4.75 mm (Thinlay) Mixes With
High Air Void Content
K ANSAS D OT
AND
SHANE BUCHANAN
K A N S A S A S P H A LT P AV E M E N T A S S O C I AT I O N
FA L L F O R U M
N OVEMBER 5 , 2 0 1 4
TOPEKA , K ANSAS
Discussion Items
 Background and History of 4.75 mm
(Thinlay) mixes
 Applications and Use
 Mix Design Considerations
 Aggregates
 Asphalt Binder
 Volumetric Property Requirements
 Asphalt Binder Demand
 Permeability
 Performance
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Kansas Highway Information
Good Roads are Critical!
 Traffic demands on roadways are becoming greater each year.
 Must maintain the serviceability of the highway system through
cost effective, long lasting pavement solutions.
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Congratulations!

The 21st Annual Highway Report (Reason), which is based on 2012 data, ranked Kansas number
one in the category of rural interstate pavement condition, third in urban interstate congestion
and fifth in rural arterial pavement condition.

Kansas’ overall rankings in recent reports are third in 2011, second in 2009, third in both 2008 and
2007, fifth in 2006, and third in 2005. There is no report for 2010.
http://www.ksdot.org/Assets/wwwksdotorg/Headquarters/PDF_Files/pressr
elease2014/reasonsept182014.pdf
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Performance
http://kdotapp.ksdot.org/perfmeasures/documents/2011_pavement_fact_sheet.pdf
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Kansas Road Miles and Vehicle Miles
http://www.ksdot.org/Assets/wwwksdotorg/PDF_Files/QuickFacts2010.pdf
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Kansas Transportation Funding
http://www.ksdot.org/Assets/wwwksdotorg/PDF_Files/QuickFacts2010.pdf
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Thinlays: Option for New Construction
and Preservation
Thinlays for New and Existing Pavements

GOAL for any mix application: Provide a cost effective, long lasting, smooth,
clean pavement surface

Primary Applications


1. Apply as the wearing surface to a new pavement system

Smooth, durable, cost effective surfacing option for driveways to
interstate highways

Can be used as the sacrificial layer in a perpetual pavement system
design
2. Apply as a pavement preservation (maintenance) or minor
rehabilitation approach to an existing pavement system


Improve safety characteristics

Increase skid resistance

Improve surface drainage

Improve smoothness
Alternative to existing pavement preservation techniques such as
micro surfacing, slurry seals, chip seals, etc.
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Desired Attributes and Thinlay Potential

