influence of filler fractional voids on mastic and mixture performance

INFLUENCE OF FILLER FRACTIONAL VOIDS ON MASTIC AND MIXTURE
PERFORMANCE
Ahmed F. Faheem (Corresponding Author)
Manager, Research Department
Bloom Companies LLC
10501 W. Research Drive, Suite 100
Milwaukee, WI 53226
Email: afaheem@bloomcos.com
Cassie Hintz
Graduate Research Assistant
Department <strong>of</strong> Civil and Environmental Engineering
University <strong>of</strong> Wisconsin - Madison, 53706
Email: cahintz@wisc.edu
Hussain Bahia
Pr<strong>of</strong>essor
Department <strong>of</strong> Civil and Environmental Engineering
University <strong>of</strong> Wisconsin - Madison, 53706
Email: bahia@engr.wisc.edu
Imad Al-Qadi
Founding Pr<strong>of</strong>essor
Department <strong>of</strong> Civil Engineering
University <strong>of</strong> Illinois-Urbana-Champaign
Email: alqadi@illinois.edu
Submitted for publication and presentation at the
Transportation Research Board Annual Meeting
January 22-26, 2012
Washington, D.C.
Submission date: August 1, 2011
Word count 4642 plus 9 Tables and 3 Figures
Total number <strong>of</strong> words: 7372
TRB 2012 Annual Meeting Paper revised from original submittal.
1

INFLUENCE OF FILLER FRACTIONAL VOIDS ON MASTIC AND MIXTURE
PERFORMANCE
ABSTRACT
This study proposes the <strong>fractional</strong> <strong>voids</strong> test for mineral <strong>filler</strong>s introduced by Rigden in 1947,
and currently adopted by the European Norms, as part <strong>of</strong> asphalt mixture design and quality
control. Laboratory testing conducted in this study included a large collection <strong>of</strong> natural and
manufactured <strong>filler</strong>s currently used in various regions <strong>of</strong> the United States. Results show that the
<strong>filler</strong> <strong>fractional</strong> <strong>voids</strong> <strong>influence</strong> the mastic viscosity and non-recoverable compliance. These
mastic properties are also found to be highly correlated with mixture performance measures. This
study utilized mixture performance limits to derive mastic limits based on the mixture-to-mastic
correlations. The regression models developed to predict the mastic performance as function <strong>of</strong>
the <strong>filler</strong>s <strong>fractional</strong> <strong>voids</strong> and asphalt binders properties are proposed as means for incorporating
the <strong>fractional</strong> <strong>voids</strong> into the mix design procedure as quality control measure. This paper covers a
summary <strong>of</strong> materials used, analysis approach, and summary <strong>of</strong> data justifying the limits
proposed.
INTRODUCTION
The capacity <strong>of</strong> <strong>filler</strong> to hold asphalt binder can be estimated using the <strong>voids</strong> entrapped in a
compacted sample <strong>of</strong> <strong>filler</strong>. The void content is estimated by compacting dry <strong>filler</strong>s in a mold
using a specified compaction effort. The concept is similar to the Fine Aggregate Angularity test
utilized in the Superpave system to measure the angularity <strong>of</strong> fine aggregates (AASHTO 304),
but includes a standard compaction device to pack the <strong>filler</strong>. Measurement <strong>of</strong> <strong>fractional</strong> <strong>voids</strong>
was introduced by Rigden in 1947 (1). Hence, most researchers refer to the <strong>fractional</strong> <strong>voids</strong> test
as the “Rigden Voids” test (2,3).
Rigden (1) considered the asphalt required to the fill the <strong>voids</strong> in the dry compacted
sample as fixed asphalt while asphalt in excess <strong>of</strong> that fixed is considered as free asphalt. Rigden
postulated that the percent free asphalt is the main factor defining the consistency <strong>of</strong> filled
systems and reported that changes in viscosity are independent <strong>of</strong> asphalt characteristics or any
<strong>filler</strong> characteristics other than the <strong>fractional</strong> <strong>voids</strong>.
