Innovations in HMA Performance Testing

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Transcript Innovations in HMA Performance Testing

Innovations in HMA
Performance Testing
John D’Angelo
D’Angelo Consulting, LLC
[email protected]
Canadian User Producer Group for Asphalt Moncton 2009
Materials Testing
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The HMA is tested in some fashion to simulate
the real world.
The tests go from simple to sophisticated.
From Empirical to Fundamental.
What is a performance test?
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It is a test that directly or indirectly relates to the
performance characteristics of the material.
These tests can be Empirical or Fundamental or
a combination of both.
Empirical tests relate results to past experience.
 Fundamental tests relate stress, strain, and
temperature to past performance.
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APA Sample
Small sample with loading
very unlike the real world.
Must be correlated over a
narrow range of conditions
and material to the real world.
Hamburg Tester
Unrealistic loading.
Again must be correlated
over a narrow range of
conditions and material to
the real world.
Next Generation of Performance
Testers
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New tests have a closer relationship to
fundamental properties of the mix.
Measured material properties tied to
performance models to estimate distress.
SST Device
Developed during
SHRP to evaluate
mix performance.
Expensive,
complicated,
difficult to
interpret results.
Simple Performance Tests (SPTs) Development
9-19 Identification of SPTs and Protocol
Development (Complete)
9-29 Equipment Specification and
Development for SPTs (Active)
9-33 A Mix Design Manual for Hot Mix
Asphalt (Active)
8
AC Mix Performance Tester
The test can evaluate the
rutting and fatigue response
of the AC mix.
The equipment is relatively
inexpensive and easy to use.
Test results are inputs for the
Mechanistic Empirical
Pavement Design Guide.
Sample Preparation
Superpave Gyratory Compactor
• 180 – 190 mm Ht.
Va = 9.5%
IPC ServoPac
Sample Preparation
Test Specimen
Va = 8%
Performance Tests
E* – Dynamic Modulus
Fn – Flow Number (Repeated Load)
Ft – Flow Time (Static Load)
Dynamic Modulus E*
s0
e0
= dynamic stress
= recoverable axial strain
s0
E* =
e0
Phase Angle

75 ~ 125 µε
Load
Displacement

Loading Frequency
log a(T)
|E*| Master Curve
Reference Temperature 21.1 °C
100,000
100,000
6
4
2
0
-2
-4
-6
E* MPa
MPa
E*


-20
10,000
10,000
0
20
40
-9°C
Temperature, °C
4.4 °C
21.1 °C
log( f r ) = log( f )  log
a(T )
37.86C
54.4°C
1,000
1,000
-9°C
4.4 °C
21.1 °C
100
100
-6-6
37.86C
-4
-4
-2-2
0 0
2
2 4
Log Reduced
Frequency
(Hz)
Log Frequency
(Hz)
46
6 54.4°C
Master Curve
60
Fatigue Cracking Model
1
N f = b f k 1 
1
 et
bf ; bf ; bf
1
2
3
k2 b f



2
k3 b f
1 
 
E 
Calibration Factors
3
HMA Performance Tester
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Dynamic Creep
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Simulates Traffic Load
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Loading on 0.1 sec
Load off for 0.9 sec
Repeat sequence
Cumulative axial strains
recorded
Simulates Traffic Load
Loading – 0.1 sec
Rest – 0.9 sec
STRAIN
Dynamic Creep
STRESS
Flow Number Test (Fn)
TIME
Flow Number
CYCLES
Repeated Load Test Results
50,000
12.5_Coarse_PG 67-22 Mix
12.5_Coarse_PG 76-22 Mix
45,000
40,000
Tertiary
Flow
35,000
Microstrain
30,000
Secondary
Flow
25,000
Flow
Number
20,000
Secondary
Flow
15,000 Primary
Flow
10,000
5,000
Primary
Flow
0
0
500
1,000
1,500
2,000
2,500
3,000
3,500
Load Cycles
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Laboratory test run at 53.4°C
4,000
4,500
5,000
Repeated Load Axial Test
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Actual test parameters are still being developed.
Parameters are based on stress conditions in the
pavement.
Beam Fatigue Test
Test provides loss of modulus with
load repetitions. This is empirically
compared to field performance.
Test is time consuming to run and
loading relation to the real world
questionable.
Axial Fatigue Test
New push pull test allows
fatigue testing in the AMPT
with inputs to the VEPCD
model.
IDT Testing
Indirect Tensile testUsed for low
temperature
properties of the
mix
Expensive, easy to
setup and run.
Use Creep Strain
and Strength
Use of the BBR device to test mix
Main obstacle: the use of smaller size specimens that may
not capture overall behavior of pavement
Volume of material tested
may not be representative
Asphalt mixtures contain
aggregate sizes larger than
smallest dimension of beam
Use of the BBR for Low
Temperature Mix Testing
Previous research at University of Minnesota suggested
use of simpler test method based on creep tests of thin
beams in three-point bending
Thin beams (6.25 x 12.5 x 100mm) can be used to
investigate effect of surface aging, microcracking, and
compaction on mechanical properties of asphalt
pavements
Loading Procedure
Predict Lowest Temperature Creep Stiffness
Creep stiffness, GPa
100
-6˚C
-18˚C
-30˚C
CAM model
10
TREF=-18˚C
PG 58-28
1
0.1
1.0E-04
1.0E-02
1.0E+00
1.0E+02
Reduce time
1.0E+04
1.0E+06
Performance Testing
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We have new tools that provide results closer to
the real world.
New modeling procedures allow us to do a
better job of interpreting the results.
We can do a better job of estimating
performance.
In the end we still have to build it right
THANK YOU
QUESTIONS