s hane b uchanan k ansas dot and k ansas a sphalt p avement a ssociation f all f orum n ovember 5,...

S H A N E B U C H A N A NK A N S A S D OT A N D K A N S A S A S P H A LT PAV E M E N T

A S S O C I AT I O N FA L L F O RU MN OV E M B E R 5 , 2 0 1 4

TO P E K A , K A N S A S

4.75 mm (Thinlay) Mixes With High Air Void Content

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

Discussion Items

KDOT | KAPA Fall Forum 2014

Kansas Highway Information

Traffic demands on roadways are becoming greater each year. Must maintain the serviceability of the highway system through

cost effective, long lasting pavement solutions.

Good Roads are Critical!


Congratulations!


http://www.ksdot.org/Assets/wwwksdotorg/Headquarters/PDF_Files/pressrelease2014/reasonsept182014.pdf

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.




Performance


http://kdotapp.ksdot.org/perfmeasures/documents/2011_pavement_fact_sheet.pdf



Kansas Road Miles and Vehicle Miles


http://www.ksdot.org/Assets/wwwksdotorg/PDF_Files/QuickFacts2010.pdf



Kansas Transportation Funding

KDOT | KAPA Fall Forum 2014http://www.ksdot.org/Assets/wwwksdotorg/PDF_Files/QuickFacts2010.pdf



Thinlays: Option for New Construction and Preservation

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.

Thinlays for New and Existing Pavements


Desired Attributes and Thinlay Potential

Low

County roads, local roads, city streets with minimal truck traffi c,

parking lots, subdivision streets/driveways

* Smooth surface* Maintain grade/curb profile* Low permeability* Good workability

MediumMedium to high traffi cked 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 traffi cked 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 AttributesTraffic Level

Typical Roadway Types


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

Thinlay for Pavement Preservation

Thinlay Solutions to Observed Performance Problems

Minor Surface

Rutting3

Major Structural

Rutting (Subgrade

Issue)

Fatigue (Load)

Cracking)

Non Load Associated

Cracking4

Reflective Cracking

Thermal Cracking

Surface Friction

LossRaveling Stripping

Bleeding / Flushing

Low

County roads, local roads, city streets with minimal truck traffi c,

parking lots, subdivision streets/driveways

MediumMedium to high traffi cked city

streets, state routes, U.S. highways, rural interstates

High

Medium to high traffi cked city streets, state routes, U.S.

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 traffi c applications, polish resistant aggregate use for high traffi c application3) Mill ing may be required prior to the thin overlay4) Longintudinal cracking in wheel path may be fatigue related. Use caution if this distress is present. Mill ing and/or crack fill ing may be required prior to thin overlay5) Mill ing and/or crack fill ing may be required prior to thin overlay6) Mill ing of excess binder may be required prior to thin overlay

Traffic Level

Typical Roadway Types

Thinlay Solutions to Observed Performance Problems


Thinlay Structural Value to the Pavement

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.

Structural Layer Benefit of Thin Overlays

Source: Jim Huddleston, Thin Lay Presentation – Rocky Mountain Asphalt Conference 2014 KDOT | KAPA Fall Forum 2014

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.

Value of 1” of Pavement Structure

Thickness Reps to Failure Increased Fatigue Life From 1", %2 302343 71537 1374 160693 1255 340507 1126 682133 100

Source: Jim Huddleston, Thin Lay Presentation – Rocky Mountain Asphalt Conference 2014 KDOT | KAPA Fall Forum 2014

Thinlay Aggregates

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

Nominal Maximum Aggregate Size (NMAS)


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

Aggregate


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

Methylene Blue Test


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.

Grading

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


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

Use of 100% Screenings for Thinlays


http://ncat.us/files/reports/2002/rep02-10.pdf

http://ncat.us/files/reports/2002/rep02-10.pdf

Thinlay 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

Asphalt Binder


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.

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

4 to 6 percent Design VMA

15 to 17% Design VFA

65 to 80% Dust to Effective Asphalt Ratio

0.6 to 2.0

Mix Design Considerations – Typical Practices

Caution:• Pay special attention to the

relationship of air voids, VMA and VFA since any two of the three will automatically define the other.

Compaction / Volumetric Rule of Thumb• 25 Gyrations = 1% VMA = 0.4 AC%


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.

Design Air Voids


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.”

NCAT Research


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

Volume of Effective Binder Volume (Vbe)


Major Goal of Mix Design is to Have the Optimum Amount of Binder to Maximize Performance and Minimize Cost

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

Required Mix Binder Content for Specified Vbe

Property/Parameter ValueAggregate Blend Apparent Specific Gravity, Gsa 2.700Aggregate Blend Bulk Specific Gravity, Gsb 2.600Aggregate Effective Specific Gravity, Gse 2.650Design Air Voids, % 4.0Target Minimum Volume of Binder Effective (Vbe min), % 11.5Target Maximum Volume of Binder Effective (Vbe max), % 13.0Total Binder Content @ Vbe min, % 5.76 ROT: 0.1% Binder = 0.2% VbeTotal Binder Content @ Vbe max, % 6.47

Binder Content Required for Target Effective Binder Volume

CALC

INPU

T

DESCRIPTIONThis 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. KDOT | KAPA Fall Forum 2014

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.


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/reports/2013/rep13-05.pdf

Values less than 100 to 125 x 10-5 cm/s are generally referred to as “low permeability”.


http://www.ncat.us/files/reports/2013/rep13-05.pdf




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

http://www.okladot.state.ok.us/materials/pp/20080320.ppt

Thinlay Performance

Thin Overlays Performance - LTPP

http://isddc.dot.gov/OLPFiles/FHWA/006648.pdfNote: SPS-3 and SPS-4 experiments were constructed in 1990 to evaluate the effectiveness of preventive maintenance treatments for flexible and rigid pavement.


http://isddc.dot.gov/OLPFiles/FHWA/006648.pdf

http://isddc.dot.gov/OLPFiles/FHWA/006648.pdf


Thin Overlay Performance - International

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 KDOT | KAPA Fall Forum 2014


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


Shane Buchanan

Asphalt Performance Manager

Oldcastle Materials Company

[email protected]

205-873-3316

Thoughts and Questions?

http://www.pennyauctionwatch.com/

mailto:[email protected]

mailto:[email protected]

s hane b uchanan k ansas dot and k ansas a sphalt p avement a ssociation f all f orum n ovember 5,...

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