13 - marshall mix design

Marshall Mix Design

CIVL 3137 46

Asphalt Concrete Properties

Stability

Workability

Skid Resistance

Durability

Stripping

Fatigue Cracking

Thermal Cracking

Bleeding

CIVL 3137 47

Stability

The ability to withstand traffic loads withoutdistortion or deflection, especially at highertemperatures.

To get good stability, use strong, rough, dense-graded, cubical aggregatewith just enough binder to coat the aggregate particles. Excess asphaltcement lubricates the aggregate particles and lets them slide past eachother more easily (which reduces stability). But a thick asphalt coatingprovides good flexibility to resist cracking, which is desirable. Hmmm

CIVL 3137 48

Workability

The ability to be placed and compacted withreasonable effort and without segregation ofthe coarse aggregate.

Too much asphalt cement makes the mix tender. Too little asphalt cementmakes it hard to compact. Too much natural sand can also make the mixtender because natural sand has smooth, round grains. Hmmm

CIVL 3137 49

Skid Resistance

Proper traction in wet and dry conditions.

To get good skid resistance, use smaller aggregate so there are lots ofcontact points, use hard aggregate that doesnt polish and make sure youhave enough air voids to prevent bleeding.

Some states now use an open-graded friction course (OGFC) that allowswater to drain to the sides of the pavement, eliminating hydroplaning. ButOGFC is not very durable because of the open pores. Hmmm

CIVL 3137 50

Durability

The ability to resist aggregate breakdown dueto wetting and drying, freezing and thawing,or excessive inter-particle forces.

To get good durability, use strong, tough, nonporous aggregate andenough asphalt cement to completely coat all of the aggregate particles(to keep them dry) and fill all of the voids between particles (to slow theoxidation of the asphalt cement). But this reduces stability. Hmmm

CIVL 3137 51

Stripping

Separation of the asphalt cement coating fromthe aggregate due to water getting betweenthe asphalt and the aggregate.

To reduce stripping, use clean, rough, hydrophobic aggregate and addenough asphalt cement to provide a thick coating of asphalt on everyaggregate particle. This improves durability but decreases stability.

CIVL 3137 52

Bleeding

The migration of asphalt cement to the surfaceof the pavement under wheel loads, especiallyat higher temperatures.

To prevent bleeding, incorporate enough air voids so the asphalt cancompress by closing air voids rather than by squeezing asphalt cementout from between the aggregate particles.

CIVL 3137 53

Fatigue Cracking

Cracking resulting from repeated flexure ofthe asphalt concrete due to traffic loads.

To minimize fatigue cracking, use the proper asphalt cement grade andhave a thick asphalt cement coating to make the concrete flexible. Thisimproves durability but decreases stability.

CIVL 3137 54

Thermal Cracking

Cracking that results from an inability toacclimate to a sudden drop in temperature.

To minimize thermal cracking, use the proper asphalt cement grade.

CIVL 3137 55

Mix Design Basics

The right grade of asphalt cementRelates to fatigue cracking, thermal cracking, stability

The right type of aggregateRelates to stability, durability, stripping, skid resistance

The right mix volumetricsRelates to stability, durability, stripping, bleeding, skid resistance

CIVL 3137 56

Right Type of Asphalt Cement

767064585246-4-10-16-22-28

PG70-22

Reliability = (1.00)(0.98) = 98%

~0% ~2%~100% ~98%

Lowest 1-dayPavement

Temperature

Highest 7-dayPavement

Temperature

CIVL 3137 57

The Right Type of Aggregate

1. Strong and Durable2. No Deleterious Substances3. Cubical (Angular and Equidimensional)4. Low Porosity5. Clean, Rough, and Hydrophobic6. Hard7. Dense-Graded

CIVL 3137 58

The Right Mix Volumetrics

BleedingLow stabilityTender mix

StrippingLow durability

Fatigue cracking

CIVL 3137 59

Marshall Mix Design

Bruce Marshall, Mississippi Highway Department

Marshall Mix Design Steps

1. Create aggregate blend to meet gradation specifications.

2. Establish mixing and compaction temperatures from the viscosity-temperature chart.

3. Compact three specimens at each of five asphalt contents spanning the expected optimum asphalt content.

4. Determine the relative density of each specimen and the mix volumetrics (mb, VTM, VMA, VFA).

5. Measure the performance properties of the each specimen at 60C (140F).

CIVL 3137 60

CIVL 3137 61

Marshall Specimens

Traffic Blows / Side

Light 35

Medium 50

Heavy 75

10#18"

