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Asphalt mixtures are commonly specified using volumetric controls in combination with aggregate gradation limits; like most transportation agencies; MnDOT also uses this approach. Since 2010 onward; several asphalt paving projects for MnDOT have been constructed using coarser asphalt mixtures that are manufactured with lower total asphalt binder contents. Due to the severe cold climate conditions in Minnesota; there are concerns of premature cracking and inferior durability in asphalt mixtures with lower asphalt binder contents. This research project evaluated 13 low asphalt binder content mixes from 10 actual field projects to determine whether there is potential for poor cracking performance and high permeability. Assessment of field performance indicated an average of 7.75 years of life until 100% transverse cracking level is reached. The pavement structure played a significant factor in controlling the cracking rates. Thin overlays showed almost ten times inferior transverse cracking performance as compared to asphalt wearing courses on full-depth reclamation. Asphalt mixture volumetric factors did not show a statistically significant effect on cracking rates; however; the asphalt binder grade did show a strong effect. Eight out of the 13 coarse asphalt mixtures evaluated in this study have higher permeability than the typical dense graded asphalt mixtures. Performance evaluations using lab measured properties predicted poor thermal cracking performances. No discernable trends were observed between measured or predicted cracking performance and mix volumetric measures. Use of performance tests based on specifications for design and acceptance purposes is reinforced through this study.

Minnesota's local highway agencies are tasked with maintaining their low-volume road networks with available financial resources, prompting increased interest in lower-cost pavement rehabilitation alternatives. In-place cold recycling technologies, such as cold in-place recycling (CIR) and full-depth reclamation (FDR), provide lower-cost opportunities to renew deteriorated roads than traditional rehabilitation methods, particularly if surfaced with a thin surface treatment such as a chip seal (seal coat) or microsurfacing rather than hot-mix asphalt. However, the resulting road surface may not meet some road users’ expectations. This study investigated the performance and economics of four pavement rehabilitation alternatives involving recycling technologies. The alternatives included CIR and FDR treatments with either an asphalt overlay or thin surface treatment. Fifteen case study sections in Minnesota and neighboring states were selected for performance evaluation and lifecycle cost analysis (LCCA). Pavement condition surveys were performed to evaluate the study sections’ pavement distresses and roughness. The results indicated satisfactory performance for fourteen sections, while a CIR section with a chip seal surface using quartzite as cover aggregate had extensive transverse cracking. The cause of the distress is not clear. The LCCA results indicate a 14% to 42% lower lifecycle cost for CIR and FDR treatments with chip seal surfaces. Costs savings may be achieved if asphalt overlay thicknesses are reduced, though chip seal surfaces may be rougher and nosier and require more maintenance than asphalt overlays. A decision tree was developed to aid local agencies during the treatment selection process.

Two methods for calculating the aggregate surface areas, the Surface Area Factor and Index methods, are discussed in this research and the results are further used to compute an average asphalt film thickness in asphalt mixtures. Field performance data from six Minnesota routes and MnROAD, including both coarse and fine gradations, were analyzed to determine significant correlations between asphalt film thickness values and the performance of asphalt mixtures. The analysis showed that the asphalt film thickness is a significant factor affecting the rutting performance for asphalt mixtures. However, the pavement performance is also affected by many other factors such as traffic level and surrounding environment. More research work is needed to investigate the relationship between the asphalt film thickness and the other performance parameters of asphalt mixtures such as fatigue cracking.

Asphalt pavements deteriorate from temperature cycling, moisture, oxidation, and loading-related distresses. Pavement preservation is critical in maintaining the functional and structural integrity of roads and extending pavement life. Surface treatments can prevent or restore the aging effects by rejuvenating and/or sealing the pavement’s surface, limiting further damage, and restoring its flexibility. This collaborative study of MnDOT, the National Road Research Alliance (NRRA), and Iowa State University investigates the efficacy of fog seal/bio-fog seal topical treatments based on soy-derived rejuvenators, epoxidized soybean oil (SESO), and BioMAG, which contains SESO and the biopolymer poly(acrylated epoxidized high oleic soybean oil) (PAEHOSO). Each topical treatment is applied at three locations in different asphalt binder grades to provide a comprehensive approach to their impacts on the dry time, reflectivity, friction, and permeability of the pavement course. It is observed that the bio-fog seal treatments improve the skid resistance of the pavement, do not affect the reflectivity of pavement markings, and are able to restore the stiffness of the asphalt mixtures. Additionally, the fog seals show fast setting and curing and allows the road to be open to traffic in less than 30 minutes.

