Study On Performance Degradation Of TRC Composite Beams Under Coupling Action Of Force And Carbonation And Coupling Action Of Force And Salt Freezing Cycles

The vigorous development of building industrialization in China is bound to bring about revolutionary progress in the history of building engineering.The textile reinforced concrete(TRC)permanent template studied in this paper is made of stainless steel mesh net fixed fiber fabric and prefabricated with high performance fine aggregate concrete.On one hand,permanent formwork can protect the cast-in-place concrete and enhance its durability.On the other hand,permanent template acts as a part of the structure to participate in the structural stress,thereby improving the mechanical properties of the structure.In harsh environment,as the outermost layer of structure,the permanent template is the first to be eroded.As the first line of defense for the whole structure,ensuring the durability of permanent formwork will play a crucial role in the durability and service life of the whole structure.This paper mainly studies the mechanical properties of TRC composite beams under the coupling of force and carbonation,and the performance deterioration of TRC composite beams under the coupling effect of salt and ice.The study is as follows:(1)The 28d accelerated carbonization test of TRC composite beams and ordinary RC beams under different stress levels was carried out,then the bending bearing capacity and carbonization depth of the normal section were measured under normal conditions,and the damage morphology and mechanical properties of the test beams were observed and compared with the normal RC beams.The test results showed that:the capacity of unloaded composite beams increased slightly after carbonization,the ultimate load was increased by 5.88%compared with that before carbonization.After carbonization,TRC composite beams had better deformation control ability than ordinary RC beams,and the the yield load and cracking load degradation degree was smaller too.Under the same carbonization age,the higher the stress level was,the greater the magnitude of the bearing capacity data of TRC composite beams subjected to different stress levels would be.But the overall decline was limited.The ultimate load of the composite beams subjected to 0.6 stress level was 8.82%lower than that before carbonization.Under stress,the carbonation speed of TRC composite beams is greater than that of carbonation under non-stress state.The higher the stress level,the greater the increase of carbonization depth is.The carbonation depth amplification at the bottom of the beams is the most obvious.Under the same stress level and carbonization age,the carbonation depth of TRC composite beam is much less than that of ordinary RC beam.(2)The influence coefficient of carbonation depth and bending stress of TRC composite beam was obtained.The carbonization depth data showed that the short term accelerated carbonization of 28d did not penetrate the concrete protection layer,and did not affect the internal reinforcement,and the stress level played a major control role in the experiment.(3)The freezing thawing cycle tests of several groups of TRC composite beams and ordinary RC beams were carried out by the coupling of three factors of freezing thawing cycle times,NaCl solution concentration and stress level.After freezing and thawing tests,the apparent form analysis was carried out,and then the flexural bearing capacity test was carried out.The concrete samples were tested by SEM and XRD to analyze the composition of the internal phase of the concrete after freezing thawing cycles.The experimental results show that under the same freeze-thaw cycles and stress levels,the degradation of mechanical properties of ordinary RC beams was much larger than that of TRC composite beams.This showed that the U-type TRC-SIP-F outside the TRC composite beam body could delay the cracking process of the beam body,and U-type TRC-SIP-F could effectively slow down the rate of chloride ion erosion and reduce the damage degree of the freeze-thaw cycle to the beam body.The number of freeze-thaw cycles had the greatest influence on the deterioration degree of the TRC laminated beam.The more times the freezing and thawing cycle was,the more serious the damage degree of concrete was.Shear failure rather than reinforced beam failure was more likely to occur,which led to the worse condition of the ultimate bearing capacity.Moreover,with the increasing number of freezing and thawing cycles,the deterioration speed of the specimen was faster and faster.Compared with high concentration of Cl~-,the corrosion of concrete caused by low and medium concentration of Cl~-was more serious.The salt solution would produce enough ice pressure in the concrete during the freezing thawing cycle,so that the concrete would be seriously damaged and the overall performance of the component would be affected.(4)The formula of bending capacity of TRC composite beam after salt freezing was derived.The derived results agreed well with the measured values.