Evaluation of Otta Seal Surfacing for Low-volume Roads in Iowa, Phase II Study: Comprehensive Laboratory Evaluation and Characterization and Full Scale Field Implementation

Project Details



18-665, TR-753






Iowa Department of Transportation
Iowa Highway Research Board

Principal Investigator
Halil Ceylan

Director, PROSPER

Co-Principal Investigator
Sunghwan Kim

Associate Director, PROSPER

About the research

Iowa has over 71,000 miles of unpaved secondary roads carrying very low daily traffic volumes, but frequently supporting heavy vehicle (i.e., farm equipment) movements. Iowa’s county road departments spend over $110 million annually for aggregate replacement on gravel roads alone. The excellent performance of Otta seal recently has greatly gained the interest of road engineers who are always in search of a more economical approach for low-volume road repair.

However, before the initiation of Phase I of this IHRB-sponsored study, only two states in the United States (Minnesota and South Dakota) had reported Otta seal construction experiences, while county engineers in Iowa desired to implement this technology to verify its short- and long-term performance.
Based on the Phase I research findings, the project Technical Advisory Committee (TAC) recommended an expanded Phase II study to address the following crucial questions for using Otta seal technique in new construction and rehabilitation projects for Iowa low-volume roads:

  • Can we use various local aggregate types in Iowa for Otta seal?
  • How to rationally determine the optimum application rates for binder and aggregate systems?
  • What road surface/base preparations are required before Otta seal application?
  • How to test and control actual field application rates?
  • How many number of passes are required for appropriate field compaction and how that should be determined?
  • What should be the time lapse between 1st and 2nd layer Otta seal layer placements (for double Otta seal) and how should this time lapse be calculated?
  • What are minimum requirements for aggregate layer thickness (with California bearing ratio [CBR] ranges for subgrade strength) to establish Otta Seal selection for an unpaved road?
  • What are minimum requirements (i.e., Pavement Condition Index (PCI) or Structural Number (SN) ranges) to identify candidates for Otta Seal placement on existing hot mix asphalt (HMA) pavements?
  • Can we use Otta seal layers as one of the holding strategy options?
  • Is it possible to use recycled materials (reclaimed asphalt pavement [RAP] or slag) as an aggregate system in Otta seal?