Study On Tensile Properties Of Basalt Fiber Reinforced Concrete Based On Fractal Theory

As one of the important indicators of the mechanical properties of concrete,the tensile property of concrete is not only the basis for the concrete structure design,but also the key parameter for evaluating the quality of concrete materials.The fiber reinforced concrete(FRC)refers to a new type of concrete material formed by the combination of fiber and concrete.The addition of fiber greatly improves the tensile mechanical property of concrete.With the study subject of different types of basalt fiber reinforced concrete(BFRC),this paper conducts an experimental study on axial tension,analyzes the failure mode,tensile stress,tensile deformation,etc.of specimens by relative principles of the fractal theory,and meanwhile discusses the factors impacting the improvement of the tensile property of concrete by fiber.The study contents are as follows:(1)To conduct an experimental study on the mechanical property of axial tension of BFRC with different fiber volume adding rates,and different fiber lengths,analyze the change law of BFRC tensile stress-strain curve at all stages,propose the characteristic relations of BFRC tensile stress-strain curve at all stages,and conduct the regression analysis by experimental data;to discuss the rules influencing the BFRC tensile mechanical property indicator and fractal characteristics of tensile fracture face by the fiber length and fiber volume adding rate.The results show that:the fiber volume adding rate and fiber length both improve the first crack strength,yield strength,first crack sign strength of tensile,yield sign strain,etc.of concrete in varying degrees;the fractal dimension can better characterize the improvement of concrete tensile failure by fiber.(2)To conduct a theoretical analysis of the tensile property of concrete by the method of fractal theory.First,based on the statistical theory,the distribution function of concrete tensile deformation is introduced to characterize the distribution law of concrete tensile deformation along with its measurement length,and the fractal expression of the distribution function is obtained by derivation.Second,the microscopic composition of concrete is analyzed,and the relation between multi-fractal strain and apparent strain of tensile specimens of concrete is derived by the multi-fractal theory,and the corresponding expression is obtained.Third,the damage constitutive relation for the fractal damage of concrete extension is established based on the energy loss,and meanwhile the fractal damage constitutive model of concrete tension conforming to the Sierpinski Tetrahedron is established based on this.(3)To analyze the multi-fractal characteristics of BFRC tensile failure carrying surfaces at different damage scales,and obtain the multi-fractal spectrums of different types of BFRC failure carrying surfaces;to introduce the fractal dimension of tensile damage of concrete to characterize the mechanical behaviors of tensile damage of concrete,establish the fractal damage constitutive model of concrete tension based on the equivalent strain method,and obtain the damage constitutive relation for the fractal damage of BFRC tension by combing with the study data of the experiment.(4)To introduce the fiber equipartition factor and fiber clustering content to characterize the fiber clustering effect,establish four kinds of ideal fiber clustering models,and derive the corresponding analysis formula of fiber equipartition factor;to analyze the change law of fiber equipartition factor along with the number of clustering fibers,and the number of peripheral fibers among clustering fibers;to establish the complex tensile strength prediction model considering the fiber clustering effect,and make a comparative analysis with the experimental results.The results show that:the complex tensile strength considering the fiber clustering effect is closer to experimental results,and satisfies the requirements of tensile strength prediction.(5)To respectively introduce the fractal dimensions of cross sectional area of clustering fiber,and cross sectional perimeter of clustering fiber,and obtain the corresponding expressions of fiber equipartition factor,and fiber clustering content;to derive the fractal expression of complex tensile strength considering the fiber clustering effect by combing with the composite material theory;to make numerical calculation of indicators such as fiber equipartition factor,fiber clustering content,and complex tensile strength based on the fractal theory.The comparative analysis with the experimental results shows that:the calculated value of complex tensile strength based on the fractal theory is closer to the experimental value.