A road structure generally comprises the following pavement courses, each composed of typical materials and having a specific function in structural design:
the subbase layer: acts as a buffer between the subgrade and the base layer and most often consists of a sand bed or crushed stone;
the base layer: may be either bound or unbound. Crushed stone is often used for unbound bases. Bound bases are obtained by adding a hydraulic binder such as cement;
the bound surfacing consists of bituminous layers, cement concrete, or a combination of both.
There are tree types of road pavement. Flexible pavements consist of a subbase layer, a crushed stone base and one or more bituminous surface layers; rigid pavements of a subbase layer, a lean concrete base and cement concrete at the surface; and semi-rigid pavements of a sand bed, a lean concrete base and bituminous surface layers.
The object of structural design is to ensure adequate service life, during which the road will require no structural adaptations. The layers in the structure should be designed with a thickness such that traffic loads are adequately distributed over the various courses, as each load causes a deflection in the pavement.
The TRIMM project (acronym of Tomorrow’s Road Infrastructure Monitoring & Management) was completed late in 2014. It was funded under the European Union’s Seventh Framework Programme for research (FP7, 2007-2013). Its objective was to strengthen the role of condition monitoring in road management and to highlight its beneficial effects. The condition of a road network is, in fact, decisive for its level of service to road users. Maintenance is required to preserve or improve the condition of bridges and roads.
The right choice of structure and constituent layers is a primary concern to designers in both the private (engineering consultants, architects) and the public sector (technical departments of municipalities, provinces and regions) who have to make designs for new roads or for maintenance, renovation and adaptation works to existing infrastructure.