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OCR for page 7
mined using one device (Gilson) and three mixtures, in the z direction and the lowest in the y direction.
yielding the three mixture-device combinations des- No noticeable change in vibration occurred until
ignated as "e" in Table 3. Setting 5. The frequency, acceleration, and energy
started to increase with the increase in the dial set-
ting of the Humboldt device after Setting 4. A max-
RESULTS AND ANALYSIS
imum frequency of 53 Hz, a maximum acceleration of
The experimental results were analyzed to de- 5.0 m/s2, and a maximum kinetic energy of 50 micro-
termine the effects of the variables discussed in the joules were achieved at Setting 8 and were maintained
previous section on Gmm. The variables included through Setting 10.
vibration settings of mechanical agitators, agitation As with the Humboldt device, for the Gilson de-
type (manual or mechanical), brand of mechanical vice the frequency was the same in the x, y, and z di-
agitators, order of placement of water and mixture in rections at each vibration setting. Also as with the
pycnometer, and the duration of the vacuum/agitation Humboldt device, the acceleration and energy were
process. The relationship between the vibration prop- most prominent in the z direction and least promi-
erties of vibrating tables and the highest Gmm measured nent in the y direction. The difference between the
by them also was examined. vibrations imparted by the Gilson and Humboldt
The significance of the effects of these variables devices was in the vibration trends. Although the
on Gmm was evaluated statistically, physically, and Humboldt device did not provide any noticeable ac-
from a practical point of view. The physical signifi- celeration up to Setting 5, the acceleration of the
cance was evaluated by visually observing the change Gilson device was noticeable starting at Setting 1, with
in water cloudiness during agitation. The practical sig- a steady increase in frequency, acceleration, and
nificance was evaluated by estimating the change in energy afterward. A maximum frequency of 52 Hz, a
air void values resulting from the observed change in maximum acceleration of 7.2 m/s2, and a maximum
Gmm. The statistical significance was evaluated using total kinetic energy of 90 microjoules were achieved
either a Scheffé test for multivariate comparisons or a at the highest setting (Setting 8).
paired t-test for two-variable comparisons. Unlike the previous devices, the Syntron device
showed substantial differences in the directional fre-
quencies. At Setting 3 and lower, the x and y direc-
Vibration Measurements tions were fairly close in magnitude, and the magni-
Using an accelerometer, frequency and accelera- tude in the z direction was about half of this value.
tion were measured in x, y, and z directions for the four However, from Setting 4 until the peak at Setting 8,
vibratory devices (Humboldt, Gilson, Syntron, and the increase in magnitude in the z direction was far
HMA shaking tables). The frequency and acceleration greater than that of the x and y magnitudes. Although
data were collected for 10 seconds at 5 minutes into the frequency peaked at Setting 8 with frequencies
the 15-minute agitation period. Data was collected of 63, 119, and 629 Hz in the x, y, and z directions,
every 0.000605 seconds, providing 16,526 accelera- respectively, the maximum acceleration and energy
tion data points and 10 frequency data points. The ac- occurred at Setting 9. The maximum acceleration
celeration data was used to calculate the kinetic energy and total energy at Setting 9 were 76.3 m/s2 and
of vibration using the kinetic energy equation, KE = 4,307 microjoules, respectively.
1
/2 mv2, where m is the mass of the object and v is the The HMA device operates at a fixed setting. Al-
velocity of vibration. The velocity was calculated by though the vibration frequencies in the x, y, and z di-
integrating the acceleration data over the 10-second rections were the same, differences occurred in the
period. The energy values in the three directions were directional accelerations and energies. The acceler-
then summed to calculate the total kinetic energy. The ation and energy in y and z directions were relatively
total energy of vibration of the various shaking tables close in magnitude, but the magnitude in the x di-
was compared to examine whether the same energy of rection was considerably less. The maximum accel-
vibration would yield the same Gmm value. eration and total energy for the HMA device were
For the Humboldt device, at each vibration set- 26 m/s2 and 1,400 microjoules, respectively.
ting, the frequency was the same in the x, y, and z di- As the above results show, the vibration proper-
rections. However, the acceleration and energy were ties of the four devices are very different. As shown
not the same in all directions; they were the highest from the comparison of the total energy from the
7
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Syntron and Humboldt devices, the total energy from The statistical significance of the difference
one device could be as much as 10 times greater than between values of Gmm was examined using a Scheffé
that from another device. The next sections discuss test.6 Whenever multivariate analysis of variance
the effect on Gmm of different vibration intensities. (MANOVA) rejects the null hypothesis, the Scheffé
test will find which comparison yielded the signifi-
cant difference. A Scheffé test was conducted to
Gmm Measurements at Various Settings compare the Gmm values that resulted from various set-
of the Vibrating Tables tings of each device. The comparison of the computed
Four vibratory tables with variable settings were F from the Scheffé test with the critical F values would
used to evaluate the effect of vibration intensity on determine whether the difference between Gmm of each
Gmm: the Humboldt Vibrating Table, Gilson Vibro- pair of vibration settings was significant.
Deaerator, Syntron Vibrating Table, and Orbital To determine the optimum vibration setting, the
Shaker. Measurements of Gmm were made at several results of both the physical evaluation and the sta-
settings of the vibrating devices, as well as at zero tistical analysis were taken into account. The setting
agitation and manual agitation. A comparison of Gmm that provided the highest Gmm without substantially
at various settings would indicate if there was a clouding the water was considered the optimum set-
systematic change in Gmm and its variability with ting for a device. The statistical tests on Gmm and the
change in vibration setting. Although measurements comparison of the computed air void values were
used to select an optimum setting of a device that
at zero agitation were performed with all four
would result in a Gmm that was not significantly dif-
mechanical devices, the manual agitation was only
ferent from the highest Gmm of the several mixtures.
performed with three of the device setups. The
The significance of the difference between the
Minnesota DOT setup with the Syntron device was
Gmm from manual agitation and the highest Gmm ob-
not used for manual agitation because it was not prac- tained with a mechanical device also was evaluated
tical to strike or shake its bell-jar vacuum chamber. statistically and from a practical standpoint. If this dif-
To examine the physical significance of the vi- ference was significant, use of manual agitation would
bration intensity, changes in the clarity of water in not be recommended for that particular mixture.
which the HMA sample was immersed were ob- The following sections discuss the analysis of
served in conjunction with the changes in intensity the results obtained from the four vibrating tables
of vibration. Substantially cloudy water would indi- with variable settings.
cate the occurrence of asphalt stripping due to in-
tensive vibration of the shaking tables. Humboldt Vibrating Table (H-1756)
The practical significance of the change in Gmm
was examined using the equation The Humboldt Vibrating Table has 11 discrete
vibration settings marked 0 to 10. Based on the re-
G mm - G mb sults of the state DOT survey, Setting 5 (mid-range)
Va = and Setting 10 (maximum) are commonly used with
G mm
the Humboldt device. The Gmm of field and labora-
where tory mixtures was measured at various settings of
the Humboldt device, and the highest Gmm values
Va = air voids, were compared with the Gmm from manual agitation
Gmm = theoretical maximum specific gravity, and and from the settings commonly used by the states.
Gmb = bulk specific gravity.
Dense-Graded Field Mixtures. For the dense-
For calculating the air voids, a Gmb that would
graded 19.0-mm field mixture, measurements were
result in air voids equal to 4% ± 1% was assumed conducted at all 11 settings of the device. For the
for each mixture. Although a change of more than dense-graded 9.5-mm field mixture, the measure-
± 0.5% in air voids is typically significant, in this study ments at Settings 1 through 4 were omitted from the
a change greater than 0.2% in air voids was consid-
ered practically significant, compensating for the po-
tential variability in the measurement of Gmb, which 6NIST/SEMATECH e-Handbook of Statistical Methods, avail-
here was assumed to be a constant for each mixture. able at http://www.itl.nist.gov/div898/handbook/.
8
OCR for page 9
analysis because the changes in Gmm at these settings ated statistically using the Scheffé test. For the 9.5-mm
with respect to the zero setting were very small. The mixture, the comparison of the computed F and the
Gmm of the mixtures increased with the increase in the critical F value for a 5% level of significance indicated
device setting until Gmm reached a maximum. Further that the highest Gmm value from Setting 8 was signif-
increases in vibration intensity resulted in decreases icantly different from those of Settings 0 through 5,
of Gmm. For the 9.5-mm mixture, the highest Gmm of Setting 10, and manual agitation. The Gmm of Setting 8
2.512 was achieved at Setting 8, and for the 19.0-mm was not statistically different from those of Settings 6,
mixture, the highest Gmm of 2.536 was achieved at 7, and 9. For the 19.0-mm mixture, comparison of
Setting 7 of the Humboldt device. For the 9.5-mm the computed F with the critical F value indicated
mixture, Gmm from manual agitation (2.506) was that the highest Gmm from Setting 7 was significantly
equivalent to Gmm at Setting 5; for the 19.0-mm mix- greater than those of Settings 0 through 2. The rest
ture, Gmm from manual agitation (2.525) was equiva- of the settings provided Gmm that were statistically
lent to Gmm from Setting 4. the same as that of Setting 7.
The change in water clarity was monitored to ex- Based on the results of the statistical analysis and
amine the physical effect of vibration on the mixtures. the air voids comparison, manual agitation and the
Visual observation of the water indicated that for both mid-range (Setting 5) and maximum (Setting 10) of
mixtures the water remained clear up to Setting 6. At the Humboldt device would most likely provide sig-
Setting 7 the water became slightly cloudy, and at Set- nificantly lower air voids than the highest achieved
tings 8, 9, and 10 the water was substantially cloudy. air voids for the 9.5-mm mixture. However, for the
The differences in replicate Gmm values at differ- 19.0-mm mixture, the statistical analysis indicated
ent settings would indicate if there is a relationship that the highest Gmm of Setting 7 was statistically the
between vibration setting and measurement variabil- same as the Gmm from manual agitation and the mid-
ity. The difference between replicate measurements range and maximum settings. This suggests that man-
of both mixtures at every setting of the device was ual agitation and lower agitation settings would be
smaller than 0.005, which is significantly smaller than adequate for measuring Gmm of the coarser mixtures.
the acceptable difference between two replicate mea- Given that the water became substantially cloudy
surements specified in AASHTO T 209. at Settings 8, 9, and 10, the possibility of using Set-
Calculated air void values were compared to ex- ting 7 for the 9.5-mm mixture was investigated. The
amine the practical significance of differences be- F values from comparison of Gmm at Settings 7 and 8
tween the highest Gmm and the Gmm at settings indi- indicate that Settings 7 and 8 produced not signifi-
cated as important by the state DOT survey. Gmb cantly different values of Gmm for the 9.5-mm mix-
values of 2.404 and 2.422 were assumed for calcu- ture. The difference between the calculated air voids
lating the air voids of the 9.5-mm and 19.0-mm mix- at Settings 7 and 8 is 0.07%, which is not considered
tures, respectively. The differences between the air practically significant. Based on the small difference
voids from the highest Gmm and from the Gmm with in the Gmm of the 9.5-mm mixture at Settings 7 and 8,
manual agitation were 0.25% for 9.5-mm mixtures Setting 7 of the Humboldt device is suggested as the
and 0.41% for 19.0-mm mixtures. The differences in optimum operational setting for measuring Gmm of
air voids between the highest Gmm and Gmm at mid- 9.5-mm and 19.0-mm dense-graded field mixtures.
range agitation (Setting 5) were 0.24% and 0.22%
for 9.5-mm and 19.0-mm mixtures, respectively. Gap-Graded (SMA) Field Mixtures. The Gmm of
Moreover, the differences between the air voids from the three gap-graded (SMA) mixtures (9.5-mm,
the highest Gmm and the Gmm of the maximum setting 12.5-mm, and 19.0-mm NMAS) were measured using
(Setting 10) were 0.21% and 0.27% for 9.5-mm and the Humboldt device. Because there was no notice-
19.0-mm mixtures, respectively. Considering other able change in the vibration level of the device up to
possible sources of variability in measuring air voids, Setting 4, the measurements were conducted at Set-
use of manual agitation and use of mid-range and tings 5 through 10.
maximum settings could result in significantly lower The highest Gmm of the 9.5-mm and 12.5-mm mix-
air voids than the actual air voids of the compacted tures (2.647 and 2.466, respectively) were achieved at
9.5-mm and 19.0-mm mixtures. Setting 8 and the highest Gmm of the 19.0-mm mixture
The significance of the differences between Gmm (2.448) was achieved at Setting 9. The Gmm of the
measurements from various settings also was evalu- 9.5-mm and 12.5-mm mixtures with manual agitation
9
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were equivalent to those from Setting 5 (2.641 and 8 is significantly greater than the Gmm from Setting
2.459, respectively) and the Gmm of the 19.0-mm mix- 0, Setting 5, and manual agitation. The rest of the
ture with manual agitation was equivalent to that of settings provide statistically the same Gmm values as
Setting 6 (2.439). that of Setting 8. For the 19.0-mm SMA mixture, the
Visual observation of the water indicated that for highest Gmm of the 19.0-mm mixture from Setting 9
all three mixtures the water remained clear up to Set- is only significantly greater than the Gmm obtained
ting 6. At Settings 7 and 8, the water became slightly with zero agitation.
cloudy, and at Settings 9 and 10, the water became Given that water became substantially cloudy at
substantially cloudy. Setting 9, the possibility of using Setting 8 instead
The differences in replicate Gmm values at dif- of Setting 9 for the 19.0-mm SMA mixture was ex-
ferent settings would indicate if there is a relation- amined. The difference between the air voids from
ship between vibration setting and measurement the two settings is 0.1%, which is practically in-
variability. The differences in Gmm of two replicates significant. The computed F values also show that
at various settings did not indicate a defined trend the Gmm values from Setting 8 and Setting 9 are sta-
as a function of vibration setting. However, the dif- tistically the same. Therefore, conducting the Gmm
ferences between replicate measurements of the measurement of the 19.0-mm mixture at Setting 8 is
19.0-mm mixture were larger than those of the 9.5-mm recommended.
and 12.5-mm mixtures. Nevertheless, at every set- Based on the highest achieved Gmm of the 9.5-mm
ting of the Humboldt device, the difference between and 12.5-mm mixtures at Setting 8 and the small dif-
replicate measurements of the three mixtures was ference between the Gmm from Settings 8 and 9 for
less than 0.007, significantly smaller than the ac- the 19.0 mixtures, Setting 8 is suggested as the opti-
ceptable difference between two replicate measure- mum operational setting of the Humboldt device for
ments specified in AASHTO T 209. measuring Gmm of the SMA mixtures.
The calculated air voids were compared to exam-
ine the practical significance of the differences be- Dense-Graded Laboratory Mixtures. The Gmm of
tween the highest Gmm and Gmm of the settings indi- 4.75-mm, 12.5-mm, 25.0-mm, and 37.5-mm dense-
cated as important by the state DOT survey. Gmb graded laboratory mixtures were measured at Set-
values of 2.532, 2.357, and 2.339 were assumed for tings 4 through 10 of the Humboldt device. The
highest Gmm of the 4.75-mm mixture (2.557) was
calculating the air voids of the 9.5-mm, 12.5-mm, and
achieved at the maximum setting (Setting 10); the
19.0-mm SMA mixtures, respectively. The difference
highest Gmm of the 12.5-mm mixture (2.580) was
between air voids from the highest Gmm and Gmm from
obtained at Setting 8; and the highest Gmm of the
manual agitation was in the range of 0.23% to 0.30%; 25.0-mm and 37.5-mm mixtures (2.617 and 2.629,
the difference between the air voids from the highest respectively) were achieved at Setting 9 of the
Gmm and Gmm of mid-range agitation was in the range Humboldt device. For the 4.75-mm and 12.5-mm
of 0.23% to 0.45%; and the difference between the air mixtures, the Gmm from manual agitation (2.548 and
voids from the highest Gmm and Gmm from the maxi- 2.572, respectively) are equivalent to the Gmm from
mum setting (Setting 10) was in the range of 0.05% to Setting 5, and for the 25.0-mm and 37.5-mm mix-
0.20%. Considering other possible sources of vari- tures, the Gmm from manual agitation (2.610 and
ability in determining air voids, using the mid-range 2.625, respectively) are equivalent to the Gmm from
settings or manual agitation would most likely provide Setting 6. This finding suggests that, for coarser
significantly lower air voids. However, operating the mixtures, manual agitation produces Gmm equivalent
Humboldt device at the maximum setting would pro- to those from higher agitation levels than are found
duce Gmm practically the same as the highest Gmm. for finer mixtures.
The significance of the differences between Gmm The change in water clarity was monitored to
measurements from various settings was evaluated examine the physical effect of vibration on the mix-
statistically. For the 9.5-mm mixture, comparison of tures. The water did not become substantially cloudy
the computed F and the critical F value indicates at any of the settings. For the four mixtures, water
that, for a 5% level of significance, the Gmm values was slightly cloudy at the settings of the highest Gmm
from manual agitation and those of various settings (Setting 10 for the 4.75-mm mixture, Setting 8 for
are statistically the same. For the 12.5-mm mixture, the 12.5-mm mixture, and Setting 9 for the 25.0-mm
the highest Gmm of a 12.5-mm mixture from Setting and 37.5-mm mixtures).
10
OCR for page 11
The differences in replicate Gmm values at dif- explored. The highest Gmm of each mixture was com-
ferent settings would indicate if there is a relation- pared with Gmm at the settings that produced the high-
ship between vibration setting and measurement est Gmm of other mixtures. The differences between
variability. For these mixtures, the difference in Gmm the air voids of the mixtures resulting from the set-
of two replicates at various settings did not follow a tings that yielded the highest Gmm were below 0.1%,
defined trend as a function of vibration setting. At which is considered not significant. Comparison of
every setting of the device, the difference between Gmm from Settings 8, 9, and 10 confirmed this finding
replicate measurements was less than 0.005, which statistically by providing F values that were smaller
is significantly smaller than the acceptable differ- than the critical F value.
ence between two replicate measurements specified Based on the highest achieved Gmm of the four
in AASHTO T 209. laboratory mixtures at Settings 8, 9, and 10 and the
The practical significance of the difference be- similarity of the air voids from Settings 8, 9, and 10,
tween the highest Gmm and the Gmm of the settings in- Setting 8 is suggested as the optimum operational
dicated as important by the state DOT survey was ex- setting for the Humboldt device for measuring the
amined by evaluating the differences between their Gmm of the dense-graded laboratory mixtures. At
corresponding air voids. Gmb of 2.444, 2.466, 2.502, Setting 8, the water was only slightly cloudy.
and 2.515 were assumed for calculating the air voids
of the 4.75-mm, 12.5-mm, 25.0-mm, and 37.5-mm Gilson Vibro-Deaerator (SGA-5R)
mixtures, respectively. The difference between the air
voids that resulted from the highest Gmm and those The Gilson device has an adjustable dial that per-
that resulted from manual agitation was 0.30% for the mits a continuous increase of the vibration level.
4.75-mm and 12.5-mm mixtures and 0.24% and Eight marks, labeled 1 through 8, were made at ap-
0.15% for the 25.0-mm and 37.5-mm mixtures, re- proximately equal intervals on the dial to represent
spectively. Considering other possible sources of eight discrete levels of vibration. Based on the re-
variability in measuring the air voids, these differ- sults of the state DOT survey, in the state laborato-
ences could be significant. Therefore, from a practi- ries the Gilson device is commonly operated in its
cal viewpoint, for obtaining the highest Gmm of mix- middle to maximum range. The Gmm of field and lab-
tures, use of manual agitation is not recommended for oratory mixtures were measured at various settings
these dense-graded laboratory mixtures. of the Gilson device, and the resulting highest Gmm
For the 4.75-mm, 25.0-mm, and 37.5-mm mix- values were compared with the Gmm from manual
tures, the difference between the highest air voids agitation and from the settings commonly used by
and those from the mid-range setting (Setting 5) av- the states.
eraged 0.30%, which could be significant. The dif-
ferences between the highest air voids and those from Dense-Graded Field Mixtures. The Gmm of the
the maximum setting (Setting 10) averaged 0.03%, 9.5-mm and 19.0-mm dense-graded field mixtures
which was not practically significant. These numbers were measured at Settings 1 through 8 of the Gilson
suggest that operation of the Humboldt device at its device, as well as at zero agitation and using manual
higher settings will achieve the highest Gmm for these agitation. The highest Gmm (2.515 for the 9.5-mm
dense-graded laboratory mixtures. mixture and 2.536 for the 19.0-mm mixture) were
The significance of the differences between Gmm achieved at Settings 6 and 7, respectively. The Gmm
measurements obtained from various settings also values from manual agitation were equivalent to Gmm
was evaluated statistically. Based on a comparison values from Setting 3 for both mixtures (2.507 for the
of the computed and critical F values, the differences 9.5-mm mixture and 2.527 for the 19.0-mm mixture).
between the highest Gmm and the Gmm from manual The change in water clarity was monitored to ex-
agitation, Setting 5, and Setting 10 were not statisti- amine the physical effect of vibration on the mixtures.
cally significant. However, use of manual agitation Visual observation indicated that the water remained
and mid-range settings are not suggested for the dense- clear up to Setting 4. From Setting 5 through Setting 6,
graded laboratory mixtures because of the potential the water became slightly cloudy, and at Setting 7 and
significance of the differences in air voids. Setting 8 the water became substantially cloudy.
The possibility of using one vibration setting for The differences between two replicate Gmm
all four dense-graded laboratory mixtures also was values at various settings of the Gilson device were
11
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examined. No defined trend existed between the through 8. For the 19.0-mm mixture, the highest
variability of measurements and the intensity of vi- Gmm from Setting 7 is only significantly different
bration; however, higher variability was observed at from the Gmm yielded by zero agitation and Setting 1.
high Gmm values for the 19.5-mm mixture. Neverthe- The rest of the settings provide statistically the same
less, the difference between replicates at any setting Gmm as that of Setting 7. This agrees with previous
was less than 0.005, which is significantly smaller observations that manual and lower vibration levels
than the acceptable difference between two replicate might provide adequately high Gmm values for coarser
measurements as specified in AASHTO T 209. mixtures.
The practical significance of the difference be- Given that water was substantially cloudy at Set-
tween the highest Gmm and the Gmm values obtained ting 7 and higher, the possibility of using Setting 6
from the settings of importance identified in the state for the 19.0-mm mixture was investigated. It was
DOT survey was examined by comparing the calcu- observed from both air voids values and from statis-
lated air voids. Gmb of 2.404 and 2.422 were as- tical results that for measuring the 19.0-mm mixture,
sumed for calculating the air voids of the 9.5-mm lower settings (up to Setting 4) would result in Gmm
and 19.0-mm mixtures, respectively. The difference not significantly different from the highest Gmm.
between air voids of the highest Gmm and the Gmm Therefore, Setting 6 can be used for accurate mea-
from manual agitation was 0.31% for the 9.5-mm surement of Gmm for both the 9.5-mm and 19.0-mm
mixture and 0.35% for the 19.0-mm mixture. Con- dense-graded field mixtures.
sidering other possible sources of variability in mea-
suring air voids, use of manual agitation for either Gap-Graded (SMA) Field Mixtures. The three SMA
mixture would most likely result in significantly mixtures of 9.5-mm, 12.5-mm, and 19.0-mm NMAS
lower air voids than the actual air voids of the com- were tested using the Gilson device. The Gmm of the
pacted mixture. mixtures were measured at Settings 1 through 8. For
The difference between air voids from the high- all mixtures, measurements also were made at zero
est Gmm and that of mid-range agitation (Setting 4) agitation and using manual agitation. The highest
was 0.23% for the 9.5-mm mixture and 0.11% for Gmm values (2.649, 2.463, and 2.447 for the 9.5-mm,
the 19.0-mm mixture. This finding suggests that 12.5-mm, and 19.0-mm mixtures, respectively) were
use of the mid-range setting would most probably achieved at Setting 7 of the Gilson device. For the
result in significantly lower air voids for the 9.5-mm SMA mixtures, the Gmm values from manual agita-
mixture; however, for the 19.0-mm mixture, the tion were equivalent to the Gmm values in the range
mid-range setting would produce air voids similar of Settings 3 through 5. Change in water clarity was
to Setting 7. monitored to examine the physical effect of vibra-
The results also showed that the difference be- tion on the mixtures. Observation of the water indi-
tween air voids from the highest Gmm and those from cated that up to Setting 4, the water remained clear.
the maximum setting (Setting 8) is 0.07% for the From Setting 5 to Setting 7, the water became slightly
9.5-mm mixture and 0.24% for the 19.0-mm mix- cloudy, and at Setting 8, the water became substan-
ture. This suggests that for finer mixtures, the Gilson tially cloudy.
device can be operated at maximum setting to achieve The differences between two replicate Gmm val-
air voids similar to those achieved at Setting 6. How- ues at various settings of the Gilson device were ex-
ever, for the 19.0 mm mixture, the maximum setting amined. No defined trend was found between the
would most likely result in stripping of asphalt and variability of measurement and the intensity of vi-
provide significantly lower air voids than the actual bration; however, the differences between replicates
air voids of the compacted mixture. were larger for the 19.0-mm mixtures. Nevertheless,
The significance of the difference between Gmm the difference between replicates at any setting was
measurements from various settings of the Gilson smaller than 0.007, which is significantly smaller
device also was evaluated statistically. The highest than the acceptable difference between two replicate
Gmm of the 9.5 mm mixture from Setting 6 is signif- measurements as specified in AASHTO T 209.
icantly different from the Gmm at zero agitation and The practical significance of the difference be-
using manual agitation, and significantly different tween the highest Gmm and the Gmm from settings of
from the Gmm yielded by Settings 1 through 4, but it importance identified in the state DOT survey was
is statistically the same as the Gmm from Settings 5 examined by comparing the calculated air voids. Gmb
12
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values of 2.532, 2.357, and 2.339 were assumed for tween the variability of measurement and the inten-
calculating the air voids of the 9.5-mm, 12.5-mm, sity of vibration, a smaller variability at the settings
and 19.0-mm SMA mixtures, respectively. The dif- of higher Gmm was observed for the 12.5-mm mix-
ference between the air voids from the highest Gmm ture. The variability of the 37.5-mm mixture was
and the Gmm at the maximum setting (Setting 8) less than those of the 4.75-mm and 12.5-mm mix-
is in the range of 0.08 to 0.10, which is not practi- tures, which might be attributed to the better release
cally significant. At 0.25% for the 9.5-mm mixture of air from coarser mixtures. Nevertheless, the dif-
and 0.28% for the 19.0-mm mixtures, the differ- ference between replicates at any setting was less
ences between air voids from the highest Gmm and than 0.005, significantly smaller than the acceptable
the Gmm from manual agitation could be significant. difference between two replicate measurements as
At 0.39% for the 19.0-mm mixture, the difference specified in AASHTO T 209.
between using the highest Gmm and using the Gmm The practical significance of the difference be-
from mid-range agitation (Setting 4) also could be tween the highest Gmm and the Gmm from settings of
significant. importance identified in the state DOT survey was ex-
The significance of the differences between Gmm amined by comparing the calculated air voids. Gmb
measurements from various settings of the Gilson values of 2.444, 2.466, and 2.515 were assumed for
device also were evaluated statistically. Based on calculating the air voids of the 4.75-mm, 12.5-mm,
the computed F values, the highest Gmm of the SMA and 37.5-mm mixtures, respectively. The difference
mixtures from Setting 7 was statistically the same between the air voids from the highest Gmm and the air
as those from manual agitation, from the mid-range voids from mid-range agitation (Setting 4) was in the
setting (Setting 4), and from maximum agitation range of 0.12% to 0.18%. The difference between the
(Setting 8). Thus, manual agitation, mid-range, and air voids from the highest Gmm and the air voids from
maximum settings would provide statistically the the maximum setting (Setting 8) was in the range of
same Gmm as that from Setting 7. However, from a 0.10% to 0.15%. The difference between the air voids
practical point of view, the differences between air from the highest Gmm and the air voids from manual
voids from Setting 7 and those from the mid-range agitation was in the range of 0.20% to 0.37%. There-
setting and from manual agitation could become sig- fore, from a practical point of view, the use of Gmm
nificant if the variability of the Gmb measurements is from manual agitation could result in significantly
considered. lower air voids for compacted mixtures.
Given that the highest Gmm was produced at Set- The statistical significance of the difference
ting 7 and water was only slightly cloudy at this set- between Gmm from various device settings was eval-
ting, Setting 7 of the Gilson device is suggested as the uated using a Scheffé test. A comparison of the com-
optimum operational setting for the SMA mixtures. puted and critical F values showed that the differ-
ence between the highest Gmm and the Gmm from
Dense-Graded Laboratory Mixtures. The Gmm of manual agitation was significant for the 12.5-mm
the 4.75-mm, 12.5-mm, and 37.5-mm dense-graded and 37.5-mm mixtures but not significant for the
laboratory mixtures were measured at Settings 1 4.75-mm mixture. Comparison of the highest Gmm
through 8, at zero agitation, and using manual agita- with the Gmm of Settings 4 and 8 revealed that the
tion. The highest Gmm of 2.555, 2.580, and 2.631 of highest Gmm values were statistically the same as
the 4.75-mm, 12.5-mm, and 37.5-mm mixtures were those from the mid-range and maximum settings.
achieved at Settings 7, 6, and 6 of the Gilson device, Based on the results from statistical comparison and
respectively. For all three dense-graded laboratory evaluation of the air void values, use of manual ag-
mixtures, manual agitation resulted in Gmm values itation for the dense-graded laboratory mixtures is
that were equivalent to or less than the Gmm values not suggested.
from Setting 2. For the 4.75-mm mixture, water be- The possibility of selecting one optimum setting
came cloudy at Setting 8, and for the 12.5-mm and of the Gilson device for the dense-graded laboratory
37.5-mm mixtures, water became cloudy at Settings mixtures was investigated. As indicated earlier, for
7 and 6, respectively. the 37.5-mm mixture, the water was substantially
The differences between the two replicate Gmm cloudy at Setting 6, so the possibility of using Set-
values at various settings of the Gilson device were ting 5 for the three mixtures was examined. The dif-
examined. Although no defined trend was found be- ference between the air voids from Settings 5, 6, and
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7 for the three mixtures was less than 0.11%, which 0.07% for the 9.5-mm mixture and 0.08% for the
is not considered practically significant. This finding 19.0-mm mixture; neither of these differences is
is reinforced by the results of the statistical analysis, considered practically significant.
where the computed F values from comparison of The significance of the difference between Gmm
Gmm of Settings 5, 6, and 7 were smaller than the crit- values from various settings also was examined sta-
ical F value. Considering the small difference be- tistically using a Scheffé test. For the 9.5-mm mix-
tween the air voids yielded from Setting 5 and those ture, the differences between Gmm values from vari-
from Settings 6 and 7, Setting 5 is suggested for the ous settings were not significant. For the 19.0-mm
4.75-mm, 12.5-mm, and 25.0-mm mixtures. mixture, only the differences between the highest
Gmm and the Gmm from Setting 10 and zero agitation
Syntron Vibrating Table (VP-51 D1) are statistically significant.
Based on achieving the highest Gmm and water
The Syntron device can be operated at ten discrete
clarity, Setting 7 is suggested as the optimum oper-
settings (Settings 1 through 10). Based on the results
ational setting of the Syntron device for measuring
of the state DOT survey, the Syntron device is com- Gmm of the 9.5-mm and 19.0-mm dense-graded field
monly operated at Setting 5 in state laboratories. Dur- mixtures.
ing this study, the device was used following the
setup used by the Minnesota DOT. Measurements at
Gap-Graded (SMA) Field Mixtures. The Gmm of
zero agitation were performed along other settings,
the 9.5-mm, 12.5-mm, and 19.0-mm SMA mix-
but manual agitation was not performed with this
tures were measured at Settings 1 through 10 of the
device as it is impractical to strike or shake the bell- Syntron device. Measurements also were conducted
jar vacuum chamber given this setup. The following at zero agitation. The highest Gmm of the 9.5-mm
results are based on Gmm measurements. (2.646), 12.5-mm (2.464), and 19.0-mm (2.448)
mixtures were achieved at Settings 8, 7, and 9, re-
Dense-Graded Field Mixtures. The highest Gmm spectively. The water appeared clear through Set-
(2.513 and 2.534 for the 9.5-mm and 19.0-mm mix- ting 5. At Settings 6 through 8 and at Setting 10, the
tures, respectively) were achieved at Setting 7 of the water became slightly cloudy. At Setting 9, the
Syntron device. Visual observation indicated that water was substantially cloudy.
the water remained clear through Setting 4. At Set- The differences between two replicate Gmm val-
tings 5 through 8 and at Setting 10, the water was ues at various settings of the Syntron device yielded
slightly cloudy. At Setting 9, the water was substan- no defined trend between the variability of mea-
tially cloudy. surement and the intensity of vibration. However,
Examination of differences between two repli- the differences between replicates of the 19.0-mm
cate Gmm values at various settings of the Syntron de- mixtures were larger than those of the other mix-
vice yielded no defined trends between the variabil- tures. Nevertheless, the difference between repli-
ity of measurements and the intensity of vibration. cates at any setting was less than 0.007, which is
The difference between replicate measurements significantly smaller than the acceptable difference
at any setting was smaller than 0.004, which is sig- between two replicate measurements as specified in
nificantly smaller than the acceptable difference be- AASHTO T 209.
tween two replicate measurements as specified in The practical significance of the differences be-
AASHTO T 209. tween the highest Gmm and the Gmm from the settings
The practical significance of the difference be- of importance indicated in the state DOT survey was
tween the highest Gmm and the Gmm from the settings examined by comparing calculated air voids. Gmb of
of importance indicated by the state DOT survey 2.532, 2.357, and 2.339 were assumed for calculating
was examined by comparing calculated air voids. the air voids of the 9.5-mm, 12.5-mm, and 19.0-mm
Gmb values of 2.404 and 2.422 were assumed for cal- mixtures, respectively. The differences between the
culating the air voids of the 9.5-mm and 19.0-mm air voids yielded from the mid-range (Setting 5) and
mixtures, respectively. Air voids resulting from the the highest Gmm were 0.40%, 0.15%, and 0.30% for
highest Gmm (at Setting 7) were compared with air the 9.5-mm, 12.5-mm, and 19.0-mm mixtures, re-
voids resulting from Setting 5, which is commonly spectively. Considering other possible sources of
used by the state laboratories. The difference was variability in measuring air voids, using Setting 5
14
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would likely result in significantly lower air voids The practical significance of the differences
than the actual air voids of the 9.5-mm and 19.0-mm between the highest Gmm and the Gmm from the set-
compacted mixtures. tings of importance indicated by the state DOT sur-
The statistical comparison indicated that the high- vey was examined by comparing the calculated air
est Gmm of the 9.5-mm mixture (from Setting 8) is sig- voids. Gmb values of 2.444 and 2.466 were assumed
nificantly different from the Gmm of Settings 0 through for calculating the air voids of the 4.75-mm and
5. For the 12.5-mm mixture, the only significant dif- 12.5-mm mixtures, respectively. The differences be-
ferences were found between the highest Gmm and the tween the air voids from the highest Gmm and the air
Gmm of Settings 0 and 1. For the 19.0-mm mixture, the voids from Setting 5, which is commonly used by
highest Gmm differed significantly from the Gmm at the state laboratories, were 0.17% for the 4.75-mm
Settings 0 through 4, but not significantly from the mixture and 0.18% for the 12.5-mm mixture. From
Gmm at Setting 5 and higher. These results suggest that a practical point of view, these differences are not
for the 9.5-mm and 19.0-mm mixtures, if the Syntron considered significant.
device is operated at the mid-range setting, the result- The significance of the difference between Gmm
ing Gmm would likely be significantly lower than the measurements from various settings of the Syntron
highest Gmm. table also was evaluated statistically. The highest
The possibility of selecting one setting of the Gmm of the two dense-graded laboratory mixtures
Syntron device for all three mixtures was explored. were not significantly different from the Gmm from
Comparing the air voids from the highest Gmm and Setting 5, which is commonly used by the state lab-
the Gmm from Settings 7, 8, and 9, the smallest dif- oratories. Computed F values also indicated that, for
ferences occurred between the air voids from the measuring Gmm of the dense-graded laboratory mix-
highest Gmm and from the Gmm of Setting 8 (a maxi- tures, any setting higher than Setting 3 would yield
mum of 0.14%). Therefore, Setting 8 can be used for Gmm values that were not statistically different.
the SMA mixtures without a significant decrease in Because water became substantially cloudy at
air voids. This finding is supported by the statistical Setting 8, the use of a lower setting as the optimum
analysis of the data. F values for comparison of Gmm setting was evaluated. Comparing the air voids from
from Setting 8 with Gmm from Settings 7 and 9 were Settings 7 and 8 yielded differences smaller than
lower than the critical F value. Based on these ob- 0.1%, which is not practically significant. This find-
servations, Setting 8 is suggested as the optimum ing also was supported by statistical analysis: Set-
operational setting of the Syntron device for mea- tings 7 and 8 were found to produce statistically the
suring the Gmm of the SMA mixtures. same Gmm values. Therefore, based on the clarity of
the water and the non-significant differences between
Dense-Graded Laboratory Mixtures. Two of the the air voids from Settings 7 and 8, Setting 7 is
four dense-graded laboratory mixtures were tested suggested as the optimum operational setting of the
with the Syntron device. The Gmm of the 4.75-mm Syntron device for measuring the Gmm of the 4.75-mm
and 12.5-mm mixtures were measured at Settings 1 and 12.5-mm dense-graded laboratory mixtures.
through 10 and at zero agitation. The highest Gmm
(2.556 and 2.582, for the 4.75-mm and 12.5-mm mix- Orbital Shaker (SHKE 2000)
tures, respectively) were achieved at Setting 8. Visual The Orbital Shaker has a digital dial for the con-
observation indicated that the water remained clear tinuous increase of vibration in the range of 15 to
through Setting 4. At Settings 5 through 7 and at Set- 500 rpm. The measurement of Gmm of the dense-
ting 10, the water was slightly cloudy. At Settings 8 graded field mixtures was conducted at nine vibra-
and 9, the water was substantially cloudy. tion intensity levels at 30-rpm intervals between 90
Comparison of the differences between two repli- and 330 rpm. Measurements also were conducted at
cate Gmm values at various settings of the Syntron de- zero agitation and using manual agitation. Based on
vice yielded no defined trend between the variability the survey of the state laboratories, 270 rpm is the
of measurement and the intensity of vibration. The most commonly used vibration level.
difference between replicate measurements at any set-
ting was less than 0.005, which is significantly smaller Dense-Graded Field Mixtures. For the dense-graded
than the acceptable difference between two replicate field mixtures, the highest Gmm (2.512 and 2.537, for
measurements as specified in AASHTO T 209. 9.5-mm and 19.0-mm mixtures, respectively) were
15
OCR for page 16
obtained at vibration levels of 240 rpm and 210 rpm for the 9.5-mm mixture. For the 19.0-mm mixture,
of the Orbital device. The Gmm values from manual however, the difference between the highest Gmm
agitation were equivalent to the Gmm values obtained (from a vibration level of 210 rpm) and the Gmm from
at 150 rpm for the 9.5-mm mixture and at 90 rpm for manual agitation was significant.
the 19.0-mm mixture. Visual observation indicated The possibility of selecting one setting for the
that the water remained clear through 150 rpm. From Orbital device for both the 9.5-mm and 19.0-mm
180 rpm through 240 rpm, the water became slightly mixtures was explored. The differences between
cloudy. At 270 rpm and higher, the water became the air voids at vibration levels of 210 rpm and
substantially cloudy. 240 rpm were 0.05% and 0.11% for the 9.5-mm and
Examination of the differences between two repli- 19.0-mm mixtures, respectively. These differences
cate Gmm values at various settings of the Orbital de- are not considered significant. Statistical analysis
vice showed no defined trend between the variabil- also indicated that, for both mixtures, the Gmm from
ity of measurement and the intensity of vibration for vibration levels of 210 rpm and 240 rpm are sta-
the 19.0-mm mixture. The difference between repli- tistically the same. Therefore, a setting of either
cate values of the 9.5-mm mixture reached a maxi- 210 rpm or 240 rpm could be selected. Based on
mum at 180 rpm; nevertheless, for both mixtures, the observation of a slight level of cloudiness in the water
difference at any setting was less than 0.005, which at 240 rpm, use of the higher setting of 240 rpm is
is significantly smaller than the acceptable difference suggested as the optimum vibration level at which
between two replicate measurements as specified in to set the Orbital device for dense-graded field
AASHTO T 209. mixtures.
The practical significance of the difference
between the highest Gmm and those from the set- Gap-Graded (SMA) Field Mixtures. The three
tings of importance indicated from the state DOT SMA mixtures (9.5-mm, 12.5-mm, and 19.0-mm
survey was examined by comparing the calculated NMAS) were tested with the Orbital shaker. Mea-
air voids. Gmb values of 2.404 and 2.422 were as- surements were conducted at nine vibration inten-
sumed for calculating the air voids of the 9.5-mm sity levels at 30-rpm intervals between 90 rpm and
and 19.0-mm mixtures, respectively. Differences 330 rpm. Measurements also were conducted at zero
between the air voids from the highest Gmm and the agitation and using manual agitation. For the 9.5-mm
air voids from manual agitation and at 270 rpm mixture, the highest Gmm (2.649) was obtained at a
(the level commonly used by the state laboratories) vibration level of 270 rpm; for the 12.5-mm mixture,
were examined. For the 9.5-mm mixture, the differ- the highest Gmm (2.464) was obtained at 240 rpm;
ence between the air voids from the highest Gmm and and for the 19.0-mm mixture, the highest Gmm (2.449)
the air voids from manual agitation was 0.18%. For was obtained at 300 rpm. Manual agitation resulted
the 19-mm mixture, the difference was 0.27%. Con- in Gmm values that were equivalent to the values ob-
sidering the possible variability of the Gmb measure- tained at vibration levels in the range of 90 rpm to
ments, use of manual agitation might result in signif- 150 rpm. Visual observation indicated that the water
icantly lower air voids for the 19.0-mm compacted remained clear at vibration levels through 150 rpm.
mixtures. From 180 rpm through 240 rpm, water became slightly
The differences between the air voids from the cloudy, and at 270 rpm and higher, the water became
highest Gmm and the air voids at a vibration level of substantially cloudy.
270 rpm is 0.11% for the 9.5-mm mixture and 0.16% The differences between two replicate Gmm val-
for the 19.0-mm mixture. For 9.5-mm and 19.0-mm ues at various settings of the Orbital device showed
mixtures, vibration at 270 rpm produced air voids that no defined trend between the variability of measure-
were not significantly different from the highest air ment and the intensity of vibration. Differences
void values. between replicate values at any vibration level were
The statistical significance of the difference be- less than 0.007, which is significantly smaller than
tween the Gmm from various settings of the Orbital the acceptable difference between two replicate
device was evaluated using a Scheffé test. The dif- measurements as specified in AASHTO T 209.
ferences between the highest Gmm (from a vibration The practical significance of the difference be-
level of 240 rpm) and the Gmm from other vibration tween the highest Gmm and the Gmm from the settings
levels or from manual agitation were not significant of importance identified in the state DOT survey was
16
OCR for page 17
examined by comparing calculated air voids. Gmb using the Orbital device. The Gmm of the 4.75-mm,
values of 2.532, 2.357, and 2.339 were assumed for 12.5-mm, and 25.0-mm dense-graded laboratory
calculating the air voids of the 9.5-mm, 12.5-mm, mixtures were measured at nine vibration intensity
and 19.0-mm mixtures, respectively. The difference levels at 30-rpm intervals between 90 rpm and
in air voids between the highest Gmm and the Gmm 330 rpm. Measurements also were conducted at
from manual agitation was 0.17%, 0.24%, and 0.53% zero agitation and using manual agitation. For the
for the 9.5-mm, 12.5-mm, and 19.0 mm mixtures, re- 4.75-mm, 12.5-mm, and 25.0-mm mixtures, the
spectively. Considering other possible sources of vari- highest Gmm of 2.556, 2.580, and 2.616 were ob-
ability in measuring air voids, using manual agitation tained at the 270, 240, and 300 rpm settings of the
would probably provide significantly lower air voids Orbital device, respectively. Visual observation
than the actual air voids for the 12.5-mm and 19.0-mm indicated that the water remained clear through a
compacted mixtures. vibration level of 150 rpm. From 180 rpm through
For the 19.0-mm mixture, the difference in air 240 rpm, the water became slightly cloudy, and at
voids between the highest Gmm and the Gmm at a vi- levels of 270 rpm and above, the water became
bration level of 270 rpm, which is the level commonly substantially cloudy.
used by the states, was 0.03%. For the 12.5-mm mix- The differences between two replicate Gmm values
ture, the difference was 0.07%. These differences in at various settings of the Orbital device showed no de-
air voids are not practically significant. fined trend between the variability of measurements
The significance of the differences between Gmm and the intensity of vibration. Also, the difference be-
values from various settings of the Orbital device tween replicate measurements at any setting was less
also was examined statistically using F values from a than 0.005, which is significantly smaller than the ac-
Scheffé test. For the 9.5-mm mixture, the difference ceptable difference between two replicate measure-
between the Gmm of any pair of vibration levels was ments as specified in AASHTO T 209.
not significant. For the 19.0-mm mixture, the highest The practical significance of the difference be-
Gmm from a vibration level of 300 rpm was only sig- tween the highest Gmm and the Gmm from the vibra-
nificantly different from the Gmm from zero agitation tion levels identified as important from the state
and from a vibration level of 90 rpm. For the 12.5-mm survey was examined by comparing calculated air
mixtures, however, the highest Gmm from a vibration voids. Gmb values of 2.444, 2.466, and 2.502 were
level of 240 rpm was significantly different from the assumed for calculating the air voids of the 4.75-mm,
Gmm from zero agitation, at 90 rpm, and using manual 12.5-mm, and 25.0-mm mixtures, respectively. The
agitation. In summary, based on differences between differences in air voids between manual agitation
the air voids, manual agitation is not suggested for the and the highest Gmm were in the range of 0.28%
12.5-mm and 19.0-mm SMA mixtures. to 0.34%. Such differences suggest that manual
Water was observed to be substantially cloudy at agitation of the Orbital shaker flasks could result
vibration levels of 270 rpm and above. Therefore, the in significantly lower air voids than the actual air
possibility of using a level of 240 rpm for the three voids of compacted mixtures. The differences in
SMA mixtures was examined on the basis of differ- air voids between the highest Gmm and the Gmm at a
ences in air voids between vibration levels at 240 rpm, vibration level of 270 rpm are 0.04% and 0.10% for
270 rpm, and 300 rpm. The differences (0.00% for the the 12.5-mm and 25.0-mm mixtures, respectively.
9.5-mm mixture and 0.01% for the 19.0-mm mixture) These differences are not considered practically
were not practically significant. This finding was con- significant.
firmed by the results of statistical analysis. For the The differences in Gmm of the dense-graded lab-
9.5-mm and 19.0-mm mixtures, F values from com- oratory mixtures using various vibration levels of
parisons of Gmm from vibration levels of 240 rpm, the Orbital device also were examined statistically
270 rpm, and 300 rpm were smaller than the criti- using F values from a Scheffé test. For the 4.75-mm
cal F values. This indicates that a vibration level of mixture, the highest Gmm at 270 rpm is statistically
240 rpm can be used for the SMA mixtures without a the same as the Gmm at every other setting. For the
significant decrease in Gmm. 12.5-mm mixture, the highest Gmm at 240 rpm dif-
fers only from the Gmm at zero agitation. For the
Dense-Graded Laboratory Mixtures. Three out of 25.0-mm mixture, the highest Gmm at 300 rpm is sig-
four dense-graded laboratory mixtures were tested nificantly different from the Gmm at zero agitation
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OCR for page 18
through 150 rpm. For the three mixtures, manual ag- the increased cloudiness of the water at Settings 6
itation produced Gmm that were not significantly dif- through 8, however, Settings 5, 6, and 7 were recom-
ferent from Gmm using the mechanical settings. This mended for dense-graded laboratory, dense-graded
finding regarding manual agitation disagrees with field, and SMA mixtures, respectively. To explore if
that based on the calculated air voids discussed in Setting 5 can be recommended for all three mixture
the previous paragraph. types, the results of the Scheffé test comparing the
Given that water was substantially cloudy at vi- Gmm values from Settings 5, 6, and 7 were examined.
bration levels of 270 rpm and above, the possibility This analysis indicated that the computed F values
of using 240 rpm for the dense-graded laboratory for the comparisons of Gmm for Settings 5, 6, and 7
mixtures was explored through an examination of were all less than the critical F values. Therefore,
the difference in air voids. Between the highest Gmm Setting 5 of the Gilson device can be recommended
and the Gmm at 240 rpm, the difference in air voids for all three mixture types.
was 0.17% for both the 4.75-mm and 25.0-mm mix- For the Syntron device, Settings 7, 8, and 9 pro-
tures, which is considered not significant. Statistical vided the highest Gmm for the three mixture types.
analysis also confirmed no significant differences Based on the substantial water cloudiness at Settings
between the Gmm at 240 rpm and the Gmm at 210 rpm 8 and 9, however, Setting 7 was suggested for dense-
for the 4.75-mm mixture and at 300 rpm for the graded field and laboratory mixtures and Setting 8
25.0-mm mixture. Based on the above observations, was suggested for the SMA mixtures. To explore the
a vibration level of 240 rpm is suggested as the op- possibility of using Setting 7 for all mixture types,
timum setting of the Orbital device for the dense- the computed F values for the comparison of Gmm
graded laboratory mixtures. from Settings 7 and 8 were examined. These differ-
ences were not significant for any of the mixtures.
Therefore, Setting 7 of the Syntron device is sug-
Selecting Optimum Device Settings
gested for measuring Gmm of all three mixture types.
Previously, the optimum setting of each agita- For the Orbital device, the highest Gmm values of
tion device was selected for each of the three mix- the mixtures were obtained using vibration levels in
ture types. A summary of the settings that resulted the range of 210 rpm to 300 rpm. Based on the sub-
in the highest Gmm and the device settings suggested stantial level of water cloudiness at vibration levels
for each mixture type are provided in Table 4. The of 270 rpm and above, however, a vibration level of
suggested settings were selected based on the eval- 240 rpm was selected for each mixture category.
uation of change in air voids, statistical significance Table 5 summarizes the suggested settings for the
of differences in Gmm, and observed substantial four vibrating devices that have adjustable settings.
changes in water clarity. This section explores the The table also provides the vibration parameters of
possibility of choosing one setting of each device for the vibrating devices at the suggested settings. The
all mixture types. manufacturers can adjust the vibration settings of
As shown in Table 4, using the Humboldt device, their devices to these suggested settings to minimize
the highest values of Gmm for the nine mixtures were the between-laboratory variability that could result
produced over a range from Setting 7 to Setting 10. from differences in vibration intensity of the Gmm
Based on the concern with water clarity at Settings 8 measuring devices.
and 9, however, Setting 7 was recommended for the
dense-graded field mixtures and Setting 8 was rec-
ommended for the SMA and dense-graded laboratory Comparison of Devices and Methods
mixtures. The possibility of using Setting 7 of the The seven devices and methods listed in Table 1,
Humboldt device for all mixture types was evaluated along with manual agitation, were compared in terms
by examining the computed F values for the compar- of the highest measured Gmm and the variability of the
ison of Gmm from Settings 7 and 8. This difference measurements. The highest Gmm values of the mixtures
was not significant for any of the mixtures. Therefore, were compared statistically and from a practical point
Setting 7 of the Humboldt device can be suggested for of view. The variability of each device was repre-
all three mixture types. sented by the pooled standard deviations of the Gmm
For the Gilson device, Settings 6 and 7 provided measurements from various settings of the device.
the highest Gmm for the three mixture types. Based on The variability of manual agitation was represented
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Table 4 Settings yielding the highest Gmm of the vibrating devices with variable settings.
Mixtures
Plant-Produced
Dense-Graded Plant-Produced Gap-Graded Laboratory-Produced Dense-Graded
9.5-mm 19.0-mm 9.5-mm 12.5-mm 19.0-mm 4.75-mm 12.5-mm 25.0-mm 37.5-mm
Percent Percent Percent Percent Percent Percent Percent Percent Percent
Passing Passing Passing Passing Passing Passing Passing Passing Passing
Device (%) (%) (%) (%) (%) (%) (%) (%) (%)
Humboldt Vibrating 8 7 8 8 9 10 8 9 9
Table (H-1756)
Suggested for Humboldt 7 (Cloudy at 8) 8 (Cloudy at 9) 8 (No significant cloudiness)
Gilson Vibro-Deaerator 6 7 7 7 7 7 6 -- 6
(SGA-5R)
Suggested for Gilson 6 (Cloudy at 7) 7 (Cloudy at 8) 5 (Cloudy at 8, 7, 6, respectively)
Syntron Vibrating Table 7 7 8 7 9 8 8 -- --
(VP-51 D1)
Suggested for Syntron 7 (Cloudy at 9) 8 (Cloudy at 9) 7 (Cloudy at 8)
Orbital Shaker Table 240 210 270 240 300 270 240 300 --
(SHKE 2000)
Suggested for Orbital 240 (Cloudy at 270) 240 (Cloudy at 270) 240 (Cloudy at 270)
OCR for page 20
Table 5 Suggested settings and associated vibration parameters of the four vibrating devices with variable settings.
Frequency, Hz Acceleration, m/s2 Energy, microjoules
Optimum
Device Setting x y z x y z x y z Total
Humboldt Vibrating 7 48.7 48.7 48.7 3.79 1.35 4.68 14.3 1.7 24.9 40.9
Table (H-1756)
Gilson Vibro- 5 44.3 44.3 44.3 3.95 2.71 6.05 16.1 7.5 38.8 62.4
Deaerator
(SGA-5R)
Syntron Vibrating 7 83.8 91.4 612.2 19.13 21.67 72.32 217 268 2899 3384
Table (VP-51 D1)
Orbital Shaker Table 240 rpm -- -- -- -- -- -- -- -- -- --
(SHKE 2000)
by the pooled standard deviations from manual agi- in Gmm between manual agitation and the mechani-
tations using different setups. The results of these cal devices were significant in five out of seven com-
comparisons are discussed below. parisons for the 9.5-mm mixture and in one out of
seven comparisons for the 19.0-mm mixture. There-
Dense-Graded Field Mixtures fore, the comparison of air voids and the results of
statistical analysis suggest that the mechanical de-
For the 9.5-mm mixture, the largest difference
vices produce the same Gmm if they are operated at
between Gmm from the mechanical devices was 0.003
their optimum settings, but that manual agitation
(between the Orbital and Gilson devices). This dif-
produces statistically lower Gmm values than the me-
ference corresponds to a 0.13% difference in air voids.
chanical devices.
For the 19.0-mm dense graded field mixture, the
An analysis of the standard deviation of the Gmm
largest difference was 0.006, between the Corelok
measurements for the 9.5-mm and 19.0-mm dense-
and Orbital devices. This difference in Gmm corre-
graded field mixtures using the various devices and
sponds to a 0.24% difference in air voids. Consider-
methods found that the highest Gmm standard devia-
ing the potential variability due to measurement of
Gmb, the difference between air voids for the 19.0-mm tions of the mechanical devices were 0.002 and
mixture could become significant. 0.003, which are below the acceptable 1s repeatabil-
For both dense-graded field mixtures, manual ag- ity standard deviation for a single-operator test con-
itation provided the lowest Gmm. For the 9.5-mm dition described in AASHTO T 209. Manual agita-
mixture, the largest difference was 0.008 with the tion provided either equivalent or smaller standard
Gilson device, which corresponds to a 0.29% differ- deviations than the majority of the devices. Between
ence in air voids. For the 19.0-mm mixture, the largest the two mixtures, none of the devices or methods was
difference was 0.010 with the Orbital device, which consistently more variable than the others.
corresponds to a 0.38% difference in air voids. Con-
sidering the potential variability due to measurement Gap-Graded (SMA) Field Mixtures
of Gmb, these differences between air voids of me- For the 9.5-mm, 12.5-mm, and 19.0-mm SMA
chanical devices and manual agitation could become mixtures, the largest differences in the highest Gmm
significant. values of the various mechanical devices were 0.005,
The F values from the Scheffé test were used to 0.003, and 0.003, respectively. These differences
compare the highest Gmm of the 9.5-mm and 19.0-mm correspond to differences of 0.17%, 0.10%, and 0.12%
dense-graded field mixtures obtained from the vari- between the air voids, which are not considered prac-
ous devices and methods. The differences between tically significant.
the Gmm values from the mechanical devices were A comparison of the Gmm from mechanical and
not statistically significant. However, the differences manual agitation shows that manual agitation pro-
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vides the lowest Gmm for the SMA mixtures. For the The F values for the comparisons of the values
9.5-mm mixture, the largest difference was 0.007, of Gmm between the seven mechanical devices and
which corresponds to a 0.26% difference in air voids. manual agitation were all less than the critical F val-
For the 12.5-mm SMA mixture, the largest difference ues for the 4.75-mm and 12.5-mm mixtures, indicat-
was 0.008, which corresponds to a 0.27% difference ing that the differences are not statistically significant.
in air voids. For the 19.0-mm SMA mixture, the largest For the 25.0-mm mixture, however, the differences
difference was 0.011, which corresponds to a 0.43% between the Gmm from manual agitation and that
difference in air voids. Considering the potential vari- from the HMA Vibrating Table and Orbital Shaker
ability due to measurement of Gmb, the differences in Table are significantly different; for the 37.5-mm
Gmm between manual and mechanical agitation could mixture, the difference between the Gmm from manual
be practically significant. agitation and the Gmm from the Aggregate Drum
The F values from the Scheffé test were used to Washer is significantly different. In light of the prac-
compare the highest Gmm of the 9.5-mm, 12.5-mm, tical significance of the difference in air voids and
and 19.0-mm SMA mixtures for the various devices the statistical significance of the differences between
and methods, including manual agitation. The com- Gmm of manual agitation and the Gmm of the several
puted F values for comparison of the Gmm of the me- mechanical devices, the use of manual agitation for
chanical devices were all below the critical F-value; measuring the Gmm of dense-graded laboratory mix-
therefore, the differences between values of Gmm for tures is not suggested.
the seven devices and methods listed in Table 1 were An analysis of the standard deviations of the
not statistically significant. A comparison of manual Gmm measurements of the dense-graded laboratory
agitation with the mechanical devices indicates that mixtures using various devices and methods found
the differences between manual and mechanical Gmm that the largest standard deviation from the devices
also were not significant. Although the statistical re- is less than 0.004, which is less than the acceptable 1s
sults do not support the significance of the difference repeatability standard deviation for single-operator
between the air voids from manual and mechanical test condition described in AASHTO T 209. No one
methods, the use of manual agitation for measuring device consistently produced the highest or the low-
the Gmm of SMA mixtures is not suggested. est standard deviation.
Dense-Graded Laboratory Mixes Relationship Between Vibration Properties
of the Devices and Highest Gmm
The Gmm of the 4.75-mm and 12.5-mm mixtures
were measured using all seven Table 1 devices; the In previous sections, the agitation devices were
Gmm of 25.0-mm and 37.5-mm mixtures were mea- compared in terms of the highest Gmm they produce
sured using five devices. The largest difference in and the variability of their measurements. It was
the highest Gmm produced by the devices for the shown that different mechanical devices produce
4.75-mm, 12.5-mm, 25.0-mm, and 37.5-mm mixtures statistically the same Gmm values at their optimum
was 0.005, 0.006, 0.008, and 0.005, respectively. settings. The vibration properties of the devices at
These differences translate into air voids differences their optimum setting also were compared to deter-
of 0.18%, 0.23%, 0.30%, and 0.20%. Although the mine if the same vibration properties produce the
Gmm of the 4.75-mm and 37.5-mm mixtures from the same highest Gmm.
various devices are not significantly different, for This analysis showed that even though the high-
the 12.5-mm and 25.0-mm mixtures, the difference est Gmm values from various devices and methods are
in Gmm between at least two devices could become very similar at the setting of the highest Gmm, the vi-
practically significant. bration properties of the devices at those settings are
The F values from the Scheffé test were used to very different. For example, the highest Gmm of the
statistically compare the highest Gmm of the four 19.0-mm dense-graded field mixture measured by
dense-graded laboratory mixtures as produced by four vibratory devices (Humboldt, Gilson, Syntron,
various devices and methods. These F values were and HMA) are in the range of 2.533 to 2.536, while the
all less than the critical F values, suggesting that total kinetic energy of the devices is in a range of 38.3
if the Gmm measuring devices are operated at their to 2,854 microjoules. This finding suggests that the
optimum setting, they should all provide the same energy produced by a device is not necessarily equiv-
Gmm value. alent to the energy transferred to the mixture.
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Relationship Between Gmm and Order in air voids that resulted from the difference in Gmm
of Placement of Water and Mixture was about 0.2%; however, the difference could be as
high as 0.35%, as found for the 19.0-mm SMA field
The effect on Gmm of the order of placement of the mixture tested using the Syntron device.
mixture and water in the vacuum container was ex- A paired t-test was conducted to evaluate whether
amined. Seven mixtures were each tested twice with the mean Gmm values from the Water First and Sample
three of the devices: once by placing the water first First procedures were the same. For the 9.5-mm,
(Water First) and once by placing the mixture first 12.5-mm, and 19.0-mm SMA mixtures, the com-
(Sample First). The significance of the difference puted t values of the Gmm from the Water First and
between the Gmm values from the two orders of place- Sample First methods were 3.636, 4.782, and 4.880,
ment was evaluated by a comparison of the resulting respectively. Comparing these computed t values with
air voids and by the use of the statistical t-test. the critical t value of 2.571 (for a 5% level of signif-
icance and 5 degrees of freedom, given 6 measure-
Dense-Graded Field Mixtures ments) indicates that the Water First method produces
Gmm values were measured for two dense-graded significantly higher Gmm values than the Sample
field mixtures using three devices at the settings found First method.
to provide the highest Gmm values. The resulting air
voids were computed using these measured Gmm val- Dense-Graded Laboratory Mixtures
ues and assumed Gmb values of 2.404 for the 9.5-mm The Gmm of the 4.75-mm and 12.5-mm dense-
mixture and 2.422 for the 19.0-mm mixture. It was graded laboratory mixtures were measured using three
found that placing the water prior to adding the mix- devices at the settings found to provide the highest
ture consistently produced higher Gmm values. The dif- Gmm values. The resulting air voids were computed
ference in air voids that resulted from the difference in using the measured Gmm values and assumed Gmb
Gmm was as high as 0.23%, as found for the 19.0-mm values of 2.444 for the 4.75-mm mixture and 2.466
mixture tested using the HMA or the Humboldt for the 12.5-mm mixture. It was found that placing
device, or as low as 0.11%, as found for the 9.5-mm the water prior to adding the mixture consistently
mixture tested using the Orbital or Humboldt device. produced higher Gmm values. On average, the differ-
A paired t-test was conducted to evaluate if the ence in air voids that resulted from the difference in
mean Gmm from the Water First and Sample First pro- Gmm was about 0.1%; however, the difference was as
cedures were the same. For the 9.5-mm and 19.0-mm high as 0.2% for the 12.5-mm mixture tested using
dense-graded field mixtures, the computed t values the Syntron device.
from the comparison of the Gmm values of the Water A paired t-test was conducted to evaluate whether
First and Sample First methods were 8.07 and 4.786, the mean Gmm from the Water First and Sample
respectively. Comparing these computed t values First procedures were the same. For the 4.75-mm and
with the critical t value of 2.571 (for a 5% level of 12.5-mm dense-graded laboratory mixtures, the com-
significance and 5 degrees of freedom, given 6 mea- puted t values from the Water First and Sample First
surements) indicates that the Water First method pro- methods were 7.073 and 3.037, respectively. Com-
duces significantly higher Gmm values than the Sample paring these computed t values with the critical t value
First method. of 2.571 (for a 5% level of significance and 5 degrees
of freedom, given 6 measurements) indicates that the
Gap-Graded (SMA) Field Mixtures Water First method produces significantly higher Gmm
The Gmm of the three SMA field mixtures were values than the Sample First method.
measured using three devices at the settings found to In summary, this experiment established that the
provide the highest Gmm values. The resulting air change in Gmm as a result of the change in the order
voids were computed using these measured Gmm val- of placement of the mixture and water in the vacuum
ues and assumed Gmb values of 2.532, 2.357, and container of the various devices was statistically and
2.339 for the 9.5-mm, 12.5-mm, and 19.0-mm mix- practically significant. Therefore, to facilitate the re-
tures, respectively. It was found that placing the lease of air from the mixture and achieve the highest
water prior to adding the mixture consistently pro- Gmm, adding water to the vacuum container before
duced higher Gmm values. On average, the difference placing the mixture is suggested.
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