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V. Cnudde P. Dubruel K. De Winne I. De Witte B. Masschaele P. Jacobs E. Schacht 《Engineering Geology》2009,103(3-4):84-92
To reduce the weathering rate of natural building stones, a wide variety of water repellents and consolidants are commercially available. Although a lot of research is performed on these products, it remains difficult to determine which product is appropriate to use for a certain type of building stone. Each type of building stone has its own petrographic characteristics (mineralogy, texture, …), leading to typical physical and technical properties which influence its rate of decay. The localisation of the products inside a stone type is not only depending on the properties of the products themselves, but also linked to the texture and structure of the stone. The impregnation depth of the products strongly influences their efficiency and is therefore a key issue in the determination if a product is functional for a certain type of stone. X-ray micro-CT has recently been introduced as a non-destructive material evaluation technique for engineering and geology purposes. The fact that micro-CT can provide information about the internal structure and properties of natural building stones, is a major advantage in the study of their conservation. Firmly linked with more classical research techniques, this non-destructive technique offers an extra dimension to the cultural heritage research.In this paper, non-destructive X-ray computed micro-tomography (micro-CT) turns out to be a powerful tool as it can visualise the presence of water repellents and consolidants inside the stone and can help to detect the influence that these treatments exert on porosity and pore-size distribution. For the visualization of the product its atomic number and density and the amount of product inside the natural building stone is crucial. Besides the contrast in attenuation, the resolution of the micro-CT also needs to be taken into account to obtain a good contrast between stone and product. By doping with 3-bromopropyltrimethoxysilane, more contrast occurs between the stone material and the conservation product. When the amount of product inside the samples is very low and the product is homogeneously spread inside the sample, the doped product is difficult to distinguish from the stone material due to the resolution of the micro-CT. When the amount of doped product inside the stone material reaches a certain threshold value, the dope will appear in the 2D cross-sections derived from micro-CT, creating a good visualization of the products inside the stone samples. 相似文献
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Elke Vandekerkhove Maarten Van Daele Nore Praet Veerle Cnudde Peter J. Haeussler Marc De Batist 《Sedimentology》2020,67(1):364-389
Lake sediments in Eklutna Lake, Alaska, reveal the presence of turbidites within varved sequences. These turbidites, which result from flood events and earthquakes, show a similar macroscopic appearance. In order to use turbidites to reconstruct flood variability and/or seismic history in the lake basin, it is crucial to determine the trigger of the turbidity currents. This study examined the turbidite caused by the ad 1964 Great Alaska earthquake as well as turbidites linked to historical flood events in order to differentiate between these earthquake-triggered and flood-triggered turbidites. In a suite of samples from throughout the lake, distinctive proxies are identified that can be associated with event-specific flow characteristics. The study presents straightforward discrimination methods related to the sedimentology and geochemical components of the turbidites. These methods are also applicable to other lakes, particularly proglacial lakes where the sediment composition of onshore and offshore sources is similar. Finally, the discrimination of the turbidite trigger can be used to reconstruct the palaeoflood and seismic history. 相似文献
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Wang Ji-Peng Lambert Pierre De Kock Tim Cnudde Veerle François Bertrand 《Acta Geotechnica》2019,14(5):1545-1559
This paper studies the effect of interfacial areas (air–water interfaces and solid–water interfaces) on material strength of unsaturated granular materials. High-resolution X-ray computed tomography technique is employed to measure the interfacial areas in wet glass bead samples. The scanned 3D images are trinarized into three phases and meshed into representative volume elements (RVEs). An appropriate RVE size is selected to represent adequate local information. Due to the local heterogeneity of the material, the discretized RVEs of the scanned samples actually cover a very large range of degree of saturation and porosity. The data of RVEs present the relationship between the specific interfacial areas and degree of saturation and gives boundaries where the interfacial area of a whole sample should fall in. In parallel, suction-controlled direct shear tests have been carried out on glass beads and the material strength has been corroborated with two effective stress definitions related to the specific air–water interfacial areas and fraction of wetted solid surface, respectively. The comparisons show that the specific air–water interfacial area reaches the peak at about 25% of saturation and contributes significantly to the material strength (up to 60% of the total capillary strength). The wetted solid surface obtained from X-ray CT is also used to estimate Bishop’s coefficient χ based on the second type of effective stress definition, which shows a good agreement with the measured value. This work emphasizes the importance to include interface terms in effective stress formulations of unsaturated soils. It also suggests that the X-ray CT technique and RVE-based multiscale analysis are very valuable in the studies of multiphase geomaterials.
