Johnson, Eddie N.

Expansion and maintenance of roadway infrastructure creates a demand for high quality paving aggregates. Taconite industry rock and tailings are a potential source of virgin paving aggregates. Currently there is limited information available for implementing these products in construction design specifications. Preliminary information of product performance within current design constraints is valuable to both state design engineers and to future pooled-fund studies. This information can identify the potential for using these products in surface courses or possibly for use in rich-bottom leveling layers. This study examined the viability of utilizing these products in the Minnesota Department of Transportation (Mn/DOT) Superpave bituminous mixture design specifications. As part of the study 40 laboratory specimens were produced from 11 asphalt mixtures and then evaluated for asphalt content, air voids, and aggregate gradation. This report summarizes the results of the laboratory mixture evaluation.

The pavement engineering community has recently been introduced to a number of nontraditional products intended for uses as surface sealers for bituminous pavements. Many new products use agricultural-based components and little is known regarding their effect on bituminous pavement performance. Several nontraditional and "bio-based" fog sealants were applied to bituminous shoulder sections less than two years old. A field evaluation was performed over a three-year period; and included documenting installation; application rates; equipment types; locations; and sampling of the product. Annual field reviews were performed; including tests of pavement marking reflectivity; friction; cracking; appearance; and permeability. Application rates varied from 0.015 to 0.10 gallons per square yard according to the product used. It was found that during the evaluation period; the applications provided various levels of waterproofing; and some test sections experienced less thermal cracking than the control. Nontraditional product applications did not adversely affect the long-term visibility of pavement markings or the overall pavement performance. Laboratory testing of pavement cores showed similar high- and low-temperature performance relative to the control.

The National Road Research Alliance (NRRA); a multi-state pooled-fund program; exists to provide strategic implementation of pavement engineering solutions through cooperative research. NRRA is led by an Executive Committee of state DOT partners; and supported by numerous agency and industry partner representatives. Members provide expertise to NRRA; from the selection of research topics; to communication; and implementation. NRRA consists of five project teams: Flexible; Rigid; Geotechnical; Preventive Maintenance; and Technology Transfer. The 2017 construction season at MnROAD saw construction of 35 new and unique pavement test sections. The sections; designed to address NRRA high-priority research topics; were conceived and planned by NRRA project teams. This report details development; design; and construction of each research project and the test sections supporting them. Individual study details are left to future reports generated by the individual research contracts and their respective teams.

The original concrete pavement test sections at the MnROAD facility, constructed in 1993, utilized older generation Minnesota concrete pavement mix designs. By 2011, several of the original concrete pavement test sections that remained in service began to exhibit materials related distress along the joints which required partial-depth repairs to keep them in service. This created an opportunity to evaluate both existing and new types of patching materials. This report describes the 3 year performance of 93 patches with 22 different materials. Subjective condition ratings, based primarily on visual observations, were made over the 3 year evaluation period. A sounding, using a ball-peen hammer, provided bond condition information for each patch in October 2014. Results were tabulated by MnROAD test cell number and patch material designation. Since patch performance can be affected by direct tire loading, tables organized by patch location and material type were also presented. Finally, a photographic record of each patch with condition ratings over time was included in the appendix. Overall, 55 of the 93 (59%) patches remained in good serviceable condition as of October 2014. The location of the patch did not seem to affect the performance significantly, with 61% and 67% of the patches in good condition near the center line and loaded areas, respectively. While they are not often used for modern projects, many of the slower setting and strength gaining products demonstrated a higher survivability rating.

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.

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 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.

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 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.

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.