|[ Top ]||Hot Rolled Asphalt and Bituminous Macadam|
Idiots' Guide to Highways Maintenance
ON SITE RECYCLING BY HOT PATCH TREATMENT
|Introduction to insitu hot recycling of bituminous materials||Adding rejuvenator|
|Heating the surface to be patched / recycled||Compaction|
|Area to be patched after heating||Hot box storage of fresh bituminous material|
|Adding fresh material from the hot box||Other forms of heating|
INSITU HOT (INFRA RED) RECYCLING OF BITUMINOUS
This process is able to be performed because of the very nature of bituminous mixtures, i.e. they are thermoplastic, meaning if you heat up a bituminous material it becomes plastic again and you are able to rework the material.
The fundamental difference between a tonne of new, hot (150°c) 10mm. close graded macadam (CGM) wearing course and a tonne of cold 10mm. CGM wearing course in an existing road pavement is the first will cost you approximately £80:00 a tonne to purchase and the other will cost you approximately £10:00 a tonne to plane out and dispose of.
I am being generous with the cost of £10:00 a tonne disposal figure because I am assuming it will be recycled into a granular capping material rather than being taken to tip at a cost of £50:00 per tonne, if they will now accept bituminous material.
It is true the bitumen in the in situ material may have oxidised and hardened a little but this can be remedied by the addition of a rejuvenator if required, but the degree of oxidation/hardening during the time in the road is unlikely to be great in "dense" bituminous mixtures, as opposed to "open" graded mixtures where oxygen will have a greater access to the bitumen within the matrix of the material.
I repeat it is the basic thermoplastic nature of bitumen that makes bituminous mixtures so readily able to be recycled and allows this process to take place, rather than the addition of rejuvenators.
The rejuvenators may enhance the recycled material but on many occasions a rejuvenator may not even be necessary.
If you wish to be absolutely sure on whether to include an additive in the recycling process take a sample of the material to be recycled and obtain a sample of reclaimed bitumen binder so that you may test for the penetration and softening point of the bitumen.
This information will inform you if modification of the bitumen component is necessary, but perhaps some rejuvenation is beneficial, however you do not want to modify the bitumen viscosity to the point where it may wheel track.
It is likely that most rejuvenators are penetration grades of bitumen suspended either in a volatile oil or as an emulsion, so you are in fact adding fresh bitumen to the existing material or components derived from bitumen (oil industry) that will enhance the engineering properties of the existing binder in the recycled material.
I would suggest that you perform an engineering examination of the properties of any rejuvenator that you are thinking of using, some are good, if you need them, some are not so good and still expensive.
be aware that this process is a generic process able to be performed because
of the already explained thermoplastic nature of bituminous mixtures
employed for road surfacing.
There are a number of companies that offer a proprietary package in this form of "infra red" heating being used to perform patching by reworking the existing road surface that has cracks and minor areas of failure.
However if you have the "in house" knowledge and the correct equipment you can conduct equally successful patching using this process.
I include pictures of a company offering a proprietary/branded process, and of a direct labour organisation, performing hot in situ patching, both were equally successful.
Where failures do occur it is usually due to poorly controlled heating of the road surface,
● either too cold when there is insufficient heat to thoroughly rework the bituminous mixture to an adequate depth, and subsequent poor compaction.
● or too hot and the bitumen in the mixture is burnt and rendered inert, i.e. it will no longer bind the aggregate together.
"Normal" temperatures quoted for hot rolled asphalt and other bituminous mixtures as found in British Standards should apply to this process.
It is good practice
to apply "gentle" heat over a period of time, time may be lost on the first
patch, but after that the second patch is heating while the first patch is
being reworked, and with jobs that I have seen there is a natural flow of
work after the initial heating of the first area, even configuring lunch
break as a heating period.
further information on the basic principles of hot remixing/recycling bituminous mixtures, press
|The infra red heater in place slowly heating the area to be patch in a controlled manner.||The heater being moved to the next area of road surface to be reworked, and patched.|
HEATING THE SURFACE
TO BE PATCHED / RECYCLED
The heating unit is placed over the area to be patched and is allowed to remain there for a period of time sufficient to heat the bituminous material to a point where it is sufficiently plastic to be able to be worked, i.e. normal laying temperature.
