SUPERPAVE

FHWA Condensed Superpave Asphalt Specifications Lecture Series

Aggregates

Usually refers to a soil that has in some way been processed or sorted.

100 100 90 72 65 48 36 22 15 9 4

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 99 89 72 65 48 36 22 15 9 4

Percent Passing 100 max density line

restricted zone control point

nom max size max size 0 .075

.3

2.36

4.75

9.5

12.5 19.0

Sieve Size (mm) Raised to 0.45 Power

Superpave Aggregate Gradation

Percent Passing 100

Design Aggregate Structure

0 .075 .3

2.36

12.5 19.0

Sieve Size (mm) Raised to 0.45 Power

Superpave Mix Size Designations

Superpave Designation Nom Max Size (mm) Max Size (mm) 37.5 mm 25 mm 19 mm 12.5 mm 9.5 mm 37.5

25 19 12.5

9.5

50 37.5

25 19 12.5

Gradations

* Considerations: - Max. size < 1/2 AC lift thickness - Larger max size + Increases strength + Improves skid resistance + Increases volume and surface area of agg which decreases required AC content + Improves rut resistance + Increases problem with segregation of particles - Smaller max size + Reduces segregation + Reduces road noise + Decreases tire wear

Percent Crushed Fragments in Gravels

• Quarried materials always 100% crushed • Minimum values depended upon traffic level and layer (lift) • Defined as % mass with one or more fractured faces

Percent Crushed Fragments in

0% Crushed

Gravels

100% with 2 or More Crushed Faces

Coarse Aggregate Angularity Criteria

Traffic Depth from Surface Millions of ESALs < 100 mm > 100 mm < 0.3

< 1 < 3 < 10 < 30 55/- 65/- 75/- 85/80 95/90 --/- --/- 50/- 60/- 80/75 < 100



100 100/100 100/100 95/90 100/100 First number denotes % with one or more fractured faces Second number denotes % with two or more fractured faces

Asphalt Cements

Background History of Specifications

Background

• Asphalt – Soluble in petroleum products – Generally a by-product of petroleum distillation process – Can be naturally occurring • Tar – Resistant to petroleum products – Generally by-product of coke (from coal) production

Penetration Testing

• Sewing machine needle • Specified load, time, temperature

Penetration in 0.1 mm 100 g Initial After 5 seconds

Penetration Specification • Five Grades

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

Ductility

Typical Penetration Specifications

Penetration Flash Point, C Ductility, cm Solubility, % 40 - 50 450+ 100+ 99.0+ 200 - 300 350+ 100+ 99.0+ Retained Pen., % 55+ Ductility, cm NA 37+ 100+

Viscosity Graded Specifications

Types of Viscosity Tubes

Asphalt Institute Tube Zietfuchs Cross-Arm Tube

Visc, 60C Visc, 135C Penetration Visc, 60C Ductility

Table 1 Example

AC 2.5

AC 40 250 + 50 4,000 + 800 80+ 200+ <1,250 300+ 20+ <20,000 100+ 10+

100 50 10 5 Penetration Grades 40 50 60 70 85 100 120 150 200 300 AC 40 AC 20 AC 10 AC 5 AC 2.5

Asphalt Cements

New Superpave Performance Graded Specification

PG Specifications

• Fundamental properties related to pavement performance • Environmental factors • In-service & construction temperatures • Short and long term aging

High Temperature Behavior

• High in-service temperature – Desert climates – Summer temperatures • Sustained loads – Slow moving trucks – Intersections

Viscous Liquid

Pavement Behavior (Warm Temperatures)

• Permanent deformation (rutting) • Mixture is plastic • Depends on asphalt source, additives, and aggregate properties

Permanent Deformation

Courtesy of FHWA Function of warm weather and traffic

Low Temperature Behavior

• Low Temperature – Cold climates – Winter • Rapid Loads – Fast moving trucks

Elastic Solid

Hooke’s Law s = t E

Pavement Behavior (Low Temperatures)

• 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

Courtesy of FHWA

Superpave Asphalt Binder Specification The grading system is based on Climate

PG 64 - 22

Performance Grade Min pavement temperature Average 7-day max pavement temperature

Pavement Temperatures are Calculated • Calculated by Superpave software • High temperature – 20 mm below the surface of mixture • Low temperature – at surface of mixture Pave temp = f (air temp, depth, latitude)

Concentric Cylinder Rheometers



Concentric Cylinder

t

R

q =

M i

2 p

R i 2 L

W

R

g =

R o - R i

Dynamic Shear Rheometer (DSR) • Parallel Plate Shear flow varies with gap height and radius Non-homogeneous flow

2 M

t

R =

g

R =

p

R 3 R

Q

h

Short Term Binder Aging

•

Rolling Thin Film Oven

–

Simulates aging from hot mixing and construction

Pressure Aging Vessel (Long Term Aging)

• • • •

Simulates aging of an asphalt binder for 7 to 10 years 50 gram sample is aged for 20 hours Pressure of 2,070 kPa (300 psi) At 90, 100 or 110 C

Bending Beam Rheometer

Computer Deflection Transducer Air Bearing Load Cell Fluid Bath

D L e

Direct Tension Test

Load Stress = s = P / A D L s f Strain e f

Summary

Construction Rutting

[RV] [DSR]

Fatigue Cracking Low Temp Cracking

[DTT] [BBR]

No aging RTFO Short Term Aging PAV Long Term Aging

Superpave Binder Purchase Specification

Superpave Asphalt Binder Specification

The grading system is based on Climate PG 64 - 22 Performance Grade Min pavement temperature Average 7-day max pavement temperature

