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SMA Mixture Design Requirements

SMA Mixture Design Requirements. Alexander W. (Sandy) Brown, P.Eng. Ontario Hot Mix Producers Association - Technical Director Asphalt Institute - Canadian Field Engineer. Overview. Introduction What is SMA? Mixture Properties Mix Production Applications for SMA SMA Concerns.

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SMA Mixture Design Requirements

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  1. SMA Mixture Design Requirements Alexander W. (Sandy) Brown, P.Eng. Ontario Hot Mix Producers Association - Technical Director Asphalt Institute - Canadian Field Engineer

  2. Overview • Introduction • What is SMA? • Mixture Properties • Mix Production • Applications for SMA • SMA Concerns

  3. Definitions “Stone Mastic Asphalt (SMA) is hot mix asphalt consisting of two parts; a coarse aggregate skeleton and an asphalt binder rich mortar. The mixture has an aggregate skeleton with coarse aggregate stone-on-stone contact.”

  4. Definitions “Stone Mastic Asphalt (SMA) Mortar means a mixture of asphalt cement (and any additives), filler (all material passing the 75 μm sieve from the dry sieving of all aggregate components including any commercial filler) and fibres blended by volume.”

  5. Stone Mastic Asphalt (SMA)

  6. Introduction • What is Stone Mastic Asphalt (SMA)? • SMA is a gap graded rut resistanthot mix asphalt • Mix is composed of: • High Quality Aggregates • Asphalt Rich Mortar • Mineral Filler • Cellulose Fibres

  7. Introduction • Key Benefits of SMA • Rut Resistant Mix • Very High Skid Resistance • Reduced Water Spray • Noise Reduction • Durable Mix

  8. Mixture Properties • Governing Specifications • AASHTO MP 8-051Standard Specification for Designing Stone Matrix Asphalt (SMA) • MTO OPSS 1151 (Nov. 2004)Material Specification for Superpave and Stone Mastic Asphalt Mixtures

  9. Mixture Properties • Ontario Mix Design Procedures • CCIL Certified Type ‘A’ or AMRL or equivalent certified laboratory • 4 point mix design • Superpave Gyratory Compactor (SGC) • Ndesign of 100 gyrations • Detailed mix design submission • Job Mix Formula (JMF)

  10. Gradation Envelope

  11. Mix Properties

  12. Air Voids • Laboratory compaction by use of Superpave Gyratory Compactor (SGC)

  13. Voids in Coarse Aggregate of Mix, VCA MIX • Specification: Less than VCA DRC • VCA MIX: The volume in between the coarse aggregate particles. This volume includes filler, fine aggregate, air voids, asphalt binder, and fibre. • VCA DRC: The volume in between the coarse aggregate particles of the final job mix formula in a dry rodded condition.

  14. Voids in Coarse Aggregate of Mix, VCA MIX • VCA MIX <= VCA DRC to give the SMA Stone on Stone Contact • This allows the coarse aggregate skeleton to transfer the traffic loads

  15. Tensile Strength Ratio, TSR • Specification: 70% Minimum • Checks the moisture susceptibility of the asphalt mixture • Two acceptable test procedures: • Tensile Strength Ratio, AASHTO T283 • Retained Stability, LS-283

  16. Tensile Strength Ratio, TSR

  17. Draindown • Specification: 0.3% Maximum • Tested at production temperature of asphalt mixture for 1 hour • Mass of asphalt mortar that has drained from total asphalt mass is determined and expressed as percent of total mass of the original sample

  18. Draindown

  19. Asphalt Mortar • Asphalt Cement, Mineral Filler, Fibres • Provides coating of coarse aggregate skeleton to: • Protect from moisture and environment • Bind the aggregate particles together

  20. Mix Production • SMA can be produced in either batch or drum plants • The production of SMA is better geared to large tonnage projects • Consistent aggregate gradations are critical for SMA production • Bailey method – 2% change in PCS results in 1% change in voids

  21. Mix Production • Production rates of SMA are based on plant layout: • 2 cold feed bins for CA, 1 for FA • Mineral filler will need to be imported • AC content is high – schedule deliveries to keep up with production • Method of fibre addition • Bagged fibres by hand • Air blown fibres • Pelletized fibres

  22. Fibre Addition by Hand

  23. Applications for SMA • MTO Directive PHY-C-016, The Use of Surface Course Types on Provincial Highways, July 2002 • SMA is warranted when:ESALS / design lane / year exceeds 3 million • DFC or SP 12.5 FC2 is for 1 to 3 million • Some Municipalities use SMA

  24. Concerns • Durability of coarse aggregate • LA abrasion < 30 ? • May be too high for some brittle aggregate • VMA collapse • Bridging over of voids • AC content too high • Low initial skid resistance

  25. Stone Mastic Asphalt (SMA)

  26. Stone Mastic Asphalt (SMA)

  27. Thank You Any Questions?

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