The vehicle is purpose built to include a large amount of storage for all components needed to mix the slurry macadam.
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.
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 highering 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.
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.
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.