CARRIAGEWAY SLURRY MACADAM - MICRO ASPHALT

	THE VEHICLE The vehicle is purpose built to include a large amount of storage for all components needed to mix the slurry macadam.
	THE "MIXING BOX" All materials are kept separate until immediately prior to laying when they are brought together in a contolled fashion and mixed vigourously in the "mixing box" before being discharged on to the road. The materials being a possible combination of the following :- Coarse aggregate, fine aggregate, ordinary portland cement, bitumen emulsion (possibly with a polymer modifier), and perhaps an amount of retard agent.
	LAYING When slurry macadam is first laid it behaves as a liquid, therefore the actual thickness deposited is more or less controlled by the nominal size of the coarse aggregate. The screed plate at the back of the machine is mainly to ensure even distribution of the material across the road surface, by increasing the height of the plate significantly you will NOT be able to lay thick layers of this material as you can with a hot mix bituminous material and a "Blaw Knox". However, if the road surface has depressions or the transverse profile of the road falls away from the crown thicker layers of the material will be laid down and the road shape improved. This process is not thought of as adding any significant strength to a road pavement, but like a surface dressing by sealing an oxidised and fretting surface it will extend the life of the existing road surface as well as improving skid resistance and appearance of the road.
	APPEARANCE Immediately after laying the slurry macadam will be brown in colour, this indicates the emulsion component of the mixture has not "broken". After about 20 minutes in reasonable ambient temperatures the material will have established an initial set and will have turned black indicating the bitumen has come out of the emulsion phase and deposited itself on the aggregate components of the mixture. The material should be safe to traffic after about one hour, it could be sooner in good summer weather. The larger nominal size materials can shed some loose aggregate in the initial stages and look a little "untidy" before they settle down.
	THICKNESS The photograph on the left shows the achieved thickness of a 6mm. slurry macadam laid on a flat road surface with a one pound coin as comparison.

BS 434-2 : 2006 : Code of Practice for the use of cationic bitumen road emulsions on roads and other paved areas
This edition provides recommendations and guidance on the general usage of cationic bituminous emulsions on roads and other paved areas.
The emulsions covered conform to BS 434 : Part 1, or BS EN 13808 (modified and none modified), or are proprietary emulsions.
The information within this document provides guidance on where the various processes using bituminous emulsions, including slurry macadam / micro asphalt, are suitable for use and indicates where suitable design procedures can be found.
Advice is also given on those situations in which the processes are unsuitable or marginally suitable.
Where there is an option, performance or outcome specifications have been used rather than input or recipe specifications.

This is a very informative British Standard, and I recommend that you have a copy if you are considering this highway maintenance process for the first time.

For an explanation of the principles of the Slurry Macadam process, which are similar to the methodology of slurry seal, Press ----------> HERE


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