COLOURED SURFACING FOR HIGHWAYS

CONTENTS

What type of coloured surface do you require
Coloured anti-skid surfacing
Colour fading
Coloured surfacing for demarcation and visual impact
Resin systems
Coloured slurry seal
Hot rolled asphalt wearing course and coloured aggregate precoats
Surface dressing
Specialised surfaces

WHAT DO YOU REQUIRE

First you must decide whether you require coloured anti-skid surfacing or just coloured surfacing, they are different products.

COLOURED ANTI-SKID SURFACING

With coloured anti-skid surfacing all the points 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.

Colour Fading After only a relatively short while, in this case 18 months, the pigment has worn off the calcined bauxite aggregate and the red pigmentation remains in the resin, but even there it is beginning to fade. This is not really failure, this is what happens, 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 they have used and how successful, over time, they have been.

The cost of coloured anti-skid surfacing costs in the region of £8 to £15 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 surfacings.

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

COLOURED SURFACING FOR DEMARCATION PURPOSES

Resin Systems

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.

Coloured Slurry Seal Systems

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 wearing 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. In the photograph to the right the bitumen coating has still to be worn off the aggregate.
Using coloured precoats could add another £1:00 / £2:00 to the price per square metre of the usual HRA and precoats surfacing.

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 (10 to 15).
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. 

For further information on hot rolled asphalt and a natural coloured aggregate precoat, press --------------> HERE

Surface Dressing

The coloured 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 modified, binder.
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 £1:50 to £3 , depending on chipping size and the source of the coloured chipping.
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.

SPECIALISED SURFACES

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 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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