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MnDOT currently owns the record for the most award winners and has received an award every year from 2002 through 2015. This study reviews all the award winning roadways in Minnesota to determine common material, design factors and considerations which may have contributed to the roadways extended life, often exceeding 50 years despite the harsh Minnesota climate. For these projects, all the available information for the 14 award winners and any pertinent supporting information were reviewed including MnDOT Highway Pavement Management Application (HPMA) data and performance histories as well as the construction histories and plans. Findings from this study showed that a combination of many different factors may have contributed to the outstanding performance of these award winning roadways. These factors include constructing the roadways over a longer period of time, performing major subgrade corrections at the time of construction, use of a select granular backfill material which enhanced drainage, use of non-frost susceptible base and subbase materials in underlying layers, placing a layer of prime coat over the aggregate base before placing the asphalt layer(s), use of a staged construction which allowed the foundation to go through seasonal cycles potentially enhancing the overall pavement structural stability, use of a stabilized base in the initial construction which may provide a flexible, fatigue resistant foundation for overlay construction and provides a bound layer which may have reduced the tensile strain levels at the bottom of the upper asphalt layers and therefore increased the pavement fatigue life. Findings also showed a similar resilient modulus of asphalt mixtures at low temperatures which is the dominant temperature condition for much of the year in the state of Minnesota.

Cold In-place Recycling (CIR) is pulverizing and rebinding existing Hot Mix Asphalt (HMA) pavements with bituminous and/or chemical additives without heating to produce a restored pavement layer. This process has become a desired rehabilitation alternative for cost, environmental, and performance advantages compared to standard practices. The process utilizes a train of equipment with either volumetric or weight control. It also utilizes various stabilization materials including emulsion, cement, combinations of emulsion/cement, and foamed asphalt. Performance-based laboratory tests to capture fracture energy of materials have shown they can correlate to field performance quite well. These tests offer an excellent opportunity to differentiate between processes and materials used in CIR for characterization and development of a performance-based specification. In this study, the performance of CIR using four different stabilization (rebinding) materials of Engineering Emulsion, High Float Emulsion (HFMS-2s), Commodity Emulsion (CSS-1) with Cement, and Foamed asphalt are compared using a newly developed testing method called Fracture Index Value for Energy (FIVE). This test is performed on notched Semi-Circular Bending (SCB) specimens by controlling the crack mouth opening displacement (CMOD) rate. The FIVE test is found to be a practical easy to perform test that is able to compare CIR material low temperature characteristics. In this study, the FIVE test first was verified against Disc-shaped Compact Tension (DCT) test results and then was applied on the four study mixtures. Furthermore, the FIVE test results went through a validation process with inter-lab comparisons by three different testing labs of Braun Intertec, American Testing Engineering, and the Minnesota Department of Transportation (MnDOT).

In this study, to evaluate the effect of emulsion reduction during the CIR process in the field, three laboratory CIR mix designs were performed using the same RAP material and emulsion at three different mixing temperatures. The mix design results showed that as the mixing temperature increased; the optimum emulsion content decreased significantly. Also increasing the mixing temperature improved the mixture compaction. Both the dry and retained stabilities were also higher for the high-temperature mixtures. The critical low temperatures of high-temperature mixtures were higher than the room-temperature mixture (indicative of a worse performance) but still lower than -20°C. From the results of this study, it appears that reducing the emulsion content of the CIR mixtures during the heat of the day does not necessarily deteriorate the mixture properties. This could result in substantial savings for agencies that use this process without sacrificing long-term performance.

In previous Local Road Research Board (LRRB) studies there has been discussion but no empirical data regarding proprietary stabilizers. The LRRB leveraged an existing rehabilitation project on the border of Beltrami and Hubbard Counties to gather data and report on two stabilizers: engineered emulsion (used on the Beltrami County portion) and BASE ONE® (used on the Hubbard County portion). The county projects were Beltrami County: CSAH 4 and Hubbard County: CSAH 46. The purpose of this study was to document as-builts/road history; collect and report pavement condition; document stabilized full depth reclamation (SFDR) rehabilitations (and mix designs); interview contractor(s) and stakeholders; conduct sampling/testing (dynamic cone penetrometer, coring, and falling weight reflectometer testing); conduct performance analysis; and write a summary report