Experiment Study On Bonding Performance And Impact Resistance Of New Fiber Reinforced Concrrete To Existing Concrete

The use of concrete has brought good economic benefits for social development,but as a highly heterogeneous non-isotropic body,it has the development of micro-cracks before and after applying loads.The development of cracks can be restrained,and the brittleness defect and durability of concrete can be obviously improved by mixing single fiber or multiple fibers.The bonding performance of new concrete and existing concrete is affected by many factors,and the material used for new concrete is an important one.The application of fiber concrete in the bond repair of existing concrete has its own advantages,so it has important practical value to study its bond performance with existing concrete.For this purpose,the main works are as follows:The compressive strength and splitting tensile strength tests of steel fiber concrete and steel-PP-PVA hybrid fiber concrete were carried out and the influence of fiber content and hybrid effect on the mechanical properties of concrete is analyzed.Through the bond splitting tensile test,bond shear test and impact resistance test after bonding,the influence of fiber content and hybrid effect on the interface bonding performance between new concrete and existing concrete was studied.The research results are as follows:（1）Adding a certain amount of steel fiber and hybrid fiber into ordinary concrete can slightly enhance the compressive strength,and the improvement effect of hybrid fiber is more obvious;It can greatly improve the splitting tensile strength of concrete,up to 1.5 times that of ordinary concrete.（2）In the bonding test of new and old concrete,there are steel fibers adhering vertically to the bonding failure surface,which indicates that the steel fibers play a certain stress role in the bonding strength test.Compared with ordinary concrete,steel fiber and hybrid fiber in new concrete have great influence on the bond splitting strength of new concrete and old concrete,and both of them can effectively improve the bond splitting strength of new concrete and existing concrete,but the gain effect of hybrid fiber on bond strength of new and old concrete is less than that only mixed with steel fiber.（3）The binding shear strength ratio of new and old concrete,which is made of SFRC and HFRC,is 11.1%～31.4%higher than that of ordinary concrete（NC-35）,it has a favorable effect on the improvement of bond shear strength.When the content of steel fiber is 1.5%,the bond shear strength enhancement effect of hybrid fiber concrete is weaker than that of steel fiber alone,which shows"negative hybrid effect".（4）The failure characteristics of the round-cake-shaped bonded specimen have certain ductility characteristics.When the specimen is damaged,the impact resistance is greatly improved compared with the ordinary concrete monolithic specimen.With the increase of steel fiber volume content（0.5%～1.5%）,the number of initial crack impact N₁,the number of failure impact N₂ and ductility coefficientβof SFRC and HFRC show a trend of stepwise increase.The results show that the impact resistance of concrete reinforced by hybrid fiber is better than that of steel fiber alone:For hybrid fibers,when the steel fiber content was 1.5%,the number of initial crack shock（N₁）and failure shock（N₂）increased by 1.81 times and 5.75 times,respectively,compared with C35 specimen group.Among them,the combination of steel fiber content of 1.5%and PP、PVA content of 1.0 kg/m³ has the most significant impact resistance improvement,which shows"positive hybrid effect".（5）Weibull distribution model is introduced to fit and analyze the impact life of bonded specimens between fiber reinforced concrete and existing concrete,the results show that Weibull distribution model is also applicable to bonded specimens.