Fatigue assessment of conventional and highly modified asphalt materials with ASTM … · 2014. 2....

Fatigue assessment of conventional and highly modified asphalt materials with ASTM and AASHTO standard specifications

Geoffrey Rowe – Abatech Inc. Phillip Blankenship – Asphalt Institute Tom Bennert – Rutgers University 3rd 4PBB Conference 17-18 September 2012 Davis, California

Objectives

To improve repeatability of fatigue test within laboratories and reproducibility between laboratories Need identified due to large reported

differences between different organizations

Need due to many states now using bending beam as part of specified requirements for materials

2

Analysis

Determination of fatigue life in test is different for AASHTO and ASTM versions AASHTO based on 50% stiffness and

curve fitting – S=AebN

ASTM based on approximation of an energy ratio

Both methods developed as part of SHRP A003a project in early 1990’s

3

Typical AASHTO format as today

4

Stiffness vs. repetitions

Original data collected during SHRP program was on a semi-log basis

What is effect of data collected on this basis versus other basis

5

Smix x Cycles

6

Definition is simple – just the maximum value of stiffness x cycles

Smix x Cycles - why

100

10

1

Stiff

ness

%

10 1000000 100000 10000 1000 100

Number of Load Cycles

Typical Fatigue Data (SHRP A003A)


Data normally plotted on log-log scale

Test normally discontinued at 50% stiffness reduction

Exponential equation fitted

e A = Stiffness bN

Number of Load Cycles (×1000)


100

80

20

60

40

0 0 400 300 500 100 200 600

Method 1

Method 2

Method 1 considers only data to 50% stiffness reduction. Method 2 considers all data obtained.

Stiffness reduction

Both methods confirm that exponential equation is not a good description of the stiffness reduction in the test method

Large errors can be introduce in the definition of number of load cycles to failure

Stiffness reduction

Controlled Strain Test

Controlled Stress Test

Definition of Failure

Energy ratio concept Stiffness x Number of Load Cycles Applicability to controlled strain and

stress data

Example of change in δ

Typical relationship

Typically the change in phase lag is related to the stiffness of the material for materials tested in fatigue

Change in phase or sinδ is significantly smaller than change in stiffness Stiffness, MPa

Phas

e an

gle,

deg

rees

Simplified Approach

) () ( n = RatioEnergy

iii

ooo

δεσπδεσπ

sinsin

Sn R =ε

Controlled strain

Sn R =σControlled stress

E*.n/E*0 versus Stiffness Reduction

0

1,000

2,000

3,000

4,000

5,000

0 10,000 20,000 30,000 Cycles

0.00

0.50

1.00

1.50

E* n

.n/E

* o

En*

/E* o

corr

0

1000

2000

3000

4000

5000

6000

7000

0 10000 20000 30000 40000 50000 LOAD CYCLES

CO

MPL

EX M

OD

ULU

S (

MPa

)

Controlled Stress Fatigue Test Stiffness Modulus vs. Load Cycles

0 10000 20000 30000 40000 50000 LOAD CYCLES

0

0.2x108

0.4x108

0.6x108

0.8x108

1.0x108

1.2x108

1.4x108

Controlled Stress Fatigue Test nS vs Load Cycles

Typical data - log basis

Specimen 6b

0.0E+00

2.0E+05

4.0E+05

6.0E+05

8.0E+05

1.0E+06

1.2E+06

1.4E+06

0 5000 10000 15000 20000

Number of Load Cycles

E* (

psi)

0.0E+00

1.0E+09

2.0E+09

3.0E+09

4.0E+09

5.0E+09

6.0E+09

7.0E+09

n.E*

(ps

i)

E* n.E*

Collection of data - how should we collect fatigue data?

Test results demonstrate need to collect data on linear basis

Recommend a minimum of 10 points per decade - or - better capture data on stiffness reduction basis

Concept of ASTM failure

The peak in the stiffness x cycles curve coincides with other key parameters

Indicative of localization of cracking

22

Typical analysis

AASHTO standard AASHTO relaxed

+50 % stiffness drop ASTM

Max 6-order poly

AASHTO – data on log basis Comparisons

23

Data from test equipment

24

IPC Global Universal Testing Machine

UTM_21 V1.06 Beam Fatigue Test

Filename C:\Documents and Settings\Tom Bennert\My Documents\Proposals\NJDOT - BDWC Design and Verifications\Stone Industries\Stone Ind BDWC #1 2000ms.B21

Operator TBNotes/Comments Stone Ind BDWC #1

2000ms

Specimen Information

********************

IdentificatioStone Ind BDWC #1

Core/Samp 2000ms

DimensionPoint 1 Point 2 Point 3 Point 4 Point 5 Average Std Dev.

Width (mm 65.0665.1

Height (mm 51.3451.3

Length(mm 380380

Cross-Sect 24722.8

Volume 1269269

Comments/Properties

Setup Parameters

****************

Inside clam 118.5

Outside cla 355.5

Default Poi 0.3

Control MoSinusiodal strain

Pulse width 100

Peak to pe 2000

Conditionin 50

Termination 500

Stop test a 50000000

Calibration Information

***********************

Channel deFilename Transducer Span Units Date Linearised

A: Axial Fo474734-03 Loadcell RL 9 kN 23/07/03 No

B: Actuato 57285.CARLVDT D5-2 10 mm 27/07/03 No

C: On Spec 55376.CARLVDT GTX- 1 mm 20/06/03 No

D: Core Te430.CAR PT100 S/N 100 Deg.C 16/06/03 Yes

E: Skin Te 431.CAR PT100 S/N 100 Deg.C 16/06/03 Yes

Test Results

************

Test start d Wednesda Septembe 2008 at 12:28 PM

Cycle coun548690 of 50000000

Loading tim 15:14:29

Applied loa 0.486

Maximum l 0.27

Minimum lo -0.215

Beam Defle 1.056

Maximum L 0.239

Minimum L -0.289

Maximum 1007

Maximum t 2014

Initial flexur 1614

Flexural st 500

Termination 500

Modulus of 532

Phase ang 42.5

Initial dissip 3.624

Dissipated 1.255

Cumulative 818.626

Initial core 15.6

Initial skin 16

Core tempe 15.4

Skin tempe 15.4

Cycles Stress Micro Stiffness Modulus Phase angEnergy Cumulative Core temp Skin temp Applied loaMax load Min Load Beam defleMax LVDT Min LVDT 284456869

(kPa) Strain (MPa) (MPa) (Deg) (kPa) (MPa) (deg.C) (deg.C) (kN) (kN) (kN) (mm) (mm) (mm)

10 3.29E+03 1.60E+03 2.06E+03 2.19E+03 3.67E+01 2.58E+00 -1.29E-02 1.56E+01 1.60E+01 1.59E+00 8.24E-01 -7.65E-01 8.38E-01 2.49E-01 -1.70E-01

20 3.28E+03 1.75E+03 1.88E+03 2.00E+03 3.72E+01 2.97E+00 2.97E-02 1.56E+01 1.60E+01 1.58E+00 8.53E-01 -7.27E-01 9.15E-01 2.41E-01 -2.17E-01 3.75E+04

30 3.28E+03 1.87E+03 1.75E+03 1.87E+03 3.71E+01 3.25E+00 5.51E-02 1.56E+01 1.60E+01 1.58E+00 8.66E-01 -7.16E-01 9.81E-01 2.41E-01 -2.50E-01 52607.032

40 3.27E+03 1.95E+03 1.68E+03 1.79E+03 3.73E+01 3.47E+00 8.33E-02 1.56E+01 1.60E+01 1.58E+00 8.62E-01 -7.14E-01 1.02E+00 2.41E-01 -2.69E-01 67174.1857
































360 2.49E+03 2.01E+03 1.24E+03 1.32E+03 4.08E+01 2.98E+00 1.02E+00 1.57E+01 1.60E+01 1.20E+00 6.55E-01 -5.45E-01 1.05E+00 2.39E-01 -2.88E-01 445861.676












Typical file has thousands of lines of data

Cycles Stress Micro Stiffness Modulus Phase angle Energy Cumulative energy Core temp Skin temp Applied load Max load Min Load Beam deflection Max LVDT Min LVDT

(kPa) Strain (MPa) (MPa) (Deg) (kPa) (MPa) (deg.C) (deg.C) (kN) (kN) (kN) (mm) (mm) (mm)

