TY - JOUR A1 - Kruschwitz, Sabine A1 - Munsch, Sarah A1 - Telong, Melissa A1 - Schmidt, Wolfram A1 - Bintz, Thilo A1 - Fladt, Matthias A1 - Stelzner, Ludwig T1 - The NMR core analyzing TOMograph: A multi-functional tool for non-destructive testing of building materials JF - Magnetic Resonance Letters N2 - NMR is becoming increasingly popular for the investigation of building materials as it is a non-invasive technology that does not require any sample preparation nor causes damage to the material. Depending on the specific application it can offer insights into properties like porosity and spatial saturation degree as well as pore structure. Moreover it enables the determination of moisture transport properties and the (re-)distribution of internal moisture into different reservoirs or chemical phases upon damage and curing. However, as yet most investigations were carried out using devices originally either designed for geophysical applications or the analysis of rather homogeneous small scale (< 10 mL) samples. This paper describes the capabilities of an NMR tomograph, which has been specifically optimized for the investigation of larger, heterogeneous building material samples (diameters of up to 72 mm, length of up to 700 mm) with a high flexibility due to interchangeable coils allowing for a high SNR and short echo times (50 - 80 m s). KW - Fire spalling KW - Moisture transport KW - Concrete KW - Cement hydration KW - Sensitivity KW - Supplementary cementitous materials KW - Frost salt attack PY - 2023 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-573755 DO - https://doi.org/10.1016/j.mrl.2023.03.004 SN - 2097-0048 VL - 3 IS - 3 SP - 207 EP - 219 PB - Elsevier B.V. AN - OPUS4-57375 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Kääriäinen, H. A1 - Rudolph, Michael A1 - Schaurich, Dieter A1 - Tulla, K. A1 - Wiggenhauser, Herbert T1 - Moisture measurements in building materials with microwaves JF - NDT & E international N2 - The method requires two parallel boreholes in the specimen in which two microwave antennae can be moved. The moisture content in the material can be calculated from the microwave intensity transmitted between the two boreholes. Moisture profiles along the boreholes can be obtained by moving the antennae in steps along the length of the boreholes and taking measurements at each step. The microwave frequencies used in the laboratory measurements ranged from 8 to 16.5 GHz in steps of 0.5 GHz. The diameters of the antennae were between 7 and 9 mm, and of the boreholes between 8 and 12 mm. The microwave method produced measurement uncertainties between 0 and 2% by volume for all the materials studied in this report. KW - Construction materials KW - Moisture transport KW - Moisture meter KW - Microwaves KW - Concrete KW - Sand KW - Wood PY - 2001 SN - 0963-8695 VL - 34 IS - 6 SP - 389 EP - 394 PB - Butterworth-Heinemann CY - Oxford AN - OPUS4-11049 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Pohl, Christoph A1 - Smilauer, V. A1 - Unger, Jörg F. T1 - A three-phase transport model for high-temperature concrete simulations validated with X-ray CT data JF - Materials N2 - Concrete exposure to high temperatures induces thermo-hygral phenomena, causing water phase changes, buildup of pore pressure and vulnerability to spalling. In order to predict these phenomena under various conditions, a three-phase transport model is proposed. The model is validated on X-ray CT data up to 320 ◦C, showing good agreement of the temperature profiles and moisture changes. A dehydration description, traditionally derived from thermogravimetric analysis, was replaced by a formulation based on data from neutron radiography. In addition, treating porosity and dehydration evolution as independent processes, previous approaches do not fulfil the solid mass balance. As a consequence, a new formulation is proposed that introduces the porosity as an independent variable, ensuring the latter condition. KW - Concrete KW - Porous media KW - Spalling KW - Dehydration KW - Moisture transport KW - Heat transfer KW - Pore pressure KW - Porosity KW - Finite elements PY - 2021 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-532840 UR - https://doi.org/10.5281/zenodo.4890635 DO - https://doi.org/10.3390/ma14175047 SN - 1996-1944 VL - 14 IS - 17 SP - 1 EP - 21 PB - MDPI CY - Basel AN - OPUS4-53284 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Stelzner, Ludwig A1 - Powierza, Bartosz T1 - Thermisch induzierter Feuchtetransport in HPC T1 - Thermally induced Moisture Transport in structure density High-performance Concrete JF - Beton- und Stahlbetonbau N2 - Die Entwicklung von leistungsfähigen Fließmitteln in den letzten Jahrzehnten ermöglicht die Herstellung von Beton mit sehr geringem w/z-Wert, bei gleichzeitig guter Verarbeitbar-keit. Die Reduzierung des w/z-Wertes geht dabei mit einer Erhöhung der Festigkeit und einer Verdichtung der Gefü-gestruktur einher. Aufgrund der hohen Druckfestigkeit finden diese Hochleistungsbetone vermehrten Einsatz im Hoch-, Brücken-, und Tunnelbau. Unter Brandbeanspruchung neigen diese Hochleistungsbetone allerdings zu explosionsartigen Abplatzungen. Diese werden nach derzeitigem Stand auf thermomechanische und thermohydraulische Prozesse zurückgeführt. Letztere beruhen auf der Generierung hoher Wasserdampfdrücke in einseitig brandbeanspruchten Beton-bauteilen, die zum einen auf die geringe Permeabilität des Hochleistungsbetons und zum anderen auf die Bildung einer wassergesättigten Zone, der sogenannten „moisture clog“ zurückzuführen sind. Dabei spielen Verdampfungs- und Kondensationsvorgänge