Fillers, irrespective <strong>of</strong> their properties, are known to stiffen the asphalt. DeSmedt was the
first to use <strong>filler</strong>s intentionally in an attempt to duplicate rock asphalt in Washington, D.C. in the
1870’s (4). Later studies found that <strong>filler</strong> gradation <strong>influence</strong>s the stiffening level <strong>of</strong> mastics (5-
7). Studies show the concept <strong>of</strong> free asphalt explains the <strong>filler</strong> stiffening effect <strong>of</strong> <strong>filler</strong>s (8). A
number <strong>of</strong> studies concluded <strong>filler</strong> geometric characteristics (size, shape, angularity, and texture)
affect Rigden <strong>voids</strong>. Thus, <strong>fractional</strong> <strong>voids</strong> is an effective indicator <strong>of</strong> the interactive effect <strong>of</strong>
these characteristics on stiffening <strong>of</strong> binders (9-22). These important studies exhibit that <strong>filler</strong>s
properties significantly <strong>influence</strong> mastic performance. However, the relevance <strong>of</strong> the results to
performance is unclear.
Since the development <strong>of</strong> the <strong>fractional</strong> <strong>voids</strong> device, some changes took place to its
design. In 1973, Anderson and Goetz proposed reducing the sample size as well as compaction
effort (23). This new design is adopted by the National Asphalt Pavement Association, the
Kansas Department <strong>of</strong> Transportation, and the Ontario Ministry <strong>of</strong> Transportation. In Europe on
the other hand, the <strong>fractional</strong> <strong>voids</strong> test as proposed by Rigden was standardized as part <strong>of</strong> the
European Norm under the designation EN 1097-4 (24). Table 1 includes the specifics <strong>of</strong> the two
different Rigden <strong>voids</strong> tests used currently, as well as the original Rigden used device.
TRB 2012 Annual Meeting Paper revised from original submittal.
2

Table 1. Comparison <strong>of</strong> the Different Fractional Voids Tests
NAPA / Ministry <strong>of</strong>
Transportation
(Ontario) / Kansas
DOT
European
Norms
(EN 1097-4)
Rigden
Apparatus
(1947)
Drop Weight 100g 350g 350g
Hammer
Diameter
12.65mm 25mm 25mm
Sample Size 1 - 1.3g 10g 10g
Number <strong>of</strong>
Impact blows
25 100 100
In this study, the effect <strong>of</strong> Rigden <strong>voids</strong> on mastic and mixture performances is evaluated
to provide a comprehensive evaluation <strong>of</strong> this test. This study is conducted with the intention <strong>of</strong>
proposing the Rigden <strong>voids</strong> test as a quality control measure for predicting <strong>filler</strong>s’ <strong>influence</strong> on
Hot Mix Asphalt (HMA) performance. The Rigden <strong>voids</strong> are measured in this study using the
European norms method. The European device is available commercially while the NAPA
device was very hard to find commercially. Based on discussion with a number <strong>of</strong> experts in the
field, it was decided to proceed with using the European version due to concerns about sample
size, repeatability, and durability <strong>of</strong> using the smaller NAPA version. The European standards
include recommendations to classify <strong>filler</strong>s in regards to their reactivity, and combines Rigden
<strong>voids</strong> with other characteristics in the classification system. Unlike the European practice, the
American standards allow extensive use <strong>of</strong> natural <strong>filler</strong>s (<strong>filler</strong>s produced during the crushing <strong>of</strong>
aggregates). Additionally, “mineral dust” collected in dust control systems, such as baghouse
fine collectors, is very common in North America. Today, there is lack <strong>of</strong> control on <strong>filler</strong>
quality, and a rather simplistic dust-to-binder ratio criterion used in the Superpave system.
EXPERIMENTAL PLAN
In this study 13 <strong>filler</strong>s from 11 different mineralogies and/or sources were selected and tested.
