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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.

Highway embankment construction progresses vertically in stages, beginning with the subgrade. For a variety of reasons, it is desirable to use naturally occurring soils for subgrade material. In some cases this is not possible due to poor soil conditions; in order to avoid realignment it is necessary to improve the subgrade material. A review of literature provides background for special construction methods to be used for subgrade soil enhancement. Additional information about modification, stabilization, reinforcement, and substitution methods and materials was gathered from a questionnaire directed to Minnesota state, county, and city highway engineers. Based on questionnaire response, a series of highway agency interviews were conducted to provide more detailed information about the enhancement methods. Enhancement selection recommendations and special practice methods for construction were developed from the agency interviews, questionnaire responses, and literature review.

This report considers the Asphalt Pavement Analyzer (APA) as a tool for evaluating the rutting susceptibility of Minnesota Hot Mix Asphalt (HMA). Its authors analyze the 25 responses to a questionnaire sent to members of the APA Users' Group and conduct a literature review. Based on this evidence, they recommend that the Minnesota Department of Transportation purchase an APA. The tool provides a measure of rutting susceptibility; is reasonably reliable and repeatable; and has been used by over 60 agencies and contractors. In addition, procedures for conducting tests are available in ASTM and AASHTO formats and the Users' Group provides a forum for discussion and support.

This report presents the results of laboratory testing to validate the use of Fine Aggregate Angularity (FAA) measurements with the Superpave method of Hot Mix Asphalt (HMA) design. A search of literature and Minnesota FAA data was conducted in preparation for FAA testing of aggregates and HMA design. Laboratory tests of aggregates included sieve analysis, specific gravity and FAA. Additional work was also performed by acquiring digital imaging data for the aggregates. Testing of asphalt mixtures included dynamic modulus tests and asphalt pavement analyzer tests. Testing was performed on four asphalt mixtures representing a range of Minnesota FAA values. Dynamic modulus testing was performed at three temperatures and five frequencies. Data from the dynamic modulus tests were processed using nonlinear regression. The resulting master curves of dynamic modulus vs. frequency were referenced to test temperature 54C. Asphalt pavement analyzer data at 54C was analyzed with respect to rutting curve. Laboratory test results for aggregates and mixtures were analyzed together using statistical methods to develop correlation coefficients and linear trends. It was found that dynamic modulus and rut resistance values are strongly related to aggregate blend FAA. Some additional parameters from digital imaging also predicted modulus and rut resistance very well and should be included in future reference.

Recycled Asphalt Shingles (RAS) include both manufacture waste scrap shingles (MWSS) and post-consumer tearoff scrap shingles (TOSS). It is estimated that Minnesota generates more than 200,000 tons of shingle waste each year. Recently, a portion of this waste has been incorporated into hot-mixed asphalt (HMA) pavement mixtures. The current technology limits the amount of RAS in HMA to no more than 5 percent by weight. This leaves a lot of underutilized shingle waste material throughout the state. This has prompted MnDOT to investigate other potential uses RAS. One potential use is to improve the performance of gravel surfacing and reduce dust by replacing common additives such as calcium chlorides with RAS. This is especially relevant as gravel sources in Minnesota have been depleted and/or have declined in quality, which has affected the performance of gravel surfacing. These poorer quality fines can increase the amount of dust generated and increase the difficulty of keeping the roadway smooth. Some agencies have used dust control additives to help the performance of these lower quality gravels. Successful implementation has the potential of removing valuable RAS materials from the waste stream to supplement the use of more expensive virgin materials and improve the performance of local roads.

This report summarizes lessons learned in evaluating the bonding strength of hot mix asphalt (HMA) layers. Testing included: determining an optimal range for the bond strength of a tacked hot mix asphalt interface, and implementing the findings. The research method used a Florida Bond Test fixture along with a Marshall asphalt mixture testing load frame to evaluate tack bond shear strength and deformation. Specimens were obtained from state, county and city paving projects from around Minnesota. Results were compared to related research conducted in the United States. Recommendations for a tack bond test program: Equipment includes the Marshall load frame already used by many HMA laboratories, HMTS software or similar, and the Florida Bond Test apparatus. Follow Minnesota modifications of Florida Bond Test protocol. Compute the average and standard deviation of peak shear stress from specimen sets. Cores exhibiting layer separation during coring or during removal will be included in the specimen set and assigned a peak shear stress of 0 psi. Average peak shear stress will be 100 psi or greater. The standard deviation of peak shear stress will be 25 psi or less.

The construction and maintenance of highways creates a demand for high quality paving aggregates, which are becoming scarce in many parts of the country. Taconite industry waste rock and tailings are a potential new source of virgin aggregates. Currently there is limited information available for implementing these products in construction specifications. The goal of this project was to assess available taconite aggregate resources that could supply a high quality, low cost aggregate for roadway use, especially in areas where aggregates are becoming scarce.

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 summarizes lessons learned about the field and laboratory performance of the Recycled Asphalt Pavement (RAP) and Fractionated Recycled Asphalt Pavement (FRAP) test cells at the Minnesota Road Research Project (MnROAD) between 2008 and 2012. The project scope included: developing specifications for FRAP, construction of FRAP and RAP test cells at MnROAD, field performance evaluations, and laboratory testing of binders and mixtures. The project that monitored 11 test cells.

This report summarizes lessons learned about the field performance of local roads containing Recycled Asphalt Pavement (RAP) and associated field and laboratory work with asphalt activation as well as the design and performance testing of high-RAP bituminous mixtures. Transverse cracking performance of Minnesota county highways averaging 20-26% RAP was improved when PG 52-34 binder was selected over PG 58-28 or other binder grades. Testing of the activation of RAP asphalt binder in plant and laboratory settings showed that coarse aggregates from plant mixing achieved a more uniform coating and were subjected to less abrasion than those from laboratory mixing. Low temperature testing of laboratory mixture designs containing up to 55% RAP, and new-to-total asphalt cement ratios as low as 43%, found that indirect tensile test (IDT) creep stiffness increased along with RAP content. IDT critical temperature results showed that the addition of RAP significantly increased the critical temperature, predicting less crack resistance. Semi-circular bend fracture testing showed that the addition of RAP lowered the fracture energy and increased the fracture toughness of the mixtures, and the highest RAP contents had the most reduced fracture performance.