sowie der vorhandene Temperatur-gradient eine wichtige Rolle. Die Interaktion des Feuchtetra-nsportes mit den Gefügeveränderungen während der thermi-schen Beanspruchung soll im Rahmen weiterer Versuche eingehend untersucht werden. Zur Analyse des Feuchtetransports während der thermischen Beanspruchung wurden miniaturisierte Prüfkörper aus Hoch-leistungsbeton hergestellt, die mit Hilfe eines elektrischen Heizelements einseitig erwärmt wurden. Zur Sicherstellung eines eindimensionalen Wärme- und Feuchtetransportes ist der Betonprüfkörper mit einer speziellen Glaskeramik und einer Hochtemperaturwolle ummantelt. Simultan zur Erwär-mung werden eine Reihe röntgentomographischer Aufnah-men durchgeführt. Durch Differenzbildung aufeinanderfol-gender Aufnahmen können Dichteveränderungen lokal und zeitlich aufgelöst werden. Diese lassen Rückschlüsse auf Än-derungen der Feuchteverteilung im Prüfkörper während der Erwärmung zu. Parallel dazu werden Untersuchungen mittels NMR-Relaxometrie (nuclear magnetic resonance) vor und nach der thermischen Beanspruchung durchgeführt. Diese Prüfmethodologie ermöglicht es erstmals, die Veränderungen der Feuchteverteilung infolge thermischer Beanspruchung im Hochleistungsbeton von den Gelporen bis hin zu vorhande-nen Verdichtungsporen abzubilden. So zeigen erste Ergebnis-se, dass die gewählten Untersuchungsmethoden Veränderun-gen der Feuchteverteilung im Prüfkörper räumlich und zeitlich auflösen können. KW - Abplatzen KW - Spalling KW - Brand KW - Feuchtetransport KW - Hochleistungsbeton KW - Röntgen-3D-Computertomographie KW - NMR KW - Fire KW - Moisture clog KW - Moisture transport KW - HPC KW - HSC KW - X-ray CT PY - 2017 DO - https://doi.org/10.1002/best.201700022 SN - 0005-9900 SN - 1437-1006 VL - 112 IS - 7 SP - 486 EP - 486 PB - Ernst & Sohn CY - Berlin AN - OPUS4-41826 LA - deu AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Strangfeld, Christoph T1 - Quantification of the Knudsen Effect on the Effective Gas diffusion Coefficient in Partially Saturated Pore Distributions JF - Advanced Engineering Materials N2 - The effective gas diffusion coefficient describes the process of gas diffusion in porous materials. Several materials have a significant number of micropores in the lower nanometre range leading to a reduction of gas diffusion (Knudsen effect). In the case of partial pore saturation during adsorption, the available pore space is further reduced, as is the gas diffusion. In this study, the influence of partially saturated pores on the Knudsen effect and on the gas diffusion is quantified. Three different pore geometries are investigated (slit, cylindrical and spherical pores) and three different types of pore size distribution, including a broad equal distribution, three narrow normal distributions and two measured distributions of concrete. Besides the intensive computation of the exact pore saturation, a simplified model with low computational requirements is suggested. This study shows that the influence of the water layer thickness on the effective diffusion becomes significant for pore radii below 50 nm and the assumed pore geometry is important. At the end, the overall effect is quantified for an amorphous material with most pore radii below 30 nm. At a moisture level of 50% relative humidity, the effective diffusion is reduced by 35% due to partial saturation. KW - Effective gas diffusion coefficient KW - Gas transport in porous media KW - Knudsen diffusion KW - Moisture transport KW - Nanopores PY - 2021 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-528509 DO - https://doi.org/10.1002/adem.202100106 VL - 23 IS - 10 SP - 2100106 PB - Wiley AN - OPUS4-52850 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Strangfeld, Christoph T1 - Determination of the diffusion coefficient and the hydraulic conductivity of porous media based on embedded humidity sensors JF - Construction and Building Materials N2 - Reinforced concrete and several other building materials deteriorate during their service life. Almost all deterioration processes are related to moisture. For understanding those processes, knowing the exact amount of the moisture content and the moisture transport characteristics is crucial. In fact, the moisture transport in porous materials is a two-phase flow; consisting of the vapour and the liquid phase. The two corresponding parameters are the diffusion coefficient and the hydraulic conductivity. By means of an inverse approach, these two coefficients are experimentally determined. The moisture transport of eight different screed types during hydration and evaporation is monitored based on embedded humidity sensors. The measured humidity profiles are converted into a pore saturation by adapting the approach of Hillerborg to the measured pore volume distribution. The summation of all pore saturations yields the total moisture content including the ink-bottle effect during desorption. The pore volume distribution was determined by mercury intrusion porosimetry as well as by gas adsorption. The measurement of the humidity and the pore saturation in the entire sample enables to invert the mass balance in order to extract the diffusion coefficient and the hydraulic conductivity. The determined diffusion coefficients of the eight investigated screeds are between m2s-1 and m2s-1. KW - Material moisture KW - Moisture transport KW - Embedded sensors KW - Diffusion coefficient KW - Partially saturated pores PY - 2020 DO - https://doi.org/10.1016/j.conbuildmat.2020.120092 VL - 263 SP - 120092 PB - Elsevier Ltd. AN - OPUS4-51029 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER -