| With the rapid economic development and continuous population growth,the number of housing constructions has also risen sharply.As the basic material of housing construction,concrete is increasingly scarce.Recycled aggregates are aggregates prepared by crushing and washing waste concrete in buildings.Replacing some or all of the natural aggregates in concrete with recycled aggregates to make recycled concrete can effectively alleviate the shortage of resources and improve the ecological environment.However,due to the presence of old mortar and other impurities on the surface of recycled aggregates,recycled aggregates have higher porosity,water absorption and crushing indicators than natural aggregates,resulting in the mechanical properties of recycled concrete being inferior to ordinary concrete.This thesis is based on experiments,combined with theoretical research on the mechanical properties of reinforced modified recycled concrete and recycled concrete with different gradations,and observed the meso-structure of aggregates and concrete with a scanning electron microscope,and analyzed the changes from a meso-level perspective,analyzing the strengthening mechanism of modified recycled concrete from a microscopic point of view.The main research contents of this paper are as follows:(1)Through the measurement of the basic properties of natural aggregates and recycled aggregates,it is concluded that recycled coarse aggregates have smaller apparent density,higher moisture content and water absorption,and large crushing indicators,which directly lead to the production of The mechanical properties of the obtained recycled concrete are inferior to ordinary concrete.(2)Based on C30 ordinary concrete,the recycled concrete is prepared with a 25%replacement rate of recycled coarse aggregate,and the recycled coarse aggregate is pretreated by soaking the recycled coarse aggregate with water glass solution and polyvinyl alcohol solution.Reinforced modification of the material,the single-grain grading and continuous grading of aggregates are used to modify the particle size of recycled concrete.Through the cube compression test,split tensile test and four-point bending test of all specimens,Analyzing the test data,it is found that the modification of recycled aggregate by sodium silicate solution and polyvinyl alcohol solution can significantly improve the compressive and flexural properties of recycled concrete,and slightly increase the splitting tensile strength;from basic mechanical tests The data shows that the continuous-graded recycled concrete with aggregate of 5～31.5mm has better mechanical properties than single-graded recycled concrete with aggregate of10～16mm and single-graded recycled concrete with aggregate of 16～25mm,aggregate is 16～25mm single grain gradation will seriously affect the mechanical properties of recycled concrete.(3)Observing the microstructure of each group of aggregates and concrete by SEM electron microscope,it can be seen that there are more cracks on the surface of recycled aggregates than natural aggregates.Sodium silicate solution and polyvinyl alcohol solution can affect the regenerated bone The modification of the material will produce CSH gel to fill the cracks in the recycled aggregate,making the surface of the aggregate smoother and denser;the surface of recycled concrete has more cracks than ordinary concrete,and the recycled aggregate is treated by sodium silicate solution and polyvinyl alcohol solution.The modified treatment produces fibrous polymers and gel pores on the surface of the recycled concrete to condense each other,making the surface of the recycled concrete more even and smooth. |
