Damage in porous media due to salt crystallization

TL;DR

This study explores how salt crystallization causes damage in porous sandstones, highlighting the different effects of sodium sulfate and sodium chloride based on their crystallization behaviors and interactions with the stone.

Contribution

It demonstrates that the damage mechanism is driven by the crystallization kinetics and interfacial properties of sodium sulfate, unlike sodium chloride which does not cause damage.

Findings

Sodium sulfate causes significant damage due to hydrate formation and rapid cluster growth.

Sodium chloride does not cause damage as it forms only anhydrous crystals.

Damage correlates with pore saturation and salt crystallization dynamics.

Abstract

We investigate the origins of salt damage in sandstones for the two most common salts: sodium chloride and sulfate. The results show that the observed difference in damage between the two salts is directly related to the kinetics of crystallization and the interfacial properties of the salt solutions and crystals with respect to the stone. We show that, for sodium sulfate, the existence of hydrated and anhydrous crystals and specifically their dissolution and crystallization kinetics are responsible for the damage. Using magnetic resonance imaging and optical microscopy we show that when water imbibes sodium sulfate contaminated sandstones, followed by drying at room temperature, large damage occurs in regions where pores are fully filled with salts. After partial dissolution, anhydrous sodium sulfate salt present in these regions gives rise to a very rapid growth of the hydrated phase of sulfate in the form of clusters that form on or close to the remaining anhydrous microcrystals. The rapid growth of these clusters generates stresses in excess of the tensile strength of the stone leading to the damage. Sodium chloride only forms anhydrous crystals that consequently do not cause damage in the experiments.