Research On Bond Properties Between Fly Ash Concrete And Bars Under The Freeze-thaw

As a green building material, fly ash concrete meets the requirements of sustainabledevelopment and environment protection. In the cold region of our country, the bondproperty between concrete and steel bar were destroyed after freezing and thawing.However, with the adding of fly ash, the durability of concrete structure has been improved.As there were few studies about the bond property of fly ash concrete in the freeze-thawenvironment, the test systematically studies above-mentioned one by combiningexperiment and theory.In this experiment, the effect of four factors―fly ash volumes, the bar diameter, therelative thickness of the protective layer and numbers of freeze-thaw cycle―to the bondproperties were considered. After sticking strain piece into the anchorage region of bar andpushing experiment, there are several main conclusions as fllowing:(1) From the study about the effect of the fly ash volumes to the bond properties, itcan be concluded that, With the increasing of fly ash volumes, there is a decline trend ofthe concrete strength and the ultimate bond strength between bar and concrete, there is aminimum displacement of the free part of bar when the volume is20%.(2) From the study about the effect of the bar diameter to the bond properties, whenthe diameter is14or16mm, the failure mode is mainly pull-out failure. With the increasingof diameter, the displacement of free part and the ultimate bond strength increases.Nevertheless, when the diameter is18or20mm, the failure mode is mainly splitting failure,with the increasing of diameter, the displacement of free part and the ultimate bondstrength decreases.(3) From the study about the effect of the relative thickness of the protective layer tothe bond properties, it can be concluded that, with the increasing of the relative thicknessof the protective layer, the ultimate bond strength firstly increases and then decreases.Especially, when the relative thickness of the protective layer is smaller than4.5, there is aproportional relationship between the relative thickness of the protective layer and the ultimate bond strength.(4) From the study about the effect of numbers of freeze-thaw cycle to the bondproperties, it can be concluded that, with the increasing of cycle number, the strength offree decreases, and when the cycle number is50, there is a significant decrease. When thecycle number is lower than75, the bond stress is locating in the anchorage region. At last,the phenomenon of stress concentration has been found in the loading part.In this test, after regression fitting the experimental data, the law between abovefactors and the ultimate bond strength, and the proposal about steel anchor of reinforcedconcrete in the freeze-thaw environment has been given. So the paper also can providetechnical reference to the fly ash concrete structure in north provinces of our country, andto subsequent study of fly ash concrete.