Study On The Basic Mechanical Properties And Damage Mechanism Of Recycled Concrete Considering The Influence Of Substitution Rate

Based on the recycled coarse aggregate sources of the abandoned concrete pavement renovated and dismantled in the school,the quasi-static uniaxial compression tests with design strengths of C20,C30 and C40 were carried out to obtain the stress-strain full curves under the level of five different replacement rates of recycled aggregate.The full curve test of uniaxial compression stress-strain of recycled concrete under dynamic strain rate(4 strain rate levels)was carried out with the design strength as C30 and the replacement rate as 0%,50%and 100%.The effects of replacement rate and dynamic strain rate of recycled aggregate on the basic mechanical properties of concrete under uniaxial compression were studied.Based on the theory of mesoscopic statistical damage,considering the mesoscopic heterogeneity of concrete materials,the effects of aggregate substitution rate and dynamic strain rate on the mesoscopic damage evolution mechanism of recycled concrete are revealed.The results show that the whole stress-strain curve has similar shape under different substitution rate and strain rate,including two stages of rising and falling.Quasi static loading,the recycled aggregate replacement rate had a great effect on macro stress-strain behavior of concrete,with the increment of replacement rate,show the same three design strength,peak stress and elastic modulus increase with the decrease of the first,when the design strength is C20,peak strain of monotone increasing,the design strength for C30 and C40 after the first peak strain decreases;Under dynamic loading,dynamic strain rate has a significant influence on the macroscopic stressstrain behavior of recycled concrete.With the increase of strain rate,the three substitution rate levels show the same rule.The peak stress and elastic modulus increase monotonically,while the peak strain decreases linearly on the whole.In addition to the rapid deformation and failure of specimens with a strain rate of 10-2/s,accompanied by crackle and splash of fine concrete,the remaining test deformation and failure characteristics are basically the same,and the whole deformation and failure process presents the characteristics of uniform damage and local failure in two stages.The statistical damage model can be used to quantitatively analyze the mesodamage evolution process of concrete,and to distinguish the peak nominal stress state from the critical state by considering the two meso-damage modes of fracture and yield.With the increase of the replacement rate and strain rate of the recycled aggregate,the characteristic parameters characterizing the meso-damage heterogeneous evolution process show obvious regular changes,which are consistent with the internal chemical and physical mechanism and the macroscopic nonlinear constitutive behavior.The yield damage pattern plays a key role in the whole process.