Characterization of bound and unbound granular materials

Using secondary granular materials for (sub)base layers helps save on natural resources and transport costs and avoids expensive run to spoil.

Secondary materials replacing well-known natural aggregates with a long-standing use in road construction must have no adverse effect on the quality and durability of the road structure, must be used under controlled cost conditions, and must not cause any pollution on the site of use. Adequate preliminary studies based on a methodical approach are required to guarantee this.

Generally those secondary materials are derived from demolition waste, industrial by-products from the steel industry, or solid residues from household refuse-burning plants. Some (e.g. treated incinerator ash, steel and stainless steel slag, recycled concrete aggregate and recycled mixed waste aggregate) have been included in Belgian standard tender specifications.

When using granular materials in base or subbase layers, it is essential to determine their mechanical performance characteristics, with a view to optimizing the thickness design and evaluating the long-term behaviour of the road structure.

A better knowledge of these characteristics makes it possible to avoid excessive layer thicknesses and to save on initial investment cost by using materials that are often less expensive, while still meeting durability requirements.

With this aim in view, BRRC continues to monitor and analyse granular materials for compliance with the requirements in the regional tender specifications, while meeting the priorities of the market.