ASPHALT BINDERS AND ASPHALT MIXTURES - Materials for Civil and Construction Engineers - page 383

3. environmental saving by reducing the amount of required new materi-
als and by eliminating the problem of discarding old materials
4. eliminating the problem of reconstruction of utility structures, curbs,
and gutters associated with overlays
5. reducing the dead load on bridges due to overlays
6. maintaining the tunnel clearance, compared with overlays

Recycling can be divided into three types: surface recycling, central plant
recycling, and in-place recycling.

■

9.12.1 Surface Recycling

Surface recycling is defined as the reworking of the top 25 mm (1 in.) of the
pavement surface using a heater-scarifier. The heater planing machine heats
the pavement surface, which repairs minor cracks and roughness. Usually, a
rejuvenating agent is added after heating, followed by slight scratching of the
surface and compaction.

■ 9.12.2 Central Plant Recycling

Central plant recycling is performed by milling the old pavement (Figure
9.39) and sending the reclaimed asphalt pavement (RAP) to a central as-
phalt concrete plant, where it is mixed with some form of rejuvenating
agent or soft asphalt and aggregates to produce hot-mixed asphalt concrete.
If the RAP materials are mixed with the aggregates in a conventional as-
phalt concrete plant, they will burn and produce smoke, causing significant

FIGURE 9.39 Milling old pavement.