Cities and counties need affordable pavement preservation treatments, but preservation strategies are often geared towards higher-volume roads. The Minnesota Local Road Research Board has developed new guidance on five lower-cost treatments that is more applicable to local agencies and can be used to preserve pavements based on the type and severity of pavement distress.

What Was the Need?

MnDOT maintains flexible pavement preservation guidelines in the MnDOT Pavement Preservation Manual; however, many of the treatments described—such as ultra-thin bonded wearing courses or micromilling— are often better suited to high-volume roads than low-volume roads. The strategies don’t always meet the scale and resources of locally managed road systems with extensive preservation needs.

The Minnesota Local Road Research Board (LRRB) decided to develop pavement preservation guidance tailored to local transportation agencies that offers the technical details, costs and benefits on a range of options for preserving low-volume pavements.

“This guidance provides a clear understanding of what pavement preservation treatments are available to local agencies, what’s involved in specifying them and the work involved in applying the treatments,” said Joel Ulring, pavement preservation engineer, MnDOT Office of Materials and Road Research.

What Did We Implement?

Investigators developed guidance for five selected treatments, which are included in an update of the MnDOT Pavement Preservation Manual and listed below from highest to lowest cost:

• Rejuvenators. Asphaltic or agriculturally developed liquid sprays are applied to distressed pavements. These products return some flexibility to asphalt roads that have become brittle from oxidation.
• Scrub seals. This treatment uses a sled fitted with brooms at different angles that scrub a polymer-modified rejuvenating emulsion into asphalt, followed by a fine aggregate in a product similar to a chip seal. These seals can return flexibility, toughness and durability to pavements.
• Slurry seals (emulsion and aggregate). Applied in a single pass, slurry seals treat raveling and oxidation, improve surface friction, seal pavement and fill minor irregularities.
• Thinlays. These thin asphalt overlays range from 5/8 inch to 1 inch thick. Thinlays can improve ride quality and address raveling, oxidation and minor cracking.
• Cape seals. This two-step treatment of a chip seal and a slurry or microsurfacing cover protects pavement from moisture, oxidation and raveling; fills ruts and some cracks; and improves ride quality and skid resistance.

Detailed descriptions of each treatment are provided in the updated manual and include specifications, applicable pavement conditions, costs, treatment procedures and photographs, crew needs and construction considerations. Minnesota local agencies that have experience using the treatment are also listed.

How Did We Do It?

Following a literature review of pavement preservation techniques suitable for local road systems, researchers worked with the Technical Advisory Panel to identify potential treatments and gather information about the technology, specifications, construction considerations and relative cost.

The project team also surveyed transportation agencies in 87 counties and approximately 150 cities in Minnesota to identify technologies used by these agencies and gather information about their experiences with the treatments. From this information, investigators selected five accessible techniques to add to the local agency preservation toolbox.

What Was the Impact?

Investigators worked with LRRB and MnDOT to incorporate the information into the MnDOT Pavement Preservation Manual. The revised manual was posted online in early 2020.

“Pavement preservation is always evolving. This recent LRRB project leverages the MnDOT Pavement Preservation Manual to provide local agencies with a quick reference guide to five relatively new preservation techniques,” said Michael Marti, principal, SRF Consulting Group, Inc.

Four treatments are presented in a chapter dedicated to local agencies. The fifth treatment—thinlays—is included in a discussion of flexible pavement treatments used statewide. A treatment selection matrix was also developed.

What’s Next?

The Minnesota Local Technical Assistance Program may develop training and workshops on techniques described in this study. Research on rejuvenators and other treatments will continue to identify products and practices that keep road crews and agency engineers abreast of the latest approaches and techniques.

This post pertains to Report 2020RIC02, issued as a new Chapter 6, Other Pavement Preservation Techniques—Local Government Focused, of the MnDOT Pavement Preservation Manual in February 2020.