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In this project, researchers examined the current practices that local agencies use and evaluated the thickness design procedures by comparing predicted lives for the current designs with those obtained from the mechanistic-empirical design procedure ROADENT. Researchers determined current practices by sending a questionnaire to all cities and counties and visiting two counties and one city. In general, the questionnaire responses show that cities and counties use a variety of practices for the design, construction, and management of low volume pavements in Minnesota. Relative to the current designs, ROADENT predictions of fatigue behavior require a thicker design for medium and high-traffic roads than the Soil Factor design, and a thicker design for high-traffic roads than the R-Value procedure. The required thicknesses based on development of rut depth are not consistent with the current designs. To develop consistent procedures for the design, construction, and management of low volume roads in Minnesota, the report recommends converting the differences in performance predictions to thicknesses through the use of existing procedures and the mechanistic-empirical procedure; developing a best practices manual; and implementing the design procedure and manual.

This report documents the research that incorporated reliability analysis into the existing mechanistic-empirical (M-E) flexible pavement design method for Minnesota. Reliability in pavement design increases the probability that a pavement structure will perform as intended for the duration of its design life. The report includes a comprehensive literature review of the state-of-the-art research. The Minnesota Road Research Project (Mn/ROAD) served as the primary source of data, in addition to the literature review. This research quantified the variability of each pavement design input and developed a rational method of incorporating reliability analysis into the M-E procedure through Monte Carlo simulation. Researchers adapted the existing computer program, ROADENT, to allow the designer to perform reliability analysis for fatigue and rutting. A sensitivity analysis, using ROADENT, identified the input parameters with the greatest influence on design reliability. Comparison designs were performed to check ROADENT against the 1993 AASHTO guide and the existing Minnesota granular equivalency methods. Those comparisons showed that ROADENT produced very similar design values for rutting. However, data suggests that the fatigue performance equation will require further modification to accurately predict fatigue reliability.

Asphalt mixture variations that result from moisture fluctuations in aggregate stockpiles pose a serious problem at dryer-drum plants. The moisture content of a stockpile is infrequently measured, if at all. If the proportion of aggregate is not adjusted to account for its moisture content, an improper mix will result. This project looked at identifying a practical and accurate field method or probe for measuring the moisture content of aggregates, testing the probe in a hot-mix plant, and developing a control strategy for asphalt oil addition to the mix. Researchers identified a suitable commercial probe by reviewing past research and conducting laboratory studies. Testing in the plant showed that this probe could rapidly measure aggregate moisture in plant conditions at the same level of accuracy as gravimetric measurements. Researchers also developed a control strategy for the asphalt oil addition. Testing showed the effectiveness of this control, in conjunction with commercial probe moisture measurements in the feed bin. A problem with probe operations robustness was identified.

This report presents information about the use of the mechanistic-empirical procedure (MnPAVE) in designing hot-mix asphalt pavements in Minnesota. Researchers developed the MnPAVE software program using information from the Minnesota Road Research Project (Mn/ROAD) test facility and from 40-year-old test sections around Minnesota. MnPAVE procedures use Equivalent Standard Axle Loads (ESALs) to evaluate traffic loading, and the report includes methods to estimate these values for design purposes over a 20-year design life, as well as a procedure to measure vehicle type distributions. In addition, the report presents an evaluation of subgrade soils for each thickness design procedure, summarizes Minnesota Department of Transportation specifications that relate to embankment soil construction and to construction of the pavement section materials, and recommends specific density or quality compaction using a control strip. It also includes best practices on setting up projects most effectively to follow specifications.

This report investigates the low temperature behavior of asphalt pavements based on experimental results obtained for three mixtures used in the construction of cells 33, 34, and 35 at Mn/ROAD facility as well as field information acquired over the years at Mn/ROAD. As a result of this research a new test method was developed to determine the low temperature fracture properties of asphalt mixtures based on tests performed on semi circular specimens tested in bending. This method can be used to select materials with better fracture resistance and therefore better performance in the field. Two models were developed to predict the low temperature cracking performance of asphalt pavements. The first model predicts the crack spacing in asphalt pavements exposed to low temperatures based on continuum mechanics and the frictional restraint provided by the aggregate base. The second model predicts the accumulation of damage and the propagation of the crack through the asphalt layer as temperature drops based on cohesive zone model.

Poor compaction can lead to early deterioration of an asphalt pavement. It often happens when paving occurs during adverse weather conditions. Yet, in Minnesota, paving must often occur under adverse conditions. A new tool now simulates the cooling of an asphalt mat behind the paver under a variety of environmental conditions. The software, PaveCool Version 2.0, offers users insights into how adverse climate conditions will affect their ability to produce a durable, quality road surface. Users input the type of existing surface, type of asphalt mix, and weather conditions. The output shows a cooling curve with recommended compaction starting and stopping times. Field tests confirm the value of this program as an aid to cold weather paving. A Windows program, PaveCool 2.0 runs on laptop computers (Windows 95, 98, or NT required). This report documents the study of thermal properties and compactibility of hot-mix asphalt, related laboratory tests on the thermal diffusivity and thermal conductivity of hot-mix asphalt at typical compaction temperatures, a literature review, and testing results. It also includes a copy of the PaveCool Version 2.0 software.

This report documents the development of a mechanistic-empirical (M-E) flexible pavement thickness design method for use in Minnesota. The report includes a comprehensive literature review of the state of the practice. The Minnesota Road Research Project (Mn/ROAD) served as the primary source of data, in addition to information from the literature, during the development of the method. The mechanistic pavement model, WESLEA, provided reasonably accurate pavement response data and was chosen as the model for Minnesota. Pavement material properties and traffic loads were characterized using Mn/ROAD data. These characterizations were used both as input to WESLEA and to calibrate pavement performance equations to Minnesota conditions. The two modes of distress considered in this method are fatigue cracking and rutting. Fatigue performance is a function of tensile strain at the bottom of the asphalt concrete layer while the rutting is a function of compressive strain at the top of the sub grade. It was recommended that load spectra be used to characterize traffic. The computer program, ROADENT, resulted from this research. An interactive design tool, the program runs in a Windows environment. The report includes a user's guide.