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Organisationseinheit der BAM
Self-ignition Behaviour of Bulk Materials: How Reliable is the Extrapolation of Laboratory Tests?
(2022)
The self-ignition behaviour of bulks is usually determined with the aid of isoperibolic or adiabatic hot storage tests; the sample volumes here are typically in the range of approx. 100 cm³ to several litres. The extrapolation to technically relevant volumes holds, however, considerable uncertainties. To reduce these uncertainties, a test stand was set up that allows to investigation sample sizes of up to 1000 dm³. These allow the study of selfignition behavior closer to the conditions that prevail in practice. The suitability (or unsuitability) of the established methods (including dangerous goods classification tests) were to be demonstrated and influencing variables that cannot be measured on a laboratory scale were to be determined.
In addition, various analytical methods were used for the determination of reaction kinetic data of solid bulk materials and to predict the self-ignition behaviour of large storages. These are thermal analyses such as differential scanning calorimetry DSC, simultaneous thermal analysis STA as well as microcalorimetry for highprecision measurement of heat flows.
Complete test series using all mentioned test methods will be presented for crosslinked polyvinyl-pyrrolidone (PVP) and conclusions regarding the applicability of the extrapolation methods will be discussed. Hot storage tests up to semi-industrial scale and their combination with various thermoanalytical methods allow a much more precise prediction of the self-ignition behaviour of large bulks. A further promising approach to estimate their heat release rates, and hence, the risk of self-ignition under technical conditions, is the use of microcalorimetric methods.
When it comes to higher accuracies, new technologies and real applications in additive manufacturing, there is one topic which cannot be avoided: The material response on the chosen processing parameters and its agreement and correspondence with literature data of the wrought material grade counterpart. In industrial Additive Manufacturing (AM) standards in terms of printing parameters, protection gas atmospheres or powder handling instructions are not obligatory. Therefore, the question must be answered whether the AM process is reproducible and reliable over different printing companies. This was the motivation to realize a round robin test between 8 European printing companies and academic partners. The consortium had printed and tested fatigue and tensile testing bars under plant-specific conditions. A commonly used cast aluminum alloy, AlSi10Mg, was chosen as test material for the PBF-LB/M process. Differences of the results between the partners and the scatter itself were discussed in detail.
Vorgestellt wird ein 2018 gestartetes Projekt zur Überprüfung der Extrapolation von im Labormaßstab ermittelten Selbstentzündungstemperaturen auf technisch relevante Volumina. Für die Ermittlung reaktionskinetischer Daten von Feststoffschüttungen stehen eine Reihe von Untersuchungsmethoden zur Verfügung. Dies sind thermische Analysen wie z. B. die differential scanning calorimetry DSC sowie Mikrokalorimetrie zur hochgenauen Messung von Wärmeströmen, bei denen sehr geringe Probenmengen zum Einsatz kommen. In der Regel wird das Selbstentzündungsverhalten jedoch mithilfe von isoperibolen oder adiabaten Warmlagerungsversuchen beurteilt, hier liegen die Probenvolumina üblicherweise im Bereich von ca. 100 cm3 bis zu einigen Litern. Die Extrapolation über mehrere Größenordnungen auf technische Volumina birgt Unsicherheiten, da mit Zunahme des Lagervolumens veränderte Start- und Randbedingungen vorliegen können. Zudem besteht die Möglichkeit, dass bei in technischen Lagern vorherrschenden niedrigen Temperaturen Reaktionen ablaufen, die in Standard-
Laborversuchen nicht erfasst werden, aber einen wesentlichen Einfluss auf das Selbstentzündungsverhalten aufweisen können. Hauptziel des Projektes ist es daher, die im Labormaßstab vorhandenen Prüfeinrichtungen durch einen Versuchsstand zur Untersuchung von Probengrößen von bis zu 1000 dm3 zu erweitern, die Eignung (oder Nichteignung) der etablierten Methoden nachzuweisen und im Labormaßstab nicht erfassbare Einflussgrößen zu ermitteln. Zudem sollen anhand der kleinskaligen Tests Entscheidungskriterien abgeleitet werden, ob eine Extrapolation nach den derzeit üblichen
Methoden zulässig ist.
