ON SITE RECYCLING BY HOT PATCH TREATMENT

CONTENTS

Introduction to insitu hot recycling of bituminous materials
Heating the surface to be patched / recycled
Area to be patched after heating
Adding fresh material from the hot box
Adding rejuvenator
Compaction
Hot box storage of fresh bituminous material
Other forms of heating

INTRODUCTION TO INSITU HOT RECYCLING OF BITUMINOUS MATERIALS

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 £40:00 a tonne to purchase and the other will cost you approximately £5:00 a tonne to plane out and dispose of.
I am being generous with the cost of £5:00 a tonne disposal figure because I am assuming it will be recycled into a granular capping material rather than being taken to tip at £20:00 per tonne, if they will now accept bituminous material.

It is true the bitumen in the insitu 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.

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.

For further information on recycling bituminous mixtures, press --------------------------> HERE

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 reworkable.
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.

For further information on temperatures of bituminous materials, press ----------> HERE

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.

ADDING FRESH MATERIAL FROM THE HOT BOX This picture shows fresh material being added to replace the removed oxidised surface layer.

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.

ADDING REJUVENATOR 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.

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.

A successful area of patching should appear little, if any, different to "normal" bituminous surfacing.

This 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.

NOTE 
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. 

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

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