| During construction and operation,hydraulic buildings are often subjected to the impact abrasion of suspended and pushed masses,which not only has a serious impact on the safety and durability of the project,but also makes maintenance work difficult and capital investment large due to the complexity of its working environment.Therefore,in this paper,in view of the impact effect of large particle size nudging mass destruction,combined with the characteristics of hydraulic concrete structure mostly using coarse aggregate maximum particle size of 40mm two-graded aggregate concrete,choose its good adaptability to the length of 60mm new end hook type steel fiber,based on fractal theory,the study of steel fiber shape(3D,4D and 5D)and volume content(0%,0.5%,1.0%,1.5%and 2.0%)on the impact resistance of two-graded aggregate concrete and explored and analyzed the effect of free water in saturated water condition on its impact resistance,mainly as follows.(1)The effects of the shape and volume of steel fiber on the compressive strength and splitting tensile strength of two-graded aggregate concrete was studied through the tests of 42 150mm×150mm×150mm cube specimens in 14 groups.The results showed that:at the same volume dosing(1.0%),the more the number of steel fiber end hooks,the more obvious the enhancement effect on the compressive and splitting strengths,in which the compressive strength increased by 7%,19.8%and 21%,and the splitting strength increased by 47.3%,58.4%and 62%,respectively;when different volume dosing,the compressive strength of 4D steel fiber two-graded aggregate concrete increased,but there was no significant relationship between the compressive strength and the splitting strength.There is no significant relationship between the volume of fiber admixture and the maximum increase of 19.8%at 1.0%,while the splitting strength increases with the increase in the volume of fiber admixture and increases by 64.8%at 2.0%.(2)The effects of the shape and volume of steel fiber on the impact resistance of two-graded aggregate concrete was studied through the drop weight impact test of 112Φ150mm × h63mm cylinder specimens in 14 groups.The results show that the incorporation of steel fibers has a significant increase in the initial cracking impact energy and damage impact energy of the two-graded aggregate concrete,and increases with the increase in the number of steel fiber end hooks and the increase in the volume dose.The improvement was 424%and 1378%for 5D steel fibers(1.0%by volume)and 633%and 2543%for 4D steel fibers(2.0%by volume)under natural conditions(in natural environment after standard curing for 28 days)and 361%and 976%for 5D steel fibers(1.0%by volume)and 4D steel fibers(2.0%by volume)under water-filled conditions(water absorption saturation after 28 days of standard curing),compared with natural conditions,the reduction was 36%and 46%,respectively.The two-graded aggregate concrete with 4D steel fiber(2.0%by volume)improved by 457%and 2512%,33%and 27%lower,respectively,than under natural conditions,respectively.(3)Based on image processing technology and Matlab procedure,the impact of steel fiber two-graded aggregate concrete damage surface cracks was analyzed in dimension,and the influence of steel fiber shape and volume doping on the fractal dimension of surface cracks was discussed.The results show that there is an exponential relationship between the fractal dimension of the surface crack of steel fiber two-graded aggregate and concrete final crack damage and the shock energy consumption of steel fiber volume doping and final crack damage,and the relationship between crack development and residual impact resistance performance based on fractal dimension in the fall hammer impact process is given,and a new idea is provided for evaluating the impact resistance of fiber concrete by fractal theory. |
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