Roads & Paving
MRDC goes the micro-surfacing route
Micro-surfacing has a proven track record on the Fredericton-Moncton Highway
By Andy Bateman
New Brunswick’s award-winning Fredericton-Moncton Highway, the MRDC,
officially opened to traffic on October 23, 2001 and this 195 km long,
four lane section of the TransCanada highway has been recognized
internationally for innovative construction methods, techniques and
New Brunswick’s award-winning Fredericton-Moncton Highway, the MRDC, officially opened to traffic on October 23, 2001 and this 195 km long, four lane section of the TransCanada highway has been recognized internationally for innovative construction methods, techniques and materials.
|New Brunswick’s award-winning Fredericton-Moncton Highway, the MRDC, has been recognized internationally for innovative construction methods, techniques and materials.|
The innovative tradition continued this year, with a micro-surfacing contractor achieving high productivity rates, despite distant raw materials and unpredictable weather.
Martin Bouvier, project manager for DJL Technologies, explains that the company’s Moncton Construction Inc. division submitted the winning tender earlier this year for a major micro-surfacing project on the MRDC. The project extends from the MRDC’s kilometre marker 257 to kilometre marker 295.7 near Fredericton, with a start date of June 1, 2009. Preparatory work by the MRDC prior to micro-surfacing included crack filling, milling and paving. There was no rut filling on this particular project.
|What is micro-surfacing? |
The Miller Group, part owner of the MRDC Operations Corporation, describes micro-surfacing systems as mixtures of a polymer-modified cationic emulsified asphalt, mineral aggregate, mineral filler, water and additives that are proportioned, mixed, and spread with a machine over a properly prepared surface.
Micro-surfacing systems, says Miller, are used to restore and preserve the surface characteristics of pavements and may be designed to correct rutting, improve inadequate pavement cross sections and enhance the frictional properties of structurally sound polished pavements.
Micro-surfacing is said to provide low-cost preventive maintenance treatment systems that retard deterioration of the pavement, maintain or improve the functional condition of roadways and extend the pavement’s service life when applied to suitable candidates. The placement of a micro-surfacing system on medium to high traffic roads offers a competitive alternative to traditional methods of restoring surface characteristics of roadways and extends the life of the pavement by four to eight years.
From Bouvier’s perspective, the micro-surfacing process itself was routine, as DJL has considerable experience with this road treatment system. What has made this job unique is the sheer quantity of raw materials involved and their distance from the job site. DJL’s largest micro-surfacing project to date totals over 750,000 m², including all four lanes on nearly 40 km of highway, its interchanges with Route 7 and Route 8, and 54 000 m² on highway off ramps. The resulting principal material quantities include 1.6 million litres of asphalt emulsion, 14,000 tonnes of aggregate and 200 tonnes of cement.
The asphalt emulsion for the micro-surfacing mixture was supplied from DJL’s
emulsion plant located at Carignan, Que., nearly 850 km from the job site. Aggregates were sourced from a quarry near Miramichi, N.B., and were relatively close at “only” 250 km from the job site. The Type 10 Portland Cement utilized for filler on this contract was supplied from the Saint-Basile, Que., plant of Ciment Québec Inc. Combined with 2009’s unpredictable weather, raw materials supply has necessitated careful management of inventories and a versatile site crew to maintain overall target production rates. Bouvier’s project diary recorded 21 days of wet weather in June and July alone. On good weather days, Moncton Construction’s crew has been completing 45 000 m² of micro-surfacing, requiring 450 tonnes of aggregates and, with each aggregate truck completing two round trips each day at best, a minimum of seven trucks have been required to maintain delivery of 14 loads per day. At the same time, daily consumption of emulsion has reached 65,000 litres, requiring six tankers on the road at any one time to maintain a delivery rate of two tanker loads per day.
Aggregate, emulsion and filler arriving at the project were stockpiled at two yards located at each end of the contract. These helped maintain adequate inventories and a steady raw material flow to the site crew, although even then tight yard space meant significant material rehandling. At peak production times, aggregates, emulsion and water were all arriving at the stockpile yards, while loaded Bergkamp micro-surfacing machines were leaving the yards and heading for the job site.
On arrival at the job site, two M216 Bergkamp trailers and an M210 truck mounted paver unit were connected in turn to a Bergkamp VSB 9-14 variable width spreader box. The micro-surfacing mixture was then spread onto the pavement until the machine was empty. The spreader box was then disconnected and the units returned to the stockpile yards to be refilled. Moncton Construction’s site crew consisted of a foreman, an operator, three labourers and a spreader box labourer. At the stockpile sites, the crew consisted of a foreman, a loader operator and three labourers for reloading the filler and the emulsion. Two more labourers were used to clean up any residue from the work zone and complete the temporary road marking every day, over a distance of some 6 km. A typical day would also see at least one change of configuration in the traffic control from passing to driving lane.
This year’s variable weather has placed additional demands on the micro-surfacing crew, with working hours frequently modified to suit changing conditions. A common scenario has been a delayed start due to morning rain or fog, resulting in a late finish and frequent 12 to 13 hour days. To give the paving crew some rest time, a separate team has been assigned to cleaning the spreader box.
