Traffic conditions vary greatly from very heavily trafficked urban and rural arterial roads (Figure 2.1) to roads with small amounts of traffic in isolated rural areas (Figure 2.2). The continuing increases in traffic volumes, vehicle mass, axle loads and tyre pressures mean that the selection, design and application of the correct surfacing type is more crucial than ever before.
The volume and composition of traffic are important considerations in the selection of treatment type, materials and design of sprayed seals. Increased traffic volumes, vehicle mass, axle loads and tyre pressures have significantly increased the demands on sprayed seals in terms of:
- dislodgment of aggregate due to braking, accelerating and turning traffic
- aggregate embedment into substrate materials
- aggregate wear and breakdown
- aggregate polishing
- cracking of binder due to increased deflection of substrate under loading.
In high-stress areas, additional performance may be obtained with the use of PMBs and/or multiple applications of binder and aggregate. Particular attention must be given to the conditions under which treatments are applied in high-stress areas, with work ideally being performed in warm and dry conditions. It may also be necessary to put in place additional measures to care for the completed seal (after‑care) before allowing unrestricted traffic use.
It is also necessary to recognise the limitations of sprayed seals and the need to consider alternative treatments, such as asphalt or concrete surfacing, for example at intersections and roundabouts.