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WESTERN REGIONAL
SUPERPAVE CENTER
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This is an on-going research program between the Nevada DOT and the WRSC to provide continuous support for issues that are critical to the design and construction of well performing HMA pavements throughout the state of Nevada. Several topics have been investigated under this program dealing with materials, testing methods, and construction techniques. The following represent summaries of some of the ideas that have been investigated.
Mechanical Properties of Nevada's HMA Mixtures: This research effort evaluated the typical mechanical properties of Nevada's HMA mixtures produced between 1993 and 1997. The evaluated mixtures included both laboratory prepared and field produced HMA mixtures from over 100 projects that were constructed throughout the state. The measured mechanical properties included tensile strength and resilient modulus at both the uncoonditioned and moisture conditioned stages. The data base generated from this research included properties of HMA mixtures manufactured with neat and polymer modified binders covering the various binder grades and mixtures gradations that are used throughout the State of Nevada. The data generated from this effort were used in the structural design of HMA pavements and to update construction specifications for HMA mixtures. Available Information: Download: Evaluation of Nevada's 1995-1997 HMA Mixtures Download: Evaluation of Nevada's 1993-1994 HMA Mixtures
Influence of Hot-Mix Asphalt Parameters on the Correction of the Ignition Oven Test: This research was completed in 2000. The objective of the research was to determine an accurate correction factor for the ignition oven test. In preparation for the implementation of the ignition oven test, the Nevada Department of Transportation (NDOT) conducted an extensive laboratory testing program to assess the impact of the various mix parameters on the determination of the correction factors. The experiment included aggregate source, binder type, lime, and testing temperature. This paper analyzes the data generated from the NDOT experiment and evaluates the impact of each of the considered factors on the correction factor. In summary, the analysis of the data generated in the NDOT experiment showed that the aggregate source and the addition of lime have the most significant impact on the determined correction factor followed by the temperature and binder type. However, if during a field project, the binder or the method of lime application change, these changes would not require the determination of a new correction factor. The data also showed that the blank aggregate method would generate correction factors that are less variable than the known asphalt content method. Available Information: Download: Impact of Mixtures Parameters on the Correction Factors of the Ignition Oven Test.
Low Temperature Properties of HMA Mixtures: This research was completed in 1999. The research evaluated several newly developed low temperature performance tests under Nevada’s conditions. The goal of the research was to determine the applicability of the tests for characterizing the low temperature response of Nevada’s asphalt binders and HMA mixtures. An investigation of the Superpave Performance Graded Binder tests has determined that the bending beam rheometer and the direct tension test correlate very well and it may not be necessary to run both tests as they are set up in the current Superpave specifications. The TSRST appears to provide the greatest value for evaluating low temperature properties of HMA mixtures. Findings from the research indicate that there are some significant correlations between the low temperature properties of asphalt binders and HMA mixtures if the mixtures are aged appropriately. This emphasizes the need to implement the appropriate conditioning procedure when low temperature cracking is used as part of the mix design and evaluation process. On the other hand, the research showed that when using polymer-modified asphalt binders, the low temperature grade of the asphalt binder maybe conservative enough where testing of the HMA mix may not be necessary. Available Information: Download: Evaluation of Low Temperature Properties of HMA Mixtures
Selection of the Most Desirable HMA Mixtures: This project was completed in 1996. The objective of this research was to identify the various combinations of aggregate gradations and binder types that would result in excellent performing HMA mixtures. Excellent performance was defined as good resilient modulus and tensile strength properties, good resistance to moisture damage, permanent deformation, and low temperature cracking. A laboratory program that evaluated four gradations and four asphalt binders in conjunction with five sources of Nevada aggregates was carried out. The data analysis indicated that the resilient modulus and tensile strength tests can be used in lieu of the more complicated triaxial repeated load test to ensure against rutting and the binder properties can be used to ensure against low temperature cracking. Available Information: Report can be obtained by contacting WRSC.
Aging Characteristics of Asphalt Binders and Asphalt-Aggregate Mixtures: This project was completed in 1995. The objective of the research was to evaluate the binder aging procedures recommended by the Superpave performance-based binder grading system (PG). A research program was designed to compare laboratory binder procedure with the aging experienced by the binder under actual field conditions. The study showed that the rolling thin film oven test (RTFOT) simulates the short term aging of binders caused by the mixing and construction activities. The effectiveness of the pressure aging vessel (PAV), on the other hand, is highly dependend on the in situ conditions of the pavement. Available information: Report can be obtained by contacting WRSC.
Impact of Aggregate Gradation on the Performance of HMA Mixtures: This project was completed in 1993. The objective of the research was to evaluate the impact of various aggregate gradations on the resistance of HMA mixtures to permanent deformation. With Nevada having a large number of mines operating throughout the state, it was critical that a rut-resistant HMA mixture be identified and used on the highway system. Triaxial testing was used as a performance test for rut resistance. The test was conducted under stresses and temperatures which are typical of field conditions throughout Nevada. The research identified that using NDOT’s Type 2C gradation would provide excellent resistance to rutting. The Type 2C gradation is a coarser gradation than the typical Type 2 gradation which allowed better aggregate interlock and high stability under elevated temperatures. NDOT have used the Type 2C very successfully to resist rutting throughout the entire state. Available Information: Report can be obtained by contacting WRSC.
