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In the past, Mn/DOT has placed emphasis on improving the structural adequacy of many rural trunk highways. These improvements were usually made by plant mix bituminous overlays since seal coats do little or nothing to improve the structure of a roadway. Future emphasis will likely shift more toward prolonging the life of existing pavements. Seal coats provide an economical means of extending pavement life on roadways below 5000 average daily traffic (ADl). Research on the use of seal coats is warranted since 75% of Mn/DOT highway miles and virtually all county and municipal roadways fit this criteria. This paper covers the basic fundamentals and current practices of this technology in Minnesota along with several alternatives. Its main purpose is to provide recommendations for developing and implementing a seal coat program. The references identified in the bibliography are recommended for review by readers with limited knowledge of this technology. Additional information can also be obtained through the Mn/DOT Physical Research Office or the Mn/DOT Bituminous Office.

This presentation pertains to report 2014RIC14, Integrated Tools for Pavement Design and Management.

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).

The research performed for this report was intended to recommend alternative mix design procedures and parameters for evaluation of asphalt mixture sensitivity, with more of an emphasis on volumetric relationships. Three Mn/DOT projects were selected to represent the following durability issues: 1) debonding of asphalt from aggregate, 2) cohesion problems, and 3) mix design problems. Materials were obtained from these construction projects and evaluated in the laboratory. Gradations were varied from the project specifications so that mixtures with more and less asphalt were evaluated along with the project mixture. Testing included the temperature susceptibility and moisture sensitivity of the mixtures, in addition to the net adsorption test on the aggregates. The results suggested means for identifying moisture sensitivity mechanisms in mixtures during the mixture design phase, although these need to be confirmed through more extensive investigation. Aggregate mineralogy, gradation, and mixture proportioning can all play a role in improving the durability characteristics of asphalt mixtures. Recommendations are made for continued research and implementation of an improved approach to asphalt mixture design.

The Minnesota Department of Transportation (Mn/DOT) has been performing asphalt extraction testing on bituminous road materials for more than 50 years. Currently, Mn/DOT annually performs about 3,500 extractions. Extraction testing requires the use of chlorinated solvents, which generates a considerable amount of hazardous liquid waste that must be disposed of by strictly following increasingly complex and stringent federal regulations. The objective of this research project was to replace or supplement the current chemical extraction method for testing the asphalt content of road construction bituminous mixtures with nuclear asphalt gauge testing. This research led to the following conclusions: 1. Nuclear asphalt gauge testing gives asphalt cement content results that are at least as accurate as solvent extraction testing. 2. Gradation testing cannot be done using nuclear asphalt gauge testing procedures. 3. Nuclear asphalt gauge testing works well for bituminous materials containing up to about 20 percent recycled asphalt pavement (RAP).

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

Significant improvements have been made in base stabilization practice that include design specifications and methodology, experience with the selection of stabilizing additives, and equipment for distribution and uniform blending of additives. For the rehabilitation of existing pavements the stabilization of base material has delivered performance as good as or better than reconstruction at a reduced cost. Many additive products exist to stabilize base materials for roadway construction, but it is not always clear which additive is the right one to use. This guidebook intends to focus on stabilization for new construction and Stabilized Full Depth Reclamation (SFDR) and to help with the selection of suitable nonproprietary stabilization additives for individual specific project(s).

Base stabilization entails mixing a stabilizing additive into an acceptable base aggregate material, imported with or without recycled material or from reclaimed hot-mix asphalt (HMA), creating a new bound pavement layer. The fundamental value of stabilizing base materials is achieving similar pavement structures more economically. Stabilizing base aggregates can allow pavement designers to develop stronger, deeper pavement structures with reduced subcut depths and thinner surfacing lifts of HMA.