7.4 Baustofftechnologie
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Erscheinungsjahr
- 2022 (29) (entfernen)
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- Zeitschriftenartikel (14)
- Beitrag zu einem Tagungsband (7)
- Vortrag (5)
- Beitrag zu einem Sammelband (1)
- Dissertation (1)
- Posterpräsentation (1)
Schlagworte
- Structural build-up (5)
- Cement (3)
- Hydration (3)
- Non-destructive testing (3)
- Rheological properties (3)
- Superplasticizer (3)
- Accelerated testing (2)
- Additive manufacturing of concrete (2)
- Alkali-activated materials (2)
- Angle of repose (2)
Organisationseinheit der BAM
- 7 Bauwerkssicherheit (29)
- 7.4 Baustofftechnologie (29)
- 3 Gefahrgutumschließungen; Energiespeicher (2)
- 3.1 Sicherheit von Gefahrgutverpackungen und Batterien (2)
- 4 Material und Umwelt (2)
- 4.4 Thermochemische Reststoffbehandlung und Wertstoffrückgewinnung (2)
- 7.1 Baustoffe (2)
- 7.7 Modellierung und Simulation (2)
- 8 Zerstörungsfreie Prüfung (2)
- 8.2 Zerstörungsfreie Prüfmethoden für das Bauwesen (2)
- 1 Analytische Chemie; Referenzmaterialien (1)
- 1.1 Anorganische Spurenanalytik (1)
- 7.2 Ingenieurbau (1)
- 7.6 Korrosion und Korrosionsschutz (1)
Paper des Monats
- ja (2)
Eingeladener Vortrag
- nein (5)
Für die flächige Instandsetzung von Stahlbetonkonstruktionen kommen nahezu ausschließlich zementgebundene Systeme mit hohem Zementgehalt zum Einsatz (1). Bereits 2008 war die Zementproduktion für 5% des weltweiten, anthropogenen CO2-Ausstoßes verantwortlich (2). Um die prozessbedingten CO2-Emissionen zu senken, wird der Zement bereits durch gewisse Mengen an Sekundärrohstoffen wie Flugasche, Silicastaub oder Hüttensandmehl (Hochofenschlacke) substituiert. Das Potenzial für weitere Modifikationen ist inzwischen begrenzt (3). Zudem ist eine hohe Lebensdauer der Konstruktionen in vielen Anwendungsbereichen nur bedingt realisierbar. Spätestens mit Erreichen der geplanten Nutzungsdauer müssen Stahlbetonkonstruktionen mit zementgebundenen Systemen instandgesetzt werden, was im ökonomischen und ökologischen Sinne keine nachhaltige Lösung darstellt. Die Verwendung neuer Baustoffe wie alkalisch aktivierte Mörtel hält sich bisher in Grenzen (4), sodass die Akzeptanz durch praxisnahe Forschung adressiert werden muss.
Vorangegangene Forschungsergebnisse zeigen, dass alkalisch aktivierte Bindemittel vielversprechende technische Eigenschaften besitzen. So zeigen sich im Vergleich zu herkömmlichem Portlandzement ein ausgesprochen wirkungsvoller Verbund zu Stahl und Zementmörtel (5), (6), eine hohe chemische Beständigkeit sowie ein Erfolg versprechendes Abwitterungsverhalten bei Frost-Tau-Wechseln (7). Mit diesen Eigenschaften können alkalisch aktivierte Mörtel einen erheblichen Beitrag zur dauerhaften Betoninstandsetzung leisten und somit durch die verringerten CO2-Emmissionen dem Prinzip des nachhaltigen Bauens gerecht werden. Wichtig für die Produktion im größeren Maßstab ist die Verfügbarkeit der möglichen Reststoffe, um eine CO2-positivere Bilanz abzubilden.
