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Wärmebehandlung und Autoklavierung von UHPC - Neue Perspektiven für die Betonfertigteilindustrie
(2011)
Das Gefüge von UHPC ist durch eine dicht gepackte und fehlstellenarme Matrix gekennzeichnet. Eine zusätzliche Optimierung ist durch eine Wärmebehandlung bzw. hydrothermale Nachbehandlung (Autoklavierung) unter einem Wasserdampfsättigungsdruck möglich. Die Wärmebehandlung von Beton ist ein in der Betonfertigteilindustrie geläufiges Verfahren, um die Erstarrungszeit zu verkürzen und höhere Frühfestigkeiten zu erreichen.
Reaction products and strength development of wastepaper sludge ash and the influence of alkalis
(2014)
Wastepaper sludge ash (WSA) from a newsprint paper mill was investigated for its mineralogical composition and its reaction products and strength development after activation with water and sodium and potassium hydroxide solutions. The results showed the WSA to consist of calcite, free lime, gehlenite, tricalcium aluminate, belite, talc, quartz and probably a glassy phase. The principle reaction product was monocarboaluminate (CO3–AFm) for the water- as well as for the alkali-activated WSA. Formation of monocarboaluminate and strength gain was more rapid for the alkali-activated WSA until 1 day of curing. However, afterwards reactions proceeded much slower when alkali solutions were used, leading to an about twice as high compressive strength for water-activated WSA mortars after 28 days of curing. The observed behavior is tentatively ascribed to a less uniform microstructure of the alkali-activated WSA. Significant differences between NaOH- and the KOH-activated WSA were not observed.
In the past decade, nanoindentation has become commonly used experimental technique for obtaining quantitative data on elastic and inelastic material properties in small volumes, typically in submicron length scale. The methodology was developed mainly for homogeneous materials or, at least, the homogeneity is assumed far enough from the tested volume in evaluation procedures1. Measurement on a heterogeneous system, in which the material phases are intermixed in small volume, is still a challenging task due to several circumstances.
First, the preparation of a flat surface on the heterogeneous sample with high differences in stiffness needs Special care. Second, the mechanical interaction between the material phases during surface loading is often unavoidable and therefore the extraction of intrinsic properties of individual phases from the heterogeneous system may not be possible. If differences between the stiffnesses of the interacting phases are low, finding of intrinsic properties can be successful using conventional Evaluation. In other cases, the error in estimating intrinsic properties can reach tens of percent.
In paper recycling several types of waste sludges are produced, which contain organics as well as inorganic fillers of the recycled paper, e.g. kaolinite, calcite, talc, or titanium dioxide [1,2]. Part of these sludges is incinerated to recover energy and to reduce the volume of waste to be handled. The ashes generated in this process are commonly referred to as wastepaper sludge ash (WSA). The quantities of WSA produced are large and at present much of it is still landfilled or otherwise handled entailing costs.
Depending on the composition of the recycled paper and the conditions during processing and incineration, WSA can have cementitious properties. In the present investigation a CaC03-rich WSA was analyzed for reaction products and strength development after hydration with water, 2 M NaOH solution and 8 M NaOH solution. The rationale for activating the WSA with NaOH was to assess the behaviour of the WSA when alkalis are introduced to the System or when the WSA is used as addition in alkali-activated binders.