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Concrete containing lightweight aggregates has been known since ancient times. To reduce weight, natural aggregates of volcanic origin, such as crushed lava or pumice, were used in construction purposes, for example for the Pyramids during the Mayan period in Mexico or for monumental structures in the Roman Empire. The most famous examples of this first application of lightweight aggregate concrete (LWAC) in Europe are certainly the Colosseum and the Pantheon. The Roman constructors used natural as well as artificial aggregates, such as pumice, crushed lava and crushed brick, to realise lightweight concrete applications in parts of these buildings. Still today, pumice is used in Germany, Italy, Japan and Iceland as aggregate for structural lightweight concrete.
Most lightweight aggregates (LWA) are produced by thermal Treatment of natural raw materials such as clay and shale. In addition to the high energy costs thereby incurred, the availability of suitable raw materials is limited. Other LWA manufactured from industrial by-products and wastes do not always meet the quality criteria for use in high-Quality lightweight concrete. A real alternative is the use of novel lightweight aggregates (referred to as LWA, aggregates and granules) made from mineral construction and demolition waste. An appropriate manufacturing technology has recently been developed in the framework of a German research project /1, 2/. Masonry rubble of variable grain size containing different amounts of brick material (25 to 70 %) serves as raw material. The LWA are obtained in a multistage manufacturing process by a thermal or hydrothermal treatment, which causes the expansion and the hardening of the material. The novel LWA meet the acceptance criteria for conventional lightweight aggregates. They are suitable for the production of lightweight concrete /2-6/. However to create tailor-made LWA from masonry rubble, the novel expanded materials and the influence of manufacturing conditions have to be understood in more detail. This paper reports on ongoing investigations of the chemico-mineralogical composition and microstructure of the novel LWA and focuses on the results of Chemical analyses, XRD, ESEM, TG/DTA and fusibility tests.
Bei der Aufbereitung von Rückständen aus der Zerkleinerung von Altfahrzeugen, weißer Ware und Mischschrotten, wie zum Beispiel durch das patentierte VWSiCon-Verfahren, fallen sogenannte Shredder-Sande an. Es handelt sich dabei um heterogene Gemische mit Korngrößen unter 5 mm. Bislang werden diese Shredder-Sande als inerter Reststoff im Bergeversatz verfüllt. Durch die Novellierungen im Kreislauf-Wirtschaftsgesetz ist fraglich, ob dieser Verwertungsweg in Zukunft noch als Recycling gewertet werden wird. So müssen sich Produkthersteller und Verwerter nun auch mit diesem Stoffstrom auseinandersetzen, um die für die Eingangsstoffe definierten Recyclingquoten erfüllen zu können. Dazu müssen neue Strategien zur Aufbereitung und Verwertung entwickelt werden, um aus dem heterogenen Stoffgemisch aus mineralischen, metallischen und organischen Bestandteilen wieder nutzbare Fraktionen zu erzeugen.