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HMA permanent deformation study:Progress report to the RPF
7 May 2008
Erik Denneman
Slide 2 © CSIR 2006 www.csir.co.za
Presentation structure
• Introduction HMA permanent deformation study,• Background & objectives• Methodology,• Properties of standard mix,• Permanent deformation phenomenon
• Results for Lab and APT testing on reference mix,• Temperature,• Loading,• Age,• compaction
• Conclusions and recommendations
• Preliminary results rut challenge mix
Slide 3 © CSIR 2006 www.csir.co.za
HMA research programme
State of the art survey Forensic study
Determine scope
Rut study (APT & Lab) Durability study (APT & Lab)
Revised design guidelines
Slide 4 © CSIR 2006 www.csir.co.za
Focus: Design for high demand situations
Slide 5 © CSIR 2006 www.csir.co.za
Main objectives permanent deformation study
• Compare deformation APT to laboratory tests to:• Identify appropriate tests for permanent deformation prediction,• Develop protocols & acceptance criteria for selected tests.
• Test should reliably forecast deformation as function of:• Mix composition• Pavement structure• Climate• Traffic
• Research structure:• First phase: standard ACM mix to provide benchmark (completed).• Second phase: test purposely designed “rut challenge mixes”
Slide 6 © CSIR 2006 www.csir.co.za
APT Study
• Field test devices:• Heavy Vehicle Simulator (HVS),• Model Mobile Load Simulator (MMLS).
• Objectives• Assess relative effects of:
• Layer thickness• Temperature• Loading conditions• (Short-term) asphalt ageing
Road R80
APT site
Slide 9 © CSIR 2006 www.csir.co.za
Laboratory study
• Sources of material• Aggregate from stockpiles and bitumen from tanks at asphalt plant• Loose HMA mix sourced from truck• Cores and slabs extracted from the test section
• Variables• Method of preparation (source of material, compaction)• Conditioning (unconditioned & short-term ageing)• Binder content (optimum & high)• Density (field & design)• Layer thickness (25, 40 & 60 mm)• Temperature• Loading • Mode of testing
Slide 10 © CSIR 2006 www.csir.co.za
Overview of lab tests• Compaction methods:
• Gyratory, Marshall, Modified Marshall, slab compaction, Kango Hammer.
• Wheel tracking tests:• Hamburg wheel tracking test, Transportek Wheel Tracking Test
(TWTT), Model Mobile Load Simulator (MMLS).
• General permanent deformation testing:• Repeated Simple Shear Test at Constant Height (RRST-CH), Static
creep, dynamic creep, Axial Load Slab test (ALS), resilient modulus (ITT).
• Binder Analysis:• Penetration, softening point, viscosity, ductility, High Performance
Liquid Chromatography (HPLC), Dynamic Shear Rheometer (DSR).
• Durability testing• Lottman test, Beam fatigue.
• General testing• BRD, MTRD, grading, binder content, ITS, Mashall stability & flow,
constant head permeability, Marvil test, MRI scan, Rigden voids, ACV, Flakiness, 10% FACT, PSV, absorption, sand equivalent test.
