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Slide 1

HMA Mix Type Selection

Three basic mixture types are

discussed, each have their own

benefits and structural or functional

usage

Slide 2

DENSE-GRADED

Most common type

Do you know what the gradation chart

look like for this mixture?

There are different size aggregates

(wide range) represented in the mix.

Asphalt contents are in the range of 4.5

to 6 percent

Air voids are typically 5 to 7 percent

Slide 3

3GAP-GRADED

Got popular in recent decades.

Do you know what the gradation chart

look like for this mixture?

There is a gap in the gradation, that is

some large aggregates and some finer

ones, mid-size range is mostly missing.

What are the benefits? Structurally is

good and allows for higher addition of

binder especially when modified. Can

provide some permeability as well

Asphalt contents are in the range of 6

to 7 or 8 percent (the higher percentage

when polymer or rubber modified)

Air voids are typically in the 7 percent

range, have seen values with 9 percent.

More permeable but you want to stay

at the 7-8 percent range for best

performance

Slide 4

OPEN-GRADED

Got popular and widely used as a

surface mixture course.

Do you know what the gradation chart

look like for this mixture?

The gradation of the aggregates are

pretty much in a very narrow band

with similar sizes, very little fines.

What are the benefits? Does it provide

structural support? How about the

functional benefits? It also allows for

higher binder content and can provide

some great permeability and therefore

reduce the standing water on the

surface.

Typically used with modified binders

such as polymers and rubbter. Asphalt

contents are in the range of 8 to 9.5

percent (the higher percentage when

polymer or rubber modified)

Air voids are typically in the 18 to 20

percent range.

Slide 5 Highway Noise

Slide 6 Highway Safety

• Increase highway safety measures by increasing driver visibility, reducing standing surface water, and improving skid resistance.

Slide 7

Slide 8

Slide 9

Slide 10

Slide 11

Slide 12

HMA MATERIALS

Slide 13 Background

• First US hot mix asphalt (HMA) constructed in 1870’s – Pennsylvania Ave.

– Used naturally occurring asphalt from surface of lake on Island of Trinidad

• Two sources – Island of Trinidad

– Bermudez, Venezuela

Slide 14

Slide 15

Slide 16 Petroleum-Based Asphalts

• Asphalt is waste product from refinery processing of crude oil – Sometimes called the “bottom of the barrel”

• Properties depend on: – Refinery operations

– crude source

Gasoline

Kerosene

Lt. Gas Oil

Diesel

Motor Oils

Asphalt

Barrel of Crude Oil

Slide 17 Asphalt Cement Components

• Asphaltenes – Large, discrete solid inclusions (black)

– High viscosity component

• Resins – Semi-solid or solid at room temperature

• Fluid when heated

• Brittle when cold

• Oils – Colorless liquid

– Soluble in most solvents

– Allows asphalt to flow

Slide 18 Refinery Operation

FIELD STORAGE

PUMPING STATION

LIGHT DISTILLATE

HEAVY DISTILLATE

PROCESS UNIT

ASPHALT CEMENTS

FOR PROCESSING INTO

EMULSIFIED AND

CUTBACK ASPHALTS

STILL

AIR

AIR BLOWN ASPHALT

STORAGE

TOWER DISTILLATION REFINERY

RESIDUUM

GAS

PETROLEUM

SAND AND WATER

CONDENSERS AND

COOLERS

TUBE HEATER

MEDIUM DISTILLATE

Slide 19 Types

• Asphalt cements

• Cutbacks

• Emulsions

Slide 20 Early Specifications

• Lake Asphalts – Appearance

– Solubility in carbon disulfide

• Petroleum asphalts (early 1900’s) – Consistency

• Chewing

• Penetration machine – Measure consistency

Slide 21 Binder Tests

• Conventional Tests

Superpave /

SHRP Tests

Penetration AASHTO T49-93

Softening Point AASHTO T53-92

Rotational Viscosity AASHTO TP48

 Dynamic Shear

Rheometer (DSR):

AASHTO PP1

 Bending Beam Rheometer

(BBR): AASHTO TP1-98

Slide 22 Penetration Testing • Sewing machine needle

• Specified load, time, temperature

100 g

Initial

Penetration in 0.1 mm

After 5 seconds

The penetration test started out using a

No. 2 sewing machine needle mounted

on a shaft for a total mass of 100 g.

This needle was allowed to sink into

(penetrate) a container of asphalt

cement at room temperature (25 oC)

for 5 seconds. The consistency

(stiffness) of a given asphalt was

reported as the depth in tenths of a

millimeter (dmm) that the needle

penetrated the asphalt.