The density and air void content of asphalt mixtures affect the durability and performance of asphalt pavements. Pavement longitudinal joints typically have a lower density than the mat because they receive less compaction than the center section of the mat for various reasons. The higher air void percentages resulting from lower densities can lead to high permeability and allow water infiltration; which in turn can cause moisture-induced damage and decrease base and subbase support to the pavement; reducing pavement life. Void-reducing asphalt membrane (VRAM) has been used at the longitudinal joints of asphalt pavements to achieve higher densities and prevent moisture infiltration; thereby reducing deterioration at the longitudinal joints. VRAM is applied before the hot-mix asphalt (HMA) layer is placed and migrates into the HMA to fill 50% to 70% of the air voids. This research evaluated the extent to which J-Band; a VRAM product; increases density and improves performance. Field cores were collected from two sections; one with and one without VRAM. Asphalt mixture performance tests; including disk compact tension and semi-circular bend tests; and push-pull tests were carried out in the laboratory on the field-collected specimens. Volumetric measurements were also taken; and ground penetrating radar was used in the field. It was determined that the pavement sections with VRAM had a lower permeability; higher bond energy; and higher fracture energy than the pavement sections without VRAM.

The objectives of this study were to document the performance of roads using full-depth reclamation (FDR) and stabilized FDR (SFDR) in Minnesota; help develop SFDR design parameters appropriate for Minnesota; provide information on FDR/SFDR design procedures and specifications from beyond Minnesota; share current Minnesota FDR practices; and catalog the characteristics of some FDR/SFDR roads. A comprehensive literature review of FDR/SFDR projects and case studies was conducted; and an online survey was distributed to Minnesota local road agencies to determine the stabilizing agents used for SFDR projects. Eighteen FDR/SFDR test sections from eight counties were then selected for a case study; and performance data and core samples were collected for the sections. Minnesota gravel equivalency (GE) analysis was performed to back-calculate the granular equivalent factor for FDR/SFDR layers based on the design equivalent single axle loads (ESALs) and R-values for subgrade soils. The back-calculated GE values indicate that designers have likely been using GE values for FDR/SFDR layers that are consistent with current recommendations. It is recommended that the current GE values be generally retained for FDR/SFDR design. However; when slower-moving vehicles are the critical design consideration; relatively robust performance of FDR/SFDR layers may be expected. Visual distress surveys indicated that the FDR/SFDR bases studied are performing well in terms of destroying crack patterns that are often reflected through traditional hot mix asphalt (HMA) overlays. Therefore; decision makers may want to consider the use of FDR/SFDR as a base for reasons other than structural capacity.

Air void content, specifically at longitudinal joints, is a crucial factor affecting pavement life. Compaction affects the Air void content achieved, which directly impacts the performance of pavement, and thus has been identified as one of the most critical factors associated with the performance of flexible pavements. This study examines pavement historical data, constructs an air void performance database, and performs a statistical analysis on factors affecting air void content and then analyzes the effect of air void content on performance. Microsoft Access is used to create a database. JMP, a statistical software program, is used for the analysis of the data from the database created for 43 projects. Air void distribution is determined across and within the projects. An analysis of variance (ANOVA) analysis shows that binder content (%), aggregate size, voids in the mineral aggregate (VMA)%, film thickness, and the amount of reclaimed asphalt pavement (RAP) (%) significantly affect the air void content achieved. The air void contents achieved for most lots of the projects are found to be within the acceptable ranges of 4-8% immediately after construction. The correlation between air void content and the distresses observed for the pavement sections used in this work have R-square values below 0.20, which does not meet the recommended value of being equal to or greater than an R-square value of 0.70. However, from previous literature, National Center for Asphalt Technology (NCAT) researchers suggest that with a 1% decrease in air voids, pavement service life would increase by 10%. Based on these increases in pavement service life, it is estimated that by increasing the density/reducing air voids by 1%, net present value cost savings could be $88,000 out of a $1,000,000 project.