The reuse of recycled materials especially in the construction industry has proved to be a blessing for the conservation of the environment. The use of resources to the fullest by recycling and reusing has led to the remarkable downfall of greenhouse gases. The use of reclaimed asphalt pavement materials is the best example of the utilisation of resources to their fullest content.
Reclaimed asphalt materials(RAP) are recycled pavement materials mainly composed of asphalt and aggregate. These materials are extracted while the reconstruction, resurfacing or excavation of road pavement. Fine grade aggregates coated with asphalt cement are extracted from pavements and are used for reconstruction or even for new construction.
Materials gathered from full-depth pavement removal, plant cleanout, excavation processes or unutilised materials from the site if recycled properly produce similar to if not better than newly extracted asphalt.
Reprocessing of RAP materials at processing plants includes crushing, screening, conveying and stacking RAP materials for further utilisation.
Processing of Reclaimed Asphalt Material
The two ways in which reclaimed asphalt materials are processed are milling and deep depth removal of pavements. Milling requires the use of milling machinery, which can excavate up to 50mm or 2cm in thickness of pavement in a single go.
In Deep depth removal, excavation or breaking of pavement is done using a rhino horn on a bulldozer or pavement breaker or both in some cases. Then the broken pavement is accumulated and loaded in haul trucks using loader machines and transported to processing facilities where these broken pavement pieces are processed through various methods to make them usable.
How much workable is Reclaimed asphalt compared to New asphalt?
Reclaimed asphalt materials constitute wreckage of old pavements from different sources hence its quality varies. Excess granular material, soils and debris are left in stockings of old pavement.
Patching and crack sealing in pavements requires the application of a sealing coat. More patching and crack sealing done to pavements requires more sealing coats which influence RAP material constituents. Hence quality control is essential to keep track of the workability of RAP material.
As per studies of some independent labs, RAP contains 4-6% of asphalt content. Most of the RAP used today are 5-30 years old. Based on supply, aggregate and climatic conditions the quality of asphalt varies from country to country and place to place. Special equipment is used to recycle the asphalt which doesn’t require any additional asphalt or emulsion.
Bagela Asphalt recycler is one such instrument that doesn’t need direct heat for recycling, this conserves energy, making it environment friendly. This restricts the burning of asphalt, and 100% of asphalt is recycled. Thus we can conclude Reclaimed Asphalt Pavement materials are as workable as the new asphalt.
Uses of Reclaimed Asphalt Pavement materials
Here are some ways in which RAP materials can be used:
1. Asphalt Concrete aggregate
RAP material can be used as asphalt concrete aggregate, as a substitute material to aggregate.
2. Asphalt Cement Supplement
Used as asphalt cement binder, thereby reducing cement requirement in new or recycled asphalt concrete mix.
3. Hot mix asphalt
Used in hot mix asphalt paving mixtures as an aggregate substitute.
4. Cold mix asphalt
RAP material is incorporated into cold mix asphalt paving mixtures as a substitute for aggregate. Apart from that, cold mix asphalt is mixed with milled out pavement material and placed and compacted again in a single pass.
5. Granular Base Aggregate
RAP materials when crushed, screened, and blended with conventional granular aggregate, this blend provides suitable materials required to attain the bearing strengths needed for most load-bearing unbound granular applications. RAP materials exhibit a somewhat lower bearing capacity than conventional granular aggregate bases.
6. Stabilised Base Aggregate
RAP materials are crushed, screened then blended with one or more stabilisation reagents to provide enough strength on being compacted.
7. Embankment or Fill
RAP materials not suitable for reprocessing that have been stockpiled for a long time can be used for making embankments, but this practice is not followed frequently. For use as embankment base or fill material, RAP which has been discarded and returned from highway use is best suited.
Physical properties of RAP
The physical properties of RAP material play a very important role in its uses and are largely dependent on its constituents. Few physical properties of RAP materials have been explained below:
1. Aggregate quality, size, and consistency mark a considerable difference between asphalt concrete mixes.
2. Aggregates on the surface are of higher quality compared to those on the binder course due to polishing resistance.
3. Milling and crushing causes degradation to some extent, thus milled RAP materials are generally finer compared to new aggregates.
4. The size of RAP material varies to some extent based on the equipment used for its excavation.
5. The moisture content of RAP material is very less when stockpiled but it has been observed that the moisture content increases in storage.
6. RAP can acquire a considerable amount of moisture if exposed to rain.
7. Moisture contents up to 5 per cent or higher have been measured for stored crushed RAP. During extensive precipitation, the moisture content of some RAP stockpiles may reach as high as 7 to 8 per cent.
8. The asphalt cement content of RAP ranges between 3 and 7 per cent by weight.
9. The RAP asphalt cement is harder than new asphalt cement due to exposure to atmospheric oxygen. This hardening is due to exposure to increasing temperature, bad compaction, and higher air void contents.
Here are some physical properties in a tabulated form:
| Type of Property | RAP Property | Typical Range of Values |
|---|---|---|
| Physical Properties | Unit Weight | 1940 – 2300 kg/m3 (120-140 lb/ft3) |
| Moisture Content | Normal: up to 5% Maximum: 7-8% | |
| Asphalt Content | Normal: 4.5-6% Maximum Range: 3-7% | |
| Asphalt Penetration | Normal: 10-80 at 25°C (77°F) | |
| Absolute Viscosity or Recovered Asphalt Cement | Normal: 4,000 – 25,000 poises at 60°C (140°F) |
Benefits of Reclaimed Asphalt Pavement(RAP) materials
1. Very cost-effective.
2. Provides environmental sustainable impact.
3. Lasts long and is as reliable as new asphalt.