COLOURED SURFACING USING HOT ROLLED ASPHALT WEARING COURSE
WITH
A COLOURED AGGREGATE PRECOATED CHIPPING

	STOCKPILING PRECOATED CHIPPINGS You will be paying considerably more for the bitumen coating of the precoated chippings because of the red pigmentation. The 20mm. chippings will also be more expensive due to the inherent red colour of the natural aggregate, and remember the aggregate must still of "road" quality. This means it must have a sufficient Aggregate Abrasion Value (AAV), Aggregate Crushing Value (ACV) and Polished Stone Value (PSV) for the particular site conditions. Colour must not be of paramount importance.
	CHIPPING SIZE AND COATING OF PIGMENTED BINDER The photograph shows a close up the chipping stockpile, clearly showing the 20mm. single size precoats, with a normal ball-point pen for scale. Initially the red colouration is quite intense, but it fades to a purple colour, and finally a sort of black with a reddish tinge, so it is very important to have a good red coloured aggregate as the chipping to be precoated, as the colour of the aggregate will ultimately determine the colour of the road surface.
	LAYING PRECOATED CHIPPINGS The chippings are spread on to the layer of 14mm./30% hot rolled asphalt (HRA) wearing course that has already been laid by a conventional paving machine, 40mm. thick. The rate of spread of chippings will be approximately 14kgs. per square metre. It cannot be stressed to highly that the chipping spreader must be in a good condition, as poorly maintained chipping spreaders are the biggest cause of poor riding quality with HRA wearing course.
	PRECOATED CHIPPINGS AFTER SPREADING Chippings that have been distributed by the chipping spreader waiting embedment from the roller. Chippings want to be as close together as possible without chippings being laid on top of chippings. Examples of rates of spread of chippings can be observed by pressing ----------------------> HERE
	PRECOATED CHIPPINGS AFTER ROLLING The chippings have been successfully embedded into the hot rolled asphalt. Contrary to popular belief the chipping is secured to the asphalt by the process of the bitumen coating of the chipping being melted by the hot asphalt and so creating a firm physical bond once the asphalt as cooled. Embedment assists the bonding but it is not the prime method of attachment of the chipping to the surface.
	PRECOATED CHIPPINGS AFTER SEVERAL YEARS OF TRAFFIC USE With time and wear from traffic the natural colour of the red aggregate will be exposed. If you have specified a good coloured aggregate the visual appearance will be much more acceptable than the red bitumen colour, which usually is of relatively short duration. The sand bitumen matrix tends to wear away over time and more chipping will be exposed increasing the colour of the road surface. Although naturally coloured aggregates do not give the bright colours of pigmented products, the aggregate will provide colour for the life of the road surface, whereas  pigments can fade quite quickly. It is also often found that residents living adjacent to coloured road surfaces prefer the natural colour rather than vivid artificial colours.

APPLICATIONS FOR THE USE OF COLOURED PRECOATS IN HOT ROLLED ASPHALT SURFACING

Where an "improvement" to a road layout is being conducted, in this case a 20mph. zone outside a school, and a new surfacing is part of the scheme, a HRA and coloured aggregate precoat is a good choice of surfacing. Not only do you achieve a a very durable road surfacing when using HRA surface course, you also obtain a long lived colour demarcation in a very cost effective manner.
The colour achieved is not "blatant" or "garish", and is accepted and appreciated by residents, but is sufficient to inform motorists that the signing indicates the road length they are driving on has special significance, i.e they should driving at less than 20mph. on the coloured road surface.

For more information on laying hot rolled asphalt and precoats, press ---------------------------------------------------------------> HERE

Personal Note
If you wish to see an excellent example of this type of surface may I suggest that when you are next in London you go and have a look at The Mall, outside Buckingham Palace, where you will find a road surface that is hot rolled asphalt wearing course with red aggregate precoats.
I realise a road surface is not what you might call a traditional tourist site, but if you are there to look at the palace, you may as well take five minutes to look at the road surface.
For those of you who cannot get to London, but are sports fans, just watch the closing stages of the London Marathon, you will get an excellent view of a red coloured road surface that was achieved by the process described above.


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