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- Acid resistance (1)
- Alkaliaktivierte Bindemittel (1)
- Biogene Schwefelsäurekorrosion (1)
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Organisationseinheit der BAM
The production and processing of ordinary Portland cement are responsible for nearly 5% of the world C02 emissions. Due to the world’s increasing requirement for building materials, this air pollution is growing up in the next decades. Alternative cement such as geopolymers can reduce these emissions effectively, Conventional geopolymer binders, produced ffom fly ash or metakaolin as aluminosilicate source and water-glass or alkali hydroxide Solutions as activator, are often used and studied. It is known that under appropriate conditions the starting materials form a three-dimensional aluminosilicate structure and create a gel-like matrix, In our case, a silica source from wastewater treatment of chlorosilane production and solid sodium aluminate as starting materials are initiated to harden by water. This procedure is known as “just add water” or “one-part” geopolymer formulation. These composites have significant advantages for use on construction site, but their Chemical structure is not extensively analyzed. In this work, a well known one-part geopolymer is investigated by 'H and 27A1 magic-angle spinning nuclear magnetic resonance (MAS NMR) spectroscopy. Furthermore, it is shown that overlapping NMR lines can resolved with echo experiments and
Einkomponentige alkaliaktivierte Bindemittel (AAB), d. h. AAB, bei denen der Aktivator als Feststoff im Bindemittel vorliegt, weisen Vorteile hinsichtlich der praktischen Anwendung im Bauwesen gegenüber konventionellen AAB auf. Einkomponentige AAB lassen sich als Gemische aus reaktiver Silica und Natriumaluminat herstellen, wobei die Reaktionsprodukte von der eingesetzten Silica und den Verhältnissen Na2O/Al2O3/SiO2/H2O abhängen: Während Mikrosilica und ähnliche Reststoffe zu zeolithreichen Produkten führen, erhält man aus Reisschalenasche vollständig amorphe Gele (sog. «Geopolymere »). Mörtel auf Basis solcher Bindemittel entsprechen den Anforderungen von DIN 19573:2016-03 hinsichtlich des Widerstands gegen Schwefelsäureangriff (Prüfung bei pH = 1 für 70 d) und sind damit potentiell als Reparatursysteme für Abwasserinfrastruktur geeignet. Untersuchungen mittels 29Si-MAS-NMR und 1H-29Si-Kreuzpolarisations(CP)-MAS-NMR sowie REM-Aufnahmen von erhärteten und dem Schwefelsäureangriff ausgesetzten AAB zeigen, dass der hohe Säurewiderstand v. a. auf die Fällung von Silicagel an der Grenzfläche Mörtel/Säure zurückzuführen ist, wodurch der Korrosionsfortschritt in darunterliegenden Schichten verlangsamt wird.
One-part geopolymers, synthesized from three different silica sources and sodium aluminate, were investigated regarding their microstructure and the evolution of their compressive strength on curing at slightly elevated temperatures. The effect of thermal treatment was studied up to 1000 °C and for the investigation of the chemical durability specific samples were treated with sulfuric acid (H2SO4, pH = 1).
Depending on the silica feedstock, different degrees of reaction were observed. One of the silicas had a significantly higher reactivity. For two of the silicas, significant amounts of zeolites occurred as reaction products besides geopolymeric gel, whereas the more reactive silica source lead to the formation of a rather fully condensed geopolymeric network.
The composites indicated promising behavior on heating in so far as no distinct shrinkage step occurred in the temperature range of dehydration. Up to 400 °C the residual strength of those mixes increased. Above 800 °C the samples underwent new phase formation. After exposure to sulfuric acid (pH 1; 70 d) specimens showed a residual compressive strength of about 77 % of the reference, indicating high acid resistance.