This Ontario municipality has made in-place recycling a major part of its road program. 

Can in-place recycling work effectively in an urban setting? Many cities in North America use in-place recycling on at least a limited basis, but more and more are making these technologies a basic part of their road management programs. 

One of the leaders in this trend is the Town of Markham, Ontario. This Toronto-area municipality of more than 200,000 citizens began employing partial and full-depth in-place asphalt recycling to rehabilitate its urban roads in 2002. The in-place recycling program was designed to maximize pavement performance, minimize the environmental impact of construction, and reduce pavement life-cycle costs. 

A new hot-mix asphalt overlay completes the full-depth reclamation of this residential street in the Town of Markham.

“The town’s move toward in-place asphalt recycling strategies stems from a need to maximize the return on capital investment while reducing the overall life-cycle cost of the road network,” explains Jeff Johnston, supervisor, Contract Administration for the Town of Markham. 

Urban in-place recycling has not only improved the quality and performance of the Ontario municipality’s road network, it has also reduced fuel consumption and the use of raw materials by reusing asphalt cement and aggregates on site, avoiding the transportation and stockpiling expenses of more conventional rehabilitation strategies such as milling and overlay.   

In the last five years, there has been a gradual trend toward the use of in-place asphalt recycling as the primary rehabilitation strategy.  Although the town continues to use conventional rehabilitation methods such as milling and overlay, the application of this strategy has been significantly reduced in recent years. Johnston expects the trend to continue in 2007, anticipating as much or more in-place recycling than in 2006. With the exception of 2004, the number of square meters rehabilitated through in-place recycling in Markham has increased each year. 

Markham uses full-depth reclamation for reconstruction; its process of pulverization and stabilization enhances the structural integrity of the existing roadway and corrects many deficiencies such as cross slope, rutting, and cracking. 

Markham also uses partial-depth recycling, also called cold in-place recycling, but to a lesser extent, because many of Markham’s residential roads do not have pavements thick enough for the process. In CIR, the recycling train removes 2 to 5 inches or more of old asphalt and replaces it as cold mix. The unprocessed asphalt must be thick enough to support the weight of the CIR machinery. 

Surveys select candidates 

The results from condition surveys, performed on the town’s entire road network every three years, are used to select the candidate street segments for rehabilitation in order to obtain an optimum network pavement condition index. If the current condition of a road segment falls below a predetermined threshold, the town’s Asset Management Department recommends rehabilitation and assigns a preliminary strategy.  

The town uses pre-engineering data and Annual Average Daily Traffic volumes to assess the structural capacity of the potential candidates and confirm the feasibility of in-place asphalt recycling.   

Markham reports that one of the added benefits of in-place full-depth asphalt recycling is the ability to enhance a roadway’s structural capacity or Granular Base Equivalency, without the need to place additional lifts of hot mix below the wearing course. The placing of additional lifts of hot mix is not only very costly, but may also necessitate the reinstatement of concrete curbs to a higher elevation. 

“In-place urban recycling candidates predominately possess relatively consistent materials with varying degrees of cracking and surface deformation,” says Stephen Damp, senior vice president of Miller Paving Limited, a contractor that works closely with Markham. “To date, in-place urban recycling has been successfully employed on local residential, local collector, and on both two-lane and four-lane major collector roadways.” 

Preparation and process 

Prior to performing the in-place recycling process, structures such as maintenance holes, valve chambers, and valve boxes must be lowered to sufficient depth to allow the recycling equipment to pass over without interference.  

Once these adjustments have been made, an area is pre-milled if the existing hot mix thickness warrants removal to achieve the desired mix blend. When determining the pre-milling depth, caution is exercised to avoid excess or insufficient curb reveal which potentially necessitates additional operations such as post milling or hot-mix padding before placing the wearing course. 

Regardless of any pre-milling, removal of pulverized material may be required prior to the injection of the binder to attain the desired curb reveal for subsequent wearing-course placement. This is usually accomplished prior to stabilization using a grader and a loader or a milling machine.  

Working in tight spaces

Markham works closely with the contractor to overcome the difficulties often encountered during rehabilitation projects in urban areas where road configurations present challenges in maneuvering the large equipment.  

In areas that are not directly accessible with the stabilization equipment, the material is removed from the original location, treated with the desired binder, and replaced to its original location, all in accordance with the desired cross fall and curb reveal.  

For example, Miller Paving uses conventional full-depth reclamation and  compaction equipment to achieve the required density of the stabilized layer, but compaction along curb faces is performed with plate-tamping equipment. This approach protects the structural integrity of the curb and achieves sufficient density to prevent curbside raveling.  

The Town of Markham continues to use in-place asphalt recycling as an urban rehabilitation strategy due to the environmental benefits, the inherent pavement performance, and expected life-cycle cost savings. Markham’s Johnston notes that the benefits of utilizing in-place recycling processes have already been realized as pavements rehabilitated in 2002 and 2003 using in-place recycling strategies show no signs of distresses normally observed three to four years following a conventional milling and overlay operation. 

Trevor Moore, P.Eng., is technical director for the Ontario Pavement Products Group of Miller Paving Limited based in Ontario. Moore received substantial support from Jeff Johnston, supervisor, Contract Administration with the Town of Markham.
 
 

From top, left to right: Markham uses in-place recycling for residential streets and collectors as seen in the two photos at the top. A Miller Paving full-depth reclamation train works quickly through a Markham residential area. A motor grader follows the reclaimer and levels the processed roadway. The reclaimed roadway, graded, compacted, and ready for an overlay.