Transcript Asphalt Technology 101

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
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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
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What is Stone Mastic Asphalt (SMA)?
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SMA is a gap graded rut resistant
hot mix asphalt
Mix is composed of:
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High Quality Aggregates
Asphalt Rich Mortar
Mineral Filler
Cellulose Fibres
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Introduction
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Key Benefits of SMA
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Rut Resistant Mix
Very High Skid Resistance
Reduced Water Spray
Noise Reduction
Durable Mix
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Mixture Properties
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Governing Specifications
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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
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Ontario Mix Design Procedures
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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
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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,
VMA %
17 Minimum
VCAmix %
Less than VCA
DRC
Tensile Strength Ratio %
70 Minimum
Draindown %
0.3 Maximum
Air Voids
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Laboratory compaction by use of Superpave
Gyratory Compactor (SGC)
Voids in Coarse
Aggregate of Mix, VCA
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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
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VCA
MIX
<= VCA
DRC
to give the SMA Stone on
Stone Contact
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This allows the coarse aggregate skeleton to
transfer the traffic loads
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Tensile Strength Ratio, TSR
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Specification: 70% Minimum
Checks the moisture susceptibility of the asphalt
mixture
Two acceptable test procedures:
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Tensile Strength Ratio, AASHTO T283
Retained Stability, LS-283
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Tensile Strength Ratio, TSR
Draindown
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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
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Asphalt Cement, Mineral Filler, Fibres
Provides coating of coarse aggregate skeleton
to:
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Protect from moisture and environment
Bind the aggregate particles together
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Mix Production
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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
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Bailey method – 2% change in PCS results in 1%
change in voids
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Mix Production
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Production rates of SMA are based on plant
layout:
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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
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Bagged fibres by hand
Air blown fibres
Pelletized fibres
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Fibre Addition by Hand
Applications for SMA
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MTO Directive PHY-C-016, The Use of Surface
Course Types on Provincial Highways, July 2002
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SMA is warranted when:
ESALS / design lane / year exceeds 3 million
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DFC or SP 12.5 FC2 is for 1 to 3 million
Some Municipalities use SMA
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Concerns
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Durability of coarse aggregate
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LA abrasion < 30 ?
May be too high for some brittle aggregate
VMA collapse
Bridging over of voids
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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