NCHRP Project 9-54Long-Term Aging of Asphalt

Mixtures for Performance Testing and Prediction

Asphalt Mixture & Construction Expert Task GroupFall River, MA

5/8/2018

Y. Richard Kim, Cassie Castorena, Michael Elwardany, and Farhad Yousefi Rad

North Carolina State University

Outline

NCHRP 09-54 Objectives Proposed Long-Term Aging Procedure Current Efforts

2

NCHRP 09-54 Objectives

Develop a calibrated and validated procedure to simulate long-term aging of asphalt mixtures for performance testing and prediction

Develop a pavement aging model as a function of climate, age, and pavement depth

3

Development of the Proposed Long-Term Aging Procedure

Selection of the aging method• Compacted specimen vs. loose mixture• Oven vs. pressure aging vessel

Selection of the aging temperature• 95ºC vs. 135ºC

Determination of required aging duration• Climate, depth, age

4

Criteria for Selecting the Aging Method

Specimen integrity• Compacted specimen

(38-mm and 100-mm) • Geometric and air void

changes • Oxidation gradient • Performance

• Loose mix• Compactability• Performance

Efficiency Practicality and versatility

5

Aging Gradient in Compacted Specimen

3.0

3.5

4.0

4.5

5.0

5.5

log

G* a

t 64°

C, 1

0 H

z (P

a)

NC 9.5-mm mixture (PG 64-22, no RAP)

4.63 4.71 4.82

Core Mid-Layer Outer-Layer

Oven, Large Spec., 85°C, 8 days

28%20%

Oven, Small Spec., 85°C, 8 days ≈

Oven, Loose Mix, 85°C, 5.25 days6

Compaction of Aged Loose Mixture 60

52 57

0

10

20

30

40

50

60

70

80

90

Num

ber o

f com

pact

ion

gyra

tions

to

ach

ieve

4%

targ

et a

ir vo

ids

Short-term AgedOven, Loose Mix, 85°C, 8 daysOven, Loose Mix, 95°C, 21 days

1E+02

1E+03

1E+04

1E+05

1E-09 1E-05 1E-01 1E+03

|E*|

(MPa

)

Reduced Frequency (Hz)

Short-term AgedOven, Loose Mix, 85°C, 8 daysOven, Loose Mix, 95°C, 21 days

0.0

0.2

0.4

0.6

0.8

1.0

0.0E+00 5.0E+05 1.0E+06 1.5E+06 2.0E+06

C

S

***

Loose mixture oven aging selected!

FHWA ALF SBS (PG 70-28, no RAP)7

Selection of Laboratory Aging Temperature

Increasing temperature expedites oxidation Aging above 100ºC has raised several

concerns• Thermal decomposition of sulfoxides• Disruption of binder microstructure• Binder/Mastic drain-down

Performance implications of aging above 100ºC unknown

8

Experimental Approach

Three mixtures considered: FHWA ALF SBS, SHRP AAD, and SHRP AAG

9

1E+01

1E+02

1E+03

1E+04

0 200 400 600

G* (

kPa)

Aging Duration (Hours)

Loose Mix Aged at 95°CLoose Mix Aged at 135°C

Chemistry vs. RheologyFHWA ALF-SBS

log G* = 41.384 (C+S) + 1.5819

log G* = 25.8756 (C+S) + 2.5129

3.5

4

4.5

5

5.5

6

6.5

7

7.5

8

8.5

0.07 0.08 0.09 0.1 0.11 0.12

log

G* (

Pa)

Carbonyl + Sulfoxide Absorbance Peak (AU)

Short-term AgedOven, Loose Mix, 70°COven, Loose Mix, 85°COven, Loose Mix, 95°COven, Loose Mix, 135°CField Core, 8 Years Old

10

Performance Test Results

SHRP AAD-1

Short-term AgedOven, Loose Mix, 135°C, 16.8 hoursOven, Loose Mix, 95°C, 8.9 days

1E+2

1E+3

1E+4

1E+5

1E-8 1E-6 1E-4 1E-2 1E+0 1E+2

|E*|

(MPa

)

Reduced Frequency (Hz)

0.0

0.2

0.4

0.6

0.8

1.0

0.0E+0 4.0E+5 8.0E+5 1.2E+6

C

S0E+00

1E+04

2E+04

3E+04

4E+04

5E+04

0E+00 5E+04 1E+05 2E+05

Cum

ulat

ive

(1-C

)

Nf (Cycle)

(c)

Loose mixture oven aging at 95ºC selected!

