TY - GEN A1 - Gehlen, Christoph A1 - Thiel, Charlotte T1 - Schnellprüfverfahren zur Bestimmung des Karbonatisierungswiderstandes T2 - Proceedings, 59. BetonTage : Betone der Zukunft, Neu-Ulm, 24.-26.02.2015 Y1 - 2015 PB - Bauverl. ER - TY - JOUR A1 - Haynack, Alexander A1 - Sekandar, Zadran A1 - Jithender, J. Timothy A1 - Gambarelli, Serena A1 - Kränkel, Thomas A1 - Thiel, Charlotte A1 - Ozbolt, Josko A1 - Gehlen, Christoph T1 - Can a Hend-Held 3D Scanner Capture Temperature-Induced Strain of Mortar Samples? Comparison between Experimental Measurements and Numerical Simulations JF - mathematics N2 - The expected lifespan of cement-based materials, particularly concrete, is at least 50 years. Changes in the pore structure of the material need to be considered due to external influences and associated transport processes. The expansion behaviour of concrete and mortar during freeze–thaw attacks, combined with de-icing salt agents, is crucial for both internal and external damage. It is essential to determine and simulate the expansion behaviour of these materials in the laboratory, as well as detect the slow, long-term expansion in real structures. This study measures the expansion of mortar samples during freeze–thaw loading using a high-resolution hand-held 3D laser scanner. The specimens are prepared with fully or partially saturated pore structures through water storage or drying. During freeze–thaw experiments, the specimens are exposed to pure water or a 3% sodium chloride solution (NaCl). Results show contraction during freezing and subsequent expansion during thawing. Both test solutions exhibit similar expansion behaviour, with differences primarily due to saturation levels. Further investigations are required to explore the changing expansion behaviour caused by increasing microcracking resulting from continuous freeze–thaw cycles. A numerical analysis using a 3D coupled hygro-thermo-mechanical (HTM) model is conducted to examine the freeze–thaw behaviour of the mortar. The model accurately represents the freezing deformation during the freeze–thaw cycle. KW - concrete KW - mortar KW - durability KW - freeze–thaw and de-icing salt resistance KW - strain KW - 3D laser scanning KW - numerical simulation KW - 3D FE numerical model KW - hygro-thermo-mechanical coupling Y1 - 2023 U6 - https://doi.org/10.3390/math11173672 VL - 11 IS - 17 PB - MDPI CY - Basel ER - TY - CHAP A1 - Thiel, Charlotte A1 - Beddoe, Robin E. A1 - Lowke, Dirk A1 - Gehlen, Christoph T1 - Accelerated carbonation: changes in water transport, porosity and phases of mortar due to different CO 2 pressures T2 - Proceedings of the 10th fib International PhD Symposium in Civil Engineering, July 21 to 23, 2014, Québec, Canada N2 - Currently, the carbonation resistance of concrete is assessed on the basis of accelerated tests performed with high (unrealistic) CO2 concentrations. It remains unclear whether these high concentrations reflect the processes occurring under natural conditions and enable the accurate prediction of field behaviour. To develop future test procedures with higher reliability, it is necessary to deepen the knowledge on the mechanisms of carbonation. Thin slices of mortar were stored in a gaseous mixture of 2 % CO2 and 98 % N2 at atmospheric pressure or 5 bar. IH-NMR equipment was used to detennine moisture profiles with aresolution of 0.2 mm. At 5 bar a drying front at the near-surface region of the mortar discs severely inhibited the progression of the carbonation reactions. This effect was prevented by exposure to altemating cycles of pressure and storage at atmospheric pressure (65%RH) which significantly increased the rate of carbonation, but was too severe to resolve the effect of cement type on carbonation resistance. Furthermore , the evolution of water beyond the carbonation front of mortar sampies under accelerated concentration and at atmospheric pressure was clearly visible. This may lead to an overestimation of carbonation resistance of sampies tested under accelerated conditions at the optimal relative humidity for natural carbonation (50-70% RH). Y1 - 2014 UR - https://mediatum.ub.tum.de/doc/1230854/1230854.pdf SP - 217 EP - 221 ER - TY - JOUR A1 - Kessler, Sylvia A1 - Thiel, Charlotte A1 - Grosse, Christian U. A1 - Gehlen, Christoph T1 - Effect of freeze–thaw damage on chloride ingress into concrete JF - Materials and Structures N2 - In cold climates, reinforced concrete structures (RCSs) are frequently and severely damaged by freeze–thaw (FT) and deicing-salt attack during winter periods. FT action can also cause additional water uptake known as frost