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.
Effects of wet processed crushed concrete fines as secondary aggregates in building materials
(2008)
In Germany, about 60 million tons of demolition waste are generated annually. Approximately 70% of the demolition waste is currently recycled. Most recycling applications, for example in roadbed substructures, can be seen as a kind of downcycling. However, there are also some high-level applications for demolition waste. For instance, crushed and sieved concrete demolition waste can be used as concrete aggregate instead of natural materials. Depending on the crushing process, about a third of the broken concrete is currently concrete sand. At present, concrete sand fraction (0-4 mm) is rarely reused as a concrete aggregate. This is due to the fact that some important characteristics of crushed concrete sand are different from those of natural sand. As a result, it does not reach the standards required for aggregates. Concrete containing such aggregate is of lower quality than concrete made of natural aggregate. This paper describes an experimental investigation on the treatment of concrete sand gained from demolition waste by wet processing using a jig whereby the sand is separated by grain size and, more importantly, by density. Concrete produced with concrete sand which has been treated in this manner should have the same quality as concrete prepared with natural aggregate. Recycled sand used as aggregate substitutes natural resources and avoids disposal of waste. It has all the characteristics of an Ecomaterial. (author abst.)
Die Abfallwirtschaft in Deutschland behandelt eine Menge von 359 Mio. Tonnen. Den größten Anteil haben Bau- und Abbruchabfälle mit 54%. Die Behandlungsverfahren dafür unterscheiden sich stark von denen für Siedlungsabfälle. Gemäß Europäischer Abfallrichtlinie ist Recycling gegenüber einer energetischen Verwertung in der Hierarchie der Abfallbehandlungsverfahren höher bewertet. Bei der thermischen Behandlung entscheidet die Energieeffizienz des Verfahrens, ob eine Behandlung als Verwertung oder Beseitigung gilt. Nach dieser Richtlinie erfolgt die Berechnung der Energieeffizienz stark vereinfacht mit der sogenannten R1-Formel. Veröffentlichte Daten zu Wärme- und Stromproduktion verschiedener thermischer Abfallbehandlungsanlagen werden mit der R1-Formel und Daten aus der Literatur verglichen. Mengen und Entsorgungswege sowie Möglichkeiten zur Bewertung von Abfallbehandlungsverfahren werden diskutiert. ---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
Waste management in Germany covers an amount of 359 million tons. The largest fraction is construction and demolition waste (C&D waste) with some 54%. The treatment processes for C&D waste differ from those for municipal solid waste. According to the European Directive on Waste a waste hierarchy shall apply where recycling has a higher priority than energy recovery. A thermal treatment is regarded as recovery operation only if the energy efficiency is above a certain limit. Under the terms of the directive a simplified calculation of the energy efficiency is perfomed using the so-called R1 formula. Published data on heat and power production of several thermal waste treatment plants are compared to the R1 formula and data from literature. Amount and waste management options for different waste fractions and how to evaluate different waste management processes are discussed.