3.4.4 High-friction Surface Treatment
For specialty sealing applications, thermosetting resin binders, including epoxy and polyurethane modified binders and other forms of polyester and resin esters can be used. These binders have been developed, in association with the appropriate aggregate, to provide good skid resistance in high‑risk areas such as sharp curves and approaches to pedestrian crossings or signalised intersections (Figure 3.14).
Specialty binder seals can be used in combination with calcined bauxite, aluminium oxide, slag or natural aggregates of suitable hardness and resistance to traffic polishing. Aggregate sizes are 1–3 mm, although larger sizes can be used. Their relatively higher cost compared to conventional binders confines their use to specialised applications.
Careful preparation of existing surfaces is necessary prior to applying specialty binders. Any failures in the existing pavement need to be rectified to provide a uniform, sound base for the seal. Best results are generally obtained on asphalt surfaces that are in good condition. New asphalt surfaces may need to be trafficked for several weeks to allow the binder film on the aggregate surface to be worn off, but this can also be achieved with a high-pressure water treatment. Concrete surfaces must be cured, structurally sound, and mechanically abraded before treatment. The treatment can also be applied over timber and steel bridge decks subject to adequate surface preparation. Any oil or detritus from the pavement surface should be removed by cleaning with detergent and allowed to dry. It is important that there is no water on the surface, as this will prevent bonding.
High-friction surface treatments are proprietary products, and design, surface preparation and application guidance should be sought from the manufacturer. The sprayed seal design methods outlined in this Guide do not apply to high‑friction surface treatments. Epoxy binder is generally applied at a rate of 1 to 1.5 L/m2 using a mechanical spreader, squeegees or brooms. Higher application rates may be required on coarse textured or porous surfaces.
The 5 mm nominal sized calcined bauxite aggregate is usually spread at a rate of 100–125 m2/m3
(6–8 kg/m2), immediately after the binder has been applied. It is not necessary to roll the aggregate as the random aggregate orientation and shape of the aggregate particles provides the desired texture.
Curing times depend on binder type, ambient temperature, and pavement temperature. Curing of polyurethane binders is further influenced by moisture and humidity.