Poultices for desalination: Difference between revisions

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<bibimport />
Autor: [[user:Hschwarz|Hans-Jürgen Schwarz]]
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zurück zu [[Salzreduzierung]] <br>


== Abstract  ==
== [[Permanently wet poultice]]  ==
The poultice material is kept humid during the application period. There is no or only a small moisture gradient, resulting in the salt transport being dominated by diffusion. After an adequate duration of the application a concentration equilibrium between poultice and substrate is effected. Permanently wet poultice material should in general only be used in cases where a moisture gradient cannot be set up due to reasons which lie in the physics of the building. These reasons can include a very damp wall or when drying possibilities are limited. There is also a risk that the salt accumulation shifts into lower  regions of the structure due to the high moisture penetration.
== [[Drying Poultice]]  ==
The poultice material dries out more or less completely, depending on the climatic conditions during the application. Capillary transport and diffusion usually effect a flow towards the poultice material because of the rectified moisture and concentration gradient. If the porosity of poultice and substrate is well matched, the capillary transport is predominant. When gradual drying takes place, salts accumulate in the poultice material.
For the treatment of relatively poorly soluble salts (e.g. gypsum) a combination of the two methods  can be used. To begin with a permanently wet  poultice is applied to dissolve the gypsum, then a drying poultice.
Due to the sheer number of influencing factors and their variation during the desalination treatment, no universally applicable procedure can be proposed. Only approximate values can be provided, the exact terms are to be tailored to each individual case.
Desalination poultices consist of one or more components (no binder) of the following groups. The components are mixed using deionized water.
*swellable materials from organic origin, no sealing properties, high water absorption and high water retention capacity (e.g. cellulose, paper pulp, aqueousgels)
*mineral components with large specific surface areas and a good ion exchange and adsorption properties (e.g. clay minerals and mixtures such as kkaolin bentonite etc.)
*inerte fillers (in combination with substances of the previous groups) to give the mixture properties such as stability, high porosity or a loose structure, to improve workability or decrease shrinkage.(Quartz sand, quartz flour, silica, good quality sand- rich in quartz, lightweight aggregates or equivalent)
or components are: highly porous, absorbent, flexible and inert mats and fleeces (foams, paper, textile etc.)
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== [[The injection poultice procedure]]  ==
This procedure <bib id="Friese.etal:1993" /> is carried out by introducing the water for desalination  not through the exterior, but through the interior of the wall. At the injection point, the water disperses spherically and when two water- spheres of adjacent injection points overlap, a capillary water flow is generated from the interior of the wall onto the surface of the poultice, where it evaporates. A disadvantage, however, is that holes need to be drilled into the wall, which allow for the injection of water to penetrate behind the  contaminated layers.
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On brickwork, for example, holes could be drilled into the joints- but this is a decision that needs serious evaluation with regards to ethics and history of the building.
When using this method it is very important to assess the structure of the wall well enough and to know exactly which materials were used for filling the core. The introduction of water into the structure could lead to an increase in weight, leakage of unknown substances, water seepage in other areas of the building, or uncontrollable swelling. Also the amount of water introduced needs to be controlled. 
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{| width="100%" cell spacing="0" cellpadding="4" border="2"
|+Tabelle 1: '''Most frequently used poultices '''(in accordance with <bib id="WTA_E 3-13-01/D:2003"/>)
|-
| bgcolor="#ffff99" align="center" | '''Poultice composition'''
| bgcolor="#ffff99" align="center" | '''Advantages'''
| bgcolor="#ffff99" align="center" | '''Disadvantages'''
|-
| bgcolor="#ccffcc" | Pure cellulose fibres of different length
| bgcolor="#ccffcc" | - pH-neutral<br>- flexible, soft, adherent<br>- high water absorption
