Aggressive highway maintenance in N.B.

MRDC Operations Corporation, a private enterprise responsible for the maintenance and rehabilitation of a 124-mile (200-km) section of New Brunswick’s Trans Canada Highway, undertook an aggressive rehabilitation program during the 2009 season.

This section of highway – recognized internationally for its innovative construction methods, techniques and practice – was designed, constructed and maintained by MRDC through the development of a 30-year public-private partnership with the province of New Brunswick. The construction of this highway, bridging the cities of Fredericton and Moncton, began in 1998 and was opened to traffic between the years of 1999 and 2001.
The rehabilitation program was composed of microsurfacing and paving programs by MRDC and its subcontractors using Wirtgen asphalt cold milling equipment, Hamm asphalt compactors and a Vögele asphalt paver.
MRDC is a private contractor owned by Miller Group, Vinci Concessions, Dragados y Construcciones and Fomento De Construcciones y Contratas.
Mark Kenny, P.Eng., MRDC operations manager said that pavements constitute one of MRDC’s most valuable assets, and it’s prudent to preserve this asset as long as technically possible balancing cost and quality.
“Ideally, it is our intention to have smooth and quiet roads, so we use pavement management systems – complete with cycle cost projections – to help optimize our plan of attack,” Kenny said. “Each year, we generally measure the condition of the pavements in terms of smoothness (IRI), surface distress (SDI) and serviceability (PSI); and rutting and strength (FWD) every four years.
“These measurements help us understand the trend of the pavements and are the basis for assessing the desired level of service and when to schedule what type of treatment at the most effective time.”
However, this pavement management approach still requires innovative thinking, and computers do not always have the answers.
“It’s all in the interpretation and how to use the information,” Kenny said. “We believe that it is more efficient to be proactive than reactive using life cycle cost analysis approaches.”

Microsurfacing

There are many factors driving the scheduling and selection of treatments for addressing pavement distresses, but MRDC has found that microsurfacing is one treatment that can be most effective and efficient when applied to pavements containing low-to-moderate levels of distresses.
“In our case,” Kenny said, “the pavement structure along the highway is generally seven to nine years old, with some sections of highway even older, since these pavements already existed prior to construction. Our main concerns were the pavement surface distresses of longitudinal/random cracks, raveling and segregation, with some of the older pavements containing low to moderate pavement strength. Wheel path ruts were generally less than 12mm (0.5 in.); therefore, rut filling was not necessary.”

The density and severity levels of each distress type varied along the highway. “Based on our assessment,” Kenny said, “we concluded a preventive treatment must be applied to most of the pavements to seal and preserve the integrity of the pavement structure, and deemed microsurfacing consisting of a scratch-and-overlay coat the most efficient treatment. Most of the pavements would require crack sealing and hot mix patching in advance of the microsurfacing.”
On other sections of the highway, the distresses were too severe for a preventive treatment; therefore, MRDC moved towards paving operations consisting of “mill and pave” or “overlay” programs.

MRDC’s expectation with microsurfacing was to improve the smoothness by as much as 20 to 30 percent, and increase the pavement service life an additional seven years. “Our expectation with mill and pave was to replace poor driving surfaces with hot mix asphalt, thus providing a high standard of smoothness. Areas subjected to low strength values are scheduled to receive a 40mm (1.5-inch) overlay, but only during the years to follow.”

MRDC’s 2009 rehabilitation plan involved the supply and placement of 47,300 tons (43,000 metric tonnes) of hot mix asphalt, and about 2.1 million square yards (1.75 million square metres) of microsurfacing.
MRDC engaged two contractors – Industrial Cold Milling and Moncton Construction, both experts in the field of microsurfacing – to complete the microsurfacing work. All work started in late May, with completion in the fall.
 

Milling

In the 2009 program, pavements too-far deteriorated were candidates for milling and paving, with the expectation of achieving an additional 10 to 12 years of service life. Hot mix asphalt paving was done by MRDC, with milling carried out by subcontractors.

When visited, Industrial Cold Milling was removing long sections east of MRDC’s patching operation. “We’re using our W 2000 to cut a 3-km (1.8-mile) ‘slug’ 55 mm (2.1 inches) deep,” said Darcy Robertson, milling foreman for the Atlantic Canada Industrial Cold Milling division, Moncton.
The W 2000 – with a 2.2-metre (7-foot 2-inch) cutter head – was cutting 13 feet wide in two passes. “That will take it into the edge of the rumble strip,” Robertson said. The Atlantic Canada region has two Wirtgen W 2000s, a W 2100, a W 1200 (predecessor to the W 120 F), and two W 600s (predecessor to the W 60). It also has a WR 2500 used for foamed asphalt and cement stabilization work.

The W 2000 uses the MOBA levelling system. “We run four sonic eyes on each corner on highway jobs,” Robertson said. “The side plate is a Multiplex ultrasonic levelling device.”
Despite its age – the W 2000 visited was purchased in 2003 – the machine continues to work well in its abrasive environment. “It’s got 7,300 hours on it, and this year we cracked over a million square metres (1.2 million square yards) with this machine,” Robertson said. “We water it on the fly and perform our own maintenance with mechanics who have visited Wirtgen’s training courses. As a result they’ve gotten a lot better at it.”
Another milling MRDC subcontractor is Perfection Paving Ltd., Fredericton, which uses a new Wirtgen W 2000 with 6.5-foot (two-metre) drum.
 

Paving

“We have one paver for all paving applications, the Vögele 2116T – an 8-foot rubber track paver, and three different Hamm compactors, a 66-inch tandem double-drum vibratory roller (HD 110HV), a rubber tire roller (GRW 18) and a 78-inch double-drum roller with Oscillation (HD O120V),” Kenny said.
The mill and pave work included the removal of the asphalt seal (approximately two inches or 50 mm), and replacement with hot mix. “Most of our paving operations include the delivery of asphalt using tri-axle, live bottom trailers right into the hopper,” Kenny said. “Unfortunately, we did not have access to a material transfer vehicle, but our workers are aware of rock and temperature segregation, so efforts are made to mitigate these occurrences.
“In terms of compaction efforts, we generally schedule the rubber tire roller in the breakdown position,” Kenny said, “and the double-drums (vibratory and oscillation) in the intermediate position, with the smaller double-drum roller rolling in static mode way behind, to ensure the mat is free of any noticeable defects.”

Most of the compaction generally is achieved at the electric vibrating screed, up to 80 percent, and the last 10 to 15 percent is achieved in the breakdown and intermediate positions.
“We basically show our workers a couple of simple rolling patterns,” Kenny said. “However, sometimes the rollers are reversed if checking is observed, or if the temperature of the mix is not coming in as planned. We generally work in high vibration and low amplitude due to the thickness size of the mat. Generally, the breakdown and intermediate roller are working together in a strategic formation and when things are running smoothly, the paving is kept to a constant speed, as slow-or-fast is more effective than start-and-go.”
Roger Cormier, area superintendent for MRDC, said the equipment has had little downtime, in fact none for 2009. “The equipment has been performing very well for us,” Cormier said. “It helps to have trained and experienced roller and paving operators, and we consider equipment preventive maintenance very important.”

Cormier tries to keep the same operator with the same roller, and conducts regular maintenance. “The guys know all the scheduled maintenance times” he said.
MRDC’s team works well together and it’s proud of their accomplishments. “We only started a few years ago in the paving end, but this year we really excelled in quality,” said Kenny.