Study On Mechanics And Durability Of Silica Fume-Steel Fiber-Rubber Concrete

As a product of waste tires,waste rubber is increasing year by year.Discarding and burning waste rubber will cause serious environmental pollution.Recycling waste rubber for the production of rubber powder and rubber products is not only conducive to environmental protection,but also can create economic value.The purpose of this study is to improve the strength of concrete on a basis of recycling through the strength complementarity between silica fume,steel fiber,and rubber.The mechanical properties of 60 mesh rubber powder modified by Na OH solution were tested by adding silica fume and steel fiber.The optimal dosage range of silica fume,steel fiber and rubber powder was determined by a single mixing test.The optimal mix ratio of silica fume-steel fiber-rubber concrete was determined by orthogonal test analysis.The optimal mix ratio specimens and plain concrete specimens were selected for freeze-thaw cycle test and electric flux test,and the test results were compared and analyzed.Finally,the internal phase composition,hydration products,and ITZ（interface transition zone）microstructure of concrete were analyzed by microscopic test.The main conclusions are as follows:（1）In the single mixing test,the mechanical properties of 7d and 28d concrete were measured.It is found that silica fume and steel fiber play a positive role in the mechanical strength of concrete,and the incorporation of rubber powder reduces the mechanical strength of concrete.The optimum range of silica fume,steel fiber,and rubber powder content was determined to be 8.0%～14.0%,1.0%～1.5%,and 5.0%～15.0%.（2）In the orthogonal test,the mechanical properties of 28d concrete were tested.The range and variance analysis were carried out to determine the optimal mix ratio of silica fume-steel fiber-rubber concrete,that is,the silica fume content is 8.0%,the steel fiber content is 1.0%,and the rubber content is 5.0%.Compared with OC group concrete（ordinary concrete）,the compressive strength,splitting tensile strength,and flexural strength of the optimal group concrete increased by 24.51%,63.01%,and8.86%respectively.（3）In the durability test,the mass loss rate of the OC group was 5.53%,and the relative dynamic elastic modulus was 55.8%.The mass loss rate of the optimal group is 4.18%,the relative dynamic elastic modulus is 64.7%,and the frost resistance of the optimal ratio of silica fume-steel fiber-rubber concrete is better than that of OC group concrete.The electric flux value of the OC group was 2368C at 28 days of maintenance,2176C at 56 days of maintenance,and the anti-Cl^-penetration grade was Q-II.The electric flux value of the optimal group was 1650C after 28 days of curing,and the electric flux value was 1467C after 56 days of curing.The anti-Cl^-permeability grade was Q-III,and the overall anti-Cl^-permeability of the optimal group was better than that of the OC group.（4）In the micro test,the internal hydration reaction of silica fume-steel fiber-rubber concrete is sufficient,and the hydration products mainly include C-S-H gel and crystals such as Ca（OH）₂and AFt,which are filled in the pores of concrete,limiting the development of cracks,improving the interface structure and enhancing the compactness.