Research On Performance Degradation Of Corroded Steel Concrete Beams Corroded By Sulfate

The steel reinforced concrete structures in the actual projects are served in various natural environments.They may be affected by harmful substances such as chloride ions,magnesium salts(mainly magnesium sulfate and magnesium chloride),sulfates(potassium,sodium,ammonia sulfate,etc.),inorganic and organic acids,sulfurous acid,strong alkali,sugar,ammonium salts,petroleum products containing naphthenic acid,etc.and cause serious adverse reactions.These reactions may result in section steel corrosion and deterioration of concrete performance,which can affect the service life of a large number of structures.At present,countries around the world have paid a huge price to repair structural problems of steel reinforced concrete structures caused by insufficient durability.Therefore,in this paper,for the steel reinforced concrete beam,considering the corrosion of the internal steel and the sulfate corrosion of the concrete part,the degradation law of its mechanical performance(mainly bending performance)is studied,which provides reference for the durability analysis and design of the steel reinforced concrete beam.Specifically,the following studies have been carried out:(1)Steel reinforced concrete beams were designed and fabricated under four conditions(sulfuric acid ion concentration of 0%,3%,6%,10%;weight loss rate of section steel caused by corrosion of 0%,12%,28%,36%).Loading and data collection were carried out for each beam under 3M age.(2)The bending cracking and crack development laws of various types of steel concrete beams under various loads were observed and analyzed.The changes in bending capacity were summarized and the main reasons have been analyzed.Besides,the bending capacity checking method for steel reinforced concrete beams in the case of steel corrosion and sulfate corrosion were discussed.(3)The deflection values of various types of steel concrete beams under various loads were observed and analyzed.The changes in bending deformation performance were summarized and the main reasons have been analyzed.The bending stiffness calculation method for steel reinforced concrete beams in the case of steel corrosion and sulfate corrosion were discussed.The results show that with the appearance and deepening of sulfate corrosion degree of concrete and corrosion degree of section steel,the cracking load value of beam increases slightly at first and then decreases gradually;the load value corresponding to the crack expanding to the upper part in the cross section decreases gradually;the ultimate bending capacity of beam decreases gradually;the nonlinear section of mid span deflection load curve appears gradually in advance;the extension of beam The ultimate deflection value decreases gradually.Furthermore,the main reasons for these laws are analyzed:1)the increasing concentration of sulfate causes the continuous decrease of concrete strength and compression area;2)the continuous increase of corrosion degree of section steel results in the continuous decrease of its own strength and bonding effect with concrete;3)the corrosion of section steel and concrete results in the beam entering the plastic section earlier and earlier.At the same time,according to the research results,the checking method of flexural capacity and the calculation method of short-term flexural rigidity B_s of corroded steel reinforced concrete beams are given.