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Stone Matrix Asphalt (SMA) for Airfield Pavements
2010 FAA Worldwide Airport Technology Transfer Conference
Brian ProwellDon WatsonGraham HurleyRay Brown
Acknowledgements• This work was conducted as part of the
Airfield Asphalt Pavement Technology Program Project 04-04, Evaluation of Stone Matrix Asphalt for Airfield Pavements.
Background
• SMA designed in Germany in the 1960’s as mix resistant to studded tires
• Adopted in US in 1991
Gradation
0
10
20
30
40
50
60
70
80
90
100
Sieve Size, mm
Pe
rce
nt
Pa
ss
ing
, %
Superpave SMA Superpave Control Points
0.075 0.60 1.18 2.36 4.75 9.5 12.5 19.0
Aggregate SkeletonStone Matrix Asphalt Mix
Aggregate SkeletonDense-Graded Mix
9.5 mm NMAS SMA Surface Texture
How is SMA Different?
• Gradation• Asphalt Content• Dust Content• Stabilizing Additives
• Marshall- 50 blow design has been used• Improved performance over HMA
SMA Performance in the USA
Objectives of AAPTP 04-04 Study
The objectives:• Evaluate performance of SMA
pavements• develop technical guidance for the FAA
to implement SMA on U.S. airfields
Documented SMA Use on Airfields
• Australia• China• Europe
• Belgium• Germany• Italy• Norway
• United States
Experimental Design
Mix Combinations
Coarse Aggregate
Binder Grade
P40175-
Blow
SMA50-
Blow
SMA50
Gyrations
SMA65
Gyrations
SMA80
Gyrations
SMA100
Gyrations
Diabase 76-22 X X X X X X
Granite 76-22 X X X X X X
Gravel 76-22 X X X X X X
Limestone 76-22 X X X X X X
Limestone 64-22 X X X
Granite 76-22 X X X X X X
Rutting Susceptibility
• Laboratory evaluations typically show SMA to have increased rutting susceptibility compared to HMA
• Experiments to compare SMA and P401
• Three tests: stability and flow, repeated-load creep, and Hamburg wheel-tracking
Stability and Flow
AggregateHigh PG
SMA P4014% Air Voids 3.5% Air Voids
AC%Stability
lbsFlow 0.01 in AC%
Stability lbs
Flow 0.01 in
Diabase 76 7.5 NA NA 5.1 4,846 11Granite 1 76 5.9 2,828 23 5.3 5,190 13Granite 2 76 7.3 1,798 21 5.3 4,720 11Gravel 76 7.6 1,808 29 5.4 3,799 11Limestone 76 6.9 1,477 24 5.4 3,940 12Granite 1 64 NA NA NA 5.3 4,200 11Limestone 64 NA NA NA 5.5 3,111 8Average 76 7.0 1,978 24 5.3 4,499 12Average 64 NA NA NA 5.4 3,656 10
Repeated Load Permanent Deformation to Asses Rutting Potential
• 100 mm diameter, 150 mm height• 6% air voids• 58 C (climatic high temp. - 6 C )• 20 psi confinement• 0.1 second load; 0.9 second rest• 100, 200, 350 psi vertical load• Continue for 10,000 cycles or until tertiary
flow
With the repeated load test the permanent deformation
performance of SMA mixtures and P401 mixtures were not significantly different.
Hamburg TestTest combines rutting performance with moisture
susceptibility• Uses a steel wheel 47 mm wide by 204 mm
diameter• Load = 685 N (154 lb)• Full test is 20,000 cycles• Temperature - 50 C• VTM - 6 + 0.5 %• Tested under water
With Hamburg, rutting very similar for P-401 and SMA
Overlay Tester Results
0
2,000
4,000
6,000
8,000
10,000
12,000
14,000
16,000
18,000
Diabase Columbus Granite
Ruby Granite Gravel Limestone PG 67-22
Limestone PG 76-22
Cycl
es to
Fai
lure
SMA P401
847%
412%
24%
258%
736%
35%
Fuel Resistance• China has reported that SMA improves
fuel resistance• AAPTP 05-02 evaluating fuel resistant
sealers and binders• Citgo Fuel Resistance Test
– Soaked in kerosene for 24 hours– Mass loss less than 5% good
Fuel ResistanceAggregate Mix Mass Loss, %
GraniteP401 7.8
SMA 4.5
GravelP401 11.6
SMA 6.6
Deicer ResistanceImmersion Tensile Test
0
200
400
600
800
1000
1200
1400
Granite P401 Granite SMA Gravel P401 Gravel SMA
Tens
ile S
tren
gth,
kPa
Dry Water 2% Potassium Acetate
98% 96%
101%
108%
Two Case Studies
• Aviano AFB, Italy• Spangdahlem AFB, Germany
Aviano SMA
• Constructed in 1999• Provided good
performance up through 2010
• Some water issues• More rubber build up• No grooving
Rubber Build Up on SMA Aviano Air Force Base 2000
Aviano Surface Texture in 2000
Seepage of Water from Underneath, Aviano 2000
Draindown, Aviano 2000
Aviano, 2006
Aviano 2008
SMA Aviano
• Provided good performance to date• Good friction• Some water issues• No grooves
Based on good performance at Aviano, SMA was used at
Spangdahlem in 2007
Spangdahlem AFB
• Milled and overlaid with SMA in 2007• High density obtained• Some water vapor (blisters) problems
Spangdahlem 2006, patch
Spangdahlem 2006, cracking and condition of grooves
After mixture was milled, approximately 2 weeks of rainfall occurred causing the asphalt mixture to become soaked with
moisture
Construction in 2007
• The contractor used two asphalt plants, two pavers, and up to 8 rollers
• In place air voids were typically 3 to 4 percent
Spangdahlem, 2007, moisture on surface of SMA
Spangdahlem, 2007, blisters caused by water vapor
Plans are underway to remove and replace the SMA at
Spangdahlem
Summary of SMA / P401 Comparison
Property Performance worse than
P401
Performance similar to
P401
Performance better than
P401Permanent Deformation X1 X2
Moisture Damage XCracking XFuel Resistance XDeicer Resistance XTexture X2
1Based on laboratory tests performed as part of this study.2Based on review of the literature or in-service performance.
Recommendations
• SMA could cost 82 to 94 percent more than dense-graded mixes and still be cost effective on a life-cycle basis.
• SMA is not typically suited to small quantity production
• 65 gyrations recommended as alternative to 50-blow Marshall
The complete report is available at: www.AAPTP.US
Contact Information for authors:Ray Brown [email protected]
Brian Prowell [email protected]
Don Watson [email protected]
Graham Hurley [email protected]
Questions?
