ASPHALT INSTITUTE SMA Mixture Design Requirements Alexander W. (Sandy) Brown, P.Eng. Ontario Hot...
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Transcript of ASPHALT INSTITUTE SMA Mixture Design Requirements Alexander W. (Sandy) Brown, P.Eng. Ontario Hot...
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.”
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 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 Very High Skid Resistance Reduced Water Spray Noise Reduction Durable Mix
November 2006 8
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
November 2006 9
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
November 2006 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 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 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 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 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