Study On Damage Evalution Mechanism Of Recycled Concrete In Cold Area

With the vigorous development of the construction field in the cold area of our country,a large number of waste concrete has been produced by the upgrading of the standardization of the common roads and the renewal of the urban infrastructure construction.These waste concrete is mainly used for the pavement of the new roads,the filling of the foundation,and rarely used again for the main structure of the concrete buildings.Therefore,in-depth study of the feasibility of recycled concrete in cold areas will become an important part of promoting the sustainable development of construction industry in cold areas.Taking the compressive and frost resistance of recycled concrete as the main research content,this paper studies the factors influencing the compressive strength of recycled concrete.According to the acoustic emission technology analysis method,it analyzes the crack evolution process,damage and failure stage,damage state and failure mode of recycled concrete in the process of compression.Through the rapid freeze-thaw cycle test of concrete,the mass loss rate and relative dynamic elastic modulus of the recycled concrete are tested and analyzed,and the attenuation of wave speed and energy generated by the acoustic emission source is studied by using the acoustic emission technology,and the damage degree of the internal and externalstructures of the recycled concrete is evaluated.The compressive strength of concrete is greatly affected by the aggregate gradation and the doping of basalt fiber.The change rule of acoustic emission b-value and acoustic emission energy can divide the compressive failure of recycled concrete into three stages: initial damage of material,stable development of material damage and material damage.In the cluster analysis,the matrix cracking is the main damage state,and the peak frequency effectively identifies the boundary between fiber cracking and interface debonding.When the compressive load grades of fiber full regeneration/recycled fine aggregate/recycled coarse aggregate concrete are 60%,90% and 40%,respectively,fiber cracking damage begins to appear.Tensile failure is the main failure mode of concrete,when the compressive load grades of fiber fully recycled/recycled fine aggregate/recycled coarse aggregate are 65~95%,90%~100%,95%~100%,respectively,the tensile failure activity of concrete increases.The variation trend of acoustic emission ringing count,energy and number of event points with load grade effectively reflects the acoustic emission activity and crack development rate of concrete.The historical indexes HI and severity Sr as well as the cumulative signal strength can effectively identify the main damage severity of different concrete.After 300 cycles of freeze-thaw,the mass loss rate of all mix concrete is less than 5%,and the relative dynamic modulus of elasticity is more than60%.Among them,natural concrete J-1,recycled concrete J-2 and J-7 have better frost resistance.The acoustic emission wave velocity of concrete is always greater than the surface wave velocity,the standard deviation of surface wave velocity isalways greater than the standard deviation of penetration wave velocity,and the attenuation degree of surface energy is always greater than the attenuation degree of penetration energy.According to the law of acoustic emission wave velocity and energy change of concrete,the damage degree of internal and external of freeze-thaw concrete can be effectively distinguished.