O’Hare Modernization Project

Reflective Cracking and Improved

Performance of Grooved Asphalt

July 20th, 2006

Research Overview

Hyunwook Kim, Research Assistant

William G. Buttlar, Associate Professor

Imad Al-Qadi, Professor

Outline

• Project Overview

• FE Fracture Model of Reflective Cracking

• Evaluation of Grooved Asphalt

• Conclusion and Discussion

• Future Plan

Project Overview

• Project initiated in January, 2006.

• Goals:– Model reflective cracking of HMA overlays

– Evaluate binder properties to design materials that are more resistant to cracking, including the evaluation of environmental effects that impact distress mechanisms

– Evaluate stability of grooves in HMA surface

FE Fracture Model ofReflective Cracking

Task Outline

• Explore new methods/materials to reduce maintenance and/or to delay reflective cracking at O’Hare.

• Study mechanisms of reflective cracking w/ new lab tests and models

• Evaluate/inform design methods

Mechanism of Reflective Cracking

• Can begin to occur as soon as the first winter after construction

• Can decrease the serviceability of the overlay

• Can cause the acceleration of other pavement distresses such as the weakening of subgrade and aggregate layers through water infiltration, stripping in HMA layers, and loss of subgrade support.

Key Factors to be Considered

• Overlay and interlayer properties, bonding

• Load transfer efficiency in underlying PCC

• Subgrade support

• Structural condition of the underlying slabs

• Fracture mechanisms (crack initiation and

propagation)

• Critical gear loading condition

• Other boundary conditions

FE Fracture Modeling

Reflective Crack

Subgrade

Subbase

PCC

AC Overlay

Boeing 777

3-D Field

2-D Model

• 2-D FE modeling is a reasonable approximation of the 3D geometry for the purpose of studying the fracture behavior of airport overlay systems.

Model Dimension

36 ft (10.97 m)

Boeing 777-200

2D Model Description--Loading

57 in 57 in

21.82 in

13.64 in

55in

One Boeing-777 200 aircraft:• 2 dual-tridem main gears • Gear width = 36 ft• main gear (6 wheels; 215 psi)• Gross weight = 634,500 lbs (287,800

kg)• Each gear carries 47.5% loading

= 301,387.5 lb

• Boeing777-200: larger gear width (36 ft = 432 in)• The 2nd gear is about 2 slabs away from 1st gear

57 in

55in

225 in

Gear 1

6.82 in

225 in

240 in

432 in

57 in

16.32 in

Note: Dimensions not drawn to scale

Gear 255in

1 Slab 2 Slab 3 4

2D Model Description--Loading

Geometry and Loading

Concrete Slabs

ESubbase = 40 ksi; = 0.20

k = 200 pciSubgrade

Subbase

18 in

8 in

AC Overlay 5 in EAC = 200 ksi; AC = 0.350.5 in0.2 in

EPCC = 4,000 ksiPCC = 0.15

Cross section

Loading Positions

Transverse Joint = 0.5in

Longitudinal Joint = 0.5in

240 in

225 in

Top view CL

Traffic Direction

A

B

C

Air Temperature Profile

2001 - 2002 2002 - 2003

* Weather Station * Weather Station

Temperature Profile - Coolest

A critical cooling event ~ January 30, 2004

2003 - 2004

On the AC surface2.2 °F(-16.6° C) at 4:00am

At the bottom of AC22.7 °F(- 5.2° C) at 7:00am

At the bottom of PCC31.5 °F(- 0.3° C) at 7:00am

10:00am – 7:00am (22 hours)

Lowest air temperature: 4:00am

January 30 – 31th, 2004

* EICM Analysis* Weather Station

-25

-20

-15

-10

-5

0

0 5 10 15 20 25 30 35

Temperature (°F)

De

pth

(in

ch)

10:00am 01/30

11:00am 01/30

12:00am 01/30

14:00pm 01/30

-25

-20

-15

-10

-5

0

0 5 10 15 20 25 30 35

Temperature (°F)

De

pth

(in

ch)

14:00pm 01/30

16:00pm 01/30

22:00pm 01/30

04:00am 01/31

Pavement Temperature Profiles

Warming

Cooling

AC Overlay

PCC

5”

18”

Different positions – Both gear loadings

R1

R0

R4L4

FE Model Description - 1

CZM

Crack Tip

FE Model Input

• Elastic properties– Young’s modulus (E)– Poisson’s ratio (ν)

• Viscoelastic properties– Creep compliance

• Fracture properties– Fracture energy (Gf)

– Tensile strength (St)

• The others– Layer thickness– LTE– Subgrade support– Thermal coefficient– Friction between PCC

and granular subbase– Gear loading time (e.g.,

0.1 sec = 50 mph)– Pavement temperature

profiles (EICM)

Temperature Loading Only

Temperature Loading Only

Temperature + Gear Loading (R0)

Temperature + Gear Loading (Ro)

- Cracking with Lower Fracture Properties and Heavy Loading -

Summary

• 2-D FE fracture modeling can be used to study reflective cracking mechanisms based on fracture properties.

• Typical asphalt overlay configurations at ORD will be studied this Fall, to evaluate current design and material methodologies.

• The current model suggests cracking potential at the crack tip in the bottom of the AC overlay; however the underlying PCC thickness limits predicted cracking rates.

Evaluation of Grooved Asphalt:

Literature Review

Improvement of Asphalt Grooves Evaluate/ improve stability of grooves in HMA surfaces

Understanding the mechanism of groove collapse

Develop a simple torture test to evaluate pavement groove stability and evaluate lab samples and field samples from O’Hare

Conduct pavement modeling to evaluate mechanisms of groove collapse and methods to mitigate this phenomenon

Make recommendations for improved groove performance – Geometry – Materials – Mix design

FAA HMA Groove Standards • Grooves reduce effects hydroplaning• Transverse grooves are common on runways• Standard dimensions are ¼ deep by ¼ wide at 11/2

centers (1)

Figure 1 Grooving on HMA runway: 5-year old saw-cut grooves at Volk Field Air National Guard Base in Wisconsin (2)

1. AC 150/5320-12C (1997); “Measurement, Construction, and Maintenance of Skid-resistant Airport Pavement Surfaces.”

Federal Aviation Administration.

2. Duval, J.; and Buncher, M. (2004). “Superpave for Airfields.” Presented for the 2004 FAA Worldwide Airport Technology

Transfer Conference, Atlantic City, NJ.

Performance of HMA Grooves

Allen and Quillen (3) evaluated the effects of aircraft loading and climatic conditions on grooved asphalt R/Ws.• Problems identified:

Grooves were severely damagedduring 180º turns

In the large aggregate asphaltsections, the ½ and ¾ inch aggregatestend to break loose from the groove

The paper recommends that

groovingshould be performed only in asphaltwith aggregates less than 3/8 inches.

3. Allen, C. R.; and Quillen, J. W. (1969): “Problem Areas Associated with the Construction and Operation of the Landing Research Runway at NASA Wallops Station.” Pavement Grooving and Traction Studies, NASA SP-5073, Paper No. 8.

4. McGuire, R.C.; (1969): “Report on Grooved Runway Experience at Washington National Airport.” Pavement Grooving and

Traction Studies, NASA SP-5073, Paper No. 19.

Damaged grooves by Convair 990 during 180º turns at Wallops Station (3)

McGuire(4) evaluated different groove patterns at 6 airports and The grooves were monitored for four seasons

Performance of HMA Grooves

5. Emery, S. J. (2005). “Bituminous Surfacing for Pavements on Australian Airports.” 24th Australia Airports Association Convention, Hobart

6. Emery, S. J. (2005). “Asphalt on Australian Airports.” Australia Asphalt Paving Association Pavement Industry Conference, Surfers Paradise, Queensland.

7. Mosher, L.G. (2002): “Results from studies of Highway Grooving and Texturing of State Highway by several state Highway

Departments. Pavement Grooving and Traction Studies, NASA SP-5073, Paper No. 27.

• Groove collapse was caused by slow moving, heavy aircraft and groove collapse was common at runway/taxiway crossings (5, 6)

• Mosher (7) concluded that asphalt binder is a critical parameter

Mechanism of Groove Collapse– Involves viscous flow. – Microscopic analysis of asphalt which has deformed into

the groove shows the binder still covers the aggregates suggesting a cohesion (or stiffness) rather than adhesion failure

– It was suggested that groove closure is related to a property of the binder that changes with time of loading and age

– Since most airfield pavements are designed to resist environmental effects (rutting is of secondary concern), the binder plays a critical role in rutting behavior

– Therefore binder viscosity/stiffness may be critical to groove closure

Mechanism of Groove Collapse

• Mechanism of groove edge breakage – It was suggested that groove edge breakage is caused

by horizontal stresses induced by aircraft tires.– It was reported that horizontal stresses could be up to

500 kPa – Repeated application of this level of stress on the

unsupported edge of the groove could lead edge failure– Examination of the broken edge asphalt shows that the

aggregates were still covered with binder indicating cohesion failure.

– Thus groove closure and groove edge breakage (groove collapse) are dependent on asphalt viscosity/stiffness.

Summary

• Need to visit O’Hare airfields to study groove collapse and deformation characteristics (August ?)

• Must investigate groove performance as a function of groove pattern, HMA mix design and binder grade

• Currently developing an experimental test for understanding the phenomenon of groove collapse

• Numerical modeling (DEM) will be developed and compared with the laboratory testing and field performance.

Thank You !!