The U.S. Army Cold Regions Research and Engineering Laboratory (CRREL) conducted resilient modulus tests on materials from the Mn/ROAD test site for the Minnesota Department of Transportation. Materials tested included samples of the lean clay subgrade at the site and the two extreme grades of base designed specifically for Mn/ROAD. Some specimens were tested in both frozen and subsequently "thawed" conditions; others were tested at room temperature without ever having been frozen. Researchers performed inear regression analysis on the data to develop equations that predict frozen modulus based on unfrozen water content and unfrozen modulus based on stress, degree of saturation and density. We also reanalyzed data from two previously tested materials. CRREL can use the study' s equations in the Mechanistic Pavement Design and Evaluation Procedure under development at CRREL to predict estimated damage in some Mn/ROAD test sections.
The U.S. Army Cold Regions Research and Engineering Laboratory is developing a mechanistic pavement design procedure for use in seasonal frost areas. The procedure was used to predict pavement performance of some test sections at the Mn/ROAD facility. Simulations were conducted in three phases, investigating the effects on predictions of water table position. subgrade characteristics, asphalt model, and freeze season characteristics. The procedure predicted significantly different performance by the different test sections and highly variable results depending on the performance model implied. The simulated performance of the tests sections also was greatly affected by the subgrade conditions, e.g., density, soil moisture, and water table depth. In general, predictions for the full-depth asphalt sections indicate that they will not fail due to cracking, but two of the three criteria for subgrade rutting indicate failure before the five- or 10-year design life of the sections. Conventional sections are predicted not to fail due to subgrade rutting; however, sections including the more frost-susceptible bases in their design are predicted lo fail due to asphalt cracking relatively early in their design life, and sections with non-frost-susceptible bases are predicted to fail towards the end of the design life.
Between January 1990 and December 1994, a study verified and applied a Corps of Engineers-developed mechanistic design and evaluation method for pavements in seasonal frost areas as part of a Construction Productivity Advancement Research (CPAR) project between the Minnesota Department of Transportation (Mn/DOT) and the U.S . Army Cold Regions Research and Engineering Laboratory (CRREL). The study involved four primary components. Mn/DOT constructed a full scale pavement test facility adjacent to Interstate 94, referred to as the Minnesota Road Research Project (Mn/ROAD). CRREL performed extensive laboratory tests on the base and subgrade materials from Mn/ROAD to characterize them and their behavior under seasonal frost conditions. Laboratory tests provided the input parameters necessary for the study' s third component, modeling with the CRREL Mechanistic Pavement Design and Evaluation Procedure. The modeling effort was conducted in three phases, which investigated the effects of freeze season characteristics, water table position, asphalt model and subgrade characteristics on the predicted performance of selected Mn/ROAD test sections. Delays in construction on the Mn/ROAD facility prevented the completion of the study's fourth component--using performance data from Mn/ROAD to validate the mechanistic pavement design and evaluation procedure. The report details results from the other three components.
The U.S. Army Cold Regions Research and Engineering Laboratory (CRREL) conducted various laboratory tests on pavement materials from the Mn/ROAD facility. The tests helped to characterize the behavior of materials under season frost conditions, and to provide input necessary for modeling the materials with the Mechanistic Pavement Design and Evaluation Procedure under development at CRREL. This report describes test results that define the physical characteristics, such as grain size, specific gravity, Atterberg limits, organic content, and compaction, as well as hydraulic properties, such as moisture retention and hydraulic conductivity, frost susceptibility, and unfrozen moisture content of two subgrade samples and two base materials from Mn/ROAD.
