Difference between Hot in place recycling vs cold in place recycling?

Answer 1

It must be recognized that the basis of both processes is rooted in the fact that asphalt is one of the few products that can be reused in its original location and on the same day without taking to a remote site for processing.

The asphalt pavement itself consists of roughly 95% rock and sand which last forever and 5% graded bituminous oil.

The oil itself is 95% carbon and about 5% lighter fractions that are subject to oxidization, leaching and evaporation

When these light ends have been depleted the material becomes brittle and cracks under load.

The extent to which they are depleted is one of the factors used to choose between Hot in place (HIR) and Cold in place (CIR) as a treatment.

HIR is a process where the existing surface is heated to a temperature where the material is soft and pliable like it was when placed there. It is then removed by mechanical means and supplemented with a small amount of new hot mix asphalt and a rejuvenating oil which will restore the properties of the material to like new.

HIR involves from 40 mm to 60 mm of the asphalt surface and requires a sound base structure to be in place.

The material is then placed and compacted in a process like a new paving process.

HIR is suitable for a new riding surface and will normally perform like new pavement.

CIR is done when the condition of the existing material is too deteriorated for HIR. There are proven design guidelines which are used to make this determination.

CIR is used to mill up to 100 mm of the existing surface and blend it with an emulsion, foamed AC or sometimes cement to produce a stabilized base over which a new riding course must be placed.

When properly designed, the two processes do not compete. Each has its own application.

Due to the requirement for a new surface, CIR is part of a much more expensive treatment on a badly deteriorated road.

Both offer the benefit of reusing scarce raw materials .

HIR in particular offers cost savings, resource conservation, energy savings and substantial reduction in greenhouse gas production over conventional methods.