Study On Durability Of Go Recycled Coarse Aggregate Concrete Under Couped Action Of Freeze-thaw And Chloride Salt Erosion

Recycled coarse aggregate concrete(RAC),as a recyclable green energy-saving material,has broad application prospects.However,due to the existence of high water absorption,high porosity and other characteristics of RAC,its durability performance is reduced,which restricts its development and application.Especially in areas with severe freeze-thaw phenomenon and salt erosion problems,the durability requirements for RAC are more stringent.As a new type of material,graphene oxide recycled coarse aggregate concrete(GO-RAC)has been widely concerned in the industry in recent years.The incorporation of graphene oxide(GO),on the one hand,will affect the pore structure distribution in different regions of RAC,and on the other hand,will have a greater impact on the crystal structure of cement hydration products,thereby improving the durability of RAC.Up to now,the research on the durability of GO-RAC is limited to the single factor effect,and the research under coupling is still lacking.In order to effectively improve the application scope of RAC in structures and promote the application of RAC,it is necessary to study the durability of GO-RAC under the coupling action of freezethaw and chloride erosion.According to the existing research,GO-RAC was selected as the research object,and the content of GO(0,0.03%,0.06%),GO oxygen content(20%,40%),recycled coarse aggregate(RA)replacement rate(0,50%,100%),the number of coupling cycles(0 times,18 times,36 times,54 times,72 times)were used as variables.The durability of GORAC under the coupling effect of freeze-thaw and chloride erosion was studied,and its failure service life under the coupling action was predicted.The work done in this thesis is as follows:(1)The physical and mechanical properties of GO-RAC with different mix ratios under the coupling action of freeze-thaw cycle and chloride erosion were studied by the quick freezing method.Compare the macroscopic damage and analyze and measure the mass loss rate,relative dynamic elastic modulus,compressive strength,the results show that: chloride erosion exacerbates GO-RAC damage in freeze-thaw cycles;the greater the RA substitution rate,the worse the frost resistance of GO-RAC;the frost resistance of GO-RAC with 0.06% GO content is better than that with 0.03% GO content;when the oxygen content of GO incorporated into the RAC was 40%,its frost resistance was significantly better than that of GO-RAC with an oxygen content of 20%.At the same time,based on the above test data,a deterioration model of GO-RAC compressive strength and coupling cycle times,GO content,and primary coarse aggregate(NA)replacement rate under the action of chloride salt freeze-thaw was established,which provided theoretical support for the application of GO-RAC in severe cold saline areas.(2)Through the chloride ion(Cl~-)permeability test under the coupling action of freezethaw and chloride erosion,the variation law of Cl~- penetration depth,free Cl~- concentration,surface Cl~- concentration and Cl~- diffusion coefficient of GO-RAC with different blend ratios was studied.The results show that: the higher the RA substitution rate,the worse the impermeability of GO-RAC;GO-RAC with different GO content can maintain good impermeability under the coupling effect,and when the content of GO is 0.06%,the improvement effect of RAC is the best;the Cl~- concentration distribution of GO-RAC satisfies Fick’s second law,the surface Cl~- concentration increases exponentially with the increase of coupling times,and the diffusion coefficient first decreases and then increases with the coupling number increasing;in addition,Fick’s second law was used to predict the lifetime of GO-RAC under the coupling action of freeze-thaw and chloride erosion.