This report presents the results of two field evaluations in rural Minnesota counties to investigate the development of bumps in asphalt overlays. The primary objective was to identify crack sealant types, reservoir geometries, and construction methods that provide a higher probability of avoiding the occurrence of bumps in an asphalt overlay. One field site evaluated various crack sealant methods and materials while holding construction methods constant, and the other site evaluated different construction practiced intended to prevent bumps while utilizing constant crack sealant methods and materials, as well as other overlay preparation methods. The results of this research indicate that there are specific types of sealant materials and methods (type of sealant, reservoir geometry) as well as specific construction activities (rolling pattern, roller type, mat temperature at rolling) that can have great impact on the formation (and prevention) of bumps in asphalt overlays.
This report describes the work conducted across the State of Minnesota to determine if an update to the distribution of the classification of vehicles on the County State Aid Highway (CSAH) system is needed. The data were collected across the state, representing many regions, and in all seasons (although very few counts were conducted during winter). The results of this investigation include the development of updated vehicle classification tables for pavement design on the CSAH system, a manual for counties to use when conducting individual vehicle classification counts for pavement design, and a new view of the distribution of vehicle types on the CSAH system, which has not been systematically counted for many years. The results of this study indicate that the vehicle classification distributions on the CSAH system (and likely the county road system) should be updated with new default values to reflect current traffic. In addition, improved information and training should be offered to local agencies to help improve estimates of vehicle classification for pavement design.
This report presents the development of a combined smoothness specification for asphalt and concrete pavements and associated training for the certification of profiler operators by highway agencies. The report discusses the analyses conducted to develop appropriate levels of incentives and disincentives approximately equivalent to previous specifications, as a baseline. A brief survey of current practices by other states is also included. Appendices include the draft specification developed for this project, and the training materials that were presented in several workshops as part of the project. Features of the combined smoothness specification include the use of the International Roughness Index for smoothness assurance on all pavements, certification of profiler operators, uniform electronic data filenames, profile measurement in both wheel paths, the use of the ProVAL software (developed by FHWA), and areas of localized roughness calculated by ProVAL.
Many low-volume roadways in the county road system in the State of Minnesota consist of unpaved aggregate surfaces. It is the responsibility of the county engineer to make determinations regarding the design and maintenance of such roads and particularly for specific needs, such as weight restrictions. One method used by several counties in Minnesota is the construction of a bituminous-stabilized layer by adding several inches of new aggregate and stabilizing it with an engineered, water-based asphalt emulsion using mix-in-place methods. This report describes a design method providing highway engineers and their staffs with the technical backing needed for the designs selected. This report describes the design method for determining the required thickness of stabilized and unstabilized layers in this type of aggregate-surfaced road. This basic design method is based on the material properties and a correlation between layered-elastic analysis, dynamic cone penetrometer, and falling-weight deflectometer testing. The load rating analysis uses the Minnesota Department of Transportation methodology of estimating load rating on low-volume roads using falling weight deflectometer data. A software package is also presented which was developed as part of this project.
This report documents the development and preparation for implementation of a specification for using International Roughness Index, using an inertial profiler, as a smoothness measure for new portland cement concrete pavements in Minnesota. This new specification represents a departure from the use of the Profile Index, using a California Profilometer, for concrete pavement smoothness. In addition to providing recommendations to the Minnesota Department of Transportation regarding the implementation of the specification, the report contains additional information and analyses. These include a summary of the specifications in use by other states for measurement and incentive/disincentive payment for concrete pavement smoothness, an analysis of the effects of pavement surface characteristics on the International Roughness Index and the Profile Index, and a comparison of IRI-based concrete pavement smoothness specifications in use by other states. The report concludes with several recommendations for the new specification and for its administration and enforcement by the Minnesota Department of Transportation.
The development of small bumps in the surface of hot-mix asphalt overlays has been a problem for state and local highway agencies for many years. Sometimes these bumps are small and are not large enough to be felt by drivers. Under many conditions, however, they can be large enough to cause ride-related problems at normal operating speeds. Under this project, a survey was conducted of local and state engineers in Minnesota responsible for highway construction and maintenance to compile corrective actions that they have used avoid these bumps and to mitigate their effects if they occur. Instrumentation sites were incorporated into this project to determine the magnitudes and profiles of temperature in the existing asphalt layer when a new layer of hot asphalt is placed on top of it. The instrumentation sites were also used to gain further information on the common practices of highway construction personnel in reducing the probability of bumps, and mitigation efforts if bumps occur. This report describes the survey, site visits, construction instrumentation, laboratory studies, and evaluation conducted by the project team. It also presents a draft booklet compiling the common practices for avoiding and mitigating bumps gathered throughout the project.
