Roads & Paving
Smooth, Continuous and Consistent
By Rick Zettler Z-Comm
Continuous, full-width paving on Autoroute 30 eliminates joints, improves mat quality.
By Rick Zettler Z-Comm
Touted as the largest public-private highway project in Canada, the
massive Autoroute 30 skirting Montreal is much more than just another
Touted as the largest public-private highway project in Canada, the massive Autoroute 30 skirting Montreal is much more than just another road job. The project’s forward-looking approach will ease traffic congestion in the Montreal area, build a more effective road network and advance economic growth.
|By developing a continuous paving process, crews can help to eliminate the occurrences of truck-end segregation. (Photo courtesy Nouvelle Autoroute 30 s.e.n.c.)|
With a matrix of bridges, tunnels, interchanges and many kilometres of new expressway, the $1.5-billion Autoroute 30 consolidates Highways 10, 15, 20, 30, 40 and 540 for easier access to markets in Montérégie, Ontario and the United States. The western section of the new highway, built by the public-private partnership Nouvelle Autoroute 30 Consortium, extends 35 km (21.7 mi.) from Vandreuil-Dorion to Châteauguay. An additional 7 km (4.3 mi.) will link the new highway to Route 201 in Salaberry-de-Valleyfield.
Nouvelle Autoroute 30 s.e.n.c. has the responsibility for designing, constructing, operating, maintaining and financing the highway’s western section. When the project is finished, estimated to be December 2012, the consortium doesn’t just walk away from the new highway. It has responsibility for the road for 35 years.
Therefore, it’s in the best interests of Nouvelle Autoroute 30 s.e.n.c. to construct the new four-lane roadway not only in the most efficient and cost-effective manner possible but also in a way that minimizes future maintenance costs. The highway pavement includes a combination of asphalt and concrete surfaces. For the asphalt segments, the Ministère des Transports du Québec (MTQ) is requiring contractors to use paving techniques designed to enable the road to last for decades with minimal maintenance.
Three Quebec paving contractors – Pavages Chenail of St. Rémi, Dorval Paving and Roxboro Excavation of Dorval – are currently paving Autoroute 30’s western asphalt section. More than 540,000 tonnes (595,250 tons) of asphalt will be used to build the new road from the ground up.
|Paving in tandem allows crews to have a hot joint to compact, which offers high quality joint construction. (Photo courtesy ministère des Transports du Québec) |
|More than 540,000 tonnes of asphalt, paved in four lifts, are being used to build Autoroute 30’s western section of highway. (Photo courtesy Nouvelle Autoroute 30 s.e.n.c.).|
A total of 275 mm (10.8 in) of asphalt is being laid in four lifts to construct the new road. The base lift consists of an ESG-5 anti-shock asphalt layer with 5-mm (0.20-in.) stone laid in one 75-mm (3.0-in.) layer. The following two, 80-mm (3.1-in.) thick intermediate lifts consist of a GB-20 mix made with 20 mm (0.79 in) aggregate. The final ESG-10 surface course with its 10-mm (0.39-in) stone is paved at a 40-mm (1.6-in.) thickness.
Contractors on the project are required to keep the paving train moving in a non-stop manner to help improve mat quality. “Paving continuously helps the contractor avoid truck-end segregation,” says Bill Rieken, paver application specialist for Terex Roadbuilding.
Developing a continuous paving process begins with the contractors ensuring they have the right number of trucks to deliver enough asphalt to keep the paving train in motion. “Determining the number of trucks required for continuous paving comprises a range of factors, including distance between the plant and jobsite, round trip travel time, truck capacity and the number of tons per hour being paved,” explains John Lefebvre, president of Lefco Equipment, Inc. of Laval, Que., a Terex Roadbuilding distributor.
Second, the paving train must have enough surge capacity to keep the paver in motion during truck exchanges. While it is possible to continuously pave by unloading asphalt directly into the mainline paver’s hopper, crews on the western section of Autoroute 30 are using a material transfer vehicle. “An MTV provides additional surge capacity for the paving train, giving crews more time to pave between truck exchanges,” says Rieken.
For the Autoroute 30 project, one common thread linking all three paving contractors is the type of paver being fed by the MTV. “The paver of choice is the Terex® CR662RM RoadMix,” says Lefebvre. Rieken adds, “The CR662RM can be used either as a paver or an MTV, and the contractors on this project have chosen to equip them as pavers.”
Rieken goes on to explain the difference between the CR662RM and a traditional mainline paver. “Whereas traditional pavers use slats to move material from the hopper to the spreading augers, the CR662RM RoadMix paver has variable-pitch, counter-rotating augers inside the hopper.”
Asphalt movement in the hopper of a traditional slat paver is from front to rear. However, the CR662RM’s counter-rotating augers draw down and remix asphalt from all areas of the hopper. The variable-pitch design of the augers aggressively reblends 100% of the asphalt prior to delivering it to the spreading augers.
