Thesis: Stone decay by salt crystallization (2007)

Title: Multiscale study of stone decay by salt crystallization in porous networks
Author: Matthieu Angeli
University: Université de Cergy Pontoise
Year: 2007
Type of document: PhD thesis
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Link: http://archives-ouvertes.fr/...


Abstract:

Crystallization of soluble salts in porous networks is a major source of decay for natural stones. The objective of this thesis is to specify this salt decay mechanism in the particular case of sodium sulphate crystallization. The basis of this work is to follow the evolution of samples of nine sedimentary stones of various origins (two biodetritic limestones, one detritic limestone, one lacustrine limestone, three quartz-rich sandstones and two layered shaly sandstones) during accelerated ageing tests. First, the mechanism of sodium sulfate crystallization is studied thanks to thermal monitoring of the samples. Different crystallization sequences are proposed to explain the decay during the cycles. Then a new way of quantifying salt decay in the long term is proposed, taking into account the hydromechanical properties of the stones. The importance of the microstructures on decay (porous network tortuosity or connectivity, intragrain cracks) is also assessed thanks to a mercury porosimetry study. Finally, the influence of the environmental conditions on decay is also evaluated: evaporation and temperature directs both the location and amplitude of salt decay.

Table of Contents (short version):

Chapter I: Decay of natural stones
1. Weathering agents
2. Influence of the stone characteristics on weathering
3. Building characteristics
4. Human causes

Chapter II: Materials and methods
1. Overview of the studied stones
2. Microstructural studies
3. Hydromechanical properties
4. Accelerated ageing by salt decay

Chapter III: Salt crystallization
1. Experimental results
2. Theories of salt damage
3. Sodium sulphate

Chapter IV: Salt damage
1. Macroscopic experiments
2. Microscale experiment:Modification of the porous network by salt crystallization of experimentally weathered sedimentary stones

Chapter V: Influence of environmental parameters
1. Influence of capillary properties and evaporation on salt weathering of sedimentary rocks
2. Influence of temperature and salt content on the salt weathering of sedimentary rocks