Transcript Flexible Overlays for Rigid Pavements

FLEXIBLE OVERLAYS
FOR RIGID PAVEMENTS
Camille Crichton-Sumners
Manager, Bureau of Research
NJ Department of Transportation
http://www.state.nj.us/transportation/refdata/research
609-530-5966
Principal Investigator: Tom Bennert, Ph.D. Rutgers University,
Center for Advanced Infrastructure and Transportation
Project Number:FHWA-NJ-2009-014
Problem Statement
• PCC reconstruction costly and timely
– Rubblization is option, but require minimum of 6 inches hot mix
asphalt cover
– HMA cover requirements restricts area with overhead clearance
and/or guide rail issues
• PCC rehabilitation generally not successful
• Most simple rehabilitation technique – Hot Mix Asphalt
(HMA) Overlay
– Unfortunately, high deflections at PCC joints/cracks creates
excessive straining in HMA overlay
– Most cases, cracking initiated in HMA above crack/joint in PCC
(called Reflective Cracking)
Problem Statement - continued
• When reflective crack reaches pavement
surface
– Affects overall integrity of pavement
• Smoothness – intermittent cracking
also affects safety
• Pathway for water intrusion
• Area for immediate raveling
• Little guidance on how to design HMA
overlays for PCC pavements
– HMA material/mixture selection
• Immediate need to develop a rational
methodology of HMA mixture
selection/design methodology for
overlaying PCC pavements
Research Approach
• Literature Review
• National Survey (Distributed to all 50 states – state
pavement designers and materials engineers)
• Develop Methodology
– Based on information collected
• Develop Test Sites (PA, Mass, NJ)
– Field Evaluation
– Laboratory Evaluation
• Analyze collected data and evaluate prediction
methodology
• Develop a Decision Tree Methodology for HMA Overlay
Design for PCC Pavements
• Conclusions/Recommendations
Major Conclusions from Literature Review
• Major mechanism generating reflective cracking is tensile strain at
bottom of PCC
– Shearing at joint/crack an accelerator not initiator (if cracking can be mitigated,
shearing should not result in cracking)
• All PCC pavements respond differently in both vertical and
horizontal mode – need methods to test/identify potential
magnitude of movements (Load and Climate related)
• Best mechanical laboratory tests for simulation
– Vertical Bending: Flexural Beam Fatigue
– Horizontal Deflection: Overlay Tester (HMA) and Coefficient of Thermal
Expansion (PCC)
• Critical cracking condition
– Air temperatures already low and climate under-going a cooling cycle
• HMA brittle – more crack prone to vertical and horizontal movements
• PCC slabs contracting
Major Conclusions from Literature Review continued
• No consensus exists on successful mitigation methods
– Did indicate geotextiles/fabrics poor in colder climates
• Strain-tolerant interlayers (asphalt mixtures) excellent
fracture resistance compared to conventional dense
graded mixtures
– Help to reduce strain magnitudes
– Residual strain still may be too high for conventional
mixes
• When field deformations at PCC joint/crack are accurately
measured, these deformations can be used in laboratory to
simulate field movements
– Provides reasonable estimates on reflective cracking life
National Survey on Reflective Cracking
28 Responding States
WA
MT
ME
ND
VT
MN
OR
NH
ID
WI
SD
WY
RI
MI
CT
PA
IA
NE
NV
OH
IL
UT
MD
WV
KS
MO
VA
KY
NC
TN
AZ
OK
NM
AR
SC
MS
AL
GA
TX
LA
FL
AK
HI
NJ
DE
IN
CO
CA
MA
NY
Responded
No Response
Reflective Cracking Mitigation Methods
30
Number of State Highway Agencies (SHA)
Successful
Unsuccessful
25
3
20
15
5
10
9
6
7
21
4
10
5
9
9
SAMI's
RCRI
10
7
0
PFG
GEO
CAL
EOT
Summary of Survey Responses
 Reflective cracking appeared to occur equally at different
traffic levels and base types
