Flexible Pavement Cracking Mechanisms Hassan Baaj, Ph.D., P. Eng. Associate Professor Associate Director, Centre for Pavement and Transportation Technology (CPATT) 1
Welcome message from author
This document is posted to help you gain knowledge. Please leave a comment to let me know what you think about it! Share it to your friends and learn new things together.
Transcript
Flexible Pavement Cracking Mechanisms
Hassan Baaj, Ph.D., P. Eng.
Associate Professor
Associate Director, Centre for Pavement and Transportation Technology (CPATT)
1
o About CPATT
o Introduction to pavement cracking mechanisms
o Some examples of common cracking modes in Canada
o Closing notes
o Questions
Presentation Outline
2
Centre of Pavement and
Transportation Technology
3
Canada Foundation for
Innovation
Ontario Innovation Trust
Regional Municipality of
Waterloo
McAsphalt Industries Limited
Ministry of Transportation
Ontario
Ontario Research and Development
Challenge Fund
Greater Toronto Airport Authority
Cement Association of Canada
Ontario Hot Mix Producers Assoc.
Stantec Consulting Ltd.
Several Universities
Public Sector Universities Private Sector
Partners
CPATT – History
Founded in 2004 at the University of Waterloo as a new initiative for
Pavement and Transportation Research in Canada
4
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
Failure
Flexible Pavements
are subjected to
Thermal
VariationsMoisture
Mechanical
loadings
Low
Temperature
cracking
Frost
Heave
FatigueRuttingStripping &
Ravelling
6
Cracking is more complex than this!!
o Thermally-induced cracking- Low temperature cracking - Frost-heave cracking- Reflective thermal cracking- Top-down longitudinal cracking (in joints and segregated
areas)
o Traffic loading-related cracking- Fatigue cracking - Top-down longitudinal cracking - Reflective cracking
o Combination of reasons
Introduction
7
Cracking is more complex than this!!
o Material related- Poorly-designed mix- Inadequate or poor binder- Binder-aggregates adhesion issues
o Construction related- Improper joint preparation- Thermal or physical segregation- Tack-coat problems- Compaction issues- Thin overlay over cracked pavement- Drainage issues (major problem)
o Structure related- Under-designed pavement- Unexpected traffic- Lack of frost protection
o Combination of different factors
Introduction
8
Tensile stress build up in the longitudinal
direction of the pavement
Low temperature cracking
9
Low temperature cracking
10
0
0.5
1
1.5
2
2.5
3
3.5
0 50 100 150 200 250 300
Time (Min)S
tress
(M
Pa)
-35
-25
-15
-5
5
0 50 100 150 200 250 300
Stress at failure
Temperature at failure
Constant
Height
10°C/hour
Tem
pera
ture
(°C
)
TSRST
Low temperature cracking
11
Fatigue cracking
12
Fatigue cracking
13
Tension-Compression testDestructive Test
Temperatures: 10 °C
Frequency: 10 Hz
Fatigue cracking
14
For each tested specimen:
Determine the number of
cycles Nf corresponding to
failure.
Log Nf
Log e
Fatigue Line
(Wöhler )
|E*|
N
|E*0|
Nf
|E0|
2
e6
10+6
Fatigue cracking
15
Tack-coat issues
16
Tack-coat issues
17
Tack-coat issues
18
Segregation
19
Transverse joints preparation
20
Transverse joints preparation
21
Longitudinal joints
22
Patching
23
Ir regularit ies
24
Ir regularit ies
25
85.4%
196.990.0%
195.594.5%
218.689.0%
186.7
94.2%
223.7
*>252.7°F
*<68.0°F
80.0
100.0
120.0
140.0
160.0
180.0
200.0
220.0
240.0
Thermal segregation
26
Compaction issues
27
Compaction issues
28
Compaction issues
29
No skirts, it sticks !!!
Compaction issues
30
Frost heave of the pavement requires three conditions:
• The subgdare is frost susceptible
• Freezing conditions (very cold weather)
• A water table close to the subgrade (moisture source)
Frost heave
31
Source: http://www.mtq.gouv.qc.ca/en/reseau/chaussees/chaussees.asp
Frost heave
32
Ice lense
Frost heave
33
Frost
Non-frost
Frost depth tube
Frost heave
34
Impact of traffic loading
Traffic analysis
35
Traffic analysis
Which one of these two highways needs a
thicker and more robust pavement
structure?
