DETERMINATION OF CRACK RESISTANCE OF CONCRETE ON THE BASIS OF DESTRUCTION MECHANICS

Abstract

Purpose The objective of the paper is to study and generalize the characteristics of heavy concretes crack resistance based on real experimental research, – the coefficient of stress intensity Kсexp, the coefficient of energy characteristic of effective surface energy γexp, opening the banks at the top of the crack δсexp and establishing the dependence of acoustic emission AE-SEq with the specified parameters of concrete crack resistance and in accordance with current standards. Methodology. To achieve this goal, a review and synthesis of scientific and technical sources were made and comprehensive experimental and analytical studies were conducted Kсexp, γexp ,δсexp and the dependences of acoustic emission are established AE–SEq with the specified parameters of crack resistance of concrete and in accordance with current standards. A series of experiments was made to study the concrete crack resistance, in particular, to determine the stress intensity coefficient (SIC). In parallel, the relationship with the measurement parameters of AE acoustic emission in heavy concretes of five series of different composition and strength was studied. Longitudinal and transverse deformations were measured with indicators, which made it possible to determine the Poisson’s coefficient V. Under load, fracture diagrams were recorded on a two – coordinate recorder in the coordinates "Force P-opening of the crack v on the line of force action". Results. The analysis of scientific and technical sources of domestic and foreign materials for determining the heavy concretes crack resistance is carried out. The characteristics of crack resistance of concrete various compositions and strength, in particular the coefficient of stress intensity, are obtained Kсexp of the coefficient of energy characteristic of effective surface energy γexp, opening the banks at the top of the crack δсexp and the corresponding dependencies are installed AE–SEq with the specified parameters of concrete crack resistance. The stress intensity coefficient is determined with the parameters α0, β0 when loading with concentrated forces at certain points of applying the load. The influence function of geometric parameters of the sample is also determined f(α0, β0,ε), which was determined by calibration curves. A diagram of calculating the energy balance and a graph of load changes from the intensity AE are obtained. Based on the P-v diagrams, a formula is obtained for determining δсtheor at the top of the crack and graphical dependency δс from change fctk. The experimentally known ratio of fracture mechanics is tested δсσ0=2γ. Scientific novelty. This paper summarizes a number of experimental and theoretical researching the heavy concrete crack resistance features based on fracture mechanics. In particular, the following was specified and established: stress intensity factor Kсexp surface energy coefficient ; opening the banks at the crack tip ; the dependences between АЕ–SEq with the specified parameters of concrete crack resistance are established; the classical relation of fracture mechanics for concretes is confirmed. In addition, based on the fracture mechanics approaches for five series of concrete disk samples the force energy γ and deformation crack resistance features are determined by independent experimental methods. Practical significance. The comparison of the specified approaches of fracture mechanics is carried out and satisfactory convergence of the received results for heavy concretes is established.