Study On Deterioration Law And Life Prediction Of Concrete Under Coupling Action Of Freeze-thaw And Sulfate In Northwest China

Since the implementation of the "One Belt And One Road" policy in China,accelerating the speed of infrastructure construction and strengthening the development of the western region has become a new focus of China’s work,which has brought great development opportunities for the western region.The number of new projects such as Bridges,tunnels and water conservancy in this area is increasing rapidly and the scale is becoming increasingly large.However,because the western region is located in the hinterland of the Eurasian continent,affected by the seasonal cold climate,many infrastructure under construction will inevitably be damaged by the freeze and thaw cycle,which leads to a series of durability problems of concrete structures;at the same time,a large number of saline-alkali land and salt lakes are distributed in the western region.The soil and water are rich in sulfate,which will have a corrosive effect on concrete structures such as Bridges and tunnels,and also cause the deterioration and destruction of concrete structures.It can be seen that the concrete structure in western China is in a complex environment,and its damage and deterioration process is the result of the interaction of many factors.Undertaking the durability experiment of concrete under the interaction of freezing-thawing cycles and sulfate attack in western China has major engineering guiding meanings.In this paper,based on the Geku Railway in western China,combined with the real climate of the engineering and the relevant experiment criteria,the durability experiment of concrete under the interaction of two factors is designed,and a variety of experiments were undertaken to consider the influence of one factor on the durability of concrete.The influence of water-binder ratio,fly ash and air-entraining agent on the morphology,mass,compressive strength and dynamic elastic modulus of the material is studied.The main research results are as follows:(1)During the freeze-thaw cycle test,mortar spalling appeared on the surface of the specimen;At the beginning of the test,the mass,compressive strength and dynamic elastic modulus of the early-age concrete was discussed,there is an increasing trend at first,and then a decreasing trend was performed.The smaller the water-binder ratio,the stronger the frost resistance;Fly ash has a negative effect on the frost resistance of early-age concrete.The appropriate amount of air entraining admixture can effectively enhance its cold-resistance characteristics;(2)In the sulfate erosion test,with the increase of the erosion age,the surface of the concrete specimen gradually became loose,and the surface peeling phenomenon appeared;At the initial stage of erosion,the quality of concrete generally increases,while at the later stage,it gradually decreases.Concrete with different water-binder ratios has a period of strength increase.With the continuous formation of erosion products,the expansion effect will occur,leading to the emergence and development of tiny cracks,resulting in the decline of strength.The relative dynamic modulus of elasticity increases rapidly at first and then decreases slowly(3)In the sulfate attack test,a small water-binder ratio means that the resistance of concrete to sulfate attack will be improved.Its compressive strength and dynamic elastic modulus change more gently in the stages of rising and falling with the small water-binder ratio,and the sulfate corrosion resistance is the best when the fly ash content is 20%.(4)In the coupling test,the change trend of its macro indicators is similar to that under a single freeze-thaw cycle,but its deterioration is significantly greater than that of the latter.The larger the water-binder ratio is,the more serious the deterioration is.The incorporation of fly ash is not conducive to the frost resistance of concrete,and the amount of fly ash should not exceed 10% if cost and other factors are considered.Air entraining agent has obvious effect on the durability of concrete,and its salt frost resistance is the best when the amount of air entraining agent is 0.1%.(5)On the basis of principle of damage mechanics,the development model of concrete failure under the action of sulfate attack is put forward,and the failure model under the inaction of freeze-thaw and sulfate attack has also been proposed.Furthermore,the summative damage formulas of concrete under different factors are put forward and the service life of concrete is predicted.