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SMA Mixture Design Requirements

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Presentation on theme: "SMA Mixture Design Requirements"— Presentation transcript:

1 SMA Mixture Design Requirements
November 2006 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 November 2006

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.” November 2006

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.” November 2006

5 Stone Mastic Asphalt (SMA)

6 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 November 2006

7 Introduction Key Benefits of SMA Rut Resistant Mix
November 2006 Introduction Key Benefits of SMA Rut Resistant Mix Very High Skid Resistance Reduced Water Spray Noise Reduction Durable Mix November 2006

8 Mixture Properties Governing Specifications
AASHTO MP Standard Specification for Designing Stone Matrix Asphalt (SMA) MTO OPSS 1151 (Nov. 2004) Material Specification for Superpave and Stone Mastic Asphalt Mixtures November 2006

9 Mixture Properties Ontario Mix Design Procedures
November 2006 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) November 2006

10 Gradation Envelope Sieve SMA 12.5 mm SP 12.5 mm FC1 19.0 mm 100
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

11 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

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. November 2006

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 November 2006

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 November 2006

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 November 2006

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 November 2006

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 November 2006

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 November 2006

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 November 2006

24 Concerns Durability of coarse aggregate Bridging over of voids
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 November 2006

25 Stone Mastic Asphalt (SMA)

26 Stone Mastic Asphalt (SMA)

27 November 2006 Thank You Any Questions?

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