Im Zuge des Forschungsvorhabens sollen Rezepturen für Instandsetzungsprodukte entworfen werden, die auf alkalisch aktivierte industrielle Reststoffe zurückgreifen und die Anforderungen an konventionelle Instandsetzungsprodukte erfüllen. Hierzu wurden potenzielle Ausgangs-stoffe mit Natriumcarbonat aktiviert und die Verarbeitbarkeit der Leime sowie die Druckfestigkeiten nach sieben Tagen verglichen. Hüttensandmehl reagiert ausreichend mit diesem Aktivator, was sich mit Ergebnissen von (8) und (9) deckt. Es werden 〖CO〗_3^(2-)-Ionen in das System eingebaut, was zu einer anfänglichen Erstarrung des Gefüges durch die Bildung von Carbonaten (Calcit und Hydrotalcit) führt. Nach einer längeren dormanten Phase bilden sich zusätzlich Hydratphasen, die die Festigkeit weiter erhöhen. Weiterhin ist die chemische Zusammensetzung der Schlacken für die Erhärtung und die späteren Eigenschaften von großer Bedeutung (10), (11), was mit einer Parameterstudie im laufenden Jahr an natriumcarbonataktivierten Schlacken näher betrachtet werden soll. Erkenntnisse aus vergleichenden Versuchen durch (12) bestätigen die Einflussnahme der chemischen Zusammensetzung. Die übrigen Reststoffe konnten mit anderen Aktivatoren (z. B. Natriumsilicat und -hydroxid) zu einer Reaktion angeregt werden. Im Hinblick auf die Akzeptanz der alkalisch aktivierten Bindemittel stellen diese Aktivatoren jedoch bei der Herstellung höhere technische Anforderungen an das Personal und die verwendeten Geräte im Vergleich zur konventionellen Beton- und Mörteltechnik. Die Aktivierung mittels Alkalicarbonaten ermöglicht die Herstellung von Beton bzw. Mörtel nach dem üblichen „just add water“-Prinzip (13).
Aktuell wird unter Einbindung einer studentischen Abschlussarbeit eine Rezeptur mit Hüttensandmehl hinsichtlich der Frisch- und Festeigenschaften charakterisiert und einer Referenzmischung – basierend auf Portlandzement – gegenübergestellt. Hieraus resultierende Ergebnisse sollen neben den Erkenntnissen aus den Vorversuchen zur Konferenz vorgestellt und ein Ausblick auf die weitere Forschungsarbeit gegeben werden.
Calcined clays as supplementary cementitious materials (SCMs) have been identified and credited to be a viable solution in mitigating the CO2 emissions related to cement production and consumption. Calcined clays range from a variety of different clay types based on an assortment of varying minerals and compositions. While extensive data is available on kaolinitic clays (based on the 1:1 clay type), other clays such as brick clays (based on the 2:1 clay type) are currently understudied, although such clays are largely more available than the kaolinitic clays.
The aim of this thesis is to draw attention to the varying compositions present in two selected brick clays in Germany and elaborate on how such compositions affect their suitability to be used as SCMs in blended cement systems. The novelty of this thesis explains the relationship between the reactivity of the bricks to their varying compositions and their suitability for their employment as SCMs. This was based on their chemical and physical transformations in the calcination temperature range 650–900 or 950 °C, and the performance of the calcined brick clays in blended cement systems measured by their heat evolution, strength development and durability-related properties. The results of their performance were compared to two kaolinitic clays with varying compositions. While the kaolinitic clays generally exhibited the best performance as SCMs, the brick clay with a lower Fe2O3 content showed promising results similar to the kaolinitic clays when an optimum calcination temperature is applied and when substituted at a moderate cement substitution rate. Thus, this finding promoted further efforts made to improve the reactivity of the brick clay by producing a mixed clay composed of 50 % brick clay (with lower Fe2O3 content) and 50 % kaolinitic clay. The mixed clay was compared to the two individual brick clays and one kaolinitic clay, whereby optimum calcination conditions were performed in large-scale simulating an industrial-scale production of SCMs. All calcined clays exhibited pozzolanic reactivity, with the performance of the brick clays inferior to the kaolinitic clay, however, the mixed clay performed very similar to the kaolinitic clay.
