The valorization of recycled and secondary materials

Using raw materials and energy economically helps to achieve sustainable road construction. As an alternative to consuming primary raw materials – which are mostly not renewable and, therefore, limited in supply and availability – secondary raw materials can be employed. These are materials used previously in an infrastructure or in some industrial process or product, which are considered as wastes when reaching the end of their service lives.

Especially stony wastes – e.g., demolition products from buildings and roads or various types of slag from the iron and steel industry – can be reclaimed and put to interesting use for example as aggregates in road construction. As such, they are substitutes to newly dug natural raw materials such as limestone, gravel, or sand. In addition, some materials / wastes such as pulverized fuel ash, plastics or waste rubber can be recycled in or as a binder, an additive or a finished product.

Valorizing wastes as secondary raw materials must not be merely an alternative form of waste treatment: the road is not a dustbin or a dumping ground. That is why these alternative materials must meet strict requirements, both for environmental safety and technical quality in construction.

Stainless steel slag as a secondary raw material
Demolition waste from a concrete road

BRRC has been investigating such alternative materials for many years as part of its research programme.

Since these secondary or recycled materials often have special characteristics and consequently differ in behaviour from the well-known traditional materials, they are an interesting topic for research. This may result in specific recommendations for the handling of these materials, or in the development of specific test methods or equipment.

Sustainable development is a topical issue in the asphalt industry as well. This concern is reflected by the ever increasing interest in the reuse of reclaimed asphalt (RA) and the use of secondary raw materials from other industrial sectors. Economic advantage to the asphalt producer is an important factor in this respect, as is the growing awareness of the need for ecological use of available materials.
That is why BRRC is very widely interested in this current topic. Research in the area of asphalt recycling is conducted at two different levels, viz. that of the basic materials and that of the asphalt mixture. In studying materials (such as reclaimed asphalt (RA) or secondary materials), attention is paid to the evaluation of both environmental and engineering characteristics. Illustrative examples in this context are the research projects into the extraction and recovery of polymer-modified binders, the detection of contaminants such as tar in RA, or the assessment of the suitability of slag for use as an aggregate in asphalt mixtures. At the level of the asphalt mixture, focus is on the development of volumetric mix design with PradoWin (see Components and mix design), the impact of reuse on the performance of recycled hot mixes (RHM) as measured in performance-oriented tests (see The development of tests for bitumens and asphalt mixtures), and the optimization of production techniques for reuse.