Physical principles and efficiency of salt extraction by poulticing

Pel, Leo L; Sawdy, Alison; Voronina, Victoria

doi:10.1016/j.culher.2009.03.007

Cited by 73 publications

(54 citation statements)

References 3 publications

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“…In the case of porous building materials salt extraction is typically accomplished by dry removal of the salt efflorescence and/ or aqueous methods-a common example of which being the use of poultices [1][2][3] to reduce salt content of the affected object. The extraction efficiency of a poultice is largely limited by the permeability and pore size distribution of both the poultice and the substrate [4,5]. Since the pore size distribution of a poultice can vary with its moisture content mainly due to its shrinkage during drying [5], it is difficult to tailor the pore size distribution of a poultice precisely to those required for optimum salt extraction efficiency.…”

Section: Introductionmentioning

confidence: 99%

Desalination of porous building materials by electrokinetics: an NMR study

et al. 2011

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This article presents the first non destructive measurements of salt ions transport through fired-clay brick during electrokinetic desalination using nuclear magnetic resonance technique. The effect of the strength of an applied electric field on the migration of salt ions is examined by varying the electrical potential gradients from 0.75-2 V cm -1 across the specimens. The measurements show that for electrokinetic to exceed ion transport by diffusion a minimum level of applied voltage is necessary. Below this threshold salt transport by diffusion is dominant over electromigration. The effect of advection on the salt transport is studied by introducing a hydraulic gradient across the specimen. The results show that advection is a major transport process in the materials studied. To assess the relative magnitude of the various active transport processes during electrokinetic desalination, a scale analysis on the basis of dimensionless numbers is presented. The value of these numbers determines which transport mechanism will dominate the desalination process in a given sample length and time scale.

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Section: Introductionmentioning

confidence: 99%

Desalination of porous building materials by electrokinetics: an NMR study

et al. 2011

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“…Lubelli et al (2010) analyzed by MIP the same type of poultice that has been applied in this research and determined that the PDS of BW40 cellulose poultice has a sharp peak at 15-20 m and the BC1000 cellulose poultice shows pores distributed in a slightly wider range between 10 and 30 m diameter. According to these authors pores of the poultice should be smaller than the pores of the substrate since for desalination the poultice needs to have smaller pores than those of the object for advection to take place (Pel et al 2010). Water content, grain packing, PDS and pore shape should be also considered in addition to adhesion in order to optimized desalination systems Bourgès and Vergès-Belmin (2008).…”

Section: Salt Reduction From Building Materialsmentioning

confidence: 99%

Preservation strategies for avoidance of salt crystallisation in El Paular Monastery cloister, Madrid, Spain

et al. 2010

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The cloister from El Paular Monastery is highly affected by salt crystallization of Mg-sulfates and presence of chlorides and nitrates. In order to avoid salt crystallization, the consequent deterioration of building materials and to keep the stability of some significant paintings that will be exposed inside the cloister, after the characterization of building materials and salts, three preservation strategies has been established based on architectural, pethophysical and physical-chemical features.The main source of Mg-sulfate salts is the high concentration of moisture and raising damp by capillarity, especially through the mortars which are the most porous materials. The dissolution of gypsum (Casulfate) as component of the mortars and its interaction with magnesium from the mortars, granite and dolostone give rise to Mg-sulfates that migrate through the porous building materials. The installation of a ventilation system would avoid the rising damp and hence the dissolution, mobilization and crystallization of salts. The salt reduction of building materials have been performed with cellulose poultices with pores between 15-20 m and between 10 and 30 m diameter. The monomodal distribution and smaller pores of dolostone (1 and 3 m) and mortars (0.1 and 10 m) is the cause of the lesser effectiveness of salt reduction in these materials compared to the granite, with a polymodal pore size distribution and pores distributed in the range 100-300 m. A higher number of cellulose poultice applications could increase the efficiency of this desalination procedure. However, there is no a warrantee of the total extraction of salts and the mixture of this cellulose poultice with clays to shift the PSD to smaller sizes would be more efficient to desalinate dolostone or mortar. The most suitable environmental conditions, inferred from thermodynamic model predictions (Runsalt software) and experimental work based on relative humidity transfer inside the stone, predict that to avoid salt crystallization these values would be 17º±2ºC and 55±2% RH.However, if there are some failures in the ventilation system or in the environmental control we recommend keeping the paintings to be exposed on the walls of the cloister inside glass cases. This research represents both a practical and experimental work useful for conservation scientists and restorers involved in the field of preservation of monuments and environmental impact to avoid salt crystallization.

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“…Mass transport rates, which play a dominant role in the induction period before salt damage, are analyzed in this section, based largely on [72][73][74][75].…”

Section: Transport Mechanismsmentioning

confidence: 99%

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

Flatt¹,

Aly

Caruso

et al. 2017

RILEM Tech Lett

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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.

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Physical principles and efficiency of salt extraction by poulticing

Cited by 73 publications

References 3 publications

Desalination of porous building materials by electrokinetics: an NMR study

Desalination of porous building materials by electrokinetics: an NMR study

Preservation strategies for avoidance of salt crystallisation in El Paular Monastery cloister, Madrid, Spain

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

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