Dowfoam – How it works

Dowfoam – The Techie Stuff
Dowfoam production is carried out using a Soter PM400 batching plant with a cement/lime silo and bitumen storage tanker. The plant has its own on board generator and operator cabin to control the production settings. Aggregate is fed via a loading shovel into two hoppers, with adjustable flow gates, and transferred on a conveyor into a mixing chamber. Cement is fed through on an auger which sits on a load cell and bitumen is fed through a flow meter and into a spray bar where it is mixed with compressed air and water in nozzles before being sprayed as foam bitumen onto the aggregate in the mixing chamber. A separate water spray bar is located at the front of the mixing chamber to add any additional water to the mix to bring the material up to its required optimum moisture content.

And here’s the science bit…

Material Characteristics
As part of our commitment to both best value and the protection of our natural resources, we have invested significant resources into the growth and development of our recycling capabilities.

This investment in research, equipment and industry leading personnel means we are now recognised as one of the regions foremost road recycling contractors.

We can now provide a complete surfacing service along with additional planning, crushing, screening and laying options, as and when a project demands. Our best value approach means we can work effectively to any brief, as well as offering bespoke design input if required.

Production Plant
Foamed bitumen occurs when small amounts of water and air are added to hot bitumen in special expansion chambers before being forced out under pressure and sprayed into the aggregate. The foaming of the bitumen increases the surface area and significantly reduces the viscosity of the bitumen.

Upon compaction of Dowfoam, thousands of microscopic bubbles of bitumen are burst causing them to form bituminous mastic with the micro-fines they have settled on. This effectively coats the aggregate at the point of compaction.

The material begins to dry on the compacted surface aided by weather and hydraulic binder but will always retain moisture of approx 2–3%. Dowfoam has very strong vertical plane bonds (aggregate interlock and compacted bitumen) and has weaker horizontal plane bonds. (Wirtgen Cold Recycling Manual 2004).

Consequently it is unlike any other rigid or flexible pavement.
“The environment impact of using this product is greatly reduced because it negates the need to transport material from outside the local area.”

Trevor Murray, Director
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