Research On The Durability Of Concrete Under Chloride Salt Freeze-thaw Environment With The Composite Action Of Multiple Measures

With the frequent premature failure of concrete structures due to durability problems,the durability of concrete has received increasing attention from engineers and scholars.To cope with the harsh environmental conditions and to meet the requirements of the increasingly long service life of architectural designs,there have been actual projects where multiple durability measures have been used simultaneously to protect concrete structures from durability problems.The purpose of this paper is to investigate whether the combined use of multiple durability measures can further improve the durability of concrete and the service life of concrete structures,and the following research work has been done for this purpose.The following tests and analyses were conducted on concrete specimens with three durability measures: cementitious capillary crystalline waterproofing(cccw),fiber,and surface coating.Three durability measures were used alone and in combination,in a total of six combinations:(1)the relative dynamic modulus of elasticity and mass loss rate of each group of specimens were tested by 300 times rapid freeze-thaw cycles to study whether the composite use of multiple durability measures can further improve the frost resistance of concrete;(2)To test the chloride ion diffusion coefficient of each group of specimens by the RCM rapid chloride ion migration coefficient test to study whether the composite use of various durability measures can further improve the chloride ion resistance of concrete;(3)Using the RCM method test.to study whether the composite use of various durability measures can further improve the concrete resistance to chlorine ion after suffering 100,200,and 300 times freeze-thaw cycles.(4)The relationship between the number of freeze-thaw cycles in the laboratory rapid freeze-thaw test and the number of freeze-thaw cycles in the actual environment was analyzed,and the relationship between the chloride ion diffusion coefficient and the exposure age of uncoated concrete as well as coated concrete under the consideration of freeze-thaw cycle damage was proposed;(5)The Duracrete concrete structure life prediction model was modified by considering the relationship between the chloride ion diffusion coefficient and the exposure age in the case of freeze-thaw cycle damage,and the effect of the composite use of multiple durability measures on the service life of concrete structures was analyzed.Based on the tests and analysis,the following conclusions were obtained:(1)when the three measures of cccw,fiber and surface coating were used alone,the fiber incorporation had the most obvious effect on improving the frost resistance of concrete,and the surface coating had the most obvious effect on improving the chloride ion resistance of concrete;(2)since the three measures of cccw,fiber and surface coating were not the same and did not interfere with each other in the mechanism of improving the durability of concrete(3)Before freeze-thawing,the further improvement of chloride ion resistance of concrete by surface coating and the other two durability measures is not obvious,but after freeze-thawing cycles,with the increase of the times of freeze-thaw cycles,the further improvement of chloride ion resistance of concrete by surface coating and the other two durability measures becomes more and more obvious.(4)after considering the freeze-thaw damage,the relationship between the chloride ion diffusion coefficient of uncoated concrete and the exposure age can be expressed as an exponential function,and the relationship between the chloride ion diffusion coefficient of coated concrete and the exposure age can be expressed as a segmental function of linear growth before coating cracking and exponential growth after cracking;(5)The synergistic effect is obvious when the cccw and fiber are used together,and the improvement of the service life of the concrete structure is much higher than the sum of the improvement when the two are used alone,while the synergistic effect of the surface coating and the other two durability measures is not obvious,and the improvement of the service life of the concrete structure is about equal to the sum of the improvement when the two are used alone.