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2-MixSelectionandGeneralHMA28129.pdf

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HMA Mix Type Selection

Conventional / Dense-Gradation

3GAP-GRADED

4 OPEN-GRADED

Highway Noise

Highway Safety • Increase highway safety measures by increasing driver visibility,

reducing standing surface water, and improving skid resistance.

HMA MATERIALS

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

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

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

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

Types • Asphalt cements

• Cutbacks

• Emulsions

Early Specifications • Lake Asphalts

– Appearance – Solubility in carbon disulfide

• Petroleum asphalts (early 1900’s) – Consistency

• Chewing • Penetration machine

– Measure consistency

• 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

Binder Tests

Penetration Testing • Sewing machine needle • Specified load, time, temperature

100 g

Initial

Penetration in 0.1 mm

After 5 seconds

Penetration Grades

40-50, 60-70, 85-100 120-150, 200-300

# - # Maximum penetration Minimum penetration

Viscosity Graded Specifications

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

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

RTFO

Flash Point

• Safety test • Minimum temperature

with sufficient vapors to “flash” when exposed to flame

Solubility (Purity)

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)

Measures viscosity • Ability to pump

binder at asphalt plant

• Establish temperature versus viscosity relationship

Rotational Viscometer

spindle

torque

sample

sample chamber

Temperature Susceptibility

Viscosity

Temperature

Too brittle (Thermal cracking)

Too soft (Rutting)

Optimum range Of viscosity

Viscosity-Temperature Relationship

Viscosity - Temperature Relationship (Original Binder)

ARAC PG 58-28: y = -2.4795x + 7.6903 R2 = 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, oRankine)

L og

(L og

v is

co si

ty , c

P )

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

Pen 59, 77oF

Soft. Point 139oF

Brookfield Viscosity 200-350oF

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

40 50

60 70

85 100

120 150

200 300

Penetration Grades AC 40

AC 20

AC 10

AC 5

AC 2.5

100

V is

co si

ty , 6

0C (1

40 F)

AR 16000

AR 8000

AR 4000

AR 2000

AR 1000

General Comparison

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

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

Chapter 9: Asphalt

Dynamic Shear Rheometer – Tests complex shear

modulus of binders

– measures the resistance to shear deformation in the linear visco-elastic range

height (h)

radius (r)

torque (T) deflection angle (Θ)

Dynamic Shear Rheometer

Applied Stress

Fixed Plate

Asphalt

Oscillating Plate

B CA

Position of Oscillating Plate

Time

1 cycle

Elastic Viscous

TimeA A

Strain

Strain in-phase δ = 0o

Strain out-of-phase δ = 90o

Viscous Modulus, G”

Storage Modulus, G’

Complex Modulus, G*

Complex Modulus is the vector sum of the storage and viscous modulus

– Tests low temperature stiffness properties of binders

– Measures midpoint deflection of a simply supported beam

Bending Beam Rheometer

Bending Beam Rheometer • S(t) = P L3

4 b h3 δ (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

Direct Tension

• thermal cracking properties

εf

stress

strain

σf

Direct Tension Tester

Load

L+ ∆ L

∆L

failure strain (εf ) = ∆

effective length (L )

change in length ( L)

Summary

Fatigue CrackingRutting

RTFO Short Term AgingNo aging

Construction

[RV] [DSR]

Low Temp Cracking

[BBR]

[DTT]

PAV Long Term Aging

PAV Components

Bottom of pressure

aging vessel

Rack of individual pans

(50g of asphalt / pan)

Vessel Lid Components

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 δ

( 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

-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 δ

(Dynamic Shear Rheometer) DSR G*/sin δ < 3 Pa.s @ 135 oC

> 230 oC

CEC RWM

58 64

Test Temperature Changes

Spec Requirement Remains Constant

> 1.00 kPa

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

6 degree increments

Aggregates

* 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

Excavation

Sizing

Stockpiling

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

• Alkaline reactivity • Affinity for asphalt

Chapter 5: Aggregates

angular rounded flaky

elongated flaky & elongated

http://pavementinteractive.org/index.php?title=Image:Flat_elongated.jpg

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

Common Aggregate Properties

Toughness Soundness Deleterious Materials Gradation

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

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

Soundness

Before After

62 Aggregates

Clay Content (ASTM D2419) • Percentage of clay in material finer than 4.75

mm sieve ASTM D2419 or AASHTO T 176 – Sand equivalent test method

Sedimented Agg.

