SMA Mixture Design Requirements

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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
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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)
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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

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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
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Mix Properties
Design Parameter Design Criteria
Air Voids 4.0
Voids in Mineral Aggregate, VMA 17 Minimum
VCAmix Less than VCA DRC
Tensile Strength Ratio 70 Minimum
Draindown 0.3 Maximum
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Air Voids

• Laboratory compaction by use of Superpave
  Gyratory Compactor (SGC)

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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 lt 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
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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
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Asphalt Mortar

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

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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
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Applications for SMA

• MTO Directive PHY-C-016, The Use of Surface
  Course Types on Provincial Highways, July 2002
• SMA is warranted whenESALS / 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 lt 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)
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Stone Mastic Asphalt (SMA)
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Thank You

• Any Questions?