Any asphalt mix is expected provide
acceptable performance in the areas of



Stability (i.e., Rutting, shoving, etc.)
 When properly designed and
constructed, Thinlays can provide
excellent resistance to rutting.
Durability (i.e., Cracking (load and
non-load associated)
 Given the binder contents, these
mixes typically provide enhanced
durability performance. The low
permeability of these mixes aids
in maintaining durability.
Moisture Susceptibility
 Low permeability helps limit the
amount of water intrusion into
the mix
Traffic
Level
Typical Roadway Types
Low
County roads, local roads, city
streets with minimal truck traffic,
parking lots, subdivision
streets/driveways
* Smooth surface
* Maintain grade/curb profile
* Low permeability
* Good workability
Medium
Medium to high trafficked city
streets, state routes, U.S.
highways, rural interstates
* Smooth surface
* Maintain grade/curb profile
* Low permeability
* Good workability
* Good stability
High
Medium to high trafficked city
streets, state routes, U.S.
highways, many interstates
(especially urban)
* Maintain grade/curb profile
* Low permeability
* Good stability
* Cost effective sacrifical surface layer
(e.g., perpetual pavement concept)
Desired Application Attributes
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Thinlay for Pavement Preservation
Thinlay Solutions to Observed Performance Problems
Thinlay Solutions to Observed Performance Problems
Traffic
Level
Typical Roadway Types
Major
Minor Structural Fatigue
Surface Rutting
(Load)
3
Rutting (Subgrade Cracking)
Issue)
Non Load
Surface
Reflective Thermal
Bleeding /
Associated
Friction Raveling Stripping
Cracking Cracking
Flushing
Loss
Cracking4
County roads, local roads, city
streets with minimal truck traffic,
Low
parking lots, subdivision
streets/driveways
Medium to high trafficked city
Medium
streets, state routes, U.S.
highways, rural interstates
Medium to high trafficked city
streets, state routes, U.S.
High
highways, many interstates
(especially urban)
Notes:
1) Symbols in each cell indicate the relative solution potential of a thin overlay to the shown distress. In general, thin overlays can provide good performance in most cases
except where major rutting (structural), fatigue cracking, and/or stripping are present. A "Caution" symbol indicates that the situation should be further analyzed to
determine the problem severity and magnitude prior to a thin overlay solution. For example, is the non load associated cracking in the wheel path, what is the width of the
thermal cracks, etc.
2)Thin overlays should be designed for the appropriate service conditions (e.g., potential polymer modified binder use for high traffic applications, polish resistant
aggregate use for high traffic application
3) Milling may be required prior to the thin overlay
4) Longintudinal cracking in wheel path may be fatigue related. Use caution if this distress is present. Milling and/or crack filling may be required prior to thin overlay
5) Milling and/or crack filling may be required prior to thin overlay
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6) Milling of excess binder may be required prior to thin overlay
Thinlay Structural Value to the Pavement
Structural Layer Benefit of Thin Overlays
 Thin overlays offer the potential to significantly improve pavement serviceability by
adding structure to the system.
 Adding structural thickness to the pavement surface will help decrease the measured
strain at the bottom of the pavement layer.

Lower strain = less fatigue cracking = longer pavement life.
Source: Jim Huddleston, Thin Lay Presentation – Rocky Mountain Asphalt Conference 2014
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Value of 1” of Pavement Structure
 Thin overlays can greatly
increase the fatigue life of a
pavement system.
 Adding 1” of structure can
increase by fatigue life by
over 100%
 Thin overlays fit well into a
perpetual pavement system
where the surface is
managed to provide infinite
service without structural
rehabilitation.
Thickness Reps to Failure Increased Fatigue Life From 1", %
2
30234
3
71537
137
4
160693
125
5
340507
112
6
682133
100
Source: Jim Huddleston, Thin Lay Presentation – Rocky Mountain Asphalt Conference 2014
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Thinlay Aggregates
Nominal Maximum Aggregate Size (NMAS)
 Thinlays utilize a small nominal
maximum aggregate size
 4.75 to 9.5 mm is typical
 Lift thickness to NMAS = 3:1 to 5:1
 Placement rates are typically 0.5 to 1.5
inches (60 – 165 lbs/sq yard)
 Ultra Thinlays = < 1 inches
 Thinlays = 1 to 1.5 inches
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Aggregate
 Aggregate for Thinlays should meet the same basic
requirements as aggregate used in other mixes.
 Fine aggregate properties will be of most concern for
Thinlays
 Fine aggregate properties are of main interest
primarily due to grading
 May add the methylene blue test if clay is suspected
in fines
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Methylene Blue Test
 A much better test for deleterious clay evaluation is the methylene blue test
(AASHTO T330)
 Evaluates adsorption capacity of the clay
 Greater the amount of MB solution adsorbed, the greater the clay reactivity
 Blue halo appears around the drop when the clay has reached capacity
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Grading
 Grading requirements can vary considerably.
 A fine grading (i.e. above the maximum density line) will typically yield a lower
permeability even at higher air voids.
 Typical master grading bands.

(Note: other gradings may provide acceptable performance and should not be
eliminated just because they are outside the master bands.)

Open the grading and allow for innovation. Verify with performance testing.
Sieve Size (mm)
Percent Passing, %
KDOT SM-4.75A
9.5
95 to 100
95 to 100
4.75
70 to 100
90 to 100
1.18
30 to 70
40 to 70
0.075
4 to 13
6 to 12
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Use of 100% Screenings for Thinlays
 100% screenings may or may not fit many developed specification bands.
 However, screenings which have different gradings may still have potential to be utilized.
 NCAT research has shown that 100% screenings mixes can be designed successfully with
these requirements.

