1. IntroductionThe specific aim of this paper is to find an experimental methodology which couldmeasure crack density in rock and its influence on the behaviour of the rockmaterial. The results of both experimental and numerical simulations showed thatrock behaviour is mainly ruled by crack density within a specific rock volume. Thebehaviour of a rock with di¤erent crack densities has been studied by severalauthors, from the theoretical point of view and through experiments.Experimental works (Sage, 1988; Rotonda, 1991; Franzini, 1995; Homard-Etienne and Houpert, 1989) have confirmed that a large, damaged area in a rockmaterial induced by heating determines variations of rock properties that areclosely connected to the degree of fracturing of the material. It has been shownthat the overall moduli of elasticity and tensile strength are influenced by thepresence of cracks (Yin and Ehrlacher, 1996; Wong et al., 1996; Laws andBrockenbrough, 1982; Bertagnini at al., 1993).2. Experimental StudiesSpecimens of two di¤erent types of marbles have been heated at di¤erent temper-atures to induce micro-cracking.The rock materials used in the testing campaign are two Italian ornamentalstones:
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