Slide 23 Penetration Grades

40-50, 60-70, 85-100

120-150, 200-300

# - #

Maximum penetration

Minimum penetration

Slide 24

Viscosity Graded Specifications

Slide 25 AC Grades

AC-2.5, AC-5, AC-10

AC-20, AC-30, AC-40

AC- # 1/100 of midpoint of the allowable viscosity range.

AC-20, viscosity range 1,600 to 2,400 poises.

Asphalt cement

Slide 26 AR Grades

AR-10, AR-20, AR-40

AR-80, AR-160

AR- # 1/100 of midpoint of viscosity after aging.

AR-40, viscosity range 3,000 to 5,000 poises.

Aged residue

Slide 27 RTFO

Slide 28 Flash Point

• Safety test

• Minimum temperature

with sufficient vapors to

“flash” when exposed to

flame

Slide 29 Solubility (Purity)

A sample of asphalt binder is dissolved

in a solvent then filtered through a

Gooch crucible mounted in the top of a

vacuum flask. The amount of

insoluble material retained on the filter

represents the impurities in the asphalt

binder.

Slide 30 Testing

Absolute viscosity

– U-shaped tube with timing marks & filled with asphalt

– Placed in 60C bath

– Vacuum used to pull asphalt through tube

– Time to pass marks

– Viscosity in Pa s (Poise)

At the 60 oC test temperature, the tube

is charged at 135 oC and then placed in

the test temperature bath. The tube

temperature is allowed to equalize

with the bath temperature, a vacuum

line is attached to the top of the small

diameter tube, and the flow is started.

The time it takes the asphalt to flow

past the timing marks times the tube

calibration constant gives the viscosity

of the asphalt in Poise.

Slide 31 Rotational Viscometer

Measures viscosity

• Ability to pump binder at asphalt plant

• Establish temperature versus viscosity relationship

Slide 32 Rotational Viscometer

spindle

torque

sample

chamber

Slide 33 Temperature Susceptibility

Viscosity

Temperature

Too brittle (Thermal cracking)

Too soft (Rutting)

Optimum range

Of viscosity

Slide 34 Viscosity-Temperature Relationship

Viscosity - Temperature Relationship (Original Binder)

ARAC PG 58-28: y = -2.4795x + 7.6903

R 2 = 0.989

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

2.70 2.75 2.80 2.85 2.90 2.95

Log (Temp, o Rankine)

L o g (

L o g v

is c o si

ty , cP

)

(41) (103) (171) (248) (335) (432)(deg F)

Pen

59, 77oF

Soft. Point

139oF

Brookfield Viscosity

200-350oF

Slide 35 Mixing/Compaction Temps

100 110 120 130 140 150 160 170 180 190 200

Temperature, C

Viscosity, Pa s

Compaction Range

Mixing Range

To establish mixing and compaction

temperatures it is necessary to develop

a temperature viscosity chart. This can

be done by determining the viscosity at

two different temperatures - generally

135 C and 165 C. These two

viscosities are then plotted on the

graph above and a straight line is

drawn between the two points.

The desired viscosity range for mixing

is between 0.15 and 0.19 Pa-s and

0.25 and 0.31 Pa-s for compaction.

Appropriate mixing and compaction

temperatures are selected as the

temperature where these viscosity

requirements are met. This

information can be obtained from the

suppliers. In many DOTs this

information is developed during the

mix design process.

If using modified binders - it is

recommended that you should contact

the supplier to determine the mixing

and compaction temperatures.

Slide 36

70 85

100

120

150 200

300

Penetration Grades

AC 40

AC 20

AC 10

AC 5

AC 2.5

100

V is

c o

s it

y ,

6 0

C (

1 4

0 F

)

AR 16000

AR 8000

AR 4000

AR 2000

AR 1000

General Comparison

This figure provides a general

comparison of the various traditional

specifications. While there is no direct

relationship between the

specifications, there is a general

relationship between stiffness and

viscosity. Higher penetration numbers

correspond with lower viscosities.

Slide 37 New Superpave Binder Specifications

Intended to improve pavement performance by

reducing the potential to:

Permanent deformation

Fatigue cracking

Low-temperature cracking

Excessive aging from volatilization

Pumping and handling

Slide 38 Test Equipment Performance Property

Rotational Viscometer

Dynamic Shear

Rheometer

Bending Beam Rheometer

Direct Tension

Tester

Handling Pumping

Permanent Deformation

Fatigue Cracking

Thermal Cracking

Flow

Rutting

Structural

Cracking

Low Temp.

