Experimental Study On Damage Constitutive And Bonding Properties Of Recycled Concrete With Lithium Slag

With the development and application of recycled concrete technology in China,the recycling of construction waste has far-reaching significance for environmental protection,alleviating the shortage of primary resources and social sustainable development.How to recycle waste concrete and use lithium slag as the main mineral admixture in building structures still needs a lot of experimental research.Therefore,based on the study of damage constitutive relationship and bond-slip behavior of concrete at home and abroad,combined with experimental and theoretical methods,the damage constitutive and bond properties of recycled concrete with lithium slag were studied.The main research work is as follows:(1)With different recycled coarse aggregate(0%,30%,50%,100%)and lithium slag content(0%,10%,20%,30%)as variables,the stress-strain curves under different factors were obtained through uniaxial compression tests.The results show that with the increase of replacement ratio of recycled aggregate,the peak stress of recycled concrete increases first and then decreases,the peak strain increases,the elastic modulus decreases gradually,and the mechanical properties of recycled concrete can be effectively improved by adding lithium slag.(2)Considering the characteristics of stress-strain curve,recycled aggregate is used as concrete material with initial damage,and uniaxial compressive stress-strain curve of ordinary concrete is used as non-destructive reference state.Based on damage mechanics,a uniaxial compressive damage constitutive model of recycled concrete with lithium slag is established.With the help of the new constitutive model,the bending capacity of recycled lithium slag concrete beams is calculated by using MATLAB program.(3)Axial compression tests of recycled lithium slag concrete under different factors are carried out based on acoustic emission technology.According to the mechanical characteristic curve,acoustic emission energy and the number of acoustic emission events obtained in the tests,the damage evolution model of recycled lithium slag concrete is established,and the relationship between damage materia and acoustic emission parameters is revealed.(4)In order to study the bond properties between recycled lithium slag concrete and steel bar,66 core pull-out specimens of recycled lithium slag concrete were designed.The effects of replacement ratio of recycled aggregate,lithium slag content and steel bar diameter on bonding properties were studied.The results show that the appropriate replacement rate of recycled aggregate and the content of lithium slag can improve the bonding performance of recycled concrete.Based on the optimal mix ratio,specimens with different steel bar diameters(12mm,16mm,20mm)were designed.The ultimate bond strength decreases with the increase of steel bar diameter.The constitutive relationship between bond stress and slip of recycled lithium slag concrete is fitted by load-slip curve and bond strength formula.