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The Idiots' Guide to Highways Maintenance
Copyright © 2000/15, C.J.Summers
ROAD MARKING WITH WHITE THERMOPLASTIC (the process is the same for yellow thermoplastic markings)
|THERMOPLASTIC ROAD MARKING MATERIALS||BASIC "TROLLY" DESCRIPTION|
|RECIPE OR PERFORMANCE BASED SPECIFICATIONS||RETRO-REFLECTIVITY|
|PRODUCING QUALITY ROAD MARKINGS||PREFORMED THERMOPLASTIC ROAD MARKINGS|
|REMOVAL OF SMALL AREAS OF THERMOPLASTIC ROAD MARKINGS||REMOVAL OF LARGE AREAS OF THERMOPLASTIC ROAD MARKINGS|
This page relates to the application of road markings using thermoplastic material that is screeded by hand using a conventional "trolly" built for the purpose. This form of road marking is widely used but takes place mainly on small sites of newly laid road surfacing and more complicated areas of markings, especially in urban locations, where it is not possible or difficult to use a fully automated vehicle.
Also, I do not have any good photographs of fully automated processes.
THERMOPLASTIC ROAD MARKING MATERIALS
thermoplastic is supplied in "poly"
bags that will melt when put in the heating pot, i.e. you put the whole
bag into the heating pot.
The thermoplastic consists of, a light coloured aggregate (silica sand), white pigment (titanium dioxide), glass beads, and it is all held together with a thermoplastic resin
|Glass beads of a suitable grade / quality for the contract specification
requirements are supplied in bags as shown.
Glass beads are applied to the surface of the still hot thermoplastic to ensure the initial retro-reflectivity requirement of the road markings is achieved.
RECIPE OR PERFORMANCE BASED
The new set of British Standards are based purely on "performance" testing and do not include a specification (recipe) for the thermoplastic.
However, many suppliers of thermoplastic still produce product to BS 3262 as there is still a demand for a standard, recipe based product amongst their customers.
This method of confirming quality of product still appears widely used in many countries around the world.
Many clients / specifiers still include a requirement for
a basic specification for the formulation of road marking
thermoplastic, and usually achieve this in one of two
1) Include the BS 3262 formulation for thermoplastic, often without reference to BS 3262, as it is now withdrawn, although still widely quoted.
2) Specify a road marking thermoplastic to the current basic AASHTO formulation which is more or less accepted world wide, and is a stronger worded document than BS 3262.
The thermoplastic is heated in one of the two heaters on the back of purpose built vehicle, when molten it is transferred to the holding tank on the "trolly" which is heated to maintain the thermoplastic in a molten condition.
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.
To obtain more information on the properties of road marking thermoplastic, press ------> HERE
The above are examples of of the materials used
to produce good quality thermoplastic road markings that are durable and
exhibit good retro-reflectivity, other good quality materials capable of
producing road markings of various standards appropriate to the site where
they are laid.
Note that these two particular products give full information of the material that they contain, or with some products should contain.
But as sampling and testing of these materials is not now required, although there is nothing to prevent you doing it, you never really know the quality of the products, but depend upon the finished performance of the road marking.
But this is very rarely tested either because of the cost of traffic management to perform the testing safely, usually the cost of the traffic management dwarfs the cost of the actual testing, which with the improvement and lower cost of the retrometers tends to be coming down.
My opinion, for what it is worth, is that we should still be sampling and testing the materials used in the road marking process. This is because you will keep all suppliers on a level playing field, and those suppliers supplying good quality product will be supported, and those supplying out of specification materials will not be paid.
But of course you cannot implement this testing when you no longer have a BS Standard for materials to comply with, as with BS 3262, and the laboratory back up to be able to perform the required tests.
But there is nothing to stop an authority including such a specification in their contract document. It would be interesting to see which companies claimed this was a restriction on trade, rather than just comply with the specification.
The careful heating of the thermoplastic is critical as it needs to be hot enough to allow the operator to correctly screed a smooth unbroken line of the correct thickness on to the road surface.
You will see from the images above that most well equipped road marking vehicles will have two "melting pots". One of which will be up to temperature supplying correctly heated thermoplastic to the operator, and a second pot which is in the process of heating up, thus allowing a fairly continuous flow of work.
