TY - JOUR A1 - Pistol, Klaus A1 - Weise, Frank A1 - Meng, Birgit T1 - Polypropylen-Fasern in Hochleistungsbetonen - Wirkungsmechanismen im Brandfall JF - Beton- und Stahlbetonbau N2 - Bauteile bzw. Tragwerke aus Hochleistungsbetonen müssen in der Regel gegen brandinduzierte Abplatzungen mit geeigneten Maßnahmen geschützt werden, um einen ausreichenden Feuerwiderstand im Brandfall zu gewährleisten. Die bisher wirtschaftlich und technologisch sinnvollste Methode zur Verhinderung von explosionsartigen Betonabplatzungen im Brandfall ist die Zugabe von Polypropylen-Fasern. Die Wirksamkeit der Fasern konnte zwar empirisch gezeigt werden, es stellt sich allerdings die Frage, welche Mechanismen zur Verhinderung der Abplatzungen führen. Der vorliegende Beitrag fasst bisherige Theorien zur Wirkungsweise von Polypropylen-Fasern in brandbeanspruchten Hochleistungsbetonen zusammen und stellt eine innovative Methodologie zur Erforschung der mikrostrukturellen Prozesse vor. Die Ergebnisse zeigen, dass die nach dem Schmelzen und Zersetzen der Polypropylen-Fasern frei werdenden Mikrokanäle durch eine gleichzeitig einsetzende Mikrorissbildung netzartig verbunden werden. Die Mikrorissbildung ermöglicht somit den Abbau von Eigen- und Zwangsspannungen im Beton (mechanischer Effekt) und die Entstehung eines Transportwegesystems für den ausströmenden Wasserdampf (Permeationseffekt).--------------------------------------------------------------------------- Structural members and bearing structures of high performance concrete generally have to be protected against explosive spalling due to fire exposure to guarantee a sufficient fire resistance. Up to now, the economically and technologically most worthwhile method to prevent explosive spalling is the addition of polypropylene fibres. Though the effectiveness of the fibres could be shown empirically, the mechanisms preventing explosive spalling are still debatable. The present article summarizes the existing theories concerning the mode of action of polypropylene fibres in fire exposed high performance concretes and presents an innovative methodology for analysing the micro structural processes. The results show that due to the thermal decomposition of the polypropylene fibres micro channels are created and simultaneously connected due to a netlike micro crack formation. This enables the relief of internal stresses (mechanical effect) and the formation of a permeable transport system for the escaping water vapour (permeation effect). KW - Polypropylen-Fasern KW - Brandschutz KW - Structural fire protection KW - Computertomographie KW - Computed tomography KW - Hochleistungsbeton KW - High performance concrete KW - Messtechnik KW - Mikrorisse KW - Micro cracks KW - Polypropylen-Fasern KW - Polypropylene fibres KW - PP-Fasern KW - Prüfmethoden KW - Rasterelektronenmikroskopie KW - Scanning electron microscopy KW - Risse KW - Schallemissionsanalyse KW - Acoustic emission KW - UHPC KW - Baustoffe KW - Brandschutz KW - Versuche PY - 2012 DO - https://doi.org/10.1002/best.201200024 SN - 0005-9900 SN - 1437-1006 VL - 107 IS - 7 SP - 476 EP - 483 PB - Ernst CY - Berlin AN - OPUS4-26174 LA - deu AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - von Werder, Julia A1 - Gardei, André A1 - Meng, Birgit ED - Caprai, V. ED - Brouwers, H. J. H. T1 - Functionalization of fibres for cement-based materials - selected test methods T2 - Proceedings ICSBM 2019 N2 - The low tensile strength of cement-based materials can be improved by the addition of fibres. In a joint research project, an industrial partner designed special coatings for polymer and carbon fibres by integrating surfactants and hydrophilic compounds. Aim of the developed functionalization was to ensure an even coverage of the fibre surfaces and to anchor them chemically in the cement-based matrix. Task of the BAM was to quantify the effect of the improved bond. In a first step a workable mortar adjusted to the strength of the tested fibres was developed and the fibre distribution assessed by light microscopy and computed tomography. To test the new coating for its efficiency to prevent cracking during hardening and to improve the loadbearing behaviour new test setups were developed or existing methods were adjusted. The experiments showed that the functionalization leads to a reduction of the crack area measured after the exposure of the wet mortar to strong drying conditions in the wind channel. Regarding the Efficiency to mitigate shrinkage cracks the functionalisation turned out to be more efficient for fibres made from polyacrylonitrile (PAN) than for carbon fibres. An improvement of the tensile strength after cracking of the cementitious matrix could only be documented for the coated carbon fibres. It could be quantified, however, only in the three-point bending tests because the fibres turned out to be too brittle for the applied single fibre pull-through test. T2 - 2nd International Conference on Sustainable Building Materials CY - Eindhoven, Netherlands DA - 12.08.2019 KW - Fibres KW - Functionalization KW - Mortar KW - Computed tomography KW - Shrinkage PY - 2019 VL - 5 SP - 16 EP - 25 AN - OPUS4-49480 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER -