AASHTO T 209: Effect of Agitation Equipment Type on Theoretical Maximum Specific Gravity Values (2012) / Chapter Skim
Currently Skimming:
Pages 1-25
The Chapter Skim interface presents what we've algorithmically identified as the most significant single chunk of text within every page in the chapter.
Select key terms on the right to highlight them within pages of the chapter.
From page 1... ...
.1 The Gmm and the density of HMA are fundamental properties whose values are influenced by the composition of the HMA mixtures in terms of types and amounts of aggregates and asphalt materials. Gmm is used to calculate percent air voids in compacted HMA and to provide target values for the compaction of HMA.
|
From page 2... ...
7. Evaluate the practical and statistical significance of the differences between the highest Gmm values from various mechanical devices and manual agitation.
|
From page 3... ...
Syntron Vibrating Table (VP-51 D1) Orbital Shaker Table (SHKE 2000)
|
From page 4... ...
The laboratory mixtures were designed according to the Superpave mix design procedure. Non4 Table 2 Mix designs of the dense-graded laboratory-prepared and plant-produced mixtures.
|
From page 5... ...
In addition to the weight measurements, the acceleration and frequency in the x-, y- and z-axes of the vibrating tables were measured to the nearest 0.01 m/s2 and 0.1 Hz, respectively. Gmm was measured using the Corelok vacuum sealing device according to ASTM D6857-09, "Standard Test Method for Maximum Specific Gravity and Density of Bituminous Paving Mixtures Using Automatic Vacuum Sealing Method."5 The specified weight of loose asphalt mixture was placed in special plastic bags provided for the vacuum sealing device.
|
From page 6... ...
Aggregate Drum b b, d b, d b b, d b b b b Washer Corelok (vacuum b b b b b b b b b sealing device) a = Change in vibration b = Equipment evaluation c = Manual versus mechanical d = Order of placement (water and mixture)
|
From page 7... ...
The practical significance was evaluated by estimating the change in air void values resulting from the observed change in Gmm. The statistical significance was evaluated using either a Scheffé test for multivariate comparisons or a paired t-test for two-variable comparisons.
|
From page 8... ...
are commonly used with the Humboldt device. The Gmm of field and laboratory mixtures was measured at various settings of the Humboldt device, and the highest Gmm values were compared with the Gmm from manual agitation and from the settings commonly used by the states.
|
From page 9... ...
The difference between the calculated air voids at Settings 7 and 8 is 0.07%, which is not considered practically significant. Based on the small difference in the Gmm of the 9.5-mm mixture at Settings 7 and 8, Setting 7 of the Humboldt device is suggested as the optimum operational setting for measuring Gmm of 9.5-mm and 19.0-mm dense-graded field mixtures.
|
From page 10... ...
Nevertheless, at every setting of the Humboldt device, the difference between replicate measurements of the three mixtures was less than 0.007, significantly smaller than the acceptable difference between two replicate measurements specified in AASHTO T 209. The calculated air voids were compared to examine the practical significance of the differences between the highest Gmm and Gmm of the settings indicated as important by the state DOT survey.
|
From page 11... ...
The Gmm of field and laboratory mixtures were measured at various settings of the Gilson device, and the resulting highest Gmm values were compared with the Gmm from manual agitation and from the settings commonly used by the states. Dense-Graded Field Mixtures.
|
From page 12... ...
Nevertheless, the difference between replicates at any setting was less than 0.005, which is significantly smaller than the acceptable difference between two replicate measurements as specified in AASHTO T 209. The practical significance of the difference between the highest Gmm and the Gmm values obtained from the settings of importance identified in the state DOT survey was examined by comparing the calculated air voids.
|
From page 13... ...
Nevertheless, the difference between replicates at any setting was less than 0.005, significantly smaller than the acceptable difference between two replicate measurements as specified in AASHTO T 209. The practical significance of the difference between the highest Gmm and the Gmm from settings of importance identified in the state DOT survey was examined by comparing the calculated air voids.
|
From page 14... ...
