Asphalt 101 – Materials: HMA Part 1 Rocky Mountain Asphalt ...Rocky Mountain Asphalt Conference and Equipment Show February 24, 2011. 2 SUPERPAVE . 2 SUPERPAVE . 3 SPECIFYING PERFORMANCE

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Asphalt 101 – Materials: HMA Part 1

Rocky Mountain Asphalt Conference and Equipment Show

February 24, 2011

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SUPERPAVE

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SUPERPAVE

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SPECIFYING PERFORMANCE

Based on Climate

PG 58 - 28

Performance Grade

Rolling average 7-day max pavement temperature, C

Min pavement temperature, C

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To characterize (test) a PG binder . . .

- 8 individual tests- 6 major pieces of equipment- 3 conditioning steps- ~25 hours total time elapse

PG Binder Tests vs. Temperature

Pavement Temperature, °C- 20 20 60 135

Brookfield

Viscosity(Workability)

DSRHigh

Temperature

(RuttingResistance)

DSRIntermediateTemperature

(FatigueResistance)

BBR & DTT

(Thermal Cracking

Resistance)

Cold Hot

Binder Test Sequence

Unaged Binder

RTFO Aged

PAV Aged

DSRLOH

DSRBBRDTT

FlashRot VisDSR

Binder Condition Test For

SafetyHandlingRutting

RuttingEnvironment / Aging

Fatigue DamageThermal CrackingThermal Cracking

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Aging

Asphalt reacts with oxygen– Becomes harder, more brittle– More Elastic, Less Viscous

Short term– During Mixing with Aggregates (280F-330F)

Long term– In Pavement– Air, Water, Sun

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Asphalt Plant and Construction Aging

Rolling Thin Film Oven (RTFO)

Fan

Rotating Bottle

Carriage

Blowing Air

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Pressure Aging Vessel

50 grams of Asphalt in Each Pan


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Courtesy of FHWA


Unaged Binder

RTFO Aged

PAV Aged

DSRLOH

DSRBBRDTT

FlashRot VisDSR





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RV

ConstructionIs the binder safe to be heated?

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Cleveland Open Cup Flash Point Tester

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Spec Requirement

Binder safe to be heated . . .

– Cleveland Open Cup (COC) Flash Point must be greater than 232oC (450oF).


Unaged Binder

RTFO Aged

PAV Aged

DSRLOH

DSRBBRDTT

FlashRot VisDSR





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RV

ConstructionWill it Flow for Mixing ?

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Rotational Viscometer (Brookfield)

Inner Cylinder

Torque Motor

Thermosel Environmental

Chamber

Digital Temperature Controller

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Spec Requirement

Make sure binder is not too thick to pump . . .– Keep Viscosity Below 3 Pa-sec at 135oC (275oF)


Unaged Binder

RTFO Aged

PAV Aged

DSRLOH

DSRBBRDTT

FlashRot VisDSR



Rutting, HardeningEnvironment / Aging


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Caused by Warm Weather, Traffic and Wrong Mixture

Cou

rtes

y of

FH

WA

Permanent Deformation ( )

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High temperature or,slow loading behavior, Rutting

High Pavement Temperature– Desert climates– Summer temperatures

Sustained loads– Slow moving trucks– Intersections

100°F

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Rutting, Hardening, and Fatigue

Dynamic Shear Rheometer (DSR)

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1 cycle

CA

B

Fixed Lower Plate

Oscillating Upper PlateAsphalt Glued In-Between

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1 cycle

Time

CA

B

Fixed Lower Plate

Oscillating Upper PlateAsphalt Glued In-Between

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1 cycle

TimeAA

B

C

CA

B

Fixed Lower Plate

Oscillating Upper Plate

A

Asphalt Glued In-Between

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1 cycle

TimeAA

B

C

CA

B

Fixed Lower Plate

Oscillating Upper Plate

A

Now, Measure the Force Required to Rotate the Upper

Plate

And, Measure When Movement Occurs in

the Binder

Asphalt Glued In-Between

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24

Elastic

Time

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Elastic

TimeAA

B

C

Strain

Strain Occurs With Stressδ = 0o

A

Stress

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Elastic Viscous

TimeAA

B

C

Strain


A

Stress

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Elastic Viscous

TimeAA

B

C

Strain


AA

B

C

AA

Stress

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Elastic Viscous

TimeAA

B

C

Strain


Strain Lags Stressδ = 90o

AA

B

C

AA

Stress

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δ

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Elastic, G’

