INDOT 401 Specifications
2017 Indiana Mineral Aggregates Association
Winter Workshop
February 1, 2017
Tom Partipilo, E & B Paving, Inc.
Elizabeth Pastuszka, E & B Paving, Inc.
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Overview
• Aggregates in Asphalt Mixtures
• INDOT HMA specifications
– What has changed?
• Previous Specification vs. New Specification
– How will it affect mix designs?
•
•
•
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Aggregate Absorption
Voids in Mineral Aggregate (VMA) in asphalt
Aggregate Specific Gravity (Gsb)
Types of Aggregates Used in Design
– What does it mean for the aggregate industry?
• Material Consistency
• Potential for new products
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Aggregates in Asphalt Mixtures
What is Asphalt?
4.00%
6.00%
Volume of Mixture
100%
90.00%
Air
Asphalt Binder
Aggregates
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Aggregates in Asphalt Mixtures
• Around 90% of Asphalt
• What is Important?
– Gradation
– Shape
– Texture
– Strength
– Bulk Specific Gravity
– Consistency
– Communication
Even More
Now!
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INDOT HMA Specifications
Change in
Specification
Asphalt mix cure
time
Dust/Asphalt Ratio
Mixture Pay Factors
VMA
Contracts let prior to
10/1/2016
Contracts let on
or after 10/1/2016
Main Aggregate
Influence
2 hours
4 hours
Absorption
Fine Mix: 0.6-1.2
Coarse Mix: 0.8-1.6
All mixes: 0.6-1.4
% Passing No. 200
Sieve
Binder = 20%
Air Voids = 35%
VMA = 10%
In-place density = 35%
LSL = Spec. - 0.50%
USL = Spec. + 2.00%
Diff from JMF ± 1.20%
Air Voids = 30%
VMA = 35%
In-place density = 35%
LSL = Spec.
USL = Spec. + 2.00%
Shape, Texture,
Strength,
Gradation, Gsb
Shape, Texture,
Strength,
Gradation, Gsb
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Asphalt Cure Time
• Dependent on the absorption of aggregate
• More absorption = More asphalt needed to
get the same effective binder in design
• How much?
– Asphalt designs prior to 2017 Pba assumed = 65%
of water absorption
– Asphalt designs in 2017
• 50% total mix absorption < 1.25%
• 65% total mix absorption is 1.25% ≤ and ≤ 2.50%
• 80% total mix absorption > 2.50%
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Dust/Asphalt Ratio
Dust/Asphalt Ratio =
Percent passing No. 200 sieve
Percent effective binder
• Material Cleanliness
• Need realistic percent passing No. 200 sieve
• Need to waste excess dust if too “dirty”
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Mixture Pay Factors
• INDOT Contracts let prior to 10/1/2016:
PF = 10% Pb + 35% Va + 20% VMA + 35% Density
• INDOT Contracts led on or after 10/1/2016:
PF = 30% Va + 35% VMA + 35% Density
• Pb removed as a PF in dense-graded mixes but still used
to calculate VMA.
• Increase in VMA PF requires improved VMA control.
8
Voids in Mineral Aggregate
• VMA PF increased, so what is the VMA specification?
Mixture Size
Minimum VMA
4.75 mm
16.0%
9.5 mm
15.0%
12.5 mm
14.0%
19.0 mm
13.0%
25.0 mm
12.0%
Contracts prior to 10/1/2016
LSL = Spec. - 0.50%
USL = Spec. + 2.00%
Diff from JMF ± 1.20%
Contracts after 10/1/2016
LSL = Minimum Spec.
USL = Spec. + 2.00%
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What is VMA?
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Voids In Mineral Aggregate
• Voids in Mineral Aggregate (VMA)
Air
Effective
Asphalt Binder
Total
Specimen
Volume
VMA
Absorbed Asphalt Binder
Aggregates
Aggregate
Volume
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Voids in Mineral Aggregate
• All about the aggregates!
• What affects VMA?
– Gradation
– Shape
– Texture
– Strength
– Aggregate Gsb
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Voids in Mineral Aggregate
• Gradation
– Have to create an aggregate skeleton to obtain
VMA
– Increasing the % Passing the No. 200 sieve
decreases VMA
• Shape and Texture
– Affects how aggregates pack together
– Cubical particles tend to pack together better
than flat and elongated particles.
– Round or natural particles pack closer together
but provide the least amount of VMA.
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Voids in Mineral Aggregate
• Strength
– Weaker particles may degrade or break down
more than another.
– Influenced by particle shape.
– Related to aggregate specific gravity.
• Aggregate Specific Gravity
– Inconsistent Gsb values create asphalt mixture
variability.
– Gsb values need to accurately represent material
being used in the asphalt mixture.
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How do we Increase VMA?
• Gradation:
– Add/increase intermediate size materials
– Reduce % passing the No. 200 sieve
• Shape:
– Increase angularity (CA and/or FA)
• Texture:
– Increase use of manufactured vs. natural products
– Increase use of rough textured vs. smooth textured
• Strength:
– Available products and their quality and shape
• Specific Gravity:
– Consistency and accuracy
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How to improve VMA
Consistency
• Consistency of gradation, shape, strength,
texture and Gsb.
• Share results regularly.
• Obtain representative samples.
• Use best practices for handling, stockpiling,
processing, crushing, etc.
• Communication between asphalt and
aggregate suppliers is more important now
than ever!
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Thank you!
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