Slide 11 © CSIR 2006 www.csir.co.za
Reference mix aggregate properties
• Aggregate fractions used (all crushed/angular)• Dolorite: 9.5 mm, 6.7 mm and crusher sand• Dolomite: crusher sand• Mine sand
• Aggregate properties• Aggregate crushing value (ACV): 7 (25 max)• 10% FACT: 344 kN (160 kN min)• Water absorption:
• Coarse fractions: 0.46-0.42% (1.0% max)• Fine fractions: 0.36-0.41% (1.5% max)
• Sand equivalent: 65-84 (50 min)• Flakiness index: 9-14% (50% max)
Slide 12 © CSIR 2006 www.csir.co.za
Reference mix grading
Basic properties of standard mix: Marshall
• Binder type: 60/70 pen grade, PG 64
• Optimum binder content: 5%
Property Test Results Specifications
% voids in mix 4.3% 3 to 6%
% VMA 15% > 14%
% VFB 72% 65 to 75%
Filler-bitumen ratio 1.1 1.0 to 1.5
Film thickness 8.2 μm > 7 μm
Marshall Stability ~11 kN 10 to 18 kN
Marshall Flow ~3.0 mm 2 to 6 mm
ITS ~1 187 kPa > 800 kPa
Static creep ~242 MPa > 100 MPa
Gyratory voids (300N) ~2.4% >2.0%
Dynamic creep modulus ~ ~ 16.4 MPa 15-20 MPa (medium - high)
Slide 14 © CSIR 2006 www.csir.co.za
Permanent deformation (creep) of HMA
Initial densification (volume change)
Steady state shear deformation
Shear failure
Slide 15 © CSIR 2006 www.csir.co.za
RSST-CH at 50C Field core March 2008
0
0.002
0.004
0.006
0.008
0.01
0.012
0.014
0.016
0 1000 2000 3000 4000 5000 6000
Number of load repititions
stra
in
Field core March 2008
Cre
ep [
mm
]Number of loading repetitions [N]
mN + a
a
mN
+ a
(1-e
-bN )
Slide 16 © CSIR 2006 www.csir.co.za
Effect of temperatureHamburg Rut Test (Field mix with different Temperatures) @ 40mm
0
2
4
6
8
10
12
14
16
18
20
22
24
26
28
30
0 2000 4000 6000 8000 10000 12000 14000 16000 18000 20000
Wheel Passes
Ru
t d
epth
(m
m)
A7c40-5 @40degA7c40-6 @40degA7c40-3 @50degA7c40-4 @50degA7c40-1 @60degA7c40-2 @60degA7c40-7 @55degA7c40-8 @55degA7c40-9 @45degA7c40-10 @45deg
Initial densification
Steady state shear deformation
Instable failure
Slide 17 © CSIR 2006 www.csir.co.za
Increase of creep slope with temperatureRelation between temperature and rut rate for standard mix under Hamburg test
y = 2E-05e0.1152x
R2 = 0.9254
0
0.005
0.01
0.015
0.02
0.025
35 40 45 50 55 60 65
Temperature ºC
Ste
ady
stat
e ru
t ra
te m
m/p
ass
Hamburg results (40mm field cores)
Expon. (Hamburg results (40mm fieldcores))
Increase of creep slope with temperature
MMLS field y = 4E-07e0.0439t
HVS: y = 2E-08e0.1181t
TWTT: y = 6E-07e0.1319tHWTT: y = 5E-08e0.1907t
MMLS lab: y = 8E-09e0.1059t
Dynamic creep y = 1E-05e0.0345t
RSST-CHy = 1E-07e0.1423t
1.00E-07
1.00E-06
1.00E-05
1.00E-04
1.00E-03
1.00E-02
35 40 45 50 55 60 65Temperature [ºC]
Def
orm
atio
n r
ate
[mm
/pas
s]
HWTT 40mm HVS 40 mm TWTT 40 mm Field MMLS 40 mm Lab MMLS 40 mm RSST-CH Dynamic creep
MMLS re-run
0.0000001
0.000001
0.00001
0.0001
35 40 45 50 55 60 65Temperature [ºC]
Def
orm
atio
n r
ate
[mm
/pas
s]
HVS 40 mm Field MMLS 40 mm Lab MMLS 40 mm MMLS LAB RE-RUN 2400 reps/h MMLS LAB re-run
Effect of loading conditionWheel tracking test (Field Mix with different Temperatures) @ 40mm
0
0.5
1
1.5
2
2.5
3
3.5
4
4.5
5
0 1000 2000 3000 4000 5000 6000 7000 8000 9000
wheel passes
Ru
t d
epth
(m
m)
A7S40-8 @50deg@900KPa A7S40-11 @50deg@900KPa A7S40-12 @50deg@750Kpa
A7S40-13 @50deg@750Kpa A7S40-14 @50deg@600Kpa A7S40-15 @50deg@600Kpa
Effect of binder ageingHMA Project
Penetration (mm-1)
0
5
10
15
20
25
30
35
40
45
50
55
60
65
70
