Bending Behavior Of Recycled Concrete Beams With Waste Fibers Under Load-salt Erosion Conditions

With the rising of construction industry and manufacturing industry,a large number of waste concrete and waste fibers are produced,and their recycling is one of the hotspots of research at home and abroad.In the offshore,near brine lake or in deicing environment,reinforced concrete structures will be eroded by chloride salt,which make the basic properties of materials gradually deteriorate.In the process of salt erosion,these components bear also loads at the same time,which is different from the unilateral damage only caused by salt erosion.The both of the causes promote and influence each other.Concrete beams are the basic components of buildings and structures.In conclusion,it is very important and meaningful to study the flexural behavior of recycled fiber reinforced concrete beams under load-salt corrosion conditions.In this paper,the test is divided into three parts.The first part,waste fiber recycled concrete beams with different mix ratios are dealt with the load-salt corrosion.Load application:the strain value is measured by static strain gauge,and the load value is calculated back.Chloride corrosion:soaking in 3.5%NaCl solution,accelerating the corrosion process by electro-corrosion;The second part,static load tests are carried out on corroded beams.The purpose of the test is to obtain the residual bearing capacity,deflection change,steel bar strain and concrete strain;The third part,the quality of the rebar in concrete beam before and after corrosion is measured and the corrosion rate of steel bar is calculated.The following conclusions are drawn from the experiment:(1)The corrosion rate of recycled concrete beams with waste fibers increases with the increase of salt corrosion time,but with the load-salt corrosion time increases gradually,the corrosion rate of steel bars slows down.The corrosion rate increases with the increase of load grade.The higher the replacement rate of recycled aggregate is,the higher the corrosion rate becomes.The addition of fiber inhibited the erosion of chloride ions.(2)The strain of concrete increases linearly,and the compressive strain and tensile strain of concrete increase proportionally,which shows the concrete beam meets the assumption of plane section under the condition of load and chloride ion.(3)The ultimate bearing capacity is inversely proportional to the pre-applied load grade and duration,because the increase of these two factors will lead to serious corrosion of steel bars and decrease of ultimate bearing capacity;the bearing capacity decreases with the increase of replacement rate of recycled aggregate;the incorporation of waste fibers will restrain the reduction of the bearing capacity of beams.(4)Compared with the load-deflection curve,the more serious the corrosion of steel bar is,during the loading process the greater the deflection will be.That is,with the corrosion time and the time load increasing,the deflection growth rate become faster.(5)The higher the load grade is and the longer the salt erosion time is,the larger the fractal dimension becomes;the higher the replacement rate of recycled aggregate is,the larger the fractal dimension becomes;but with the number of the waste fiber increasing,the fractal dimension decrease first and then increase;and the fractal dimension is proportional to the graded load of the beam.(6)Referring to the formulas for calculating the bending capacity of cross section of waste fiber recycled concrete beams and salt-corroded reinforced concrete beams,the formulas for calculating the bending capacity of cross section of waste fiber recycled concrete beams under load-salt corrosion conditions are derived.