Air Voids (Va):
4 to 6%

Effective Volume of Binder (Vbe), %
12% minimum

Voids filled with asphalt (VFA)
67 – 80

http://ncat.us/files/reports/2002/rep02-10.pdf
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Thinlay Asphalt Binder
Asphalt Binder
 Generally, an unmodified binder would be the best choice
 Try to utilize the softest binder possible that will provide acceptable performance
 For higher volume roads, consider using a modified binder to help with stiffness
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Thinlay Mix Design Considerations
4.75 mm AASHTO M323 Specification
Notes for 4.75 mm mixes:
1. Dust-to-binder ratio shall be 1.0 to 2.0, for design
traffic levels <3 million ESALs, and 1.5 to 2.0 for
design traffic levels ≥3 million ESALs.
2. Relative density (as a percent of the theoretical
maximum specific gravity) shall be within the range
of 94.0 to 96.0 percent (4 to 6 percent design air
voids.
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Mix Design Considerations – Typical Practices

Thinlay mixes can be designed using a variety of methods (Superpave, Marshall and Hveem)

Compactive Effort


Superpave design gyrations are typically 50 to 80, depending on local conditions; Marshall can be
either 50 or 75 blows.

Key is to select gyration level sufficient to achieve aggregate interlock without degradation of the
aggregate (NAPA IS-135)

Higher compactive effort mixes can be dry and difficult to compact
Design Air Voids


Design VMA


15 to 17%
Design VFA


4 to 6 percent
65 to 80%
Dust to Effective Asphalt Ratio

0.6 to 2.0
Compaction / Volumetric Rule of Thumb
• 25 Gyrations = 1% VMA = 0.4 AC%
Caution:
• Pay special attention to the
relationship of air voids, VMA and VFA
since any two of the three will
automatically define the other.
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Design Air Voids
 What is the appropriate design air void level?
 Historically, 4 percent air voids during design has been the




standard.
With 4.75 mm mixes, generally 4 to 6 percent air voids are
specified
Higher air voids can help reduce “unnecessary” and
potential “detrimental” binder in the mix.
Higher air void content for small NMAS mix not as critical
as mixes are usually much less permeable.
Based on the results, make a decision on the best mix for
performance and economics.
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NCAT Research
Recommendations

“For mixes designed for over 0.3 million equivalent single-axle loads (ESALs), the aggregate blend should
contain no more than 15 percent natural sand and have a minimum fine-aggregate angularity of 45 for
improved rut resistance, moisture damage resistance and low permeability.

The target air void content for selecting the design binder content should be changed to a range of 4.0 to 6.0
percent

Criteria for VMA and VFA should be replaced with minimum and maximum Vbe requirements. This is a more
sensible approach when working with a range of design air voids. For less than 3.0 million design ESALs, a Vbe
range of 12.0 to 15.0 percent is recommended. For 4.75 mm mixtures designed for projects more than 3.0
million ESALs, a minimum Vbe of 11.5 percent and a maximum Vbe of 13.5 percent is recommended.

The minimum dust-to-binder ratio should be increased slightly from 0.9 to 1.0. The maximum dust-to-binder
ratio should be maintained at 2.0.

Fine-graded 4.75 mm NMAS mixtures are practically impermeable, even with high in-place air voids.”
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Volume of Effective Binder Volume (Vbe)

Effective binder volume (Vbe) is calculated by the
voids in mineral aggregate minus the air voids.

Vbe = VMA – Air Voids

VMA was established as a way to help ensure
adequate mix durability (i.e., sufficient binder content
in the mix).

With varying air voids (4 to 6 percent) and VMA (15 to
17), Vbe becomes a good way to quickly ensure the
mix has the correct (not too much and not too little)
binder content.

Vbe is similar to recommending a minimum effective
binder content by mass (Pbe)

Specifying binder content by volume takes into
account changing aggregate specific gravities
(limestone/granite/syenite/rhyolite/quartzite/etc.)

