Proposed Small Specimen Geometry Specifications

Specimen Fabrication, AMPT Dynamic Modulus, and AMPT Cyclic Fatigue

Cassie Castorena, Y. Richard Kim, Kangjin Lee,

and Sonja Pape North Carolina State University

Presented to the Asphalt Mixture ETG Ames, IA 5/1/2017

Outline

Introduction Experimental Plan Results Proposed Specifications

Introduction Small Specimen Geometries

Proposed to enable field core testing (Kutay et al. 2009, Park and Kim 2013, Li and Gibson 2013, and Bowers et al. 2015)

130 mm

100 mm

110 mm

38 mm

25 mm

110 mm Thin layer

Improve the efficiency of laboratory specimen fabrication

Introduction Small Specimen Geometries

Fatigue Tests

Large Specimen

|E*| Tests

Small Specimen

|E*| Tests Fatigue Tests

Introduction NCHRP IDEA Project Objectives

Evaluate the effects of specimen geometry on dynamic modulus and direct tension fatigue tests using mixtures with various NMAS values.

Optimize the laboratory fabrication of small specimens extracted from gyratory-compacted specimens.

Experimental Plan Materials

Plant-produced loose mixtures

Mixture Type NMAS (mm) Asphalt Binder RAP Content (%) RSF9.5A 9.5 PG 64-22 30 RS9.5D 9.5 PG 76-22 20

SM12.5A 12.5 PG 64-22 30 RI19.0B 19.0 PG 64-22 20

RI19.0B(2) 19.0 PG 64-22 34 RB25.0B 25.0 PG 64-22 30

Experimental Plan Test Methods

Dynamic Modulus

Cyclic Fatigue

Large Specimen Small Specimen Test Temperatures 4, 20, 40, and (54)°C Test Frequencies 25, 10, 5, 1, 0.5, and 0.1 Hz

Large Specimen Small Specimen Test Temperature 18°C

Test Frequency 10 Hz Epoxy Curing Time 16 hours 1 hour

Experimental Efforts Specimen Fabrication

178 mm

150 mm

100 mm

150 mm

110 mm

38 mm

178 mm

150 mm

110 mm

38 mm

140 mm

150 mm

Results Specimen Geometry Effects

1.0E+02

1.0E+03

1.0E+04

1.0E+05

1.0E-08 1.0E-05 1.0E-02 1.0E+01

|E*|

(MPa

)

Reduced Frequency (Hz)

RSF9.5A

1.0E+02

1.0E+03

1.0E+04

1.0E+05

1.0E-08 1.0E-05 1.0E-02 1.0E+01|E

*| (M

Pa)

Reduced Frequency (Hz)

RI19.0B

Solid: large specimenLine: small cylindrical specimenEmpty: small prismatic specimen

Blue: 4°C test temperatureGreen: 20°C test temperature

Yellow: 40°C test temperatureRed: 54°C test temperature

Results Specimen Geometry Effects - RSF9.5A

0.0

0.2

0.4

0.6

0.8

1.0

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

Pseu

do S

tiffn

ess

(C)

Damage Parameter (S)

RSF9.5A-Large-1RSF9.5A-Large-2RSF9.5A-Large-3RSF9.5A-Small-1RSF9.5A-Small-2RSF9.5A-Prism-1RSF9.5A-Prism-2

y = 0.4898xR² = 0.9998

0.0E+00

2.0E+04

4.0E+04

6.0E+04

8.0E+04

1.0E+05

0 50,000 100,000 150,000 200,000

Sum

(1-C

)

Nf

RSF9.5A-LargeRSF9.5A-SmallRSF9.5A-Prism

Damage Characteristic Curves Failure Criterion

0.0

0.2

0.4

0.6

0.8

1.0

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

Pseu

do S

tiffn

ess

(C)

Damage Parameter (S)

RI19.0B-Large-1RI19.0B-Large-2RI19.0B-Large-3RI19.0B-Small-1RI19.0B-Small-2

Results Specimen Geometry Effects - RI19.0B

Damage Characteristic Curves Failure Criterion

y = 0.4424xR² = 0.9992

0.0E+00

5.0E+03

1.0E+04

1.5E+04

2.0E+04

2.5E+04

0 20,000 40,000 60,000

Sum

(1-C

)

Nf

RI19.0B-Large

RI19.0B-Small

Results FlexPAVE Pavement Performance Prediction

Results Effect of Coring Direction - RI19.0B

0.00.10.20.30.40.50.60.70.80.91.0

0.0E+0 5.0E+5 1.0E+6 1.5E+6

Pseu

do S

tiffn

ess

(C)

Damage Parameter (S)

Vertical-1Vertical-2Horizontal-4core-1Horizontal-4core-2Horizontal-4core-3Horizontal-2core-1Horizontal-2core-2

1E+2

1E+3

1E+4

1E+5

1E-6 1E-3 1E+0

|E*|

(MPa

)

Reduced Frequency (Hz)

100mm-1100mm-2100mm-338mm-Vertical-138mm-Vertical-238mm-Vertical-338mm-Horizontal-138mm-Horizontal-238mm-Horizontal-3

Results Effect of Coring Direction

All of the horizontally-extracted specimens subjected to fatigue testing experienced end failure • Vertical coring preferred!

