Communities have long favoured asphalt for repairs. Now, cities like Lloydminster find that concrete puts an end to rutting woes at intersections.
When it comes to the maintenance and repair of high-volume traffic corridors, the transportation departments of a growing number of Alberta towns and cities are opting to replace asphalt with the kind of concrete paving used for airports.
Leduc, Medicine Hat, Edmonton, and Grande Prairie have all used concrete paving on some of their highest volume sections of roadways-typically at or near traffic light-controlled intersections-for some time, says Gerard Kennedy, a senior project manager with EBA Engineering Consultants Ltd. He estimates that Edmonton started to use concrete paving on some stretches of road perhaps as much as 20 or more years ago to deal with severe asphalt rutting.
The City of Lloydminster, which has a population of about 27,000, has now started to use concrete paving.
It was perhaps to be expected. The growth of the Lloydminster-area conventional heavy oil industry and the series of vast oilsands construction projects in the Fort McMurray region over the last decade have pushed up traffic volumes on sections of Highway 16, part of the Trans-Canada Highway system. This has produced a sharp rise in the number of big trucks moving along the section of the highway that runs through downtown Lloydminster.
With the higher volumes of those heavy trucks, the result has been increasingly severe rutting in high-volume traffic areas. It's especially noticeable around intersections, where traffic is often either speeding up or hitting the brakes.
"The damage is typical of high-volume, slow-moving corridors," Kennedy says.
"There is significant rutting along parts of highway 16, but it's extreme at some intersections. Until now, the typical way of dealing with it has been to mill and inlay or just do a rut fill with standard asphalt mix. In Lloydminster, this would last only two to four years, especially in recent years with a busy oilpatch."
Besides the worsening problem of asphalt rutting itself and the resulting poor road surface, Lloydminster's type of intense road maintenance cycle with asphalt produces other problems and inconveniences.
The rutting problem begins, of course, in the summer. That is when the asphalt is at its softest. In winter, it is somewhere between difficult and impossible to properly snowplough the road's uneven, rutted surface. This can be a safety issue, says Kirk Morrison, a transportation/works engineer with the City of Lloydminster.
On the other hand, with concrete paving, which has a service life of at least 30 years, intersections are easier to maintain.
The biggest benefit, no doubt, from the standpoint of the road users and drivers, is that road repairs, with their attendant barriers, delays, and detours, go from an all-too-frequent annoyance to a once-in-a-generation event.
Before moving ahead with the concrete paving it did last summer, the City of Lloydminster commissioned EBA to do a study.
"It looked at various treatments, looked at up-front construction costs and life-cycle costs," Kennedy says. "Some [asphalt] treatments had a 5-, 10-, or 12-year service life, and some [like concrete] had a 30-year service life. We even looked at the feasibility of the status quo. In the end, we recommended a combination of treatments."
This made sense. Typically, a section of 100 or more metres either way from a traffic intersection would be the worst rutted and require the most frequent maintenance. These sections were targeted for a concrete rebuild. Nearby high-use sections, which being less rutted and requiring less maintenance, were prescribed a less drastic-and costly-treatment. This involved conventional milling out down to two or three inches but filling with a high-performance, not standard, asphalt.
"By using a high-performance asphalt, you extend from around four to six years to eight or nine years the service life of the asphalt," Kennedy says. "You about double the lifespan without doubling the cost."
For the sections of road selected for concrete paving, work began with milling out all of the asphalt, which was typically down to a depth of about 12 inches (30 cm). Next, the top few inches of the subgrade was removed. In some areas, says Kennedy, there was little to no aggregate, just clay.
Then, about 20 cm of fresh aggregate was laid prior to slip-form concrete paving to a depth of 24 cm.
Besides being used for freeways and other major routes in many U.S. cities, slip-form concrete paving is being used more frequently in Canada, and was applied to recently completed sections of Edmonton's ring road, Anthony Henday Drive. It is also de rigueur at airports for runways, taxiways, and aprons.
"The slip-form paving equipment we used in Lloydminster is suitable for paving airport runways," says Curtis Bouteiller, CEO of Proform Concrete Services Inc. of Red Deer. Indeed, as he notes, the company, which is the only Alberta-based firm providing slip-form concrete paving services, has done paving jobs at nine airports in the province, from High Level in the north, to Pincher creek, in the south.
A series of vibrators in the machine consolidate the concrete before it is placed. Sensors and a computerized line-grade system all assist the machine in staying on track.
Like asphalt pavers, the slip-form concrete machine paves one traffic lane at a time. It can pave between 250m and 500m per day.
"At five cubic metres per truck load, and paving at a rate of 250 metres per day, you would need around 50 truck loads of concrete a day," Bouteiller says.
Although the cost of slip-form concrete paving is higher than asphalt paving, comparing the cost over the 30-year service life of the concrete with that of asphalt and its frequent maintenance requirements and you wind up with a wash, Morrison says.