Numerische Modellierung von textilbewehrtem Beton

Numerical Modelling of Textile Reinforced Concrete The paper provides a short survey of the state‐of‐the‐art approaches to numerical modelling of the textile‐reinforced concrete with the focus on the special requirements arising from the heterogeneity of the material structure. The presented models make it possible to thoroughly interpret and generalize the experimental results and, thus, to contribute to the goal‐oriented development of the textile reinforced concrete in general.     

Betontechnologie und Dauerhaftigkeit von glasfaserbewehrten Bauteilen

Concrete Technology and Durability of Glass Fibre Reinforced Structures The durability of glass fibre reinforced concrete structures is significantly determined by matrix composition, the type of glass and its surface quality including necessary coatings. In the paper an experimental overview is given concerning special material influences and their interaction in the composite.     

Tragverhalten von textilbewehrtem Beton

Load‐bearing Behaviour of Textile Reinforced Concrete. Bond Cracking Behaviour and Load‐bearing Behaviour The load‐bearing behaviour of Textile Reinforced Concrete (TRC) is similar to concrete reinforced by steel, however, it is more influenced by the bond of the technical textile in the fine concrete. Thus the cracking behaviour, loading capacity, the deformation behaviour and the durability are investigated besides the material properties. Based on the results of these investigations, design models have been developed and first applications have been realized. The article summarizes the recent results in the field of load‐bearing behaviour of TRC.     

Vorgespannte Bauteile aus textilbewehrtem Beton

Prestressed Textile reinforced Elements The paper shows that prestressing of textile reinforcement results in a higher load bearing capacity and stiffness of a textile reinforced element. Particularities of textile reinforcement for prestressing compared to textile reinforcement for non‐prestressed elements will be described. Special requirements for textiles used for prestressing are explained, which take clamping techniques, bond behaviour and the design of prestressed textile reinforced elements into consideration. In this context, the importance of internal and external bond are discussed.     

Mechanisms of Fabric Reinforcement of Cement Matrices

The present paper discusses the mechanisms involve in fabric‐cement composites focusing on the effects of fabric geometry and the properties of the yarns. It was found that the geometry of a given fabric could enhance the bonding and enable one to obtain strain hardening behavior from low modulus yarn fabrics, due to the special shape of the yarn induced by the fabric. On the other hand, variations of the geometry in a fabric could drastically reduce the efficiency, resulting in a lower strengthening effect of the yarns in the fabric, relative to single yarns not in a fabric form. Therefore, in cement composites the fabrics can not be viewed simply as a means for holding together continuous yarns to be readily placed in the matrix, as is the case in composites with polymer matrix.     

Auswirkungen der Matrixzusammensetzung auf die Dauerhaftigkeit von Betonen mit textilen Bewehrungen aus AR‐Glas