suction. If a critical degree of water saturation is exceeded, severe deterioration of the microstructure of the concrete is likely, enhancing chloride ingress and increasing the probability of corrosion of its reinforcement. We present herein a test method to characterize the resistance of concrete to FT and chloride ingress. Chloride migration tests were performed on concretes with different degrees of FT deterioration, with and without deicing agents. The performance of RCSs is decisively affected under these combined actions. Quantitative description of the resulting FT damage is achieved using ultrasonic measurements and resonance frequency analysis. The test results confirm that the latter nondestructive test method provides more reliable evaluation of FT damage compared with usual ultrasonic pulse velocity measurements. Different concretes with supplementary cementitious materials and different degrees of FT deterioration with and without deicing agents were tested. While concrete made with air-entraining agents clearly showed the best FT resistance, concrete with ground-granulated blast-furnace slag showed superior resistance to both chloride migration and FT attack, both being positively affected by appropriate curing conditions. KW - Chloride ingress KW - Combined environmental attack KW - Freeze–thaw damage KW - Resonance frequency analysis KW - Ultrasonic measurement Y1 - 2017 U6 - https://doi.org/10.1617/s11527-016-0984-4 VL - 50 IS - 2 PB - Springer ER - TY - CHAP A1 - Thiel, Charlotte A1 - Keßler, Sylvia A1 - Chillé, R. A1 - Gehlen, Christoph T1 - Effect of internal freeze-thaw deterioration on chloride migration in concrete T2 - Life-Cycle and Sustainability of Civil Infrastructure Systems : proceedings of the third International Symposium on Life-Cycle Civil Engineering, Vienna, Austria, 3 - 6 October 2012 N2 - Depending on the specific exposure conditions, reinforced concrete structures (RCS) are simultaneously subjected to different physical and chemical loads. While in the field of reinforcement corrosion, service life prediction based on full-probabilistic models is well-established, the consequences of combined attack have been neglected until now. The most frequent “load” combination on RCS in cold climates are freeze-thaw attack which can lead to inner or outer damage and chloride ingress which can lead to reinforcement corrosion. In an experimental study four different concrete compositions are exposed either to a defined freeze-thaw attack or stored in moist environment. Afterwards, the chloride migration coefficient of the specimens which were both exposed to freeze-thaw-cycles and not, was determined with a modified rapid chloride migration test. The results clearly show an influence of freeze-thaw-induced internal damage on chloride ingress depending on concrete composition. Y1 - 2012 PB - CRC Press ER - TY - CHAP A1 - Lataste, Jean-François A1 - Hansen, Kurt Kielsgaard A1 - Nilsson, Lars-Olof A1 - Thiel, Charlotte A1 - Schießl-Pecka, Angelika A1 - Göller, Arndt A1 - Gehlen, Christoph T1 - Spatial Distributions T2 - Methods of Measuring Moisture in Building Materials and Structures N2 - In many applications moisture measurements are made to estimate the moisture differences between different points in a structure. Here, it is often more important to use a “simple” method that is easy and rapid to use in many points instead of necessarily obtain the exact moisture level in each point. The objective with “moisture indications” like that could very well be to select points where more accurate moisture measurements are to be made. The measuring principle to apply is of course a trade-off between accuracy and simplicity. Y1 - 2018 U6 - https://doi.org/10.1007/978-3-319-74231-1_19 SP - 173 EP - 190 PB - Springer ER - TY - CHAP A1 - Thiel, Charlotte A1 - Gehlen, Christoph T1 - Compliance testing for probabilistic durability design purposes T2 - Proceedings of the Sixth International Symposium on Life-Cycle Civil Engineering (IALCCE 2018), 28-31 October 2018, Ghent, Belgium Y1 - 2018 PB - Taylor & Francis ER - TY - CHAP A1 - Thiel, Charlotte A1 - Lowke, Dirk A1 - Gehlen, Christoph T1 - Detection of Transport Processes during Freeze-Thaw Deicing Salt Attack Using Single-Sided NMR T2 - Microstructural-related durability of cementitious composites : Second International Conference on Microstructural-related Durability of Cementitious Composites, 11 - 13 April 2012, Amsterdam N2 - Damage of concrete structures exposed to a combined freeze-thaw deicing salt attack (FTDSA) is one of the major deterioration mechanisms in cold climates. Before damage