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- 2017 (22) (entfernen)
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- Cement (14)
- Rheology (9)
- Concrete (8)
- Sustainability (5)
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- Admixtures (3)
- Africa (3)
- Bio-based materials (3)
- Monitoring (3)
- Starch (3)
Eingeladener Vortrag
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Rising temperatures worldwide pose an increasing challenge for safe and healthy living conditions. Particularly inner cities have been affected by these environmental changes because of the materials used to build houses, streets and infrastructure. The most common building material is concrete. It shows a specific heat capacity, while the heat conductivity for Standard concrete is low. Thus, the use of concrete generates a high capacity of heat storage. In addition, extensive soil sealing also contributes to the temperature rise of inner city areas compared to
their surroundings. To mitigate this so-called urban heat island effect, a self-cooling concrete paver was developed. This paver is able to store water. The evaporation of the water at elevated temperatures provides a cooling effect. This paper focuses on determination of this new paver’s capability to cool the surface and the surrounding. The new paver’s cooling Qualities were analysed in a series of laboratory tests. To prove the results outside of laboratory conditions, two fields (12 m × 8 m) with self-cooling and reference pavers were installed in Spain.
This paper presents and discusses the results of the tests. Correlation between reduced surface temperature of the self-cooling concrete pavers and the air temperature is examined.
Rohrleitungssysteme sind aufgrund ihrer Funktion und Ausdehnung für den Betrieb, die Verfügbarkeit und die Sicherheit von Industrieanlagen von besonderer Bedeutung. Die bisher in definierten Intervallen durchgeführten, wiederkehrenden Prüfungen zur Sicherstellung leckagefreier Rohrleitungen sind kostenintensiv und mit einem erhöhten Aufwand verbunden.
Mit dem interdisziplinären Forschungsprojekt AGIFAMOR (Ageing Infrastructures – Akustisches Monitoring von Rohrleitungen) arbeitet die BAM an der Entwicklung und Erprobung einer örtlich und zeitlich kontinuierlichen Zustandsüberwachung von Rohrleitungen basierend auf einem faseroptischen akustischen Messsystem, welches einen vergleichsweise geringen Installationsaufwand der Sensoren erfordert. Mit diesem Verfahren sollen vor allem betriebsbedingte Schädigungen infolge von Korrosion sowie daraus entstehende Pittings oder Risse erkannt und damit Leckagen verhindert werden.
Im Rahmen einer Machbarkeitsstudie zum Teilaspekt „Detektion von Risswachstum“ wurde ein 2,5 m langes, definiert vorgekerbtes Stahlrohr mit der faseroptischen Sensorik (FOS) ausgestattet und quasistatisch unter 4-Punkt-Biegung belastet. Mit fortschreitender Belastung wächst, ausgehend vom vorhandenen Außenumfangskerb, ein Riss im Stahlrohr bis zum Erreichen der Leckage – in der Praxis ein gefährliches Schadensszenario.
Parallel zur FOS erfolgten Messungen mit Schallemissionssensoren, Beschleunigungssensoren und Potentialsonden, deren Ergebnisse die Interpretation der FOS-Messergebnisse unterstützen sollen.
In der Prozessindustrie werden häufig gefährliche Stoffe eingesetzt, so dass auch kleinste Leckagen der medienführenden Anlagenteile zu Gefährdungen der Arbeitnehmer sowie zur Belastung der Umwelt führen können. Für die Gewährleistung einer dauerhaften Verfügbarkeit der Infrastruktur ist die frühzeitige Erkennung und Ortung von potentiell gefährlichen Veränderungen an den Wandungen von Rohrleitungen und Behältern (in Form von Rissen, Pittings und Ablagerungen) erforderlich. Am Beispiel von Rohrleitungen, sollen im Rahmen des Projekts AGIFAMOR an der Bundesanstalt für Materialforschung und -prüfung (BAM), im Sinne einer Machbarkeitsstudie die Verfahren der verteilten akustischen und faseroptischen Sensorik zur kontinuierlichen Überwachung und Detektion potentiell gefährlicher Veränderungen in Industrieanlagen erprobt und qualifiziert werden. Dabei sollen die Applikation der optischen Sensorfasern hinsichtlich der Signalübertragung auf den Sensor optimiert und die Erkennung der für dieses Anwendungsgebiet relevanten Schallsignaturen entwickelt werden. Mithilfe eines solchen Messsystems können mit geringem Aufwand ausgedehnte Strukturen, auch unter erschwerten Bedingungen (z.B. hohe Temperatur, Einfluss von Chemikalien) kontinuierlich überwacht werden.
Pipelines and industrial piping systems are particularly relevant regarding technical safety, availability and maintenance. Large flow rates of hazardous substances imply that even smallest leakages can lead to high environmental impacts. Therefore, and to ensure the availability of infrastructure, an early detection and localization of potentially hazardous degradations to the walls (e.g. cracks, pittings, sedimentation, etc.) of the containments is necessary. However, in many cases it is not feasible to equip pipelines with a large number of point sensors at reasonable expense.
The principle of distributed fibre optic sensing relies on one single optical fibre, which simultaneously acts as a spatially continuous sensor as well as the signal transducer. Therefore, extensive structures can be provided with this type of sensor with comparatively low efforts.
