D. Scorza et alii, Frattura ed Integrità Strutturale, 34 (2015) 70-73; DOI: 10.3221/IGF-ESIS.34.06 69 Focussed on Crack Paths Investigation of Mode I fracture toughness of red Verona marble after thermal treatment Daniela Scorza, Andrea Carpinteri, Giovanni Fortese, Sabrina Vantadori, Daniele Ferretti, Roberto Brighenti Department of Civil-Environmental Engineering and Architecture University of Parma - Parco Area delle Scienze, 181/A, 43124 Parma, Italy A BSTRACT . The present paper aims to assess the effect of freeze/thaw cycles on fracture behaviour of a natural stone: the red Verona marble. A wide variety of specimen types and methods to determine Mode I fracture toughness of natural stones are available in the literature and, in this context, the model originally proposed for plain concrete, i.e. the Two-Parameter Model (TPM), is adopted. Such a method is able to take into account the slow nonlinear crack growth occurring before the peak load, typical of quasi-brittle materials, with the advantage of easy specimen preparation and simple test configuration. In the present paper, the atmospheric ageing is simulated by means of thermal pre-treatments consisting of freeze/thaw cycles. Experimental tests are carried out using three-point bending Single-Edge Notched (SEN) specimens, according to the TPM procedure. The effects of thermal treatment on both mechanical and fracture parameters are examined in terms of elastic modulus and fracture toughness, respectively. K EYWORDS . Mode I Fracture Toughness; Red Verona Marble; Thermal Treatment; Two-Parameter Model. I NTRODUCTION xterior building panelling made in natural stone was widely employed in the past, but it is used even today. One of the materials for such a panelling is the red Verona marble, a natural sedimentary stone, composed of lime- kilns and fine grains, with a colour variation from red to pink. Due to its formation, it contains defects such as inclusions and cracks. For such a reason, the evaluation of its mechanical properties is needed in order to ensure suitable safety of marble panelling in service. In particular, fracture toughness is able to describe the material behaviour related to fracture failure [1, 2]. While a single- value measure of such a mechanical parameter is appropriate for brittle materials, a resistance-curve (R-curve) is required in the case of quasi-brittle materials, as the red Verona marble is, to take into account that fracture resistance increases with crack extension, promoting stable crack growth before the load peak. Moreover, the above panelling is directly subjected to atmospheric agents during service life, of both chemical and physical nature, able to produce an ageing of the marble. Among the physical atmospheric agents, the temperature variations induced by seasonal range are also included. E