The characterization of marble by cyclic compression loading: experimental results

The degradation process of natural stones is reproduced by performing low-cycle-number, uniaxial compression fatigue tests on three different qualities of marble. A typical feature of fatigue tests is that repetition of loading cycles produces a progressive accumulation of permanent strain in the specimen, rather than any significant decay in the material's elastic moduli. This permanent deformation has been recognized as both due to the opening of micro-cracks as well as due to shear-like mechanisms. The relative contribution of each of these mechanisms to the overall behaviour of the materials depends heavily upon the orientation of the rift plane of the specimen, that is, whether the specimen has been cut with its axis orthogonal to the marble rift plane or parallel to it. In the first case, shear-like deformations are the most evident signs of the failure mechanism, while in the second, the marked increases in volume due to micro-cracking are evident early. Scanning electron microscope studies performed, evidence that there are two different phases in the marble's behaviour: the first one is characterized by calcite grain decohesion, that is, the grains remain integral, but detach along their interfaces upon repeated load cycles (grain de-cohesion); while in the second stage, there are evident signs of transgranular micro-cracking. These two distinct phases are shown to correlate with different stages in the material's macroscopic response to cyclic loading. Copyright © 2000 John Wiley & Sons, Ltd.