Assessing energy balance via seismic and mechanical observations in high temperature induced crack damage in marbles

Assessing the rock physical and mechanical behavior under different temperatures has become of utmost importance. It is well known that thermal stresses induce significant crack damage in rocks due to thermal expansion or phase transformation and volume changes. Quantifying and forecasting the evolution of rock physical and mechanical parameters with temperature is thus crucial for evaluating rock integrity in many applications such as geothermal fields, nuclear waste storage, wildfire or volcanic processes. In marbles the degree of previous exposure to temperature and the chemical composition (i.e. calcite vs dolomite) plays a key role for controlling the mechanical evolution under temperature. Moreover separating out the energy contribution provided by anelastic processes driving crack damage and elastic reversible deformation under increasing temperature remains an open challenge. With these aims, three sample sets of marbles with different contents of calcite and dolomite from two Brazilian quarries were tested under different temperature conditions (from room temperature up to 600 degrees C). A marked increase of thermal cracking was observed after 400 degrees C, accompanying mass loss up to 1% and porosity increase. Moreover, a significant drop in seismic wave velocities, uniaxial compressive strength and electrical resistivity, in wet conditions, was also detected. Spectral behavior from seismic traces and energy dissipation from stress-strain curves were analyzed. A dominance of the dissipated energy compared to the elastic one was observed and related to the generation of new fracturing surfaces. This hypothesis was supported by the spectral behavior showing multiple scattering effects in the high frequency components, with an increase in attenuation. The results suggested that the percentage of dolomite has a high influence on the mechanical behavior even at low temperature, mirroring the prevalence of brittle processes in dolomitic marbles. This study represents a comprehensive benchmark for the study of effect of temperature on rocks because of its multidisciplinary and multimethod approach and the demonstrated sensitivity to subtle textural changes. Moreover, it provides a reliable tool for crack damage analysis at each thermal stress.