Study On Mechanical Properties And Meso Mechanism Of Steel Fiber Modified Rubber Concrete Under Freeze-Thaw Cycle

The structure of buildings and structures in severe cold areas degenerates after longte-rm freezing and thawing,and the maintenance cost is high.Waste rubber powder can effect-ively enhance the frost resistance of ordinary concrete and improve the disposal of waste r-ubber.Due to the hydrophobic characteristics of rubber materials,the strength of concrete is reduced.After adding steel fiber into concrete,it not only prevents cracking and improves s-trength,but also can inhibit the occurrence and continuation of cracks when concrete is da-maged.Which is valuable for practical engineering application.In this paper,based on ordinary C50 high strength concrete,the equal volume of fine aggregate is replaced by 5%,10%and 15%rubber powder,and steel fibers with volume ra-tios of 0.5%,1.0%,1.5%and 2.0%are added respectively to make steel fiber concrete（S_n-R_mC）specimens,a total of 20 groups and 900 specimens,including 600 non-standard speci-mens with100×100×100mm and 300 non-standard specimens with 100×100×400mm.In or-der to analyze the changes of porosity and strength,the cured specimens were carried out i-ndustrial CT scanning,compression test,splitting tensile test and four point bending test af-ter the freeze-thaw cycle experiment.The results show that:（1）With the increase of rubber powder content,the brittleness of concrete is improved in varying degrees,but the strength decreases significantly;The addition of steel fiber effe-ctively improves the mechanical properties of rubber concrete.With the increase of steel fi-ber content,the splitting tensile strength and flexural strength enhance,When the content of steel fiber exceeds 1.5%,the compressive strength decreases to a certain extent,but it is sti-ll higher than the specimen with the content of 1.0%;The strength of specimens decrease g-radually as the number of times are increased.In addition,the more content rubber powder has,the smaller strength loss rate will make.In the compression test,tensile test and four p-oint bending test before freeze-thaw cycle,the specimens with the highest strength of steel fiber rubber concrete are S_1.5R₅C,S_2.0R₅C and S_2.0R₅C respectively;The minimum strength loss rates are S_1.0R₁₅C,S_2.0R₁₅C and S_0.5R₁₅C,which are 5.93%,14.18%and 31.25%respe-ctively.（2）As the number of freeze-thaw times are increased,the more content rubber powder has,the greater of relative dynamic elastic modulus is.The higher content steel fiber has,t-he greater relative dynamic elastic modulus is.After 200 cycles,the relative dynamic mod-ulus of S_2.0R₁₅C is the largest,which is 91.44%.（3）The higher content rubber powder has,the smaller porosity will be.The higher content steel fiber has,the greater porosity will be.As the number of freeze-thaw times are increased,the porosity of the specimen increases gradually.The higher content rubber powder has,the smaller porosity growth rate will be;The porosity of S_0.5R₁₅C in high strength steel fiber rubber concrete is the smallest,which is 0.71%;S_2.0R₁₅C has the smallest pore growth rate of 7%.（4）When the content of rigid fiber exceeds 1.5%,agglomeration will occur in the mix-ing process,so it is impossible to mix evenly;Considering the changes of compressive stre-ngth,tensile strength,flexural strength,freeze-thaw damage and porosity,S_1.0R₁₅C is the o-ptimal mix proportion.