Experimental Study On Fatigue Properties Of Basalt Fiber Recycled Concrete Subjected To Freeze-thaw Damage

The scale of roads in China is increasing year by year.Road construction needs to consume a large number of natural sand and stone materials.It can not only solve the problem of resource depletion caused by overexploitation,but also reduce land occupation and environmental pollution,and reduce carbon emissions.In the high latitude and cold area of northern China,the basic facilities such as concrete highways and bridges often encounter the joint action of bending fatigue load and freeze-thaw damage caused by vehicle driving in the course of service.The interaction and coupling between each other accelerates the damage process of concrete and shortens its service life.The mechanical properties,frost resistance and fatigue life after freeze-thaw damage of basalt fiber recycled concrete are studied in this paper,including:(1)The physical properties of coarse and fine aggregate were measured,including the apparent density,packing density,particle gradation,mud content and apparent density,packing density,particle gradation,water absorption,crushing index,mud content of fine aggregate.The slurry content of recycled coarse aggregate is determined by freeze-thaw cycle method,and the basic mix ratio is designed according to the requirements of first class highway.(2)The recycled coarse aggregate was replaced by natural aggregate with the volume of 0,25%,50%,75%,100%,and the basalt fiber with the volume ratio of 0%,0.1%,0.2%,0.3%,respectively.the effect of the recycled coarse aggregate substitution rate and basalt fiber content on the mechanical properties of recycled concrete was studied.The results show that the compressive and flexural strength of recycled concrete decreases with the increase of the replacement rate of recycled coarse aggregate,and increases first and then decreases with the increase of basalt fiber content.The strength loss rate of recycled concrete can be effectively reduced by reasonable fiber content.(3)Taking the replacement rate of recycled aggregate as 25%,the recycled concrete with different basalt fiber content was subjected to rapid freeze-thaw cycles of 0 times,75 times,150 times and 225 times respectively.The effects of freeze-thaw cycles times and basalt fiber content on the morphology,mass and relative dynamic elastic modulus,compressive and flexural strength of recycled concrete were studied.The results show that basalt fiber can effectively improve the frost resistance of recycled concrete and reduce the mechanical loss after freeze-thaw cycle,in which the loss rate of flexural strength after freeze-thaw is higher than that of compressive strength.(4)Fatigue loading tests of basalt fiber recycled concrete after 0,75,150 and 225 rapid freeze-thaw cycles were carried out at stress levels of 0.6,0.7,0.8 to investigate the variation of fatigue life of recycled concrete under different freeze-thaw cycles and stress levels.The results show that the bending fatigue life of basalt fiber recycled concrete is distributed according to two parameters Weibull,which decreases with the increase of freeze-thaw cycle times and stress level,and the effect of stress level on fatigue life is more obvious than that on freeze-thaw damage.At the same time,the fatigue strength corresponding to the fatigue life of 2 million times decreases with the increase of thawing cycle times and reliability,and the decrease of fatigue strength caused by the increase of reliability decreases with the increase of freeze-thaw times.