Diss. Stockholm : KTH Land and Water Resources and Engineering, 2003

For recycled aggregates and industrial by-products to be used correctly in road construction, it is necessary to know their properties. Existing material specifications and test methods for aggregates used in Sweden and in many other countries are indirect and are based on empiricism. Over the years they have been adjusted to conventional aggregates, which make the introduction of new materials difficult. Research of their properties is being conducted in many places although knowledge has been inadequately disseminated. The objective of this thesis is to increase knowledge of the mechanical properties of certain selected residues for improved design of pavements using these residues. The study has concentrated on residues in unbound road layers. The materials selected were processed municipal solid waste incinerator (MSWI) bottom ash, crushed concrete and air-cooled blast furnace slag (AcBFS). The deformation on loading, the possible strength development over time and the resistance to mechanical and climatic action were studied in the laboratory and in the field. The results were compared with those of the conventional aggregates they could possibly replace, such as sand, gravel and crushed rock. The methods used in the laboratory were cyclic load triaxial tests, Los Angeles tests, micro-Deval tests and freeze-thaw tests. In the field, test sections with residues and reference sections with conventional aggregates in the unbound layers were monitored by means of falling weight deflectometer (FWD) measurements. The laboratory results showed that a high content of unburned material in MSWI bottom ash limits the resilient modulus but not the permanent deformation to the same extent. Both laboratory and field results showed several years' growth in stiffness for unbound layers with crushed concrete and AcBFS, which is not present for unbound layers with natural aggregates. This was thought to be caused by calcium dissolution and precipitation in the compacted material layer. A special investigation of the material in question, together with knowledge of the planned construction, could permit a higher value to be used in the design modulus than for crushed rock and thus benefit from the increased stiffness. The Los Angeles test and other tests developed for single-sized aggregates did not really justify the performance of the materials studied. Recycled aggregates and other residues, as well as conventional unbound road materials, should be analysed using cyclic load triaxial tests in the laboratory and FWD measurements in the field, both of which take into account the whole composite material or layer. Consequently, a new methodology for material assessment and comparison is proposed, based on permanent deformations in cyclic load triaxial tests. According to the laboratory and field tests, some bottom ash could be used, not only in embankments and capping layers but also to bear the stress levels expected in a sub-base. Recycled aggregates and other residues should be used near the source of production and not necessarily in roads with low traffic volumes. Their properties should be used to the greatest possible extent although their limitations must be taken into account.