At a similar degree of hydration compared to plain Portland cement, the good performance of the mixed clays was especially evident in the strength development and improved chloride penetration resistance, which was caused by a refinement in the pore structure in the cementitious systems. Moreover, it was deduced that not only the high surface area, but also, the solubility of Si and Al ions in the resulting calcinate of the mixed clays plays a significant role when calcined at ~600–700 °C, which points to viable options for optimal employment of brick clays in cementitious systems.
To ensure safety when transporting dangerous goods, it is important to specify the flow properties of the respective solid filling substance of the packagings. For this purpose, the angle of repose is currently used for the UN approvals in Germany. Measurements were carried out on 12 powdery or granular substances applying the angle of repose measuring methods customary in the test centres. The results of the methods differ significantly from each other. In addition, some of the techniques cannot be applied for very cohesive or coarse-grained materials. The results for the angle of repose show a strong scatter for some constellations (coefficient of variation more than 20 %). Safety during transport of dangerous goods cannot be guaranteed with this currently practiced system of measuring the angle of repose. As a consequence, an alternative parameter to characterize the flow properties of bulk materials should be used in the recognized test centers for dangerous goods packagings, such as the Hausner ratio. This approach leads to more precise test results for the substances examined (maximum coefficient of variation 2.8 %). It also has advantages in terms of applicability and occupational safety.
Since the flow properties are safety-relevant, both in terms of mechanical safety and safety against the release of dangerous substances, the testing practice in the recognized test labs should be improved and standardized.
In general, pH-sensitive colorants such as phenolphthalein are applied on freshly split surfaces of building structures to determine the state of carbonation. For years, it has been known that the aerosols of phenolphthalein are suspected of being carcinogenic. Hence, more work has currently being done on alternative indicators for the use in research and the use on construction sites. Over the past years, mainly pH indicators from other research areas and natural dyes were investigated for their usability to cementitious systems. This paper presents the experimental results of using phenolphthalein solution bound in agar-agar gel. This gel-bound indicator allows the future use of the already known phenolphthalein dye without the health hazards for the user. To demonstrate the flexibility of the gel-bound colorant, different application forms of the indicator were carried out and assessed. In addition, the results obtained by the different methods were statistically evaluated to ensure validity.
The accuracy of the results was confirmed by thermogravimetric analysis and IR spectroscopic studies as reference methods. It has also succeeded to demonstrate the comparability of the results achieved by the gel-bound colorant with the results of the common sprayed application method. As an additional gain in knowledge, comparative results of indicator tests, TGA analysis, and FTIR investigation are shown.
To ensure safety when transporting dangerous goods, it is important to specify the flow properties of the respective solid filling substance of the packagings. For this purpose, the angle of repose is currently used for the UN approvals in Germany. Measurements were carried out on 12 powdery or granular substances applying the angle of repose measuring methods customary in the test centres. The results of the methods differ significantly from each other. In addition, some of the techniques cannot be applied for very cohesive or coarse-grained materials. The results for the angle of repose show a strong scatter for some constellations (coefficient of variation more than 20 %). Safety during transport of dangerous goods cannot be guaranteed with this currently practiced system of measuring the angle of repose. As a consequence, an alternative parameter to characterize the flow properties of bulk materials should be used in the recognized test centers for dangerous goods packagings, such as the Hausner ratio. This approach leads to more precise test results for the substances examined (maximum coefficient of variation 2.8 %). It also has advantages in terms of applicability and occupational safety.
Since the flow properties are safety-relevant, both in terms of mechanical safety and safety against the release of dangerous substances, the testing practice in the recognized test labs should be improved and standardized.
Alkali-silica reaction (ASR) is a chemical reaction within concrete which can lead over time to cracking and spalling. Due to the complexity of the problem, it still causes damage to concrete constructions worldwide.
The publication aims to illustrate the interdisciplinary research of the German Federal Institute for Materials Research and Testing (BAM) within the last 20 years, considering all aspects of ASR topics from the macro to the micro level. First, methods for characterization and assessment of ASR risks and reaction products used at BAM are explained and classified in the international context. Subsequently the added value of the research approach by combining different, preferably nondestructive, methods across all scales is explained using specific examples from a variety of research projects. Aspects covered range from the development of new test-setups to assess aggregate reactivity, to analysis of microstructure and reaction products using microscopical, spectroscopical and X-ray methods, to the development of a testing methodology for existing concrete pavements including in-depth analysis of the visual damage indicator and the de-icing salt input using innovative testing techniques. Finally, research regarding a novel avoidance strategy that makes use of internal hydrophobization of the concrete mix is presented.