The <strong>filler</strong>s were also classified based on hardness <strong>of</strong> the base rock. The classification <strong>of</strong> <strong>filler</strong>
hardness is based on the Los Angeles Abrasion (LAA) loss test on the rocks. A hard rock
correspond to LAA loss less than 20. A s<strong>of</strong>t rock correspond to LAA loss greater than 40. The
LAA loss results were provided by the <strong>filler</strong> suppliers. Table 2 lists the <strong>filler</strong>s evaluated.
Table 2 List <strong>of</strong> Fillers Incorporated in this Study
Number Filler Code Mineralogy (Source)
Name
1 AN1 Andesite
2 BH1 Hard Basalt (1)
3 BH2 Hard Basalt (2)
4 CA2 Calicies
5 DH1 Hard Dolomite (1)
6 DS2 S<strong>of</strong>t Dolomite (2)
7 GH1 Hard Granite (1)
8 GH2 Hard Granite (2)
TRB 2012 Annual Meeting Paper revised from original submittal.
3

9 GRQ2 Gravel Quartzite (2)
10 GS1 S<strong>of</strong>t Granite (1)
11 GS2 S<strong>of</strong>t Granite (2)
12 LH1 Hard Limestone (1)
13 LS2 S<strong>of</strong>t Limestone (2)
Two base binders were used from two sources with the same performance grade (PG64-
22), One binder has high asphaltene content (heavy). The other binder has low asphaltene
content (light). The heavy asphalt is modified with SBS and PPA to obtain two additional
binders <strong>of</strong> PG 76 grade. The four binders (two modified, and two unmodified) are blended with
the 13 <strong>filler</strong>s at one <strong>filler</strong> to binder (F/B) ratio, which was kept at the mass ratio <strong>of</strong> 1.0 for a total
<strong>of</strong> 52 mastics. Based on the distribution <strong>of</strong> the mastic population, 12 mastics are selected to be
used to construct mixture specimens for two gradations (fine, course). The selected mastics cover
the range <strong>of</strong> data observed and balance between the binders such that all four binders are equally
present in the selection. The following sequential diagram represents the sequence <strong>of</strong> work in
this study. Table 3 lists the mastic characteristics measured and the associated test methods.
13 <strong>filler</strong>s
52 Mastics: Combine 13 <strong>filler</strong>s with 4 binders
24 mixtures: 12 mastics selected combined with two gradations
TABLE 3 Mastic Testing Program
Mastic Response Test Method Temperature Aging
Characteristic Variable
1. Constructability Viscosity
Rotational
Viscosity
135°C Un-aged
Accumulated Dynamic Shear
Strain Rheometer
2. Rutting
Resistance
Non
Recoverable
(DSR)/ Multiple
Stress Creep and
Recovery
64°C
Un-aged
Compliance (MSCR)
25 mm PP
Constructability
To evaluate the effect <strong>of</strong> <strong>filler</strong> on mastic workability, viscosity was measured at 135°C using a
Brookfield Rotational Viscometer. Viscosity testing was conducted using a size 27 spindle. In
the procedure, the spindle is rotated at 20rpm for 600sec after 40 minutes <strong>of</strong> thermal
TRB 2012 Annual Meeting Paper revised from original submittal.
4

equilibration. Viscosity measurements over the last 300sec <strong>of</strong> testing are averaged as the
apparent viscosity. It should be mentioned that several experiments were conducted to evaluate
the effect <strong>of</strong> shear rate on viscosity <strong>of</strong> mastics. Although the mastics were found to be shear
dependent, the relative ranking <strong>of</strong> mastics did not change as a function <strong>of</strong> the shear rates covered
in the testing. It was therefore determined most appropriate to use the results at only one shear
rate. The shear rate <strong>of</strong> 20rpm was used because it is currently the most frequently used shear rate
in binder testing. Mixture constructability was measured as the number <strong>of</strong> gyrations to 92%
maximum density in the Superpave Gyratory Compactor. The number <strong>of</strong> gyrations to 92% is
used as an indicator for workability since it is the typical target density for field projects.
