Research On Durability And Bond Stress Damage Of Reinforcement And Concrete Under Salt Corrosion And Freeze-thaw Cycles

Durability damage of reinforced concrete structures has become a worldwide concern,and it is an urgent problem to be solved.The deterioration of bond stress between reinforcement and concrete is one of the important causes of durability damage.For now,domestic and foreign scholars study on the bond stress between steel and concrete under the action of environmental factors such as freeze-thaw cycles and salt corrosion.However,there are few studies on the bond stress damage between reinforcement and concrete under the coupling action of load and environmental factors.Western Jilin is located in the seasonal frozen area of China,and the soil contains a large number of bicarbonate ions,sulfate ions and chloride ions,which will degrade the bond stress of reinforced concrete,shorten the service time of buildings and damage the use function of buildings.Therefore,in view of the specific situation of Western Jilin,it is of practical significance to study the damage of bond stress between steel bar and concrete under freeze-thaw cycle,salt corrosion and load,which can provide some theoretical data for the design of reinforced concrete structures in Western Jilin and similar areas.At the same time,in order to reduce the bond stress damage between steel bar and concrete at the same time,the method of adding PVA fiber into concrete is proposed.The experiment in this paper is divided into four parts and the specific experimental research work is as follows:(1)Through the composite salt immersion test and the central pull-out test after immersion,it is concluded that the quality and dynamic modulus of elasticity of the sample increase slightly after short-term immersion in composite salt solution,and there is a law that the higher the concentration of salt solution,the larger the increase.The bond stress of all specimens increased slightly compared with that before immersion,and the loading had little effect on the specimens which did not produce cracks or produced few cracks.(2)Through freeze-thaw test and center pull-out test of specimens after freeze-thaw,it is concluded that the mass loss rate of specimens after freeze-thaw increases,the relative dynamic modulus of elasticity and bond stress decrease,and the degradation process of bond performance between steel bar and concrete is aggravated by the coupling effect of freeze-thaw cycles and load-holding.The bearing capacity has a great influence on the three parameters of the specimens.The larger the holding capacity,the greater the mass loss rate of the specimens.(3)Through the salt freeze-thaw test and the center pull-out test of the samples after salt freeze-thaw,it is concluded that the mass loss rate of the samplesincreases after salt freeze-thaw,and the damage degree and damage rate of the three parameters are significantly more serious than those under load-freeze-thaw conditions.(4)By comparing the parameters of ordinary concrete and PVA fiber concrete under different working conditions,it is concluded that the addition of PVA fiber can improve the anti-denudation and anti-freezing performance of concrete and reduce the damage of bond stress of reinforced concrete.The improvement of these three aspects increases with the decrease of mass,dynamic elastic modulus and bond stress.This paper summarizes the damage law of bond stress of reinforced concrete under the coupling action of load and different environmental factors through the above tests,which has certain reference value and guiding significance for practical engineering.