High Air Void Designed Mixes: Update. Rebecca McDaniel Missouri Asphalt Conference 11/28/17

Transcription

1 High Air Void Designed Mixes: Update Rebecca McDaniel Missouri Asphalt Conference 11/28/17

2 Perception Dry Mixes Various Approaches Minimum binder contents Changing Ndesign Lowering design air voids Others

3 Indiana s Approach Superpave5 Reduce field air voids in field to reduce permeability, improve durability without sacrificing rutting resistance. 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.

4 EXPECTATIONS OF CHANGING GYRATIONS Use same aggregate stockpiles Some changes may be needed to meet VMA (e.g., crushed sand) Decreasing gyrations Change in gradation/proportions Lower mix stiffness in lab Easier compaction in field Need equal or better final mechanical properties to prevent traffic densification 4

5 Research Approach Lab Start with three existing 100 gyration mix designs (4% air voids) Two 9.5 mm and one 19 mm 3-10 and million ESAL designs (~50% of INDOT work) Dolomite, limestone and blast furnace slag with PG 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

6 Experimental Matrix Traffic Level 3 10 million million No of Gyrations 30 X 50 X 70 X 100 * Mixture Type 9.5 mm 19.0 mm 30 X X 50 X X X 100 * *

7 Gradation Changes in 19.0 mm Mixes Sieve N100 N70 N50 N mm (¾ in) mm (½ in) mm (⅜ in) mm (#4) (#30) (#200) Mixes getting finer on fine sieves.

8 Summary of Mix Volumetrics Effective asphalt content was held constant (± 0.1 or 0.2%). As design air voids increased, VMA increased and VFA decreased. 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.

9 Conclusions from Lab Testing 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. 9

10 1 st Field Trial November 2013 SR-13 near Middlebury, IN 1.5 in (38 mm) mill and fill, million ESALs, 9.5-mm Original design, N100, 4% design air voids, 7% field target Redesigned, N50, 5% design air voids, 5% field target Steel slag coarse aggregate, limestone and natural sands, 7% RAS (20% BRR), PG 70-22

11 QA Volumetric Properties Property Superpave5 Superpave4 Binder Content, % Air Voids, % (at N des ) VMA, % (at N des ) Air Voids from Cores (6) No change in compaction equipment nor patterns!

12 Laboratory Testing Plant-produced mix N100 mix was stiffer than the N50 mix and had higher flow number. May or may not mean N50 will rut. Binder grading of recovered binders postconstruction and after simulating aging in the lab indicated the N50 mix aged less than the N100 mix.

13 2 nd Field Trial December 2014 Georgetown Rd, Indianapolis Reconstruction and widening Intermediate layer 3 inches, 330 lbs/yd million ESALs, 19.0-mm Original design, N100, 4% design, 7% field target Redesigned, N30, 5% design, 5% field target

14 QA Volumetrics Property N30 N100 DMF Sublot 1 Sublot 2 DMF Sublot 1 Binder Content Voids at Ndes VMA at Ndes Air Voids from Cores* * 20 cores each

15 Loose Mix Testing Results N30 mix had higher modulus (stiffer) than original at higher temperatures, similar at low temperatures. N30 mix had lower flow number but higher strain at flow number than original. Re-designed mix had higher critical strain energy release rate (J c ) in SCB tests. Similar or better rut resistance, better cracking resistance.

16 Third Field Trial November 2016 US40, Richmond 1.8 centerline miles; 4 lanes + turn lane 5 in. asphalt over concrete; mill and fill 1.5 in. Existing raveling, cracking, rutting AADT 17,790, 5% trucks 3-10 million design ESALs

17 FHWA Enhanced Density Initiative

18 Mix Designs (JMF) Property Control Superpave5 Gyrations Air Voids, % Binder Content, % Effective Binder VMA, % VFA, % PG 64-22, BRR ~ 23%

19 Gradations (JMF) Sieve Control Superpave

20 Mix Components Aggregate Control Superpave5 #11 Stone #12 Stone #24 Sand 22.0 Crushed Gravel Sand RAP RAS Baghouse Fines

21 Placement and Compaction 2 10-ton breakdown rollers 5 vib + 2 static passes each 1 finish roller 4 static passes

22 Sampling and Testing

23 Field Densities Results Control Superpave5 Average Density, % G mm Average Air Voids, % Standard Deviation % higher density without additional compactive effort!

24 Performance? SR13 US40

25 Conclusions to Date It is possible to design mixes at 5% air voids and maintain effective binder using mostly the same materials. Mixes designed with lower gyrations can have properties equal to or better than conventional designs. 50 gyrations seems reasonable for most mixes. Maybe 30 gyrations for low traffic volumes. Mixes designed at 5% air in lab can be compacted to 5% in the field with minimal to no changes in compaction process 25

26 What s Next? 2 Superpave5 projects in each district in 2018 (total of 12) Unique Special Provision

27 How to Spec Superpave5 Air Voids at Optimum Binder Content: 5.0% vs 4.0% 9.5, 12.5, 19.0 and 25.0mm mixes (not 4.75) Design Gyrations: 50 vs 75 or 100 <3 million, 3-10 million, >10 million VMA: 1.0% higher (16.0 for 9.5mm to 13.0 for 25mm) Minimal changes

28 Acceptance PWL VMA at Ndes LSL = Spec, USL = Spec+2.50 Air Voids at Ndes LSL = 3.60; USL = and 5.40 previously In-Place Density LSL = 93.00; USL = n/a 91.0 previously Smoothness up to 6% incentive

29 More Information JTRP Report on lab work and first two projects AAPT 2015, Modifying Laboratory Mixture Design to Improve Field Performance, pp JTRP Report on third project in publication search for author = Montoya Thanks to Ali Hekmatfar, Miguel Montoya and John Haddock

30 Questions? Rebecca S. McDaniel Technical Director North Central Superpave Center Purdue University West Lafayette, IN 765/ ext