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- ja (22) (entfernen)
Schlagworte
- Earth block masonry (4)
- Diagonal compression test (3)
- Earthen materials (3)
- Anchor pins (2)
- Artificial weathering (2)
- Compression test (2)
- Numerical modelling (2)
- Pull-out tests (2)
- Stearates (2)
- Uniaxial compression test (2)
Organisationseinheit der BAM
The study evaluates Portland limestone cement mortars, natural hydraulic lime mortars and pozzolan-lime mortars modified with water-repellent admixtures (metal soaps and siloxanes) for their use in the maintenance of historic buildings. The chemical-physical characteristics, the durability and the resistance to artificial weathering (exposure to UV light and artificial rain) were examined. The exposure conditions used in the ageing test were chosen in order to simulate outdoor environmental conditions, in particular the processes caused by UV-light and thermal shock induced by rain water.
Es ist bekannt, dass eine Faserbewehrung die Schrumpfrissbildung in Beton vermindern kann. In der Literatur finden sich jedoch zum Teil widersprüchliche Angaben über die Wirksamkeit unterschiedlicher Faserarten, und deren Wirkungsmechanismus ist noch nicht vollständig geklärt. Fasern, die in Deutschland als Betonzusatzstoff eingesetzt werden sollen, bedürfen einer Zulassung durch das DIBt, das für den Nachweis ihrer Wirksamkeit zur Verminderung der Schrumpfrissbildung ein Prüfverfahren mit großformatigen Platten vorschreibt. In diesem Bericht werden die Ergebnisse einer Studie vorgestellt, in der die Eignung verschiedener Prüfverfahren hinsichtlich der Beurteilung der Wirksamkeit von Polymerfasern untersucht wurde. Dieser Bericht ist eine verkürzte Fassung eines Beitrags zum 52. Forschungskolloquium des DAfStb.
Connections improvement plays a key role in seismic upgrade of historical buildings. Their global response is related to the behaviour of the single structural elements as well as by their mutual connections. Up to now limited data is available on the performance of grouted anchor pins in earthen materials where the critical point is the bond between the grout and the earthen substrate.
In this paper results of the experimental testing performed on earth block masonry are presented. Pull-out tests were carried out to investigate the bond strength and failure modes of stainless steel as well as glass fiber reinforced polymer (GFRP) rods with a lime based hydraulic grout and their compatibility with earth block masonry. GFRP rods were investigated as an alternative bonded-in anchorage material to the commonly used steel. In comparison with steel, they have a reduced weight and a reduced coefficient of thermal expansion. Their lower modulus of elasticity seems to be more compatible with the modulus of elasticity of earthen materials, although they exhibit a brittle fracture with lack of plastic phase.
Connections improvement plays a key role in seismic upgrade of historical buildings. Their global response is related to the behavior of the single structural elements as well as to their mutual connections. Up to now only few data are available about the performance of grouted anchor pins in earthen materials where the critical point is the bond between the grout and the earthen substrate. In this paper, results of the experimental testing performed on earth block masonry, rammed earth and cob are presented. Pull-out tests were carried out to investigate the bond strength and failure modes of stainless steel rods with a lime based hydraulic grout and their compatibility with earthen materials. Rods with nuts were investigated to improve the pull-out capacity of the anchors. They showed higher pull-out capacity than rods without nuts. The performances of rods with nuts in cob were influenced by the rough surface at/of the earthen substrate. It is assumed that the non homogeneous surface caused an interlocking mechanism, which allowed to reach a pull-out capacity of about 54% higher than in earth block masonry.
The study presents the results from the development of a grouting material based on hydrated lime with addition of pozzolana, which is referred to as hydraulic lime, suitable for the repair of cracks in a variety of earthen building techniques. The goal was to develop a material also compatible with earthen structures exposed to dynamic loads. The grouting mortar was designed to be adaptable in strength properties and at the same time to have sufficient robustness for preparation and use on the construction site.
Results showed a satisfactory performance of the grout concerning fresh and hardened mortar properties as well as injectability.
The main aim of the research was the development of a first valid database for material parameters of earth block masonry (EBM) with particular regard to statistical characteristics. A solid database is needed for the determination of the materials partial safety factor. Therefore, compressive strength tests were carried out with two types of earth blocks and two types of prefabricated earth mortar.
The evaluation has shown that the mean variation of the compressive strength was remarkably less than expected, which indicates high quality standards of the components earth block and mortar with regard to industrial production. Using the reliability method, a partial safety factor for EBM subjected to compression was determined on the basis of these test results. The findings have shown that a common calculation method for EBM based on partial safety factors following the valid masonry construction standard is feasible.
Mittels Wärmebehandlung lassen sich die hervorragenden Eigenschaften von UHFB nochmals verbessern. Die für eine optimale Umsetzung relevanten Randbedingungen werden aktuell in der Fachwelt diskutiert. In dieser Veröffentlichung werden die Ergebnisse eines Forschungsprojekts vorgestellt, das die Wirkung verschiedener Einflussgrößen bei der Wärmebehandlung auf die Eigenschaften von UHFB zum Thema hatte. Dabei wurden die Art des Schutzes gegen das Austrocknen, die Vorlagerungszeit und die Haltezeit variiert. Um die zugrunde liegenden Prozesse zu verstehen, wurde der Phasenbestand mittels Röntgendiffraktometrie untersucht. Die höchsten Druckfestigkeiten des UHFB ließen sich bei einer Wärmebehandlung mit Wasserlagerung erzielen, da hierbei eine weitere Hydratation begünstigt wird. Vergleichsweise niedriger waren die Steigerungen bei einer Behandlung mit Schutz vor Austrocknung, während eine ungeschützte Behandlung zu deutlich geringeren Festigkeiten führte. Die Vorlagerungszeit beträgt im Idealfall einige Tage, um die Ausbildung eines offenbar günstigen Ausgangsgefüges sicherzustellen. Die Haltezeit sollte möglichst ausgedehnt sein, weil die Hydratation entsprechend lange gefördert wird. Im oberflächennahen Bereich war unter bestimmten Bedingungen eine Zonierung zu beobachten, deren Ursachen und Folgen, insbesondere in Bezug auf die Dauerhaftigkeit, weitere Forschung erfordern.
This paper focuses on the experimental evaluation of one of the key microstructural Parameters of a short-fiber reinforced composite – the orientation distribution of fibers. It is shown that computed tomography (CT) produces results suitable for reconstruction of the orientation distribution function. This function is used for calculation of the effective elastic properties of polymer-fiber reinforced concrete. Explicit formulas are derived for overall elastic moduli accounting for orientation distribution in the frameworks of the noninteraction approximation, the Mori–Tanaka–Benveniste scheme, and the Maxwell scheme.
The approach illustrated can be applied to any kind of composite material.
The current paper focuses on the determination of reliable numerical models of earth block masonry wallettes under different loading conditions. Uniaxial compression and diagonal compression tests were performed. Experimental behaviour was modelled with a non-linear model able to describe the cracking behaviour. The simplified approach based on macro-modelling shows a satisfactory accuracy and low computational costs. The results reproducing the uniaxial compression are in good correspondence with the post-elastic behaviour observed in the experimental campaign. The micro-modelling approach adopted to reproduce the shear behaviour, even with high computational cost, represents a suitable tool to predict the masonry collapse mechanism.