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.
Vorgestellt wird ein 2018 gestartetes Projekt zur Überprüfung der Extrapolation von im Labormaßstab ermittelten Selbstentzündungstemperaturen auf technisch relevante Volumina. Für die Ermittlung reaktionskinetischer Daten von Feststoffschüttungen stehen eine Reihe von Untersuchungsmethoden zur Verfügung. Dies sind thermische Analysen wie z.B. die differential scanning calorimetry DSC sowie Mikrokalorimetrie zur hochgenauen Messung von Wärmeströmen, bei denen sehr geringe Probenmengen zum Einsatz kommen. In der Regel wird das Selbstentzündungsverhalten jedoch mit Hilfe von isoperibolen oder adiabaten Warmlagerungsversuchen beurteilt, hier liegen die Probenvolumina üblicherweise im Bereich von ca. 100 cm³ bis zu einigen Litern. Die Extrapolation über mehrere Größenordnungen auf technische Volumina birgt Unsicherheiten, da mit Zunahme des Lagervolumens veränderte Start- und Randbedingungen vorliegen können. Zudem besteht die Möglichkeit, dass bei in technischen Lagern vorherrschenden niedrigen Temperaturen Reaktionen ablaufen, die in Standard- Laborversuchen nicht erfasst werden aber einen wesentlichen Einfluss auf das Selbstentzündungsverhalten aufweisen können. Hauptziel des Projektes ist es daher, die im Labormaßstab vorhandenen Prüfeinrichtungen durch einen Versuchsstand zur Untersuchung von Probengrößen von bis zu 1000 dm³ zu erweitern, die Eignung (oder Nichteignung) der etablierten Methoden nachzuweisen und im Labormaßstab nicht erfassbare Einflussgrößen zu ermitteln. Zudem sollen anhand der kleinskaligen Tests Entscheidungskriterien abgeleitet werden, ob eine Extrapolation nach den derzeit üblichen Methoden zulässig ist.
Chemical admixtures allow to create a variety of fresh and hardened state properties in cementitious materials. In the case of self-compacting concrete, plasticizers or superplasticizers are introduced with the aim to decrease the yield stress and the viscosity of the materials.
However, in order to prevent segregation and bleeding, and to improve the water retention of cement-based system, stabilizing agents or viscosity agents are often introduced in addition.
Among these admixtures, polysaccharides are most commonly used. The aim of this study is to provide an understanding of competitive or synergetic effects induced by the combination of hydroxypropyl guar stabilizing agents (HPG) and superplasticizers on cement pastes. Two polycarboxylate superplasticizers (PCE) exhibiting different charge densities and one HPG were studied. It was found that the combination of HPG with PCE superplasticizer strongly affects the rheological behavior of cement pastes. Despite the presence of HPG, the viscosity of the pastes strongly decreased with increasing dosage of PCE until it became close to the viscosity of a cement paste with PCE only. However, the use of HPG in combination with PCE allows maintaining a significant yield stress in the cement paste compared to PCE alone. The increase in the charge density of the PCE seemed to amplify the drop of the viscosity and to reduce the gain on the yield stress induced by HPG. The results also highlight a delay in the setting-time of the cement paste by adding HPG and PCE. The delay induced by HPG is significantly lower than that generated by PCEs. However, the combination of the both kind of admixtures leads to a slightly shorter setting-time compared to the PCE alone.
Chemical admixtures allow to the create a variety of fresh and hardened state properties in cementitious materials. In the case of self-compacting concrete, plasticizers or superplasticizers are introduced with the aim to decrease the yield stress and the viscosity of the materials. However, in order to prevent segregation and bleeding, and to improve the water retention of cement-based system, stabilizing agents or viscosity agents are often introduced in addition. Among these admixtures, polysaccharides are most commonly used.
