Superpave Mix

Superpave Asphalt Mix Design

Louisiana State University

Joshua Board

Superpave Asphalt Mix Design Page 2

Purpose

The purpose of Superpave Asphalt Mix Design is to ensure that the optimum amount of

asphalt cement is selected in order to satisfy the prescribed volumetric and densification

criteria. It is this criteria that will identify what the asphalt is used for in the field.

Significance

There are two types of criteria that govern how and asphalt will be used, Volumetric and

Densification. These criteria are set in order to make certain that an asphalt will perform up to the

standards. The volumetric criteria that will be found include: voids in the total mix (VTM), voids in the

mineral aggregate (VMA), and voids filled with asphalt (VFA). Densification will also be looked at which

will measure the specific gravity at different stages of the compaction process including: the primary

consolidation which represents the construction phase and secondary consolidation which represents

the end of life performance. Examination of both the criteria will allow the engineer to select the

appropriate asphalt content.


Equipment

This experiment requires the following equipment:

1. A metric scale accurate to 0.1 gram.

2. A bowl or pan in order to thoroughly mix the sample.

3. An oven.

4. A mixer to evenly distributed asphalt cement over the entire sample aggregate.

5. A sample mold and test papers to prevent adhesion of the sample to the mold.

6. A funnel used to pour the sample into the mold.

7. A Superpave Gyratory Compactor.

Test Specs and Sample

The sample of asphalt concrete is made up of 55% #57 SST, 20% #11 SST, and 25% gravel

aggregate. An asphalt cement binder was also used with the following percentages: 4.7%, 5.4%, or

5.9%. The final weight of each sample was 4800 grams.


Test Procedure

The experiment followed the following procedures:

1. Select the aggregate that is to be used as your sample and measure out the proper

amounts.

2. Blend the aggregate to develop the aggregate structure.

3. Design the asphalt content

a) Compact the sample at three different asphalt cement contents.

b) Determine the compaction energy (Ninitial, Ndesign) for each asphalt cement

content, where N is the number of gyration applied by the laboratory

compactor.

4. Compute the volumetric and densification properties for each asphalt content.


Analysis of Results

The data produced by the experiment resulted in the following values which are shown below in

Table 1 and 2. Table 1 shows the measured values for the experiment and Table 2 contains the

calculations for volumetrics and densification.

Table 1- Measured Values

Content HG H125 H205 WAIR WSUB WSSD

I 4.80% 128.6 116 114.2 4543.9 2612.0 4564.7

I 4.80% 140.6 127.1 125.3 4968.6 2874.1 4989.8

Avg 4.80%

II 5.30% 128.2 115.5 113.5 4560.9 2639.4 4568.0

II 5.30% 129.6 116.7 115 4602.8 2662.3 4618.2

Avg 5.30%

III 5.80% 125 115 112.5 4499 2611 4502.3

III 5.80% 132.3 118.9 117.2 4710.4 2718.4 4717.4

Avg 5.80%

Weight (g)Height (mm)

Group AC

Table 2 - Volumetrics and Densification

GMB at GMB %GMM %GMM

N205 GMM NDESIGN125 N9 N205 VTM VMA VFA

2.327 2.438 2.291 84.8 95.4 6.0 14.6 58.6

2.348 2.438 2.315 85.8 96.3 5.0 13.7 63.1

2.338 2.438 2.303 85.3 95.9 5.5 14.1 60.9

2.365 2.424 2.324 86.4 97.6 4.1 13.8 70.1

2.353 2.424 2.319 86.1 97.1 4.3 14.0 69.0

2.359 2.424 2.322 86.3 97.3 4.2 13.9 69.5

2.379 2.386 2.327 89.7 99.7 2.5 14.1 82.5

2.356 2.386 2.323 87.5 98.8 2.7 14.3 81.4

2.368 2.386 2.325 88.6 99.2 2.6 14.2 82.0

Volumetrics @ NdesignDensificationMis Specific Gravity

Aggregate Bulk Specific Gravity (Gsb) = 2.553

Asphalt binder Gravity (Gb) = 1.030


0

2

4

6

4.00% 4.50% 5.00% 5.50% 6.00%

Air

Vo

ids

%

Asphalt Content %

VTM vs %AC

Series1

Figure 1 - VTM vs. %AC

60

70

80

90

4.00% 4.50% 5.00% 5.50% 6.00%

VFA

%

Asphalt Content %

VFA vs %AC

Series1

Figure 2 - VFA vs. %AC

13.8

13.9

14

14.1

14.2

14.3

4.00% 4.50% 5.00% 5.50% 6.00%

VM

A %

Asphalt Content %

VMA vs %AC

Series1

Figure 3 - VMA vs. %AC


85

86

87

88

89

4.00% 4.50% 5.00% 5.50% 6.00%

Gm

m a

t N

init

ial

9

Asphalt Content %

Gmm(initial) vs %AC

Series1

Figure 4 Gmm at N(initial) vs. %AC

95

96

97

98

99

100

4.00% 4.50% 5.00% 5.50% 6.00%

Gm

m N

fin

al 2

05

Asphalt Content %

Gmm(final) vs %AC

Series1

Figure 5 Gmm at N(final) vs. %AC

From Figure 1, the optimum asphalt content at 4% air voids is found to be 5.35%. This asphalt

content is then used in Figures 2 through 5 in order to calculate the volumetric and densification

properties of the sample. The optimized values for volumetrics and densification calculated from Figures

2 5 are: VFA is 72%, VMA is 13.93 %, Gmm(initial) is 86.6% and Gmm(final) is 97.6 %.


Findings

For this Superpave Asphalt Mix Design laboratory, it was determined from a graph of air voids

vs. % asphalt content that the optimum asphalt content at 4% air voids is 5.35%. The volumetric

requirements for this aggregate state that the voids filled with asphalt must be between 70% and 80%.

From Figure 2 using the 5.35% AC, it is shown that the VFA is between 70 and 80% and the optimum

value is 72%. Figure 3 shows a graph of Voids in Mineral aggregate vs. % asphalt content. The minimum

value for VMA is found to be 13.9 which corresponds to a nominal maximum aggregate size of 12.5 mm.

The optimum VMA = 13.93%. The densification requirements for this lab are: Gmm(initial) < 89% and

Gmm(final) < 98%. From Figure 4, it is shown that at 5.35% asphalt content, the Gmm(initial) = 86.6%

and from Figure 5, the Gmm(final) = 97.6%. Both numbers are within the specified requirement. Since all

requirements are met by the optimum asphalt content of 5.35%, this must be a correct % asphalt

content.


Sample Calculations

Volumetrics:

Air Voids:

VTM = ((2.438 2.372)/2.438)*100 = 6.0

Voids filled with asphalt:

where: VFA = Mixture voids filled with asphalt

VTM = Mixture air voids content

VFA = ((14.6 6.0)/14.6)*100 = 58.6 %

Voids in the Mineral Aggregate

where: VMA = Mixture Voids

%AC = Asphalt percent

VMA = (1 ((2.327)(1-0.04)/(2.553))*100 = 14.6 %

Densification:

Mixture Density at Ninitial:

Given N = 9

%Gmm(N,9) = ((100)(114.2/128.6)(2.327))/2.438 = 84.8%

Mixture Density at Nfinal:

Given N = 125


%Gmm(N,9) = ((100)(114.2/116.0)(2.327))/2.438 = 95.4%


References

1. Dr. Mohammad, L. Lecture 6. CE 3700 Laboratory Lecture Notes and Data Worksheets. Pages, 1-19.

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Superpave Mix