The chemomechanics of crystallization during rewetting of limestone impregnated with sodium sulfate

摘要

Breakdown of porous materials by salts occurs when growing crystals exert pressure on the pore walls, inducing stress in the material that exceeds its tensile strength. In this work, we quantify the mechanical stresses caused by a particularly destructive mechanism: the dissolution of an anhydrate (thenardite, Na_2SO_4) followed by precipitation of a hydrated salt (mirabilite, Na_2SO_4·10H_2O). Stresses are measured using a composite specimen consisting of a plate of glass bonded to a plate of limestone (CaCO_3) whose pores are impregnated with thenardite. As water wicks into the limestone, thenardite dissolves and mirabilite precipitates. The limestone expands from the pressure exerted by the salt resulting in deflection of the composite, and the stresses can be obtained from an elastic analysis. Synchrotron x-ray diffraction reveals the dissolution-crystallization rate. Numerical modeling shows that the stresses are affected by the kinetics of crystallization and dissolution, permeability, and mechanical properties of the stone, allowing us to determine the amount of salt that causes material fracture.