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The Idiots' Guide to Highways
RECYCLING IN HIGHWAY MAINTENANCE
|ON SITE RECYCLING / RETREAD / LINEAR RECYCLING/FULL DEPTH RECYCLING (FDR)||
OFF SITE RECYCLING/MIXING OF
USING FOAMED BITUMEN AND/OR CEMENT
RECYCLING / RETREAD / LINEAR RECYCLING/FULL DEPTH RECYCLING (FDR)
|Heavy machinery is used to pulverise and mix the in-situ road pavement that has suffered complete road failure.|
|Showing drum with replaceable hardened steel tines which do the work.
The same drum will be used to add and mix in the foamed bitumen or bitumen emulsion component, but if cement or pulverised fuel ash is used as a hydraulic binder this is usually spread on the surface of the pulverised material at the appropriate rate prior to the mixing pass of the plant, and the addition of the bituminous binder.
|The pulverising / mixing drum can be set at the depth required.|
|This is the site after pulverisation and before "trimming" of excess material to allow for the wearing course.|
|Note, in this and
similar cases kerbs have not needed to be raised which is a
An amount of excess material is removed before the bitumen and cement is added to allow for a conventional hot mix bituminous wearing course to be laid without causing problems with existing levels.
At this site a depth of approximately 250mm. had been recycled using "Retread", "Linear Recycling", "Full Depth Recycling", the process is more or less the same whatever it is called.
All these processes will have a "virgin" surface course and where traffic weight and numbers is high will even have a bituminous mixture binder course and surface course. The thickness of the layer of binder course again depending on type of traffic (HGV's) and the amount of traffic.
Although this is an excellent process and has a number of environmental benefits it should only be considered where you have a more or less complete failure of the road pavement.
Where the underlying strength of the road is still good a less cost option is to plane off 50mm. of the road surface and replace with a strong, durable load spreading surfacing surface course such as 50mm. layer of a "design" hot rolled asphalt or an "original" design impervious stone mastic asphalt
It is quite common to even perform a 200mm plane and replace all bituminous layers if the granular base to the road is sound and well drained.
The correct choice of the replacement bituminous mixtures is paramount, and will vary according to the type of road and the traffic it carries.
THE MATERIAL REMOVED BY PLANING CAN STILL BE RECYCLED EITHER IN TO A GRANULAR SUB-BASE MATERIAL.
PREFERABLY IN TO A NEW HOT BITUMINOUS MIXTURE BY HEATING AND REMIXING.
If surrounding levels to the road surface are not a problem regarding drainage or access, it may be possible to utilise the strength in the existing road pavement as a strong foundation/sub-base and overlay with a binder course and wearing course to provide a new, long lasting, road pavement.
A competent and experienced highway engineer / engineering technician should be able to consider all the options and arrive at a course of action to provide the most appropriate solution to the particular nature of individual cases of road failure, based upon engineering requirements and the budget available.
There is not just one solution to all types of road failure, the job of a highways maintenance engineer would be a pretty uninteresting occupation if there was.
To access further items of information relating to recycling in highways maintenance, and reference to the many technical documents supporting this subject, Press ----------------------> HERE
But the recently published,
TRL REPORT 386 : Design guide and specification for structural maintenance of highway pavements by cold in-situ recycling, by L.J.Milton and M.Earland
is particularly relevant to LINEAR RECYCLING.
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