TY - CONF A1 - Stelzner, Ludwig A1 - Weise, Frank A1 - Oesch, Tyler A1 - Dlugosch, R. A1 - Powierza, Bartosz T1 - Transport and reconfiguration of moisture in HPC due to unilateral heating T2 - Proceedings of the 6th International Workshop on Concrete Spalling due to Fire Exposure N2 - Explosive spalling is caused by, among others, the thermohydraulic spalling mechanism. During this process, vaporization, dehydration, moisture-transport and condensation processes interact. As a result, a drying and dehydration zone as well as a saturated zone, known as a moisture clog, are observed inside the unilaterally-heated concrete. The presented research is focused on the experimental investigation of the underlying thermohydraulic processes. To investigate these, a test methodology based on X-ray computed tomography (CT) and nuclear magnetic resonance (NMR) was developed. Thereby, the X-ray CT scans are carried out simultaneously during the application of a defined unilateral-heating regime on a specially-constructed specimen. This miniaturized specimen, equipped with a double-layer casing, reproduces the condition within a planar, unilaterally-heated building component. A preliminary test methodology and the first experimental results were presented at the 5th International Workshop on Concrete Spalling in Borås, Sweden (2017). The contribution for the upcoming workshop presents an improved version of this test methodology and new results for a high-performance concrete (HPC) mixture exposed to temperatures up to 500 °C. Regarding the CT measurements, a higher time-resolution of 15 min was achieved and a quantification of the moisture changes was implemented. Due to an increase in signal quality of the NMR measurements, a pore-size specific moisture distribution can now be resolved. This allows to conclude about the moisture reconfiguration between small gel pores and larger interhydrate pores. Additionally, the NMR measurement are no longer limited to first 2.5 cm below the heated surface but a one-dimensional moisture distribution can now be estimated over the whole 10 cm long specimen. The presented results demonstrate that the combination of X-ray CT and NMR measurements enables to image and quantify the thermally-induced moisture transport and reconfiguration from small gel pores up to macro pores. This provides important insights into the thermohydraulic damage mechanism and leads to a better understanding of spalling avoidance strategies, like the addition of polypropylene fibres. T2 - 6th International Workshop on Concrete Spalling due to fire exposure CY - Sheffield, UK DA - 19.09.2019 KW - Moisture clog KW - X-ray CT KW - NMR KW - Moisture transport KW - HPC PY - 2019 UR - https://firespallingworkshop2019.group.shef.ac.uk/wp-content/uploads/2019/09/Fire-Spalling-Workshop_Proceedings.pdf SN - 978-1-5272-4135-0 SP - 181 EP - 190 CY - Sheffield AN - OPUS4-49161 LA - deu AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Stelzner, Ludwig A1 - Weise, Frank A1 - Oesch, Tyler A1 - Dlugosch, R. A1 - Powierza, Bartosz T1 - Transport and reconfiguration of moisture in HPC due to unilateral heating N2 - Explosive spalling is caused by, among others, the thermohydraulic spalling mechanism. During this process, vaporization, dehydration, moisture-transport and condensation processes interact. As a result, a drying and dehydration zone as well as a saturated zone, known as a moisture clog, are observed inside the unilaterally-heated concrete. The presented research is focused on the experimental investigation of the underlying thermohydraulic processes. To investigate these, a test methodology based on X-ray computed tomography (CT) and nuclear magnetic resonance (NMR) was developed. Thereby, the X-ray CT scans are carried out simultaneously during the application of a defined unilateral-heating regime on a specially-constructed specimen. This miniaturized specimen, equipped with a double-layer casing, reproduces the condition within a planar, unilaterally-heated building component. A preliminary test methodology and the first experimental results were presented at the 5th International Workshop on Concrete Spalling in Borås, Sweden (2017). The contribution for the upcoming workshop presents an improved version of this test methodology and new results for a high-performance concrete (HPC) mixture exposed to temperatures up to 500 °C. Regarding the CT measurements, a higher time-resolution of 15 min was achieved and a quantification of the moisture changes was implemented. Due to an increase in signal quality of the NMR measurements, a pore-size specific moisture distribution can now be resolved. This allows to conclude about the moisture reconfiguration between small gel pores and larger interhydrate pores. Additionally, the NMR measurement are no longer limited to first 2.5 cm below the heated surface but a one-dimensional moisture distribution can now be estimated over the whole 10 cm long specimen. The presented results demonstrate that the combination of X-ray CT and NMR measurements enables to image and quantify the thermally-induced moisture transport and reconfiguration from small gel pores up to macro pores. This provides important insights into the thermohydraulic damage mechanism and leads to a better understanding of spalling avoidance strategies, like the addition of polypropylene fibres. T2 - 6th International Workshop on Concrete Spalling due to fire exposure CY - Sheffield, UK DA - 19.09.2019 KW - Moisture clog KW - X-ray CT KW - NMR KW - Moisture transport KW - HPC PY - 2019 AN - OPUS4-49159 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Stelzner, Ludwig T1 - Explosionsartiges Abplatzen gefügedichter Betone im Brandfall N2 - Beton, der heutzutage meist verwendete Baustoff, weist neben gutem Festigkeits- und Dauerhaftig-keitsverhalten ebenfalls erhöhte Brandschutzeigenschaften auf. Jedoch zeigen zahlreiche Schadensfälle, dass vor allem gefügedichte Betone im Brandfall zu explosionsartigen Abplatzungen neigen. Diese führen zum Freilegen der vorhandenen Stahlbewehrung und zur Verminderung des tragfähigen Bauteilquer-schnitts. Das wiederum kann im schlimmsten Fall eine Gefährdung der Standsicherheit eines Bauwerks zur Folge haben. Nach derzeitigem Stand werden die explosionsartigen Abplatzungen auf thermomechanische und thermohydraulische Prozesse zurückgeführt. Letztere beruhen auf der Generierung hoher Wasserdampfdrücke in einseitig brandbeanspruchten Betonbauteilen, die zum einen auf die geringe Permeabilität des hochfesten Betons und zum anderen auf die Bildung einer wassergesättigten Zone, der sogenannten „moisture clog“ zurückzuführen sind. Die experimentelle Analyse der dabei ablaufenden Feuchtetransport- und Feuchteumlagerungsmechanismen ist Gegenstand des Vortrags. Dazu wurde an der BAM im Rahmen eines MI-Typ 2 Projektes (FB 7.1, 7.3, 8.5) ein Versuchsstand aufgebaut, der die dreidimensionale, simultane Analyse und Quantifizierung des Feuchtetransports an einsei-tig erwärmten, miniaturisierten Prüfkörpern aus gefügedichtem Beton mittels Röntgencomputertomographie erstmals ermöglicht. Zusätzlich wird die eindimensionale Feuchteverteilung im Prüfkörper mittels Nuclear Magnetic Resonance (NMR) Technik vor und nach einseitiger Erwärmung untersucht. Mithilfe dieser Prüfmethodologie ist es möglich, die Ausbildung einer Trocknungs- bzw. Dehydrationszone sowie einer tiefergelegenen Feuchteakkumulationszone zeitlich aufgelöst abzubilden. Darüber hinaus können die Einflüsse einer Polypropylenfaserzugabe auf den thermisch induzierten Feuchtetransport quantifiziert werden. T2 - Abteilungs-Vortragsseminar CY - Berlin, Germany DA - 30.04.2019 KW - Explosionsartiges Abplatzen KW - Moisture clog KW - X-ray-CT KW - 1H-NMR KW - High-performance concrete PY - 2019 AN - OPUS4-48729 LA - deu AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER -