9th European FWDUG MeetingApril 9th 2019, TU Darmstadt

Monitoring of crack propagation in asphalt pavement

using FWD during an APT experiment

April 9th 2019

M.L. Nguyen

Outline

Context and objectives of the study

Traffic simulator, full-scale pavement and

instrumentation

Experimental results and discussions

Conclusions and perspectives

2

Context and objectives

• Evaluation of the durability of asphalt pavement

against fatigue crack propagation

• Comparison of different pavement structure

solutions with different asphalt materials

Research program investigating fatigue crack

propagation in asphalt pavement: Experimental study using accelerated full-scale test

3

4 dual-wheel loads

(65 kN each)

Linear heavy traffic simulator

2 m testing length

Characteristics:Single or dual-wheel:

30 – 75 kNTesting length: 2 mMax. speed: 7 km/h1 million loads/month

4

4 dual-wheel loads

(65 kN each)

5 cm BC

6 cm HMAM

Subgrade 70 MPa

Full-scale pavement

Defect to initiate crack

propgation

2 m testing length

5

Pavement instrumentation

2 m loaded length

65 kN dual-wheel

5 cm BC

6 cm HMAM

Subgrade 70 MPa

Temperature probes

Defect to initiate crack

propgation

0.4m

Longitudinal strain

gaugesL13

L12L11

L14

Vertical strain gauges

1mZ12Z11

6

7

Monitoring of pavement responses using FWD

Pavement responses monitoring using FWD

400

500

600

700

800

900

-1.2 -1 -0.8-0.6-0.4-0.2 0 0.2 0.4 0.6 0.8 1 1.2

Def

lect

ion

(m

icro

n)

Distance from the defect (m)

D0 1m cycles

T(asphalt)=20.1°C

D0 0.35m cycles

T(asphalt)=13.1°C

D0 0m cycles

T(asphalt)=10.1°C

Global increase of deflection in the loaded area

Local deflection peaks presence, development of vertical cracks

BC

HMAM

L13

L12L11

L14

FWD

8

See appendix:

(Nguyen et al., 2012), RILEM annual meeting, Zurich:

“Detection of Debonding and Vertical Cracks with Non-Destructive Techniques during Accelerated Pavement Testing”

Pavement monitoring using strains gauges

-5

0

5

10

15

-150

0

150

300

450

Tem

per

atu

re ( C

)

Str

ain

s (m

icro

stra

in)

Number of cycles (103)

L13_BC_before_defect L14_BC_after_defect

L11_HMAM_before_defect L12_HMAM_after_defect

T° (-5cm)

3.68 100 200 300

Similar responses from both sidesof the defect bonded interface

BC

HMAM

L13

L12L11

L14

9

Pavement monitoring using strains gauges

-5

0

5

10

15

-150

0

150

300

450

Tem

per

atu

re ( C

)

Str

ain

s (m

icro

stra

in)

Number of cycles (103)

L13_BC_before_defect L14_BC_after_defect

L11_HMAM_before_defect L12_HMAM_after_defect

T° (-5cm)

3.68 100 200 300

Similar responses from both sidesof the defect

Rising of the apparent neutral axis of asphalt layers vertical crack

BC

HMAM

L13

L12L11

L14

10

Pavement monitoring using strains gauges

-5

0

5

10

15

-150

0

150

300

450

Tem

per

atu

re ( C

)

Str

ain

s (m

icro

stra

in)

Number of cycles (103)

L13_BC_before_defect L14_BC_after_defect

L11_HMAM_before_defect L12_HMAM_after_defect

T° (-5cm)

3.68 100 200 300

Similar responses from both sidesof the defect

Rising of the apparent neutral axis of asphalt layers

Loss of symmetry of responsesfrom both sides of the defect

Evolution of strain, in particular for L13 from contraction to extension

Strain amplitude

BC

HMAM

L13

L12L11

L14

11

Pavement monitoring using strains gauges

0

5

10

15

20

25

0

300

600

900

1200

1500

0.0E+00 2.5E+05 5.0E+05 7.5E+05 1.0E+06

Tem

per

atu

re ( C

)

Str

ain

am

pli

tud

e (m

icro

stra

in)

Number of cycles

L13_BC_before_defect L14_BC_after_defect

L11_HMAM_before_defect L12_HMAM_after_defect

T° (-5cm)

Confirmation of loss of symmetryof pavement response

Consolidation of crack propagation scenario: vertical crack developsup to the BC layer after partial debonding of the interface

BC

HMAM

L13

L12L11

L14

12

Pavement surface visualisation after 1 million cycles

BC

HMAM

13

Conlusions and perspectives

Analysis of pavement responses to better

understand mechanisms of fatigue crack growth in

asphalt pavement under repeated APT traffic.

Measurements allow to detect and follow crack

propagation even not visible on the pavement

surface.

Numerical modelling of experimental results

Forensic evaluation to confirm crack propagation

scenario

Comparison of different pavement structure

solutions

14

Save the date:

15

Main conference themes :1.Establishing APT Facilities2.APT of Asphalt Concrete3.APT of Portland Cement Concrete4.APT for Airfield pavements5.APT of Sustainable and innovative Materials6.Testing of maintenance and rehabilitation solutions7.Testing of smart and multi-functional pavements8.Data Analysis and modelling9.Instrumentation and data processing10.Monitoring and non destructive testing11.Future applications of APT

Thank you for your attention !

Questions and comments are kindly welcome !

16

APPENDIX: NDT FOR DETECTION OF INTERFACE DEBONDING

Fatigue carrousel of the IFSTTAR

► Moving load in fatigue configuration: dual-wheel 65 kN

► Speed: up to 100 km/h (15 rounds/min.)

► Cadence: up to 50 000 cycles/day

(Nguyen et al., 2012), RILEM annual meeting, Zurich:

“Detection of Debonding and Vertical Cracks with Non-Destructive Techniques during Accelerated Pavement Testing”

DESCRIPTION OF THE TEST SITE (BUILT IN MARCH 2011)

Test section with

interface defects

(25 m long)

Sand 0-6

Textile

Withouttack coat

6cm BC 0/10

8cm RBA 0/14

UGM + Soil

Tack coat: 300g/m² binder

FWD MEASUREMENTS – DETECTION OF DEBONDING

0

100

200

300

400

500

600

700

800

-1 -0,5 0 0,5 1 1,5

Def

lect

ion

(µm

)

Distance (m)

Without tack coat Sand 0-6 Textile

Road Base Asphalt material

Bituminous Concrete

Interface defect zone

Maximum deflections measured with the FWD (80kN load) above the 3 types of defect

Measurement every 10cm