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X-Ray computed tomography and traditional analysis of a capillary absorption test in cement pastes
(2020)
Water absorption testing has the attraction of being simple, relatively quick and use water as a fluid which is the key substance in the possible concrete deterioration. However, in spite of the advantages its application has remained empirical, except for the testing of resistance to frost, through the identification of the critical degree of saturation. Rilem TC-116 studied this test, among others, for the characterization of concrete resistance against transport through the concrete pore network. Results indicated a low discriminating ability of the absorbency for qualifying concrete resistance and then, it seemed necessary to try to move forward by making the link between the absorption testing and the concrete pore microstructure. In the present work, thanks to the X-Ray computed tomography, it is described the evolution of the water front in three paste-specimen with different w/c ratios (different pore radius distributions). The observations allowed us to deduce that all the pores start to fill simultaneously, but the bigger ones fill quicker and rise less. The saturation degree is measured along the height of the sample, showing that each pore size has a different rate which becomes constant after the first hour. Washburn’s equation was applied to the progressive advance of the water front, resulting in a pore radius much smaller than the one expected.
The Stone Age site Riņņukalns, Latvia, is the only well-stratified shell midden in the Eastern Baltic. In this paper, we present new interdisciplinary results concerning its dating, stratigraphy, features, and finds to shed light on the daily life of a fisher population prior to the introduction of domesticated animals. The undisturbed part of the midden consists of alternating layers of unburnt mussel shell, burnt mussel shell and fish bone, containing artefacts, some mammal and bird bones, and human burials. Two of them, an adult man and a baby, are discovered recently and date to the calibration plateau between 3350 and 3100 cal BC, and to the later 4th millennium, respectively. Stable isotopes suggest a diet based heavily on freshwater fish, and this is supported not only by ten thousands of identified fish remains, but also by a fish bone concentration nearby the skull of the man, which is interpreted as remain of a grave gift (possible fish soup). Of special interest are the baby’s stable isotope values. It shows that the mother’s diet was atypical (perhaps because she was non-local), and/or that dietary stress during pregnancy increased fractionation between the mother’s diet and her bloodstream
In der anthropologischen Rudolf-Virchow-Sammlung der Berliner Gesellschaft für Anthropologie, Ethnologie und Urgeschichte (BGAEU) befindet sich eine größere Anzahl menschlicher Schädel aus dem Gebiet des heutigen Lettlands, die Mehrzahl dabei von der im Norden Lettlands am Burtnieksee gelegenen Fundstelle Riņņukalns. Der nachfolgende Aufsatz beschreibt die Gründe, warum diese Stücke in den 1870er Jahren in die Sammlung gelangt sind, und präsentiert eine anthropologische Dokumentation und Analyse der Schädelfunde vom Riņņukalns aus der Sammlung.
The combination of tomographic, microstructural data with other experimental techniques and with modeling is paramount, if we want to extract the maximum amount of information on material and component properties. In particular, quantitative image analysis, statistical approaches, direct discretization of tomographic reconstructions represent concrete possibilities to extend the power of the tomographic 3D representation to insights into the material and component performance. This logic thread holds equally for industrial and academic research, and valorizes expensive experiments such as those carried out at synchrotron sources, which cannot be daily repeated. We shall show a few examples of possible use of X-ray tomographic data for quantitative assessment of damage evolution and microstructural properties, as well as for non-destructive testing. We will also show how X-ray refraction computed tomography (CT) can be highly complementary to classic absorption CT, being sensitive to internal interfaces.
Die Computertomographie (CT) ist in der Medizin als Standardtechnik etabliert, in der zerstörungsfreien Prüfung wird sie zunehmend angewendet, in einzelnen Fällen sogar als Referenzverfahren eingesetzt. Gegenwärtig ist eine starke Zunahme von Anwendungen der CT in der Materialcharakterisierung zu verzeichnen. Zudem werden weitere moderne 3D-Techniken für werkstoffwissenschaftliche Fragestellungen genutzt, um die Mikrostruktur - auch in situ (z.B. Druck, Temperatur) - aufzuklären. Hier werden neben der konventionellen Absorptions-CT auch die Potenziale der Refraktions-CT zur Beantwortung prozesstechnischer sowie werkstofflicher Fragestellungen aufgezeigt, die ein „ganzheitliches Bild“ des jeweiligen Werkstoffs zum Ziel haben.
