fatigue assessment of conventional and highly modified asphalt materials with astm … · 2014. 2....
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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)
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)
Typical Fatigue Data (SHRP A003A)
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
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 80679.7822
60 3.26E+03 2.08E+03 1.56E+03 1.66E+03 3.74E+01 3.78E+00 1.46E-01 1.56E+01 1.60E+01 1.57E+00 8.62E-01 -7.10E-01 1.09E+00 2.41E-01 -3.05E-01 93829.4673
70 3.23E+03 2.12E+03 1.52E+03 1.62E+03 3.72E+01 3.85E+00 1.79E-01 1.56E+01 1.60E+01 1.56E+00 8.62E-01 -6.97E-01 1.11E+00 2.36E-01 -3.21E-01 106454.294
80 3.23E+03 2.18E+03 1.48E+03 1.57E+03 3.76E+01 3.98E+00 2.13E-01 1.56E+01 1.60E+01 1.56E+00 8.62E-01 -6.95E-01 1.14E+00 2.36E-01 -3.35E-01 118375.314
90 3.00E+03 2.08E+03 1.44E+03 1.53E+03 3.95E+01 3.60E+00 2.51E-01 1.56E+01 1.60E+01 1.45E+00 7.76E-01 -6.70E-01 1.09E+00 2.53E-01 -2.93E-01 129639.991
100 2.89E+03 2.02E+03 1.43E+03 1.52E+03 3.91E+01 3.36E+00 2.85E-01 1.56E+01 1.60E+01 1.39E+00 7.58E-01 -6.35E-01 1.06E+00 2.40E-01 -2.89E-01 143147.762
110 2.86E+03 2.01E+03 1.42E+03 1.51E+03 3.91E+01 3.32E+00 3.15E-01 1.57E+01 1.60E+01 1.38E+00 7.52E-01 -6.26E-01 1.05E+00 2.39E-01 -2.89E-01 156156.56
120 2.83E+03 2.01E+03 1.41E+03 1.50E+03 3.90E+01 3.30E+00 3.45E-01 1.57E+01 1.60E+01 1.37E+00 7.47E-01 -6.20E-01 1.05E+00 2.38E-01 -2.89E-01 168994.137
130 2.81E+03 2.01E+03 1.39E+03 1.48E+03 3.93E+01 3.26E+00 3.75E-01 1.57E+01 1.60E+01 1.35E+00 7.41E-01 -6.13E-01 1.06E+00 2.37E-01 -2.91E-01 181143.24
140 2.78E+03 2.01E+03 1.39E+03 1.47E+03 3.94E+01 3.23E+00 4.04E-01 1.57E+01 1.60E+01 1.34E+00 7.32E-01 -6.11E-01 1.05E+00 2.37E-01 -2.89E-01 194032.396
150 2.77E+03 2.01E+03 1.38E+03 1.46E+03 4.01E+01 3.22E+00 4.34E-01 1.57E+01 1.60E+01 1.34E+00 7.30E-01 -6.07E-01 1.06E+00 2.37E-01 -2.91E-01 206296.997
160 2.74E+03 2.02E+03 1.35E+03 1.44E+03 3.99E+01 3.22E+00 4.62E-01 1.57E+01 1.60E+01 1.32E+00 7.19E-01 -6.02E-01 1.06E+00 2.39E-01 -2.91E-01 216515.2
170 2.70E+03 2.01E+03 1.35E+03 1.43E+03 3.99E+01 3.18E+00 4.92E-01 1.57E+01 1.60E+01 1.30E+00 7.08E-01 -5.96E-01 1.05E+00 2.38E-01 -2.88E-01 228669.697