Performance Grades

CEC

Avg 7-day Max, o C 1-day Min, o C > 230 o C < 3 Pa .

s @ 135 o C PG 46 PG 52 PG 58 PG 64 PG 70 PG 76 PG 82 -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 ORIGINAL (Flash Point) FP (Rotational Viscosity) RV (Dynamic Shear Rheometer) DSR G*/sin



> 1.00 kPa 46 52 58 64 70 76 82 > 2.20 kPa 20 Hours, 2.07 MPa < 5000 kPa 46 90 (ROLLING THIN FILM OVEN) RTFO Mass Loss < 1.00 % 52 58 64 (PRESSURE AGING VESSEL) PAV 90 (Dynamic Shear Rheometer) DSR G*/sin



100 100 100 (110) 70 100 (110) (Dynamic Shear Rheometer) DSR G* sin



76 110 (110) 82 S < 300 MPa m > 0.300

Report Value > 1.00 % ( 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 (Bending Beam Rheometer) BBR Physical Hardening (Direct Tension) DT -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

How the PG Spec Works

CEC

Avg 7-day Max, o C PG 52 PG 58 PG 64 PG 70 PG 76 PG 82 1-day Min, o C -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 Remains Constant ORIGINAL > 230 o C < 3 Pa .

s @ 135 o C (Flash Point) FP (Rotational Viscosity) RV > 1.00 kPa 46 52 (Dynamic Shear Rheometer) DSR G*/sin



64 64 70 76 82 (ROLLING THIN FILM OVEN) RTFO Mass Loss < 1.00 % (Dynamic Shear Rheometer) DSR G*/sin



> 2.20 kPa 46 70 52 58 64 (PRESSURE AGING VESSEL) PAV 20 Hours, 2.07 MPa 90 90 100 100 Test Temperature (Dynamic Shear Rheometer) < 5000 kPa Changes 100 (110) DSR G* sin



S < 300 MPa m > 0.300

100 (110) 110 (110) ( Bending Beam Rheometer) BBR “S” Stiffness & “m” - value 76 Report Value > 1.00 % 82 -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 (Bending Beam Rheometer) BBR Physical Hardening (Direct Tension) DT -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

PG 52-28

PG Binder Selection

> Many agencies have established zones PG 58-22 PG 58-16 PG 64-10

Summary of How to Use PG Specification • Determine – 7-day max pavement temperatures – 1-day minimum pavement temperature • Use specification tables to select test temperatures • Determine asphalt cement properties and compare to specification limits

Asphalt Concrete Mix Design

History

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

MARSHALL MIX DESIGN

Marshall Mix Design

• Developed by Bruce Marshall for the Mississippi Highway Department in the late 30’s • WES began to study it in 1943 for WWII – Evaluated compaction effort • No. of blows, foot design, etc.

• Decided on 10 lb.. Hammer, 50 blows/side • 4% voids after traffic • Initial criteria were established and upgraded for increased tire pressures and loads

Marshall Mix Design

• Select and test aggregate • Select and test asphalt cement – Establish mixing and compaction temperatures • Develop trial blends – Heat and mix asphalt cement and aggregates – Compact specimen (100 mm diameter)

Marshall Design Criteria

Light Traffic ESAL < 10 4 Medium Traffic Heavy Traffic 10 4 < ESAL< 10 ESAL > 10 6 Compaction Stability N (lb.) Flow, 0.25 mm (0.1 in) Air Voids, % Voids in Mineral Agg.

(VMA) 35 3336 (750) 8 to 18 3 to 5 50 5338 (1200) 8 to 16 3 to 5 Varies with aggregate size 75 8006 (1800) 8 to 14 3 to 5

Asphalt Concrete Mix Design

Superpave

Superpave Volumetric Mix Design

• Goals – Compaction method which simulates field – Accommodates large size aggregates – Measure of compactibility – Able to use in field labs – Address durability issues • Film thickness • Environmental

Compaction

Key Components of Gyratory Compactor

height measurement reaction frame control and data acquisition panel loading ram mold tilt bar rotating base

Compaction

• Gyratory compactor – Axial and shearing action – 150 mm diameter molds • Aggregate size up to 37.5 mm • Height measurement during compaction – Allows densification during compaction to be evaluated

Ram pressure 600 kPa 1.25

o

Three Points on SGC Curve

% G mm N des N max N ini 10 100 Log Gyrations 1000

SGC Critical Point Comparison

%G mm = G mb / G mm G mb = Bulk Mix Specific Gravity from compaction at N cycles G mm = Max. Theoretical Specific Gravity Compare to allowable values at: N INI : %G mm < 89% N DES : %G mm < 96% N MAX : %G mm < 98%

Design Compaction

• N des based on – average design high air temp – traffic level • Log N max • Log N ini = 1.10 Log N des = 0.45 Log N des

% G mm N ini N des 10 100 N max 1000 Log Gyrations

Superpave Testing

• Specimen heights • Mixture volumetrics – – Air voids Voids in mineral aggregate (VMA) – Voids filled with asphalt (VFA) – Mixture density characteristics • Dust proportion • Moisture sensitivity

Superpave Mix Design • Determine mix properties at N Design criteria and compare to – Air voids – VMA – VFA – %G mm at N ini – %G mm at N max – Dust proportion 4% (or 96% G mm ) See table See table 0.6 to 1.2

< 89% < 98%

Superpave Mix Design Gyratory Compaction Criteria