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Hendrickx R.,Royal Institute for Cultural Heritage KIK IRPA
Materials and Structures/Materiaux et Constructions | Year: 2013

Over the last decades the Karsten tube has been used as a versatile testing device to measure the water absorption of porous walls. It is non-destructive and it can give reproducible results when used accurately. A major drawback however is the lack of a physical interpretation of the results. This paper uses analytical models and a numerical simulation in 3D to allow a more fundamental and general interpretation of the test results. A relatively simple model for a soil infiltrometer test was proven to give a good fit to experimental field data and to lab test results. 3D numerical simulations, performed with Delphin 5 software, provide extra insight about the correctness of the model assumptions of a sharp front process and a simplified shape of the wetting front. A supplementary measurement of the increase of the diameter of the wetted zone during the test allows a straightforward calculation of the capillary saturated moisture content and the sorptivity of the material. Moreover an analytical relation is presented between the results of the Karsten test as described in the old standards and the sorptivity. © 2012 RILEM.

Linnow K.,University of Hamburg | Steiger M.,University of Hamburg | Lemster C.,University of Hamburg | De Clercq H.,Royal Institute for Cultural Heritage KIK IRPA | Jovanovic M.,Royal Institute for Cultural Heritage KIK IRPA
Environmental Earth Sciences | Year: 2013

Several double salts have been detected in building materials and most of these salts are incongruently soluble compounds. In contrast to single salts, however, no systematic investigations of the crystallization behavior and deleterious effects of incongruently soluble double salts exist. To assess the damage potential of these salts, a systematic investigation of their highly complex behavior is desirable. This paper deals with the crystallization behavior of various solids in the ternary mixed NaNO3-Na2SO4 system including the formation of the double salt darapskite, Na3NO3SO4·H2O. The crystallization sequence during droplet evaporation experiments at room conditions was determined using Raman and polarization microscopy. The basic idea of this research is to use deviations of the crystallization sequence of a salt or a mixed salt solution from the equilibrium pathway as an indicator to detect the degree of supersaturation. The observed crystallization pathway includes the formation of the metastable phases Na2SO4(III), Na2SO4(V) and darapskite. The experimental observations are discussed on the basis of the NaNO3-Na2SO4-H2O phase diagram and the results provide evidence for crystal growth from highly supersaturated solutions in both systems. If the crystals growing under these conditions are confined, these supersaturations result in substantial crystallization pressures. © 2012 Springer-Verlag Berlin Heidelberg.

De Clercq H.,Royal Institute for Cultural Heritage KIK IRPA | Jovanovic M.,Royal Institute for Cultural Heritage KIK IRPA | Linnow K.,University of Hamburg | Steiger M.,University of Hamburg
Environmental Earth Sciences | Year: 2013

The behaviour of two types of limestones having a different porosity, Maastricht and Euville limestone, laden with aqueous solutions of equimolar mixtures of sodium sulphate/sodium nitrate or sodium sulphate/potassium sulphate was investigated. At 50 % RH, the efflorescences on Maastricht samples during the first 30 h of drying consisted of similar amounts of thenardite and darapskite in case of an equimolar mixture of sodium sulphate/sodium nitrate while those on Euville samples under the same conditions contained mainly darapskite. After drying at 20 °C and 85 % RH, thenardite, formed through the precipitation and dehydration of mirabilite, was mostly detected in the efflorescences on both Maastricht and Euville samples. Re-wetting by increasing the RH from 50 to 85 % resulted in substantial damage on Maastricht stone laden with an equimolar mixture of sodium sulphate/sodium nitrate as a consequence of high supersaturation of mirabilite. In case of a contamination with equimolar amounts of sodium sulphate and potassium sulphate, the efflorescence on both limestones during drying at 50 % RH contained predominantly aphthitalite. The observed crystallisation behaviour is compared to the theoretical behaviour. The results indicate a strong influence of stone properties on the crystallisation behaviour of salt mixtures. © 2012 Springer-Verlag Berlin Heidelberg.

Fremout W.,Royal Institute for Cultural Heritage KIK IRPA | Saverwyns S.,Royal Institute for Cultural Heritage KIK IRPA
Journal of Raman Spectroscopy | Year: 2012

Identification of pigments in modern and contemporary arts is indispensable to determine correct conservation strategies, to study degradation processes and to answer authenticity-related questions. Since the early 20th century, the introduction of synthetic organic pigments (SOPs) has enormously increased the number of available pigments. Micro-Raman spectroscopy has proven to be the first line technique for the identification of these pigments, which often only show small variations on the same basic chemical structures. To ensure a correct identification, however, an as complete as possible library of reference spectra is needed. Although reference spectra of SOPs have been published before, they have always been limited to a certain number of pigments. Some publications discuss only one or a few chemical classes, and others are limited to a certain number of pigments belonging to different classes; none, however, have attempted to create an extensive library of commercially available pigments. Moreover, most of the reference spectra published so far are only available as small imprints or as peak lists and, as such, hardly usable for spectral matching algorithms. Often, flow charts have been developed on the basis of the pigments studied, to help in identifying unknown SOPs. In this paper, a digital spectral library that comprehends almost 300 spectra of different SOPs is presented. The library was tested by means of non-invasive analysis of four contemporary paintings from the collections of the Stedelijk Museum voor Actuele Kunst (Ghent, Belgium). Published flow charts have been evaluated in relation to digital search algorithms by using the extensive library of SOPs. To enable fellow research and conservation institutes to make use of these data, the nearly 300 reference spectra of synthetic organic pigments are available in digital format on http://modern.kikirpa.be. Copyright © 2012 John Wiley & Sons, Ltd.

Cnudde V.,Ghent University | Dewanckele J.,Ghent University | Boone M.,Ghent University | de Kock T.,Ghent University | And 6 more authors.
Microscopy Research and Technique | Year: 2011

Diestian ferruginous sandstone has been used as the dominant building stone for monuments in the Hageland, a natural landscape in east-central Belgium. Like all rocks, this stone type is sensitive to weathering. Case hardening was observed in combination with blackening of the exterior parts of the dressed stones. To determine the 3D petrography and to identify the structural differences between the exterior and interior parts, X-ray computed tomography was used in combination with more traditional research techniques like optical microscopy and scanning electron microscopy. The 3D characterization of the ferruginous sandstone was performed with a high-resolution X-ray CT scanner () in combination with the flexible 3D analysis software Morpho+, which provides the necessary petrophysical parameters of the scanned samples in 3D. Besides providing the required 3D parameters like porosity, pore-size distribution, grain size, grain orientation, and surface analysis, the results of the 3D analysis can also be visualized, which enables to understand and interpret the analysis results in a straightforward way. The complementarities between high-quality X-ray CT images and flexible 3D software and its relation with the more traditional microscopical research techniques are opening up new gateways in the study of weathering processes of natural building stones. © 2011 Wiley Periodicals, Inc.

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