11

Determination of the Aging Duration

12

Field Sections

13

log 𝐺𝐺∗ = log𝐺𝐺0∗ + 𝑀𝑀(1 −𝑘𝑘𝑐𝑐𝑘𝑘𝑓𝑓

) 1 − exp −𝑘𝑘𝑓𝑓𝑡𝑡 + 𝑘𝑘𝑐𝑐𝑀𝑀𝑡𝑡

𝑘𝑘𝑓𝑓 = 𝐴𝐴𝑓𝑓 exp �−𝐸𝐸𝑎𝑎𝑓𝑓𝑅𝑅𝑅𝑅 ,

𝑤𝑤ℎ𝑒𝑒𝑒𝑒𝑒𝑒

𝐺𝐺∗= shear dynamic modulus at age t,

𝐺𝐺0∗ = shear dynamic modulus at short-term aged condition,

NCHRP 9-54 Kinetics Model

𝑀𝑀 = binder aging rate,

𝑘𝑘𝑐𝑐 = 𝐴𝐴𝑐𝑐 exp �−𝐸𝐸𝑎𝑎𝑐𝑐𝑅𝑅𝑅𝑅 , and

𝑅𝑅 = temperature in Kelvin.14

Required Duration to Match Field Aging

Field (EICM) Lab Oven Aging

95°C

AgingDuration?

log 𝐺𝐺𝐹𝐹𝐹𝐹𝑒𝑒𝐹𝐹𝐹𝐹∗ = log 𝐺𝐺𝑜𝑜∗ + 𝑀𝑀[(1 − �𝑘𝑘𝑐𝑐 𝑘𝑘𝑓𝑓) 1 − exp −𝑘𝑘𝑓𝑓𝑡𝑡 + 𝑘𝑘𝑐𝑐𝑡𝑡]𝐹𝐹𝐹𝐹𝐹𝐹𝐹𝐹𝐹𝐹

log 𝐺𝐺𝐿𝐿𝐿𝐿𝐿𝐿∗ = log 𝐺𝐺𝑜𝑜∗ + 𝑀𝑀[(1 − �𝑘𝑘𝑐𝑐 𝑘𝑘𝑓𝑓) 1 − exp −𝑘𝑘𝑓𝑓𝑡𝑡 + 𝑘𝑘𝑐𝑐𝑡𝑡]𝐿𝐿𝑎𝑎𝐿𝐿

[(1 − �𝑘𝑘𝑐𝑐 𝑘𝑘𝑓𝑓) 1 − exp −𝑘𝑘𝑓𝑓𝑡𝑡 + 𝑘𝑘𝑐𝑐𝑡𝑡]𝐹𝐹𝐹𝐹𝐹𝐹𝐹𝐹𝐹𝐹 = [(1 − �𝑘𝑘𝑐𝑐 𝑘𝑘𝑓𝑓) 1 − exp −𝑘𝑘𝑓𝑓𝑡𝑡 + 𝑘𝑘𝑐𝑐𝑡𝑡]𝐿𝐿𝑎𝑎𝐿𝐿

Required aging duration to match field aging is

independent of binder source/type (i.e., STA G* and

M value)

15

CAI = ∑𝐹𝐹=124 (𝐷𝐷 × 𝐴𝐴 × exp �−𝐸𝐸𝑎𝑎𝑅𝑅𝑇𝑇𝑖𝑖 /24) = 𝑡𝑡𝑜𝑜𝑜𝑜𝐹𝐹𝑜𝑜

whereD = depth correction factor,𝐴𝐴, 𝐸𝐸𝑎𝑎= fitting parameters,R = universal gas constant, T = pavement temperature (Kelvin), andd = depth of interest (mm).

𝐷𝐷 = �3.4311 𝐹𝐹−0.683 for 6 𝑚𝑚𝑚𝑚 ≤ 𝐹𝐹 ≤ 35 𝑚𝑚𝑚𝑚0.3026 for 𝐹𝐹 > 35 𝑚𝑚𝑚𝑚

Climatic Aging Index (CAI)

16

y = 1xR² = 0.7142

0

5

10

15

20

25

30

0 5 10 15 20 25 30

Mea

sure

d D

urat

ion

at

95°C

(Day

s)

Climatic Aging Index, CAI

Surface Layer(6 mm)

20-mm depth

Deeper Layers(below 20 mm)

Climatic Aging Index (CAI)

17

Aging Duration Maps for 6 mm Depth4 Years

8 Years

16 Years

18

Aging Duration Maps for 20 mm Depth4 Years

8 Years

16 Years

19

Aging Duration Maps for 50 mm Depth4 Years

8 Years

16 Years

20

Validation of the Developed Aging Procedure

y = 0.9863x + 0.0461R² = 0.7674

0

0.5

1

1.5

2

2.5

3

0 0.5 1 1.5 2 2.5 3

Fiel

d M

easu

red

log

G*

from

Fie

ld C

ores

Estimated log G* of Laboraoty aged Loose Mixture

LTPP-WA LTPP-CALTPP-OH MnROADNCAT-Control MIT-Control

21

log G* of Laboratory Aged Loose Mixture

Proposed AASHTO Standard

22

Summary

Oven aging of loose mixture at 95ºC recommended

A climatic aging index (CAI) developed by simplifying the kinetics model prescribes the laboratory aging duration to match field aging as a function of hourly pavement temperature history and depth

Draft AASHTO standard developed for long-term aging of asphalt mixtures for performance testing

23

Current Efforts

Refinement of the aging duration maps Finalization of pavement aging model Investigation of effects of binder aging on

asphalt mixture cracking performance

24

Questions?

25