Predicting salt damage in practice: A theoretical insight into laboratory tests.

Abstract

Salt crystallization represents one of the major causes for the degradation of building and ornamental stone. As such, it has attracted the attention of researchers, who over the years have progressively unraveled most mechanisms involved in salt damage. Despite this mechanistic understanding, many questions subsist about how to quantitatively predict damage or its progression, and in particular how to relate performance on site to that in laboratory tests. In this context, a new RILEM TC 271-ASC has been started with the objective of defining laboratory tests that deliver more reliable predictions of field behavior. One deliverable of this TC is to provide a theoretical insight into this question based on recent progress on the understanding of salt damage. This paper presents a summary of this work, highlighting key aspects relating to crystallization pressure, chemo-mechanics and mass transport. Implications are discussed in relation to the most used accelerated salt crystallization tests in an attempt to better define which field exposure conditions that these tests best represent and may be used for, or define effective test procedures representing specific field conditions. A simple conceptual model for the development of salt damage is introduced. During an initial "induction" phase, transport of ions and accumulation of salt in the porous materials occurs without causing detectable damage until a critical point, termed "damage onset" is reached. Beyond this point, during the "propagation phase", the material degrades, typically losing strength and cohesiveness. The implications of these two phases are discussed in relation to the selection of appropriate salt weathering tests and conservation interventions.

Selection of Method of Chemical Analysis in Measuring the Salinity of Mineral Materials

“…Prolonged moisture of walls has an adverse effect on the functional properties of buildings, hinders conservation works and also affects the mechanical parameters [25]. Moreover, depending on the cation, sulphate salts are characterised by different crystallisation pressure and different preferential crystallisation site [12,13,26,27]. Therefore, their impact on the durability of bricks will vary.…”

“…Moreover, salt solubility is not a measure of aggressiveness of a given solution although it is true that salts with the highest solubility are more dangerous [10]. The main and direct cause of salt aggressiveness towards the mineral material is not the salt solution itself but first of all crystallisation of salt from this solution [8,[11][12][13][14][15].…”

Testing properties governing the durability of lime-based repair mortars

“…Two EU Projects ASSET (2000) and COMPASS (2001) gave a great impetus to research and precious knowledge acquisition [5,13]. Smart mathematical models are proposed for calculating excess crystallization pressure [14] and indices such as (Pe) [12], relating capillarity moisture with diffusion coefficient and drying rate. The concept that the drying behavior of a plaster substrate layer depends on the pore size distribution of both (plaster +substrate) is supported by researchers working separately.…”

Recommendation of RILEM TC 243-SGM: functional requirements for surface repair mortars for historic buildings

“…Ordinary Portland cements have SO3 content around 3% (wt.). Recent papers from a RILEM TC provide initial information on the nature and relevance of salt test methods [42,43].…”