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The Idiots' Guide to
SURFACING FOR HIGHWAYS
What type of coloured surface do you require
Coloured anti-skid surfacing
Coloured surfacing for demarcation and visual impact
Coloured slurry seal
Hot rolled asphalt wearing course and coloured aggregate precoats
WHAT TYPE OF COLOURED SURFACE DO YOU REQUIRE
First you must decide whether your site requires coloured anti-skid surfacing or just coloured surfacing, they are different products, with different engineering properties,
COLOURED ANTI-SKID SURFACING
|With coloured anti-skid surfacing all the
engineering requirements ( polished stone value, aggregate abrasion value) applying to a
purely anti-skid surfacing will also apply.
Colour is usually provided in these surfacings by adding the appropriate pigment to the resin, whatever type the resin may be, epoxy, polyurethane or thermoplastic, (these comments also apply to slurry seals and bituminous mixes).
There are several pigments used to colour resins, some of a better quality than others, e.g.'s some are more resistant to ultra violet light and will be slower to fade and change colour.
|Also the amount of pigment that is added to the resin is
extremely important to provide effective colouration, and as
pigment is very expensive manufacturers will be tempted to add as
little as possible to remain competitive.
It may be more cost effective to pay a little more for a well specified product with a sufficient amount of good quality pigment than to buy a less expensive option,
BUT a good specification, MUST accompany the higher priced material.
|The calcined bauxite can also be strongly surface pigmented with the
appropriate colour, but you will find this strong coloration is
short lived, very short lived in some cases.
This is because the hardness of the calcined bauxite means the colour pigment is only on the surface of the aggregate and quickly wears off with the "scrubbing" from traffic wheels.
The calcined bauxite will fairly quickly, according to traffic volume, return to its natural colour,
a buff/creamy colour if it is Chinese, which itself is a fairly distinctive colour,
and grey if it is Guyanan in origin.
This inability of calcined bauxite to retain its coloration makes the pigmentation of the binding resin essential.
|This is a close up of a "normal" hot applied red coloured high friction surfacing.|
|After only a relatively short while, in this case 18
months, the pigmented resin has worn off the calcined bauxite
aggregate and the red pigmentation remains in the resin,
but even there it is beginning to fade.
But, from an engineering point of view you do want the resin to wear off the calcined bauxite aggregate so that the high friction properties of the surface attain their maximum potential. So if you can use an appropriate coloured aggregate this is a benefit, here a buff coloured Chinese sourced calcined bauxite has been used.
This is not really failure, this is what happens with pigment colouration, the better specified and more expensive products should contain better, stronger pigment, e.g. chrome rather than iron compounds, and a larger percentage of the pigment in the mixture.
You get what you pay for, but sometimes you pay for what you do not get.
It is often wise, if you do not have a reliable contractor, to consult colleagues in other organisations as to what products and contractors they have used and how successful, over time, they have been.
The cost of coloured
anti-skid surfacing costs in the region of £10 to £25 per square
metre according to the process, site conditions and the quantity
you are purchasing.
For information on anti-skid / high friction surfacing, 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, the following three sites
all contribute worthwhile information on the subject of coloured
For further information on the colour retention of pigment on calcined bauxite, press -----> HERE
Information on adding colour pigment to an asphalt, macadam or slurry, press ---------------> HERE
FOR DEMARCATION PURPOSES
The use of the three resin systems already outlined but with the use of an appropriate coloured natural aggregate of suitable quality, ( PSV, ACV, etc. ), in place of the calcined bauxite.
E.g. Actual red aggregate from "Harden" or "Cloburn" quarries for a red coloured surface, so that when the pigmented binder has worn away the aggregate exposed will be red.
This process is generally used for smaller areas, and it is expensive at approximately £10 per square metre.
A pigmented emulsion slurry seal is used with the appropriate coloured aggregate. This, as with the resin systems, is a thin veneer coloured surfacing, varying in thickness from as little as 1mm. up to 5mm. depending on the aggregate grading.
This is quite a quick process, and it can be used for quite large areas, but it is less hard wearing than the resin systems, and still quite expensive for the thickness of the product at approximately £2:50 to £5:00 a sq. metre according to layer thickness.
For information on the slurry seal process, press ---------------------------------------------------------------> HERE
HOT ROLLED ASPHALT SURFACE COURSE AND SUITABLE COLOURED AGGREGATE FOR THE PRECOATED CHIPPINGS
|This process can be used for road pavements carrying normal
traffic and the colour will last as long as the asphalt surface.
Most common aggregate colours used are red and green, and it is important to choose your aggregate source carefully, and because these sources are few, and sometimes a good distance away the precoats can be expensive.
It is also usual to pigment the binder that the precoats are coated with to obtain an initial colour demarcation before the binder is worn off by traffic exposing the natural aggregate colour.
It is of course important to get a good shoulder to shoulder cover of the chippings to obtain maximum colour.