PRODUCING QUALITY ROAD
Most thermoplastic road markings on local authority highway networks will be applied in the manner described on this page.
Providing it is performed correctly, with good quality materials it is a highly successful and proven process.
However I will make the comment that the bidding for local authority road marking contracts, and subsequent sub-contracting is very competitive, little testing of these road markings takes place, and it is my opinion that the standard of the finished road marking generally is not what it should be.
But standards of the road marking will vary throughout the UK according to contractor and the vigilance of the Engineer, whether working directly for the local authority or the consulting engineer / contractor who is contracted to undertake, and be responsible for, the highways maintenance work of the employing authority.
The Road Marking "Trolley" and its Operation
The apparatus in the photograph may seem rather basic, but let me assure you that this machine, in the hands of a skilled operator, will produce excellent road markings that will comply with most contract documents.
That is, providing a well formulated thermoplastic material has been used at the correct temperature, and the correct amount of good quality glass beads have been applied to the still molten surface.
This equipment is used for the bulk of thermoplastic road marking for local authority networks, because it is relatively cheap, basic in function and robust, i.e. nothing complicated to go wrong, and it is easy to maintain.
This procedure, correctly performed, will ensure a durable marking that has good initial retro-reflectivity which should be retained during the life of the line as the traffic slowly abrades the line surface exposing the glass beads incorporated in the thermoplastic mixture.
It really is not that difficult to produce good quality road markings providing the contractor uses good thermoplastic product, well maintained machinery and correctly trained operators.
The factor that is outside the control of everybody is the weather, but if the weather is unsuitable then road marking should not be taking place.
The hopper at the back contains the glass beads.
The glass beads are discharged from the hopper on to a flat plate that spreads the beads to the width of the line.
The flow of beads is adjusted to a rate to achieve the initial retro-reflectivity requirement stated in the contract document.
It is not uncommon to state a rate of beads as 70% of the amount that would be required to achieve shoulder to shoulder cover when tested in the laboratory.
But less than this amount may achieve the required retro-reflectivity stated in a performance based specification.
The element that is critical is that the glass beads must be applied to the surface of the screeded thermoplastic while it is still in a molten state to ensure that the beads will form a firm bond with the thermoplastic.
There are various "coatings" that can be applied to the glass beads in manufacture to improve the bonding process.
The thermoplastic flows on to the road surface and is spread to the required width and depth by a small screed plate.
It is the skill of the operator pushing the "trolly" at the correct speed according to the heat and viscosity of the thermoplastic that will achieve a consistent road marking of the required width and thickness.
It is also necessary to point out that the nature of the road marking industry in the UK is such that the majority of operators are often self employed working "on contract", almost a franchise arrangement, to the main company.
This results in the situation that the more "line" they lay with provided equipment and product, in a minimum time, the more money they will earn.
Therefore, and I repeat myself, as I have given this advice in many forms, in many aspects of the highways maintenance industry, unless the "authority" / managing Engineer has some on site supervision and some random testing regime that they enforce, i.e. do not pay for road markings that fail to meet the specified standard, you will not be supporting the contractors who make the effort to provide good quality road marking as specified in the contract document.
If you do not support the contractors / suppliers who offer the better product and workmanship, they will revert to the general standard in the industry, they have no incentive not to do so, and this will bring about a general decline in road marking standards, which in my opinion, is already happening.
This is not just my opinion, many comments have been made recently by a number of respected highways maintenance engineers that the quality of roads markings in the UK is falling because of the lack of maintenance of markings and a decline in the standard and durability of the new markings.
I am one who believes that good quality road markings contribute a great deal to safety on local highway networks, providing the motorist with much visual assistance, especially at night.
However I expect them to be durable and I expect them to be able to be seen at night, it is not rocket science.
|Yes, the glass bead hopper is a bit "bashed about", but it is still functioning and if you look really close, especially in the enlarged image you can see the the glass beads being spread on to the molten, newly laid, thermoplastic road marking.|
It is not difficult to test the retro-reflectivity of a laid line, as the cost of the testing apparatus, a retrometer, is not that expensive, and their reliability is much improved compared to earlier models.
The difficulty and cost of the traffic management can be the main factor when conducting performance tests on laid road markings.
