7.4 Baustofftechnologie
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- 2022 (29) (entfernen)
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- 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)
Paper des Monats
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Eingeladener Vortrag
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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.
Ziel des Projekts HYTEGRA ist die Herstellung leichter Gesteinskörnungen durch hydrothermale Behandlung quarz- und kalkreicher Reststoffe. Als Ausgangsstoffe dienen heterogener Mauerwerkbruch aus Bau- und Abbruchabfällen als SiO2-Träger und Papierasche aus dem Altpapierrecycling als CaO-Träger. Für beide Reststoffe besteht derzeit ein Verwertungsdefizit. Das Verfahren beruht auf der Idee des rohstofflichen Recyclings, d. h. die chemisch-mineralogischen Stoffeigenschaften werden für die hydrothermale Stoffumwandlung genutzt. Bei der Härtung der Hydrothermalgranulate bilden sich Calciumsilicathydrat-Phasen (CSH) aus der Reaktion zwischen Quarzpartikeln und Kalk im Autoklav bei 200 °C und 16 bar Sattdampf.
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.
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.
Influence of the hydroxypropylation of starch on its performance as viscosity modifying agent
(2022)
Synopsis: Starch is a commonly used viscosity modifying agent (VMA). The performance of starch as VMA depends on its origin (e.g. potato, corn, cassava, etc.) and corresponding molecular properties, such as molecular weight, ratio between amylose and amylopectin etc. Depending upon the application, the efficiency of starch can be enhanced by hydroxypropylation. The maximum degree of substitution (DoS) cannot be greater than 3.0, which is the number of hydroxy groups per glucose monomer in the polymer. In the current research three potato starches exhibiting the DoS of 0.4, 0.6 and 0.8 were utilised. The influence of the modified starch on the rheological properties and hydration of cement paste, as well as the viscosity of the pore solution were investigated. Our findings show that the starch with the highest DoS increases the dynamic yield stress the most, while the plastic viscosity is less dependent on the DoS. Additionally, starch with the highest DoS retards hydration to lower degree than other starches.
Organic admixtures are an indispensable component of modern concrete. Thus, their purposeful application is not only technically and economically viable but in addition an inevitable tool to make concrete more environmentally friendly. In this context, the use of polysaccharides has increasingly gained interest in the built environment as sustainable resource for performance enhancement. However, due to its origin, biopolymers possess a vast variety of molecular structures which can result in incompatibilities with other polymers present in concrete, such as superplasticizers. The present study highlights effects of the joint application of different types of starches and polycarboxylates with respect to their influence on cement hydration and structural build-up of cement pastes.
Introduction of a monitoring system for Bingham fluids in additive manufacturing with concrete
(2022)
Freeform additive manufacturing of concrete structures is a rising technology in civil engineering with several fascinating advantages. Nonetheless, to ensure reliability and structural integrity, standards and quality control are required in the future to bring this technology into the market. As the concrete is manufactured continuously, continuous quality control of the printing process is also required, i.e. comprehensive process monitoring. At BAM, a test rig will be installed, enabling the printing of concrete structures with a maximum size of 2 m x 1 m x 1 m (l x w x h). Here, process monitoring is the focus of the test rig. In this study, we show the results of the first pump tests, including the measurement of several parameters such as temperature and pressure along the supply system, i.e. from the concrete pump to the printer head.
Introduction of a monitoring system for Bingham fluids in additive manufacturing with concrete
(2022)
Freeform additive manufacturing of concrete structures is a rising technology in civil engineering with several fascinating advantages. Nonetheless, to ensure reliability and structural integrity, standards and quality control are required in the future to bring this technology into the market. As the concrete is manufactured continuously, continuous quality control of the printing process is also required, i.e. comprehensive process monitoring. At BAM, a test rig will be installed, enabling the printing of concrete structures with a maximum size of 2 m x 1 m x 1 m (l x w x h). Here, process monitoring is the focus of the test rig. In this study, we show the results of the first pump tests, including the measurement of several parameters such as temperature and pressure along the supply system, i.e. from the concrete pump to the printer head.
The oxidation of sulfur in aqueous solutions is an important process in several geochemical and industrial contexts. In concrete technology, it is particularly relevant for the protection of steel reinforcement in slag cement-based concretes, as the presence of sulfides affects the passivation of the steel and corrosion initiation in the presence of chlorides. However, the knowledge about the kinetics of sulfide oxidation in alkaline solutions, such as concrete pore solutions, is incomplete. To address this issue, we prepared solutions with 0.80 M NaOH, and nominally 10, 100 and 350 mM HS−, respectively, and followed the evolution of the sulfur species during bubbling with oxygen-containing gas (concentration 100% or 22%) using X-ray absorption near-edge structure (XANES) spectroscopy at the sulfur K-edge. Polysulfide, thiosulfate, sulfite and sulfate were identified and quantified via linear combination fitting of the spectra, using previously measured standards. A preliminary analysis of the results shows that the initial rate constant of sulfide oxidation depends strongly on the HS− concentration, while it less strongly depending on the oxygen concentration, in line with previous results for lower pH values. Approaches to fit the data to obtain the rate constants of all relevant reactions will be discussed.
Ein zentrales Fundament moderner Gesellschaften ist eine intakte Abwasserinfrastruktur. Schäden infolge biogener Schwefelsäurekorrosion von konventionellen Betonen haben jedoch zu einem erheblichen Sanierungsbedarf geführt. Alkaliaktivierte Mörtel besitzen aufgrund eines hohen Säurewiderstands das Potential, einen Beitrag zur langfristigen Lösung dieses Problems zu leisten. Dazu müssen jedoch zunächst die Faktoren, die den Haftverbund zwischen diesen Mörteln und dem Betonsubstrat bestimmen, besser verstanden werden, um die Eigenschaften der Beschichtungssysteme gezielt anpassen und verbessern zu können. Die vorliegende Arbeit liefert hierzu einen Beitrag und zeigt dadurch Wege zu einer technisch machbaren und nachhaltigen Sanierung von Abwasserbauwerken auf.