Pavements

Asphalt rejuvenators, or recycling agents (RA), are used to incorporate higher amounts of Reclaimed Asphalt Pavement (RAP) in Hot Mix Asphalt (HMA) without detrimentally impacting the long-term performance of the pavement. The National Road Research Alliance (NRRA) Flexible Team constructed field test sections as part of a mill and overlay project in northern Minnesota in August of 2019. These field sections included wearing courses with 40% RAP that incorporate seven different RA products, with the dosage determined by the supplier to meet a target extracted and recovered performance grade (PG) of XX-34. In addition to the RA test sections, there were control sections with 40% RAP and 30% RAP (the maximum level allowed on the remainder of this project). The objective of this research project was to evaluate the effectiveness of the seven RA products over time and evaluate their performance as compared to the control mixtures. This was accomplished through a combination of binder (chemical and rheological) and mixture characterization and performance testing using different laboratory aging levels, field core testing, and performance monitoring of the field sections over time. This report documents the results after four years in service with cores taken annually. The study showed that all RAs exhibit improved rheological properties in 1-year field cores. However, the benefits of RA diminish with field aging, and after four years, some RAs show comparable properties with controls. In terms of mixture properties, the inclusion of RA enhances both rheological properties and fracture and fatigue crack resistance initially.

Asphalt milling is an essential construction activity. It requires concentrated high-intensity applications of force to the existing pavement to remove the asphalt material. The impact that the induced stresses have on the pavement below the mill line is unknown. Consequently, selected milling parameters rarely consider the impact the milling may have on the remaining layers. This study evaluates milling parameters to provide an enhanced understanding of their impacts on the layer directly below the mill line. Five parameters were evaluated and include the time between milling and post-mill overlay construction, existing pavement structure, temperature while milling, depth of milling relative to layer interface, and rotor speed. Pre- and post-milling cores were collected adjacent to each other and evaluated for physical and mechanical properties. The measured properties of the pre- and post-milling cores were statistically compared to determine the impact of milling operations on the integrity of the asphalt concrete immediately below the mill line. Based on the results from this study, it was determined that leaving milled pavement exposed for longer periods of time or milling at cooler temperatures can cause a decrease in the strength of the layer below the mill line and a decrease in the expected pavement life of the new pavement structure. The depth of milling or changing the rotor speed while milling did not have significant impacts on the layer directly below the mill line. In consideration of the results of this study, research with a wider variety of pavements and milling conditions is warranted.

This report is issued to comply with 2022 Minnesota Statutes 174.185.1 Changes to this section were made in the 2024 Legislative Session but do not become effective until July 1, 2025 (see Appendix D). The statute requires a life-cycle cost analysis for every project in the reconditioning, resurfacing and road repair funding categories constructed after July 1, 2011. The LCCA is a comparison of life-cycle costs among competing paving materials using equal design lives and equal comparison periods. Documentation required by the statute includes: • Lowest life-cycle cost • Alternatives considered • Chosen strategy • Documented justification, if the chosen strategy is not the low-cost option

Managing MnDOT’s network of roadways to a satisfactory level of performance requires pavement investment selection methods and activities that consider performing the “right fix” at the “right place” at the “right time” and the “right way.” Although these investment selections consider a broad assortment of investment methods and activities beyond traditional maintenance, maintenance investments and activities play a significant role in roadway pavement performance, often affected by the availability of localized and regionalized resources. To optimize roadway pavement maintenance investment methods and activities, MNDOT Maintenance has determined that the Smooth Roads Project Management Team should be re-established to address this topic.