Comparison of the Performance of AC-30 and AC-20P binders: This project was completed in 1993. The objective of the project was to compare the performance of polymer-modified mixtures with non-modified mixtures. NDOT have used the AC-20P binder in the northern part of the state with a great success. in the southern part of the state, neat AC-30 has been used which showed good resistance to rutting but mixed performance in resisting cracking. It was believed that the polymer-modified binder offers good resistance to both cracking and rutting due to its flexibility under the wide range of anticipated in-service pavement temperatures. This project evaluated the mechanical properties of polymer-modified mixtures as compared to the neat mixtures typically used in the Las Vegas area. The evaluated properties included the resistance of the HMA mixtures to rutting and cracking. Conclusions from the program indicated that the overall performance of the AC-20P mixtures was far superior than that of the conventional AC-30 mixtures. Available Information: Report can be obtained by contacting WRSC.
Evaluation of Materials Properties as Related to Long Term Performance: This project was completed in 1992. A flexible pavement project located in the southern part of the state on I-15 was selected for this investigation. The pavement section consists of an overlay that was constructed in 1970. Twenty-two years later, this pavement was still showing excellent performance under the severe weather conditions and heavy traffic loading. As part of this investigation, slabs and cores were cut from the pavement section and laboratory tests were conducted on the various materials. The rheological properties of the recovered asphalt binder were evaluated and compared to the Superpave grading system. The properties of mixtures that were evaluated included the following: in situ air voids, resilient modulus at various temperatures, and permanent deformation characteristics. The extracted aggregates were also tested for any degradation and their gradation curves were compared to the FHWA and Superpave recommendations. Available Information: Report can be obtained by contacting WRSC.
Comparison of Resilient Modulus Data from Laboratory Tests and FWD: This research was completed in 1992. The objective of the research was to investigate the relationship between resilient modulus of granular bases and subgrade soils determined through laboratory testing and those evaluated from the FWD testing. The program tested materials from numerous sites around Nevada. The analysis of the data generated from this program indicated that the correlation between the two methods is very weak. The relationship can be improved if the laboratory tests are conducted under stress conditions that are very close to the conditions generated by the FWD loading. Based on this study NDOT decided to use the FWD backcalculation approach to determine the in-situ resilient modulus of pavement layers. Available Information: Report can be obtained by contacting WRSC.
Evaluation of the
moisture Sensitivity Test Moisture
sensitivity is a major problem facing the HMA industry in Nevada. The sources of this problem stem from the highly
moisture sensitive aggregates and the extreme weather conditions throughout the state. NDOT has been very successful in combating the
moisture sensitivity problem through the use of lime additive in HMA mixtures throughout
the state. NDOT evaluates the moisture
sensitivity of all HMA mixtures used in the state at the mix design and during production
stages. This process has assured high quality
HMA mixtures with excellent resistance to moisture damage on all pavements throughout the
state. The laboratory test method used by NDOT to evaluate the moisture sensitivity of HMA mixtures is a customized version of the AASHTO T-283 method to fit Nevada’s unique conditions. This method has served NDOT for several years and significantly reduced the occasions of pavement failures due to moisture damage. However, the current method needed some updates in the area of repeatability and variability within and between laboratories. Such an effort will ensure that test results can be confidently replicated in various laboratories and with different laboratory technicians. Once the repeatability and variability of the test are improved, then tighter specifications can be implemented to ensure the production of excellent HMA mixtures in the field. This research identified the needed modifications of the NDOT’s moisture sensitivity test to ensure high repeatability of the measured properties. All mixtures that were evaluated in this Task were designed following the NDOT Hveem mix design procedure. The aggregates were treated with 1.5% hydrated lime and marinated for 48 hours prior to mixing with the binder following NDOT procedure. Available
Information: Pavement Design and Materials
Research, 2003-2005 Design and Evaluation
of HMA Mixtures for Intersections Permanent
Deformation is a major failure mode of flexible pavements, consisting of both rutting and
shoving of the hot mix asphalt (HMA) mixture. Typically,
a rutting failure alone occurs under traffic loads moving at highway speed, while both
rutting and shoving failures may occur under traffic loads at intersections. In many instances, the same HMA mixture that has a
history of good performance in rutting did not perform well at the intersections. This behavior can be related to two basic
phenomena: a) slow and/or stopped traffic at intersections subjects the pavement to more
complex stresses and b) the HMA mixture behaves more weakly as it is subjected to slow
moving or stopped vehicular loads. The
slower-moving loads are not the only reason that intersections are more prone to rutting
and shoving. Braking, accelerating, and
turning movements that occur at intersections impose different stress conditions on the
pavement surface layer. The intersection must
be able to sustain the interface friction forces caused by the braking and acceleration of
heavily loaded trucks (e.g., the eighteen-wheeler trucks).
The
objective of this research was to develop special and practical requirements that can be
used to specify an asphalt mixture highly resistant to permanent deformation at
intersections. The study is mainly conducted for the hot climate part of the state of
Nevada (i.e., Las Vegas). Available
Information: Pavement Design and Materials
Research, 2003-2005 |
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