An innovative asphalt recycling technique at a rate of 50% was used for the scheduled heavy maintenance applications on the A28 motorway north of Le Mans. A high-rate recycling kit, adapted to fit an existing 300T/h continuous asphalt plant, was designed in conjunction with COLAS Centre Ouest.
Lasting 9 weeks, this project involved 40,000T of hot-mix asphalts with recycled aggregates and 34,000 tonnes of traditional hotmix asphalt, and took place under excellent conditions. The results were technically equivalent to those achieved on conventional projects, but the overall energy balance improved by 17.7%, greenhouse gas emissions were reduced by 17.7% and the solution was, of course, more economical.

CONTEXT OF THE A28 MOTORWAY SECTION AND DEFINITION OF THE WORKS
The scheduled replacement of wearing courses was intended to stabilise the carriageway and involved a major reconstruction of the slow lane. The project took
place over a nine-week period during the summer of 2007, between Reference Points 112+375 and Reference Points 129+690. Project management was
carried out by the S.C.A.O. (Société de construction des autoroutes de l’Ouest).

The existing structure consisted of :
- 35 cm of cement-treated capping layer
- 9.5 cm of asphalt base course 0/20 (used as a foundation layer)
- 7 cm of asphalt base course 0/14
- 3 cm of thin asphalt concrete as a wearing course

The variant solution implemented by COLAS reuses a large proportion of the deconstructed part (60%) of the carriageway, which can be schematised in the following way.
Deconstruction D
Simultaneous milling of the wearing course, the base course (0/14), and 5 centimetres of the road-base
course, i.e. a total thickness of 15cm (referred to as the D1 phase) for direct use, adding up to a volume
of 105,000 m3. Milling of an additional 10cm of asphalt base course 0/20;  the product was stored for
subsequent use and added up to a volume of 102,000 m3 (phase D2).

Reconstruction R
Phase R3: application of 10cm of natural gravel 0/14, for a total of 23,000T
Phase R4: one-coat surface dressings 2/4 (40,000 m2)
Phase R5: application of high-modulus asphalt based on recycled materials (ERMEL) (24.000T)
Phase R6: emulsion tack-coat
Phase R7: high-modulus asphalt concrete with 50% recycled aggregates, BBME R50 (16,000T)
Phase R8: tack coat
Phase R9: 5cm of thin asphalt concrete-type wearing course with an elastomer binder (34.000T)

A high-rate recycling is possible if the sections in question are homogeneous and traceability is good,
which was the case. The addition of 48.5% of recycled aggregates containing 4.6% of residual bitumen
to the high-modulus asphalt concrete, and 48.3% to the high-modulus asphalt based on recycled materials,
helped to reduce the amount of added binder (35/50 bitumen) to 3.01% and 3.38% respectively.

Equipped by the FAYAT Group, the Colas Centre Ouest mobile plant originally featured a dryer drum with
an external mixer. The bitumen is injected into the mixer, far from the hot gases which cause cracking and
emit harmful gases. The innovative aspects of this solution relate to the addition of a recycling drum, fitted
parallel to the main drum. The recycled aggregates are heated in the recycling drum, while the main drum
gently overheats the virgin aggregates. Both flows of materials are then thoroughly mixed together with
the bitumen in the external mixer.

Production output according to the recycling rate.the production outputs are given according to
the temperatures of the aggregates, on the one hand, and of the virgin aggregates according to the humidity,
on the other. The project was carried out at an average rate of 50 % and no particular problems arose.

Measurements and emissions
The TSR Ermont is programmed to operate at low temperatures, in the 110/130°C range, with the burner
adjusted to between 3 and 12MW for outputs of 60 to 200T/h. The temperature difference between the
gases and recycled materials is 7°C at 120T/h, with an output temperature of 110°C for the aggregates and
moisture content of 4%.
With a heavy fuel oil at 125°C and at an output of 140 T/hour in the TSR, we recorded emissions of 500ppm
of CO at 7% of O2. This equates to 178 mg/m3, which corresponds to 17% of O2 according to the
standards. These results are considered to be very satisfactory, as the industry target is 500 mg/m3.

Compaction was performed by Caterpillar 524 and BOMAG rollers without any problems and the
acceptance tests proved to be excellent. Longitudinal profile analysis was performed on 8 October 2007
at 72km/h and no particular observations were made.

Overall assessment and energy balance
As far as resources are concerned, 18,500 tonnes ofaggregates and 890 tonnes of bitumen were saved.
In terms of the energy balance, an overall reduction of 17.7% was achieved compared with the standard
solution. Greenhouse gas emissions were reduced by 15.6%.

CONCLUSION
High-rate recycling is possible, provided that the projects are well prepared and the production chain is
properly managed. The results prove that it is possible to obtain characteristics that are equivalent and/or
conform to the characteristics obtained using virgin products.
The next stage is recycling at 60% which, in terms of production and thermal balance, would seem to
pose no problems.