Manufacturing Techniques:

Central Plant:

A hot mixed asphalt plant that is capable of making cold mixes ( has a pug­mill) can be used for making recycle mixes. Also road side pugmills may be used. In the latter type the emulsion and water pumps should be interlocked with aggregate flow to make an even mix.

The plant is fed with sized aggregates sourced from the RAP, virgin aggregates and emulsion accurately metered or weighed. Water ( as determined in mix design) will be added also.

Emulsion mixes usually require shorter mixing times than hot mixes, this is because of a tendency for the aggregate to scrub the emulsion off . This must be balanced against the need for stone coating. Stone coating of 100% will not always be achieved, however extra coating will occur during handling and spreading.

Mixes should not be broken in the mixer, in most mixes the emulsion type will not include high levels of cutter and workability will be compromised.

In Place Recycling

Several commercial operations will handle all aspects of the in place process.

The steps to be taken may include-

Drainage
Ripping/Scarifying
Size Reduction
Cold Milling
Mixing
Spreading\Compaction
Surface Treatment.

Drainage A drainage evaluation is essential.

Ripping/ Scarifying/ Size Reduction

The road surface must be broken up, this can be accomplished by ripping/ scarifying and then size reduction or by cold milling.

This can be accomplished by separate ripping with purpose built ripper scari­fyers or as a part of a total recycling machine.

Size reduction is achieved with a crushing phase, again in a separate machine or as part of an integrated recycling machine.

Cold Milling

Drum planing can rip and size art the same time.

Mixing

This blends all additives with the sizes recycle. This can be accomplished with blade mixing (grader), rotary mixing or in a travel plant.

Additives are added by spray distribution on to windrows or direct injection into the mixing chamber from the plant tanks or tankers hooked up to a travel plant.

Control of addition is critical.

Placement Techniques

Central Plant

Spreading

Mixes that require aeration are generally placed in windrows to be picked up by the paver using a pick up device. Alternatively the mix may be placed directly into a paver.

Which method is best is decided by the need to aerate the mix allowing some water to escape. In hot conditions direct pave placement is used.

The successful placement relies on sufficient fluids being present, dry mixes will be torn by the screed. The screed should never be heated.

The mix should be spread uniformly on the pavement beginning at a point that is furthest from the plant.

Compaction

Rolling is delayed until the mat can support a roller without rutting and shoving of the mix. If too long is taken however the stiffer mix will be more difficult to compact and bitumen aggregate bonds can be broken down. Breakdown rolling can be carried out with vibrating steel rollers and finishing with conventional multi tyred rubber wheel rollers.

Breakdown rolling should begin as the emulsion starts to break. The moisture content present will act as a lubricant without filling voids and preventing compaction. At this time the mix should support the mix. If the mix does rut and shove stop rolling immediately. Rolling can resume after moisture has reduced ( either by itself or by mechanical aeration.

The mix should be placed in lifts until the required crossection is achieved.

Final rolling may be with a multi tyred roller or a flat steel.

Good practice for joint position and creation should be followed. (as for hotmix).

In Place

Spreading

Mixtures that have been windrowed by blade mixing or travel mixer can be spread with a grader or picked up and spread by paver.

Mixes that do not require aeration can be spread to correct thickness direct­ly. Windrows should be to the side of the road to prevent humping.

Compaction

As for plant mixes. Some travel mixers incorporate spreading using a screed and place the layer in one thickness. This is subject to the constraints men­tioned above