| The durability of concrete structures is one of the key research topics of scholars from various countries in recent years.In actual engineering,concrete structures face different types of environments,among which the marine environment is a harsh environment that will pose a great threat to its durability.The main reason is seawater contains a large amount of chloride and sulfate components,which will cause great corrosion effects on the concrete and the steel bars in it.At present,there have been many solutions to the problem of insufficient durability of reinforced concrete structures in the ocean,such as increasing the thickness of the concrete protective layer,using steel bars with anti-corrosion coatings,high-strength marine concrete,and fiber reinforced materials.The application of Fiber Reinforced Polymer(FRP)tendons to concrete structures can effectively improve the durability of the structure.FRP bars are bonded with epoxy resin and other adhesives to form a bundle like whole.It has good corrosion resistance,high tensile bearing capacity,lighter weight,and good electromagnetic resistance.It can replace steel bars in concrete structures and can extend the service life of the structure.Compared with other types of fiber reinforcement,basalt fiber reinforced polymer(BFRP)reinforcement has many advantages.First of all,it has abundant raw materials and high basalt output,which can meet the needs of larger batches.Secondly,its strength is relatively high,which is significantly improved compared to the strength of steel bars of the same size.Finally,its cost is low,the price is only about 1/6 of carbon fiber reinforcement,which can reduce the actual engineering application cost,so BFRP reinforcement has a good development prospect.In this paper,42 beam specimens are used to carry out the experimental research on the bending performance in the marine environment.The chloride salt solution is prepared from industrial sodium chloride,and the concentration of the chloride salt solution is 3.5%.According to the types of reinforcement materials,the specimens are divided into steel bars,BFRP bars and mixed reinforcement of steel bar and BFRP bars.There are three environmental conditions:the first one is stress-free and non-corrosive,with a total of 3 specimens.The second is non-stress chloride salt solution erosion with a total of 12 specimens.The third is the coupling of load and chloride salt,a total of 27 test pieces.The main research results are as follows:(1)In terms of reinforcement materials,the mechanical properties of steel bars and BFRP bars decrease under the environment of no stress chloride corrosion.When the erosion time is 180 days,the ultimate tensile strength of the steel bar is reduced by 7.7%,and the BFRP bar is reduced by 3.6%.Under the coupling action of load and chloride salt,the performance degradation of the two types of reinforcement has accelerated.When the erosion time is 180 days and the load-holding level is the maximum,the ultimate tensile strength of the steel bar is reduced by 12.4%,and the BFRP bar is reduced by 4.7%.BFRP bar has obvious advantages in the ultimate tensile strength.(2)Under the stress-free chloride salt erosion environment,compare the changes of the limit bending moment values of each group of specimens.It can be seen that the change trend of all specimens is basically the same,all increase first and then decrease,and the peak value of the ultimate bending moment appears between 90-135 days of erosion.When the erosion time is 180 days,the ultimate bending moment of steel bar specimen decreases by 3.6%,BFRP specimen decreases by 2.2%,and mixed reinforcement specimen decreases by 0.3%.(3)Under the coupling effect of load and chloride salt,comparing each group of specimens,it can be found that the minimum value of the ultimate bending moment appears at the load of 60kN,and the erosion time is 180 days.The ultimate bending moment of the steel bar specimens decreased by 7.5%,the BFRP specimens decreased by 5.4%,and the ultimate load of the mixed reinforcement specimens decreased by 4.7%.The ultimate load-bearing capacity of the steel bar specimens has decreased significantly,and the reduction value of the ultimate bending moment of the BFRP bar and the mixed-reinforced specimens is closer,and both are lower than the reduction value of the steel bar specimens.(4)Under the coupling effect of load and chloride erosion,the bending performance of the uncracked steel bar specimens and the steel bar specimens with smaller cracks are basically the same.It shows that when the cracks are small,there is no obvious acceleration effect on the corrosion rate of steel bars.When the load-bearing grade is 60kN,the crack width is larger and the number is large.Under this kind of erosion condition,the bending performance of the steel bar specimens is significantly degraded.(5)Under the coupling action of load and chloride salt,three grades of long-term load of 15kN,30kN and 60kN were applied to the BFRP bar specimens.The test results show that with the increase of erosion time and load-holding grade,the bending performance of the BFRP bar specimens degrades more obviously,the crack width increases,and the deflection deformation increases.The main reason is that with the increase of erosion time and load-holding grade,the performance of the reinforcement at the cracks of the specimen is significantly degraded,and the elastic modulus of BFRP reinforcement decreases.(6)The failure modes of various specimens are distinguished,and the simplified calculation formula of ultimate bearing capacity of BFRP reinforced concrete beam and mixed reinforced concrete beam is deduced.The test value and formula calculation value are compared,the calculated value is in good agreement with the test value.The simplified calculation formulas of cracking load,stiffness,deflection and crack width of mixed reinforcement specimens are derived,which can provide reference for practical engineering application. |
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