Testing

At the Minnesota Road Research Project (Mn/ROAD), asphalt concrete mixtures were used to evaluate both warm and cold temperature material properties with selected text methods and a wide range of testing parameters. These parameters were selected to approximate different levels of environmental conditions, traffic speeds, traffic loads, and, in certain cases, confining pressures. The underlying theories used to calculate stress and strain from various loading configurations also were rigorously evaluated to determine the appropriateness of comparing results from one testing configuration to another. Mn/ROAD mixtures were evaluated as the first step in linking laboratory measurements and test method selection to live traffic pavement responses and performance. A comparison of axial and diametral testing using harmonic loading showed that experimental results did not agree with theory. That is, the complex deviatoric modulus determined for diametral testing should have been less than the Young's modulus determined from testing axially loaded samples. This was not the case. This suggested that a further examination of the sample instrumentation, testing variability, and the possibility of anisotropic mixture behavior due to particle orientation during compaction are needed to resolve these differences. Other findings indicated that the influence of load duration is minimized as the test temperature decreases, there was little influence in rest period times in repeated loading tests on modulus, and confining pressure only had a significant influence on modulus above about room temperature.

The Minnesota Department of Transportation along with other partners, constructed forty 500-foot test sections from 1992 to 1994. The site, known as Mn/ROAD, is located along 1-94, 40 miles northwest of the Twin Cities. Since the test sections are located at the same site, they are all subject to the same environmental conditions and traffic load. This makes direct comparisons of the pavement condition of the various cells possible. To accomplish this task, this paper will rely primarily on the use of computer graphics, due to the volume of the data collected and the number of test sections involved, to illustrate the changes in pavement condition that have occurred. Corresponding observations will be very general in nature and should be considered preliminary at this stage. More detailed analyses will be done on a cell by cell basis after all testing and final forensics have been completed. This paper will include a history of rutting, thermal cracking, fatigue cracking, ride, faulting, friction numbers, and construction costs.

This paper presents the results of a blind test evaluation of various nondestructive testing techniques including well established methods such as chain dragging, rod sounding, and GPR as compared to an emerging ultrasonic array technology in determining the extent of the concrete joint deterioration. Nondestructive testing at two concrete pavement joints at MnROAD was performed and the results were independently evaluated and submitted to MnDOT. Significant discrepancies in subsurface deterioration assessments were observed among these techniques. Forensic evaluation (trenching and coring) were utilized to resolve the discrepancies in test results. It was concluded that the ultrasound array analysis was the only method able to accurately determine the horizontal extent of the deterioration otherwise undetected by the other available nondestructive evaluation methods. Additionally, ultrasonic tomography analysis was able to determine the depth of the deterioration. This makes this emerging technology an attractive alternative to traditional NDT methods for concrete pavement joint assessment. Paper submitted for the Transportation Research Board 92nd Annual Meeting, 13-17 January 2013.

The sound absorption test measures the sound absorptiveness of a pavement surface. The sound analyzed is not generated by the interaction of the rolling tire with pavement surface but by noise source above the impedance tube. During the test, the impedance tube is placed on the pavement surface and a set of sensitive microphones are attached to the pre-installed housing at the lower end of the tube. These microphones are also connected to an analyzer. The noise source sends the incident sound energy (white noise) to the surface and the incident and reflected waves are captured by the two microphones. Software analyzes the reflected waves and converts the data to the 3rd octave sound absorption coefficient at 315, 400, 500, 750, 1000, 1250 and 1650 Hertz. Thus, the sound absorption coefficients at each frequency are between one and zero, where a value of one would mean that all of the sound is being absorbed by the pavement surface.

The Minnesota Department of Transportation (Mn/DOT) is currently conducting a research project aimed at reducing longitudinal joint (Ljt) deterioration in hot mixed asphalt (HMA) pavements through improved construction techniques, preventive maintenance practices, and repair treatments. Constructing durable HMA pavements, with adequate Ljt performance, has been well documented and extensively researched, however preventive maintenance and repair treatments specific for Ljt have received little attention in the literature. It is commonly accepted that adequate density is critically important in achieving a durable HMA pavement. Insufficient density, or high air voids, usually results from the difficulty of compacting an unconfined pavement edge, and the localized area of low density creates a density gradient. Pavements with lower densities can have more interconnected air voids, leaving them more susceptible to moisture and environmental deterioration resulting in distresses such as weathering and raveling.