10 3.29E+03 1.60E+03 2.06E+03 2.19E+03 3.67E+01 2.58E+00 -1.29E-02 1.56E+01 1.60E+01 1.59E+00 8.24E-01 -7.65E-01 8.38E-01 2.49E-01 -1.70E-01

20 3.28E+03 1.75E+03 1.88E+03 2.00E+03 3.72E+01 2.97E+00 2.97E-02 1.56E+01 1.60E+01 1.58E+00 8.53E-01 -7.27E-01 9.15E-01 2.41E-01 -2.17E-01

30 3.28E+03 1.87E+03 1.75E+03 1.87E+03 3.71E+01 3.25E+00 5.51E-02 1.56E+01 1.60E+01 1.58E+00 8.66E-01 -7.16E-01 9.81E-01 2.41E-01 -2.50E-01

40 3.27E+03 1.95E+03 1.68E+03 1.79E+03 3.73E+01 3.47E+00 8.33E-02 1.56E+01 1.60E+01 1.58E+00 8.62E-01 -7.14E-01 1.02E+00 2.41E-01 -2.69E-01

50 3.25E+03 2.02E+03 1.61E+03 1.72E+03 3.69E+01 3.62E+00 1.14E-01 1.56E+01 1.60E+01 1.57E+00 8.62E-01 -7.08E-01 1.06E+00 2.40E-01 -2.89E-01

AASHTO standard

25

AASHTO - strict Stiffness,measured, N=50 1,614 A 1.05E+03 b -1.49E-05 Stiffness (fitted) N=50 1,052

nf.50 46,673

y = 1.05268E+03e-1.48511E-05x R² = 6.48434E-01

1.00E+02

1.00E+03

1.00E+04

10 100 1000 10000 100000

Stiff

ness

, MPa

Load Cycles

AASHTO - Strict (50 cycles to first point at which 50% of initial estimated stiffness is obtained)

Note – that life is calculated as longer than data set included in calculation.

AASHTO relaxed and 50%

26

AASHTO - relaxed - all data Stiffness,measured, N=50 1,614 A 9.16E+02 b -1.15E-06

nf.50 604,856 % of Stiffness (N=50) at Termination 31.0

Difference in AASHTO and compared to 50% 50% of measured stiffness 807 First record below 24,480 Point when all records below 28,690 Average 26,585 Percent error (AASHTO methods) -92% Percent error (AASHTO vs. 50%) 76%

y = 9.15823E+02e-1.14597E-06x R² = 6.45320E-01

1.00E+02

1.00E+03

1.00E+04

10 100 1000 10000 100000 1000000

Stiff

ness

, MPa

Load Cycles

AASHTO - Relaxed (all stiffness data)

ASTM – Stiffness x Cycles

27

ASTM Method 6-order poly fit method

-3.51E-26 x6 5.21E-20 x5 -3.13E-14 x4 8.97E-09 x3 -1.52E-03 x2 8.22E+02 x1

dy/dx = 0 at turning point dy/dx 0.00 x (by POLY/SOLVER) 514,564 Max (strict definition) 284456869 x (at Max) 530,880

y = -3.50568E-26x6 + 5.20521E-20x5 - 3.12781E-14x4 + 8.97228E-09x3 - 1.51542E-03x2 + 8.21969E+02x + 4.87067E+05

R² = 9.99938E-01

0.0E+00

5.0E+07

1.0E+08

1.5E+08

2.0E+08

2.5E+08

3.0E+08

0 100000 200000 300000 400000 500000 600000

n x

Stiff

nes

Load cycles

The choice of method for the definition of the peak make very little difference to the ASTM result. Always less than 10%.

AASHTO standard - reduced data

28

AASHTO - strict Stiffness,measured, N=50 1,614 A 1.18E+03 b -1.37E-05 Stiffness (fitted) N=50 1,180 nf.50 50,752

y = 1.18027E+03e-1.36576E-05x R² = 5.06715E-01

100

1000

10000

10 100 1000 10000 100000 1000000

Stiff

ness

(MPa

)

Load Cycles

AASHTO - Strict (50 cycles to first point at which 50% of the Initial estimated stiffness is obtained)

Note – the life is very similar to the other AASHTO standard plot.

