How Road Crews Fix Potholes in Winter
There’s more than one way to fix a pothole. Some fixes are temporary, some permanent, some were preventable – and maybe a type of bacteria is the future solution.
At midwinter in much of North America, transportation authority road crews are busy with pothole repairs. It’s a time of year when motorists call in a pothole (or use one of the apps, such as See Click Fix) to the city, county or state department of transportation to request a repair – which sets off a legal responsibility to smooth out that broken asphalt road.
Ideally, cracks and small potholes were repaired in the fall with crack sealer and permanent asphalt pothole filler. In some places microsurfacing (an all-over application of asphalt emulsion and finely crushed stone) or fog seals (a light application of a diluted, slow-setting asphalt emulsion) are used on roads riddled with cracks and deterioration. Preventing moisture from getting into the subsurface of the road is most economical. Once those crevasses experience the freeze-thaw cycles with water in and under the asphalt, they grow.
When those potholes pop up in winter, they are often only treated with temporary, “throw and go” loose asphalt. This is because a more permanent repair with standard hot-mix asphalt requires that all loose debris and moisture be absent from the hole to allow the new filler to affix to the surrounding surfaces. In the colder regions in the coldest months, asphalt plants shut down because hot mix can’t be delivered and applied in time before the mix cools. The exception to this is higher-quality cold mix, which can be used in wet environments and still adhere to the asphalt around it.
Just as weather conditions vary, so too do the means of fixing the pavement. There are many different types of asphalt being researched, as previously reported here on Pothole.info. Those innovations run the gamut from temporary bagged pliable material (like Silly Putty), using high-power leaf blowers to remove debris and moisture, and heating the surrounding area with infrared rays to improve the bond between existing asphalt and what is applied to fix a fissure.
Among the newer innovations is a bacteria-based solution that came out of Polytechnique Montreal. The bacteria, sourced from inside rocks near the harsh conditions around volcanoes, generates calcium carbonate when exposed to calcium salt. Together, the solid particles bond with sand and gravel to form a resilient bond. Early indications are it can withstand the abuse of heavy traffic better than traditional asphalt.
The bacteria might be used to reinforce concrete in buildings as well. Delft University of Technology in the Netherlands is experimenting with what they’re calling “self healing concrete,” embedding the bacteria in the building material in tandem with calcium lactate. When water invades the concrete through a crack, the bacteria, which can remain dormant for as long as 200 years, is awakened and secretes limestone that fills the crack. This only works on the smallest of cracks, about 0.8 millimeters wide, and is prohibitively more expensive than standard concrete.
Much more affordable for road repairs is permanent cold-mix, which can be applied in wet, winter conditions and does not require a second repair in warmer weather. So while potholes plague us most in present day winters, pothole seasons of the future might be shorter, smaller and fixed by little bugs instead of maintenance crews.