Roundabouts

In many European countries, traffic at major junctions is managed increasingly by constructing right-of-way roundabouts, which allow safer and smoother traffic flow. The intense heavy traffic at these roundabouts induces extreme stresses in the pavement, both as a result of centrifugal forces as well as the overloading exerted by the offside wheels of tilting vehicles. The effects of such stresses include rut formation, the sideways displacement of the wearing course, the loss of surface aggregate, and cracking as a result of insufficient bearing capacity in the road structure beneath the offside wheels.

These findings encouraged designers to think of ways of using concrete for the construction of roundabouts.

When designing a concrete slab pavement for a roundabout, special attention must be given to the positioning of the contraction and construction joints. Indeed if the slabs are too large or are sharply angled the finished pavement may quickly develop unpredictable and undesirable cracks. The project designer must therefore carefully define the location of all the joints during the project design phase. When it is expected that the roundabout will have to bear higher volumes of traffic, the joints will of course be dowelled. Here too the satisfactory positioning of the dowels during the construction work is vital if the joints are not to become locked up.

Continuously reinforced concrete offers several important advantages:

1. the presence of transverse reinforcement makes it possible to distribute the outward thrust due to radial loads;
2. the presence of continuous longitudinal reinforcement makes it possible to eliminate the conventional contraction joints required in unreinforced concrete pavement and thus avoid loading at the corner of the slab.

Concrete roundabouts offer:

1. sufficient strength to stand up to the stresses;
2. a range of different solutions, such as slabs in concrete or in continuously reinforced concrete, small or large radii of curvature, a multiple choice of textures and colours, satisfactory integration into all kinds of environments;
3. rapid execution and low maintenance.