occurs, concrete structures subjected to freeze-thaw cycles (FTC) in the presence of water or deicing salt solution exhibit fast moisture uptake known as frost suction. There is still need for research in describing and modelling the mechanisms that lead to freeze-thaw induced surface scaling of concrete. Therefore, the moisture transport under FTDSA was investigated using single-sided 1 H NMR. The technique enables the observation of dynamic transport processes of water inside the sample non-destructively. Furthermore, porosity and pore size distribution of water saturated samples can be determined. The method also provides information on the mobility of water, i.e. water in capillaries or in gel pores. Water redistribution in pores as well as changes in the pore structure inside the near surface concrete sample under FTDSA were observed with single-sided 1 H NMR. The measurements confirmed the additional saturation of gel pores during thawing previously described by the micro ice lens model. The results are discussed within the context of the mechanisms of freeze-thaw deicing salt attack of concrete and contribute to a deeper understanding of the mechanisms that lead to freeze-thaw deterioration of concrete. Y1 - 2012 PB - RILEM ER - TY - JOUR A1 - Thiel, Charlotte A1 - Goetzfried, Franz Xaver A1 - Gehlen, Christoph T1 - Physikalische und chemische Auswirkungen von tauenden Chloriden auf Betone von Verkehrsbauwerken JF - Straße und Autobahn N2 - Zur Untersuchung des Einflusses von Loesungen der Tausalze Natriumchlorid, Calciumchlorid und Magnesiumchlorid auf die Dauerhaftigkeit von Beton wurden unter praxisnahen Bedingungen im Labor Betonprobekoerper, mit typischen Qualitaeten fuer Verkehrsbauwerke, unterschiedlichen Belastungszyklen unterzogen. Auch bei extremer Belastung durch wiederholte Nass- und Trockenphasen mit anschliessenden zyklischen Frost-Tau-Wechseln waren die physikalischen und chemischen Auswirkungen auf die Betone gering. Die festgestellten Unterschiede der verschiedenen Tausalze im Schaedigungsverhalten sind fuer die Praxis vernachlaessigbar. Fuer die Winterdienstpraxis laesst sich die Schlussfolgerung ziehen, dass zur Herstellung von Feuchtsalz im Hinblick auf die Dauerhaftigkeit von Strassenbeton und XF4-Beton die Loesungen der Chloride von Natrium, Calcium und Magnesium gleichermassen geeignet sind. Auch bei vorbeugender Fluessigstreuung mit NaCl-Sole ist auf Fahrbahnen mit normkonform zusammengesetztem Beton lediglich ein extrem geringer Angriff zu erwarten. (A) ABSTRACT IN ENGLISH: To investigate the influence of solutions of the de-icing salts sodium chloride, calcium chloride and magnesium chloride onto the durability of concrete, concrete specimens, with typical qualities for roads and bridges, were subjected to different load cycles under practical conditions. Also in the case of extreme load through repeated wet and dry phases with subsequent cyclical freeze-thaw-attack the physical and chemical effects on the concrete were low. The found differences of the different de-icing salts in the damage behaviour are negligible for the practice. The results prove that for the generation of pre-wetted salt, the solutions of the chlorides of sodium, calcium and magnesium are equally suitable with regard to the durability of concrete used in road construction and of XF4 concrete. Also in the case of preventive liquid spraying with NaCI-brine only an extremely small attack is to be expected on roads constructed with concrete conform to the current standards. Y1 - 2013 VL - 64 IS - 9 SP - 684 EP - 688 PB - Kirschbaum ER - TY - CHAP A1 - Gehlen, Christoph A1 - Thiel, Charlotte T1 - Specification of building materials for in service durability T2 - Proceedings ICSBM 2019: 2nd international conference of sustainable building materials, 2019, Eindhoven N2 - To assess whether a structural element made of a given building material can withstand the expected mechanical load and environmental exposure in service, designers need information on the material resistances and loads as well as the local conditions. The durability of a building material in the structure can only be assessed if these factors are taken into account. Usually, the material resistances are obtained from laboratory tests. However, the performance of materials under standardized laboratory conditions differs from those occurring in the field. This paper considers this assessment problem and develops a solution strategy based on carbonation-induced corrosion as an example. Y1 - 2019 SN - 978-90-386-4898-9 SP - 31 EP - 40 PB - Technische Universiteit Eindhoven CY - Eindhoven ER -