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- Construction and demolition waste (1)
- Ettringen tuff (1)
- Filtration Residues (1)
- Hydrothermale Herstellung (1)
- Leichtgranulat (1)
- Lightweight aggregates (1)
- Mauerwerkbruch (1)
- Mercury porosimetry (1)
- Mikrostruktur (1)
- Nitrogen sorption (1)
Organisationseinheit der BAM
Zeolite synthesis was studied using two silica rich filtration residues (FR 1 and FR 2) as Si-source
and sodium aluminate in a direct synthesis at 60°C at strong alkaline conditions (8 M - 16 M NaOH).
In addition to these one-pot syntheses, a two-step process was investigated. Here, an alkaline digestion
of FR at 60°C was followed by gel precipitation with sodium aluminate and gel crystallization
under usual conditions of 80°C - 90°C. The results show that the substitution of chemical
reagent sodium silicate by a waste material like FR as Si-source is possible but requires fine tuning
of the reaction conditions as zeolite crystallization is a process under kinetic control. The
solubility behaviour and impurities of the inserted filtration residues strongly influenced the
course of reaction. Thus zeolites like hydrosodalite or intermediate zeolite between cancrinite
and sodalite, or zeolite NaA or Z-21 in cocrystallization with hydrosodalite could be observed in
the one pot syntheses already in a short time interval between 1 - 4 h depending on the alkalinity.
The two step process yield to zeolites NaA and NaX in very good quality. The reaction process of FR
in both reaction methods was characterized by chemical analyses, X-ray powder diffraction,
Fourier transform infrared spectroscopy as well as scanning electron microscopy. Surface area
and water content of selected products were further characterized by the BET-method and by
thermogravimetry. Summing up the results, we can show that zeolite formation from filtration residues
is possible by several reaction procedures as model cases for a re-use of industrial waste
materials. Beside the importance for environmental protection, the reactions are of interest for
zeolite chemistry as the re-use of FR is possible under economically conditions of low energy consumption
at 60°C and short reaction periods.
The pore structure of lightweight granules made from masonry rubble was studied in order to better understand their engineering properties. Thermally and hydrothermally hardened granules were tested. Analysis by ESEM, mercury porosimetry and sorption methods yield important insight into their microstructure. The thermal granules are characterised by partly melted vitreous areas and large internal macropores that are connected via narrow throats. They show a marginal specific surface area along with a hydrophobic behaviour. In contrast, the hydrothermal granules have an accessible mesoporous system containing plate-like and ink-bottle pores. The shape of their water isotherms depending on the granules CaO content is sensitive to the morphology of calcium silicate hydrate phases (CSH). The hysteresis changes from a narrow loop that closes at low pressures, which can be attributed to coarser more crystalline CSH, to a large triangular-shaped loop along with a low pressure hysteresis, which is characteristic for fine fibre-like CSH with ink-bottle and plate-like pore morphologies. Granules with fibre-like CSH have the higher specific surfaces areas but those with more crystalline CSH show stronger physisorption of water molecules.
Die Herstellung hydrothermal erhärteter Granulate ist eine Möglichkeit zur Wiederverwertung von ziegelhaltigem Mauerwerkbruch, der derzeit aufgrund der heterogenen Zusammensetzung und hoher Feinanteile ein besonders hohes Verwertungsdefizit aufweist. Dabei ist die hydrothermale Erhärtung in einem Autoklav bei 200 °C und 1.6 MPa in gesättigter Wasserdampfatmosphäre eine Alternative mit geringerem Energieverbrauch im Vergleich zur thermischen Herstellung von Leichtgranulaten aus mineralischen Abfällen (Blähgranulate) oder Tonen und Schiefer (kommerzieller Blähton bzw. Blähschiefer), die bei Temperaturen von 1200-1300 °C im Drehrohrofen erfolgt.
Die Festigkeit der Hydrothermalgranulate entwickelt sich bei diesem Prozess durch die Ausbildung von Calciumsilicathydrat-Phasen (CSH), die durch die Reaktion zwischen Quarzpartikeln und hydratisiertem Kalk entstehen. Die so erzeugten Hydrothermalgranulate haben Rohdichten zwischen 1500 kg/m3 und 2000 kg/m3. Damit und auch durch andere Eigenschaften unterscheiden sie sich von den thermisch erhärteten Blähgranulaten bzw. Blähtonen. Ursache dafür ist letztendlich eine sehr unterschiedliche Gefüge- und Porenstruktur. Im vorliegenden Beitrag wird hauptsächlich über die Ergebnisse der Mikrostrukturuntersuchungen an Hydrothermalgranulaten zusammen mit ihren technologischen Eigenschaften, wie Kornfestigkeit, Rohdichte und Wasseraufnahme, berichtet.
Stone deterioration is the result of a complex interaction of external physical, chemical and biological forces with the mineralogical-petrophysical properties of the stone. With a better understanding of how these properties are linked to material behavior and durability, more effective measures for stone conservation can be developed. Studying these interactions in tuff is particularly complex due to the naturally high heterogeneity of tuff rocks.
The first aim of a current research project is to combine the results of recent and older studies on tuff deterioration. Furthermore, the literature overview is complemented by our own investigation of Weibern and Ettringen tuff, with a focus on pore structure characteristics.