Lasting the Winter

Mar 05, 2015

“After four tough winters, it has fewer cracks than the hot-mix roads that we paved last year.” What county commissioner wouldn't want to be able to say that? 

The high today in Madison, Wisconsin is 30 degrees. The harsh winters and colder temperatures experienced in northern Wisconsin can have a significant negative impact on long-term performance of asphalt pavements. Cold weather contraction and brittleness of asphalt driving surfaces can result in cracking and other defects. Cities and counties in northwestern Wisconsin have been eager to experiment with WMA technologies for enhanced cold-weather performance and other advantages over traditional hot-mix asphalt, especially when Wisconsin has experienced some of the harshest winters on record.

In 2010, the Sawyer County Highway Department was the first agency in the region to utilize WMA with Evotherm supplied by Monarch Paving, a division of Mathy Construction Co. According to Gary Gedart, Sawyer County Highway Commissioner, improvements in pavements constructed with WMA have been calculable. While Sawyer County does not maintain crack-count data, Gedart observed that roads constructed with WMA have exhibited notably less cracking than Sawyer County roads paved with HMA. Additionally, with work that needs to be completed at colder ambient temperatures and with higher moisture content in aggregates, Gedart added that Evotherm is essential to assure proper coating of aggregate.

Last year's long winter and cold temperatures, combined with a wet May and June, resulted in a 2014 paving season that went well into October. This made the improved cold-weather compaction properties of Evotherm an important quality for Sawyer County paving crews. Having used warm mix successfully for more than four years, Sawyer County has made WMA their asphalt material of choice. 

“We’re very happy with it. We only bid warm mix this year (2014) for the first time. Our crews like working with it, and it’s more environmentally friendly,” Gedart said.

Neighboring Washburn County noted the pavement improvements seen in Sawyer County and followed suit. Jon Johnson, Washburn County Commissioner, was concerned with the performance of his asphalt pavements when it came to transverse cracking, so he decided to try something new. 

As a result, Johnson selected a section of Washburn County Road A that had exhibited problems with cracking of the asphalt-driving surface. This project was paved in cool ambient temperatures, ranging from the upper 30s to low 40s.  

“The asphalt rolled out good and set up great. The warm-mix asphalt with Evotherm had better density and easier compaction than hot-mix asphalt laid in the middle of the summer,” Johnson said.

An inspection of the work on County Road A conducted the following spring revealed that there had been a significant decrease in thermal cracking. Johnson observed that the warm-mix roads have exhibited roughly 50% fewer cracks per a given length of roadway than roads paved with hot mix. Of the crack performance on the County A project, he stated, “After four tough winters, it has fewer cracks than the hot-mix roads that we paved last year.” 

Johnson also believes that the key to better crack resistance is that, by using a warm-mix additive such as Evotherm, the asphalt cement is not subjected to the accelerated aging effects of the high temperatures required in the hot-mix process. The lower temperatures have resulted in other benefits as well. Johnson noted, “Our operators like it because there are less emissions at the paver.”

To learn more, check out the February issue of Roads & Bridges


Author: Courtney Sullivan