HMA permanent deformation study: Progress report to the RPF 7 May 2008 Erik Denneman.

HMA permanent deformation study:Progress report to the RPF

7 May 2008

Erik Denneman

© 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


HMA research programme

State of the art survey Forensic study

Determine scope

Rut study (APT & Lab) Durability study (APT & Lab)

Revised design guidelines


Focus: Design for high demand situations


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”


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


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


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.


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)


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)


Permanent deformation (creep) of HMA

Initial densification (volume change)

Steady state shear deformation

Shear failure


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 )


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


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


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)


Stresses and strains under various tests

FEM Elastic displacement under MMLS in Laboratory


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.


(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.


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


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


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!


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

HMA permanent deformation study: Progress report to the RPF 7 May 2008 Erik Denneman.

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Transcript of HMA permanent deformation study: Progress report to the RPF 7 May 2008 Erik Denneman.