What is Hot Asphalt
Recycling?
Hot asphalt recycling
implies a set of operations during which the worn-out pavement is first removed
from the road surface, with or without resurfacing materials, and then is
broken, crumpled, and granulated. The resulted mixture is then blended with
bitumen and asphalt rejuvenating agents in the hot mixed asphalt plant, and
finally is spread on the road surface and compacted. These materials can be
modified with new stone materials, hot asphalt, or bitumen under some
circumstances. Cold asphalt recycling is another form of pavement recycling
that works independently of a hot mixed asphalt plant. In the cold recycling
process, the surfacing materials are reused in place, with or without the base
material. Indeed, asphalt recycling is a form of waste management operation.
Asphalt recycling
yields benefits such as economic saving, preserving the environment, and a huge
drop in air pollution.
Recycling can be done
in-situ or with the help of a plant.
In-situ recycling
During in-situ
recycling, the whole hot recycling process is done in-place inside the
recycling machine. The recycled asphalt is then spread on the road surface and
compacted. Materials do not need to be transported during in-situ recycling.
This technique is mainly useful for patching or resurfacing damaged areas on
the road with a thickness of 25 to 50 mm and does not alter the load-bearing
capacity of the pavement.
Plant-based recycling
In plant-based
recycling, reclaimed asphalt pavement (RAP) is transported to the plant and
blended with stone materials, bitumen, rejuvenating agents, or fillers, and
then cured. The new asphalt is transported to the damaged area, spread on the
damaged place, and compacted.
Asphalt produced for
application in distinct layers (e.g., Topka and Binder layers) shall conform to
relevant standards and specifications.
Bitumen selected to
make hot asphalt has generally high penetration and low viscosity so that it
can impregnate new stone materials and fulfill requirements and specifications
by mixing with hardened bitumen in recycled materials. The mixture of new and
old bitumen in RAP gives the basic properties of bitumen in the design (e.g.,
environmental conditions and load-bearing under traffic).
The percentage of
bitumen in RAP is determined through burning pavement surfaces in extreme fire
scenarios. This process requires determining the softening point, rate of
penetration, and viscosity.
Bitumen in RAP is
hardened over time and its oily and effective materials are lost through
evaporation. It gradually loses its properties under weather conditions. Thus,
it is necessary to use rejuvenating materials to modify its viscosity and rate
of penetration. Simply put, the bitumen shall undergo chemical and physical
modification.
Rejuvenating agents
are petroleum hydrocarbons showing the properties of bitumen. They can be
utilized as a substitute for the demanded bitumen.
Benefits of hot
asphalt recycling
- Conservation
of natural resources;
- Improving
the bearing capacity and strength of the pavement layer without
considerable alteration of its thickness;
- Repair
of road surface damages (e.g., cracks, removed rock grains, grooves, and
wheel track on asphalt);
- Extending
sliding resistance;
- Improving
the hardness of bitumen and the life of asphalt;
- Avoiding
changes in the project's figures and adaptation to the geometric
conditions of the road; and
- Diminishing
waste and eliminating a need for a discharge place.