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Idiots' Guide to Highways Maintenance
IMPRINTING OF HOT THERMOPLASTIC MATERIALS
|INTRODUCTION TO IMPRINTING (BLOCK PATTERN) RESIN BASED THERMOPLASTIC "MASTIC"||APPLYING HOT THERMOPLASTIC MATERIAL TO THE ROAD SURFACE|
|CREATING A VISUAL AND TEXTURED DEMARCATION BETWEEN A SIDE ROAD AND A MAIN ROAD||PREPARING THE SURFACE OF THE MATERIAL PRIOR TO IMPRINTING|
|EQUIPMENT||POSITIONING THE IMPRINT PATTERN|
|HEATING THE THERMOPLASTIC MATERIAL||APPLYING PATTERNED IMPRINT TO THE HOT SURFACE|
|PREPARATION OF THE ROAD SURFACE||FINISHED BLOCK PAVING EFFECT|
TO IMPRINTING (BLOCK PATTERN) RESIN BASED THERMOPLASTIC "MASTIC"
This process uses the thermoplastic principle, used in many highways maintenance and construction materials.
That principle being that thermoplastic materials are plastic, workable, able to be moulded when hot, and for all practical purposes solid when cold.
The thermoplastic component of the material used for imprinting is a resin, not a bitumen.
The resin can be a natural resin obtained from natural sources such as old tree roots and waste timber from commercial forests, or it can be a synthetic resin obtained from the oil industry.
An appropriate amount of resin is mixed with suitable proportions of fine aggregate, sand and fillers, and pre-packed in a mixed condition in polythene sacks ready to be placed in a boiler and heated and mixed.
As with nearly all thermoplastic material there are temperature guidelines that must not be exceeded and recommended times for storage at particular temperatures.
Overheating or keeping material hot for long periods of time will cause the degradation and embrittlement of the resin component and hence a reduced life of the laid material.
Performed correctly by a skilled gang, with well designed thermoplastic material, this process does produce long lived patterned road surfaces.
The main cause of failure that I have encountered with this process has been caused by weakness in the underlying road pavement, causing cracking and detachment of the resin bound layer.
There are several patterns available to choose from according to the effect desired.
CREATING A VISUAL AND TEXTURED DEMARCATION BETWEEN A SIDE ROAD AND A MAIN ROAD
Although the material itself is durable and quite long lived, often the colour does not share the same length of life, and fades to the neutral shade of the aggregate and fillers used in the mixture.
I have often asked the question of contractors and suppliers why the fine aggregate portion of the mixture cannot be a natural coloured aggregate to provide indefinite significant colour, even if not of the original brightness of the pigment, which always fades, eventually.
Examples of sources of aggregate being Harden red or Cloburn, where a red colour is required, and Ingleton or Criggion for a prolonged green(ish) colour.
The responses I received suggested that it would make the process more expensive, by having to hold separate stocks of different coloured mixtures.
Personally I think it was just too much trouble for them to provide a material that has a demarcation colour of equivalent length of life to that of the laid surface.
It might be nice to have the option to spend a little more money to have a surface chosen for all its particular qualities, in order that those qualities be retained throughout its life, and I know of many sites where this process has achieved significant life, in excess of ten years.
I have noted that damage usually occurs from underlying weakness of the road pavement, and if the road cracks or deteriorates so will the patterned surfacing.
If the material itself fails by fretting or "breaking out" it usually happens relatively quickly, i.e. the first couple of years, this probably being due to overheating at the time of laying, or due to a low resin content in the mixture.
To my knowledge all these materials and processes are proprietary, so it is unlikely you will obtain a specification for the mixture, but companies do provide heating "guidelines" for their materials.
There are companies that just manufacture the thermoplastic material for contractors to lay, but this is a skilled operation, a "general" gang will not be able to undertake this work without some considerable training.
However small repairs to "utility" reinstatements should be possible, with care, and some training, and if you were really careful you could even recycle the reclaimed thermoplastic material, as it is thermoplastic, heat it gently in a small "boiler" and it will become workable once again.
Investing in some good, knowledgeable engineers and technicians, perhaps even a Materials Engineer, can save an authority or contractor quite a lot of money, even if you are ignoring the fact they will be responsible for providing better quality highway networks.
"People" who do not know, in my experience, tend to buy from the best put together "shiny" brochure, is this really highway engineering, no, it is good marketing, the two are not necessarily the same thing.
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