Aim of this study is to provide information about moisture dependent material behaviour of unstabilised loadbearing earth blocks and mortars. Compressive strength and Young’s modulus were investigated after conditioning in varying relative humidity reaching from 40 % up to 95 %. The material composition and physical properties were investigated to understand the influence of relative humidity onto the mechanical properties. A normalisation of strength and stiffness by the values obtained at 23 ◦C and 50 % relative humidity reveals a linear dependence of compressive strength and Young’s modulus that is regardless of the material composition.
Thus, it is possible to describe the influence of relative humidity onto the load-bearing behaviour of unstabilised earth masonry materials in a generally valid formulation.
Die Zementindustrie erzeugt etwa 6-7% der globalen CO2-Emissionen und steht damit als Industriezweig vor dem Hintergrund einer anvisierten Klimaneutralität vor gewaltigen Herausforderungen. Der Prozess der Klinkerherstellung wurde über die vergangenen Jahrzehnte bereits kontinuierlich optimiert. Seit 1990 ist es der deutschen Zementindustrie gelungen, die spezifischen CO2-Emissionen der Zementproduktion u. a. durch den Einsatz alternativer, nicht fossiler Brennstoffe und durch Absenkung des Klinkergehalts im Zement um 20 % zu senken. Weitere konventionelle Minderungsstrategien versprechen jedoch nur noch wenig zusätzliche Reduktion. Im Falle des Portlandklinkers besteht die Schwierigkeit darin, dass zwei Drittel der CO2-Emissionen rohstoffbedingt durch die Entsäuerung des Kalksteins (CaCO3) anfallen, die durch die beschriebenen Maßnahmen nicht weiter abgesenkt werden können. Vielmehr wird es erforderlich sein, noch zu entwickelnde oder zu optimierende Technologien anzuwenden und ggf. alle relevanten Ebenen wie Produktion, Weiterverarbeitung und Anwendung von Zement und Beton neu zu denken. Neben technologischen Ansätzen zur CO2-Abscheidung mit nachfolgender langfristiger Speicherung (Carbon Capture and Storage – CCS) oder Verwertung (Carbon Capture and Utilisation – CCU) werden auch alternative Rohstoffe für die Zementproduktion und alternative Bindemittel in Betracht zu ziehen sein.
The 87Sr/86Sr isotope ratio can, in principle, be used for provenancing of cement. However, while commercial cements consist of multiple components, no detailed investigation into their individual 87Sr/86Sr isotope ratios or their influence on the integral 87Sr/86Sr isotope ratio of the resulting cement was conducted previously. Therefore, the present study aimed at determining and comparing the conventional 87Sr/86Sr isotope ratios of a diverse set of Portland cements and their corresponding Portland clinkers, the major component of these cements. Two approaches to remove the additives from the cements, i.e. to measure the conventional 87Sr/86Sr isotopic fingerprint of the clinker only, were tested, namely, treatment with a potassium hydroxide/sucrose solution and sieving on a 11-µm sieve. Dissolution in concentrated hydrochloric acid/nitric acid and in diluted nitric acid was employed to determine the 87Sr/86Sr isotope ratios of the cements and the individual clinkers. The aim was to find the most appropriate sample preparation procedure for cement provenancing, and the selection was realised by comparing the 87Sr/86Sr isotope ratios of differently treated cements with those of the corresponding clinkers. None of the methods to separate the clinkers from the cements proved to be satisfactory. However, it was found that the 87Sr/86Sr isotope ratios of clinker and cement generally corresponded, meaning that the latter can be used as a proxy for the clinker 87Sr/86Sr isotope ratio. Finally, the concentrated hydrochloric acid/nitric acid dissolution method was found to be the most suitable sample preparation method for the cements; it is thus recommended for 87Sr/86Sr isotope analyses for cement provenancing.