Research On Fundamental Behavior Of Reinforced Concrete Deck Slab Strengthened With BFRP Grids

As a kind of load-carrying structure, deck slab is directly subjected to the wheel pressure loading of vehicles and a variety of corrosive medium, leading to the high possibilities of material aging problem and structural damage as time goes by, determining the necessity of strengthening for a large number of deck slab in the aspects of bearing capacity and durability. Polymer mortar bonding FRP grid strengthening barely increases the self-weight of structures and performs corrosion resistance compared to traditional stick steel strengthening. Furthermore, it can increase the stiffness of component more significantly than fiber cloth strengthening and avoid debonding failure. It also shows its favorable application prospect due to low construction cost and advantageous strengthening behavior. However, FRP grid strengthening performs large scatter in its strengthening effect because of non-standardized manufacture technology of FRP grid and imperfect strengthening construction method. In addition, excessively high cost of the traditional carbon FRP (CFRP) grid and creep problem of low-cost glass FRP (GFRP) have restrained the popularization and application of FRP grid. Therefore, integrated with basalt FRP (BFRP) grid intensively developed recently, systematical researches were conducted on the manufacture of standardized grid and the normalized grid strengthening. The following researches were conducted:1. To solve the node and size controlling issues of pressure molding during the manufacture of FRP grid, optimization was conducted in this paper on the basis of the existing pressure molding. Improvements of fiber dimensions, resin type and mold were attempted with satisfactory achievements. Finished FRP grid product can meet the requirements both for tensile strength and elasticity modulus.2. The type and mechanical properties of polymer cement mortar affect the strengthening effect greatly. Based on the analysis of the raw material of cement mortar, a large number of tests were conducted to determine the mix ratio of polymer cement mortar. With the optimized mix ratio, significant enhancements in the aspects of compressive and rupture strength and bond behavior of polymer cement mortar were observed compared to the ordinary cement mortar.3. The bond behavior of polymer cement mortar bonding FRP grid was studied through double shear test. The effects of the factors, including the type of FRP grid (BFRP/GFRP), thickness of FRP grid (lmm/3mm/5mm), type of polymer cement mortar (NBS/HPM-S) and interfacial treatment mode (roughening and daubing adhesion agent), on the bond behavior were investigated. The results show that the behavior strength of the BFRP grid strengthened component is relatively large with the identical thickness. The bond behavior improves as the grid thickness increases with the identical material. The cracks on the HPM-S mortar performed fine and thick while those on NBS acrylic mortar behaved wide and thin. Components strengthened by NBS mortar performed larger bond strength. Roughening and painting adhesion agent can enhance bond behavior effectively and prevent bond failure at the interface.4. On the basis of the above researches, flexural tests were conducted on five polymer mortar bonding FRP grid strengthened deck slab and one control slab. The effects of fiber material, grid thickness, the number of grid layer and mortar type, on the strengthening performance were studied. The results show that the cracking load, ultimate load and stiffness of the strengthened slabs have been significantly improved and the crack width of the strengthened slabs can be effectively controlled under the identical load. Ultimate bearing capacity of the components strengthened by BFRP grid is higher than those strengthened by GFRP grid with the identical grid thickness. Thicker grid contributes to better strengthening effect with the identical fiber material. Furthermore, daub thickness also has a certain effect on the flexural bearing capacity of the strengthened slab. Slightly higher bearing capacity was observed on the components strengthened by NBS acrylic mortar in comparison to those strengthened by HPM-S.5. Calculation methods for the flexural bearing capacity and cracking load applying to the strengthened component were obtained through theoretical analysis on the flexural behavior of polymer mortar bonding FRP grid strengthened deck slab. The calculation methods were validated to be preferably consistent with the actual situation, with the relative error less than 15% compared with the experimental results.