Permanent Deformation
Mastic and binder rutting resistance was evaluated using the Multiple Stress Creep and Recovery
(MSCR) test in accordance with ASTM D7405. Testing included three stresses (0.1kPa, 3.2kPa,
and 10kPa) and two temperatures (58°C and 64°C). The non-recoverable creep compliance, (Jnr),
and percent recovery, at a stress level <strong>of</strong> 3.2 kPa and 58°C, were chosen as the indicators <strong>of</strong>
rutting resistance. These test conditions are chosen since changing the temperature to 64°C and
the stress level to 10kPa led to the same ranking <strong>of</strong> mastics.
Flow number testing was used to determine mixture rutting resistance according to
procedures recommended in the NCHRP 9-19 project report with target air <strong>voids</strong> in the mixture
equal to 7%. According to NCHRP 9-19, the deviator stress level used in the flow number test
should be within the range <strong>of</strong> 70 to 210kPa for unconfined tests. In this study, the flow number
tests were conducted using uniaxial compression loads without confinement at 58°C. A loading
stress level <strong>of</strong> 200kPa was selected to attain tertiary flow in a reasonable number <strong>of</strong> cycles for
various mixtures with different binders, gradations, and mineral <strong>filler</strong>s. The mixtures were tested
with 0.1sec <strong>of</strong> creep loading and 0.9sec <strong>of</strong> recovery per cycle. Flow number, which represents
the number <strong>of</strong> cycles <strong>of</strong> repeated creep at which the mixture enters a tertiary creep flow region,
was used as the indicator <strong>of</strong> rutting resistance (25).
FILLER TEST RESULTS
The Rigden <strong>voids</strong> results collected in this study are shown in Figure 1. The results show a wide
range <strong>of</strong> values (29.4 % - 47.1%) for the tested <strong>filler</strong>s. There appears to be no trend in
Rigden Voids values with source or mineralogy <strong>of</strong> natural <strong>filler</strong>s.
TRB 2012 Annual Meeting Paper revised from original submittal.
5

Rigden Voids (%)
50.0
45.0
40.0
35.0
30.0
25.0
Rigden
Voids (%)
DS2 LH1 BH1 BH2 LS2 GRQ2 GH2 GS1 AN1 GH1 DH1 CA2 GS2
29.4 32.2 33.2 33.8 35.4 36.5 38.8 40.2 41.9 42.6 42.8 45.0 47.0
FIGURE 1 Rigden <strong>voids</strong> results.
EFFECT OF FILLERS FRACTIONAL VOIDS ON MASTICS
The effect <strong>of</strong> the <strong>filler</strong>s’ <strong>fractional</strong> <strong>voids</strong> on the mastics was investigated using multivariate
regression analysis. This analysis was conducted to highlight the level <strong>of</strong> <strong>influence</strong> <strong>of</strong> the Rigden
Voids and to quantify this effect in the form <strong>of</strong> a regression equation relating the mastic
performance measure to <strong>filler</strong> Rigden Voids and binder properties. The regression analysis
indicates that <strong>fractional</strong> <strong>voids</strong> has significant <strong>influence</strong> on two mastic properties: viscosity and
non recoverable compliance ( Jnr). The authors confirmed that the data set used in the analysis
satisfy the basic assumptions for regression modeling.
Constructability
The <strong>influence</strong> <strong>of</strong> the <strong>fractional</strong> <strong>voids</strong> and base binder viscosity were found to best predict mastic
viscosity. It is important to note that the analysis included multiple <strong>filler</strong> properties; however, the
<strong>fractional</strong> <strong>voids</strong> and the binder viscosity were the only two parameters to show significant
<strong>influence</strong> on the mastic viscosity. Table 4 shows the results <strong>of</strong> the regression analysis for mastic
viscosity.