10122 10175 10182* 10122 10175 10182* 10117 10118 10119 10120 10123 10128 A5D2D-2+3
A7C40-1
A7C40-2
A7C40-3
12Months
A5D2A-22+23
Original
RTFOT
Hot mix recovered
Field cores recovered0 months
Lab mix STA
Lab mix LTA
Effect of binder ageingChemical Analysis
0
10
20
30
40
50
60
10122 10175 10182* 10122 10182* 10117 10118 10119 10120 10123 10128 A5D2D-2+3
A7C40-1
A7C40-2
A7C40-3
12Months
A5D2A-22+23
%
Aromatics Resins Asphaltenes
Original RTFOT Hot mix recovered
Field cores recovered0 months
Lab mix STA
Lab mix LTA
Effect of binder ageing
0.00E+00
2.00E-03
4.00E-03
6.00E-03
8.00E-03
1.00E-02
1.20E-02
1.40E-02
1.60E-02
1.80E-02
2.00E-02
0 1 2 3 4 5 6 7 8
Condition
De
form
ati
on
ra
te (
mm
/wh
ee
l p
as
s)
1) 60 mm field cores 2) Plant mix design voids 3) Plant mix field voids
4) Lab mix design voids 5) Lab mix ST aged 6) Lab mix high b/c
7) lab mix LT aged
Slide 24 © CSIR 2006 www.csir.co.za
Density of the test sections
2.300
2.350
2.400
2.450
2.500
2.550
2.600
0 10 20 30 40 50 60 70
Design thickness [mm]
BR
D
Density vs thickness Average4.3 % voids 7% voids
Effect of Compaction
600
700
800
900
1000
1100
1200
1300
1400
1500
1600
2.40 2.45 2.50 2.55 2.60 2.65 2.70
BRD
Te
ns
ile s
tre
ng
th [
kP
a]
Marshall unconditioned Gyratory unconditionedSlab unconditioned Marshall ST agedGyratory ST aged Slab ST agedField samples Linear (Field samples)
Slide 26 © CSIR 2006 www.csir.co.za
Stresses and strains under various tests
FEM Elastic displacement under MMLS in Laboratory
Slide 27 © CSIR 2006 www.csir.co.za
Conclusions
• Objective: Identify appropriate tests
• Test methods that provide consistent trends with respect to variation in age, loading, temperature, compaction:• Wheel tracking tests (TWTT, HWTT, MMLS)• RSST-CH, and• ITS, ITT.
• Test methods that did not provide consistent results:• Marshall stability and flow,• Dynamic creep,• Axial loading slab test, and• Static creep.
Slide 28 © CSIR 2006 www.csir.co.za
(Main) Recommendations
• Include short term ageing in protocols of rutting tests,
• Slab compaction and gyratory compaction preferred over Marshall compaction
• Develop representable method for water permeability testing,
• Calibrate model for rutting prediction using HVS and RSST-CH results.
Slide 29 © CSIR 2006 www.csir.co.za
Rut challenge mix
• Objective: assess performance of a mix with coarse aggregate skeleton
• Mix properties:• 13.2 mm ACM• Coarse graded (in Bailey terms 99% of CA LUW, and DASR 48.2 %
porosity)• 60/70 Pen grade binder
Slide 30 © CSIR 2006 www.csir.co.za
Rut challenge mix
0
10
20
30
40
50
60
70
80
90
100
0
Sieve size (raised to power 0.45)
per
cen
tag
e p
assi
ng
Reference mix Rut challenge mix
PC
S (
2.36
mm
).
SC
S (
0.60
mm
).
TC
S (
0.15
mm
).
Hal
f sie
ve (
4.75
mm
).
0.075 0.300 1.18 2.36 4.75 6.7 9.5 13.2 0.015 0.600
Slide 31 © CSIR 2006 www.csir.co.za
Preliminary findings
• Sections constructed to the target density
• First lab test results (MMLS, RSST-CH) indicate performance similar to reference mix.
• HVS results (in 2nd week of testing) start to indicate better performance of challenge mix
• Too early to tell!
Slide 32 © CSIR 2006 www.csir.co.za
RSST-CH result reference & challenge
0
0.005
0.01
0.015
0.02
0.025
0.03
0.035
0.04
0.045
0 1000 2000 3000 4000 5000 6000
Repititions
Reference mix Rut challenge
Disclaimer: Individual test result do not derive conclusions!
The end… for now