbles,and the compressive strength increases with the decrease of the average bubble radius.Through the observation of SEM,it is found that the structure of concrete after freezing and thawing is gradually developed from tight to loose,the SAC structure is the most loose and the P.O is the best.In SAC and JS,the corrosion products of AFt and Fridel salt increased significantly,which was related to the higher content of SO3 and C3 A in the cement base,as a result it made the concrete structure produce more serious erosion damage.