Cracking

Slide 39 Dynamic Shear Rheometer

–Tests complex shear

modulus of binders

–measures the resistance

to shear deformation in

the linear visco-elastic

range

Chapter 9: Asphalt

height (h)

radius (r)

torque (T)

deflection angle (Q)

Slide 40 Dynamic Shear Rheometer

Applied Stress

Fixed Plate

Asphalt

Oscillating

Plate

B C A

Position of

Oscillating Plate

Time

1 cycle

Slide 41

Elastic Viscous

Time A

Strain

Strain in-phase

d = 0o Strain out-of-phase

d = 90o

If a material is elastic, then the strain

response will be in-phase with the

applied stress. If a material is viscous,

then the response will be 90o out of

phase.

Slide 42

Viscous Modulus, G”

Storage Modulus, G’

Complex Modulus, G*

Complex Modulus is the vector sum of the

storage and viscous modulus

When a material has both an elastic

and viscous component to its behavior,

this type of testing can sort out the

contribution of each to the total

response. Delta is the phase angle, that

is, the degrees that the strain response

is out of phase with the applied stress.

The complex modulus, G*, is the

vector sum (Pythagorean's theorem).

If delta is 0, the G* equals the storage

modulus. In other words, the response

is all elastic. If delta is 90o, then the

response is all viscous (G* = viscous

component).

Slide 43 Bending Beam Rheometer

–Tests low temperature stiffness properties of binders

– Measures midpoint deflection of a simply supported

beam

Slide 44 Bending Beam Rheometer

• S(t) = P L3

4 b h3 d (t)

Where:

S(t) = creep stiffness (M Pa) at time, t

P = applied constant load, N

L = distance between beam supports (102 mm)

b = beam width, 12.5 mm

h = beam thickness, 6.25 mm

d(t) = deflection (mm) at time, t

The equation used to determine the

change in stiffness with time is that for

a simply supported beam. The

geometry parameters remain constant

throughout the test. The only values

that change are the deformation of the

beam due to the static load and the

stiffness calculated using this time-

dependent deformation.

Slide 45 Direct Tension

• thermal

cracking

properties

FHWA

Slide 46 Direct Tension Tester

Load

L+  L

L

failure strain (f ) = 

effective length (L )

change in length ( L)

f

stress

strain

f

Slide 47 Summary

Fatigue

CrackingRutting

RTFO

Short Term AgingNo aging

Construction

[RV] [DSR]

Low Temp

Cracking

[BBR]

[DTT]

PAV

Long Term Aging

This figure summarizes the testing

required for the PG asphalt binder

specification.

Slide 48

PAV Components

Bottom of

pressure

aging

vessel

Rack of individual

pans

(50g of asphalt /

pan)

Vessel Lid Components

This photograph provides an example

of an older type of pressure aging

vessel equipment. This old version is

shown because it clearly shows all of

the key elements in all PAV units (old

or new). There are currently several

makes and models of PAV ovens

available.

Slide 49 PG 46 PG 52 PG 58 PG 64 PG 70 PG 76 PG 82

(Rotational Viscosity) RV

90 90 100 100 100 (110) 100 (110) 110 (110)

(Flash Point) FP

46 52 58 64 70 76 82

(ROLLING THIN FILM OVEN) (ROLLING THIN FILM OVEN) RTFO RTFO Mass Loss Mass Loss << 1.00 % 1.00 %

(Direct Tension) DT

(Bending Beam Rheometer) BBR Physical Hardening

-34 -40 -46 -10 -16 -22 -28 -34 -40 -46 -16 -22 -28 -34 -40 -10 -16 -22 -28 -34 -40 -10 -16 -22 -28 -34 -40 -10 -16 -22 -28 -34 -10 -16 -22 -28 -34

Avg 7-day Max, oC

1-day Min, oC

(PRESSURE AGING VESSEL) (PRESSURE AGING VESSEL) PAVPAV

ORIGINALORIGINAL

< 5000 kPa

> 2.20 kPa

S < 300 MPa m > 0.300

Report Value

> 1.00 %

20 Hours, 2.07 MPa

10 7 4 25 22 19 16 13 10 7 25 22 19 16 13 31 28 25 22 19 16 34 31 28 25 22 19 37 34 31 28 25 40 37 34 31

