Performance of Stone Matrix Asphalt Pavements in Maryland L. Michael G. Burke C. Schwartz AAPT 2003 Lexington, KY

Maryland’s First SMA 1992 First Superpave 1995

Since 1996 Maryland has been designing SMA with SGC

Since 1997 Maryland has been using PG Binders

N design 100 VTM4.0 VMA18.0 External1.25 Internal1.16

GRADATION SPECIFICATION mm mm mm

COARSE AGGREGATE Gap-Graded Mixes Test Property LA Abrasion Loss, % Max. Flat & Elongated Particles, % Retained on the #4 Sieve Max. 3:1 5:1 PV Test Method T96 D MSMT 411 Specification Limits (d)

The Gap-Graded Specimen shall conform to the following Hot Mix Asphalt Gap-Graded Plant Control VMA 18.0 Min Min. VTM 4.0 ±1.2 N des 100 AC 6.5 Min. ±0.4 Binder Draindown % Max. Stabilizer By Weight of Total Mix % Specification Plant Tolerance 0.3 Max. ±0.1

CHARACTERISTICS Superpave SMA Rut Resistant Durable Skid Resistant Reduced Spray Reduced Hydroplaning Reduced Sound

DECISION POINTS FOR USING SMA DECISION POINTS FOR USING SMA 2000 ESAL’s per day 55 mph 2000 ESAL’s per day 55 mph

MD SMA LANE MILES

NUMBER OF PROJECTS BY MIX TYPE

12.5 mm 19 mm

12.5 mm 19 mm

12.5 mm 19 mm

12.5 mm 19 mm

RUTTING PERFORMANCE

ROUGHNESS (IRI)

FRICTION

CORRELATIONS 12.5 mm 19 mm SMALL RANGE OF PERFORMANCE SMALL RANGE OF MIX PROPERTIES

SUMMARY Performance and material property data for 85 SMA projects – 1300 lane miles – Up to 10 years service life – Primarily 19 and 12.5 mm SMA mixes Excellent performance: – Rutting: 0.04 inches/year (avg) – Roughness (IRI): 3.2 in/mile-year (avg) – Friction (FN): 1.3/year (avg)

SUMMARY Inconclusive correlations between performance and mix properties – Too little variation/deterioration of performance – Too little variation in mix properties Many of the Maryland SMA sections look better today than when first opened to traffic!

SMA looks good... …Let’s use it!