block 4 sp 14

Asphalt Binders Superpave Binder Tests 1

Asphalt Binders

Superpave Performance Graded Specification

Senior/GraduateHMA Course


Superpave Asphalt Binder Specification

The grading system is based on Climate

PG 64 - 22

Performance Grade

Average 7-day max pavement temperature

Min pavement temperature


Pavement Temperatures are Calculated

• Calculated by Superpave software• High temperature

– 20 mm (.8”) below the surface of mixture

• Low temperature– at surface of mixture

Pave temp = f (air temp, depth, latitude)

www.tfhrc.gov/pavement/ltpp/ltppbind.htm

http://www.tfhrc.gov/pavement/ltpp/ltppbind.htm


PG Specification Tests

• Rheology– Fundamental properties related to HMA

performance• Test parameters

– Selected to represent in-service & construction temperatures

• Asphalt binder conditioning– Environmental factors

•Short and long term aging


Rheological Tests Selected

• Concentric Cylinders• Dynamic shear rheometer• Bending beam• Direct tension


RV DSR BBR

Construction

Tests Used in PG Specifications


Construction Asphalt Binder Properties

• Concentric cylinder rheometer– Used to insure a minimum

workability (pumpability) at typical mixing temperature

– Maximum viscosity 3kPa at 135oC (275 F)

Construction

[RV]


RV

DSR

BBR

Rutting


Rutting• High in-service temperature

– Desert climates– Summer temperatures

• Sustained loads– Slow moving trucks– Intersections

Viscous Liquid


Rutting

• DSR testing– Minimum stiffness requirement

•Original asphalt binder•Immediately after construction

–Short term aging Rutting

[DSR]


High In-Service Temperatures

• Permanent deformation (rutting)• Mixture is plastic• Depends on asphalt binder source,

additives, and aggregate properties

Function of warm weather and traffic


Short Term Aging

• Simulates stiffening of asphalt binder during storage, mixing, and hauling

• Function of:– Oxidation hardening

•Asphalt binder reacts with oxygen•Volatilization of specific components

• Simulated using rolling thin film oven


Short Term Aging• Rolling Thin Film Oven Test (RTFOT)

– Simulates aging from hot mixing and construction


Mass Loss is Monitored

• Calculate mass loss after RTFO

Mass loss, % =Original mass - Aged mass

Original mass

x 100


RuttingSuperpave DSR test requirements:

G*/sin on unaged (original) asphalt binder > 1.00 kPa

G*/sin on RTFO aged asphalt binder > 2.20 kPa

For the early part of the service life


RV

DSR

BBR

Fatigue


Fatigue Cracking

Function of repeated traffic loads over time(in wheel paths)


DSR

• Aged PG asphalt binder– Since long term performance

problem, include:•Short term aging•Long term aging

• Determine DSR parameters using 8 mm plate and intermediate test temperature

FatigueCracking

[DSR]


Long Term Aging

• Simulates aging of an PG asphalt binder for 7 to 10 years

• Starts with RTFO aged PG asphalt binder– Additional aging with Pressure Aging

Vessel (PAV)•50 gram (1.75 oz)


PAV Components

Bottom of pressure

aging vessel

Rack of individual pans

(50g of asphalt / pan)

Vessel Lid Components


PAV Testing

• After RTFO aging– 50 gram sample/pan aged for 20 hours

in PAV•Pressure of 2,070 kPa (300 psi)•Test temp 90, 100 or 110o C (194,

212,or 230 F)• The parameter addresses the later part of

the fatigue life


Equipment Examples


RV DSRBBR

Thermal Cracking


Low Temperature Behavior

• Low Temperature– Cold climates– Winter

• Rapid Loads– Fast moving trucks

Elastic Solid

E

Hooke’s Law


Low Temperature

• Thermal cracks– Stress generated by contraction due

to drop in temperature– Crack forms when thermal stresses

exceed ability of material to relieve stress through deformation•Material is brittle

• Depends on source of asphalt and aggregate properties


Thermal Cracking


Low Temperature

• Two rheological tests– Bending beam

•Stiffness– Direct tension

•Strength

Low TempCracking

[BBR]

[DTT][DTT]


Superpave Requirements

• BBR Stiffness Properties– Max stiffness, S, at 60 seconds of 300

MPa– Min rate of change in stiffness

•Min slope, m, of 0.300 MPa/sec• Strength

– Currently being finalized


Summary

FatigueCrackingRutting

RTFOShort Term AgingNo aging

Construction

[RV] [DSR]

Low TempCracking

[BBR]

[DTT][DTT]

PAVLong Term Aging


QUESTIONS ?

block 4 sp 14

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