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S HANE B UCHANAN K ANSAS DOT AND K ANSAS A SPHALT P AVEMENT A SSOCIATION F ALL F ORUM N OVEMBER 5, 2014 T OPEKA, K ANSAS 4.75 mm (Thinlay) Mixes With High.

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Presentation on theme: "S HANE B UCHANAN K ANSAS DOT AND K ANSAS A SPHALT P AVEMENT A SSOCIATION F ALL F ORUM N OVEMBER 5, 2014 T OPEKA, K ANSAS 4.75 mm (Thinlay) Mixes With High."— Presentation transcript:

1 S HANE B UCHANAN K ANSAS DOT AND K ANSAS A SPHALT P AVEMENT A SSOCIATION F ALL F ORUM N OVEMBER 5, 2014 T OPEKA, K ANSAS 4.75 mm (Thinlay) Mixes With High Air Void Content

2 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

3 Kansas Highway Information

4 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! KDOT | KAPA Fall Forum 2014

5 Congratulations! KDOT | KAPA Fall Forum elease2014/reasonsept 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 There is no report for 2010.

6 Performance KDOT | KAPA Fall Forum 2014

7 Kansas Road Miles and Vehicle Miles KDOT | KAPA Fall Forum 2014

8 Why Focus on Thin Overlay Potential? KDOT | KAPA Fall Forum 2014 National Stats 2/3 of the US Highway system is classified as low volume roadways ~5,600,000 lane miles Carry only 13% of total vehicle miles KANSAS Stats

9 Kansas Transportation Funding KDOT | KAPA Fall Forum 2014

10 Significant National Funding is Going Toward PP Efforts Source: Bureau of Transportation Statistics Obligation of Federal Funds for Roadway Projects  2/3 of funds go toward system preservation! Year 2012 =$18,363,789 System Preservation67% New Route9% Capacity Addition24% Year 2011 =$17,301,304 System Preservation65% New Route11% Capacity Addition24% KDOT | KAPA Fall Forum 2014

11 Thinlays: Option for New Construction and Preservation

12 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 KDOT | KAPA Fall Forum 2014

13 Desired Attributes and Thinlay Potential KDOT | KAPA Fall Forum 2014 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

14 Thinlay for Pavement Preservation

15 Thinlay Solutions to Observed Performance Problems KDOT | KAPA Fall Forum 2014

16 Thinlay Structural Value to the Pavement

17 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

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

19 Thinlay Aggregates

20 KDOT | KAPA Fall Forum 2014

21 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) KDOT | KAPA Fall Forum 2014

22 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 KDOT | KAPA Fall Forum 2014

23 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 KDOT | KAPA Fall Forum 2014

24 For the potentially relative small portion of coarse aggregate present the requirements (LA, soundness, flat and elongated, fractured face) should be in line with local agency requirements. Aggregate KDOT | KAPA Fall Forum 2014

25 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 to to to to 7040 to to 136 to 12 KDOT | KAPA Fall Forum 2014

26 100% 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  Use of 100% Screenings for Thinlays KDOT | KAPA Fall Forum 2014

27 Thinlay Asphalt Binder

28 Thinlay Binders KDOT | KAPA Fall Forum 2014

29 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 KDOT | KAPA Fall Forum 2014

30 Thinlay Mix Design Considerations

31 4.75 mm AASHTO M323 Specification KDOT | KAPA Fall Forum 2014 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. 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.

32 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% KDOT | KAPA Fall Forum 2014

33 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 KDOT | KAPA Fall Forum 2014

34 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 KDOT | KAPA Fall Forum 2014

35 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) KDOT | KAPA Fall Forum 2014 Major Goal of Mix Design is to Have the Optimum Amount of Binder to Maximize Performance and Minimize Cost

36 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 KDOT | KAPA Fall Forum 2014

37 Thinlay Permeability

38 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. KDOT | KAPA Fall Forum 2014

39 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.” s/2013/rep13-05.pdf s/2013/rep13-05.pdf Values less than 100 to 125 x 10-5 cm/s are generally referred to as “low permeability”. KDOT | KAPA Fall Forum 2014

40 Permeability KDOT | KAPA Fall Forum 2014 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 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).

41 Thinlay Performance

42 Thin Overlays Performance - LTPP Note: SPS-3 and SPS-4 experiments were constructed in 1990 to evaluate the effectiveness of preventive maintenance treatments for flexible and rigid pavement. KDOT | KAPA Fall Forum 2014

43 Thin Overlay Performance - International KDOT | KAPA Fall Forum 2014

44 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

45 4.75 mm Mix at the NCAT Test Track KDOT | KAPA Fall Forum 2014 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, N design = 50, 6.1% asphalt binder ¾” thickness (~75 lb/yd2) Very little cracking (1%) ~ 7 mm rutting ~50 IRI

46 Shane Buchanan Asphalt Performance Manager Oldcastle Materials Company Thoughts and Questions? KDOT | KAPA Fall Forum 2014


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