9. hma mix design ( highway engineering dr. sherif el-badawy )

1

Mansoura University - Faculty of Engineering – Public Works Engineering Dept.

Hot Mix Asphalt Design

Mansoura University - Faculty of Engineering – Public Works Engineering Dept.

Hot Mix Asphalt Concrete (HMA)

Mix Designs

• Objective:

• Develop an economical blend of aggregates and

asphalt binders that meet design requirements

• Historical mix design methods

• Marshall

• Hveem

• New

• Superpave gyratory

Mansoura University - Faculty of Engineering – Public Works Engineering Dept.

Requirements in Common

• Sufficient asphalt binder to ensure a durable pavement

• Sufficient stability under traffic loads

• Sufficient air voids

• Upper limit to prevent excessive environmental damage

• Lower limit to allow room for initial densification due to traffic

• Sufficient workability

Mansoura University - Faculty of Engineering – Public Works Engineering Dept.

Low binder contents can lead to raveling, stripping,

Fatigue Cracking, and premature aging.

2

Mansoura University - Faculty of Engineering – Public Works Engineering Dept.

High binder contents can lead to flushing, or bleeding,

and Rutting.

Mansoura University - Faculty of Engineering – Public Works Engineering Dept.

Marshall Mix Design

• Aggregate evaluation

• Binder evaluation • Establish mixing and compaction temperatures

• Specimen preparation • Heat and mix asphalt binder and aggregates

• Compact specimen (100 mm diameter)

• Marshall stability and flow

• Density and void analysis

• Determine asphalt content

Mansoura University - Faculty of Engineering – Public Works Engineering Dept.

Mansoura University - Faculty of Engineering – Public Works Engineering Dept.

3

Mansoura University - Faculty of Engineering – Public Works Engineering Dept.

Specimen preparation

Mansoura University - Faculty of Engineering – Public Works Engineering Dept.

HMA Mix Designs 10

Specimen preparation

Mansoura University - Faculty of Engineering – Public Works Engineering Dept.

HMA Mix Designs 11 Mansoura University - Faculty of Engineering – Public Works Engineering Dept.

Automatic Marshall Hammer

4

Mansoura University - Faculty of Engineering – Public Works Engineering Dept.

Extrude Sample from the mold

Mansoura University - Faculty of Engineering – Public Works Engineering Dept.

HMA Mix Designs 14

Mansoura University - Faculty of Engineering – Public Works Engineering Dept.

HMA Mansoura University - Faculty of Engineering – Public Works Engineering Dept.

Measure

stability and

Flow

5

Mansoura University - Faculty of Engineering – Public Works Engineering Dept.

HMA Mix Designs 17

Marshall Stability and Flow

Mansoura University - Faculty of Engineering – Public Works Engineering Dept.

Correction Factors for Marshall Stability

Values

Volume of

specimen

(cm)

Thickness

of specimen

(mm)

Correction

Factor

457 - 470 57.1 1.19

471 - 482 68.7 1.14

483 - 495 60.3 1.09

496 - 508 61.9 1.04

509 - 522 63.5 1.00

523 - 535 65.1 0.96

536 - 546 66.7 0.93

547 - 559 68.3 0.89

560 - 573 69.9 0.86

Mansoura University - Faculty of Engineering – Public Works Engineering Dept.

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 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

(see the following table)

Mansoura University - Faculty of Engineering – Public Works Engineering Dept.

Minimum VMA

Nominal Max. Size

(mm)

Minimum VMA, %

Design Air Voids, %

3.0 4.0 5.0

2.36 19 20 21

4.75 16 17 18

9.5 14 15 16

12.5 13 14 15

19.0 12 13 14

25.0 11 12 13

6

Mansoura University - Faculty of Engineering – Public Works Engineering Dept. Mansoura University - Faculty of Engineering – Public Works Engineering Dept.

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

Mansoura University - Faculty of Engineering – Public Works Engineering Dept.

Marshall Design Use of Data

Asphalt Institute Procedure

Air Voids,

%

Asphalt Binder

Content, %

Stability Unit Wt.

Target optimum asphalt binder content = average

4%

Asphalt Binder

Content, %

Asphalt Binder

Content, %

Mansoura University - Faculty of Engineering – Public Works Engineering Dept.

Marshall Design Use of Data

Asphalt Institute Procedure

Flow VMA, %

Use target optimum asphalt binder

content to check if these criteria are met

UL

Min

OK OK

Asphalt Binder

Content, % Asphalt Binder

Content, %

LL

VFA, %

Asphalt Binder

Content, %

UL

LL

7

Mansoura University - Faculty of Engineering – Public Works Engineering Dept.

Marshall Samples Volumetrics

b

b

se

s

mm

G

P

G

P

100G

mm

mb

G

G1100Va

b

b

mm

sse

G

P

G

100

PG

sb

sbm

G

PG001VMA

Mansoura University - Faculty of Engineering – Public Works Engineering Dept.

26