Client: Knowsley Borough Council
Completion Date: February 2005
Duration: 20 weeks
Location: Knowsley, Liverpool, Merseyside
This contract involved the resurfacing of the M62 motorway between junctions 5 & 6 for Knowsley Borough Council, using foamed bitumen stabilised material (foamix) as the base layer.
The cold planning was carried out by Bruce Cook Road Planning Ltd and the recycling work by Roadstone Recycling Ltd for the main contractor Dowhigh Ltd.
The recycling work was split into six visits that involved planning out the existing carriageway to the specified depths and replacing it with:
- 60 – 130mm Foamix
- 60mm Heavy Duty Binder Course
- 40mm Wearing Course
The aggregate grading is a very important part of using foamed bitumen stabilised material.
AGGREGATE GRADING
The foamed bitumen has a tendency to mix and conglomerate with the fines while only partially coating the coarse aggregate component. As a result, it has been found that the amount passing the 75 – micron BS sieve should ideally be restricted to a range of not less than 5% and not more than 20% none of which should be clay. The planned out aggregate of the M62 carriageway mainly consisted of asphalt planings. When screened, these do not produce much in the way of fines, so it was decided that 7 – 8% pulverised fuel ash (PFA) would need to be added.
The general design for this job was based on previous contract knowledge of recycling this type of aggregate that we were going to find in the existing M62 carriageway.
FOAMIX DESIGN
Past contracts using a feedstock aggregate comprising of 93% recycled asphalt planings and 7% PFA, with the addition of 3% foamed bitumen and 2% ordinary Portland cement, mixed to the correct moisture content, have produced a strong, durable and flexible material equivalent to a heavy duty hot mix macadam.
SUMMARY
The use of foamix as an alternative road base in this contract has shown a number of economical and environmental advantages over hot bitumen mixes which include:
• Incorporates waste of marginal materials.
• Energy efficient manufacture.
• Resilient base which can be trafficked immediately.
• No specially insulated transport required.
• Reduced number of wagon movements.
• Easy to lay and workable material.
• Quality controlled process.
