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Zur Bestimmung der reaktionskinetischen Daten von Schüttgütern und iur Vorhersage des Selbstentzündungsverhaltens großer.Lager kommen verschiedene Analysemethoden zum Einsatz. Dabei handelt es sich .um thermische Verfahren wie die Differential-Scanning- Kalorimetrie OS(. die simultane Thermoanalyse STA sowie die Mikrokalorimetrie zur hochpräzisen Messung von Wärmeströmen. Für die oben genannten Methoden werden sehr kleine Probenmengen verwendet. In der Regel wird das Selbstentzündungsverhalten jedoch mit Hilfe von isoperibolen oder adiabatischen Warmlagerungsversuchen ermittelt: die Probenvolumina liegen hier meist im Bereich von ca. 100 cm3 bis zu mehreren Litern.
Die Extrapolation auf technisch relevante Volumina birgt jedoch erhebliche Unsicherheiten. Diese Unsicherheiten zu identifizieren und zu reduzieren ist das Hauptziel eines 2018 gestarteten Forschungsprojekts. Dies soll in erster Linie durch den Aufbau eines Versuchsstandes zur Untersuchung von Probengrößen von bis zu. 1000 dm 3 geschehen.
Sowohl Warmlagerungsversucl1e im Labormaßstab als auch thermoanalytische Verfahren. die mit Hilfe verschiedener Methoden ausgewertet werden. lassen, einzeln betrachtet. häufig nur bedingt zuverlässige Aussagen über das Selbstentzündungsverhalten von großen Schüttgütern zu. Es werden komplette Versuchsreihen mit allen genannten Prüfverfahren vorgestellt und Aussagen zur Anwendbarkeit der Extrapolationsmethoden diskutiert.
Composition and microstructure stability of cement compound under cyclic hydrothermal condition
(2020)
There have been many researches focused on the performance improvement of ultra-high performance concrete (UHPC) by autoclaving treatment. The goal of autoclaving is to increase the pozzolanic reaction, and to densify the cement stone and the transition zone which originates from the incorporation of supplementary cementitious materials (SCMs), such as silica fume, fly ash and blast furnace slag. Due to the superior properties, UHPC can also be utilized under high mechanical load and aggressive condition, for example, the fabrication of water tanks for thermal storage which is of great significance for saving energy and reducing CO2 emission. It is known that mineral stability of the hydration products of an inorganic binder is highly related to the temperature and pressure of the environment. A certain stable composition at room temperature, however, may undergo a phase transformation at high temperature and the performance decrease under this severe condition will generally be more severe. In this way, the rationale behind this deterioration under long-term hydrothermal condition involving many cycles and long duration has to be clarified, and then appropriate optimizing methods will be performed in order to obtain a kind of construction with high durability under aggressive environment. For this purpose, different types and amounts of SCMs are introduced into the standard mixture of UHPC and the phase compositions after autoclaving at 200 °C and 15.5 bar are determined by combined X-ray diffraction and scanning electron microscope. Mercury intrusion porosimeter is used to characterise the microstructure of the samples. In order to establish the relationship between microstructure and macroscopic properties, compressive and flexural strength are also investigated.
Ultra high performance concrete (UHPC) is known for its high compressive strength of more than 150 MPa and its high durability. Thermal treatment at 90°C can accelerate the strength development so that the 28-days-strength can be achieved immediately after the treatment and an additional increase up to 30 % in some cases. The reason for the strength development is an accelerated hydration of the clinker minerals and an intensified pozzolanic reaction leading to a denser microstructure.
In previous research inhomogeneities in form of a zonation after unprotected thermal treatment were observed and analysed in respect to changes in the microstructure. This zonation is defined by a different microstructure in the core compared to the outer zone in the matter of porosity, mineral phase composition and a significant change in the potassium and sulphur concentration of the zones is measurable.
To isolate different transport mechanisms responsible for these element distributions UHPC samples were thermally treated at 90 °C and the microstructure was investigated under dry conditions and after immersion in water to investigate the influence of dehydration during and rehydration after the thermal treatment on the microstructure. Through durability testing via water absorption, water vapour diffusion, permeability testing and sulfuric acid resistance transport mechanisms like diffusion, migration, capillary suction are under investigation in correlation with the microstructure analysis. For the microstructure analysis measurements with µXRF, mercury intrusion porosity, XRD and SEM were conducted.
