Pre-normative research on the use of mixed recycled aggregates in unbound road sections

This paper presents and discusses the results arising from a pre-normative study aimed at determining the physical, chemical and mineralogical characteristics of mixed recycled aggregates produced from the treatment of mixed rubble for use in unbound structural layers of road. The results of this research show that the combined presence of concrete and ceramic materials induces pozzolanic reactions, which contribute to an increase in the bearing capacity of the compacted mixed recycled aggregate. From an analysis of their chemical characteristics, it can be inferred that the total sulphur compound content, the gypsum content and soluble salt contents can be regulated with reference to the water soluble sulphates test, given the high correlation that exists between those parameters. Generally, mixed recycled aggregates with ceramic material contents below 35%, organic matter contents below 0.8% and water soluble sulphate contents below 0.4% constitute a granular material that is technically feasible for use in unbound structural road sections.

Research highlights
► We examine characteristics and composition of mixed recycled aggregates for use in unbound road sections.
► Constituents govern physical–chemical behaviour of the mixed recycled aggregates.
► Maximum water soluble sulphate contents of around 0.4% should be permitted.
► Ceramic material contents should be below 35%.
► Mixed recycled aggregates can be used in unbound road sections under determined conditions.