7/31/2019 AC Mix Design

1/28

1

Asphalt Concrete MixDesign

History

7/31/2019 AC Mix Design

2/28

2

Hot Mix Asphalt Concrete (HMA)

Mix Designs Objective:

Develop an economical blend of

aggregates and asphalt that meetdesign requirements

Historical mix design methods

MarshallHveem

New

Superpave gyratory

7/31/2019 AC Mix Design

3/28

3

Requirements in Common

Sufficient asphalt to ensure a durable pavement

Sufficient stability under traffic loads

Sufficient air voids

Upper limit to prevent excessiveenvironmental damage

Lower limit to allow room for initial

densification due to traffic Sufficient workability

7/31/2019 AC Mix Design

4/28

4

MARSHALL

MIXDESIGN

7/31/2019 AC Mix Design

5/28

5

Marshall Mix Design

Developed by Bruce Marshall for theMississippi Highway Department in the late30s

WES began to study it in 1943 for WWII

Evaluated compaction effort No. of blows, foot design, etc.

Decided on 10 lb.. Hammer, 50blows/side

4% voids after traffic Initial criteria were established and

upgraded for increased tire pressures andloads

7/31/2019 AC Mix Design

6/28

6

Automatic Marshall Hammer

7/31/2019 AC Mix Design

7/28

7

Marshall Mix Design

Select and test aggregate

Select and test asphalt cement

Establish mixing and compaction

temperatures Develop trial blends

Heat and mix asphalt cement and

aggregatesCompact specimen (100 mm

diameter)

7/31/2019 AC Mix Design

8/28

8

.1

.2

.3

.5

1

10

5

100 110 120 130 140 150 160 170 180 190 200

Temperature, C

Viscosity, Pa s

Compaction Range

Mixing Range

Mixing/Compaction Temps

7/31/2019 AC Mix Design

9/28

9

Marshall Design Criteria

Light Traffic Medium Traffic Heavy Traffic

ESAL < 104 10 4 < ESAL< 10 ESAL > 106

Compaction 35 50 75

Stability N (lb.) 3336 (750) 5338 (1200) 8006 (1800)

Flow, 0.25 mm (0.1 in) 8 to 18 8 to 16 8 to 14

Air Voids, % 3 to 5 3 to 5 3 to 5

Voids in Mineral Agg.(VMA) Varies with aggregate size

7/31/2019 AC Mix Design

10/28

10

Minimum VMA Requirements

7/31/2019 AC Mix Design

11/28

11

Marshall Mix Design Tests

Heights

Used to correct stability measurements

Bulk specific gravity of compacted sample

Maximum specific gravity of loose mix

Stability and flow

60oC water bath (30 to 40 minutes)

50 mm/min loading rate

Max. load = uncorrected stability

Corresponding vertical deformation = flow

7/31/2019 AC Mix Design

12/28

12

Marshall Stability and Flow

7/31/2019 AC Mix Design

13/28

13

Marshall Design Use of DataAsphalt Institute Procedure

Air Voids,

%

Asphalt Content, %

Stability

Asphalt Content, %

Unit Wt.

Asphalt Content, %

Target optimum asphalt content = average

4%

7/31/2019 AC Mix Design

14/28

14

Marshall Design Use of DataAsphalt Institute Procedure

Flow

Asphalt Content, %

VMA, %

Asphalt Content, %

Use target optimum asphalt contentto check if these criteria are met

Lower Limit

Upper limit

Minimum

OKOK

7/31/2019 AC Mix Design

15/28

15

Marshall Design Use of DataNAPA Procedure

Air Voids,%

Asphalt Content, %

Target optimum asphalt content =

the asphalt content at 4% air voids

4%

7/31/2019 AC Mix Design

16/28

16

Marshall Design Use of DataNAPA Procedure

Stability

Asphalt Content, %

The target stability is checked

OK

7/31/2019 AC Mix Design

17/28

17

Marshall Design Use of DataNAPA Procedure

Flow

Asphalt Content, %

VMA, %

Asphalt Content, %

Use target optimum asphalt contentto check if these criteria are met

Lower Limit

Upper limit

Minimum

OKOK

7/31/2019 AC Mix Design

18/28

18

Marshall Design Method

AdvantagesAttention on voids, strength, durability

Inexpensive equipment

Easy to use in processcontrol/acceptance

Disadvantages

Impact method of compaction

Does not consider shear strength

Load perpendicular to compaction axis

7/31/2019 AC Mix Design

19/28

19

HVEEM MIX

DESIGN

7/31/2019 AC Mix Design

20/28

20

Hveem Mix Design Method

Francis Hveem developed for CaliforniaDOT in mid 1920s

Limited usePrimarily in West coast states

Addresses similar design considerations

as Marshall Considers asphalt absorption by

aggregate

7/31/2019 AC Mix Design

21/28

21

Hveem Mix Design Method

Selection and testing of aggregates

Selection and testing of binders Centrifuge kerosene equivalent (CKE)

Surface capacity of aggregate

Estimate optimum asphalt content

7/31/2019 AC Mix Design

22/28

22

Use kneading compactor to prepare specimens Determine stability with Hveem stabilometer

Evaluates horizontal deformation under axial

loadSpecimen loaded along axis of compaction

Visual observation, volumetrics, and stabilityused to select optimum asphalt content

Hveem Mix Design Method

7/31/2019 AC Mix Design

23/28

23

Hveem Kneading Compactor

7/31/2019 AC Mix Design

24/28

24

Hveem Stabilometer

H Mi D i M th d

7/31/2019 AC Mix Design

25/28

25

Hveem Mix Design Method

Stability

Asphalt Content, %

AirVoids,

%

Asphalt Content, %

VMA

Asphalt Content, %Heavy traffic = 37 stability min.

Medium = 35 min.Light = 30 min.

Minimum

Minimum

7/31/2019 AC Mix Design

26/28

26

Hveem Mix Design Method

Step 1

Design Series

Step 2

Flushing

Step 3

Min. Stability

Step 4Max. AC with 4% Voids

7/31/2019 AC Mix Design

27/28

27

Hveem Mix Design

Advantages

Attention to voids, strength, durability

Kneading compaction similar to field

Strength parameter direct indication of

internal friction component of shearstrength

Disadvantages

Equipment expensive and not easilyportable

Not wide range in stability measurements

7/31/2019 AC Mix Design

28/28

28

Questions - ?