TABLE 4 Regression Analysis for Mastic Viscosity
Predictor Coefficient
T-
Value
P-
Value
Constant -8244.00 -6.03 0.00
Binder Viscosity 4.68 8.21 0.00
Fractional Voids
(%)
204.83 6.24 0.00
R-Squared 67.20%
N 52
Standard Error 1229.72
TRB 2012 Annual Meeting Paper revised from original submittal.
6

The regression analysis indicates that <strong>fractional</strong> <strong>voids</strong> have a significant <strong>influence</strong> on
mastic viscosity. Examining the output <strong>of</strong> the regression analysis, the coefficient for the binder
viscosity and <strong>fractional</strong> <strong>voids</strong> indicate a positive relation with mastic viscosity. This means that
as the binder viscosity and <strong>fractional</strong> <strong>voids</strong> increase, the overall mastic viscosity increases which
follows the expected trend. This is in line with the observations <strong>of</strong> many researchers as indicated
in the introduction section <strong>of</strong> this paper.
Permanent Deformation
The regression analysis with respect to mastic Jnr shows a strong correlation between the
regression model and measured Jnr (R 2 = 73.9%).
TABLE 5 Regression Analysis for Jnr
Predictor Coefficient
T-
Value
P-
Value
Constant 1.01 7.59 0.00
Binder Jnr 0.16 9.91 0.00
Fractional Voids -0.02 -6.94 0.00
R-Squared 73.90%
N 52
Standard Error 0.12
The coefficients for the regression model demonstrate trends with independent variables
that make sense. The binder Jnr shows a positive relation with the mastic Jnr. Additionally, the
<strong>fractional</strong> <strong>voids</strong> show a negative relationship with the mastic Jnr. An increase in the Jnr indicates a
decrease in resistance to rutting. Therefore, according the model, the use <strong>of</strong> a binder with low Jnr
or <strong>filler</strong> with high <strong>fractional</strong> <strong>voids</strong> increases the permanent deformation resistance <strong>of</strong> the mastic.
EFFECT OF FILLER ON MIXTURE RESULTS
The asphalt mixtures were prepared using short-term aging. The <strong>filler</strong>s were introduced during
the mixing processes at the same time the binder was added. The mix design called for 4% <strong>filler</strong>
for the fine-graded mix and 5% for the coarse-graded mix by mass. The fines passing #200
(0.075mm) sieve were removed from the mix by dry sieving for the coarse aggregate and
washing for the fine aggregate. This would allow for a controlled mix that isolates the effect <strong>of</strong>
the added <strong>filler</strong>. When adding different <strong>filler</strong>s in the mix, the amount was adjusted to equate the
volume <strong>of</strong> the original <strong>filler</strong> included in the mix design. This ensured that any change in the mix
performance is due to the mineral <strong>filler</strong> type and not the change in mix components’ volumetrics.
The asphalt content for the fine graded mixtures is 5.6% by weight <strong>of</strong> total mix and for the
coarse graded mix it is 5.3%
In this section, the relationship between mastic and mixture performance is evaluated.
The mastic serves as a bridge between the <strong>filler</strong> <strong>fractional</strong> <strong>voids</strong> and the mixture performance.
The mastic test results that were found to be <strong>influence</strong>d by the <strong>filler</strong> <strong>fractional</strong> <strong>voids</strong> will be
correlated with the corresponding mixture performance measures in order to determine the
<strong>influence</strong> <strong>of</strong> the <strong>fractional</strong> <strong>voids</strong> on the mixture performance. This can be done by establishing
performance limits on mixtures that can be translated to mastics. Therefore, the regression
equations can be used to establish <strong>fractional</strong> <strong>voids</strong> limits.
TRB 2012 Annual Meeting Paper revised from original submittal.
