Fracture Characteristics of Concretes and Cement-Stabilized Soil

Abstract

Application of fracture mechanics to the cracking and failure of concrete under stress has been receiving considerable attention. Most of these investigations have been directed towards the determination of the critical stress intensity factor or fracture toughness of concrete, mortar, or cement paste, failing in tension. Studies on an experimental determination of fracture toughness for concrete subjected to a compressive stress field have limited report so far. This project applies the concept of linear elastic fracture mechanics to investigate the Mode II shear type of failure of mortar and soil-cement. Fracture studies are particularly important in mortars and other cement composites as these materials are generally weak in shear. The fracture toughness is determined using both the stress intensity factor K approach and the strain energy release rate & approach. Both experimental and numerical methods are applied to determine the fracture toughness (K JT ) and results are compared on a range of specimen geometries. The numerical work was carried out on 100mm double-notched, single-notched and 150mm double-notched cubes and their stress intensity factors were determined using the displacement approach of the finite element method. The results of the numerical analysis indicate that with decreasing notch spacing and increasing notch depth the shear failure mechanism assumes the greater significance. The experimental work consisted of a series of fracture tests which were carried out on 100mm double-notched and single-notched cubes applied to both mortar and soil-cement. The standard 100mm concrete cube was modified and a testing arrangement developed which would appear to be suitable for the testing of cement composites for fracture mechanics purposes in the Mode II type of failure. All these tests were carried out on the INSTRON testing machine. The fracture toughness values were determined using the strain energy release rate utilizing the 'pop-in' load P, corresponding to the appearance of the first crack introduced on the load-displacement curves. The experimental results confirmed that linear elastic fracture mechanics can be applied to mortar and soil-cement.Good correlation between the stress intensity factor K approach and the strain energy release rate -6 approach is obtained provided correction for the machine/specimen interaction or the machine stiffness characteristics is applied to experimental results.

Date of Award	Jun 1986
Original language	English
Awarding Institution	Polytechnic of Wales