Study On Impact Splitting Tensile Properties Of High Strength Concrete With Steel Polypropylene Hybrid Fiber

Nowadays,in order to meet a higher requirement of some important engineering structures,high-strength concrete have been widely used and promoted.However,high-strength concrete still has some inherent disadvantages such as low tensile strength and poor toughness which likes conventional concrete,and it shows tremendous unbalance between tension strength and compression strength.The concrete structure inevitably encounters the effect of dynamic load during its working process.This inherent disadvantage is particularly acute and poses a serious hidden danger to the structure in case of dynamic loads.Therefore,it is necessary to improve the tensile properties of high-strength concrete.Previous studies show that one of the most effective ways to solve this problem is to mix reinforced fiber in concrete.For the sake of better tensile properties of concrete,it is necessary to incorporate two or more fiber into concrete.Fiber-reinforced concrete falls into two categories according to its mechanical properties:high elastic modulus fiber reinforced concrete and low elastic modulus fiber reinforced concrete.The high elastic modulus fiber can enhance the concrete material from both strength and ductility,while the low elastic modulus fiber mainly improves the ductility of the concrete material.At present,steel fiber reinforced concrete and polypropylene fiber reinforced concrete,which is a typical hybrid fiber,has been widely used.Researches in this paper mainly centered around the static and dynamic splitting mechanical properties of the high-strength concrete mixed with two kinds of fibers.The researches in this paper mainly focus on the following points:(1)A static splitting tensile test was carried out with the benefit of a pressure tester under a load rate of 5kN/s on C60 high-strength concrete mixed with different proportions of steel fibers and polypropylene fibers.Combined with a high-speed camera as well as its supporting system we shot the crack propagation process.In this paper we studied the failure process and failure strength of the concrete specimens through experimental data in the static splitting test.The influence of the ratio of fiber mixed incorporation on the tensile strength of concrete was obtained.The hybrid fiber mixed with steel fibers began to bear force and played a role after the larger cracks occurred in the concrete matrix material,which improved the tensile strength of the specimens.When the content of steel fiber is below 2%,the mixing effect of polypropylene fiber is not good in terms splitting strength while the content of steel fiber increased to 2.5%and 3%,mixed polypropylene fiber can improve the static splitting strength,which shows a better mixing effect.(2)By using the SHPB device independently developed by Southwest University of Science and Technology,a dynamic splitting tensile test with a loading rate of approximately 11×10~5k N/s and 15×10~5kN/s was performed on C60 high-strength concrete specimens with different proportions of steel fibers and polypropylene fibers.We also took pictures of the crack propagation process and analyzed the test results with the help of a high-speed camera and its associated system equipment.The failure process and failure strength of the concrete specimens in the dynamic splitting test were studied via experimental data.Besides,we obtained the regular of the influence on the tensile strength of concrete of under different loading rates?different fiber doping ratios.The results show that the concrete specimens of all kinds of fiber show a similar splitting failure mode that crack comes from the center.Loading rates have a significant effect on splitting tensile strength of concrete specimens with different fiber.The concrete with steel fibers alone can significantly increase the dynamic splitting tensile strength,while concrete with polypropylene fiber alone gets a bad effect on its splitting strength.When we mix polypropylene fibers and steel fibers into concrete,it shows different enhancement effects on dynamic splitting strength due to the change content of the two kinds of fiber.In the addition range studied in this paper,the hybrid fiber have better effects as a whole when the steel fiber content is 2.5%as well as polypropylene fiber is0.22%.