InTrans / Jan 15, 2020

Otta seal research shows it to be economic surfacing option for low-volume roads

Otta seal construction process: binder spraying, aggregate application, and rolling compaction

County roads departments in Iowa spend more than $110 million per year maintaining the over 71,000 miles of unpaved, gravel road surfaces in the state.

Otta seal surfacing, a technology used throughout northern Europe and Africa, offers a low-cost solution to county road engineers. Until recently, however, the technology had not been tested in Iowa.

Halil Ceylan, a professor in Civil, Construction and Environmental Engineering and director of the Program for Sustainable Pavement Engineering and Research (PROSPER) at InTrans, has been studying the issue for the past few years to determine both the feasibility of using Otta seals in the state and their cost-effectiveness.

“We can provide a better surface for around the same investments,” said Ceylan during a workshop on Otta seal. “Otta seal can be utilized as an alternative rehabilitation strategy to both unpaved roads and deteriorating road infrastructure systems.”

The initial Iowa test was on a Cherokee County hot-mix asphalt roadway, which had been treated with crack seal, in 2017. Since then, the project has expanded to include at least 40 segments in six Iowa counties (Buchanan, Cherokee, Humboldt, Louisa, Ringgold, and Winneshiek) and seals were completed on both gravel roads and deteriorating portland cement concrete pavements.

One of the more recent test sites had county staff and equipment complete the work, rather than using a contractor as the other test sites had employed.

The process involves binder spraying the roadway, then aggregate application, and rolling compaction. The process is typically done twice on a stretch of roadway about two weeks apart and sweeping before the second application. Ceylan emphasizes the importance of base stabilization before Otta seal application and proper compaction and applying the right rates of binder and aggregates for long-term successful performance of Otta seal technology.

Ceylan stresses that communication with communities is key, particularly when using Otta seal surfacing on non-gravel roads as the process does initially leave roadways looking like they’re gravel but over time do resemble an asphalt road. International Roughness Index (IRI) tests bear out that the ride on an Otta seal surface is smoother than gravel roads.

More information is available on the LTAP site from a series of recordings at an Otta seal workshop. More details on Ceylan’s research can be found here for the completed Phase I study and here for the ongoing Phase II study.