It is also usual for the red colour of the surface to improve, as the red pigmented black bitumen can often be a poor red if sufficient good quality pigment has not been added to the bitumen.
Using coloured precoats could add another £1:50 / £3:00 to the price per square metre of the usual HRA and precoats surfacing, but this is a cost effective process to achieve both a durable surface to your highway and a long lasting, pleasing, colouration to the road surface.
|Alright, it is
not the Mall, it is Hinckley town centre on a dull Sunday morning.
But it shows the demarcation of the restricted traffic area by the use of red precoats in a hot rolled asphalt surface course.
With a higher rate of spread of the precoated chippings a greater overall
red colouration would have been achieved.
The moral being that if you want a higher (shoulder to shoulder) rate of spread of chippings make sure you are on site when the HRA is laid.
These chippings are expensive and the contactor will want to use as few as possible, not that you will get a reduction in the price, but I blame myself as I knew the situation.
|This is a different site where I was present at the time of laying, hence the photographs, and you can see the increased rate of spread of the chippings|
photograph to the right the bitumen coating has still to be worn off the
aggregate, so the colour will improve over time, but never become too
bright, but will achieve a natural colour.
The colour achieved is not bright but is often preferred by local residents to the more obvious colours produced by pigments.
From a highways maintenance point of view, which I represent, this will be a long lived coloured surface that will require no attention for many years (15 to 20).
Even if utility work occurs the colour can be quite cheaply restored by applying red recoated chippings to a conventional hot rolled asphalt surfacing, and the utilities will appreciate this and should see resurfacing is carried out correctly.
Information on hot rolled asphalt and a natural coloured aggregate precoat can be found on the page, Coloured Surfacing using Hot Rolled Asphalt Surface Course
Above is an image of 10mm. single sizes surface dressing of red aggregate
either from Harden Quarry in Northumberland or Colburn Quarry in Scotland,
sources of natural red aggregate of road surfacing quality.
I know that this surface is over ten years old, and a resident I was chatting to said that he thought it was nearer fifteen years old.
It is not a highly traffic site being the south road access to the village of Stoke Golding, but it still shows the durability of a well designed and laid surface dressing.
The bus was purely good luck, but once I had it in a photograph I could not resist using this image.
will see that the first area of red surfacing approaching the village, is
beginning to fail.
However this is also relatively old for this type of surfacing, probably over five years. I say this because the subsequent road widening and new kerbing that was performed at the time of constructing the "golden gravel" footway to the A5 is at least five years old. You can see that the hot applied red surfacing was in place at that time of construction by the presence of the untreated strip of road surfacing adjacent to the new kerb.
It is the second area of red surfacing that is the beginning of the coloured surface dressing.
It is likely that some of the damage on the surface dressing and the hot applied thermoplastic areas was caused when the road widening and new kerbing took place. The dropped kerbs show the an access to local land where the construction equipment was kept and there would have been frequent turning in an out of this area by construction traffic. Also construction vehicles would have been operating along this area during the construction of the kerbing and new footway.
Images of an excellent 10mm. single sized surface dressing, over 10 years after being laid, which happens to be with the use of a natural red aggregate.
surfacing shown in the photographs above has been achieved by
the relatively simple and inexpensive process of surface
dressing with a red aggregate and a premium, polymer
There are natural red aggregates that will have a deeper red colouration than the aggregate used on this site.
It is the principle I am describing, while observing all the site conditions necessary to lay a good surface dressing.
This is probably the lowest cost system for obtaining large areas of coloured surface able to withstand normal, non surface stressing, traffic flows.
You do not use a pigmented binder but a standard suitable product, and this keeps the cost down. You are relying on the complete aggregate cover that you create with a surface dressing to obtain a fully coloured surface.
The cost per square metre is likely to be £2:00 to £5:00 , depending on chipping size, the size of the area being dressed, and of course how close you are to the source of the coloured aggregate, transport could be a significant contribution to the cost of the chippings.
It is very important when using a coloured aggregate to enhance or create a coloured surface to choose the aggregate carefully, the engineering characteristics of the aggregate in truth take precedence over colour.
The basic aggregate properties such as resistance to crushing, resistance to polishing, good shape and size index, etc., should match the site conditions.
|There are on the market highly specialised products, with very
distinct colours and textures, which although providing excellent
colour properties can be ruled out in general highway maintenance
situations due to very high cost, or the low quality of the
properties of the aggregate in relation to those that are needed
to withstand normal road trafficking.
These materials can be considered to enhance the look and feel of pedestrian areas in town and city situations where small areas of these materials can contribute a pleasing visual impact.
It may be worth considering a policy where conventional bituminous mixtures are used for pedestrian and vehicle areas, these being the areas that take all the load and wear.
Future maintenance costs would then be much reduced, and your high cost coloured areas would have a much longer life, and as already mentioned you are able to use coloured aggregates not suitable for trafficking.
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