Study On Mechanical Properties Of Lithium Slag Recycled Concrete After High Temperature

With the development of the construction industry,a large number of waste concrete has been produced.In order to solve this problem,we recycle,crush and decompose the waste concrete to replace a certain proportion of aggregate in the concrete to make "recycled concrete" from the perspective of solving the resource shortage and environmental protection.In the process of industrial development,a large amount of waste slag will be produced in the process of calcining spodumene.In order to reduce the pollution caused by waste slag,lithium slag can be added into recycled concrete as an admixture.Among them,scholars from Xinjiang University have carried out some research on mechanical properties of adding "double waste" into concrete,etc.At present,the building fire in China accounts for 80% of the total fire.In order to better understand the fire resistance performance of the structure,this paper studies the mechanical properties of lithium slag recycled concrete after high temperature.This test mainly studied the effects of different replacement rates of recycled coarse aggregate(0,50%,100%),temperature(20 ℃,200 ℃,400 ℃,600 ℃),lithium slag content(0,10%,20%,30%)and cooling methods(natural cooling and water spray cooling)on the mass loss rate,tensile compressive strength,flexural strength and axial compressive stress-strain curve of lithium slag recycled concrete specimens.The main research contents are as follows:(1)The lithium slag recycled concrete was tested at high temperature.The results show that with the increase of heating temperature,the surface color of lithium slag recycled concrete test block will change from dark gray to light gray,then to light white,and finally to light red.Cracks,looseness and angle dropping will appear on the surface,in which the micro cracks will continue to extend and finally form a network.After different high temperatures,the mass loss rate of lithium slag recycled concrete is between2.26%～14.15%,and the most serious mass loss occurs at 200 ℃ ～400 ℃.The mass loss rate of lithium slag recycled concrete increases with the increase of temperature;With the increase of lithium slag content,it first increased,then decreased and then increased;It increases with the increase of the replacement rate of recycled coarse aggregate,and the relationship between them is almost linear.(2)The effects of heating temperature,the content of lithium slag and the replacement rate of recycled coarse aggregate on the mechanical properties of lithium slag recycled concrete were studied.The results show that with the increase of heating temperature,the splitting tensile strength and flexural strength of recycled concrete mixed with 20% lithium slag increase first and then decrease when it is naturally cooled,while the cube compressive strength and axial compressive strength of recycled concrete decrease gradually,the peak strain increases gradually,and the peak stress decreases gradually.With the increase of lithium slag replacement rate,the compressive strength,splitting tensile strength and flexural strength of lithium slag recycled concrete first increase and then decrease,the peak stress first increases and then decreases,and the peak strain gradually increases.With the increase of the replacement rate of recycled coarse aggregate,the axial compressive strength,splitting tensile strength and flexural strength of lithium slag recycled concrete first increased and then decreased at 400 ℃,and the cube compressive strength gradually decreased;The peak stress decreases first and then increases,while the peak strain shows a decreasing trend.(3)The mechanical properties of recycled concrete mixed with 20% lithium slag under water spray cooling were studied and compared with natural cooling.The results show that the compressive strength of lithium slag recycled concrete increases slightly at200 ℃,while the strength damage of lithium slag recycled concrete increases at 400 ℃and 600 ℃;After high temperature heating,water spray cooling will reduce the splitting tensile strength and flexural strength.(4)By analyzing the mechanical test data of lithium slag recycled concrete after high temperature,the relationship between the compressive strength,splitting tensile strength,flexural strength retention and heating temperature of lithium slag recycled concrete under different lithium slag replacement rates is established.(5)The stress-strain relation curve,peak stress and peak strain of lithium slag recycled concrete after high temperature were studied,and the variation laws of lithium slag replacement rate,heating temperature and recycled coarse aggregate replacement rate were studied;The stress-strain relation equation of lithium slag recycled concrete after high temperature is established.