Construction zone safety
Bouvier notes that the contractor is responsible for the traffic control in accordance with the New Brunswick Department of Transportation’s 2009 Work Area Traffic Control Manual (WATCM). The new manual came into effect on Monday, May 4, 2009 and provides a uniform set of traffic control guidelines for all work carried out on New Brunswick provincial roads and includes the use of a buffer (blocker) truck to protect construction zone workers. Before micro-surfacing operations, the work zone was prepared each day by a traffic control subcontractor’s crew of four equipped with half tonne capacity trucks and trailers. Each secured work zone involved 26 signs, 20 drums, 350 delineators and arrow boards and a full setup would typically take an hour and a half to install.
|Micro-surfacing treatments have performed very well, preserving the pavements an additional five to seven years.|
|Raw materials were hauled from two stockpile yards to the job site by two M216 Bergkamp |
trailers and an M210 truck-mounted unit.
Materials and specifications
The micro-surfacing process began with the application of an SS1 diluted tack coat at a rate of 0.2 to 0.4 l/m². The tack coat was followed by a scratch (levelling) coat and surface coat, with a combined minimum application rate of 14 kg/m². The asphalt emulsion used in the mixture, Emulplast EC, was a polymer modified CSS1-H emulsion produced at DJL’s plant in Carignan QC and meeting ASTM D244 specifications.
Specification for the aggregate included 100% crushed rock with a 9.5 mm minus gradation and a minimum specified sand equivalent value of 65. The sand equivalent test indicates the relative portion of undesirable clay-like or plastic fines and dust passing the No. 4 sieve that may be present and the tight value specified here compares to typical values of 26 to 60 for fine aggregate in hot mix asphalt, with the most common being 45. The aggregate is also required to have a maximum 16% loss maximum result for the Micro-Deval test for both coarse and fine fractions, compared to a limit of 17% often allowed for coarse aggregate in an asphalt surface course application.
Turning to site equipment, Bergkamp literature indicates that the M216 trailer-mounted, slurry seal and micro-surfacing paver is the company’s largest self-contained slurry seal and micro-surfacing paver. The M216 has the capacity for 12.2 m3 of aggregate, 5,678 litres of asphalt emulsion, 3,780 litres of water and 200 litres of additive. The smaller M210 truck mounted unit has the capacity for 7.7 m3 of aggregate, 2,250 litres of asphalt emulsion, 2,250 litres of water and 200 litres of additive.
DJL Construction Inc. is a recognized name in Quebec’s infrastructure industry as a general contractor providing multiple specialized products and services in the civil engineering environment. Based in Boucherville, Que., DJL has an extensive network of quarries, sand and gravel pits and asphalt manufacturing plants.
|MRDC applies micro-surfacing solution |
Mark Kenny is operations manager for the MRDC Operations Corporation and explains that MRDC has applied micro-surfacing treatments including rut filling to the Fredericton-Moncton Highway (FMH) over the years to address rutting and/orsurface distress issues, and indicated that micro-surfacing treatments have performed very well preserving the pavements an additional five to seven years. Kenny explains that pavements are one of their most valuable assets, and it is prudent to preserve this asset as long as technically possible. “As most understand, there are many factors driving the scheduling and selection of treatments, but we have found that micro-surfacing can be most effective and efficient when applied to pavements containing low to moderate levels of distresses. When considering a pavement candidate for micro-surfacing treatments, we first measure the condition of the pavement in terms of strength based on the falling weight deflectometer (FWD) test, the surface distress index (SDI), the smoothness based on the international roughness index (IRI), and rutting. As well, a present serviceability index (PSI) is computed from the measurements of the condition survey. Generally, micro-surfacing becomes a candidate when the PSI is less than 60, and assessments regarding expected life of treatments are evaluated based on these condition indices as well as the levels of service desired.”
“In our case,” says Kenny, “the pavement structure is seven to nine years old and our main concerns were pavement surface distresses comprised of longitudinal/random cracks, ravelling and segregation. Wheel path ruts were generally less than 12 mm; therefore, rut filling was not necessary. The density and severity levels of each distress varied along the highway. Based on our assessment, we concluded a preventive treatment must be applied to pavements to seal and preserve the integrity of the pavement structure, and deemed micro-surfacing consisting of a scratch and overlay coat the most efficient treatment. Further, our expectation was to improve the smoothness by as much as 20 to 30 percent. We also acknowledged that most of the pavements would require crack sealing and hot mix patching in advance of the micro-surfacing.
The Fredericton-Moncton Highway (FMH), consisting of a 200 km four lane divided highway (RAD-120), was designed and constructed by MRDC between years 1998 and 2001, part of a Public Private Partnership (PPP) 30 year development by the Province of New Brunswick. MRDC, a private contractor owned by Miller Paving, Vinci Concessions, Dragados Y Construcciones and Fomento De Construcciones Y Contratas (FCC), also became responsible in 1998 for the Maintenance and Rehabilitation of the FMH containing older sections as well as the sections constructed in stages between 1998 and 2001.