Filtern
Erscheinungsjahr
Dokumenttyp
- Zeitschriftenartikel (58) (entfernen)
Sprache
- Englisch (30)
- Deutsch (22)
- Mehrsprachig (6)
Schlagworte
- Rheology (13)
- Rheologie (6)
- Concrete (5)
- Betoninstandsetzung (4)
- Cement (4)
- Geopolymers (4)
- Instandsetzung (4)
- Self-compacting concrete (4)
- Alkali-activation (3)
- Beton (3)
Organisationseinheit der BAM
Paper des Monats
- ja (2)
In this work, engineered recycled mineral admixtures were obtained from four different industrial residues: basic oxygen furnace slag, iron ore tailings, quartz mining tailings and quartzite mining tailings.
The grinding performance was evaluated in two different programs and the characterization included chemical and mineralogical composition, particle morphology, and physical properties. Performance evaluations were carried out in blended pastes and mortars, including flow properties, hydration kinetics, soundness, pozzolanic activity, and compressive strength. Coarser-than-cement admixtures allowed better flow performance, greater dimensional stability and more economical production, while finer-thancementn admixtures improved mechanical performance by both filler effect and cementing activity.
The present work addresses powder bed binder jetting additive manufacturing by selective magnesium phosphate cement activation. Despite the potential of this technology to aid the digitalization of the construction industry, the effect of processing parameters on the mechanical performance of printed materials has not yet been studied to generate a guideline for the further development of the technology. Statistical methodologies were used to screen the effect of four printing process parameters (printing speed, layer thickness, raster angle, and build direction on flexural and compressive strength). As the exploited technology works with constant fluid pressure, the physical interpretation of the effect of each factor can be considered taking into account the interactions between the binder materials in the powder bed. Analysis of variance (ANOVA) indicated that printing speed and layer thickness significantly affect mechanical performances. Furthermore, the layout of samples for the printing process is preferable to be parallel the printhead movement. An anisotropic behavior was observed, and the samples subjected to compressive forces parallel to the layer plane possessed lower strength values. This effect can be interpreted as a result of a weak area of low density in between layers, leading to a pronounced delamination under compression. Even though the strength of the printed material is not suitable for a structural concrete, it can be marginally improved by design of experiment and optimized for non-structural applications, such as for porous artificial stone. Design of experiment coupled with ANOVA methods can be used in the future to support the development of novel material mixtures, thus expanding the fields of application of this novel additive manufacturing technology.
Design : and use of engineered recycled mineral admixtures obtained from industrial and mineral waste are promising strategies to increase the range of materials suitable for use in cement-based composites. In this work, Portland cement-blended pastes containing mineral admixtures designed for improving particle packing were evaluated in the presence of low- and high-charge polycarboxylate-based superplasticizers. The powders were obtained from basic oxygen furnace slag, iron ore tailings, quartz mining tailings, and quartzite mining tailings. The zeta-potentials of the particles were obtained via electrophoretic mobility. The flow properties were evaluated by rheological tests performed in a Couette type rheometer. The hydration kinetics was evaluated by isothermal calorimetry and an adapted method based on the Vicat needle test. The high-charge PCE and the finer mineral admixtures produced more stable blends. Coarser mineral admixtures led to increased flowability and delayed hydration compared to finer ones. Steel slag powders presented the most significant plasticizer effects, but also the largest setting delays and segregation tendency. Quartz-rich superfines reduced the setting delays caused by the superplasticizers. In summary, both superplasticizers were effective in improving flow properties, but the high-charge PCE was effective in preventing segregation in pastes containing mineral admixtures coarser and heavier than cement.
While calcined clays in general have been credited with a great potential to mitigate CO2 emissions related to cement production and consumption, calcined brick clays are currently understudied in this regard. In the present work, two brick clays, a low-grade kaolinitic clay, and a mixed clay composed of 50% brick clay and 50% low-grade kaolinitic clay were studied regarding transformations on calcination, and strength and durability performance as well as pore structure of mortars made with the blended cements. All calcined clays exhibited pozzolanic reactivity, with the performance of the brick clays inferior to the low-grade kaolinitic clay. However, the mixed clay performed very similar to the low-grade kaolinitic clay, which points to a viable option for optimal use of brick clays in cementitious systems. The carbonation resistance of the blended cement mortars was generally worse than that of the plain Portland cement mortar, as expected, but the former exhibited a significantly improved chloride penetration resistance. The latter improvement was due to pore structure refinement in the blended cement mortars, compared to the Portland cement mortar.
The most common method for determination of the carbonation depth is the sprayed application of indicator solutions, Phenolphthalein in particular. Since the aerosols of Phenolphthalein are suspected to be carcinogenic, efforts have been intensified to use alternative indicators for the determination of carbonation depth. The subject and aim of this research paper are to examine indicator solutions from Alizarin Yellow R, Thymol Blue and a Mixed Indicator. These indicator solutions are commercially available and are not suspected to be carcinogenic.
For the purpose of this research, samples previously stored under accelerated carbonation conditions (1% CO2) were examined by thermogravimetric analysis (TGA) and examination of the pH value. Additionally, the electrolytic back-titration for determination of total CO2 amount was carried out comparatively to TGA.