As a consequence, monitoring oil and gas pipelines using distributed fibre optic sensors is on the upswing. Besides the established methods to measure temperature and strain, distributed acoustic sensing (DAS) has lately received considerable attention as a means to detect and localize third party threats to pipelines (approach of vehicles, digging, mechanical manipulation).
The so far not utilized potential of DAS as a means for continuous condition monitoring of pipes by detecting and localizing acoustic signals that point to certain damage scenarios, is currently under investigation in an interdisciplinary research project at BAM (AGIFAMOR, Ageing Infrastructures – Fibre Optic Monitoring of Pipes).
In order to qualify distributed acoustic fibre optic sensors for this application area, we especially focus on detecting and identifying the relevant acoustic emissions of interesting degradations as well as on the optimal way of application of the optical fibres to the specimen to achieve an optimal signal transmission of acoustic signals.
Potentials for sustainable cement and concrete technologies - Comparison between Africa and Europe
(2017)
Cement and concrete technologies in Africa provide vast potentials for sustainable future technologies as well as enormous challenges. The main focus of the symposium is to address existing challenges, possible solutions, and future potentials with all participants. This symposium also aims at offering a platform for networking with relevant players in science and industry.
With ongoing innovation in process technology, the challenges of concrete technology are more and more focused on the rheological optimisation for these processes, since improper mixture stability or poor compaction ability negatively affect the concrete homogeneity and quality. However, along with the increasing complexity of today’s concrete mixture compositions, concrete becomes more prone to failure regarding the casting process. Variable properties of the raw materials typically cause changing workability. The reasons can be found among others in scattering water contents, physical or chemical properties of the cement or varying environmental temperatures. Robustness in the delicately adjusted rheology, however, is of utmost importance for modern and future process technology, from sprayed concrete over pumpable concrete towards 3D-printing, with regard to the long-term strength, the function and the durability. Typically, material induced changes cannot be identified easily due to the complex interactions of concrete constituents. Therefore, a precise and prompt counteraction is impossible. However, it is known that the yield stress can be controlled by addition of supplementary superplasticizer or stabilising agent. In combination with computerized process observation tools that can rapidly interpret and react on changes in the rheology, it is therefore thinkable, that only these two admixture types can adjust the rheology steadily and permanently, regardless of the actual root cause for observed macroscopic rheology change. The presentation will firstly give a comprehensive overview of effects at the interface between pore solution, particles and hydrates, which affect the rheology of fresh concrete. Secondly, ways are recommended how the rheology can be actively manipulated before eventually computerized methods are demonstrated that help to actively and rapidly assess and counteract performance scatter during steady casting processes.
The African cement, concrete and construction business are growing at rapid pace. The cement sales are expected to grow tremendously until 2050. The number of newly built cement plants increases dramatically and in addition more cements are being imported from outside the continent, e.g. from Turkey, Pakistan, Indonesia, and China, driven by overcapacities in the countries of origin. This causes a high number of potentials and challenges at the same time. New cement plants can operate directly at best technological state of the art and thus incorporate more sustainable technologies as well as produce new and more sustainable products such as cements blended with sustainable supplementary cementitious materials such as calcined clays, and industrial or agricultural by products. At the same time the new variety of binding agent as well as the international imports, which are driven by price considerations, make the cement market prone to quality scatter. This puts pressure on the quality control regulations and institutions to ensure safety of construction, healthy application, and environmental safety for the population.
The paper presents possible solutions to build up the rapidly increasing African cement production more sustainably than in the rest of the world as well as the related challenges and obstacles that need to be overcome. Based on experiences with a series of pan-African cement testing laboratory proficiency schemes conclusions are made on technical, regulative and political level.
After a brief introduction into past and modern concrete, the relevance of sustainable concrete technologies is emphasised from a global perspective. In order to minimise the environmental impact of cement and concrete in the world, solutions for alternative binder materials as well as rheology and performance modifying additives are presented based on local bio-based resources.
However, the perception of bio-based constituents is typically rather negative in construction materials and its application is often limited to low-end construction. In order to show that this is not inevitable, the lecture ends with a number of case studies for the use of bio-based materials for high performance concrete applications.
The cement proficiency testing (PT) scheme was set up by the German Metrology Institute (PTB) and the Federal Institute for Materials Research and Testing (BAM) in 2012. The PT scheme was a spin-off from a European Commission and African, Caribbean and Pacific-Group of States funded project entitled SPIN – Spearhead Network for Innovative, Clean and Safe Cement and Concrete Technologies (www.spin.bam.de). The SPIN project aimed at crosslinking experts in industry and policy making bodies, with the prospect of establishing a sustainable cement and concrete construction capacity in Africa.
After a successful first pan-African proficiency testing scheme in 2012/2013, it was decided to establish the scheme permanently and independent of the SPIN project.
The main focus of setting up a testing scheme was to enable all cement testing laboratories in Africa to evaluate their competence and efficiency in cement testing and further enhance their capacity to obtain better quality products according to their environment. The acronym developed for the PT scheme is PACE-PTS (Pan-African Cement Proficiency Testing Scheme). The framework for the PT scheme was set up jointly among the organisers and the first participants. The first PT scheme was initiated in Dar Es Salaam in 2012 followed by a final workshop in Berlin in 2013. The second PT scheme began in 2014. A final workshop was organised in Dar es Salaam in 2015. The third and current scheme was started in 2016 and the final workshop is held in Yaoundé.