Study On The Mechanical Properties Of Lithium Slag Mortar And Lithium Slag Concrete Before And After High Temperature

As a new type of building material,lithium slag is cheap and abundant in supply,which not only saves resources,reduces environmental pollution,but also is beneficial to environmental protection.At present,the research on lithium slag as an admixture to replace cement is extremely lacking.To this end,this paper focuses on the effect of lithium slag replacing cement on the basic mechanical properties of concrete and mortar.The chemical composition of the lithium slag was tested by XRD and the particle size of the ground lithium slag was tested with a laser particle size distribution analyzer.At the same time,simple physical tests were carried out on natural coarse and fine aggregates,and the mix ratio of lithium slag concrete and mortar was designed,and the effect of lithium slag replacing part of cement on the mechanical properties of the specimen was studied.The results show that the average particle size of lithium slag D50=29.36μm,the compressive strength of lithium slag concrete cubes after grinding for 60 min at room temperature is8.5%～8.84% and 13.13% higher than that of 40 min and 0min grinding lithium slag concrete cubes,respectively.～15.24%.The uniaxial compressive strength of the lithium slag mortar grinded for 40 min and cured for 7d at room temperature was 12.95% ～15.05% and23.32%～26.34% higher than that of the lithium slag mortar after grinding for 0min.The flexural strength of the lithium slag mortar specimen was not significantly affected.The uniaxial compressive strength of the lithium slag mortar specimens cured for 28 d was11.92%～16.91% and 18.87%～26.26% higher than that of the specimens ground for 0min.When the curing age is 28 d,the lithium slag replacement rate can improve the mechanical properties of the lithium slag mortar grinded for 60 min to a certain extent.The uniaxial compressive strength of lithium slag concrete prisms and the flexural strength of lithium slag concrete prisms increase first and then decrease with the increase of the substitution rate.When the substitution rate of lithium slag is 20%,the strength can reach the best Effect.For the high temperature test with the gradients of 100 ℃,300 ℃,400 ℃ and 500 ℃for the lithium slag mortar specimen,the color of the lithium slag mortar specimen changes to blue-gray,gray-white,powder white and brown after high temperature.The surface of the specimen at ℃ began to peel off and small cracks;for the high temperature test with the designed gradient of 100℃,300℃,500℃ and 700℃ for the lithium slag concrete specimen,the color of the lithium slag concrete specimen changed to blue-gray after high temperature,gray-white,powder-white,brick red,high temperature 500 ℃,700 ℃specimen surface cracks appear in large numbers,and cracking occurs.The crack characteristics of lithium slag concrete specimens after high temperature are obvious.In this paper,a total of 30 lithium slag concrete cubes,24 lithium slag concrete prisms,30 lithium slag mortar prism specimens cured for 7 days,and 30 lithium slag mortar prisms cured for 28 days were fabricated in the normal temperature test.The main design parameters are grinding time,curing age,and substitution rate.The results show that when the grinding time of lithium slag is 60 min and the substitution rate is 20%,the strength of the specimen is the best.A total of 72 lithium slag concrete cubes,144 lithium slag concrete prisms,and 144 lithium slag mortar prisms cured for 28 days were produced in the high temperature test.The effects of temperature,cooling method and substitution rate on the compressive strength,flexural strength,peak stress and elastic modulus of the specimen are mainly studied.The results show that with the increase of temperature,the mechanical properties of the specimens continue to weaken,and the strength of the specimens after water spray cooling is lower than that after natural cooling.With the increase of the substitution rate,the strength of the specimens increased first and then decreased.By studying the mechanical properties of lithium slag concrete and lithium slag mortar before and after high temperature,the relationship between the mechanical properties and temperature of the specimens after high temperature is theoretically analyzed,and the corresponding theoretical formula is established.Mainly include: the theoretical formula of the relationship between the peak stress and temperature of the lithium slag concrete prism,the theoretical formula of the relationship between the peak stress and temperature of the lithium slag concrete prism,the theoretical formula of the relationship between the elastic modulus of the lithium slag concrete prism and the temperature,the lithium slag concrete Theoretical formula for the relationship between the flexural strength of the prism and temperature,the theoretical formula for the relationship between the peak stress of the lithium slag mortar and the temperature,the theoretical formula for the relationship between the peak stress and the temperature of the lithium slag mortar,the elastic modulus of the lithium slag mortar Theoretical formula for the relationship with temperature,the theoretical formula for the relationship between the flexural strength of lithium slag mortar and temperature,and the uniaxial compressive stress-strain full curve constitutive model after high temperature are used to evaluate the performance of lithium slag concrete and lithium slag mortar materials.Provide a reference for the degree of damage after experiencing a fire.