Flocculating Solution

Suspended Clay Clay Reading

Sand Reading

SE = Sand Reading Clay Reading *100

Chapter 5: Aggregates

• Aggregate Gradation – The distribution of particle sizes expressed as

a percent of total weight. – Determined by sieve analysis

Gradations

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

100.0 98.9 75.2 56.0 42.6 30.6 19.5 4.2 0.0

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

Chapter 5: Aggregates

Types of Gradation

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

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

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

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

sample

Mass agg. and AC

Vol. agg., AC, air voids Gmb =

Maximum Specific Gravity Loose (uncompacted) mixture

Mass agg. and AC

Vol. agg. and AC Gmm =

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

Vol. agg, AC, Air Voids

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

Effective Specific Gravity

Gse is an aggregate property

Gse = 100 - Pb

100 - Pb Gmm Gb

Voids in Mineral Aggregate

VMA is an indication of film thickness on the surface of the aggregate

VMA = 100 - Gmb Ps Gsb

Volumetric Abbreviations

• Va - Air voids • VMA - Voids Mineral Aggregate • Pbe - Effective Asphalt Content • VFA - Voids filled with Asphalt • Vba - Volume of absorbed asphalt

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

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

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

Chapter 5: Aggregates

HMA Mix Design

Marshall Hveem

Superpave

Marshall Mix Design • Uses impact hammer to prepare specimens • Determine stability with Marshall stabilometer • Uses volumetrics to select optimum asphalt

content

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

• Use kneading compactor to prepare specimens • Determine stability with Hveem stabilometer • Visual observation, volumetrics, and stability used to

select optimum asphalt content

Hveem Mix Design

Hveem Mix Design Method

Step 1 Design Series

Step 2 Flushing

Step 3 Min. Stability

Step 4 Max. AC with 4% Voids

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

Superpave Mix Design

• Uses gyratory compactor to prepare specimens • Uses volumetric analysis to select optimum

asphalt content

• Basis – Corps of Engineers – Texas equipment – French / Australian operational

characteristics • 150 mm diameter

– up to 37.5 mm nominal size • Height Recorded

Superpave Gyratory Compactor

% binder

VMA

% binder

VFA

% binder

%Gmm at Nini

% binder

%Gmm at Nmax

% binder

Blend 3

Selection of Design Asphalt Binder Content

4 Steps of Superpave Mix Design

1. Materials Selection 2. Design Aggregate Structure

3. Design Binder Content 4. Moisture Sensitivity

TSR

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

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

• 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

c) Design Aggregate Structure

<0.3 >30 Nini Ndes Nmax

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

Chapter 9: Asphalt

• 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

Moisture Susceptibility

Chapter 5: Aggregates

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

HMA Mix Type Selection
Slide Number 2
Slide Number 3
Slide Number 4
Highway Noise
Highway Safety
Slide Number 7
Slide Number 8
Slide Number 9
Slide Number 10
Slide Number 11
HMA MATERIALS�
Background
Slide Number 14
Slide Number 15
Petroleum-Based Asphalts
Asphalt Cement Components
Refinery Operation
Types
Early Specifications
Binder Tests
Penetration Testing
Penetration Grades
Viscosity Graded Specifications
AC Grades
AR Grades
RTFO
Flash Point
Solubility (Purity)
Testing
Rotational Viscometer
Rotational Viscometer
Temperature Susceptibility
Viscosity-Temperature Relationship
Mixing/Compaction Temps
General Comparison
New Superpave Binder Specifications
Slide Number 38
Dynamic Shear Rheometer
Dynamic Shear Rheometer
Slide Number 41
Slide Number 42
Bending Beam Rheometer
Bending Beam Rheometer
Direct Tension
Direct Tension Tester
Summary
Slide Number 48
Slide Number 49
Superpave Asphalt Binders
Slide Number 51
Aggregates
Excavation
Sizing
Aggregate Properties
Slide Number 56
Coarse Aggregates Particle Shape & Surface Texture Evaluation
Common Aggregate Properties
LA Abrasion Test
Slide Number 60
Soundness
Clay Content (ASTM D2419)
Slide Number 63
Gradations
Slide Number 65
Aggregate Size Definitions
Slide Number 67
Slide Number 68
Hot Mix Asphalt Concrete (HMA)�Mix Designs
Requirements in Common
HMA Volumetric Terms
BSG of Compacted HMA
Maximum Specific Gravity
Percent Air Voids
Effective Specific Gravity
Slide Number 76
Slide Number 77
Volumetric Abbreviations
Volumetric Terms�Continued
Slide Number 80
Slide Number 81
Slide Number 82
HMA Mix Design
Marshall Mix Design
Marshall Design Method
Hveem Mix Design
Hveem Mix Design Method
Hveem Mix Design
Superpave Mix Design
Superpave Gyratory Compactor
Slide Number 91
Slide Number 92
Slide Number 93
Slide Number 94
c) Design Aggregate Structure
Slide Number 96
Slide Number 97
Moisture Susceptibility
Slide Number 99
Slide Number 100