Study On Damage Of Recycled Concrete Under Freeze-Thaw And Sulfate

China's ore resources can only be mined for another 50 years.At the same time,due to the demolition of a large number of old buildings,a large amount of construction waste is generated.Therefore,the recycling of concrete has become the primary issue of green sustainable development of buildings,and recycled concrete has emerged at the historic moment.In order to provide theoretical support for the popularization and application of recycled concrete,extensive research is needed on the durability of recycled concrete.China has a wide area and sulfate is widely distributed.In the sulfate environment and cold areas,the concrete structure will be affected by sulfate and freeze-thaw cycles.The degradation mechanism is more complicated.The recycled concrete is under the coupling of sulfate and freeze-thaw.The durability research is particularly important.In this paper,the recycled concrete with different replacement rates is used to prepare recycled concrete.The changes of apparent morphology,quality,dynamic elastic modulus and compressive strength of recycled concrete with different recycled aggregate content are studied.The Weibull two-factor probability model is used.The damage equation of recycled concrete was established,and the equation was used to predict the service life of recycled concrete.The following conclusions are obtained:(1)Because recycled aggregate has more initial cracks and is susceptible to freeze-thaw and sulfate erosion,as the number of recycled aggregate increases,the freezing resistance of recycled concrete in sulfate solution gradually weakens.(2)Predict the life of recycled concrete according to the fitting equation.It is found that the life of recycled concrete decreases rapidly with the increase of recycled aggregate content.The life of concrete with content of 100%recycled coarse aggregate is 31%of concrete content of 30%recycled coarse aggregate.Therefore,for structures with high durability and life requirements,the amount of recycled aggregates should be limited,and the recommended amount is not more than 30%.(3)After the same number of freeze-thaw cycles,the concrete of high amount recycle aggregate generated more ettringite and gypsum crystals,and the amount of calcium hydroxide decreases faster.Sulfate erosion intensifies,and the antifreeze performance accelerates.