Marble decay caused by thermal expansion: microstructure-based mathematical and physical modeling

Marbles have been considered to be among the most important building materials since ancient times. Regarded as special stones, they are captivating because of their pureness, formability, and translucence. However, degradation of sculptures, architectural heritage, and façade stone made from marbles is problematic. Such deterioration of building stones depends mainly on ambient climate. Environmental conditions such as temperature changes, both increases and decreases, induce significant deterioration. The rock-forming minerals in marble, like calcite and dolomite, have large anisotropy in their coefficients of thermal expansion. Hence, apart from the expansion (or contraction) that results from heating (or cooling), internal residual stresses will develop in the stone fabric due to the thermal expansion anisotropy between the constitutive crystalline grains. These stresses can result in thermally induced microcracking, and an additional concomitant expansion. Such behavior is exacerbated by moisture due to moisture-assisted subcritical crack growth, and hence degradation can accumulate with cycling and over time, resulting in significant time-dependent deterioration. This research thesis presents the first systematic study of the prediction of degradation phenomena in marble structures caused by thermal expansion by applying numerical simulations and experimental techniques. The objective is to elucidate the influence of fabric parameters on factors that affect the marble degradation. Artificial microstructures with modeled textures as well as the real fabric of marble samples with different fabric parameters were examined. Microstructure-based finite-element simulations in combination with electron microscopy (EBSD technique), and experimental measurements of the thermal expansion behavior were used to study the influence of the rock’s fabric on thermal-elastic responses and the extent of microcracking. Additionally, in order to characterize the degradation potential of a marble, a volumetric extension index was developed as a decay index and was evaluated and validated from thermal expansion measurements under dry and water-saturated conditions for the investigated marble samples. The results revealed that certain combinations of fabric parameters such as lattice preferred orientation (LPO), shape preferred orientation (SPO), marble composition, grain size and grain-boundary fracture toughness have a significant influence on the thermal-elastic response of marble and on the onset and extent of microcracking. It was seen that dolomitic marbles are more resistance to thermal-related marble decay than are calcitic marbles with the same structure and fabric parameters. However, fabric parameters, especially SPO and LPO, also play an important role in the thermal behavior of marble and therefore should be taken into account for the characterizing the durability and stability of marble. Finally, it was shown that microstructure-based finite-element modeling provides excellent insight and elucidation of influences of rock fabric on the degradation phenomena of marble, since the results from simulations are in good agreement with experimental findings.