Effect Of Corrosive Environment On The Durability Of Bond Interface Of FRP Strengthened Masonry Structure

At present,most of the structures that need to be reinforced and repaired at home and abroad are still concrete structures and masonry structures.There are a large number of bridges,buildings,warehouses and other outdoor structures.These structures bear the erosion of different environments for a long time.China is a big country of masonry structure,with a large number of masonry structures of cultural relics,long-term exposure to a variety of erosion environment,its maintenance and restoration is of great significance.Fiber reinforced polymer composites(FRP)has the advantages of easy operation and good corrosion resistance,which is more attractive to the reinforcement of structures.Bonding FRP sheet to strengthen concrete structure and masonry structure can effectively improve the bearing capacity of the structure and avoid brittle failure.For the structure strengthened with FRP sheet,the strengthening effect depends on the bonding performance of the interface between FRP and matrix,especially the durability of the interface under corrosive environment.Therefore,it is urgent to carry out the research on the durability of bond interface of FRP masonry structure under corrosive environment.In this paper,the normal tension test and single shear test are used to study the interface between FRP block and FRP brick wall under high and low temperature and freeze-thaw cycles.The high and low temperature tests include-20 ℃,room temperature 20 ℃,40 ℃ and60 ℃,and the freeze-thaw tests are designed with 10,20 and 30 cycles.The main research contents and conclusions are as follows:1.Temperature testFor clay brick,the tensile bond strength of strengthened specimens is greatly affected by the high temperature of 40℃ and 60℃.For C-N specimens,the decrease of the normal tensile bond strength at-20℃,40℃ and 60℃ is 10.39%,16.35% and 13.95% respectively;for G-N specimens,the decrease of the normal tensile bond strength is 3.64%,27.45% and 21.19%respectively.For the reinforced clay brick wall,the tensile strength is greatly affected by high temperature,and it decreases by 9.59%,12.86% and 30.11% respectively at-20℃,40℃ and60℃ for 7 days.The typical failure mode is that the steel standard block adheres to the brick wall and separates from the reinforced matrix.The shear debonding force of the specimens strengthened by carbon sheet was reduced,but the reduction was within 8%.The failure mode of the specimens was the failure of the masonry under the interface,and the fiber was pulled down;the erosion was carried out at40℃,60℃ and-20℃ for 7 days.The debonding force of the specimens strengthened by carbon sheet was all reduced.But after the cycle is completed at high temperature,the debonding force decreases by less than 30%.The failure mode of the specimen is that the masonry and mortar joints under the interface are damaged,and the fiber cloth pastes the brick chips and is pulled down.2.Freeze thaw cycle testThe results show that the freeze-thaw cycle has a certain influence on the bond strength of single brick strengthened with FRP,and the greater the number of freeze-thaw cycles,the greater the influence.After 10,20 and 30 freeze-thaw cycles,the positive tensile bond strength of C-N specimens decreased by 14.10%,20.93% and 51.13% respectively,and that of G-Y specimens decreased by 2.76%,20.99% and 45.49% respectively.With the increase of freeze-thaw cycles,the shear debonding force of the strengthened specimens decreases more.The failure mode of the specimens is that the masonry under the interface is damaged and the fiber sheet adheres to the brick chips.For C-Y specimens,the debonding force decreases about 40% when the number of freeze-thaw cycles is 30;four different FRP strengthened brick wall specimens are obviously affected by the freeze-thaw cycles,and the debonding force decreases obviously with the increase of the number of freeze-thaw cycles.For carbon sheet reinforced clay brick wall,the debonding force decreases about 50%.After 10,20 and 30 freeze-thaw cycles,the stiffness of G-Y specimen has no obvious change.The slip near the loading end is 0.56 mm,0.53 mm and 0.62 mm respectively,and the change range is 24.44%,17.78% and 37.78% respectively.3.Numerical simulationThe results show that the debonding force,load slip curve and stress distribution obtained by simulation and test are basically consistent,and the error of debonding force between simulation value and test value is less than 10%,which indicates that the bond element of finite element software ABAQUS can better simulate the bond performance of FRP block interface.The results show that the debonding force increases with the increase of the thickness of FRP sheet,but the increasing range of debonding force decreases gradually;With the increase of block strength,the debonding force also increases,but the difference of debonding force is very small.