Im Rahmen der Integritätsbewertung einer zementierten 13 3/8" Rohrtour einer Sole-Produktionsbohrung wurden erstmals 2018 zeitgleich faseroptische Temperaturmessungen (DTS, Distributed Temperature Sensing) und faseroptische Akustikmessungen (DAS, Distributed Acoustic Sensing) durchgeführt und ausgewertet. Dazu wurde die Bohrung zeitweise mit Stickstoff bespannt und wieder entlastet. Durch die Bespannung der Bohrung mit Stickstoff in Kombination mit dem Herunterdrücken des Stickstoff-Sole-Spiegels unter den Rohrschuh der 13 3/8" Rohrtour, konnte Stickstoff aus der Kavernenbohrung durch eine Leckagestelle in die Zementation übertreten und dort ein Stickstoff-Reservoir bilden.
Bei der anschließenden Stickstoffentlastung erfolgte der Wiederanstieg des Stickstoff-Sole-Spiegels deutlich schneller als die Entleerung des in der Zementation angelegten Stickstoff-Reservoirs. Der dadurch entstandene Druckgradient hatte zur Folge, dass an der Leckagestelle der Stickstoff aus der Zementation in die aufsteigende Sole in Form von Bläschen eingetreten und dort aufgestiegen ist. Dieser Übertritt der Stickstoffbläschen war sowohl mit der Entstehung eines akustischen Geräusches als auch mit einer Temperaturänderung verbunden, welche mit der DAS- und DTS-Technik nachgewiesen werden konnten.
Um die Ergebnisse bzgl. ihres physikalischen Hintergrundes zu überprüfen und basierend auf einer mathematisch-physikalischen Grundlage eine nachvollziehbare Interpretation der Messergebnisse zu ermöglichen, wurde ein numerisches Simulationsmodell der gekoppelten Festkörper- und Druckakustik für die Bohrung aufgebaut. Das Modell berücksichtigt die Geologie und die Komplettierung der Kavernenbohrung. Nach Identifikation der Schallquelle konnte mit dem Modell die Ausbreitung des Schalldrucks in der Bohrung erfolgreich nachgestellt werden.
Um dieses Verfahren einer simultanen DAS-DTS-Messung in eine feldtaugliche Version zu überführen, läuft seit November 2019 ein breit angelegtes und vom BMWi gefördertes ZIM-Kooperationsprojekt zwischen der Bundesanstalt für Materialforschung und -prüfung (BAM), der IAB Weimar gGmbH, der GESO GmbH & Co. Projekt KG, der DEEP.KBB GmbH sowie der Rembe Consulting PartG mbB.
Durch die Messdatenkopplung und den Wegfall der bewegungsbedingten Nachteile einer Messsonde werden präzisere Ergebnisse zur Bewertung der Bohrlochintegrität erwartet. Das Ziel ist, mit Hilfe der noch zu entwickelnden einfachen und robusten Technik, quantitative Aussagen über die Zustände im verrohrten Bohrloch direkt am Messplatz treffen zu können, wobei ein Fokus auf Detektierung und Quantifizierung von Kleinstleckagen liegt. Im Rahmen dieses Forschungsprojektes kommt neben numerischen Berechnungen auch ein geplanter Bohrlochsimulator zum Einsatz, mit dem umfangreiche Untersuchungen zur Ermittlung der Grenzparameter und Detektionsschwellen durchgeführt werden sollen.
Climate change, CO2 reduction, resource efficiency are only 3 current keywords that describe the current industrial-economic situation. In order to influence climate change effectively, the conversion of supply systems with technically usable forms of energy must succeed in the next decade. The international network founded in Baku in 2015 bundles research activities in the broad field of energy supply and energy efficiency.
Discuss current research approaches and results with scientists and experts from renowned universities and follow Azerbaijan's efforts to implement the energy revolution.
Wood protection technology in the marine environment has changed over the last decades and will continue to do so. New active ingredients, newer formulations, and novel wood-based materials including physically- and chemically-modified wood, together with increasing concerns over environmental impacts of wood preservatives, urgently demand a major revision of EN 275 “Wood preservatives – Determination of the Protective Effectiveness against Marine Borers”, dated from 1992. This IRG document reports on the technical work in CEN TC 38 regarding the revision of this standard. A Task Group within WG 24 of CEN TC 38 was formed consisting of experts from different field of competence (e.g. wood preservatives industry, wood scientists, marine biologists, archaeologists and cultural heritage conservators). Starting by e-mail correspondence in 2014, and continuing with four physical meetings (Berlin 2x, Florence, Venice) with experts from Germany, Italy, Sweden, and UK were held so far. Significant items for revision in EN 275 were identified as: number of replicates, duration of the test, dimension of specimens, number of test sites, number of reference species, reference material including reference preservative, re-immersion of specimens after non-destructive periodical evaluation for longer periods of time vs higher number of replicates for successive destructive examinations without re-immersion, utilization of X- ray apparatus and specific software to ease evaluation, etc.
