Presentation on theme: "O’Hare Modernization Project Reflective Cracking and Improved Performance of Grooved Asphalt July 20 th, 2006 Research Overview Hyunwook Kim, Research."— Presentation transcript:
O’Hare Modernization Project Reflective Cracking and Improved Performance of Grooved Asphalt July 20 th, 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
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
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 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 2 nd gear is about 2 slabs away from 1 st 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 2 55in 1Slab 2 Slab 3 4 2D Model Description--Loading
Geometry and Loading Concrete Slabs E Subbase = 40 ksi; = 0.20 k = 200 pci Subgrade Subbase 18 in 8 in AC Overlay 5 in E AC = 200 ksi; AC = 0.35 0.5 in 0.2 in E PCC = 4,000 ksi PCC = 0.15 Cross section Loading Positions Transverse Joint = 0.5in Longitudinal Joint = 0.5in 240 in 225 in Top view C L Traffic Direction A B C
Air Temperature Profile 2001 - 20022002 - 2003 * Weather Station
Temperature Profile - Coolest A critical cooling event ~ January 30, 2004 2003 - 2004 On the AC surface 2.2 °F(-16.6° C) at 4:00am At the bottom of AC 22.7 °F(- 5.2° C) at 7:00am At the bottom of PCC 31.5 °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
Pavement Temperature Profiles Warming Cooling AC Overlay PCC 5” 18”
Different positions – Both gear loadings R1 R0 R4 L4 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 (G f ) –Tensile strength (S t ) 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)
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 1 1 / 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 damaged during 180º turns In the large aggregate asphalt sections, the ½ and ¾ inch aggregates tend to break loose from the groove The paper recommends that grooving should be performed only in asphalt with 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.