Make 3 specimens at each of5 different asphalt contents

CIVL 3137 62

Marshall Hammer

Mold

Hammer

CIVL 3137 70

Stability and Flow Test

140oF

flow

stability

deflection(0.01 in)

load(lbs)

CIVL 3137 71

Stability and Flow Test

CIVL 3137 72

Marshall Mix Design

159

160

161

162

163

164

3.5 4.0 4.5 5.0 5.5 6.0 6.5

Asphalt Content (%)

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CIVL 3137 73

1500

1600

1700

1800

1900

2000

3.5 4.0 4.5 5.0 5.5 6.0 6.5

Asphalt Content (%)

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Marshall Mix Design

CIVL 3137 74

1

2

3

4

5

6

3.5 4.0 4.5 5.0 5.5 6.0 6.5

Asphalt Content (%)

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V

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%

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Marshall Mix Design

CIVL 3137 75

0

5

10

15

20

25

3.5 4.0 4.5 5.0 5.5 6.0 6.5

Asphalt Content (%)

F

l

o

w

Marshall Mix Design

CIVL 3137 76

50

60

70

80

90

100

3.5 4.0 4.5 5.0 5.5 6.0 6.5

Asphalt Content (%)

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Marshall Mix Design

CIVL 3137 77

Marshall Mix Design

%7.43

3.47.41.5AC

MaximumDensity

MaximumStability

4% AirVoids

(The Asphalt Institute Procedure)

CIVL 3137 78

Marshall Mix Design

5.1AC 4.7 4.3 4.3%1

MaximumDensity

MaximumStability

4% AirVoids

(The NAPA Procedure)

ThisiswhatTDOTuses

CIVL 3137 79

Marshall Mix Design(Asphalt Institute Criteria)

Criteria Min. Max. Min. Max. Min. Max.

Number of Blows

Stability (lbs) 500 750 1500

Flow 8 20 8 18 8 16

Air Voids (%) 3 5 3 5 3 5

VMA (%) See Next Slide

Light Traffic Medium Traffic Heavy Traffic

35 50 75

16 14

1800TDOTuses2000

18

750 1200

CIVL 3137 80

VMA CriteriaM

i

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%

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10

Nominal Maximum Particle Size

20

30

40

50

2"1"1"""4 3/8"840

Deficient in eitherasphalt or air voids

(Assuming 4% Design Air Voids)

CIVL 3137 81

VMA CriteriaM

i

n

i

m

u

m

V

M

A

(

%

)

10


20

30

40

50

2"1"1"""4 3/8"840



1%

CIVL 3137 82

VMA CriteriaM

i

n

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m

u

m

V

M

A

(

%

)

10


20

30

40

50

2"1"1"""4 3/8"840



1%

CIVL 3137 83

1500

1600

1700

1800

1900

2000

3.5 4.0 4.5 5.0 5.5 6.0 6.5

Asphalt Content (%)

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Marshall Mix Design

CIVL 3137 84

0

5

10

15

20

25

3.5 4.0 4.5 5.0 5.5 6.0 6.5

Asphalt Content (%)

F

l

o

w

Marshall Mix Design

CIVL 3137 85

1

2

3

4

5

6

3.5 4.0 4.5 5.0 5.5 6.0 6.5

Asphalt Content (%)

A

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V

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(

%

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Marshall Mix Design

CIVL 3137 86

50

60

70

80

90

100

3.5 4.0 4.5 5.0 5.5 6.0 6.5

Asphalt Content (%)

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Marshall Mix Design

CIVL 3137 87

VMA CriteriaM

i

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(

%

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10


20

30

40

50

2"1"1"""4 3/8"840


CIVL 3137 88

13

14

15

16

17

18

3.5 4.0 4.5 5.0 5.5 6.0 6.5

Asphalt Content (%)

V

M

A

(

%

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Marshall Mix Design

TDOT requiresthe AC to be lessthan that whichminimizes VMA

CIVL 3137 89

Ways to Increase VMA

1. Reduce the dust content2. Open the aggregate gradation3. Gap-grade the aggregate blend4. Increase manufactured sand5. Reduce flat-and-elongated particles