Furthermore, the task group is working on a standardized lab test for time-saving evaluation of different wood qualities for their potential to resist attack by limnorids. The suitability of this lab test will be determined by round robin tests as soon as safe face-to-face collaboration permits. The outcome will be published as a CEN TR (Technical Report) document, with a view to eventual adoption within the revised standard.
Thermography is one on the most promising techniques for in-situ monitoring of metal additive manufacturing processes. Especially in laser powder bed fusion processes, the high process dynamics and the strong focus of the laser beam cause a very complex thermal history within the produced specimens, such as multiple heating cycles within single layer expositions. This complicates data interpretation, e.g., in terms of cooling rates. A quantity that is easily calculated is the time a specific area of the specimen is at a temperature above a chosen threshold value (TOT). Here, we discuss variations occurring in time-over-threshold-maps during manufacturing of an almost defect free cuboid specimen.
Composite Facade Elements with Self-Cleaning Surface made of Ultra-High-Performance Concrete (UHPC)
(2020)
In the framework of the European project H-House various concrete façade elements were developed with the aim to ensure a long service life by combining a very durable material with self-cleaning properties. The façade elements presented are made of a shell of UHPC filled with blocks of aerated autoclaved concrete as insulating material. Self-cleaning properties were realized amongst others by imprinting a microstructure into the surface during casting. The paper focuses on selected technological aspects of the manufacturing process of prototypes which had to be performed in two concreting sections. Furthermore the challenges faced when upscaling the self-cleaning properties are addressed and the strategy to assess the self-cleaning properties by measuring the contact and the roll-off angel is presented. The results show that a successfull upscalaing process requires detailed planning and that the best results can often be achieved with a moderate work effort or material use.
SENSO JOINT - An innovative sensor system for a sustainable joint design of concrete pavements
(2020)
Inacceptable capability and durability of joint sealing systems but also inadequate traffic performance (noise emission; overrolling comfort) up to traffic safety aspects reflect the still enormous demand for data-based description of concrete pavements performance under heavy loading conditions. Especially the deformation behavior of concrete pavement slabs in the joint region in consideration of new pavement construction types and improved concrete mixtures meanwhile established but also under the steeply rising traffic loads is not sufficiently explored. To create a data basis for advanced design rules, evaluation methods and product standards - and with it to improve quality, durability and finally sustainability of pavements - an innovative 3-D sensor system SENSO JOINT adapted to german roadworking requirements and suitable for heavy-duty operating conditions was developed. The contribution introduced describes the development of an extensive technical solution based on the analysis of decisive loads, interactions and boundary conditions. Based on calibration data, results of laboratory testing and finally field-testing on different concrete pavement construction types the outcome of a multi-level evaluation process shall introduce the potential of the new sensor system.
Since ancient times, marble has been the preferred material for monuments, sculptures, Ornaments and architecture. Though the stone is often a Chosen material, long-term exposure of marble results in cumulative deterioration of the rock fabric. The rate and extent of deterioration depends on the rock fabric and the climatic conditions. Besides the thermal vulnerability of marble, a combination of thermal and hygric fluctuation accelerates the deterioration process. The weathering sensitivity of marbles can be characterised by the irreversible length change of samples after heating under thermohygric conditions as residual strain. This residual strain is a non-reversible deterioration and caused by microcracking induced by a pronounced anisotropy of the thermal dilatation coefficient of calcite.
In brittle materials like marble, cracking and crack growth or friction on crack surfaces are accompanied by release of acoustic waves. The analysis of these acoustic emissions can give a deeper insight into the deterioration mechanism of marble.
In this study, acoustic emissions of thermohygric treated marble were analysed and correlated with ultrasonic velocities, thermal dilatation and residual strains. Therefore, different types of calcitic marble were cyclically heated from 20 °C to 90 °C and after equilibration of the samples cooled down again to 20 °C. While the first cycles were performed under dry conditions, the following were
executed in a humid environment. The analysis of acoustic emissions enables one to determine when cracking occurs during the thermal treatment. It is also possible to differentiate microcracking from internal friction. Furthermore, the evolution of Deterioration can be estimated based on ultrasonic velocities. The combination of acoustic Methods and strain measurement gives an insight into the disintegration mechanism and Supports the development of prevention strategies.