Theoretical evaluation of the tensile strength of pet fibroconcrete

Abstract

By calculating the bearing capacity of the elements of PET-fiber concrete structures, it is necessary to determine the tensile strength of this material. There are two cases of tensile failure of fiber concrete. In the first case, part of the fiber is torn, and part is pulled out, and in the second - the entire fiber is pulled out. If the required fiber anchoring length is less than half its length, then the first case of tensile failure of fiber concrete is realized, and if this condition is not fulfilled, then the second case is realized. The required length of anchoring l_fb depends on the coefficient that takes into account the anchoring of the fiber η_f, so its experimentally justified purpose is important, since it will affect the correctness of the calculation of both the tensile strength of PET- fiber concrete and the bearing capacity of elements made of this material. In this regard, experimental studies of the adhesion of PET fiber to fine-grained concrete were performed and recommendations were developed for calculating the tensile strength of PET-fiber concrete.

 The research program involved the production and tensile testing of a PET- fiber with a cross-section of 3 x 0,2 mm, embedded in the end of a 100 x 50 x 50 mm prism with a length of 10, 15 and 20 mm. For each of the classes of concrete (C20/25, C25/30 and C30/35) and each fiber laying length, 6 twin samples were manufactured and tested. Thus, a total of 54 samples were tested.

According to the results of experiments on pulling PET- fiber from concrete prisms, a coefficient that takes into account the anchoring of the fiber η_f, which is equal to 1,25, was determined. Determination of the length of PET- fiber is ubstantiated, taking into account the results of tensile tests. It is recommended to appoint a fiber with dimensions of 40 x 3 x 0,2 mm. It is proposed to calculate the tensile strength of PET- fiber concrete by analogy with steel fiber concrete. The corresponding formula can be used to preliminarily estimate the tensile strength of PET fiber concrete, and then refine it after testing PET- fiber concrete tensile samples. It is shown that the tensile strength of PET fiber concrete with a fiber reinforcement ratio of 0,02 is lower than the strength of concrete. Therefore, it is impractical to use PET- fiber concrete in stretched elements, unlike bent ones.