Microsurfacing Mix Design Evaluation

Microsurfacing treatments are becoming more prevalent in North Carolina as a preservation treatment and pavement surfacing option. Microsurfacing treatments are placed by spreading a mixture of dense graded aggregate, polymer-modified asphalt emulsion, water, and mineral fillers in a layer that is usually 0.4 to 0.5 in. thick. This treatment is typically applied over an existing pavement surface as preventive maintenance. Such treatments, when properly applied, provide pavement life extension of between 7 to 9 years. In addition, as the recent RP2024-12 project has shown, microsurfacing can also have substantially higher macrotexture and friction values than traditional dense graded mixes. These improvements may lead to reduced crash rates and safer roadways. The use of microsurfacing in North Carolina is still relatively new and as a result, the current North Carolina Department of Transportation (NCDOT) special provision for microsurfacing design have been borrowed largely from the guidelines developed by the International Slurry Surfacing Association (ISSA). However, there are some limitations with this approach: these guidelines are not adapted to account for North Carolina aggregate specifications, they are not adapted to the specific performance concerns in the State, and they do not address functional performance. To address these state-specific concerns, a revised set of mix design guidelines, notably gradations, need to be developed. In light of this need, the proposed research plan will seek to achieve three objectives: (1) establish a North Carolina specific microsurfacing mix design procedure, (2) recommend microsurfacing finishing practices for improved pavement surface texture and friction, (3) and develop documentation to support further microsurfacing deployment. These objectives will be met with six tasks: literature review to update the reviews completed under RP2024-12 with any new findings or information; review existing stockpile and gradation data from NCDOT approved sources; conduct experiments to evaluate the sensitivity of microsurfacing performance to mix design; conduct experiments to evaluate the effect of surface preparation methods on microsurfacing macrotexture and friction; update NCDOT special provisions with respect to mixture design and approval based on findings from previous tasks; and prepare a final report summarizing the methodology, results, and recommendations. The primary outcome of the proposed research will include mixture design and finishing recommendations for microsurfacing, which will allow NCDOT engineers and their contractors to design cost effective and high performing microsurfacing. The research results are thus anticipated to improve overall pavement performance by increasing service life, improving pavement skid resistance (where possible), and reducing life cycle costs. This research will produce two key outcomes towards NCDOT Strategic Goals; (1) preserve existing pavement structures that are in overall good condition and (2) improve the surface texture and friction of an existing roadway. The research outcomes will provide the data and guidelines for expanded implementation of microsurfacing.

Language

• English

Project

• Status: Active
• Funding: $339,931.00
• Contract Numbers:

  RP2026-11

• Sponsor Organizations:

  North Carolina Department of Transportation

  Research and Development
  1549 Mail Service Center
  Raleigh, NC  United States  27699-1549
• Managing Organizations:

  North Carolina Department of Transportation

  Research and Development
  1549 Mail Service Center
  Raleigh, NC  United States  27699-1549
• Project Managers:

  Kadibhai, Mustansir

• Performing Organizations:

  North Carolina State University, Raleigh

  Department of Civil Engineering, Campus Box 7908
  Raleigh, NC  United States  27695-7908
• Principal Investigators:

  Underwood, B

• Start Date: 20250801
• Expected Completion Date: 20270731
• Actual Completion Date: 0
• USDOT Program: Pavements and Materials

Subject/Index Terms

• TRT Terms: Mix design; Pavement maintenance; Surface course (Pavements); Surface treating
• Geographic Terms: North Carolina
• Subject Areas: Design; Highways; Maintenance and Preservation; Materials; Pavements;

Filing Info

• Accession Number: 01957961
• Record Type: Research project
• Source Agency: North Carolina Department of Transportation
• Contract Numbers: RP2026-11
• Files: RIP, STATEDOT
• Created Date: Jun 13 2025 12:17PM