Johnson, Gregory D.

An Otta seal is an asphalt surface treatment constructed by placing a graded aggregate on top of a thick application of relatively soft bituminous binding agent. Minnesota has used emulsified asphalt exclusively (HFMS-2s); it could be constructed with cutback asphalt if desired. The binder works its way into the aggregate with rolling and traffic. In comparison to other surface treatments, material and construction specifications are not as strict. Local aggregates that would not meet the requirements for high quality paving aggregate are often used in Otta seals.

Minnesota’s temperature changes over a wide range on a daily and a seasonal basis. Our roads are expected to perform without major distress over this range of temperature extremes. The effects of temperature cause thermal stress, warping and curling and joint design for Portland Cement Concrete (PCC), and freezing/thawing of moisture sensitive materials. Temperature is one of the most basic pieces of information needed to design a pavement. Temperature is used to specify Performance Grades (PG) for asphalt binders, timing of spring load limits, base thickness for frost free design and modeling parameters for pavement performance and design. This report provides a summary of the various temperature phenomena seen in select the pavement systems. All data is from the Minnesota Road Research Project (Mn/ROAD), located in south central Minnesota. All available data was not analyzed for this report, but rather a few selected cells were analyzed. Therefore, the temperature extremes may not be the exact maximum or minimum for all the cells that were monitored, but should be within a few degrees.

Rises in construction and asphalt binder costs, as well as the growing pressures on landfills, have contributed to the increased use of tear-off scrap shingles (TOSS) and manufacturer waste scrap shingles (MWSS) into hot-mixed asphalt (HMA) pavement mixtures. This research project was undertaken to address the responsible incorporation of recycled asphalt shingles (RAS) into HMA pavement mixtures to ensure environmental benefits are realized and pavement durability is retained or improved. The research consisted of a literature review, extensive laboratory testing and field evaluations of in service RAS/RAP HMA pavements. Binder testing established a strong correlation between the new asphalt binder to total asphalt binder ratio and the extracted high/low binder performance grade temperatures. Dynamic modulus testing on HMA mixtures proved to be an invaluable tool in comparing the effects of RAS and RAP on mixture properties across a wide range of temperatures. Field performance appeared to validate the laboratory findings in some instances.

This report describes a research project that provides Minnesota counties, and townships with information and procedures to make informed decisions on when it may be advantageous to upgrade and pave gravel roads. It also provides resources to assist county and township governments in explaining to the public why certain maintenance or construction techniques and policy decisions are made. The research involved three major efforts. The first is a historical cost analysis based on the spending history for low volume roads found in the annual reports of selected Minnesota counties. The effects of traffic volume and type of road surface on cost was included in the analysis. The second was the development of a method for estimating the cost of maintaining gravel roads, which is useful when requirements for labor, equipment and materials can be predicted. The third is the development of an economic analysis example that can serve as a starting point for analyses to aid in making specific decisions. Additional information was gleaned from numerous interviews with local road officials. Maintenance and upgrading activities considered included: maintenance grading, re-graveling, dust control/stabilization, reconstruction/re-grading, paving, and others. As part of this report, an analysis is developed that compares the cost of maintaining a gravel road with the cost of upgrading to a paved surface. This analysis can be modified to address local conditions. Such an analysis may be used as a tool to assist in making decisions about upgrading a gravel road to a paved surface.

This project focuses on the second construction phase of the Minnesota Road Research facility (Mn/ROAD) and evaluates three typical, locally available, surfacing aggregates along with a rollover section from the initial phase for performance. The project results indicate that the adsorption test did not predict the performance of the sections in this experiment. All of the aggregates were characterized as marginal in terms of moisture and frost susceptibility. The sections with the greatest percentage of fines typically performed better than sections with a low percentage of fines. The Minnesota Department of Transportation issued a technical memorandum to change the specification from 0-15% to 8-15% passing the No. 200 sieve for Class 1 surfacing aggregate. The project also compared freezing and thawing rates on the aggregate sections to nearby hot mix asphalt (HMA) sections. Soil at any particular depth froze four to five days before HMA sections. The aggregate sections also thawed at exponential slower rates as depth increased from 11 to 35 days, which means that an aggregate surfaced road will freeze sooner and thaw slower than an HMA surfaced road. This information impacts the management of spring load restrictions and winter load limits.