This study examines various new textures and monitors them over time with a litany of standard tests. In the process certain analytic initiatives are performed. This study was part of the basis for Report 2015-48, "Pavement Surface Characteristics Concrete New Construction (MnROAD Study)."

A study examined thirty one pavement test sections in the Minneapolis St Paul area to determine if tire pavement noise (OBSI) from the pavement surface affects perception of pavement smoothness (MPR). Forty six volunteers rode as passengers in 2010 Chevrolet Malibu sedans over the contiguous ½ mile long rigid or flexible pavement test sections scoring MPR. Results of MPR were compared to the International Roughness Index (IRI) measured with the digital inspection vehicle at the same time. The AASHTO TP 76-09 procedure for OBSI procedure for near field measurement was used to measure tire pavement noise. Using statistical analysis and tests, the MPR and OBSI were examined for correlation of the latter to anomalies in the former. OBSI did not seem to explain anomalies in MPR referenced from measured IRI. However, the sequencing of the test sections for the ride survey appeared to have influenced some of the ratings of some test sections. Moreover there was some evidence of correlation of IRI and MPR to OBSI. This paper was submitted to the Transportation Research Board Annual Meeting in 2012.

Three test sections were constructed in 2008 on Interstate 94 at the MnROAD test facility to study pavement performance with stabilized full depth reclamation base using engineered emulsion. Each section used a different emulsion content due to the inherent differences in the sections. Pavement testing, including rut and crack measurements, was performed, along with falling weight deflectometer tests. The three sections had slight increases in rutting from April 2009 to July 2009 but leveled off by September 2009. This was likely due to material consolidation, which is commonly observed for most asphalt pavements immediately after opening to traffic. The amount of rutting is still low, with most of rutting less than 0.15 inches. No cracking has been observed. FWD testing showed the least average deflection occurred in cell 3, but cell 4 was the stiffest material, based on the Area index. Laboratory testing characterized the mechanical properties of the three mixtures. The testing results showed that the mixture used in cell3 has the highest dynamic modulus, slightly greater than cell 4 at most frequencies. Cell 3 also has the best fatigue life, which indicates that this mixture type is probably an optimal design in terms of material strength and performance. Ultimate performance, however, will be determined from field results, dependent on materials and design of all layers and construction quality. The sections were designed for 3.5 million ESALs in five years, and it must be pointed out that the sections are still in early stage of the study and performing well. Prepared for presentation and publication at the 90th Annual Meeting of Transportation Research Board, January, 2011, Washington, D.C.

Sustainability in the design of pavements can be accomplished in two different ways. Either a pavement is designed to be more robust, so that it will have a significantly longer service life, or a pavement is optimized and designed to use significantly less materials, with the potential for a shorter service life. This paper examines the design concepts and field performance related to the latter type of concrete pavement systems in a cold climate. Several thin full-depth concrete and thin unbonded concrete overlay pavements have been recently constructed in Minnesota. These pavements are being intensely studied to examine how truly optimized the design can be and still deliver safe, economical, and reliable performance. This paper summarizes the early and long-term performance of several thin concrete pavement test sections at the MnROAD test facility, as well as early performance observations from a larger scale project in northern Minnesota. Design concepts and details of multilayered concrete pavement test sections utilizing recycled concrete and other low cost materials are also discussed. Based on the many valuable lessons learned from test sections at the MnROAD facility and throughout the state, local engineers are now comfortable designing and constructing thinner full-depth concrete pavements, as well as thin bonded and unbonded concrete overlays.

In 2008, Mn/DOT initiated a five year study that examines the performance of two thin unbonded concrete overlay projects: Cell 5 of the MnROAD Phase II (SP 8680‐157) and a section of TH 53 near Duluth, Mn (SP 6916‐99). These pavement test locations provide a unique opportunity for researchers to include additional environmental and traffic factors in validating performance results. It is anticipated that the results from these studies will improve the understanding of the behavior of this complicated composite system, which will lead to the development of better distress and life prediction models and ultimately contribute to more sustainable pavement designs.