Research On Long-term Performances Of Steel Fiber Reinforced Concrete Under Sulfate Attack

Sulphate attack is the most widespread and common environment erosion that leads to the deterioration and damage of concrete structures in underground engineering,which seriously affects the long-term performance of concrete structures,thereby jeopardizing structural safety and performance.As a new type of composite material,steel fiber reinforced concrete has good reinforced crack resistance and durability,and is widely used in engineering construction,especially in tunnels and underground engineering,and is often used in broken or weak sections of surrounding rock.The process of corrosion of steel fiber reinforced concrete by sulfate is more complicated than ordinary concrete,and it has more influencing factors.Once it fails,it will be more harmful.Therefore,the research on sulfate attack of steel fiber reinforced concrete is of guiding significance for the maintenance and improvement of its long-term performance,and it has practical significance for the safety assessment and risk assessment of steel fiber reinforced concrete structures in service under sulfate attack environment.In this paper,the damage and deterioration mechanism and long-term performances change law of steel fiber reinforced concrete under the combined action of sulfate attack and dry-wet cycle were researched by integrated combination of theoretical analysis and indoor experiments,macro experiment and micro analysis.This paper first analyzes the destruction mechanism of sulfate-attacked concrete and the steel fiber reinforced concrete crack inhibition mechanism.On this basis,laboratory experiments were conducted to study the changes of physical and mechanical properties of sulfate-attacked steel fiber concrete.Finally,In order to obtain the damage evolution law and deterioration mechanism of sulfate-attacked steel fiber reinforced concrete and to study in-depth the internal causes of the changes of macroscopic properties of sulfate-eroded steel fiber reinforced concrete,a microscopic analysis was carried out by SEM electron microscope scanning experiment.The main research contents are as follows:(1)The long-term performances of steel fiber concrete under sulfate attack were obtained by carrying out the experimental research on the long-term performance of steel fiber reinforced concrete under the combined action of sulfate attack and dry-wet cycle,and considering the long-term effects of steel fiber content and erosion solution concentration on the axial compression strength and splitting tensile strength of steel fiber reinforced concrete.With the increase of the age of erosion,the axial compression strength and splitting tensile strength of steel fiber concrete showed a trend of increasing first and then decreasing;the higher the concentration of sulfate solution,the more the strength loss of the specimen;in different erosion solutions In the concentration,the splitting tensile strength and compressive strength loss of ordinary concrete is greater than that of steel fiber concrete specimens.Increasing the fiber content can effectively reduce the strength loss of specimens under sulfate attack;later in the experiment,the splitting tensile strength damage of ordinary concrete was more serious than the compressive strength.(2)The long-term performances of steel fiber concrete under sulfate attack were obtained by carrying out the experimental research on the long-term performance of steel fiber reinforced concrete under the combined action of sulfate attack and dry-wet cycle,and considering the long-term effects of steel fiber content and erosion solution concentration on steel fiber concrete mass loss rate,stress-strain relationship and appearance changes,and the state of mechanical failure.In the early stage of erosion,under the effect of the filling of erosion products and salt crystals,the compactness of the test piece is strengthened,the ductility is increased,the mass and ultimate compressive strain are increased,and the failure form of the test piece is not significantly changed.As the sulfate attack continues,under the combined action of the expansion stress of the corrosion products and the crystallization pressure of the sulfate,the performance of the specimen begins to deteriorate and the surface cement mortar gradually loosens and falls off,and the edges and corners of the surrounding cracks appear and penetrate gradually The brittleness of the test piece increased significantly,and the mass and ultimate compressive strain decreased accordingly.(3)Microscopic analysis was carried out by SEM scanning electron microscopy technology to observe the distribution and development of internal cracks in steel fiber reinforced concrete under sulfate attack,the changes in the bonding of the interface between steel fiber and concrete matrix,and the growth characteristics and morphological changes of the main erosion products.The evolution process of the damage of the microstructure of the steel fiber reinforced concrete,and revealed the mechanism of the deterioration of the microstructure of the steel fiber reinforced concrete under the combined action of sulfate attack and dry-wet cycle,explaining that the change of the microstructure is the root cause of the deterioration of the macroscopic performance.