If you are able to conduct the retro-reflectivity testing at the time the road marking takes place, perhaps on a random basis, you will save on traffic management costs and be able to inform the contractor of the quality of the road markings he is, or is not, producing.
The random nature of the testing will mean that the contractor will not know if you will be turning up or not, and they are likely to make sure all markings are of the required standard.
To obtain more information about road markings, when using the recently introduced performance based specifications, press -----> HERE
Retro-reflectivity testing of newly laid thermoplastic road markings with
surface applied glass beads, being performed at the time of laying to avoid
traffic management costs.
An example of a retrometer for testing the retro-reflectivity of road markings, other makes are available, and the models now available are much improved in accuracy, reliability and ease of use to early models.
They can also be easily calibrated by performing tests on a reference panel supplied with the apparatus.
PREFORMED THERMOPLASTIC ROAD
It is possible to purchase reformed thermoplastic road markings in one metre strips as shown here, it is also possible to buy it in "rolls" of longer length, but the principle is the same as shown here.
The principle being is that they are thermoplastic, so carefully applied heat to the road surface and the preformed road marking will bond it to the road surface without damaging the thermoplastic.
The process is fairly self explanatory if you follow the photographs. I must add that there is only so many people about is because this was a demonstration of the product.
The procedure could quite easily be carried out by a small patching gang after laying the patch or by an "emergency gang" / "highway patrol gang" that most local highway authorities possess. You can see that you do not need a lot of equipment, and it is likely that the gang will already be carrying it for other uses.
Just use the correct amount of heat, i.e. just enough to make the thermoplastic molten, so that it will bond with the road surface, and that is all.
|Preheating the road surface to which the preformed thermoplastic road marking is to be applied.|
|Removing the preformed line from the backing paper and applying it to the preheated road surface.|
|Carefully heating the applied preformed thermoplastic road marking until it is molten thus ensuring a complete bond with the road surface.|
|The applied preformed road marking.|
|The process being repeated to achieve an unbroken continuation of the double yellow line system.|
|The job not yet complete but showing the general appearance of the reinstated yellow road markings.|
REMOVAL OF THERMOPLASTIC ROAD
MARKINGS (Small Areas of Road Marking)
Small areas of thermoplastic road markings can be removed using a "thermic lance", I am sure it has a correct name but I do not know it, it is usually referred to as a thermic lance.
I believe it uses a combination of propane and compressed air. It removes the line by vaporising it and produces a "stream" of tiny molten droplets so you do not want to use this process in close proximity to stationary vehicles or properties.
It is also very noisy. But it is a relatively inexpensive process that does not require a lot of bulky equipment and therefore is very useful for removing small areas of road marking.
REMOVAL OF THERMOPLASTIC ROAD MARKINGS (Large Areas of road Marking)
Large areas / lengths of road that need to have thermoplastic road markings removed are usually treated with a high pressure water treatment. These pictures are of one such process.
There are other "scabbling" processes for similar large areas of road marking removal, but I have no experience of these processes.
Above is the lorry that carries all the equipment, i.e. the small work unit,
the clean water, the high pressure pump and the holding tank for all the
removed road markings and the water used in the procedure.
The aluminium side to the lorry, just behind the cab, is in fact a fold down ramp which allows access on and off the lorry for the actual work unit that performs the road marking removal.
small self powered work unit that controls/positions the high pressure
You can see the various pipes that feed, from and back to, the various units on the back of the lorry, i.e. water, compressed air and the large pipe taking the removed marking and the used water back to the holding tank.
|Image of the high pressure head whilst working. I have seen underneath but the supervisor preferred that I did not take a photograph, but it did not seem that much different from other high pressure water devices that I have seen. Perhaps an expert in this type of equipment may have noticed something special.|
Image showing the work unit and lorry, as work is undertaken.
Please note the straight pass of road marking removal to the left of the roundel was from another device trialled earlier.
This particular process seemed very efficient
causing the minimum of damage to the road surface beneath, even when working on
the red pigmented hot applied resin treatment. The process was quick and clean.
However the operators were very competent and knew exactly what they were doing, and this was a trial so it is likely that the best men were sent to provide the demonstration, but it does show the potential of this and similar processes.
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