Fracture parameters of high strength concrete-an experimental study

Abstract

ACI 446.1R-91 (Re-approved 1999) strongly recommends the application of fracture mechanics principles to the quasibrittle material like concrete. The behaviour of concrete is governed by the fracture parameters viz., fracture energy (GF ) and effective length of fracture process zone (Cf ). Determination of these fracture parameters for normal strength as well as high strength concrete is essential to characterize the degree of brittleness of concrete. The present paper analyses the size dependency of the fracture energy (GF ) and the effective length of fracture process zone (CF ) of concrete determined as per the Bazant’s Size effect method (SEM) and RILEM Work-of-fracture methods (WFM). The fracture parameters (GF and Cf ) are determined by measuring the maximum loads of geometrically similar notched high strength concrete (78MPa) specimens of different sizes in a size ratio of 1:4 with different notch depths (a0/d = 0.10, 0.15 and 0.20) under three point bending through load-deflection curves. The variation of both the fracture energy and the effective length of fracture process zone as a function of the specimen size and notch depth were determined using Bazant’s Size effect method and RILEM Work-of-fracture method. Fracture energy and Fracture process zone length determined by Size effect method are found to be decreasing with the increasing notch depth ratios. Fracture energy calculated using Work-of-fracture method is increasing with the increase in size of specimen and decreasing with the increasing notch depth ratios.