180 2.70E+03 2.02E+03 1.34E+03 1.42E+03 4.01E+01 3.18E+00 5.20E-01 1.57E+01 1.60E+01 1.30E+00 7.08E-01 -5.93E-01 1.06E+00 2.39E-01 -2.90E-01 240596.617
190 2.67E+03 2.01E+03 1.33E+03 1.41E+03 4.02E+01 3.15E+00 5.49E-01 1.57E+01 1.60E+01 1.29E+00 6.99E-01 -5.89E-01 1.05E+00 2.38E-01 -2.89E-01 252555.144
200 2.67E+03 2.02E+03 1.32E+03 1.41E+03 4.05E+01 3.14E+00 5.77E-01 1.57E+01 1.60E+01 1.29E+00 6.99E-01 -5.87E-01 1.06E+00 2.37E-01 -2.91E-01 264290.601
210 2.63E+03 2.01E+03 1.31E+03 1.40E+03 4.04E+01 3.10E+00 6.06E-01 1.57E+01 1.60E+01 1.27E+00 6.90E-01 -5.80E-01 1.05E+00 2.37E-01 -2.89E-01 275584.757
220 2.64E+03 2.02E+03 1.31E+03 1.39E+03 4.07E+01 3.13E+00 6.34E-01 1.57E+01 1.60E+01 1.27E+00 6.90E-01 -5.85E-01 1.06E+00 2.41E-01 -2.88E-01 288101.805
230 2.62E+03 2.01E+03 1.30E+03 1.38E+03 4.06E+01 3.10E+00 6.62E-01 1.57E+01 1.60E+01 1.26E+00 6.84E-01 -5.78E-01 1.05E+00 2.38E-01 -2.89E-01 299186.536
240 2.61E+03 2.01E+03 1.30E+03 1.38E+03 4.02E+01 3.10E+00 6.90E-01 1.57E+01 1.60E+01 1.26E+00 6.84E-01 -5.76E-01 1.06E+00 2.39E-01 -2.89E-01 311074.156
250 2.59E+03 2.01E+03 1.29E+03 1.37E+03 4.07E+01 3.07E+00 7.18E-01 1.57E+01 1.60E+01 1.25E+00 6.79E-01 -5.71E-01 1.05E+00 2.37E-01 -2.90E-01 322369.98
260 2.58E+03 2.01E+03 1.29E+03 1.37E+03 4.10E+01 3.07E+00 7.46E-01 1.57E+01 1.60E+01 1.25E+00 6.75E-01 -5.71E-01 1.05E+00 2.39E-01 -2.88E-01 334396.257
270 2.56E+03 2.00E+03 1.27E+03 1.36E+03 4.04E+01 3.03E+00 7.73E-01 1.57E+01 1.60E+01 1.23E+00 6.70E-01 -5.63E-01 1.05E+00 2.37E-01 -2.89E-01 344221.598
280 2.56E+03 2.01E+03 1.28E+03 1.36E+03 4.07E+01 3.03E+00 8.01E-01 1.57E+01 1.60E+01 1.24E+00 6.70E-01 -5.65E-01 1.05E+00 2.37E-01 -2.89E-01 357274.817
290 2.55E+03 2.01E+03 1.27E+03 1.35E+03 4.06E+01 3.02E+00 8.28E-01 1.57E+01 1.60E+01 1.23E+00 6.68E-01 -5.60E-01 1.05E+00 2.38E-01 -2.89E-01 367717.93
300 2.55E+03 2.01E+03 1.27E+03 1.35E+03 4.07E+01 3.02E+00 8.55E-01 1.57E+01 1.60E+01 1.23E+00 6.66E-01 -5.63E-01 1.05E+00 2.39E-01 -2.88E-01 380045.312
310 2.53E+03 2.01E+03 1.26E+03 1.34E+03 4.04E+01 3.00E+00 8.82E-01 1.57E+01 1.60E+01 1.22E+00 6.66E-01 -5.54E-01 1.05E+00 2.37E-01 -2.89E-01 390627.429
320 2.52E+03 2.01E+03 1.25E+03 1.33E+03 4.08E+01 3.01E+00 9.09E-01 1.57E+01 1.60E+01 1.22E+00 6.62E-01 -5.54E-01 1.05E+00 2.39E-01 -2.89E-01 400659.197
