FLEXIBLE OVERLAYS FOR RIGID PAVEMENTS

Camille Crichton-SumnersManager, Bureau of ResearchNJ Department of Transportationhttp://www.state.nj.us/transportation/refdata/research609-530-5966

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

MT

WY

ID

WA

OR

NV

UT

CA

AZ

ND

SD

NE

CO

NM

TX

OK

KS

AR

LA

MO

IA

MN

WI

IL IN

KY

TN

MS AL GA

FL

SC

NC

VAWV

OH

MI

NY

PA

MD

DE

NJ

CTRI

MA

ME

VT

NH

AK

HI RespondedNo Response

28 Responding StatesNational Survey on Reflective Cracking

Reflective Cracking Mitigation Methods

9 97

10

3

59

7

4

6

10

21

0

5

10

15

20

25

30

PFG GEO SAMI's RCRI CAL EOT

Num

ber o

f Sta

te H

ighw

ay A

genc

ies

(SH

A)

SuccessfulUnsuccessful

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

• Each pavement had traffic information, Falling Weight Deflectometer testing, material sampling and climatic conditions

Total of Eleven (11) Test Sections

Rt 34N, New Jersey – Extracted Core

9.5H76

RCRI

12.5M76

Rt 34N, New Jersey (Section #3)

0

10

20

30

40

50

60

0 1 2 3 4 5 6 7 8 9 10Time After Construction (Years)

Perc

ent o

f Tra

nsve

rse

Join

ts C

rack

ed (%

) 9.5H7612.5M76RCRI (Strata)Measured

RCRI

12.5M76 9.5H76

Measured

I495, Massachusetts – Extracted Core

RCRI

LevelingCourse

IntermediateCourse

I476, Pennsylvania (75 Gyration Surface Mix)

0

10

20

30

40

50

60

70

80

90

100

0 6 12 18 24 30 36Time After Construction (Months)

% o

f Tra

nsve

rse

Join

ts C

rack

ed (%

)

100 Gyr - Leveling CourseRCRI75 Gyr - Surface CourseMeasured

RCRI

Leveling Course

Measured

Surface Course

I476, Pennsylvania (100 Gyration Surface Mix)

0

10

20

30

40

50

60

70

80

90

100

0 6 12 18 24 30 36Time After Construction (Months)

% o

f Tra

nsve

rse

Join

ts C

rack

ed (%

)

100 Gyr - Leveling CourseRCRI100 Gyr - Surface CourseMeasured

RCRI

Leveling Course

Surface Course

Measured

Decision Tree ProcedureHMA Overlay Design

AndMix Type Selection

Determine h(Equation 6.4 and

Figure 7.23)

h < 0.01inches h > 0.01inches

Select Conventional

HMASelect

RCRI/SAMI

Check Vertical Mode(Deflection Spectra Approach,

Section 7.1)

Pass

Fail

Evaluate Intermediateand/or Wearing Course Materials (Section 7.1)

Pass

Final Design Passes

Select NewMixture

Fail

Decision Tree Procedure

FLEXIBLE OVERLAYS FOR RIGID PAVEMENTS

Camille Crichton-SumnersManager, Bureau of ResearchNJ Department of Transportationhttp://www.state.nj.us/transportation/refdata/research609-530-5966

Principal Investigator: Tom Bennert, Ph.D. Rutgers University, Center for Advanced Infrastructure and Transportation

Project Number:FHWA-NJ-2009-014