ASPHALT INSTITUTEwww.ohmpa.org

SMA Mixture Design Requirements

Alexander W. (Sandy) Brown, P.Eng.Ontario Hot Mix Producers Association - Technical Director

Asphalt Institute - Canadian Field Engineer

November 2006 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.”

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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.”

Stone Mastic Asphalt (SMA)

November 2006 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

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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)

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, VMA %

17 Minimum

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)

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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 <= 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

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

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

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 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

Stone Mastic Asphalt (SMA)

Stone Mastic Asphalt (SMA)

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