Click for next page ( 2

The National Academies | 500 Fifth St. N.W. | Washington, D.C. 20001
Copyright © National Academy of Sciences. All rights reserved.
Terms of Use and Privacy Statement

Below are the first 10 and last 10 pages of uncorrected machine-read text (when available) of this chapter, followed by the top 30 algorithmically extracted key phrases from the chapter as a whole.
Intended to provide our own search engines and external engines with highly rich, chapter-representative searchable text on the opening pages of each chapter. Because it is UNCORRECTED material, please consider the following text as a useful but insufficient proxy for the authoritative book pages.

Do not use for reproduction, copying, pasting, or reading; exclusively for search engines.

OCR for page 1
1 SUMMARY Aggregate Tests for Hot-Mix Asphalt Mixtures Used in Pavements NCHRP Project 4-19, "Aggregate Tests Related to Asphalt Concrete Performance in Pavements," recommended a set of performance-related aggregate tests for evaluating aggregates for use in hot- mix asphalt (HMA) pavements. Performance indicators considered in the research included perma- nent deformation resulting from laboratory traffic loading (both with and without stripping), fatigue cracking, and surface defects (e.g., raveling, popouts, and potholes). The performance relationships were developed based on tests performed using the Superpave Shear Tester (SST) and the Georgia Loaded Wheel Tester (GLWT); however, the relationships were not validated. As part of their results, the NCHRP 4-19 researchers recommended a follow-on experiment for additional research to achieve validation. The proposed research involved tests of both coarse and fine aggregate uncompacted voids as well as the flat or elongated particle test, 2:1 ratio (FOE21). These three tests were to be validated for their ability to predict HMA rutting and fatigue perfor- mances. Additionally, particle size analysis and methylene blue values (MBV) of the HMA mixture aggregate fraction smaller than the 0.075-mm sieve (p0.075) were to be tested to validate their abil- ity to predict rutting in HMA mixtures. The researchers further suggested that the MBV of the fine aggregate be validated for ability to predict moisture susceptibility of HMA. Finally, the results of Micro-Deval (MDEV) and Magnesium Sulfate Soundness (MGSO4) tests on aggregates were to be evaluated for predicting HMA toughness and durability. The object of this research was to use accelerated pavement testing techniques to conduct the rut- ting, fatigue, and moisture susceptibility validation experiments identified in NCHRP Project 4-19. For each aggregate test, a descriptive ranking indicating how well it relates to HMA performance is given.Also, an attempt has been made to suggest appropriate tests for given combinations of climatic conditions, materials, and traffic loads. A literature review was completed first and was used to guide the research team in selecting five coarse and six fine aggregates for use in the study. The selected aggregates were tested and used in var- ious combinations to produce five coarse-graded and six fine-graded mixtures that were then tested for rutting characteristics in the accelerated loading facility. The five coarse aggregates covered a wide array of aggregate types and properties; each was combined with a common natural sand to produce the five coarse-graded mixtures. The six fine aggregates also represented various aggregate types and properties; each of these was combined with a common coarse aggregate to produce the six fine- graded mixtures. On completing the rutting tests, six of the original eleven mixtures were chosen for accelerated testing to determine their fatigue characteristics. The mixtures were chosen so as to represent a wide range of aggregate and mixture characteristics. Although the rutting testing proceeded well, prob- lems were encountered with the fatigue testing. Construction of the conventional flexible pavement sections in the accelerated loading facility proved to be more difficult than anticipated. Lack of tem- perature control in the facility also made it difficult for the test slabs to exhibit fatigue signs during the test, at least two mixtures exhibited excessive rutting before showing signs of fatigue.

OCR for page 1
2 In addition to the rutting and fatigue tests, five additional HMA mixtures were designed using five of the six fine aggregates and one common coarse aggregate. These mixtures were placed in the accel- erated loading facility and tested for rutting in the presence of moisture to determine if the aggregate tests predict moisture susceptibility in HMA mixtures. Test results showed that the UVA of both fine and coarse aggregates reasonably predict rutting per- formance of HMA mixtures. The FOE21 test also appears to predict HMA rutting performance. These three tests also may show trends in relation to HMA fatigue performance, but the fatigue data are limited. A minimum coarse aggregate UVA of 40 percent is recommended for traffic less than 100,000 Equivalent Single Axle Loads (ESAL); a minimum coarse aggregate UVA of 45 percent is rec- ommended for traffic of 100,000 ESAL and greater. A minimum fine aggregate UVA of 40 percent is recommended for traffic volumes less than 500,000 ESAL; a minimum fine aggregate UVA of 45 per- cent is recommended for traffic volumes above this level. An upper limit of 50 percent is recom- mended for the FOE21 value for all traffic levels. The MDEV and MGSO4 tests also appear reasonably predictive of HMA performance. Maximum values of 15 and 20 percent for MDEV and MGSO4, respectively, are recommended. Although the particle size analysis of the p0.075 material and the MBV tests appear to have some performance predictive ability, the relationships were weak. Neither of these tests is recommended for routine aggregate specifications. Finally, research is suggested to gather additional information about the relationship between the recommended aggregates tests and HMA fatigue performance. Because the relationship between lab- oratory and in-service fatigue typically is a scaling factor, adequate information can be obtained from a laboratory experiment. Full-scale testing is not required.