The length of time will depend upon the depth of material to be reworked, the viscosity of the bitumen in the material to be patched, and the the existing ambient temperature of the material.
The heat applied to the surface is a radiated, indirect heat, and the radiating elements are heated by gas burners.
The heat from the gas burners can be regulated by the amount of
gas being burnt, or by a pulsed system of switching the burners
on and off in a pattern to supply the appropriate amount of heat
to the road surface.
The heating of the road surface must be performed in a controlled manner, the bituminous material must NOT be heated above the temperature that was appropriate to the material when it was originally mixed.
It is not a just a matter of heating up the material to be patched as quickly as possible, I repeat, the heating must be done in a controlled manner to prevent damage to the bituminous binder.
All information and warnings that are given about overheating bituminous material referred to in other pages of this guide equally apply to this recycling process.
further information on temperatures of bituminous materials,
press ----------> HERE
|The heated surface are to be patched, this is a hot rolled asphalt and precoats.||The area to be patched being marked out.|
AREA TO BE PATCHED AFTER HEATING
The heater is being moved from a now heated area to a new area that is to be heated, where it will sit gently heating the road surface while the newly heated area is worked upon.
This particular area of bituminous surfacing failure has occurred around a road gully and the area has been heated until the material is now at a temperature it can be reworked.
In this particular situation it
has been decided to remove the oxidised layer at the actual road surface and
replace it with fresh material from a hot box.
This is not always deemed to be necessary depending upon the nature of the surface material and the position of the site.
HOT BOX FOR KEEPING
FRESH MATERIAL AT REQUIRED TEMPERATURE
The material to be added to the heated area will have been held in a hot-box to keep the material at the required temperature through the working day.
This particular type of hot box is oil jacketed, and the circulating oil can be heated by gas burners to keep the material it contains at a constant suitable temperature.
Bituminous materials must not be kept in a hot box for prolonged periods because binder hardening can occur.
|Breaking up and remixing of the heated material starting to to be performed.||A heated hot box containing, and keeping hot, additional hot rolled asphalt.|
ADDING FRESH MATERIAL FROM THE HOT BOX
|Additional hot rolled asphalt from the hot box being added.||Fully reworked patch.|
|A "rejuvenator" being added prior to the application of the precoated chippings.||A successful area of patching should appear no different to a "normal" bituminous surfacing.|
|A completed patch being being compacted.||A "sealer" being applied to the surface after compaction.|
The same compaction regime is required as if the patch had been constructed in a conventional manner.
It is interesting to note that in this situation a larger patch has been undertaken by heating adjacent areas, as long as you are working against a hot "edge" the separately heated areas will blend together as one homogenous area of surfacing.
It is at this point that a rejuvenator may be added, before the fresh material is blended into the existing reheated material by raking.
The adding of a rejuvenator, and how it is applied, and how much is applied is usually associated with the particular process you choose to employ.
Various claims will be made for the benefit derived from this process and it is up to the engineer in charge to decide if the benefit can be quantified, but the principle is good, the practice is not always what it should be.
The need for a rejuvenator is much dependent on the quality of the bituminous mixture being recycled.
|"Sealer" being applied to the completed patch.||In this proprietary operation a sharp grit is applied to the sealer.|
|A finished patch after early trafficking.||Above is a completed patch using a generic approach to the procedure.|
|A continuous large patch achieved by continually, and gradually moving the heater.||A generic sealer being applied to the fully compacted surface.|
particular type of heating unit can be folded over as shown,
to be conveniently towed behind the works vehicle that carries the hot-box and tools.
Closer view of the "sealed" hot rolled
asphalt patch surface,
the surface exposed sealer is removed by vehicle wheels quite quickly.
Although the above form of heating is the most widely used in this process there are other forms of controlled heating coming on to the market that employ hot air generated by efficient diesel burning heaters.
The prime consideration with any method of heating is that the bituminous material, or more accurately the bitumen in the bituminous material, must NOT be overheated or its binding properties will be impaired or even destroyed, for further information press, HERE.
I try to
refer to as few commercial sites as possible in compiling my
site, but when a site offers particularly useful information
about a subject I make an exception.
For further information on the process, press HERE
[ Top of Page ]