Beyond reblending capabilities, Rieken offers an additional benefit of the variable-pitch auger design and spread auger drive system of the CR662RM over traditional slat pavers with a centre gearbox spreading auger design. “The variable-pitch augers do not fracture the aggregate like the slat chains can,” he says. “This fractured stone typically falls underneath the centre gearbox drive of most pavers, resulting in centreline segregation.” Since there is no aggregate fracture and the spreading augers are driven by outboard drive motors, “the CR662RM’s design eliminates the possibility of this type of segregation.”
The end result for the contractors is a more homogeneous blend of asphalt delivered to the spreading augers, which is void of both material and thermal segregation. “The MTQ has workers on the job with thermal imaging cameras to ensure that the mat has a uniform temperature reading across the width of the mat,” mentions Lefebvre. A paving superintendent from one project contractor adds that the MTQ is looking for the hotter red and orange temperature readings in the camera, and the readings have been very consistent behind the screed.
Full-Width, Hot Joint
What makes this uniform temperature accomplishment all the more impressive is the width at which the crews were paving. Each paver is equipped with a Terex Fastach screed built to pave two traffic lanes plus the small inside shoulder in one pull. “Each contractor has enough screed sections to pave up to 10 m (32.8 ft.) wide,” says Lefebvre. Currently, the contractors are paving the two 4.2-m (13.8-ft.) travel lanes and one 0.8-m (2.6-ft.) small shoulder in a single pass, for a total paving width of 9.2 m (30.2 ft.).
|Crews are using the Terex CR662RM RoadMix to pave full width at 9.2 m wide, leaving no joint in the travel lanes to improve the road’s longevity. (Photo courtesy Lefco Equipment, Inc.).|
|The combination of continuous paving combined with the CR662RM’s remixing capabilities is resulting in a smooth mat void of material and thermal segregation. (Photo courtesy ministère des Transports du Québec)|
The Fastach screed comes with a standard 3.0-m (10-ft.) paving width and wide, 863.6 mm (34 in.) screed bottoms to increase mat smoothness. Screed extensions offer a unique pin-lock attachment design for quick installation and are available in 152-, 305-, 610-, 914- and 1,524-mm (6-, 12-, 24-, 36- and 60-in.) widths to meet a wide range of paving applications. The main screed and extensions, excluding the 152-mm (6-in.) and 610-mm (24-in.) slopeable, offer up to 50-Hz (3,000-vpm) vibration to provide initial asphalt consolidation.
The 610-mm (24-in.) slopeable extension allows crews to place crowns in the road where required. The screeds paving on Autoroute 30 have two slopeable extensions, allowing crews to place a crown on either side of the paver for the small shoulder, depending on which direction the paver is paving. The main, 3.0-m (10-ft.) screed section of the Fastach provides the crown in the centre travel lanes. The screed comes standard with power crown control with crown capabilities ranging from 76 mm (3 in.) positive to -25.4 mm (-1 in.).
With its powerful 194-kW (260-hp) diesel engine and high tractive effort rubber track drive system, the CR662RM delivers the power and traction required to efficiently pave at the 9.2-m (30.2-ft.) width. “The screed configuration includes six oil-fired burners to provide initial warm-up for the screed bottoms,” says Rieken. “The screed is also ballasted for excellent ground contact pressure to deliver the required ride smoothness.”
Following closely behind the mainline paver, the 2.4-m (8-ft.) Terex CR362 rubber track paver is used to pave the 2.5-m-wide (8.2-ft.-wide) shoulder.
By paving in tandem, crews have a hot joint to compact, which offers high-quality joint construction. “Since the mainline paver is paving at full width, the joint is not in the travel lanes, which is what the MTQ prefers,” says Lefebvre. Rieken further explains, “The joint is typically where the first signs of failure will develop, so having the joint in the non-travelling lane should make it last much longer.”
With paving operations rapidly coming to an end and opening date for Autoroute 30 scheduled for the end of 2012, all quality and smoothness reports from the field have been positive. The combination of continuous paving, the CR662RM paver’s variable-pitch counter-rotating augers and full-width paving with the Fastach screed has resulted in a road surface void of segregation and without joints in the traffic lanes.
In addition, contractors are receiving excellent ride smoothness results. To receive maximum bonus on the project, contractors must adhere to a stringent 1.2-mm deviation per 100 m under the International Roughness Index. Preliminary field results show the paving train is achieving IRI readings ranging from 0.8 to 1.1 mm per 100 m.
The combination of uniform mat temperatures behind the screed, remixed asphalt, full-width paving and bonus-level smoothness results should give Nouvelle Autoroute 30 s.e.n.c. a durable asphalt road surface that will require minimal maintenance throughout its 35-year ownership of the new highway. “The ultimate winner, however, is the travelling public, who will have a much more efficient way of travelling around the Montreal region,” says Lefebvre.
Rick Zettler of Z-Comm in Cedar Rapids, Iowa, is an award-winning writer. He researched and wrote this article on behalf of Terex Roadbuilding for Aggregates & Roadbuilding magazine.