Experimental Study On Fracture Properties Of Basalt Fiber Reactive Powder Concrete

Basalt fiber reinforced reactive powder concrete?BFRPC?is a new type of composite building material.It has the advantages of high compressive strength,good toughness and low permeability.The research and application of basalt fiber reinforced reactive powder concrete is still in the primary stage.It can be seen that the study on fracture behavior of BFRPC is no more from the existed research results.To explore the releationship between stress characteristics and crack development of basalt fiber reactive powder concrete,and reveal the development mechanism of cracks and its quantitative description is a basic topic in the theory of concrete structures.So this paper carried out the following studies to determine the failure criterion of the fracture,and reveal the fracture development regularity and cracking characteristics.This study set of five kind of BFPC specimens and baslat fiber volume ratio are0%,0.5%,1%,1.5%and 2%respectively and mainly performs the research on the fracture mechanics properties of basalt fiber reinforced reactive powder concrete.Three-point bending test is used to determine the flexural strength and fracture toughness.The load-displacement of midspan curve and the load-CMOD curve are drawn according to the test results.It can been seen from these two curves that the ultimate load increases with the increasing of basalt fiber content.Based on the test results,fracture energy,characteristic length and ductility index were calculated.The results show that the three fracture parameters increase monotonically with the increasing of fiber content.Compared with plain reactive powder concrete,the three parameters increase by 7.79,7.65,3.6 times respectively.Fracture toughness is an important parameter which measures the fracture properties of the material.This paper abandoned fracture toughness which is based on early fracture model.This toughness is used to characterize the turning point from the crack extension phase to extended instability phase.Double-K fracture model which is proposed by Xu Lang and Reinhardt is not only retains the fracture toughness in the early fracture model but also proposes a new fracture toughness:initiation fracture toughness.Fracture toughness control the turning point from the linear elastic to the non-linear stage.Double-K fracture model provides a comprehensive theoretical foundation to understand the fracture process of concrete.In this paper the initial fracture toughness and unstable fracture toughness will be discussed deeply.Elastic modulus of BFRPC test specimen are obtained according to the P-CMOD curves at first,then the_ca,CTODC andK^c_Ic are calculated according to elastic modulus.Unstable fracture toughness can be calculated directly with the formula of linear elastic fracture mechanics.The initiation toughness can be obtained according to relationship among cohesive toughness,initiation toughness and unstable toughness.The regulation of fracture parameters associated with fracture toughness is as follows:K_Ic^{in i} increases monotonically with the increasing of BF.The value ofK_Icⁱⁿⁱ gets maximum when the volume ratio of BF is 2%,and this value is 0.23 times higher than RPC without BF._ca,K_Ic^unandCTOD_c do not change monotonously with different basalt fiber dosage,but this three fracture parameters with BF are all higher than reactive powder concrete without BF on the whole.They all get maximum when the volume ratio of BF is 2%and increase by 10.17,10.34 and 31.35 times respectively at most.It indicats that BF can improve the ductility of reactive powder concrete.In summary,optimal dosage of BF for the fracture properties of BFRPC is2%.This paper also studies the basic mechanical properties of BFRPC.In the basic mechanical properties of the test includes cube compression test,prism compression test,splitting tensile test.The test results show that the axial compressive strength,prism compressive strength,splitting tensile strength all gradually increases when the balalt fiber volume fraction changes from 0%to 1%,then the intensity decrease when basalt fiber content vary from 1%to 2%.It can be clearly seen that the basalt fiber best content is 1%.This three trength were increased respectively 10.56%,7.9%,38.4%than the reactive powder concrete without baslat fiber.