 General trends to greater reflective cracking life at
stronger base materials (PCC and Bit-treated)
 Shorter joint spacing generally had longer life
 HMA overlay material (asphalt binder type) had large
impact on reflective cracking
 HMA overlay needs to be resistant to cracking at low
temperatures (different than thermal-induced cracking)
 Using one grade or more less than LTPPbind was more
successful
Summary of Survey Responses
 PCC Treatments
 Variety of treatments have been used but with varying
success – based on responses, joint/slab replacement
most effective
 Reflective Cracking Mitigation Methods
 Better performing mitigation methods were asphalt based
(SAMI’s and RCRI mixes)
 Both commonly use low temperature, crack-resistant
binders
 Performance influenced by RCRI overlay material
 States in warmer/milder climates had better success with
paving fabrics, geosynthetics, and geogrids (similar
conclusions by Lytton and Button, 2007)
 Excessive Overlay thickness successful 33% of time
Proposed Analysis Methods
• Since shear mode mainly a crack accelerator, to mitigate
reflective cracking, methodology to concentrate on bending
(vertical) and expansion/contraction (horizontal)
• Bending – Vertical Mode
– Utilize Falling Weight Deflectometer to model PCC joint/crack vertical
deflections
– Model movements in Flexural Beam Fatigue
• Expansion/Contraction – Horizontal Mode
– Utilize pavement characteristics, Coefficient of Thermal Expansion, and
climate conditions to determine horizontal movements
– Model movements in Overlay Tester
– Overlay Tester used to assess cracking limits of hot mix asphalt in
horizontal mode
Test Sections in Research Study
• Rt 34N – New Jersey
– 3 Test Sections (1 Control; 2 Reflective Crack Relief Interlayers)
• Rt 202S – New Jersey
– 4 Test Sections (1 Control; 3 Various Materials)
• Interstate 495 – Massachusetts
– 2 Test Sections
• Interstate 476 – Pennsylvania
– 1 Test Section
Total of Eleven (11) Test Sections
• Each pavement had traffic information, Falling Weight Deflectometer testing,
material sampling and climatic conditions
Rt 34N, New Jersey – Extracted Core
9.5H76
12.5M76
RCRI
Rt 34N, New Jersey (Section #3)
Percent of Transverse Joints Cracked (%)
60
9.5H76
12.5M76
9.5H76
12.5M76
50
RCRI (Strata)
Measured
40
30
20
Measured
10
RCRI
0
0
1
2
3
4
5
6
7
Time After Construction (Years)
8
9
10
I495, Massachusetts – Extracted Core
Intermediate
Course
RCRI
Leveling
Course
I476, Pennsylvania (75 Gyration Surface Mix)
100
Leveling Course
% of Transverse Joints Cracked (%)
90
80
100 Gyr - Leveling Course
RCRI
75 Gyr - Surface Course
Measured
70
60
50
40
Surface Course
30
20
10
RCRI
Measured
0
0
6
12
18
24
Time After Construction (Months)
30
36
I476, Pennsylvania (100 Gyration Surface Mix)
100
Leveling Course
% of Transverse Joints Cracked (%)
90
80
70
60
Surface Course
50
40
Measured
30
100 Gyr - Leveling Course
RCRI
100 Gyr - Surface Course
Measured
20
10
RCRI
0
0
6
12
18
24
Time After Construction (Months)
30
36
Decision Tree Procedure
HMA Overlay Design
And
Mix Type Selection
Decision Tree Procedure
Determine h
(Equation 6.4 and
Figure 7.23)
h < 0.01inches
Select
Conventional
HMA
h > 0.01inches
Select
RCRI/SAMI
Check Vertical Mode
(Deflection Spectra Approach,
Section 7.1)
Pass
Evaluate Intermediate
and/or Wearing Course
Materials (Section 7.1)
Pass
Final Design
Passes
Fail
Select New
Mixture
Fail
FLEXIBLE OVERLAYS
FOR RIGID PAVEMENTS
Camille Crichton-Sumners
Manager, Bureau of Research
NJ Department of Transportation
http://www.state.nj.us/transportation/refdata/research
609-530-5966
Principal Investigator: Tom Bennert, Ph.D. Rutgers University,
Center for Advanced Infrastructure and Transportation
Project Number:FHWA-NJ-2009-014