@article{ThielKratzerGrimmetal., author = {Thiel, Charlotte and Kratzer, Johanna and Grimm, Benedikt and Kr{\"a}nkel, Thomas and Gehlen, Christoph}, title = {Effect of Internal Moisture and Outer Relative Humidity on Concrete Carbonation}, series = {CivilEng}, volume = {4}, journal = {CivilEng}, number = {3}, publisher = {MDPI}, address = {Basel}, doi = {10.3390/civileng3040058}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:898-opus4-56091}, pages = {1039 -- 1052}, abstract = {With steadily rising CO2 concentrations in the ambient air and fast-changing concretecompositions with reduced clinker contents, the availability of reliable and accelerated concrete car-bonation tests is of crucial importance to design durable structures. This paper focuses on the effectsof moisture under accelerated conditions and the effects of different CO2 exposure conditions. Mor-tar prisms incorporating three different cement types were cured and stored at either 50\% or 65\%relative humidity (RH). Afterwards, the prisms were carbonated at different ambient humidities(50, 57 and 65\%), different CO2 concentrations (0.04, 1 and 3 vol.\%) and complemented by a seriesof tests at increased gas pressure (2 barg). High-resolution test methods were used to explain theunderlying carbonation mechanisms. The results show that pre-conditioning for two weeks—ascurrently suggested by the European Standard—seems to be too short because the initial inner mois-ture content severely affects the carbonation rate. Relative humidity during carbonation of 57\% ledto higher carbonation rates compared to 50\% and 65\%. In addition, climate data needs to be period-ically (preferably permanently) recorded in research experiments and in laboratory testing to ensurefair interpretation of experimental results.}, language = {en} } @article{HaynackSekandarJithenderetal., author = {Haynack, Alexander and Sekandar, Zadran and Jithender, J. Timothy and Gambarelli, Serena and Kr{\"a}nkel, Thomas and Thiel, Charlotte and Ozbolt, Josko and Gehlen, Christoph}, title = {Can a Hend-Held 3D Scanner Capture Temperature-Induced Strain of Mortar Samples? Comparison between Experimental Measurements and Numerical Simulations}, series = {mathematics}, volume = {11}, journal = {mathematics}, number = {17}, publisher = {MDPI}, address = {Basel}, doi = {10.3390/math11173672}, abstract = {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.}, language = {en} } @inproceedings{HaynackSchneiderTimothyetal., author = {Haynack, Alexander and Schneider, Alexander and Timothy, Jithender J. and Kr{\"a}nkel, Thomas and Gehlen, Christoph and Thiel, Charlotte}, title = {Effect of Chloride Concentration on the Freeze-Thaw Resistance of Concrete}, series = {International RILEM Conference on Synergising expertise towards sustainability and robustness of CBMs and concrete structures, SynerCrete'23 - Volume 2}, booktitle = {International RILEM Conference on Synergising expertise towards sustainability and robustness of CBMs and concrete structures, SynerCrete'23 - Volume 2}, publisher = {Springer}, address = {Cham}, doi = {10.1007/978-3-031-33187-9_83}, pages = {911 -- 921}, abstract = {Performance test methods intend to provide a fast, accurate and precise determination of a particular building material property and thus determine the associated material performance. In concrete, various performance tests are used to classify existing or to approve new materials, to compare concrete compositions or to determine causes of damage in existing structures. The challenge of such test methods is to accelerate natural (very slow) mechanisms to determine the material performance precisely within a short time. However, the attack on the material must not be unrealistically intensive, but must represent reality, just in fast motion. The performance tests used to demonstrate the freeze-thaw resistance of concrete employ a 3\% NaCl solution, with literature data ranging from 1\% to 10\% showing that low concentrations can result in higher surface scaling. In this paper, mortar and concrete specimens are tested at 0, 1, 3, 6, and 9\% NaCl solution following the CDF procedure (DIN CEN/TS 12390-9:2017-05). The results are discussed against the background of the existing literature and show that the damage is critically dependent on the pore system and thus also on the effect of the micro-ice lens pump. With increasing freeze-thaw exposition, the pessimum in the external damage shifts towards a de-icing salt concentration of 6\%. Furthermore, a novel test methodology based on 3D-laserscanning is presented to determine scaling accurately by eliminating side effects that are typically present in current standards.