Experiment And Research On The Impact Toughness And Crack Resistance Of The Shrinkage Compensating Concrete Reinforced By Nanometer SiO₂and Steel Fiber

In this paper, set the expansive concrete in which the expansive agent content is6%of the amount of cement as the basic proportion, add nanometer SiO2and steel fiber, carry on the orthogonal experiment. Study the impact toughness and crack resistance of the shrinkage compensating concrete by adding nanometer SiO2and steel fibers. And contrast the compressive and splitting tensile strength with the shrinkage compensating concrete which contain Micro silicon powder in test.In the Impact test, set nanometer SiO2content and steel fiber volume fraction as the variable, carry on the orthogonal experiment, in which the Mix amount is16and the total amount of round cake block is96. According to the United States ACI544committee recommended test methods, used the self-designed free falling hammer impact test device. The research shows that, adding nanometer SiO2singly into the shrinkage compensating concrete, the frequency of the initial crack and the final failure will reach the largest number when its content is0.6%, it means adding nanometer SiO2singly can not improve the brittleness of concrete. Adding steel fiber singly into the shrinkage compensating concrete, with the increase of steel fiber volume fraction, the frequency of the initial crack and the final failure increasing,and the energy difference between initial crack and final failure damage and crack impact will also be larger. The energy difference between initial crack and final failure when the steel fiber volume fraction is0.8%is9.1times of the concrete without steel fiber. The energy difference between initial crack and final failure when the steel fiber volume fraction is1.2%will rise to15.1times of the concrete without steel fiber. And the energy difference between initial crack and final failure when the steel fiber volume fraction is1.6%will run up to maximum, rise to20.3times of the concrete without steel fiber,it means adding steel fiber will improve the brittleness of concrete obviously. Adding nanometer SiO2and steel fiber at the same time, the enhancement effect of impact toughness of the shrinkage compensating concrete will be better, the energy difference between initial crack and final failure will run up clearly. compare to no adding nanometer SiO2, when the steel fiber content is0.8%,1.2%and1.6%, the energy difference will respectively improve31.9%,24.5%and33.7%. In the stage from initial crack to final failure, the steel fiber turns into the main medium for the impact load. And by adding nanometer SiO2, it can enhance the bond strength between steel fiber and concrete matrix, improve the cohesive force between the two, and it directly affect the actor on strength and toughness of concrete by adding steel fiber.The nanometer SiO2and steel fiber improve the impact toughness of shrinkage compensating concrete.The crack resistance of the shrinkage compensating concrete will be improved obviously by adding nanometer SiO2and steel fiber evenly, and the anti-split effect will be better by adding steel fiber than adding nanometer SiO2.The early anti-crack grade of the shrinkage compensating concrete is three-grade by adding nanometer SiO2singly and the early anti-crack grade of the shrinkage compensating concrete is second-grade by adding steel fiber singly. Adding nanometer SiO2and steel fiber into the shrinkage compensating concrete at the same time, it can function all the advantage of nanometer SiO2and steel fiber, the anti-split effect will run up to the best, and the early anti-crack grade will reach first-grade.Adding micro silicon powder and nanometer SiO2respectively into the shrinkage compensating concrete and steel fiber shrinkage compensation concrete, the compressive and splitting tensile strength of these two kinds of concrete will be enhanced and they will all get the strength at early time. The enhancement effect and early strength effect will be clearer on compression. And adding micro silicon powder and nanometer SiO2respectively into the shrinkage compensating concrete, the enhancement effect and early strength effect will be more obvious than steel fiber shrinkage compensation concrete.After adding micro silicon powder, the compressive strength of the concrete of28d can be increased by2.1%, the compressive strength of7d will reach64.3%of28d. While adding nanometer SiO2, the compressive strength can be increased by9.4%, the compressive strength of7d will reach71.7%of28d. It means that nanometer SiO2can enhance the compressive strength of compensating shrinkage concrete more significantly than micro silicon powder at the same amount of mixing, and also the early strength effect is more obvious.