The Minnesota Department of Transportation (MnDOT) recognizes the importance of subsurface drainage in pavements. Various studies have indicated that adequate drainage of pavement layers enhances performance of pavements in general. MnDOT thus uses various types of subsurface drainage in varying degrees of styles, frequency of use, and minor variation in construction practices in the various transportation districts of the state. The subsurface drainage technologies include Open Graded Aggregate Base (OGAB), Drainable Stable Base (DSB), Permeable Asphalt Stabilized Base (PASB), Geocomposite Joint Drain (GJD) and Class 5Q aggregate. This study examines the various drainable bases in the network and identifies their locations and limits. Using performance data from the pavement management system, the performance, measured via Ride Quality Index (RQI), of test sections with drainable base systems was compared to contiguous sections without the systems so that traffic and environmental factors as well as other variables were held constant. Reliability and logistic analysis were conducted to ascertain if there were performance advantages in the drainable systems. The difference between the systems was found to be advantageous in certain districts, and an operations research survey reflected advantages in the drainable systems where and when they were associated with proficiency in construction practice.

The Minnesota Department of Transportation (Mn/DOT), contracted with Donohue and Associates, Inc. of Sheboygan, Wisconsin to survey five bridge decks and approximately 79 lane miles of continuously reinforced concrete pavement (CRCP) and asphalt-overlaid jointed reinforced concrete pavement in Minnesota. All of the work was in the St. Paul-Minneapolis metropolitan area except for two bridge decks, located in Moose Lake and Cloquet. Several test sections were also surveyed with Mn/DOT's Delamtect for purposes of comparing the results produced by the two techniques.

In September 1978, a Mn/DOT Task Force was established to conduct an in-depth analysis of rehabilitation measures for the 5.2 mile section of l-92 (see map, page 9) continuously reinforced concrete pavement (CRCP) located between Snelling Avenue in St. Paul and the Lowry Hill Tunnel in Minneapolis. The pavement is rapidly deteriorating due to ruptures of the reinforcing steel and spalling of the driving surface. This section of highway averages 30,000 vehicles per day. The rehabilitation of this pavement will have significant impacts. during construction in terms of social and economic cost to the traffic user and public served by the facility. In addition, the magnitude of the rehabilitation will have a major impact on the financial resources of Mn/DOT. Because of the impacts, Mn/DOT management, felt it imperative to investigate and evaluate all possible measures in terms of design, engineering, project staging, timing, and cost. This report discusses the findings of the Task Force.

This summary report is an illustrated description of a surface condition rating procedure for flexible pavements. A slide tape presentation has also been prepared on this subject. This report and the slide tape can be used together to supplement each other and the report can be used as a reference during field condition surveys. Both documents are intended to be training aids for people who are responsible for evaluating pavement conditions and selecting appropriate maintenance procedure

The purpose of this three month study has been to determine whether it is feasible to simulate an asphalt pavement section using the elastic theory. This has been done by first obtaining samples from Investigation 183, Test Section 102 and determining the stress-strain properties of the various layers using the repeated load triaxial test under various conditions. Appropriate moduli have then been put. into an elastic layered system which is used to calculate stresses and strains within the system. The Benkelman beam deflections measured in the field have been simulated in this manner and the comparison between computed and measured deflections is used to show whether the elastic theory simulates a flexible pavement. The possibility of determining equivalencies between stabilized base courses and granular base courses are explored as are the use of other parameters for design purposes.

The Minnesota Department of Transportation has collected pavement distress and ride data from the pavements in their system since 1967. In 1986, the data was analyzed to develop pavement performance prediction models that were based on the growth of pavement distresses such as cracking, rutting, and roughness. The analysis at that time was limited by the amount of data available and was considered to be an interim study. The amount and quality of data presently available has improved from that available in 1986 and new or improved models could be developed. The work involved the analysis of all of the pavement condition data collected since 1983 when improved collection procedures were implemented. A literature search was also conducted. The results of the study was the evaluation of pavement life and the development of mathematical models that describe the growth of the distresses rated and the change in roughness over time. Over 100 pavement groupings were evaluated. The groupings were selected on the bases of a variety of pavement attributes including surface type, functional class, and region (construction district). The life of the pavements were evaluated based on the number of years they remained in service and on the basis of performance indices. It was found that the number of years a pavement remains in service can not be used to infer performance potential since a number of pavements were rehabilitated for reasons other than condition; the predicted pavement condition provides a better indication of the performance life of a pavement. The prediction of future pavement performance is accomplished by using the distress growth models to predict the growth of the distresses; the future condition indices are than calculated from the predicted distress amounts.