The Process
The process involves firstly pulverisation of the existing carriageway in-situ and then second, spread and mixing in a cementitious powder to create a Hydraulically Bound Material layer to form a strengthened pavement. Throughout the operation the materials are trimmed, graded and compacted to return the recycled layer back to required finish levels before an asphalt surfacing or surface dressing is applied.
Fundamental is the requirement to undertake extensive site investigations and laboratory testing in advance of works taking place with the findings and resulting treatment proposal presented to clients through a Project Quality Plan.
On a scheme in an urban location or with fixed thresholds, the upper layer of the existing road may need to be planed in advance to provide a sufficient drop in the road level to accommodate the required thickness of asphalt surfacing.
Full Width Carraige Way Treatment
Using TRL 611 a pavement design can be defined with due regards to traffic volume and foundation strength.
It is important to read Table 7.4 with due regard to the Highways Agency design document HD26/06 which reinstates the different permitted HBM material classifications as original allowed in TRL 386 through which lower material classifications can be adopted on lower msa roads.
Haunch Treatment
Also in accordance with industry standards a nominal 1.0 metre haunch treatment is available for failing carriageway edges.
Figure below illustrates the final pavement construction when an asphalt surface course is applied, along with the recommended incorporation of a geotextile to bridge the construction joint. In essence, a two phase operation, the technique involves a thicker layer of recycling with the upper 40-50mm then planed out to permit inlay of the asphalt surfacing and geotextile.
Regen Roads
Working to a depth of no more than 150mm, SPL pulverise and stabilise in situ, using a low percentage of blended cement powder – typically around 2% in order to bind the recycled material prior to surfacing. On occasion, these evolved roads may not have sufficient depth of material to recycle, in this instance planings have been imported to provide additional integrity.
Immediately following the recycling - Surface Dressing using a double application of 12mm and 6mm stone is utilised, for cost, function and speed of completion. The result is a re-shaped, structurally sound road, protected against water ingress with restored surface characteristics at a cost appropriate to use.