Middle Failure

End Failure

Results Air Void Variability

Charging the center of the gyratory compaction mold reduces air void variability

Produced three gyratory-compacted samples for each mixture evaluated • Extracted four small specimens from inner 100-mm diameter • All of the specimens were tested regardless of air void content

All air void contents within the range of ± 0.7% of the average

0%

5%

10%

15%

20%

25%

30%

35%

40%

PP 60 Center Pour

Perc

enta

ge o

f Spe

cim

ens

Out

side

of ±

0.5%

* Based on ~50 specimens for each

method

Results Statistics on the Middle Failure using Vertical Coring

Fabricated two gyratory specimens for each mixture Extracted four cores from a gyratory specimen Tested all eight specimens for each mixture

Mixture End failures/ Number of Tests

RS9.5D 0/8

SM12.5A 1/8

RI19.0B 2/8

RB25.0B 0/8

Middle Failure

End Failure

Results Specimen-to-Specimen Variability – RS9.5D

0.0

0.2

0.4

0.6

0.8

1.0

0E+0 2E+5 4E+5 6E+5

Pseu

do S

tiffn

ess

(C)

Damage Parameter (S)

2BL - 3.9% 2BR - 3.9%2FL - 4.0% 2FR - 3.5%3BL - 4.1% 3BR - 3.7%3FL - 3.5% 3FR - 3.6%

1E+2

1E+3

1E+4

1E+5

1E-4 1E-2 1E+0 1E+2 1E+4

|E*|

(MPa

)

Reduced Frequency (Hz)

1BL - 3.9%1FL - 3.7%1FR - 3.5%

05

10152025303540

1E-4 1E-2 1E+0 1E+2 1E+4

Phas

e An

gle

(°)

Reduced Frequency (Hz)

1BL - 3.9%1FL - 3.7%1FR - 3.5%

y = 0.6253xR² = 0.9986

0E+0

2E+3

4E+3

6E+3

8E+3

1E+4

1E+4

1E+4

0E+0 5E+3 1E+4 2E+4 2E+4

Sum

(1-C

)

Cycles to Failure (Nf)

2BL - 3.9%2BR - 3.9%2FL - 4.0%2FR - 3.5%3BL - 4.1%3BR - 3.7%3FL - 3.5%3FR - 3.6%

Results Specimen-to-Specimen Variability – RB25.0B

1E+2

1E+3

1E+4

1E+5

1E-4 1E-2 1E+0 1E+2 1E+4

|E*|

(MPa

)

Reduced Frequncy (Hz)

3BL - 5.2%3BR - 4.1%3FR - 5.0%

05

10152025303540

1E-4 1E-2 1E+0 1E+2 1E+4

Phas

e An

gle

( °)

Reduced Frequncy (Hz)

3BL - 5.2%3BR - 4.1%3FR - 5.0%

0.0

0.2

0.4

0.6

0.8

1.0

0E+0 1E+5 2E+5 3E+5

Pseu

do S

tiffn

ess

(C)

Damage Parameter (S)

1BL - 4.0%1BR - 4.0%1FL - 4.4%1FR - 5.3%2BL - 4.8%2BR - 4.8%2FL - 4.9% - void

y = 0.4678xR² = 0.9675

0E+01E+32E+33E+34E+35E+36E+37E+38E+3

0E+0 5E+3 1E+4 2E+4 2E+4

Sum

(1-C

)

Cycles to Failure (Nf)

1BL - 4.0%1BR - 4.0%1FL - 4.4%1FR - 5.3%2BL - 4.8%2BR - 4.8%2FL - 4.9%

Results Summary

Small specimen testing provides equivalent dynamic modulus test results to large specimen testing at low and intermediate temperatures. • Do not recommend testing at 54°C

Small specimen testing provides equivalent cyclic fatigue test results to large specimen testing

Anisotropy in gyratory-compacted samples does not affect dynamic modulus or cyclic fatigue test results.

Horizontal coring in laboratory specimen fabrication should be avoided because it leads to end failure in cyclic fatigue tests.

The recommended procedure for laboratory fabrication of small specimens is the vertical coring of four specimens from the inner 100-mm diameter of gyratory-compacted samples.

Proposed Specifications Overview

Three specifications • Fabrication

Follows AASHTO PP60 Covers laboratory specimen fabrication and

extraction of small specimens from field cores

• AMPT Dynamic Modulus Testing Follows AASHTO TP79

• AMPT Cyclic Fatigue Testing Follows AASHTO TP107

Proposed Specifications Key Differences from Large Specimen Specs &

Questions Fabrication

• Prepare 180-mm tall SGC sample Charge the center of the mold in two lifts,

rod each lift Question: Does anyone have suggestions for

facilitating charging the center of the mold? • Extract four specimens from inner 100-mm

diameter of SGC sample • Extract two specimens per lift from 6-in field core

Proposed Specifications Key Differences from Large Specimen Specs &

Questions AMPT Dynamic Modulus

• Select test temperatures using AASHTO PP61 3 temperatures

• Apply 50 to 75 peak-to-peak on-specimen microstrain

AMPT Cyclic Fatigue • 5 min epoxy • Use adapters to attach specimen to AMPT • Apply reduced seating load of 10 N • Question: For fatigue testing, would it be better to

require the testing of three or four specimens? Both

• Increase air void tolerance to ± 0.7%, to be refined upon Ruggedness Testing

• Question: Agree or adopt ± 0.5% from large specimen testing?

Thank you!

Questions?