δ

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Vis

cous

, G”

Elastic, G’

δ

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Vis

cous

, G”

Elastic, G’

Complex M

odulus, G*

δ

Complex Modulus is the vector sum of

Elastic and Viscous Components

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Early part of pavement life

Spec Requirement

Mitigate rutting by . . . G*/sin δ on Unaged binder > 1.00 kPa G*/sin δ on RTFO Aged binder > 2.20 kPa


Unaged Binder

RTFO Aged

PAV Aged

DSRLOH

DSRBBRDTT

FlashRot VisDSR





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Caused by repeated traffic loads in wheel pathsFatigue Cracking

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Spec Requirement

Reduce Fatique Cracking by . . . G*sin δ on RTFO & PAV aged binder < 5000 kPa

Later part of pavement service life


Unaged Binder

RTFO Aged

PAV Aged

DSRLOH

DSRBBRDTT

FlashRot VisDSR





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Courtesy of FHWA

Thermal Cracking

Caused by Low Temperatures, Rapid Loads, Hard Binder

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Low Temperature, or Fast Loading Behavior-aka Cracking

Low Temperature– Cold climates– Winter

Rapid Loads– Fast moving trucks

σ

ε

Cracking Failure

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RV BBR

Thermal Cracking

Bending Beam Rheometer

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Bending Beam Rheometer

Load Cell

Deflection Transducer

Fluid Bath

Computer

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BBR Measures Stiffness at Low Temperatures using Beam Theory

S(t) =PL3

4 bh3 δ (t)

Creep stiffness at

t = 60 secs100 grams

Clear Span of Beam, 102 mm

Beam Width, 12.5 mm

Beam Thickness, 6.25 mm

Deflection at t = 60 secs

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Bending Beam Rheometer Creep Stiffness Stiffness v. Time Slope

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8 15 30 60 120 240

Log

Cre

ep

Stif

fnes

s, S

(t)

Log Loading Time, t (sec)

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8 15 30 60 120 240

Log

Cre

ep

Stif

fnes

s, S

(t)


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8 15 30 60 120 240

Log

Cre

ep

Stif

fnes

s, S

(t)


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8 15 30 60 120 240

Log

Cre

ep

Stif

fnes

s, S

(t)


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8 15 30 60 120 240

Log

Cre

ep

Stif

fnes

s, S

(t)


m

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Spec Requirement

Protect against cracking . . . BBR “m” value > 0.300 BBR “S” value < 300 MPa


Unaged Binder

RTFO Aged

PAV Aged

DSRLOH

DSRBBRDTT

FlashRot VisDSR





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Thermal Cracking

Question: How Much Should the Asphalt Be Able to Stretch before Breaking?

Answer: at least 1% (in Colorado possibly even more)

How: Find the Temperature Where the Asphalt Can Stretch 1% or More

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Direct Tension Test

Δ Le

Δ L

Load

Stress = σ = P / A

Strain εf

σf

Conventional AC Grades vs. SHRP Performance Grades

(typical comparisons)

AC-5 AC-10 AC-20 AC-40

PG 52-34 PG 58-28 PG 64-22 PG 70-16

Typical (not absolute) for unmodified asphalts only

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Documents

Asphalt 101 – Materials: HMA Part 1 Rocky Mountain Asphalt ...Rocky Mountain Asphalt Conference and Equipment Show February 24, 2011. 2 SUPERPAVE . 2 SUPERPAVE . 3 SPECIFYING PERFORMANCE