(Dynamic Shear Rheometer) DSR G* sin d

( Bending Beam Rheometer) BBR “S” Stiffness & “m”- value

-24 -30 -36 0 -6 -12 -18 -24 -30 -36 -6 -12 -18 -24 -30 0 -6 -12 -18 -24 -30 0 -6 -12 -18 -24 -30 0 -6 -12 -18 -24 0 -6 -12 -18 -24

(Dynamic Shear Rheometer) DSR G*/sin d

< 3 Pa.s @ 135 oC

> 230 oC

CEC RWM

58 64

Test Temperature

Changes

Spec Requirement

Remains Constant

> 1.00 kPa

Slide 50 Superpave Asphalt Binders

• Grading System and Selection Based Primarily on Climate

PG 58-22

Performance

Grade

Average 7-day

max pavement

design temp

Min pavement

design temp

Slide 51

6 degree increments

Slide 52 Aggregates

Slide 53 Excavation

* Natural sands and gravels - Underwater sources

+ Rivers & lakes Barge-mounted dredges, draglines,

scoop, conveyors, or pumps

+ Relatively clean

- Land sources

+ Gravel or sand pits Bucket loader

Slide 54 Sizing

Stockpiling

Slide 55 Aggregate Properties

• Shape and texture • Soundness • Toughness • Absorption • Specific gravity • Strength and modulus • Gradation • Deleterious materials and

cleanness • Alkaline reactivity • Affinity for asphalt

Slide 56

Chapter 5: Aggregates

angular rounded flaky

elongated flaky & elongated

Slide 57 Coarse Aggregates Particle Shape & Surface Texture Evaluation

• Texture and angularity –

Fractured faces

visual inspection to determine the percent of

aggregates with:

• no fractured faces

• % one fractured face

• % more than one fractured face

Slide 58

Common Aggregate Properties

Toughness

Soundness

Deleterious Materials

Gradation

Source aggregate properties are those

properties which are measured for the

aggregate as-stockpiled and are

commonly used for aggregate source

acceptance control. These properties

are toughness, soundness, and

deleterious materials. In addition, the

gradations of individual stockpiles

may be evaluated.

Slide 59 LA Abrasion Test

- Approx. 10% loss for extremely hard igneous rocks - Approx. 60% loss for soft limestones and sandstones

Rotate for 500 revolutions at 30 to 33 rpm’s

This photo shows the equipment

needed for the Los Angeles abrasion

test. The panel on the side of the drum

is removed and the aggregate and steel

balls are placed inside. The panel is

replaced and the drum rotated the

prescribed number of cycles.

Examples of typical values are noted at

the bottom of this photo.

Slide 60

Soundness

* Estimates resistance to weathering .

* Simulates freeze/thaw action by successively wetting

and drying aggregate in sodium sulfate or magnesium

sulfate solution

+ One immersion and drying is considered one

cycle

* Result is total percent loss over various sieve intervals

for a prescribed number of cycles

+ Max. loss values typically range from

10 to 20%per 5 cycles

Weathering of aggregates is simulated

by repeated immersion in saturated

solutions of either sodium or

magnesium sulfate followed by oven

drying. The internal expansive force

from the expansion of the rehydration

of the soluble salts upon re-immersion

simulates freeze-thaw damage. The

difference between the original and

final mass, expressed as a percent of

the original mass is the percent loss. A

weighted percentage is used when

several fractions are tested. The

soundness of both fine (passing the

4.75 mm sieve) and coarse aggregate

can be determined using this test.

Slide 61 Soundness

Before After

Damage to the aggregate after a

number of wet-dry cycles can be seen

by visual examination as well as in the

change in gradation.

Slide 62

Chapter 5: Aggregates

Slide 63

Clay Lumps and Friable Particles

ASTM C 142

Dries a given mass of agg., then soaks for 24 hr., and each particle is rubbed. A washed

sieve is then performed over several screens,

the aggregate dried, and the percent loss is

reported as the % clay or friable particles.

Deleterious material is the mass

percent of contaminants such as clay

lumps, shale, wood, mica, and coal in

the blended aggregate. This test can

also be performed for both fine and

coarse aggregates. The mass

percentage of the material lost during a

wet sieve is reported as the percent of

clay lumps and friable particles.

Slide 64 Gradations

• Aggregate Gradation

– The distribution of particle sizes expressed as

a percent of total weight.

