Stretching pavement life with micro-surfacing

Jeff Jorgenson
Roadways Engineer
City of Saskatoon, Saskatchewan

The City of Saskatoon is located in western Canada, and has a population of approximately 200,000. The City continues to be anchored by a lush natural river valley as it was when it was founded in 1881.

As with most other North American towns and cities, Saskatoon faces many challenges in dealing with worn-out infrastructure. Prior to 1996, some reinvestment had occurred on high-volume collector and arterial roads, but virtually no major works had occurred on residential streets. Citizens had to wait for sewer and/or water system replacement projects before they could expect any major reconstruction of their street.

In 1995, City staff prepared a report for council that addressed the need for reinvestment in residential streets. The report, based on the findings of a comprehensive condition study and pavement management analysis, concluded that a significant investment was required in order to keep residential streets in a reasonable condition.

The report went on to discuss the potential for introducing micro-surfacing as a treatment for residential streets. Micro-surfacing is a mixture of emulsion, aggregate, water, and mineral filler which is cold-placed in a thin layer on the road surface, thus sealing surface irregularities and reducing moisture infiltration into the road structure. Micro-surfacing was invented in the 1930s in Germany, and has been used successfully by many agencies throughout the world as a pavement preservation treatment.

Based on a life-cycle cost analysis, the report concluded that should micro-surfacing be introduced as a treatment in Saskatoon, the five-year funding requirements for the network would be approximately $3.9 million.

If only "traditional" methods of treatment were used, the average annual investment required to keep streets in a similar overall condition would be $8.1 million. In Saskatoon, "traditional" meant to perform routine maintenance until the road failed; then reconstruct.

City council accepted the report, including administration's recommendation to introduce micro-surfacing as a treatment, and dedicated $1.25 million dollars for the 1996 construction season.

In 1996 and every year since, the City has tendered a yearly micro-surfacing program for residential streets. The objectives of the program are to repair road failures, ensure that there is positive drainage from the pavement surface, and resurface the pavement with micro-surfacing. Road repairs and leveling are performed by City crews using hot-mix asphalt for fills and road profilers for cuts. All micro-surfacing is carried out through publicly-tendered contracts.

One key to the success of the micro-surfacing program was convincing council, City staff, and the public that the City needed to spend money on roads that, from a driver's perspective, were performing fine. Preventive maintenance treatments, such as micro-surfacing, would prevent these roads from failing prematurely. The City could not dedicate sufficient funds at that time to both rehabilitate streets that had failed as well as perform micro-surfacing on streets requiring preventive maintenance.

City council accepted administration's recommendation to focus efforts on the preventive maintenance approach. Statements such as "an ounce of prevention is worth a pound of cure," or "think of it like changing oil in your car—a small cost now will save you huge costs down the road" were often used to calm down taxpayers who didn't understand why we were fixing up other roads while their road was in need of reconstruction.

Council, administration, and the general public have raved about the program ever since its introduction. To date, approximately 24 percent of the City's residential streets have been micro-surfaced.

In 2000, City administration reviewed the condition of micro-surfaced streets in order to determine whether the treatment was meeting the desired intent. Failures were measured and categorized as either "delamination" failures (micro-surface had peeled off) or "thinness" failures (micro-surface had worn through).

Of the 461,886 square metres that were rated, only 1.1 percent (4,968) square metres had failed. Further analysis showed that, on average, micro-surfacing on residential streets was failing at a rate of 0.4 percent per year (4 square metres failed for every 1,000 square metres placed). This failure rate exceeded administration's expectations and confirmed observations that the treatment was performing extremely well. Success of the program is attributed to the skill and commitment of both the City crews who perform the preparatory work as well as the contractors who carry out the micro-surfacing itself.

The report also made two major recommendations for further work to be undertaken. The first recommendation was based on quantifying the overall cost effectiveness of the program. Although administration believes that the program is extremely cost effective, a comprehensive study, including life-cycle cost comparisons, needs to be done in order to ensure that the funding being dedicated to micro-surfacing is in fact the most appropriate way to preserve pavements.

The second recommendation is based on ensuring that life expectancy of the micro-surfacing treatment is maximized. "Influence factors," such as emulsion source, relative humidity during construction, mix design results, aggregate quality, application rate, and other factors will be tracked in detail during construction to help enable the City to develop correlations between these factors and actual performance. This type of analysis, combined with keeping on top of industry research and best practices, will help ensure that the City of Saskatoon is getting the maximum life out of our micro-surfacing treatment.

Due in large part to the success of the leveling/micro-surfacing initiative, the City of Saskatoon's residential streets are now in much better overall condition than they were in 1996. In 2000, council began phasing in an annual program of $1.5 million annually which is dedicated to the rehabilitation of residential streets that have failed completely.

The City is now reaping the benefits of a preventive maintenance approach. Had the City maintained our "fix it when it fails" approach rather than the micro-surfacing approach, we would be facing a much different residential street condition than we are now. The micro-surfacing program has allowed us to get the most out of our existing pavements, resulting in surplus funds that can now be used to rehabilitate roads that have reached the end of their service life.

To reach Jeff Jorgenson, call (306) 975-2632 or send a Fax to (306) 975-2500.