7

Constructability
Mastic and mixture workability were compared using the correlation between mixture number <strong>of</strong>
gyrations to 92% Gmm and mastic relative viscosity. Relative viscosity was used in place <strong>of</strong>
mastic viscosity as the SBS modification produces extreme viscosities but not extreme mixture
performance. Analyses were separated by gradation because gradation was found to have a very
important effect on workability <strong>of</strong> mixtures as measured by number <strong>of</strong> gyrations to 92% Gmm.
Results <strong>of</strong> the correlation are shown in Figure 2 for the fine and the coarse aggregate gradations.
Number <strong>of</strong> Gyrations to 92% Gmm
60
50
40
30
20
10
0
±One
Standard
Deviation
y = 0.67x + 13.97
R² = 0.20
y = 2.26x + 26.95
R² = 0.40
0.0 2.0 4.0 6.0 8.0 10.0
Relative Viscosity
Coarse
FIGURE 2 Correlation between mixture and mastic workability indicators.
Figure 2 shows the expected trend that the mixtures with higher relative viscosities are
less workable. For fine mixtures there is little variability in the number <strong>of</strong> gyrations to reach 92%
Gmm regardless <strong>of</strong> relative viscosity. The results also suggest that the coarse mixtures are more
sensitive to mastic viscosity than fine mixtures. Thus, gradation demonstrates more <strong>influence</strong> on
workability than the other factors.
Permanent Deformation
The mixture flow number (FN) results were correlated with the measured mastic Jnr. Coarse and
fine mixtures were separated to prevent bias in the analysis by gradation. Additionally, coarse
mixtures with SBS and AN1 or GRQ2 <strong>filler</strong>s were not included as they exhibited extremely high
FN. Results <strong>of</strong> the correlations are displayed in Figure 3.
TRB 2012 Annual Meeting Paper revised from original submittal.
Fine
8

Mixture Flow Number
Mixture Flow Number
1600
1400
1200
1000
800
600
400
200
0
1800
1600
1400
1200
1000
800
600
400
200
0
±One Standard
Deviation
(a)
y = ‐1,208.73x + 1,271.92
R² = 0.61
0.00 0.20 0.40 0.60 0.80 1.00 1.20
±One Standard
Deviation
Mastic Jnr (1/kPa)
y = ‐1,169.24x + 1,409.82
R² = 0.66
0.00 0.20 0.40 0.60 0.80 1.00 1.20
Mastic Jnr (1/kPa)
(b)
FIGURE 3 Correlation between mixture flow number and mastic Jnr for (a) fine gradation
and (b) coarse gradation.
The plots include the average trend lines represented by the center lines and reliability
represented as one standard deviation above and below the average trend lines. A clear trend
between mixture flow number and mastic Jnr exists for both gradations. The correlation trends for
the gradations show similar slope value. The linear correlations have R 2 values <strong>of</strong> 66% and 61%
for coarse and fine mixtures, respectively.
TRB 2012 Annual Meeting Paper revised from original submittal.
9

PROPOSED LIMITES ON FILLER RIGDEN VOIDS FOR WORKABILITY AND
RUTTING RESISTANCE
To incorporate the <strong>fractional</strong> <strong>voids</strong> into design <strong>of</strong> HMA, mastics were used as the bridge between
<strong>filler</strong> and mixture properties. Limits <strong>of</strong> mastic properties that result in acceptable mixture
performance are presented in this section. To relate the mastic limits to <strong>filler</strong> characteristics, the
regression equations relating Rigden Voids and mastic properties previously presented are used.
Thus, in design, one has two options:
• Conduct mastic testing to quantify the mastic property value and compare to
acceptable limit directly, or
• Perform binder and <strong>filler</strong> tests and use the regression equation to estimate mastic
property value and compare to acceptable limit.
In limit development analysis, it was necessary to sort limits by gradation. For the
purpose <strong>of</strong> this study, a coarse aggregate gradation is defined according to the Asphalt Institute’s
definition. Any aggregate gradation that crosses below 0.45 power maximum density line at or
before sieve #8 (2.36mm). The fine gradation is that which passes above the sieve #8.