The thermal gravimetric analysis (TG) is a common method for the examination of the carbonation progress of cement-based materials. Unfortunately, the thermal properties of some components complicate the evaluation of TG results. Various hydrate phases, like ettringite (AFt), C-S-H and AFm decompose almost simultaneously in the temperature range up to 200 °C. Additionally, physical bound water is released in the same temperature range. In the temperature range between 450 °C and 600 °C the decomposition of calcium hydroxide and amorphous or weakly bound carbonates takes place simultaneously. Carbonates, like calcite, from limestone powder or other additives may be already contained in the noncarbonated sample material. For this research an attempt was made to minimise the influence of these effects. Therefore, differential curves from DTG-results of non-carbonated areas and areas with various states of carbonation of the same sample material were calculated and evaluated. Concretes based on three different types of cement were produced and stored under accelerated carbonation conditions (1 % CO2 in air). The required sample material was obtained by cutting slices from various depth of previously CO2-treated specimen and subsequent grinding. During the sample preparation, a special attention was paid that no additional carbonation processes took place. As reference method for the determination of the carbonation depth the sprayed application of phenolphthalein solution was carried out. Microscopic analysis where examined to confirm the assumptions made previously. Furthermore, the observed effect of encapsulation of calcium hydroxide by carbonates caused by the accelerated carbonation conditions was examined more closely.
Üblicherweise werden Werkzeuge für den industriellen Einsatz aus hochlegierten Chromstählen hergestellt. Für den Einsatz in explosionsgefährdeten Bereichen werden oft Werkzeuge aus speziellen Nichteisen-Metalllegierungen (NE-Metall) verwendet. Für diese sogenannten funkenarmen Werkstoffe und deren mögliche Schlagpartner gibt es bisher keine umfassenden Untersuchungen mit Aussagen zur Zündwahrscheinlichkeit.
Die TRGS 723, Abschn. 5.15, fordert den Nachweis der Funkenfreiheit der verwendeten Werkstoffpaarung. Jedoch sind Werkzeuge keine Geräte oder Schutzsysteme im Sinne der Richtlinie 2014/34/EU. Deshalb ist es nicht möglich, Werkzeuge in Übereinstimmung mit dieser Richtlinie zu zertifizieren. Der Nachweis der Erfüllung dieser Anforderungen ist durch Zertifizierungen im sogenannten "gesetzlich nicht geregelten" Bereich möglich. Die BAM bietet diese Zertifizierung für "Funkenarme Werkzeuge" im Rahmen ihres Zertifizierungsprogrammes an.
Die bisherigen Ergebnisse der hier vorgestellten Untersuchung haben gezeigt, dass es keine funkenfreien, metallischen Werkzeuge (non-sparking Tools) gibt. Entscheidend ist im Hinblick auf die TRGS 723, ob zündfähige Funken entstehen oder nicht. Es ist immer die Frage, worauf die Werkzeuge im praktischen Anwendungsfall schlagen oder fallen gelassen werden können, d.h. aus welchem Material der mögliche Schlagpartner besteht. Dies können metallische Schlagpartner, aber auch Betonoberflächen sein. Unterschiedliche Kombinationen von Werkstoffen ergeben bei Schlagbeanspruchung im explosionsgefährdeten Bereich jeweils unterschiedliche Zündwahrscheinlichkeiten. Aber auch die Höhe der beim Einsatz der Werkzeuge möglichen kinetischen Schlagenergie und der Brenngas/Luft-Atmosphäre im betreffenden explosionsgefährdeten Bereich sind wichtige Einflussgrößen.
Grouted connections are intensively used in offshore rigs, platforms as well as jacket and monopile offshore wind turbine structures. Being located in remote offshore conditions, these connections can experience considerable adverse loading during their lifetimes. Degradation was reported inside similar connections, which were installed in the last three decades. Grouting in the offshore sites may often be proven difficult, which eventually leads to reduced load-bearing capacity of connections in the long run. Thus, repair and rehabilitation of such connections should be planned ahead to minimize operational delays and costs. In this study, scaled grouted connections were manufactured using a novel mould, whose integrity were monitored using digital image correlation (DIC). The connections were loaded under static load to visualize the main failure pattern using distributed fibre optic sensors and acoustic emission (AE) analysis. Grouted connections were then repaired using a cementitious injectable grout. The effectiveness of the grout injection was monitored using dye penetration technique. Finally, specimens are reloaded to identify the potential of such repair for grouted connections.
Properties of alkali-activated mortars with salt aggregate for sealing structures in evaporite rock
(2021)
Concrete structures for sealing of tunnels in the host rock are an essential part of systems for nuclear waste storage. However, concretes based on blended cements or magnesium oxychloride cements, which are commonly considered for this application, can deteriorate severely due to a significant heat of hydration and associated deformation and cracking. Alkali-activated materials (AAMs) offer a potential solution to this problem because of their low heat release during hardening. To explore their suitability for the construction of sealing structures in evaporite rock, various AAMs with salt aggregate were studied regarding fresh properties, heat release, mechanical properties and microstructure. The heat of reaction of the AAMs was up to 55% lower than that of a blended cement designed for sealing structures, indicating significant benefits for the intended application. Other relevant properties such as mechanical strength and permeability depended strongly on the mix-design of the AAMs and curing conditions.