– Determined by sieve analysis

Slide 65

Gradations - Computation

Sieve Mass Cumulative

Retained Mass Retained % Retained % Passing

9.5

4.75

2.36

1.18

0.60

0.30

0.15

0.075

Pan

0.0

6.5

127.4

103.4

72.8

64.2

60.0

83.0

22.4

0.0

6.5

133.9

237.3

310.1

374.3

434.3

517.3

539.7

0.0

1.2

24.8

44.0

57.5

69.4

80.5

95.8

100.0

98.9

75.2

56.0

42.6

30.6

19.5

4.2

0.0

This is an example of the calculations

necessary for a sieve analysis. What is

not shown is that the 22.4 g of material

in the pan is the sum of the mass which

was washed past the0.075 mm sieve in

the first part and the mass of the

aggregate retained in the pan after the

mechanical sieve analysis. This is an

important point as the final gradation

reported needs to reflect the true

percentage of fractions in the stockpile

which will be used during

construction.

Slide 66 Aggregate Size Definitions

• Nominal Maximum Aggregate Size –one size larger than the first sieve to retain

more than 10%

• Maximum Aggregate Size –one size larger than nominal maximum size

100 100 90 72 65 48 36 22 15 9 4

100 99 89 72 65 48 36 22 15 9 4

For HMA pavements these are the

definitions for gradations.

Slide 67

Chapter 5: Aggregates

Slide 68

Chapter 5: Aggregates

Types of Gradation

Slide 69 Hot Mix Asphalt Concrete (HMA) Mix Designs

• Objective:

– Develop an economical blend of aggregates and asphalt that meet design requirements

• Historical mix design methods

– Marshall

– Hveem

• New

– Superpave gyratory

Slide 70 Requirements in Common

• Sufficient asphalt 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

Slide 71 HMA Volumetric Terms

• Bulk specific gravity (BSG) of compacted HMA

• Maximum specific gravity

• Air voids

• Effective specific gravity of aggregate

• Voids in mineral aggregate, VMA

• Voids filled with asphalt, VFA

Slide 72 BSG of Compacted HMA • AC mixed with agg. and compacted into sample

Mass agg. and AC

Vol. agg., AC, air voids

Gmb =

Slide 73 Maximum Specific Gravity

 Loose (uncompacted) mixture

Mass agg. and AC

Vol. agg. and AC

Gmm =

Slide 74 Percent Air Voids  Calculated using both specific gravities

Gmb

Gmm Air voids = ( 1 - ) 100

Mass agg + AC

Vol. agg, AC, Air Voids

Mass agg + AC

Vol. agg, AC

Vol. agg, AC, Air Voids

Slide 75

Effective volume = volume of solid aggregate particle +

volume of surface voids not filled with asphalt

Gse = Mass, dry

Effective Specific Gravity

Effective Volume

Absorbed asphalt

Vol. of water-perm. voids

not filled with asphalt

Surface Voids

Solid Agg.

Particle

Slide 76 Effective Specific Gravity

Gse is an aggregate property

Gse = 100 - Pb

100 - Pb

Gmm Gb

Slide 77 Voids in Mineral Aggregate

VMA is an indication of film thickness on

the surface of the aggregate

VMA = 100 - Gmb Ps

Gsb

Slide 78 Volumetric Abbreviations

• Va - Air voids

• VMA - Voids Mineral Aggregate

• Pbe - Effective Asphalt Content

• VFA - Voids filled with Asphalt

• Vba - Volume of absorbed asphalt

Slide 79 Volumetric Terms Continued

• Gsb - Bulk Specific Gravity of Stone

• Gse - Effective Specific Gravity of Stone

• Gb - Bulk Specific Gravity of Asphalt

• Gmb - Bulk Specific Gravity of Mix

• Gmm - Theoretical Maximum Specific

Gravity of Mixture

Slide 80 Gmb = 2.329

air

asphalt

Gb = 1.015

Pb = 5% by mix

aggregate

Gsb = 2.705

Gse = 2.731

absorbed asph

VOL (cm3 ) MASS (g)

1.000

Volumetric Properties - Phase Diagrams

Slide 81 air

asphalt

Gb = 1.015

aggregate

Gsb = 2.705

Gse = 2.731

absorbed asph

2.3291.000

0.108

0.008

0.116

2.213

0.182

VOL (cm3 ) MASS (g)