Constructability
An extensive literature search was conducted to determine what limits can be used to define
satisfactory workability limits <strong>of</strong> mixture. No such limits for the number <strong>of</strong> gyrations to
92%Gmm could be found. The most comprehensive comparison between laboratory measured
and field measured compactability found was a study by Leiva and West (26). Leiva and West
evaluated the ability <strong>of</strong> multiple laboratory measured compactability indicators to predict actual
mixture compactability in the field. The authors did not recommend limits on number <strong>of</strong>
gyrations to reach 92%Gmm. They developed a multiple linear regression model to incorporate
the multiple factors found to affect mixture compactability.
Since no limits for number <strong>of</strong> gyrations to reach 92%Gmm exist in the literature, limits
are based on the results <strong>of</strong> mixture workability testing conducted within the scope <strong>of</strong> this study
by establishing the limit at the average number <strong>of</strong> gyrations to reach 92%Gmm measured for
coarse mixture plus one standard deviation measured for all coarse mixtures. Because all fine
mixtures exhibit low values <strong>of</strong> number <strong>of</strong> gyrations to reach 92%Gmm, the results for the fine
mixtures were excluded from the limits analysis. Using this strategy, the corresponding limit for
number <strong>of</strong> gyrations to reach 92%Gmm is 43 gyrations. Mixture with number <strong>of</strong> gyrations to
reach 92%Gmm less than 43 gyrations are deemed satisfactory. To increase the reliability <strong>of</strong> the
limit and account for variability in the results, the relative viscosity limit was developed based on
the corresponding relative viscosity minus one standard deviation, rounded to the nearest 0.5.
Using the trend line in Figure 2 for the coarse gradation minus one standard deviation, the
limiting relative viscosity corresponding to the proposed mixture limit is 5.0. A summary <strong>of</strong> the
proposed limits is provided in Table 6. Binder viscosity and Rigden <strong>voids</strong> can be measured and
the regression equation presented in Table 3 can be used to determine if the mastic meets the
proposed limit.
TABLE 6 Proposed Workability Limits
Parameter Value
Maximum N92 43
Maximum Relative 5.0
Viscosity
TRB 2012 Annual Meeting Paper revised from original submittal.
10

Permanent Deformation
To derive <strong>filler</strong> specification limits to ensure acceptable rutting performance <strong>of</strong> mixture, the
definition <strong>of</strong> what is acceptable was taken from previous studies. In the NCHRP Project 9-43,
minimum flow numbers are proposed based on flow number data collected on several field
projects (27). These flow number limits, which are based on traffic level, are displayed in Table
7.
It is important to note that the results reported in NCHRP 9-43 are based on testing at
600kPa, which is three times higher than the stress level applied in this study. As discussed
previously, 200kPa was selected for this study based on NCHRP 9-43 recommendations for
unconfined tests. Due to the differences in stress levels, there is a need for a transfer function
between stress levels. In the Airfield Asphalt Pavement Technology Program (AAPTP) Project
04-02: PG Binder Grade Selection for Airfield Pavements, the following equation relating the
number <strong>of</strong> load repetitions and stress level was developed through the combination <strong>of</strong> equations
to predict rutting used in the Mechanistic-Empirical Pavement Design Guide (MEPDG) and
other mathematical relations used in the MEPDG (28):
·
.
Using the above equation, the flow number limits at 600 kPa can be derived for a stress
level <strong>of</strong> 200kPa to arrive at the minimum flow numbers in Table 7, which are applicable to the
results <strong>of</strong> this study.
TABLE 7 Minimum flow number at 600 kPa (28)
Traffic Level
(Million
ESALs)
Minimum
Flow Number
@ 600kPa
Minimum
Flow Number
@ 200kPa
< 3 ----------- -----------
3 to < 10 53 530
10 to < 30 105 1,050
≥ 30 415 4,120
It should also be noted that in the NCHRP 9-43 project, testing was conducted at the 50
percent reliability performance grade temperature determined using LTPP Bind at a depth <strong>of</strong>
20mm without traffic volume or speed adjustments. In this study all testing was conducted at
58°C irrespective <strong>of</strong> performance grade. Based on these limits, three (25%) <strong>of</strong> coarse mixtures
and five (42%) <strong>of</strong> fine mixtures do not pass the criterion for traffic levels between 3 million and
10 million ESALs.
