Study On The Resistance To Chlorine Salt-freeze-thaw Performance Of Recycled Coarse Aggregate Concrete

In recent years,the resource utilization of construction waste has attracted much attention.On the one hand,it can reduce the use of natural stones,and on the other hand,it solves many environmental problems caused by construction waste stacking,and achieves the purpose of energy saving and emission reduction.However,the durability of recycled concrete caused by defects such as high water absorption and poor robustness of recycled coarse aggregate hinders its application in actual engineering structures.In northern China,concrete structures will face the combined effects of chloride erosion and freeze-thaw damage.Therefore,it is necessary to study the performance of recycled concrete under the effect of chloride erosion and freeze-thaw damage,and explore measures to improve the durability of recycled concrete.In this paper,the influence of microwave heating modification enhancement technology on the performance of recycled coarse aggregates is studied through experiments,and the influence of modified recycled coarse aggregate,fly ash content and fineness on the compressive strength of recycled concrete is discussed.The surface salt freezing method simulates the coupling effect of chloride salt and freeze-thaw,compares and analyzes the appearance,mass loss,relative dynamic elastic modulus and compressive strength loss rate of recycled concrete after salt freezing.The chloride ion content of recycled concrete at different erosion depths after salt freezing was studied,and analyzed the influence of chloride salt concentration in the freezing and thawing environment on the durability of recycled concrete.With the help of scanning electron microscope and XRD analysis technology,the salt freezing of recycled concrete was analyzed microscopically after the change of the microscopic morphology and hydration products.The research results show that:(1)10 times of microwave heating-water cooling cycle under microwave power(960W)can remove the old mortar on the surface of more recycled aggregates and obtain recycled aggregates with better physical properties;(2)When the amount of fly ash and the replacement rate of recycled coarse aggregate are suitable,the mechanical properties of recycled concrete can be optimized to a certain extent;(3)When the fineness of fly ash is too large,it will weaken the mechanical properties of recycled concrete;(4)The degree of erosion damage of recycled concrete in different corrosive environments is from high to low:3%sodium chloride solution>10%sodium chloride solution>clean water;(5)The complex interface transition zone of recycled concrete itself makes the internal structure of recycled concrete looser,and the micro-cracks and pores contained in the salt freeze Later,it gradually penetrated and widened,which intensified the salt-freezing damage.In summary,the fineness,content of fly ash,and the replacement rate of recycled coarse aggregate have varying degrees of influence on the strength and freeze-thaw resistance of recycled concrete.Choose appropriate fly ash fineness,content,and recycled coarse aggregate.The preparation of recycled concrete with aggregate replacement rate can improve the strength and durability of recycled concrete,and improve its resistance to salt and freezing corrosion,thereby ensuring the application of recycled concrete structures in actual engineering structures.