Sets all mixes on equal binder addition basis on
which to evaluate performance
Major Goal of Mix Design is to Have the
Optimum Amount of Binder to Maximize
Performance and Minimize Cost
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Required Mix Binder Content for Specified Vbe
 Spreadsheet can provide the target binder content for a specified Vbe.

Input aggregate gravities, design air voids and minimum/maximum Vbe
 A quick rule of thumb is that 0.1% Binder = 0.2% Vbe
Binder Content Required for Target Effective Binder Volume
CALC
INPUT
Property/Parameter
Aggregate Blend Apparent Specific Gravity, Gsa
Aggregate Blend Bulk Specific Gravity, Gsb
Aggregate Effective Specific Gravity, Gse
Design Air Voids, %
Target Minimum Volume of Binder Effective (Vbe min), %
Target Maximum Volume of Binder Effective (Vbe max), %
Total Binder Content @ Vbe min, %
Total Binder Content @ Vbe max, %
Value
2.700
2.600
2.650
4.0
11.5
13.0
5.76
6.47
DESCRIPTION
This spreadsheet calculates the mix total binder content which results in the user
input values of volume of binder effective (Vbe, % of total mix) being obtained.
Values of apparent, bulk, and effective aggregate specific gravity; and design air
voids are used with the Vbe values to calculate the binder contents. This process
is similar to determining the binder content necessary to provide a target air void
and VMA level. Minimum and maximum Vbe have been recommended by various
research as an alternative to a sliding VMA scale.
ROT: 0.1% Binder = 0.2% Vbe
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Thinlay Permeability
Permeability
 Laboratory permeability
testing can be used to help
optimize the mix in terms of
grading and binder content.
 ASTM PS129 (Withdrawn
in 2003, but still can be
used)
 Smaller NMAS mixes (i.e.,
4.75 and 9.5 mm) require
significantly more air voids
than larger NMAS before
becoming permeable.
Smaller NMAS mixes have
smaller internal voids which
are typically not
interconnected.
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Permeability
 “These mixtures
(“Thinlays”) have been
shown to be resistant to
rutting and have low
permeability if
compacted (field) to 12%
air voids or less.”
http://www.ncat.us/files/report
s/2013/rep13-05.pdf
 Values less than 100 to
125 x 10-5 cm/s are
generally referred to as
“low permeability”.
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Permeability
 Thinlay mixes may exhibit substantially lower
permeabilities than the 100 to 125 x 10-5 cm/sec
 Results from Oklahoma DOT showed that 100% of
existing 9.5 mm NMS mix designs tested @ 7% air voids
met their proposed lab permeability limit of 12.5 x 10-5
cm/s.
 (Note: this is a much tighter specification than the
100 to 125 x 10-5 cm/sec referenced earlier).
www.okladot.state.ok.us/materials/pp/20080320.ppt
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Thinlay Performance
Thin Overlays Performance - LTPP
http://isddc.dot.gov/OLPFiles/FHWA/006648.pdf
Note: SPS-3 and SPS-4 experiments were constructed in 1990 to evaluate the
effectiveness of preventive maintenance treatments for flexible and rigid pavement.
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Thin Overlay Performance - International
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Thin Overlay Performance - Ohio
 Actual service life of
two lane general system
Ohio projects at the
time they were
terminated or
resurfaced.
 For flexible pavements,
it takes nearly 16 years
for the smoothness
level of a thin overlay to
return to the same IRI
level of the existing
pavement prior to the
overlay
From: NCHRP Synthesis 464, Thin Asphalt Concrete Overlay, July 2014
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4.75 mm Mix at the NCAT Test Track

Constructed August 2003

~40+ Million ESALs to date (more than most Interstates)

69% Screenings, 19% gravel, 11% natural sand, 1%
hydrated lime

PG 76-22, Ndesign = 50, 6.1% asphalt binder

¾” thickness (~75 lb/yd2)

Very little cracking (1%)

~ 7 mm rutting

~50 IRI
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Thoughts and Questions?
http://www.pennyauctionwatch.com/
Shane Buchanan
Asphalt Performance Manager
Oldcastle Materials Company
shane.buchanan@oldcastlematerials.com
205-873-3316
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