| bgcolor="#ccffcc" | - low stability<br>- Risk of mould formation
|-
| bgcolor="#ccffcc" | Bentonite, Attapulgit, Kaolin, pure or mixed with cellulose
| bgcolor= "#ccffcc"| any alkali can be mobilised
| bgcolor="#ccffcc" | - extremely hard when high clay mineral content is present<br>- sometimes increased pH- values<br>- Kaolin: Risk of white residue on the surface
|-
| bgcolor="#ccffcc" | Clays (no further specification)
| bgcolor="#ccffcc" | - high water retention capacity
| bgcolor="#ccffcc" | - extremely hard<br>- sometimes increased pH-values<br>- Contamination and  soluble paper pulp / hemicellulose/ lignin bleaches- high water absorption
| bgcolor="#ccffcc" | - bleaches, additives and colors could be introduced
|-
| bgcolor="#ccffcc" | cellulose-mixtures with high sand content
| bgcolor="#ccffcc" | - with good quality sands pH-neutral
| bgcolor="#ccffcc" | - Properties vary<br>- difficult to process<br>- low stability
|-
| bgcolor="#ccffcc" | Clay mineral-cellulose-sand- mixture (different mixtures, commercially available, predominantly  on bentonit basis)
| bgcolor="#ccffcc" | - good stability<br>- machine processable<br>- Strength and shrinkage can be controlled through composition
| bgcolor="#ccffcc" | - any mix can become too heavy or too hard<br>- sometimes increased pH-values
|-
| bgcolor="#ccffcc" | Clay minerals-light aggregates-mix, sometimes with cellulose
| bgcolor="#ccffcc" | - good stability<br>- machine processable<br>- low shrinkage, low density
| bgcolor="#ccffcc" | - sometimes increased pH-values<br>- can become too hard, depending on the mix<br>- Kaolin: Risk of white residue on the surface
|}
<!--
Strikt abzuraten ist von der Verwendung von Komponenten, die:
den Stofftransport behindern (Gefahr besteht bei filmbildenden oder hydrophobierenden Zusätzen und bei Quellstoffen wie Agar-Agar, Gelatinen, Protein-Gelen, Methylcellulosen),
wasserlösliche Salze enthalten oder erzeugen,
mineralische Bindemittel (Gipse, Kalke, Zemente) oder
oberflächenaktive Substanzen (Reiniger oder waschaktive Substanzen) enthalten.
Jede Materialzusammensetzung bietet gewisse Vor- und Nachteile, die in der Tabelle aufgeführt sind. Aus diesem Grunde muss für den jeweiligen Einsatzzweck unter Berücksichtigung der Randbedingungen das am besten geeignete Material ausgewählt werden.
Als weitere Qualitätsanforderungen müssen folgende Anforderungen erfüllt werden:
*Kompressenbestandteile dürfen keine (d.h.<nowiki><</nowiki> 0,1 M-% Gesamtsalz) löslichen Salze enthalten.
*Der Salzgehalt der Kompressen ist über ein übliches Eluationsverfahren an mindestens 3 reprä-sentativen Proben zu bestimmen. Die Abweichungen der Messwerte vom Mittelwert sind an-zugeben. Bewährt hat sich eine Eluation mit der 20-fachen Menge ''entionisierten Wassers ''über 24h bei Raumtemperatur unter mehrfachem Schütteln.
*Die angemachte, gebrauchsfertige Mischung muss einen pH-Wert von 6 bis maximal 10 aufweisen (gemessen bei 25 °C).
*Die Kompressenmischung muss gut auftragbar sein, darf auch bei der Abtrocknung keine Span-nungen auf den Untergrund übertragen und muss dennoch gut haften.
*Die Kompressenmischung muss frei sein von färbenden Anteilen.
*Die Kompresse muss nach der Anwendung rückstandsfrei entfernbar
Die Kompressen-Methode kann am Objekt vor Ort oder in der Werkstatt durchgeführt werden Je nach Art der Kompresse, dem vorliegenden Klima, der Oberflächenbeschaffenheit u.a. sind die oben genannten Parameter entsprechend zu variieren.
Bei der Anwendung an senkrechten Flächen stellen sich z. B. die Probleme einer ausreichenden Haftung. Die Kompresse darf nicht durch ihr Eigengewicht abrutschen und so eventuell auch zu Schäden führen. Mürbe Oberflächen sollten aus diesem Grund vorgefestigt werden.
Die Anwendung der Kompressen ist mehrmals zu wiederholen. Der Erfolg ist wie bei der Wasserbadentsalzung von Porengefüge, Art und Verteilung der Salze und salzbildenden Ionen abhängig und ist durch analytische Untersuchungen zu überprüfen.
Genauere Hinweise sind oben genannten Markblatt zu enrnehmen.
</gallery>
<gallery caption=width="100%" cellspacing="0" cellpadding="4" border="1">
Image:Dokument3 05.png|Abbildung 3: Kompressenmuster mit und ohne Putzüberdeckung
Image:Dokument3 02.png|Abbildung 4:Kompressenentsalzung mit Buchenholzzellulose mit Probenentnamestellen
</gallery>
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== Literatur  ==
<bibprint />
[[Category:Maßnahmen]][[Category:Salzreduzierung]] [[Category:HSchwarz]] [[Category:R-GGrassegger]] [[Category:R-SLaue]] [[Category:Bearbeitung]]
[[User:SLeithaeuser|SLeithaeuser]] 18:35, 16 February 2012 (CET)still in progress

Revision as of 17:37, 16 February 2012

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