RAP Use in Construction and Maintenance

Hot Recycling in Hot Mix Asphalt (HMA): At a central batch or drum plant, operators add reclaimed asphalt pavement (RAP) to hot new aggregate and asphalt – or a recycling agent – to produce asphalt concrete. Usually, a cold-planing machine supplies the RAP, but ripping or crushing operations can also provide RAP.

Backfilling Pavement Edges: Placing and compacting RAP at the pavement edge stabilizes the shoulder and protects the pavement edge from undue wear.

Full-Depth Reclamation: Processing together all of the asphalt pavement section and a portion of the underlying materials produces a stabilized base course. After crushing the materials and introducing additives, construction crews shape and compact the material and apply a surface, or wearing, course.

Cold-Mix Asphalt (Central Processing Facility): RAP processing requirements for cold-mix recycling are similar to those for recycled hot mix. The facility, however, substitutes graded RAP for some of the aggregate in cold-mix asphalt paving mixtures and processes it with an emulsion in a pug mill.

Hot In-Place Recycling: Specialized equipment driven over the pavement heats and softens the pavement, scarifies or hot mills it, and mixes it to a depth of 0.75 to 1.5 inch. In a single pass, the equipment adds new hot-mix material, a recycling agent, or both. With an additional pass, the equipment may also add a new wearing course after compaction.

Cold In-Place Recycling: Specialized equipment driven over the pavement removes 3 to 4 inches of depth by cold planning. The equipment pulverizes and sizes the material and mixes in an additive. The operation may add virgin aggregate to modify RAP characteristics. It also add an asphalt emulsion – or a recycling agent – and then place and compact the material. Some projects include an additional layer, such as a chip seal or 1 to 3 inches of hot-mix asphalt.

Some contractors use a “train,” consisting of a cold-planing machine, a screening and crushing unit, a mixing device, and conventional laydown and rolling equipment. This “train” occupies only one lane, thus maximizing traffic flow.