Influencing Factors Of Drawing Mechanical Properties Of Reinforced Concrete Specimens

In this paper,based on the existing experimental data and the same concrete mix ratio,three batches of specimens are prepared to test and analyze the pull-out mechanical properties of reinforced concrete by selecting the factors which have great influence on the bond performance,such as the type of reinforcement,the degree of corrosion,the number of freeze-thaw cycles and the size of specimens.The main conclusions are as follows:(1)After the pull-out test of the test block group with different kinds of steel bars,the different surface shape,diameter and yield strength of steel bars will influence the ultimate tensile capacity measured by the pull-out test.Especially,the increase of the diameter from 12 mm to 16 mm and yield strength from 335 MP to 400 MP of steel bars will increase the ultimate tensile capacity by 1.7 times and 2.1 times as much as the original.The influence of steel bar types on the pull-out mechanical properties of reinforced concrete blocks can be summarized as follows: yield strength of steel bar > diameter of steel bar > surface shape of steel bar.(2)The ultimate tensile strength of reinforced concrete specimens varies with the change of steel corrosion rate: before the corrosion rate reaches 5%,the corrosion of steel will increase the ultimate tensile strength of specimens;when the ultimate tensile strength increases from 0% to 5%,then decreases to 3%,where the ultimate tensile strength of reinforced concrete specimens reach the maximum value.After 5% corrosion rate,the ultimate tensile strength of rusted reinforced concrete specimens is lower than that of non-rusted reinforced concrete specimens.(3)Unlike the effect of corrosion on the ultimate tensile strength of reinforced concrete specimens,freeze-thaw cycling only has cracking effect on the tensile properties of specimens,and the ultimate tensile strength of specimens decreases with the increase of freeze-thaw cycles.When the freeze-thaw cycle reaches 50 times,the ultimate tensile capacity of reinforced concrete specimens decreases by 50%,and when the freeze-thaw cycle reaches 100 times,the ultimate tensile capacity of specimens is even less than 2KN.The size effect of the test block is equivalent to the influence of the thickness of the protective layer.Compared with the corrosion effect of 100 mm x 100 mm x 100 mm x 100 mm,150 mm x150 mm x 150 mm has no improvement on the ultimate tensile strength of the test block.It only makes the ultimate tensile strength-corrosion rate curve shift and strengthen the tensile strength of specimens of early corrosion to protect the test block.(4)The stress-strain law of reinforced concrete surface is analyzed by digital image technology.It is found that in the process of drawing,the concrete on the surface of specimens with different types of reinforcing bars and specimens with different freeze-thaw cycles changes from tension to force-free;while in the process of drawing,the concrete on the surface of specimens with different corrosion rates changes from compression to force-free.(5)Through LINK3 D numerical simulation,the real-time development of displacement field,interface stress and strain,and crack during drawing process is found.The results are compared with the physical experimental data to verify and explain the phenomena in the experiment,such as splitting failure of the threaded steel bar in the drawing process.