Mastic Jnr limits were derived based on the average trend line minus one standard
deviation for Jnr to increase the reliability <strong>of</strong> the limits and account for any variability in the
results. Using the models relating mastic and mixture results for coarse and fine aggregate
gradations, the resulting mastic limits are presented in Table 8. The mastic limit for Jnr is lowest
for fine aggregate gradations and thus most conservative. Therefore the recommended mastic
limit, irrespective <strong>of</strong> gradation follows the fine aggregate gradation limit. Thus, one can measure
Rigden Voids and binder Jnr and use the equation presented in Table 4 to determine if the mastic
meets permanent deformation resistance requirements.
TRB 2012 Annual Meeting Paper revised from original submittal.
(1)
11

TABLE 8 Maximum values for mastic Jnr at 3.2kPa
Mixture Maximum Mastic Jnr at
Gradation 3.2kPa (1/kPa)
Fine 0.40
Coarse 0.55
Summary <strong>of</strong> Recommended Limits
Table 9 is proposed as the framework for controlling effects <strong>of</strong> <strong>filler</strong>s in HMA to ensure
acceptable performance. The table lists the mixture performance indicators that were considered,
the mastic properties measured, and the proposed limits. The table includes the best fit models
derived from this project to estimate mastic properties in terms <strong>of</strong> <strong>filler</strong> and binder properties.
Due to the limited number <strong>of</strong> binders used in this study, it is high recommended that these
models be verified, and modified if needed, in future studies.
Table 9 Mastic property and limits to ensure proper mixture performance
Performance Mastic Mastic
Mastic Models
Indicator Property Limit
Workability Relative

characteristics) vary significantly between natural <strong>filler</strong>s and have important <strong>influence</strong> on
mastic and mixture behavior.
• It is important to note that although the mastic performance is used to relate <strong>filler</strong> to
mixture properties; it is limited to the ability <strong>of</strong> the mastic test to serve its purpose.
Therefore, a weak correlation between the mastic and mixture test results is not necessary
due to lack <strong>of</strong> <strong>influence</strong> <strong>of</strong> <strong>filler</strong>s, but because <strong>of</strong> the complexity <strong>of</strong> interactions between
various components <strong>of</strong> a mixture, including mineral <strong>filler</strong>s.
• Specification limits for mastic properties for rutting resistance and workability were
proposed. Due to the high <strong>filler</strong>-binder interactions measured in this study, the
specification criteria proposed are based on mastic properties rather than <strong>filler</strong> properties.
Best fit models are used to derive mastic properties in terms <strong>of</strong> <strong>filler</strong> and binder
properties to allow for incorporation <strong>of</strong> <strong>filler</strong> properties into design. Since binder
viscosity is routinely conducted based on the current specifications, the Rigden Voids test
can be used as quality control test to insure mixture performance within the desirable
ranges for workability and permanent deformation resistance. Due to the limited number
<strong>of</strong> binders used in this study, it is highly recommended that these models be verified, and
modified if needed, in future studies.
• Varying mass ratio was not studied, therefore, further study is required to evaluate the
role <strong>of</strong> the <strong>filler</strong> concentration on mastic performance.
ACKNOWLEDGEMENTS
The research team acknowledges the support <strong>of</strong> NCHRP and in particular the NCHRP 9-45
project panel and Dr. Ed Harrigan. The authors would also like to acknowledge the support and
input <strong>of</strong> Dr. Erv Dukatz and Mr. Gerald Reinke <strong>of</strong> Mathy Construction for their efforts and
leadership in collecting <strong>filler</strong>s and binders.
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