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OCR for page 35
C-8 Special Mixture Design Considerations and Methods for Warm Mix Asphalt
Table 6. Mix design experiment.
Mixing/Compaction Temperature, °F,
Mixture Identification
for Process:
Aggregate
No. Evotherm
Water Advera Sasobit
Ndesign RAP HMA 3G
Absorption, WMA WMA
WMA
%
1 50 1.5 Yes 320/310 225/215 225/215 270/260
2 50 0.8 No 320/310 270/260 270/260 225/215
3 75 1.0 Yes 320/310 270/260 225/215 270/260
4 75 1.6 No 320/310 225/215 270/260 225/215
5 100 1.2 Yes 320/310 270/260 270/260 225/215
6 100 1.3 No 320/310 225/215 225/215 270/260
d
Test statistic: t=
sd
n
Rejection region: Reject the null hypothesis and accept the alternative hypothesis if
t > t for n-1 degrees of freedom.
where
µWMA = population mean for WMA mixtures
_ = population mean for HMA mixtures
µHMA
d = average of the differences between WMA and HMA mixtures
sd = standard deviation of the differences
n = number of mixtures compared
One way to present the results is to develop 95% confidence intervals for the mean differ-
ence in the properties for WMA compared to HMA. If the 95% confidence intervals capture
zero, the properties are statistically the same for WMA and HMA. The paired difference com-
parisons for design binder content and binder absorption are shown in Figures 3 and 4,
respectively.
Figure 3 shows that the average design binder content for the WMA mixtures was 0.05%
lower than that for HMA mixtures made with the same aggregates and binder. This difference,
however, was not statistically significant. Figure 4 shows that the binder absorption was sig-
nificantly less for the WMA mixtures. The average difference was 0.1%. The average absorp-
tion for the mixtures tested was approximately 1.0%. Thus, absorption for WMA was about
90% of that for HMA. Based on these data it was recommended to use 45% of the water
absorption as the initial estimate binder absorption in WMA compared to 50% of the water
absorption for HMA.
Step 7. Calculate Aggregate Content by Volume
These calculations are identical to those for HMA.
Step 8. Proportion Aggregates
for Trial Mixtures
These calculations are identical to those for HMA.
OCR for page 36
II. Commentary on Special Mixture Design Considerations and Methods for Warm Mix Asphalt (WMA) C-9
Average Difference in Design Binder Content, wt. % 0.40
0.30
0.20
0.10
0.00
Advera Evotherm Sasobit All WMA
-0.10
-0.20
-0.30
-0.40
Mixture
Figure 3. Average difference in design binder content (WMA-HMA)
from the NCHRP 9-43 mix design study (error bars are ± 95% one-sided
confidence intervals).
0.40
Average Difference in Binder Absorption, wt %
0.30
0.20
0.10
0.00
Advera Evotherm Sasobit All WMA
-0.10
-0.20
-0.30
-0.40
Mixture
Figure 4. Average difference in binder absorption (WMA-HMA) from the
NCHRP 9-43 mix design study (error bars are ± 95% one-sided confidence
intervals).
