Research On Fracture Properties Of Hybrid Fiber Reinforced Concrete Under Sulfate Attack Environment

In the failure of concrete structure caused by the decrease of durability,sulfate is one of the important factors affecting the damage of concrete.Especially for concrete structures in marine environments,which have been eroded by sulfate ions for a long time and are often in the area of water level fluctuation.Under the coupling environment of drying-wetting cycle and sulfate,the concrete structure will be damaged even more severely.Therefore,this test simulates the coupling environment of drying-wetting cycle and sulfate.A total of 20 groups of concrete with different fiber mixing and different matrix strength are designed to be eroded in 10%Na₂SO₄solution.When the erosion time is reached,the compressive strength of concrete shall be tested respectively,and the three-point bending beam test shall be carried out.The changes of compressive strength,double-K fracture toughness and fracture energy of sulfate eroded concrete were studied under different erosion age,erosion mode,fiber content and matrix strength.The main conclusions are as follows:（1）The compressive strength of concrete increases first and then decreases with the increase of erosion time.The compressive strength increases with the addition of fibers,and steel fiber plays a major role in improving the compressive strength.Under the test conditions,the compressive strength is the highest when the content of steel fiber and imitation steel fiber is 0.8%and 0.6%respectively（2）The crack initiation toughness,instability toughness and fracture energy of hybrid fiber reinforced concrete increase first and then decrease.When the erosion time is 4 months,each index value of the specimen reaches the maximum.（3）The addition of fiber can significantly improve the surrounding area of load displacement curve and load deflection curve,and also significantly improve the fracture toughness and fracture energy.The type and content of fiber have an obvious influence on the fracture properties.Steel fiber can significantly improve the fracture energy and fracture toughness,while polypropylene coarse fiber can greatly improve the fracture energy.（4）With the increase of matrix strength,the compressive strength,crack initiation toughness and fracture energy are also improved.The improvement of matrix strength shows better sulfate resistance.Due to the change of the main failure mode of fiber,the instability toughness decreases under high matrix strength.（5）In sulfate environment,the compressive strength and fracture properties of specimens under drying-wetting cycle are more degraded than those under soaking environment.