SMA Mixture Design Requirements by xhc42564

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




www.ohmpa.org                                                            ASPHALT INSTITUTE
Overview

   Introduction
   What is SMA?
   Mixture Properties
   Mix Production
   Applications for SMA
   SMA Concerns



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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.”




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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.”



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Stone Mastic Asphalt (SMA)
Introduction

   What is Stone Mastic Asphalt (SMA)?
       SMA is a gap graded rut resistant
        hot mix asphalt
       Mix is composed of:
            High Quality Aggregates
            Asphalt Rich Mortar
            Mineral Filler
            Cellulose Fibres




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Introduction

   Key Benefits of SMA
       Rut Resistant Mix
       Very High Skid Resistance
       Reduced Water Spray
       Noise Reduction
       Durable Mix




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Mixture Properties

   Governing Specifications

       AASHTO MP 8-051
        Standard Specification for Designing Stone Matrix
        Asphalt (SMA)

       MTO OPSS 1151 (Nov. 2004)
        Material Specification for Superpave and Stone Mastic
        Asphalt Mixtures


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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)




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Gradation Envelope

   Sieve    SMA 12.5 mm   SP 12.5 mm FC1
  19.0 mm       100            100
  12.5 mm     90 – 99        90 – 100
  9.5 mm      50 – 85
  4.75 mm     28 – 40        45 – 60
  2.36 mm     16 – 28        28 – 58
   75 μm       8 – 11         2 – 10
Mix Properties

    Design Parameter           Design Criteria

        Air Voids %                  4.0
 Voids in Mineral Aggregate,
                                 17 Minimum
           VMA %
         VCAmix %              Less than VCA   DRC


  Tensile Strength Ratio %       70 Minimum

       Draindown %              0.3 Maximum
Air Voids

    Laboratory compaction by use of Superpave
     Gyratory Compactor (SGC)
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.


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 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




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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




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Tensile Strength Ratio, TSR
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




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Draindown
Asphalt Mortar

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




November 2006                                       19
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


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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


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Fibre Addition by Hand
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



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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




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Stone Mastic Asphalt (SMA)
Stone Mastic Asphalt (SMA)
Thank You


                Any Questions?



www.ohmpa.org                    ASPHALT INSTITUTE

								
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