There’s more than one way to patch a pothole, and the City of Greater Sudbury is analyzing the most effective and affordable way — or combination of ways — to address its perennial issue with pitted pavement.
“When evaluating the decision to purchase pothole repair equipment, it is important to evaluate the benefit the equipment provides compared to the cost to purchase and maintain it,” reads a report prepared for city council.
“It is therefore recommended to prepare a business case that includes a net present value analysis of each (type of) pothole repair equipment,” staff advise. “This analysis would evaluate the initial equipment investment and ongoing maintenance expenses compared to the benefits realized through labour savings and efficiency of performed repairs.”
The report highlights the range of equipment currently available for pothole repairs, while providing a comparison of what each machine or method can accomplish for its price.
“The City of Greater Sudbury is committed to continuously reviewing and testing creative solutions for roads maintenance,” the report states, adding that smooth asphalt isn’t only important for sparing motorists a jarring ride or a trip to the garage, but key to a humming economy.
“It is well understood that the effective repair of potholes as part of a routine road maintenance program minimizes the interruption of movement of goods and services across the city,” staff write.
There are many forms of pavement maintenance, the report notes, but no single approach will be sufficient on its own.
“A combination of techniques, applied at the right time, is required for a program to be effective,” staff say.
The City of Greater Sudbury takes a threefold approach: Preventive maintenance (treatments like crack sealing to extend the life of pavement); corrective maintenance (repairing significant defects, like a pothole); and holding maintenance (keeping the paved surface together until a more substantial rehab can be carried out).
Pothole repair would fall into both the second and third categories.
“These repairs are to address potentially hazardous conditions affecting the safety of the travelling public,” the report states, and are considered “temporary or semi-permanent,” depending on the technique used.
The most popular temporary fix among city crews is termed “throw and roll.”
This approach is used “regardless of the weather and is considered an efficient method of repair due to how quickly it can be completed,” staff write. “Because of this, it is the most commonly used repair method during pothole repair campaigns or where high productivity is required due to a high volume of potholes.”
Throw and roll involves cleaning out the hole and applying asphalt (it can be a cold, warm, hot or recycled mix), then tamping it down with a vibratory roller or hand tamper.
Examples of semi-permanent repairs include detailed patching, spray patching and infrared patching.
The former is also a frequent approach employed by the city, as long as the conditions are favourable — namely dry, and not too cold.
“Occasionally, this method is also utilized when potholes are particularly severe during the spring melt and increased freeze-thaw cycle periods,” the report states.
In these cases, warm-mix asphalt is hauled in a heated truck box from southern Ontario.
“This type of repair takes more time to complete than the throw-and-roll technique but provides greater performance,” according to the report.
With detailed patching, a mechanical grinder is used to clear out the hole and a tack coat applied before the new asphalt is inserted, tamped down and rolled.
“Also in this category is the large asphalt patching program completed each year through contract services,” the report notes. “This program uses techniques very similar to the approach described above, the difference being that the areas are generally larger, removing further deleterious materials and the hot mix asphalt is placed using a mechanical spreader rather than by hand, providing increased compaction and smoothness.”
When used as corrective or holding maintenance, this type of patching can extend the life of a pavement by three to five years, staff indicate, and when used as preventive maintenance it can prolong pavement life up 11 years.
Spray patching and infrared patching are less commonly used in Sudbury at the moment.
With the spray method, a nozzle is used to first blast air into the hole, then apply a tack coat, and finally to inject heated asphalt. A coat of heated aggregate is added at the end.
Spray patching can be used to effectively address potholes on surface-treated roadways, but the durability of the repair is “dependent on the quality of the aggregate and the curing of the asphalt emulsion,” the report points out.
“Colder temperatures can affect the curing process and dry aggregate may be difficult to access during the winter months.”
Infrared patching involves heating the surface surrounding the pothole to a high enough temperature — about 190 C — that it can be reworked with hand tools, then augmented with additional asphalt and/or an asphalt rejuvenator.
“Infrared is generally a more costly repair,” staff write. “Colder air temperatures affect the equipment’s ability to reach the temperatures required to heat and rework the asphalt; therefore the time it takes to complete the repair can result in loss of productivity.”
The city’s roads department currently has a small infrared device that is used for small patches and to level off asphalt around structures.
Each patching technique requires its own type of equipment, some more costly to acquire than others.
Hot boxes — the colloquial term for an asphalt heater or recycler — are used to transport asphalt to various locations year-round while maintaining a temperature of up to 150 C.
The city currently has five hot boxes, each of a two-tonne capacity, that are mounted on a trailer and towed by a truck. Other versions are mounted on a truck and can hold up to eight tonnes.
“When utilizing a two-tonne trailer-mounted hot box, there can be significant crew down time depending on the distance to the pothole repair area and where the crew refills the hot box with more asphalt,” the report notes. “The benefit to the truck-mounted hot box would be the ability to carry more material, reducing down time.”
This would be a bigger investment, however. Whereas a four-tonne trailer-mounted hot box will cost approximately $50,000, a self-contained all-in-one unit would cost about $250,000, including the truck, staff indicate.
Spray patchers can be either trailer-mounted or self-propelled with an aggregate hopper.
The self-propelled spray patcher is a two-person operation, including traffic control requirements. Repairs are performed from the truck cab with minimal disruption and the road can be opened to traffic immediately upon the completion of the repair.
Self-propelled spray patchers vary in capacity and may carry eight tonnes of aggregate. They provide a relatively quick pothole repair using a spray-injection system.
Rear-mounted boom systems are also available; these are operated and controlled from the ground.
Depending upon options required, a trailer-mounter spray patcher might cost approximately $100,000, and a self-propelled all-in-one spray patcher approximately $300,000.
Manufacturers of infrared equipment offer different-sized equipment and configurations to fit repairs of differing size and shape.
Larger infrared road repair units are mounted on a truck with space for a hot box, propane tanks, hand tools, compaction equipment and rejuvenator tank storage, while smaller units may be loaded and transported by trailer.
“Infrared road repairs are generally suitable for shallow-surface distress-patch repairs up to 50 to 75 mm in depth,” the report indicates.
“An advantage of the infrared road repair method is that it recycles asphalt, compared to removing and replacing distressed pavement areas and replacing with new asphalt.”
Repairs can take over 20 minutes, depending upon the size of the repair area, but generally it will result in a more durable patch.
“The result is a sealed surface preventing water penetration that may cause additional damage, providing a longer-lasting repair,” staff write.
Trailer-mounter infrared units can cost in excess of $50,000, while self-propelled all-in-one infrared units can cost in excess of $300,000.
There is also the option of an automated pothole repair unit.
“When compared to conventional hot-box repair systems, this equipment does not require the operator to leave the cab to complete the repair,” staff point out.
The operator has a good view of the repair area from the cab and just one other person is needed to carry out the work.
“This equipment can dispense either hot- or cold-mix asphalt that is maintained at the desired temperature and repairs potholes typical to the throw-and roll technique,” the report states. “To complete detailed patching, a separate municipal tractor equipped with a grinder would be required.”
Depending upon the options required, an automated self-propelled pothole patcher will cost about $350,000 to $400,000.
A pothole repair study is currently underway to monitor the effectiveness of the various materials and techniques that are currently available, staff note, as well as any new pothole repair equipment or technology that is on the horizon.