Superpave5

Asphalt Paving Conference Kansas University December 3, 2015

Marshall mix design – 3-5% Superpave mix design – 4%

Field Compaction – 7-8% air voids target Expect traffic to further densify mix to 4% Actual air voids can be >9%

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Reduce air voids in field to reduce permeability without sacrificing rutting resistance.

How? Design mixes at 5% air voids. Keep effective binder content constant for durability. Change gyration levels and adjust gradation. Maintain equal or better mechanical properties at

expected field conditions. Then compact to 5% air voids in the field.

Start with three existing mix designs Two 9.5 mm and one 19 mm 100 gyration mixes 3-10 and 10-30 million ESAL designs (~50% of INDOT work) Dolomite, limestone and blast furnace slag with PG 64-22

Re-design each mix at 5% voids at different gyration levels with same aggregates 70, 50 and 30 gyrations Maintain VMA and effective binder content in 5% void mixes Bailey method used to guide adjustments

Traffic Level No of Gyrations

Mixture Type

9.5 mm 19.0 mm

3 – 10 million

30 X

50 X

70 X

100 *

10 – 30 million

30 X X

50 X X

70 -- X

100 * *

0.0

10.0

20.0

30.0

40.0

50.0

60.0

70.0

80.0

90.0

100.0

Perc

ent P

assi

ng

Sieve Size Raised to the 0.45 Power, mm

N100N70N50N30

19.0 4.75 0.60 2.36 9.5 0.075 25.0 12.5

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12.5 4.75 1.18 0.075 0.0

20.0

40.0

60.0

80.0

100.0

Perc

ent P

assi

ng

Sieve Size raised to 0.45 power, mm

N100

N70

N50

N30

Sieve N100 N70 N50 N30 19.0 mm (¾ in) 97.4 97.4 96.1 95.3 12.5 mm (½ in) 86.4 86.4 79.9 75.5 9.5 mm (⅜ in) 77.0 77.4 68.4 62.1 4.75 mm (#4) 51.2 52.7 48.6 46.8 0.600 (#30) 14.6 15.3 15.3 16.6 0.075 (#200) 4.4 4.5 4.4 5.1

Mixes getting finer on fine sieves.

Effective asphalt content was held constant (within 0.1 or 0.2%)

As design air voids increased, VMA increased and VFA decreased then held fairly constant with changes in gyration levels.

Dust to binder ratio increased by up to 0.3% as gyration levels decreased (fines content increased), especially for N30 mixes.

Targeted volumetrics were achieved.

Dynamic Modulus Test

Stiffness

Rutting

Fatigue Cracking

Flow Number Test

Rutting

100 gyration mix tested at 7% air, redesigned mixes at 5% air (field compaction level)

With changes in gradation, mixes can be designed at 5% air voids with same effective binder content.

Re-designed mixes at 5% air can have equivalent or higher stiffnesses and higher rut resistance than mixes designed at 4% air compacted to 7% air.

Concept looked promising.

Field trial recommended and identified.

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1st Field Trial

• SR-13 near Ft. Wayne, IN

• 1.5 in (38 mm) mill and fill, 10-30 million ESALs, 9.5-mm

• Original design, N100, 4%, 7%

• Redesigned, N50, 5%, 5%

• Steel slag coarse aggregate, limestone and natural sands, 7% RAS (20% BRR), PG 70-22

Re-designed mix at 5% air voids had higher modulus and flow number than original mix (4% design compacted to 7%).

Original mix compacted to 5% air voids also had higher modulus and flow number than original mix at 7% air voids. Without changes in mix, however, compaction

could be difficult.

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Property Superpave5 Superpave4 DMF Average Average

Binder Content, % 5.2 5.2 5.1 Air Voids, % (50 gyr) 5.0 4.2 3.8 VMA, % (50 gyr) 17.0 16.7 14.8

Air Voids from Cores (6) 5.0 5.3 8.2

No change in compaction equipment nor patterns!

In-place Densities • N100, 9 sublots

• N50, 3 sublots

• N100, 18 cores, average density 91.8%

• N50, 6 cores, average density 94.7%

• Same rollers and rolling patterns

Laboratory Testing

Plant-produced mix – N100 mix was stiffer than the re-designed mix and had higher flow number. May or may not mean re-designed will rut.

Binder grading of recovered binders post-construction and after simulating aging in the lab indicates the re-designed mix aged less than the original mix.

2nd Field Trial • Georgetown Rd, Indianapolis

• Reconstruction and widening

• Intermediate layer 3 inches, 330 lbs/yd2

• 3-10 million ESALs, 19.0-mm

• Original design, N100, 4%, 7%

• Redesigned, N30, 5%, 5%

Conditions • 12-13 Dec 2014

• Temp 34 to 43F, light wind

QA Volumetric Properties N-30 N-100

DMF Sublot 1 Sublot 2 DMF Sublot 1

Pb, % 4.8 4.44 4.76 4.6 4.68

Va,% 5.0 5.8 5.2 4.0 4.4

VMA, % 15.1 14.5 14.7 13.4 12.9

Va from Cores* 3.6 4.9 7.8

* 20 cores each

Laboratory Testing Plan • Loose Mixtures (Post Construction, 8-year)

• Dynamic Modulus • Flow Number • Semi-Circular Bend (SCB)

• Cores (Post Construction, 8-year) • Density • Dynamic Modulus • Flow Number • SCB • Binder Recovery, Binder Grading

Re-designed mix had higher modulus (stiffer) than original at higher temperatures, similar at low temperatures.

Re-designed mix had lower flow number but higher strain at flow number than original.

Re-designed mix had higher critical strain energy release rate (Jc) in SCB tests.

Field Core Testing

Dynamic Modulus, Cores 38x110 mm vs.

100x150mm

Hamburg – both mixes had comparable, low rutting levels (<6 mm at 20,000 cycles, 50C)

Re-designed mix had slightly higher modulus values.

Small specimen protocol used. SCB – re-designed mix was similar to original post-

construction and significantly better after aging.

Suggests less cracking with re-designed mix. Recovered binder – somewhat less aging for re-

designed mixture.

It is possible to design mixes at 5% air voids and maintain effective binder using same materials.

Mixes designed with lower gyrations can have properties equal to or better than conventional designs.

Optimum gyrations levels ~42-53 for these mixes. 50 gyrations seems reasonable for most mixes. Maybe 30 gyrations for low traffic volumes.

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Mixes designed at 5% air in lab can be compacted to 5% in the field with minimal to no changes in compaction process

Testing of plant-produced mixes was generally favorable, especially when using field cores.

Field trial will show if rutting develops.

None to date.

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Potential 2-3 years of increased service life. Potential savings of $20-30 million a year.

Based on $300 million HMA rehab budget and that 50% of the HMA pavements reaching end of life do so because of durability problems.

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Concept of designing at higher voids (lower gyrations) still appears promising.

Time will tell how the field trial performs.

Need more field trials and tests of more mixes, more traffic categories.

Concept deserves further evaluation.

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Rebecca S. McDaniel Technical Director

North Central Superpave Center Purdue University West Lafayette, IN

765/463-2317 ext 226 rsmcdani@purdue.edu

https://engineering.purdue.edu/NCSC

Thanks to Gerry Huber, Bill Pine, HRG, Walsh & Kelly, Milestone Contractors, INDOT, Study Advisory Committee