The difference between replicate measurements at any setting was smaller than 0.004, which is significantly smaller than the acceptable difference between two replicate measurements as specified in AASHTO T 209. The practical significance of the difference between the highest Gmm and the Gmm from the settings of importance indicated by the state DOT survey was examined by comparing calculated air voids.
|
From page 15... ...
The difference between replicate measurements at any setting was less than 0.005, which is significantly smaller than the acceptable difference between two replicate measurements as specified in AASHTO T 209. The practical significance of the differences between the highest Gmm and the Gmm from the settings of importance indicated by the state DOT survey was examined by comparing the calculated air voids.
|
From page 16... ...
The difference between replicate values of the 9.5-mm mixture reached a maximum at 180 rpm; nevertheless, for both mixtures, the difference at any setting was less than 0.005, which is significantly smaller than the acceptable difference between two replicate measurements as specified in AASHTO T 209. The practical significance of the difference between the highest Gmm and those from the settings of importance indicated from the state DOT survey was examined by comparing the calculated air voids.
|
From page 17... ...
The difference in air voids between the highest Gmm and the Gmm from manual agitation was 0.17%, 0.24%, and 0.53% for the 9.5-mm, 12.5-mm, and 19.0 mm mixtures, respectively. Considering other possible sources of variability in measuring air voids, using manual agitation would probably provide significantly lower air voids than the actual air voids for the 12.5-mm and 19.0-mm compacted mixtures.
|
From page 18... ...
This finding regarding manual agitation disagrees with that based on the calculated air voids discussed in the previous paragraph. Given that water was substantially cloudy at vibration levels of 270 rpm and above, the possibility of using 240 rpm for the dense-graded laboratory mixtures was explored through an examination of the difference in air voids.
|
From page 19... ...
5 (Cloudy at 8, 7, 6, respectively) Syntron Vibrating Table 7 7 8 7 9 8 8 -- -- (VP-51 D1)
|
From page 20... ...
Therefore, the comparison of air voids and the results of statistical analysis suggest that the mechanical devices produce the same Gmm if they are operated at their optimum settings, but that manual agitation produces statistically lower Gmm values than the mechanical devices. An analysis of the standard deviation of the Gmm measurements for the 9.5-mm and 19.0-mm densegraded field mixtures using the various devices and methods found that the highest Gmm standard deviations of the mechanical devices were 0.002 and 0.003, which are below the acceptable 1s repeatability standard deviation for a single-operator test condition described in AASHTO T 209.
|
From page 21... ...
For the 25.0-mm mixture, however, the differences between the Gmm from manual agitation and that from the HMA Vibrating Table and Orbital Shaker Table are significantly different; for the 37.5-mm mixture, the difference between the Gmm from manual agitation and the Gmm from the Aggregate Drum Washer is significantly different. In light of the practical significance of the difference in air voids and the statistical significance of the differences between Gmm of manual agitation and the Gmm of the several mechanical devices, the use of manual agitation for measuring the Gmm of dense-graded laboratory mixtures is not suggested.
|
From page 22... ...
Dense-Graded Field Mixtures Gmm values were measured for two dense-graded field mixtures using three devices at the settings found to provide the highest Gmm values. The resulting air voids were computed using these measured Gmm values and assumed Gmb values of 2.404 for the 9.5-mm mixture and 2.422 for the 19.0-mm mixture.
|
From page 23... ...
In addition, the difference between air voids from manual agitation and from mechanical devices ranged from 0.2% to 0.4%, which could be practically significant. Therefore, use of manual agitation for the measurement of Gmm is not suggested.
|
From page 24... ...
Although the highest Gmm was obtained after the 20-minute vacuum/agitation period, statistical analysis of Gmm values and evaluation of the air voids indicated that the difference in Gmm and air voids between the 15-minute and 20-minute agitation periods was not significant. In addition, the variability of measurements was slightly greater after 20 minutes than after 15 minutes of vacuum/agitation.
|
From page 25... ...
Transportation Research Board 500 Fifth Street, NW Washington, DC 20001 These digests are issued in order to increase awareness of research results emanating from projects in the Cooperative Research Programs (CRP)
|
Key Terms
This material may be derived from roughly machine-read images, and so is provided only to facilitate research.
More
information on Chapter Skim is available.