Experimental Study On Crack Resistance Of Nylon Fiber Self-compacting Concrete Beams

With the modern building shape more and more novel,more and more steel bars inside the members,the reinforcement interlaced with each other,complex and dense,make the construction of concrete more and more difficult,the requirements of the pouring workers are also becoming higher and higher.In order to overcome this difficulty,self-compacting concrete emerged as the times require.Self-compacting concrete with its own high flow degree,relying on gravity automatic filling in the construction process,does not need to vibrate,so the difficult problem of the complex component pouring is solved.As a by-product of industrial fly ash,mineral admixtures such as slag and silica fume are also used to replace cement as cementing materials and are widely used in self-compacting concrete.However,the self-compacting concrete needs high sand rate and large amount of cementing materials in the process of preparation,which leads to the increase of its own shrinkage rate,and it is easier to produce cracks than ordinary concrete.According to the research results,adding fiber into concrete can effectively restrain the formation of cracks,and most of the fibers have water absorption,which will seriously affect the working performance of self-compacting concrete.By consulting a lot of data,the author found that nylon fiber had no obvious effect on the fluidity of high fluidity concrete.In order to improve the crack resistance of self-compacting concrete,the basic mechanical properties of the self-compacting concrete and the crack resistance of the beam are analyzed by the method of adding different length and amount of nylon fiber in this paper.The test results are as follows.(1)The test of self-compacting concrete's working performance was carried out by adding nylon fiber into the test of T500 collapse extension degree J ring test,and L-shaped groove test of self-compacting concrete.The experimental results show that the nylon fiber has little effect on the workability of the self-compacting concrete.(2)The concrete cube test block was tested by single or mixed fiber with different length and quantity.It was found that the compressive strength of self-compacting concrete was improved by adding nylon fiber.When add 0.2%and 12mm length nylon fibers(group N6),the compressive strength increased most.The tensile strength of self-compacting concrete can be improved by adding nylon fiber.The increase of splitting tensile strength in N9 group is the maximum.(3)Through the experimental study on the crack resistance of self-compacting concrete beams with nylon fiber.It is found that the failure modes of self-compacting concrete beams with nylon fibers are basically similar to those of self-compacting concrete beams without nylon fibers.The cracks are produced from the tensile zone in the middle span of the beam and extend vertically,and the width of the crack becomes wider with the increase of the load.And there are slight oblique cracks between the loading point and the bearing,until the concrete in the upper compression zone produces cracks and falls off,and the specimens are destroyed.Adding fiber has little effect on the ultimate load of self-compacting concrete beam,but it will reduce the number of cracks(The specimen beams with single 6mm nylon fiber produced the least cracks),reduce the maximum crack width(The crack width is the smallest when nylon fiber of different length is mixed with equal amount),reduce the deflection of member beams(The deflection of nylon fibers with different lengths is minimum when the same amount of fiber is mixed with the same amount of fiber)and strain reduction of steel bar in mid span(The strain of tensile steel bar is minimum when nylon fiber of different length is mixed with equal amount).(4)Based on the experimental results of fiber self-compacting concrete beams,correction coefficients K and N are introduced to modify the formula of maximum crack width and deflection of members in the Code for Design of concrete structures.The formula for calculating the maximum crack width and deflection of nylon fiber self-compacting concrete beam is obtained.(5)The finite element analysis of nylon fiber self-compacting concrete beam was carried out by using ANSYS software.The stress of concrete and steel bar,the development of crack,the load-deflection curve were obtained when cracking and yielding.It is concluded that the crack load and yield load agree well with each other,which indicates that the software is suitable for the analysis of the mechanical behavior of the members.element Analysis of Nylon Fiber Self-compacting concrete Beams with ANSYS.By comparing the simulated values with the experimental values,it is found that the software is basically consistent with the experimental data,which indicates that the software is suitable for the mechanical performance analysis of the components.