}, language = {en} } @inproceedings{GrimmMuenchmeyerKraenkeletal., author = {Grimm, Benedikt and M{\"u}nchmeyer, Sebastian and Kr{\"a}nkel, Thomas and Gehlen, Christoph and Thiel, Charlotte}, title = {Developing a New Rapid, Relevant, and Reliable (R3) Method for Accelerated Measurement of Carbonation Progress at Gas Overpressure}, series = {International RILEM Conference on Synergising expertise towards sustainability and robustness of CBMs and concrete structures, SynerCrete'23 - Volume 1}, booktitle = {International RILEM Conference on Synergising expertise towards sustainability and robustness of CBMs and concrete structures, SynerCrete'23 - Volume 1}, publisher = {Springer}, doi = {10.1007/978-3-031-33211-1_30}, pages = {336 -- 346}, abstract = {The determination of durability-relevant material resistances of concrete is of great importance. They serve as input to engineering models to predict the durability of structures under real environmental conditions. The natural resistances have to be determined in time-consuming experiments, since the processes in nature are very slow. This is particularly important for new materials where long-term experience is not yet available. Thus, accelerated testing is required. Only that way new materials can be evaluated regarding their durability and subsequently be used in practical applications. For carbonation, a new R3 accelerated test method is presented in this contribution. An automated carbonation pressure chamber was developed. It consists of a pressure vessel, automated in such a way that it can apply gas overpressure of various intensities up to 8 bar to mortar and concrete samples. Simultaneously, it can control and regulate the ambient CO2 concentration from 0 to 99.5\% in a fully automated and continuously variable procedure. Experiments were carried out with varying combinations of gas overpressure at CO2 concentrations of 3 vol.-\% to achieve the most time-efficient carbonation of mortars and concretes. Mortars with different material compositions were used to evaluate the general suitability of the test procedure with the developed equipment. The automated carbonation pressure chamber enables reliable carbonation testing with a total duration under accelerated conditions of only 7 days.}, language = {en} } @article{HaynackTimothyKraenkeletal., author = {Haynack, Alexander and Timothy, Jithender J. and Kr{\"a}nkel, Thomas and Gehlen, Christoph and Thiel, Charlotte}, title = {Analyse des Frost-Tausalz-Widerstands zementgebundener Baustoffe mittels 3D-Laserscanning}, series = {ce/papers: Proceedings in Civil Engineering}, volume = {6}, journal = {ce/papers: Proceedings in Civil Engineering}, number = {6}, publisher = {Ernst \& Sohn}, issn = {2509-7075}, doi = {10.1002/cepa.2951}, pages = {1189 -- 1196}, abstract = {Eine Herausforderung performancebasierter Pr{\"u}fverfahren zur Bewertung der Dauerhaftigkeit ist die Beschleunigung nat{\"u}rlicher Mechanismen. Dies ist notwendig, um innerhalb kurzer Zeit die Langzeit-Leistungsf{\"a}higkeit ermitteln zu k{\"o}nnen. Die Bestimmung der Frost-Tausalzbest{\"a}ndigkeit von Beton kann durch den CDF-Test erfolgen, welcher f{\"u}r Betone mit ausreichendem Frost-Tausalz-Widerstand sehr gut funktioniert. Bei Proben mit einer unzureichenden bzw. unbekannten Performance k{\"o}nnen erh{\"o}hte Randabwitterungen auftreten, welche durch das Abl{\"o}sen des seitlichen Abdichtbands entstehen. Der zunehmende Randeinfluss f{\"u}hrt so zu einer Verf{\"a}lschung der Ergebnisse und zu einer Untersch{\"a}tzung der tats{\"a}chlichen Performance des Bauteils. In diesem Beitrag werden M{\"o}rtel- und Betonprobek{\"o}rper mit unterschiedlichen Abwitterungsraten in Anlehnung an das CDF-Verfahren untersucht. Zus{\"a}tzlich wird die Oberfl{\"a}chensch{\"a}digung der Proben anhand einer neuartigen Messmethode mittels hochaufl{\"o}sendem 3D-Laserscanning ausgewertet. Die Ergebnisse zeigen, dass die Randeffekte mit der Laserscan-Methode umgangen und vergleichbare Ergebnisse zu den CDF-Untersuchungen erzielt werden k{\"o}nnen. Somit k{\"o}nnen Betone ohne Randeinfl{\"u}sse charakterisiert und eine pr{\"a}zise Prognose der Langzeitbest{\"a}ndigkeit getroffen werden.