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Although a large proportion of building rubble is already being recycled, most recycling applications, e.g. in roadbed foundations, can be considered as downcycling. This study is aimed at improving the material properties of crushed concrete fines by wet treatment, using a jig for density separation. Trial runs in a pilot plant with a flow rate between 0.45 and 0.65 t/h were conducted with two different materials (A and B). The materials were separated into heavy fraction, light fraction and finest fraction. Laboratory tests and tests for building materials were carried out on the output fractions and on the input materials. Laboratory tests showed an improvement of material properties such as loss by washing and content of binder matrix as well as water absorption for both materials A and B. The tests for building materials on mortar specimens showed that strength properties of specimens containing crushed concrete fines (heavy fraction) of type A were improved by wet treatment, but not for test specimens of material type B. Strength tests on concrete showed that a replacement of natural aggregates with wet-treated concrete fines up to 50 % had little effect on compressive strength, while untreated material exhibited a clearly lower compressive strength.
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.