Impact of traffic loading
36
Traffic analysis Traffic (EASL)
Determine the number of expected repetitions of 18-kip (80 kN or
8.165 tons) Equivalent Single-Axle Load (EASL) applied to the
pavement on two sets of dual tires.
Equivalent Single-Axle
Impact of traffic loading
37
Equivalent Single Axle Load (ESAL)
Converts wheel loads of various magnitudes and repetitions ("mixed traffic") to an equivalent
number of "standard" or "equivalent" loads
Based on the amount of damage they do to the pavement
Commonly used standard load is the 18,000 lb. (80 kN) equivalent single axle load
Load Equivalency
Generalized fourth power approximation
Traffic analysis: ESAL and LEF
4
loadgroupaxlestandard
loadgroupaxlespecificFactoryEquivalencLoad
RAV 4
Average empty weight
= 1.2 tons LEF = 2 (0.6/8.2)4 = 0.000057
LEF = 2 (1.3/8.2)4 = 0.0013
Suburban Average
empty weight
= 2.6 tons
Impact of traffic loading
38
The standard axle weights for a standing-room-only loaded Metro articulated bus (60 ft. Flyer)
are:
Axle Empty Full
Steering 58 kN 75 kN
Middle 67 kN 89 kN
Rear 40 kN 62 kN
Using the 4th power approximation, determine the total equivalent damage caused by this bus
in terms of ESALs when it is empty. How about when it is full?
LEF calculation example
Empty
(58/80)4 = 0.276
(67/80)4 = 0.492
(40/80)4 = 0.063
Total = 0.831 ESALs
Full
(75/80)4 = 0.773
(89/80)4 = 1.532
(62/80)4 = 0.361
Total = 2.666 ESALs
Increase in total weight = 61 kN (about 80 people) or 37%Increase in ESALs is 3.2 times
37% load increase 320% Damage increase
165 kN 226 kN
Impact of traffic loading
39
Impact of traffic loading
40
Unladen (240 t) Laden (560 t)
- front 49% = 117.6 t 33% = 184.8 t
- rear 51% = 122.4 t 67% = 375.2 t
- LEF LEFU = ? LEFL = ?
Load Equivalency Factor: Generalized fourth power approximation would give an
approximate value of LEF (Rough estimation of ELF values).
4
loadgroupaxlestandard
loadgroupaxlespecificFactoryEquivalencLoad
Impact of traffic loading
Maximum payload capacity, kg 320,000
Unladen weight, kg 240,000
Gross weight, kg 560,000
41
Maximum payload capacity, kg 320,000
Unladen weight, kg 240,000
Gross weight, kg 560,000
Unladen (240 t) Laden (560 t)
- front 49% = 117.6 t
LEF = (117.6/8.2)4 = 42303
33% = 184.8 t
LEF = (184.8/8.2)4 = 257960
- rear 51% = 122.4 t
LEF = (122.4/8.2)4 = 49644
67% = 375.2 t
LEF = (375.2/8.2)4 = 4383246
- LEF LEFU ≈ 92 000 LEFL ≈ 4641200
Impact of traffic loading
Rough estimation of ELF values
42
Closing notes
Pavement cracking mechanisms are diverse
• External factors
o Environmental conditions
o Traffic loading
• Internal factors
o Materials
- Mix design & binder properties
o Construction
- Compaction, segregation, joints, etc.
o Pavement Structure- Under-designed pavement, unexpected traffic, lack
of frost protection
o Combination of different factors43
Closing notes
Pavement cracking could be avoided or reduced
o The identification of the reason of cracking is crucial to solve the problem and to avoid it in the future
o The cracking pattern could be a good indicator to identify the source of the problem
o Most of cracking could be avoided through:
- The right selection and design of construction materials
- Good pavement design
- Good construction practices
o Role of Pavement Management and Preservation Systems is important to increase the life of the pavement
44
THYANK YOU
45
Related Documents