}, language = {de} } @article{GrimmThielKraenkeletal., author = {Grimm, Benedikt and Thiel, Charlotte and Kr{\"a}nkel, Thomas and Gehlen, Christoph}, title = {Einfluss der Permeation auf die Carbonatisierung von Beton}, series = {ce/papers: Proceedings in Civil Engineering}, volume = {6}, journal = {ce/papers: Proceedings in Civil Engineering}, number = {6}, publisher = {Ernst \& Sohn}, address = {Berlin}, issn = {2509-7075}, doi = {10.1002/cepa.3005}, pages = {1348 -- 1357}, abstract = {Die Carbonatisierung von Beton kann einerseits zu Sch{\"a}den bei Stahlbetonbauwerken f{\"u}hren, andererseits kann der Beton so CO2 speichern und damit seinen CO2-Fußabdruck verringern. In diesem Beitrag wird dargestellt, wie eine effiziente Beschleunigung der Carbonatisierung durch Anlegen eines geringen {\"a}ußeren Drucks erreicht werden kann. Damit wird neben der Diffusion der wesentlich schneller ablaufende Transportmechanismus der Permeation ausgenutzt, der das CO2 tiefer in das Probeninnere transportiert und damit in kurzer Zeit die Bestimmung des Carbonatisierungswiderstand zementgebundener Materialien erm{\"o}glicht. Hierzu wurde eine Pr{\"u}feinrichtung entwickelt, die es erm{\"o}glicht, die CO2-Konzentration und in gewissen Grenzen auch relative Luftfeuchte sowie die Temperatur gezielt einzustellen und zu steuern, um so M{\"o}rtel- und Betonproben schnell und pr{\"a}zise zu carbonatisieren. Der Einfluss verschiedener Druckstufen und Wechselzyklen wird dargelegt und die resultierenden chemischen und physikalischen Ver{\"a}nderungen der Proben bestimmt. Als besonders effizient und gleichzeitig realit{\"a}tsnah erwies sich die konstante CO2-Beaufschlagung mit 3 Vol.-\% CO2 mit zus{\"a}tzlichem, moderatem Gasdruck. Das hier entwickelte Verfahren kann daher genutzt werden, um Betone schnell und effizient in zeitraffenden Materialtests hinsichtlich Carbonatisierungswiderstand zu charakterisieren.}, language = {en} } @inproceedings{ThielHechtlGehlenetal., author = {Thiel, Charlotte and Hechtl, C. Maximilian and Gehlen, Christoph and Kr{\"a}nkel, Thomas}, title = {Sustainability Potential of Additive Manufactured Concrete Structures - Studies on the Life Cycle Assessment and Circularity of an Extruded Exterior Wall}, series = {Fourth RILEM International Conference on Concrete and Digital Fabrication (DC 2024), Munich, Germany, September 2024}, booktitle = {Fourth RILEM International Conference on Concrete and Digital Fabrication (DC 2024), Munich, Germany, September 2024}, editor = {Lowke, Dirk and Freund, Niklas and B{\"o}hler, David and Herding, Friedrich}, publisher = {SPRINGER INTERNATIONAL PU}, isbn = {978-3-031-70030-9}, doi = {10.1007/978-3-031-70031-6_2}, pages = {13 -- 21}, abstract = {The Brundtland Report defined sustainable development as a development that meets the needs of the present without compromising the ability of future generations to meet their own needs. If this definition is applied to the construction sector, a new, circular approach to cementitious materials is required. Additive manufacturing (AM) enables to design material-efficient and monolithic structures that meet physical and chemical requirements of building standards while allowing reuse or high-quality recycling of concrete. Here, the environmental impact as well as the circularity potential of an additively manufactured exterior wall, produced by 3D concrete extrusion, are determined. To classify the results, the additively manufactured exterior wall is compared with a conventional concrete construction. Finally, various options for optimizing the printed wall are considered and evaluated. Additive manufacturing enabled significant material savings compared to conventional construction. The environmental impacts strongly depend on the used concrete composition. For example, greenhouse gas emissions could be reduced by 20\% when changing the type of lightweight aggregate. The additively manufactured exterior wall exhibited advantages in terms of circularity. Through further development and research, additive manufacturing of concrete can promote a paradigm shift towards sustainable practices.}, language = {en} }