0.818

0.076

0.106 0.114

0.810

0.008

Air Voids = 7.6% Effective Asphalt Content = 4.6%

VMA = 18.2 % Absorbed Asphalt Content = 0.4%

VFA = 58.2 % Max Theo Sp Grav = 2.521

Slide 82

Chapter 5: Aggregates

Slide 83

HMA Mix Design

Marshall

Hveem

Superpave

Slide 84 Marshall Mix Design

• Uses impact hammer to prepare specimens

• Determine stability with Marshall stabilometer

• Uses volumetrics to select optimum asphalt content

Slide 85 Marshall Design Method • Advantages

– Attention on voids, strength, durability

– Inexpensive equipment

– Easy to use in process control/acceptance

• Disadvantages

– Impact method of compaction

– Does not consider shear strength

– Load perpendicular to compaction axis

Slide 86 Hveem Mix Design

• Use kneading compactor to prepare specimens

• Determine stability with Hveem stabilometer

• Visual observation, volumetrics, and stability used to select optimum asphalt content

Slide 87 Hveem Mix Design Method

Step 1

Design Series

Step 2

Flushing

Step 3

Min. Stability

Step 4

Max. AC with 4% Voids

The following steps are followed in

determining the design asphalt content:

• Step 1 - Record the four asphalt

contents used for preparing the mix

specimens. Record them in order of

increasing amount from left to right.

• Step 2 - Select from Step 1 the

three highest asphalt contents that do

not exhibit moderate or heavy flushing

and record them in step 2.

• Step 3 - Select from Step 2 the

two specimens that provide the

specified minimum stability and enter

them in step 3.

• Step 4 - Select from Step 3 the

highest asphalt content that provides at

least 4% air voids.

Slide 88 Hveem Mix Design • Advantages

– Attention to voids, strength, durability

– Kneading compaction similar to field

– Strength parameter direct indication of internal friction component of shear strength

• Disadvantages

– Equipment expensive and not easily portable

– Not wide range in stability measurements

Slide 89 Superpave Mix Design

• Uses gyratory compactor to prepare specimens

• Uses volumetric analysis to select optimum asphalt content

Slide 90 Superpave Gyratory Compactor

• Basis – Corps of Engineers

– Texas equipment

– French / Australian operational characteristics

• 150 mm diameter – up to 37.5 mm nominal size

• Height Recorded

Slide 91

% binder

VMA

% binder

VFA

% binder

%Gmm at Nini

% binder

%Gmm at Nmax

% binder

Blend 3

Selection of Design Asphalt Binder Content

Slide 92

4 Steps of Superpave Mix Design

1. Materials Selection 2. Design Aggregate Structure

3. Design Binder Content 4. Moisture Sensitivity

TSR

Slide 93 a) Aggregate Selection –depending on traffic level and how deep under surface

–coarse agg. angularity -- min. % crushed particles

–fine agg. angularity -- measured by unpacked air voids

(min.)

–Flat & elongated particles -- max.

–Clay content -- need small amount for bonding

–Gradation -- 0.45 power chart

• curve must pass through control points

Slide 94

b) Binder Selection based on service temps. as discussed earlier

Course Fine

Aggregate Aggregate Flat and Sand

Angularity Angularity Elongated Equivalency

Design Level (% min) (% min) (% max) (% min)

Light Traffic 55/- — — 40

Med. Traffic 75/- 40 10 40

Heavy Traffic 85/80 45 10 45

Superpave Consensus Aggregate Properties

Slide 95 c) Design Aggregate Structure

• prepare trial specimens with different aggregate gradations & asphalt contents using the gyratory compactor

• No. of gyrations is based on design high temp. & traffic volume

• Design criteria:

–Nini < 89% Gmm –Ndes = 96% Gmm –Nmax < 98% Gmm

Slide 96 0.3 30 N

ini N

des N

max

Traffic Level (106 ESAL)

<0.3 0.3 - 3 3 - 30 >30

Nini 6 7 8 9

Ndes 50 75 100 125

Nmax 75 115 160 205

Number of Gyrations at Specific Design Traffic

Levels

Slide 97

Chapter 9: Asphalt

Slide 98 Moisture Susceptibility • Stripping is loss of bond between asphalt & agg.

– several methods differing by specimen preparation, conditioning,

and strength requirements

– 2 sets of specimens: control & conditioned

– evaluate strength before and after conditioning

– Retained strength = conditioned strength / reference strength

– must have min. retained strength

Slide 99

Chapter 5: Aggregates

Slide 100 How to Improve Moisture Susceptibility

–Increase asphalt content

–Higher viscosity asphalt

–Clean aggregate of dust and clay

–Change aggregate gradation

–Add anti-stripping additives

• liquid

• portland cement or lime