Composite pavements: concrete slab on a bitumen aggregate foundation

Since they first appeared in France at the beginning of the 20th century, concrete pavement design has constantly evolved, sometimes to keep pace with changes in traffic volumes and loads, sometimes to take into account the variability of climatic conditions (frequency of frost, degree of rainfall), sometimes to incorporate technical data obtained either from feedback on the behavior of materials or pavement structures in situ, or from new knowledge of materials acquired through laboratory research, and sometimes thanks to new calculation methods for pavement design.

From a single-layer concrete pavement structure, the technique gradually evolved to a two-layer structure by the 1980s/1990s, the interface of which was deliberately detached during construction to protect against the surface of the pavement rising due to shrinkage cracks in the sub-base. The typical concrete structure consisted of :

• a concrete covering, which may be in the form of unreinforced concrete slabs with ungrooved "BC" joints, or unreinforced concrete slabs with grooved "BCg" joints, or in the form of Continuous Reinforced Concrete (BAC) without transverse shrinkage joints;

• a foundation layer of hydraulically bound materials (cement gravel or lean concrete).

These structures are accompanied by state-of-the-art joint layout rules (shrinkage joints, construction joints and expansion joints). In the case of heavily trafficked roads, they are subject to strict construction provisions (non-erodible sub-base, extra width on the hard shoulder side, effective drainage at the pavement/sub-base/ hard shoulder interface).

In addition, these structures are efficient and durable, but suffer from an economic handicap linked to their very design. This is because the interface between the concrete pavement and the hydraulically bound sub-base, which is deliberately detached during construction, has the disadvantage of increasing the horizontal stresses generated by the traffic at the base of the pavement, and therefore requiring greater thicknesses than would be the case with a bonded interface.

With the aim of optimizing the design of concrete pavement structures and thus improving their competitiveness, we have been looking for a solution that will enable bonding at the interface between the pavement and the base of a concrete structure, without causing harmful problems on the surface.

On the one hand, the cement industry, represented by its promotional association CIMBETON (Centre d'information sur le ciment et ses applications), and concrete road contractors, represented by the trade association SPECBEA (SPEcialistes de la Chaussée en BEton...