@article{MuellerLudwigTangeHasholt, author = {M{\"u}ller, Matthias and Ludwig, Horst-Michael and Tange Hasholt, Marianne}, title = {Salt frost attack on concrete: the combined effect of cryogenic suction and chloride binding on ice formation}, series = {Materials and Structures}, volume = {2021}, journal = {Materials and Structures}, number = {issue 54, article 189}, doi = {10.1617/s11527-021-01779-7}, url = {http://nbn-resolving.de/urn:nbn:de:gbv:wim2-20211207-45392}, pages = {1 -- 16}, abstract = {Scaling of concrete due to salt frost attack is an important durability issue in moderate and cold climates. The actual damage mechanism is still not completely understood. Two recent damage theories—the glue spall theory and the cryogenic suction theory—offer plausible, but conflicting explanations for the salt frost scaling mechanism. The present study deals with the cryogenic suction theory, which assumes that freezing concrete can take up unfrozen brine from a partly frozen deicing solution during salt frost attack. According to the model hypothesis, the resulting saturation of the concrete surface layer intensifies the ice formation in this layer and causes salt frost scaling. In this study an experimental technique was developed that makes it possible to quantify to which extent brine uptake can increase ice formation in hardened cement paste (used as a model material for concrete). The experiments were carried out with low temperature differential scanning calorimetry, where specimens were subjected to freeze-thaw cycles while being in contact with NaCl brine. Results showed that the ice content in the specimens increased with subsequent freeze-thaw cycles due to the brine uptake at temperatures below 0 °C. The ability of the hardened cement paste to bind chlorides from the absorbed brine at the same time affected the freezing/melting behavior of the pore solution and the magnitude of the ice content.}, subject = {Beton}, language = {en} } @article{KleinerRoesslerVogtetal., author = {Kleiner, Florian and R{\"o}ßler, Christiane and Vogt, Franziska and Osburg, Andrea and Ludwig, Horst-Michael}, title = {Reconstruction of calcium silicate hydrates using multiple 2D and 3D imaging techniques: Light microscopy, μ-CT, SEM, FIB-nT combined with EDX}, series = {Journal of Microscopy}, volume = {2021}, journal = {Journal of Microscopy}, publisher = {John Wiley \& Sons Ltd}, address = {Oxford}, doi = {10.1111/jmi.13081}, url = {http://nbn-resolving.de/urn:nbn:de:gbv:wim2-20220106-45458}, pages = {1 -- 6}, abstract = {This study demonstrates the application and combination of multiple imaging techniques [light microscopy, micro-X-ray computer tomography (μ-CT), scanning electron microscopy (SEM) and focussed ion beam - nano-tomography (FIB-nT)] to the analysis of the microstructure of hydrated alite across multiple scales. However, by comparing findings with mercury intrusion porosimetry (MIP), it becomes obvious that the imaged 3D volumes and 2D images do not sufficiently overlap at certain scales to allow a continuous quantification of the pore size distribution (PSD). This can be overcome by improving the resolution and increasing the measured volume. Furthermore, results show that the fibrous morphology of calcium-silicate-hydrates (C-S-H) phases is preserved during FIB-nT. This is a requirement for characterisation of nano-scale porosity. Finally, it was proven that the combination of FIB-nT with energy-dispersive X-ray spectroscopy (EDX) data facilitates the phase segmentation of a 11 × 11 × 7.7 μm3 volume of hydrated alite.}, subject = {Zementklinker}, language = {en} } @techreport{MuellerSeidelLudwigetal., author = {M{\"u}ller, Christoph and Seidel, Maik and Ludwig, Horst-Michael and M{\"u}ller, Matthias}, title = {Pr{\"u}fung des Frost-Tausalz-Widerstandes von Beton f{\"u}r die Expositionsklasse XF2}, doi = {10.25643/bauhaus-universitaet.4887}, url = {http://nbn-resolving.de/urn:nbn:de:gbv:wim2-20240226-48877}, pages = {34}, abstract = {In cold and moderate climates concrete can be subjected to a combined salt frost attack, which can cause scaling damage. Consequently, numerous test procedures were developed to determine the resistance of concrete compositions against this kind of attack. These tests typically mimic a severe attack with high levels of saturation, e.g. as for concrete pavements. Very few approaches exist for testing the salt frost scaling resistance of concretes, which are subjected only to medium levels of saturation, as such concrete elements typically don't show notable scaling damage. However, the increasing use of low carbon cements with high clinker substitution rates might affect the salt frost scaling resistance of such concrete elements to some extent. To ensure adequate durability of such concretes it is thus desirable to determine their performance in an actual test procedure instead of relying on past experience. Thus, less severe test methods was developed, which are based on the Slab test and the CDF test, repectively.}, subject = {Beton}, language = {de} }