Study On The Evolution Of Mechanical Properties Of Steel Fiber Concrete Under Chloride Ion Erosion And Neutralization

Steel fiber concrete（SFRC）has been gradually applied in the construction of marine,dam,port and bridge projects because of its excellent crack resistance,tensile strength and toughness.With the expansion of applications and diversification of service environments,it is necessary to consider the durability of SFRC in marine and acidic environments.In this paper,the evolution of mechanical properties of steel fiber concrete and its corrosion mechanism under chloride salt erosion,chloride-carbonation coupling and acid rain environment are studied.The main research contents and conclusions are as follows.（1）Na Cl solution with a concentration of 3%was used as mixing water to accelerate the corrosion deterioration of steel fiber concrete and to explore the evolution of steel fiber concrete properties under chloride salt erosion.The results showed that the cubic compressive strength of steel fiber concrete gradually increased with the increase of erosion time under the effect of chloride ion erosion and stabilized after 12 months;the axial compressive performance of the specimens did not deteriorate significantly during the erosion time of up to 24 months;the flexural strength and toughness index of the specimens showed an increase and then a decrease with the increase of erosion time,but they were higher than the initial value（0 months）.（2）Steel fiber concrete was prepared by using Na Cl solution with 3%concentration as mixing water and carbonated for 3 months after curing,after which the specimens were placed under high humidity environment to investigate the evolution of steel fiber concrete properties under the coupling effect of chloride ion erosion-carbonation.The results showed that the cube compressive strength of steel fiber concrete gradually increased with the increase of erosion time under the coupling of chloride ion erosion-carbonation;the axial compressive strength of the specimens gradually increased with the increase of erosion time,and the energy absorption capacity and axial compressive toughness ratio first increased and then decreased,and the axial compressive toughness of pure cement concrete specimens（O2）deteriorated,while the steel fiber concrete specimens compounded with 20%fly ash+40%slag（OFS）were found to be more stable.The bending strength and bending toughness index I of the specimens increased and then decreased with the increase of erosion time.The mechanical properties of specimen O2 under the action of chloride ion erosion-carbonation coupling are better than OFS,but the ability of specimen OFS to resist chloride ion erosion-carbonation coupling is better than O2.（3）Steel fiber concrete was prepared using tap water as mixing water,and after curing,it was placed in sulfuric acid solution at p H=4.The evolution of the properties of steel fiber concrete under the action of acidic environment was investigated using total immersion,and the specimens with different erosion times were analyzed by physical phase analysis（XRD）.The results showed that the cubic compressive strength of the steel fiber concrete increased and then decreased with the increase of the erosion time under the effect of sulfuric acid solution,and was stable after 12months,and the cubic compressive strength of the specimens did not deteriorate;the axial compressive bearing capacity of the specimens increased and then decreased with the increase of the erosion time,and the axial compressive strength of each test time was greater than the initial value,while the axial compressive toughness deteriorated to different degrees with the increase of the erosion time.The bending strength of the specimens did not deteriorate,and the bending toughness deteriorated slightly.Ca SO₄-2H₂O was deposited on the surface of the steel fiber concrete under the action of sulfuric acid solution,and the internal phase composition of the specimens did not change.（4）When the p H value of steel fiber concrete is<11,the internal steel fiber of the specimen is very easy to rust;when the p H value is>11,the internal steel fiber surface of the specimen still remains bright and there is no sign of corrosion.