AASHTO relaxed – reduced data

29

AASHTO - relaxed - all data Stiffness,measured, N=50 1,614 A 1.06E+03 b -1.71E-05 nf.50 40,557 % of Stiffness (N=50) at Termination 38.9

Difference in AASHTO and compared to 50%

50% of measured stiffness 807 First record below 40,010 Point when all records below 40,010 Average 40,010 Percent error (AASHTO methods) 25% Percent error (AASHTO vs. 50%) 27%

y = 1.05598E+03e-1.70909E-06x R² = 4.44900E-01

100

1000

10000

10 100 1000 10000 100000 1000000

Stiff

ness

, MPa

Load Cycles

AASHTO - Relaxed (all stiffness data)

Also shown here is the result compared to 50% stiffness reduction.

Life summary

30

Gave 7 methods for calculation life

AASHTO fatigue life variation

31

1,000

10,000

100,000

1,000,000

9.5mm64-22

9.5mm64-22

9.5mm76-22

12.5mm64-22

12.5mm64-22

12.5mm76-22

SMA 76-22

SMA-PmB

BDWC-1 BDWC-2 BDWC-3 BDWC-4 BDWC-5

Mix type

Fatig

ue L

ife b

y va

rrio

us m

etho

ds

AASHTO (S) (IPC) AASHTO (S) (SHRP) AASHTO (R) (IPC) AASHTO (R) (SHRP)

Fatigue life from analysis method AASHTO 321 using different data inclusion/exclusion schemes

Effect of data inclusion

32

0

20

40

60

80

100

120

140

160

180

20253035404550

% Sini (defined by in AASHTO method) that test data was included analysis of Nf

Nf c

hang

e, %

9.5mm 64-22 650

9.5mm 64-22 500

BDWC-1500

BDWC-1000

Analysis is much more sensitive for modified asphalt mixtures

Fit type

33

This example is a cubic spline fit. The method is generally insensitive to data included – except ….

Data trimming

34

If data is included which goes significantly beyond a 15-20% value of the original stiffness the Stiffness x Cycles curve can go through a minimum and then start to increase. The data past this point needs to be removed from the analysis.

This type of data inclusion can cause a difference typically of 10%.

AASHTO (Relaxed) vs. ASTM (by two methods)

35

1,000

10,000

100,000

1,000,000

9.5mm64-22

9.5mm64-22

9.5mm76-22

12.5mm64-22

12.5mm64-22

12.5mm76-22

SMA 76-22

SMA-PmB

BDWC-1 BDWC-2 BDWC-3 BDWC-4 BDWC-5

Mix type

Fatig

ue L

ife b

y va

rrio

us m

etho

ds

AASHTO (R) (IPC) ASTM (poly) ASTM (max)

The analysis shows that the relaxed AASHTO method (more data in analysis) gives similar results to the ASTM method. Note – the AASHTO relaxed included typically 25/30% stiffness as test stop.

Discussion

Two choices exist Keep AASHTO definitions largely the

same but define data more accurately Use similar definition in AASHTO as

used in ASTM

36

Recommendation 2 - analysis

Make the AASHTO analysis part consistent with ASTM Current method depends on initial

stiffness, data collected, termination point, etc. etc.

37

Summary The AASHTO method currently does not define a comparable

failure condition for modified materials Data with conventional materials will produce similar fatigue

curves regardless of standard ASTM or AASHTO methods Failure for modified materials should be based on definition as

currently in ASTM method and the AASHTO method should be changed to be consistent with this

New materials with high modification levels will then have a performance level more correctly defined

Excess data should be trimmed beyond the first significant peak - need to establish rule – suggest max 10% drop in ratio from peak value

Changing the AASHTO definition of life will not have a significant impact on lives calculated in previous evaluations – i.e. – legacy relationships will be valid

Some discussion was made by group on if this should be new standard – but only part that would change is the end definition – so would prefer to modify existing standard since effect on legacy data will be minimal

38

Acknowledgements

Discussions with members of the mix ETG working group – including: Arizona State University Louisiana State University Invia Pavement Technologies National Center for Asphalt Technology Road Science

… and support of staff at Abatech, Asphalt Institute and Rutgers

39

The end ….

Greetings from the Roman

Capital of England – they even left some

roads!

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