The Role of Calcite Dissolution and Halite Thermal Expansion as Secondary Salt Weathering Mechanisms of Calcite-Bearing Rocks in Marine Environments

Javier Martínez-Martínez,David Benavente,Anna Arizzi

doi:10.3390/min11080911

Javier Martínez-Martínez, David Benavente + Show 1 more

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https://doi.org/10.3390/min11080911

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Abstract

This research focuses on the analysis of the influence of two secondary salt weathering processes on the durability of rocks exposed to marine environments: chemical dissolution of rock forming minerals and differential thermal expansion between halite and the hosting rock. These processes are scarcely treated in research compared to salt crystallisation. The methodology followed in this paper includes both in situ rock weathering monitoring and laboratory simulations. Four different calcite-bearing rocks (a marble, a microcrystalline limestone and two different calcarenites) were exposed during a year to a marine semiarid environment. Exposed samples show grain detachment, crystal edge corrosion, halite efflorescences and microfissuring. Crystal edge corrosion was also observed after the laboratory simulation during a brine immersion test. Calcite chemical dissolution causes a negligible porosity increase in all the studied rocks, but a significant modification of their pore size distribution. Laboratory simulations also demonstrate the deterioration of salt-saturated rocks during thermal cycles in climatic cabinet. Sharp differences between the linear thermal expansion of both a pure halite crystal and the different studied rocks justify the registered weight loss during the thermal cycles. The feedback between the chemical dissolution and differential thermal expansion, and the salt crystallisation of halite, contribute actively to the rock decay in marine environments.

Highlights

Rock weathering by salt crystallization is considered one of the most important processes acting on the building stones in monuments under marine environments [1,2,3,4]
Halite can crystallise only when the environmental relative humidity is lower than its critical deliquescence point (75.3%) [7]
Notwithstanding, several authors consider that halite damage is linked to other secondary weathering mechanisms such as thermal expansion [11] and/or the dissolution of the host rock, mainly in the calcite fraction [12,13]

Summary

Introduction

Rock weathering by salt crystallization is considered one of the most important processes acting on the building stones in monuments under marine environments [1,2,3,4] In these cases, halite (NaCl) is the most frequent, if not the only, mineral phase observed in efflorescences and subefflorescences [4,5]. Notwithstanding, several authors consider that halite damage is linked to other secondary weathering mechanisms such as thermal expansion [11] and/or the dissolution of the host rock, mainly in the calcite fraction [12,13] These other two decay processes have received much less attention than the salt crystallization effect, despite the fact that the effectivity of the last one is thrown into question

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