Experimental Study Of The Bond Performance Between FRP Bars And Concrete In NSM Reinforcement

Near-Surface Mounted (NSM) reinforcement is a new emerging applications in the field of strengthening concrete structure, using this technology can be fast and effective repair buildings and Bridges in erosion damage, aging, harsh environment. Compared with externally bonded method, the use of NSM technique,in which FRP reinforcement is embedded in the structure of the surface, thus avoiding the external unfavorable factors(high temperature, freeze-thaw, abrasion and Strike)on strengthening effect, can effectively perform the bond behavior between FRP bars and concrete interface. Therefore, NSM technique can make up for the deficiencies of externally bonded reinforcement technology for structural reinforcement effect with special requirements environment, such as in the ports, sea-related construction, heat resistant buildings, bridge and floor panels negative moment zone, playing better reinforcement results.Currently, the bonding materials in NSM technique used mainly are composed of two categories:organic materials such as epoxy resin and epoxy mortar;inorganic materials such as high-strength cement-based grout, high strength cement mortar and cement mortar. Large numbers of tests having carried by domestic and foreign scholars on selecting the appropriate adhesive materials, but due to the different nature of the bonding material, leading component of the loading capacity and failure modes are different. Test failure mode was observed in most of the bonding materials brittle fracture without obvious warning. PVA-ECC is a kind of special material with high ductility and durability, can significantly improve the failure mode, suitable for high temperature, freeze-thaw, abrasion and Strike environment, also it’s low cost. In view of this, the author using self-designed PVA-ECC as a new type of bonding material, study the bonding performance of FRP bars and concrete interface,comparative with the epoxy resin adhesive, fischer Steel sticking glue andhigh strength mortar. The main research content are as follows:(1) Through the first four groups of domestic PVA fiber with different mix by cubic compression and beam specimens mechanical properties test to determine the optimal ratio of preparation PVA-ECC. Tests showed:fiber volume content increased significantly improved PVA-ECC brittle fracture, but the compressive strength is reduced; lower than the mastic can improve fluidity, is more conducive to fiber dispersion, improved PVA-ECC ductility; increase of fly ash makes the ultimate bearing capacity of PVA-ECC decreased, but increased the limit deflection.(2) On the basis of the first batch of results, choosing the most common Japanese Kuraray PVA fiber for beam four-point bending test. Study shows:Japanese Kuraray PVA fiber preparation PVA-ECC specimen bending performance is more excellent, bilinear curve rising more obvious; fiber volume content there is a boundary, the dosage is too low or too high dosage ductility effect will reduce cement-based composite materials, the test when the fiber volume content of 1.7%, the specimen ductility best effect. Comparative analysis of two batches of test results, and ultimately select the volume content of 1.7% of Kuraray fiber preparation for the pull-out test of the bonding material.(3) Through the C-type concrete specimens directly pullout tests, studying four kinds of different adhesive materials on the bonding properties of FRP bars and concrete interface, and considering the impact of different types of FRP bars and different bond lengths two factors on interface regular pattern, fiber-reinforced cement-based composite lower limit of the material specimen failure load in bond length of 5D case up to 70% epoxy specimen, when the basic bond length 10D can reach 50%. bond length increases,especially in the 10D bond length, after a long horizontal section after friction began to decline, which is very beneficial for improving component failure modes and improve ductility.