This paper deals with the initiation and propagation of corrosion in mortar specimens precracked under mechanical loading and carbonated in climate accelerated conditions (50 % CO2–65 % RH)for 15–23 weeks. Mechanical loading led to transverse macro-cracks and damage at the steel-mortar interface characterized by micro-cracks (cover controlled cracking) which favour the carbonation of crack walls and the interface with the steel bar. Wetting–drying cycles performed after carbonation favoured corrosion initiation all along the steel bar because of the carbonated interface and corrosion propagation because of the creation of corrosion cracks which appear to develop from the micro-cracks induced by the mechanical load. Results also show that rust develops all around the perimeter of the carbonated steel bar but that the corrosion layer is thicker in the lower half surface of the reinforcement than that observed in the upper half. Results indicate that the distribution and composition of corrosion products depend on the thickness of the rust layer and that the multilayered structure of rust depends mainly on its thickness.
This paper deals with the initiation and propagation of corrosion in mortar specimens pre-cracked under mechanical loading and carbonated in climate accelerated conditions (50 % CO2–65 % RH) for 15–23 weeks. Mechanical loading led to transverse macro-cracks and damage at the steel-mortar interface characterized by micro-cracks (cover controlled cracking) which favour the carbonation of crack walls and the interface with the steel bar. Wetting–drying cycles performed after carbonation favoured corrosion initiation all along the steel bar because of the carbonated interface and corrosion propagation because of the creation of corrosion cracks which appear to develop from the micro-cracks induced by the mechanical load. Results also show that rust develops all around the perimeter of the carbonated steel bar but that the corrosion layer is thicker in the lower half surface of the reinforcement than that observed in the upper half. Results indicate that the distribution and composition of corrosion products depend on the thickness of the rust layer and that the multilayered structure of rust depends mainly on its thickness.
Investigation of chloride-induced pitting corrosion of steel in concrete with innovative methods
(2016)
The combination of electrochemical and 3D computed tomography (CT) investigations offers the possibility of verifying electrochemical measurements non-destructively. Determining the steel surfaces damaged by pitting corrosion allows developing specimens having damage pattern corresponding to practice. Corrosion phenomena like decoupled pitting corrosion cannot be verified by electrochemical measurements only, but with the combination of those two kinds of investigations it is possible. Another advantage is the minimization of the number of samples. The classical experimental procedure requires the destruction of samples after each damage step.This can be avoided by the use of 3D computed tomography. As long as the corrosion phenomena are completely within the examination zone shown by the 3D computed tomography, the electrochemical measurements can be calculated on an area basis to get the specific corrosion rate or polarization resistance.
Die Kombination elektrochemischer und computertomographischer Untersuchungs-Verfahren bietet die Möglichkeit, elektrochemische Messungen zerstörungsfrei verifizieren und richtig interpretieren zu können. Die Ermittlung der durch Lochkorrosion geschädigten Stahloberflächen ermöglicht es Probekörper zu entwickeln, die ein der Praxis entsprechendes Schadensbild aufweisen. Ein weiterer Vorteil stellt sich in der Minimierung der Probenmatrix dar. Die klassische Versuchsdurchführung erfordert die Zerstörung von Proben nach jeder Vorschädigungsstufe. Dies kann durch den Einsatz der Computertomografie vermieden werden. Die elektrochemischen Messwerte können flächenbezogen ermittelt werden, solange sich die Korrosionserscheinungen vollständig innerhalb des durch die CT abgebildeten Untersuchungsbereiches befinden.