330 2.51E+03 2.00E+03 1.25E+03 1.33E+03 4.10E+01 2.98E+00 9.37E-01 1.57E+01 1.60E+01 1.21E+00 6.57E-01 -5.54E-01 1.05E+00 2.37E-01 -2.88E-01 413215.905
340 2.50E+03 2.00E+03 1.25E+03 1.33E+03 4.05E+01 2.98E+00 9.63E-01 1.57E+01 1.60E+01 1.20E+00 6.55E-01 -5.49E-01 1.05E+00 2.37E-01 -2.88E-01 424208.099
350 2.50E+03 2.01E+03 1.24E+03 1.32E+03 4.07E+01 2.98E+00 9.90E-01 1.57E+01 1.60E+01 1.20E+00 6.57E-01 -5.47E-01 1.05E+00 2.39E-01 -2.88E-01 435064.456
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
370 2.47E+03 2.00E+03 1.23E+03 1.31E+03 4.07E+01 2.95E+00 1.04E+00 1.57E+01 1.60E+01 1.19E+00 6.51E-01 -5.41E-01 1.05E+00 2.37E-01 -2.88E-01 455735.124
380 2.48E+03 2.02E+03 1.23E+03 1.31E+03 4.08E+01 2.97E+00 1.07E+00 1.57E+01 1.60E+01 1.20E+00 6.53E-01 -5.43E-01 1.06E+00 2.39E-01 -2.90E-01 466742.987
390 2.46E+03 2.00E+03 1.23E+03 1.30E+03 4.06E+01 2.93E+00 1.10E+00 1.57E+01 1.60E+01 1.18E+00 6.46E-01 -5.38E-01 1.05E+00 2.37E-01 -2.88E-01 478377.466
400 2.46E+03 2.00E+03 1.23E+03 1.31E+03 4.07E+01 2.94E+00 1.12E+00 1.57E+01 1.60E+01 1.19E+00 6.48E-01 -5.41E-01 1.05E+00 2.37E-01 -2.88E-01 492006.232
410 2.46E+03 2.01E+03 1.22E+03 1.30E+03 4.10E+01 2.95E+00 1.15E+00 1.57E+01 1.60E+01 1.19E+00 6.48E-01 -5.41E-01 1.05E+00 2.39E-01 -2.89E-01 502205.111
420 2.45E+03 2.01E+03 1.22E+03 1.30E+03 4.07E+01 2.93E+00 1.18E+00 1.57E+01 1.60E+01 1.18E+00 6.44E-01 -5.36E-01 1.05E+00 2.38E-01 -2.88E-01 512072.714
430 2.44E+03 2.00E+03 1.22E+03 1.30E+03 4.07E+01 2.92E+00 1.20E+00 1.57E+01 1.60E+01 1.18E+00 6.46E-01 -5.32E-01 1.05E+00 2.37E-01 -2.89E-01 523774.964
440 2.43E+03 2.01E+03 1.21E+03 1.28E+03 4.09E+01 2.92E+00 1.23E+00 1.57E+01 1.60E+01 1.17E+00 6.42E-01 -5.32E-01 1.06E+00 2.39E-01 -2.89E-01 531486.211
450 2.42E+03 2.01E+03 1.21E+03 1.28E+03 4.09E+01 2.91E+00 1.26E+00 1.57E+01 1.60E+01 1.17E+00 6.40E-01 -5.30E-01 1.05E+00 2.37E-01 -2.90E-01 542533.379
460 2.41E+03 2.00E+03 1.20E+03 1.28E+03 4.05E+01 2.88E+00 1.28E+00 1.57E+01 1.60E+01 1.16E+00 6.35E-01 -5.27E-01 1.05E+00 2.37E-01 -2.88E-01 553256.915
470 2.42E+03 2.01E+03 1.21E+03 1.28E+03 4.10E+01 2.89E+00 1.31E+00 1.57E+01 1.60E+01 1.17E+00 6.37E-01 -5.32E-01 1.05E+00 2.38E-01 -2.88E-01 567698.241
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!