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Maarten Van Daele Veerle Cnudde Philippe Duyck Mario Pino Roberto Urrutia Marc De Batist 《Sedimentology》2014,61(4):861-880
On 21 April 2007, a Mw 6·2 earthquake struck Aysén fjord (Chilean Patagonia) and caused onshore and offshore mass movements which triggered tsunamis and density flows in the fjord. To better understand the facies successions in, and the intercalation of, the density‐flow deposits, a study was made of the 2007 deposits in 22 short sediment cores taken in the inner Aysén fjord. By combining grain‐size analysis with X‐ray computed tomography scanning, it was possible to demonstrate that the encountered facies correspond to classical divisions of debrites and turbidites. The single‐event deposits consist of a succession of several sub‐deposits deposited under different flow directions and can be interpreted as stacked turbidites. Orientations of: (i) folds; (ii) imbricated mud clasts; (iii) backsets and foresets of climbing ripples; and (iv) asymmetrical convolute lamination were used to determine relative flow directions at the location of the cores. By assigning the basal flow of the stacked debrites and turbidites to the closest principal mass flow, the absolute flow directions of the sub‐deposits were determined which, in combination with multibeam basin‐floor morphology, allowed reconstruction of the 2007 density‐flow successions in Aysén fjord. Furthermore, alternating flow directions provide evidence for a seiche induced by the density flows. It was concluded that X‐ray computed tomography scans provide crucial information for reconstructing palaeoflows and can be a useful tool in marine and lacustrine sedimentology and palaeoseismology. The multidirectionality of sub‐deposits in turbidites is, next to differences in mineralogy, a new criterion to identify stacked turbidites. These multidirectional, stacked turbidites are an indication of simultaneous triggering of density flows and can therefore, in most cases, be attributed to earthquakes, ruling out other triggers, such as floods, storms or other sediment failures. 相似文献
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The St Bavo's Cathedral tower in Ghent, Belgium, is currently under restoration. This tower was built during the fifteenth and sixteenth centuries over a period of 73 years, using Eocene white stone. Restorations over the last two centuries introduced different Jurassic limestones from the Paris Basin. Documentation of these interventions, however, is very poor for the period before the twentieth century, and documentation on the original construction is non‐existing. Nevertheless, the use of the different stones in their historical context forms a typical example of the historical mindset on the use of white stone, representative for Ghent and by extension northwestern Belgium. 相似文献
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X-ray computed microtomography (µCT) is a promising non-destructive imaging technique based on measurements of the attenuation of X-rays. It provides information on the internal structure of small samples with a maximum resolution of 10 µm. For this study, two porous local natural building stones, the sandstone of Bray and the limestone of Maastricht, were selected. Possible applications of the µCT-technique for qualitative monitoring of changes comprise (1) to non-destructively determine porosity based on 3-D images, (2) to visualise weathering phenomena at the micron-scale, (3) to understand the rationale of weathering processes, (4) to visualise the presence of water repellents and consolidation products, (5) to monitor their protective effects during decay in order to understand the operating mechanisms and (6) to provide advise on the suitability of products for the treatment of a particular rock type. The µCT-technique proves to be a powerful monitoring tool for the future as the combination of 3-D visualisation and 3-D data provide new insights that could optimise conservation and restoration techniques of building materials. 相似文献
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The microstructure of building materials greatly influences engineering properties like permeability, strength and durability. To determine this microstructure, different techniques were developed, each with its own limitations. The purpose of this study on concrete and natural building stones was to compare and to combine data obtained by X-ray computed micro-tomography (micro-CT), water absorption under vacuum and mercury intrusion porosimetry (MIP). Pore-size distribution curves ranging from 10 nm to 1 mm and total porosity results were obtained. Furthermore, micro-CT revealed the presence of an interfacial transition zone (ITZ) and of micro-cracks inside the aggregates of the concrete samples after mercury intrusion. Micro-CT visualized mercury inside large air bubbles within the concrete samples. Both micro-CT and MIP were compared and their respective advantages and disadvantages discussed. 相似文献
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B. Masschaele M. Dierick L. Van Hoorebeke V. Cnudde P. Jacobs 《Environmental Geology》2004,46(3-4):486-492
In the paper we present our results for element sensitive high-energy X-ray tomography and high-speed thermal neutron tomography applied to geological samples. The tuneable monochromatic X-ray beam was used for element sensitive tomography of geological samples containing heavy elements using the K-edge dichromatic scanning technique. This type of NDT (non-destructive testing) allowed us to reveal the quantity and location of uranium, lead and mercury in Oklo samples (natural nuclear reactor) and Cinnabar stones. Fast 3-D thermal neutron imaging of dynamical processes was successfully tested at the high flux neutron tomography station of the ILL. The qualitative investigation of water repellents and consolidants applied on sandstones of Bray and limestones of Maastricht were the first samples to be studied with the new imaging technique. 相似文献
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