Asphalt 101 Materials: HMA Part 1. Rocky Mountain Asphalt Conference and Equipment Show. February 24, PDF Free Download

Asphalt 101 Materials: HMA Part 1 Rocky Mountain Asphalt Conference and Equipment Show February 24, 2011 1

SUPERPAVE 2

SPECIFYING PERFORMANCE Based on Climate PG 58-28 Performance Grade Min pavement temperature, C Rolling average 7-day max pavement temperature, C 3

To characterize (test) a PG binder... - 8 individual tests - 6 major pieces of equipment - 3 conditioning steps - ~25 hours total time elapse 4

PG Binder Tests vs. Temperature BBR & DTT (Thermal Cracking Resistance) DSR Intermediate Temperature (Fatigue Resistance) DSR High Temperature (Rutting Resistance) Brookfield Viscosity (Workability) Cold - 20 20 60 135 Pavement Temperature, C Hot

Binder Test Sequence Binder Condition Test For Unaged Binder Flash Rot Vis DSR Safety Handling Rutting RTFO Aged PAV Aged DSR LOH DSR BBR DTT Rutting Environment / Aging Fatigue Damage Thermal Cracking Thermal Cracking

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 7

Asphalt Plant and Construction Aging Rolling Thin Film Oven (RTFO) Fan Rotating Bottle Carriage Blowing Air 8

Pressure Aging Vessel 50 grams of Asphalt in Each Pan Pressure Aging Vessel 9

Pressure Aging Vessel Courtesy of FHWA 10

Is the binder safe to be heated? Construction RV 12

Cleveland Open Cup Flash Point Tester 13

Spec Requirement Binder safe to be heated... Cleveland Open Cup (COC) Flash Point must be greater than 232 o C (450 o F). 14

Will it Flow for Mixing? Construction RV 16

Rotational Viscometer (Brookfield) Torque Motor Inner Cylinder Thermosel Environmental Chamber Digital Temperature Controller 17

Spec Requirement Make sure binder is not too thick to pump... Keep Viscosity Below 3 Pa-sec at 135 o C (275 o F) 18

Binder Test Sequence Binder Condition Test For Unaged Binder Flash Rot Vis DSR Safety Handling Rutting RTFO Aged PAV Aged DSR LOH DSR BBR DTT Rutting, Hardening Environment / Aging Fatigue Damage Thermal Cracking Thermal Cracking

Permanent Deformation ( ) Courtesy of FHWA Caused by Warm Weather, Traffic and Wrong Mixture 20

High temperature or, slow loading behavior, Rutting High Pavement Temperature Desert climates Summer temperatures Sustained loads Slow moving trucks Intersections 100 F 21

Dynamic Shear Rheometer (DSR) Rutting, Hardening, and Fatigue 22

Asphalt Glued In- Between Oscillating Upper Plate B A C Fixed Lower Plate 1 cycle 23

Asphalt Glued In- Between Oscillating Upper Plate B A C Fixed Lower Plate Time 1 cycle 23

Asphalt Glued In- Between Oscillating Upper Plate B A C Fixed Lower Plate B A A A Time 1 cycle C 23

Asphalt Glued In- Between B B A C Oscillating Upper Plate Fixed Lower Plate Now, Measure the Force Required to Rotate the Upper Plate And, Measure When Movement Occurs in the Binder A A A Time 1 cycle C 23

Elastic Time 24

Elastic B Stress A Strain A A Time Strain Occurs With Stress δ = 0 o C 24

Elastic Viscous B Stress A Strain A A Time Strain Occurs With Stress δ = 0 o C 24

Elastic Viscous B Stress B A Strain A A Time A A A C C Strain Occurs With Stress δ = 0 o 24

Elastic Viscous B Stress B A Strain A A Time A A A Strain Occurs With Stress δ = 0 o C C Strain Lags Stress δ = 90 o 24

δ 25

δ Elastic, G 25

δ Viscous, G Elastic, G 25

Complex Modulus, G* δ Viscous, G Elastic, G Complex Modulus is the vector sum of Elastic and Viscous Components 25

Spec Requirement Mitigate rutting by... G*/sin δ on Unaged binder > 1.00 kpa G*/sin δ on RTFO Aged binder > 2.20 kpa Early part of pavement life 26

Caused by repeated traffic loads in wheel paths Fatigue Cracking 28

Spec Requirement Reduce Fatique Cracking by... G*sin δ on RTFO & PAV aged binder < 5000 kpa Later part of pavement service life 29

Thermal Cracking Courtesy of FHWA Caused by Low Temperatures, Rapid Loads, Hard Binder 31

Low Temperature, or Fast Loading Behavior-aka Cracking Low Temperature Cold climates Winter Rapid Loads Fast moving trucks σ Cracking Failure ε 32

Bending Beam Rheometer Thermal Cracking RV BBR 33

Bending Beam Rheometer Computer Deflection Transducer Load Cell Fluid Bath 34

BBR Measures Stiffness at Low Temperatures using Beam Theory Creep stiffness at t = 60 secs 100 grams Clear Span of Beam, 102 mm S(t) = PL 3 4 bh 3 δ (t) Deflection at t = 60 secs Beam Width, 12.5 mm Beam Thickness, 6.25 mm 35

Bending Beam Rheometer Creep Stiffness Stiffness v. Time Slope 36

Bending Beam Rheometer Creep Stiffness Stiffness v. Time Slope Log Creep Stiffness, S(t) 8 15 30 60 120 240 Log Loading Time, t (sec) 36

Bending Beam Rheometer Creep Stiffness Stiffness v. Time Slope Log Creep Stiffness, S(t) m 8 15 30 60 120 240 Log Loading Time, t (sec) 36

Spec Requirement Protect against cracking... BBR m value > 0.300 BBR S value < 300 MPa 37

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 39

Direct Tension Test Load Stress = σ = P / A Δ L σ f Δ L e Strain ε f 40

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

Asphalt 101 Materials: HMA Part 1. Rocky Mountain Asphalt Conference and Equipment Show. February 24, 2011