Alternative aggregates, including recycled (concrete) aggregates as well as artificial aggregates (such as crushed stainless steel slag), are increasingly used in road construction in the context of a more circular economy, e.g. in base and subbase layers. As these materials are applied higher up in the structure (surface and binder courses), stricter requirements are made to allow for higher loads and the stronger influence of the environment, and the application of these aggregates becomes less straightforward. The Belgian standard specifications, for instance, allow incorporation of recycled concrete aggregates in concrete pavements or linear elements in concrete, but only if certain stringent requirements are met and only up to certain percentages of substitution of the natural coarse aggregates. Furthermore, artificial aggregates originating from stainless steel slag are not even allowed for the time being in pavement quality concrete, although a Belgian standardization working group has recently been installed to investigate this matter in more detail.
This paper presents an overview of laboratory research conducted in Belgium to characterize several types of alternative aggregates and concrete mixtures incorporating them, while focusing on practical execution as well as on the durability of pavement concrete. In addition, several concomitant pilot applications in Belgium are discussed in view of future perspectives for the application of alternative (recycled and/or artificial) aggregates in road construction.