Verbundmaterialien aus Feinbetonen mit textiler Bewehrung aus alkaliresistentem Glas (AR‐Glas) können ausgeprägten zeitabhängigen Veränderungen hinsichtlich des mechanischen Leistungsvermögens unterliegen. Für eine zielsichere Anwendung solcher Werkstoffe im Bauwesen sind genaue Kenntnisse über die Höhe und die Ursachen dieser Leistungsverluste unabdingbar. In diesem Artikel werden anhand von Ergebnissen aktueller Untersuchungen entscheidende Mechanismen für die Alterungsprozesse dargestellt, die aus der Zusammensetzung der Feinbetone resultieren. Dazu wurden aus verschiedenen Betonzusammensetzungen, die sich maßgeblich in ihrer Hydratationskinetik und Alkalität unterschieden, textilbewehrte Dehnkörper hergestellt und nach beschleunigter Alterung geprüft. Dehnkörper aus Feinbeton mit hoher Alkalität (das Bindemittel bestand nur aus CEM I) zeigten dramatische Einbußen bei Zugfestigkeit und Bruchdehnung. Das Leistungsvermögen von Proben aus Feinbetonen mit puzzolanisch abgepufferter Bindemittelzusammensetzung und gleichzeitig reduziertem Portlandzementklinkeranteil zeigte sich dagegen weitgehend unbeeinflusst von Alterungsprozessen. Mit Hilfe von beidseitigen Garnauszugversuchen an beschleunigt gealterten Feinbetonproben wurden die für das unterschiedliche Materialverhalten verantwortlichen Degradationsmechanismen aufgeklärt. Neben der mechanischen Prüfung wurde dazu auch die Interphase zwischen Fasern und umgebendem Feinbeton mit bildgebenden und analytischen Verfahren charakterisiert. Die festgestellten Einbußen im Leistungsvermögen des Garn‐Matrix‐Verbundes konnten überwiegend auf die Neubildung von ungünstig strukturierten Hydratationsprodukten in der Interphase Filament‐Matrix bzw. in Filamentzwischenräumen zurückgeführt werden. Die Morphologie dieser Phase wird maßgeblich von der Bindemittelzusammensetzung bestimmt. Korrosion des AR‐Glases als Schadensursache kann unter ungünstigen Umständen auch eine große Rolle spielen, ist aber bei geeigneter Matrixformulierung von untergeordneter Bedeutung. Effect of Matrix Composition on the Durability of Concretes Reinforced with Glass Fibre Fabric The mechanical performance of composites made of finegrained concrete and textile reinforcement can worsen markedly with increasing age if alkali‐resistant glass (AR‐glass) is used as the reinforcing material. For reliable practical applications of textile‐reinforced concrete, precise knowledge as to the extent and causes of such degradation is indispensable. This paper discusses important aging mechanisms resulting from the composition of fine‐grained concrete. Tensile tests on composites made of different concrete compositions distinguished from one another by their hydration kinetics and alkalinity were performed before and after accelerated aging. Composites made of concrete with high alkalinity showed dramatic losses of tensile strength and strain capacity. In contrast the mechanical performance of composites whose binders had reduced Portland cement clinker content plus added puzzolana was hardly affected by the accelerated aging. To clarify the mechanisms of degradation, yarn pullout tests were performed on specimens of equal matrix composition and age. Additionally, the morphology of the interphase between matrix and fibre was characterised using direct microscopic examination and analytical methods. The new formation of unfavourably structured products of hydration in the filament‐matrix interphase and/or in the empty spaces between filaments was found to be the main reason for the performance losses observed. The morphology of these hydration products is determined to a great extent by the binder composition. Under unfavourable conditions corrosion of AR‐glass can occur as well and lead to distinct composite damage. However, if the formulation of the binder is proper, bulk glass corrosion is of minor importance.     

Tragwiderstand von Betonbauteilen nach dem Brand

Load carrying capacity of concrete structures after fire exposure. The mechanical and thermal properties of building materials change at elevated temperatures. This change of material properties has an important influence on the load carrying and deformation behaviour in case of fire. The rate of increase of temperature through the cross section in a concrete element is relatively slow and so internal zones are protected against heat. Only a small part of the cross‐section is affected by the temperature action (loss of strength and stiffness). For these reasons reinforced concrete structures with adequate structural detailing usually reach high fire resistance without any additional fire protection. However after the fire has been extinguished the heat penetration into the cross section continues for hours. Additionally calcium hydroxide reformats during the cooling phase widening up micro cracks. The combination of these two phenomena can lead to a significant reduction of the compressive strength of concrete after the fire. This paper analyses the influence of the loss of strength during and after the cooling on the load carrying capacity of concrete elements. The numerical calculations presented in this study showed that after the cooling phase concrete elements can exhibit a load carrying capacity lower than during the fire. The design of concrete structures based on equivalent time of standard fire exposure without cooling phase can lead to unsafe results. For this reason it may be important to take into account the cooling phase of the fire for the calculation of the load bearing capacity of concrete structures.