The aim of this study is to provide an understanding of competitive or synergetic effects induced by the combination of hydroxypropyl guar stabilizing agents (HPG) and superplasticizers on cement pastes. Two polycarboxylate superplasticizers (PCE) exhibiting different charge densities and one HPG were studied. It was found that the combination of HPG with PCE superplasticizer strongly affects the rheological behavior of cement pastes. Despite the presence of HPG, the viscosity of the pastes strongly decreased with increasing dosage of PCE until it became close to the viscosity of a cement paste with PCE only. However, the use of HPG in combination with PCE allows maintaining a significant yield stress in the cement paste compared to PCE alone. The increase in the charge density of the PCE seemed to amplify the drop of the viscosity and to reduce the gain on the yield stress induced by HPG.
The results also highlight a delay in the setting-time of the cement paste by adding HPG and PCE. The delay induced by HPG is significantly lower than that generated by PCEs. However, the combination of the both kind of admixtures leads to a slightly shorter setting-time compared to the PCE alone.
Rwanda is a landlocked country in the East Africa. It is surrounded by Uganda, Tanzania, Congo and Burundi. Rwanda is a fast developing country and it spends most of its revenues to import fossil fuels from either through Mombasa Port in Kenya or Dar es Salaam port in Tanzania because the energy production in Rwanda is not sufficient for its development.
Transporting the fuels from these ports, add on to the cost of all materials, cement industry being no exception. There are three cement companies in Rwanda. The cement industries could not run in full production due to the shortage of fuel. Moreover, Rwanda is importing all the construction materials such as steel, roofing materials, etc from its neighbouring countries. This increases the cost of construction and the common man find difficult to own a house. In order to sustain the energy needs of Rwanda, different sources of energies should be focused. They are Peat, Geothermal, Methane gas, solar, wind, waste materials and Municipal wastes. Without affecting the environment, there is an urgent need to find a solution on sustainable energy in Rwanda. This paper discusses about the possible sources of energy in Rwanda which will improve the energy sustainability and turn the economy of Rwanda.
A number of very relevant processes for protection and reconstruction of buildings can be supported by controlled heating: elimination of pests without using hazardous Chemicals, drying and decontamination of timber and many other building materials. For this purpose, radio-frequency (RF) dielectric heating is an advantageous Option because the materials and structures can be heated directly by energy absorption in the volume, homogeneously and, if required, relatively fast.
Compared to microwaves, the penetration depths are usually much larger and the flexibility with respect to different materials is wider. Namely, heating can also be realized for dry materials because the dielectric loss is as not closely related to the presence of water as for microwave applications.
Innovative admixture technology has significantly widened up the ränge of possibilities of concrete engineers. For many decades the water to cement ratio (w/c) was the major influencing factor for the performance of concrete. Due to the need to adjust a consistency, which still allowed reasonable workability, the w/c was typically significantly higher than technologically reasonable. Rheology modifying admixtures Support adjusting the concrete consistency largely independent of the w/c. It was only after the invention of the first superplasticizers that modern concrete technology significantly evolved in terms of flowability, strength, and durability, and only due to the steady evolution of the technology modern innovations, such as Self-Compacting Concrete, Ultra-High-Performance Concrete, or Engineered Cementitious Composites were made possible. Today’s superplasticizers are extremely versatile and can be adjusted to individual technological specifications. However, the other side of the coin of versatility is that cementitious Systems incorporating superplasticizers have become more sensitive against environmental influences, such as the environmental temperature, which may cause unwanted effects or demand for supplementary admixture use such as stabilizing admixtures. Hence, concrete mixture composition with admixtures demands for a high level of expertise and offen there is lack of awareness about the mode of Operation of rheology modifying admixtures among concrete technologists. The paper gives a comprehensive overview about rheology modifying admixtures such as superplasticizers or stabilizing agents, and how they can be used depending upon the application in the most favourable way. Based on experiences with the sub-Saharan African concreting boundary conditions, which exhibit many challenges in terms of environmental boundary conditions and construction site logistics, conclusions are finally drawn, how admixtures can be used in the most beneficial way to improve the concrete casting Situation.