Flexible Pavement Cracking Mechanisms Hassan Baaj, Ph.D., P. Eng. Associate Professor Associate Director, Centre for Pavement and Transportation Technology (CPATT) 1

Presentation Outline About CPATT Introduction to pavement cracking mechanisms o Some examples of common cracking modes in Canada o Closing notes o Questions o o

2

Centre of Pavement and Transportation Technology

3

CPATT – History Founded in 2004 at the University of Waterloo as a new initiative for Pavement and Transportation Research in Canada Partners

Public Sector

4

 Canada Foundation for Innovation  Ontario Innovation Trust  Regional Municipality of Waterloo  McAsphalt Industries Limited  Ministry of Transportation Ontario

Universities

Private Sector

 Ontario Research and Development Challenge Fund  Greater Toronto Airport Authority  Cement Association of Canada  Ontario Hot Mix Producers Assoc.  Stantec Consulting Ltd.  Several Universities

Centre of Pavement and Transportation Technology CPATT Goals 1. CPATT’s initiative involves an integrated program of field and laboratory research. 2. Focus on emerging and innovative technologies.

3. State-of-the-art research infrastructure. 4. Train and educate next generation. 5. Sustained partnerships. 6. Provide national and international leadership. 5

Introduction

Flexible Pavements are subjected to

Thermal Variations Low Temperature cracking

Moisture

Frost Heave

Stripping & Ravelling

Failure 6

Mechanical loadings

Rutting

Fatigue

Introduction Cracking is more complex than this!! Thermally-induced cracking

o -

Traffic loading-related cracking

o -

o

7

Low temperature cracking Frost-heave cracking Reflective thermal cracking Top-down longitudinal cracking (in joints and segregated areas) Fatigue cracking Top-down longitudinal cracking Reflective cracking

Combination of reasons

Introduction

Cracking is more complex than this!! Material related

o -

Construction related

o -

-

o

Improper joint preparation Thermal or physical segregation Tack-coat problems Compaction issues Thin overlay over cracked pavement Drainage issues (major problem)

Structure related

o

8

Poorly-designed mix Inadequate or poor binder Binder-aggregates adhesion issues

Under-designed pavement Unexpected traffic Lack of frost protection

Combination of different factors

Low temperature cracking Tensile stress build up in the longitudinal direction of the pavement

9

Low temperature cracking

10

Stress (MPa)

Low temperature cracking 3.5 3 2.5 2 1.5 1 0.5 0

Stress at failure

0

50

100 150 200 Time (Min)

250

300

0

50

100

250

300

Temperature (°C)

Constant Height

TSRST 11

150

200

5 -5 -15 -25 -35

10°C/hour Temperature at failure

Fatigue cracking

12

Fatigue cracking

13

Fatigue cracking

Tension-Compression test Destructive Test

Temperatures: 10 °C Frequency: 10 Hz

14

Fatigue cracking For each tested specimen: Determine the number of cycles Nf corresponding to failure.

|E*| |E*0|

|E0| 2

Log e

Fatigue Line (Wöhler ) Nf

e6 15

N

10+6

Log Nf

Tack-coat issues

16

Tack-coat issues

17

Tack-coat issues

18

Seg reg ation

19

Transverse joints preparation

20

Transverse joints preparation

21

Longitudinal joints

22

Patching

23

Ir regularities

24

Ir regularities

25

Ther mal seg reg ation *>252.7°F 240.0 220.0 200.0 180.0 160.0 140.0 120.0 100.0 80.0 *