At present, heterogeneous and fine-grained masonry rubble can only be recycled at very low level. To overcome this limitation, the material was employed as feedstock for the production of lightweight aggregates in a thermal process similar to that used in the manufacture of expanded clay and expanded slate. To that end, the fundamental suitability of masonry rubble as a raw material was evaluated. Experiments were carried out which indicated that lightweight granules with defined, adjustable properties similar to those of natural-materialbased aggregates could be manufactured from masonry rubble. Structural lightweight concretes produced with these secondary aggregates achieved comparable performance to lightweight concretes produced with conventional expanded clay. Lightweight recycled building material aggregates represent a product that hardly requires any primary resources in its manufacture.Keywords: Masonry rubble, feedstock recycling, expansion process, rotary kiln, lightweight aggregate.
Characterization of masonry rubbleAt present, the mix of various wall construction materials, mortar, plaster, and further components that make up masonry rubble cannot be adequately utilized. This results from the considerable heterogeneity of the material composition and the large proportion of fines. In the future, strict closed-loop recycling laws and limited landfill capacity will prevent the disposal or application of these materials as fill or in the construction of landfills. In this context, a new technology for the manufacture of lightweight aggregates from masonry rubble was developed. These lightweight construction aggregates are produced from mineral construction waste and can be employed in the manufacture of lightweight mortars and concretes.Masonry rubble consists of multiple components. As well as brick, other construction materials present can include calcium-silicate brick, aerated autoclaved concrete, precast concrete, or natural stone. Additional components can include lime mortar, lime cement mortar, cement mortar, interior gypsum plasters, exterior plasters, insulation, tiles, and façade panels. Recycled aggregates manufactured from this material through comminution and screening can vary greatly in their composition. This has been confirmed by the results of sorting analyses of processed masonry rubble (Figure 1). The brick and other ceramic material content vary between a minimum and a maximum of 24 and 92 mass-% respectively, with a mean value of 50 mass-%. Concrete and mortar are the second most dominant material group. The mean is 46 mass-% with a range between 8 and 70 mass-%.Within a batch of material there may be a variety of building materials with greatly differing properties. This diversity of materials is reflected by the range of the particle density. Even
