Compression testing and cracking of plain concrete

Abstract

Synopsis Flaws such as pores and voids are present in cement paste, and thereforein concrete. These flaws act as stress-raisers and cause the initiation of cracks in compressive stress fields. By analysing the stress state in compressive test specimens – recognizing that testing machines apply displacement conditions – and examining the stresses which may then exist around a spherical void, it is possible to explain the typical cracking patterns observed in such specimens. It is also possible to explain the cracking patterns and apparent changes in strength observed under externally applied biaxial stress conditions. This analytical work is restricted to elastic isotropic media and spherical voids, so the potential effect of aggregate particles is examined. Aggregate is shown to cause stress variation on a local basis, which may aid crack formation close to aggregate particles, andthe extension of cracks around aggregatelcement paste interfaces. It is concluded that cracks are initiated at flaws such as pores or voids. It is suggested that, since fracture mechanics deals with the fracture of heterogeneous non-brittle materials, it may be worth while considering the application of appropriate fracture mechanics methods to the fracture of concrete.