Exploring the Mechanical Properties of Stone Heritage: Investigating the Effects of Low Temperatures on Ductile — Brittle Transition

Abstract

Ductility is the ability of a material to deform without suffering brittle failure under stresses. Once the load ceases, the acquired deformation maintains over time. On the contrary, a stone is fragile when, subjected to a load, it deforms but, if the load continues, it suddenly breaks. The ductile or fragile facets are homogeneous and isotropic in the stones, but they can mainly vary according to the operating load and temperature. At low temperatures, particularly in polar and subpolar climates, limestone used as a building material and in stone heritage presents an increase in the yield stress. The fragile behavior at lower temperature is higher than at room temperature (20 °C). In this research, the mechanical performance of the Portuguese Blue limestone in dry and saturated conditions and different operating temperatures was accessed in three steps of −20 °C, 0 °C, and + 20 °C. A series of mechanical properties (e.g., uniaxial compressive and flexural strengths, point load strengths index, abrasion resistance, anchorage rupture load, impact resistance, hardness, and abrasion resistance) have been estimated. The results evidence a general progressive increase of the stone’s strengths at low temperature. This is due to a stone decrease in thermal energy and associated reduction in atomic or molecular motion. The reduced motion results in a decrease in internal friction, and it allows the solid to become more rigid, leading to increased mechanical strength. Studying the mechanical properties at various steps of temperatures supports the correct selection of stone materials proper for specific environmental conditions and intended application.