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Sup erior Per forming Asphalt Pave ments

Sup erior Per forming Asphalt Pave ments. Performance based design system testing and design procedures simulate closer to the actual loading and climatic conditions performance graded asphalt binders aggregate specifications hot mix asphalt design and analysis system

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Sup erior Per forming Asphalt Pave ments

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  1. Superior Performing Asphalt Pavements • Performance based design system • testing and design procedures simulate closer to the actual loading and climatic conditions • performance graded asphalt binders • aggregate specifications • hot mix asphalt design and analysis system • Level 1 material selection and volumetric design • Level 2 Level 1 design + performance testing • Level 3 Level 1 design + more performance testing • Enhanced mix performance • Permanent deformation • Fatigue Cracking and Low temperature cracking ENCI 579 8

  2. Superpave • SHRP established 1987 - 5 yrs. • Binder specs in use by 100% of US, Ont., Quebec in Canada • Level 1 Mix design - partial use • Still to come • simple performance tests • performance prediction models ENCI 579 8

  3. Superpave Mixture Design • Key features are laboratory compaction and performance testing • Laboratory compaction • Superpave gyratory compactor (SGC) • compacts test specimens to simulate actual pavement and loading conditions • provides information about the compactability of a particular mixture • design mixtures that do not exhibit tender mix behavior and do not densify to low air voids under traffic ENCI 579 8

  4. Superpave Mixture Design • Performance testing and performance prediction models • detailed predictions of actual pavement performance in terms of ESAL’s • Superpave Shear tester (been replaced by triaxial) • Indirect Tensile tester • Short term aging protocol • performance of HMA immediately after construction is influenced by mix properties from hot mixing and compaction • oven aged mix at 135 C 4 hours to simulate delays that can occur during construction ENCI 579 8

  5. Superpave Mixture Design ENCI 579 8

  6. Level 1 Mix Design • Volumetric mix design • Select asphalt and aggregate materials • develop several aggregate trial blends (3) that meet Superpave aggregate specs • blend asphalt, compact, analyze • use best blend with several asphalt contents to determine the design asphalt content at 4% air voids and compare to other criteria ENCI 579 8

  7. Gyratory Compactor • Better simulates field compaction than hammer • Compacts specimen but also measures density during compaction • Measures compactibility so tender mixes are identifies • Larger size aggregate blends can be used (50 mm max size) because of larger mold sizes ENCI 579 8

  8. Amount of compaction depends on traffic and climate • Ndes is the design number of gyrations used for volumetric properties • Nmax < 98%, Nini < 89% of max. density - used to indicate compactibility • Log Nmax = 1.1 Log Ndes • Log Nini = .45 Log Ndes

  9. Trial Blends • The available aggregate stockpiles are combined in varying percentages, 3 blends are usually considered • Aggregate properties are determined (either on blends or estimated from individual aggregates) • Compact each blend and estimate volumetric properties ENCI 579 8

  10. Trial Blends • For each aggregate trial blend: • Asphalt binder grade selected • Mixing temperature (non modified) • viscosity .15 - .19 Pa-s (150 – 190 mm2/s) • Compaction temperature • viscosity = 0.25 - .31 Pa-s (250 – 310 mm2/s) • Prepare aggregates • 2 specimens for each trial blend : 2 x 4700g for compaction • 1 approx. 2000g for max density (uncompacted mix) • 1 x 3700 g for moisture sensitivity ENCI 579 8

  11. Trial Blends • Heat, mix with asphalt and short term age for 4 hours at 135°C representing possible delays in the field • Compact specimens for Nmax gyrations, recording height ENCI 579 8

  12. Data Analysis • Measure density at Nmax, using volume of cylinder calculate estimated density at Nmax, Nini, Ndes • Errors in estimated densities due to surface irregularities of briquette are corrected using ratio of measured to estimated density at Nmax • Measure Max. theoretical density of the uncompacted mix • Calculate air voids, VMA, VFA at Ndes ENCI 579 8

  13. Data Analysis • When you calculate your air voids you want to be at 4%……….. • Estimate asphalt content at 4% using Pb,est = Pbi - (.4x(4-AV%)) • Calculate corrected values of design VMA and VFA for 4% air voids using • VMAest = VMAinitial+C x (4-AV%) where C = .1 if AV% < 4% or .2 if AV% > 4% • VFAest = ( VMAest- 4) / VMAest ENCI 579 8

  14. Blend Selection • Check blend properties against design criteria • VMA VFA meets table 6-14,6-15 in text • Nini < 89%, Nmax < 98% of max density • passes moisture sensitivity (T283) • 80 % minimum indirect tensile strength • dust content (% passing 0.075 mm sieve divided by effective asphalt content) between .6 and 1.2 • Choose best blend - new samples ( 2 compaction 2 max density) are made and checked • Pb @ 4% AV • one at 0.5% less • 2 more at 0.5% and 1% higher • volumetric properties calculated at each a/c content • a/c content at 4 % chosen other criteria checked ENCI 579 8

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  16. Level 2 & 3 Design • Performance tests for permanent deformation fatigue cracking and low temperature cracking • Superpave Shear Tester (SST) (been replaced by triaxial) • Indirect Tensile Tester (IDT) • Lab testing has not yet been validated with field results and is still in experimental stage • Current expectations are that Level 2 & 3 will be combined into one and Level 1 will include an additional simplified stability test • At present research - triaxial testing for rutting and fatigue and indirect tension test for thermal cracking - presently being evaluated ENCI 579 8

  17. Example - Level 1 • Interstate 43 in Milwaukie, Wisconsin • Nominal max aggregate size = 19mm • Design ESALs = 18,000,000 • this would actually require a level 3 design ENCI 579 8

  18. Select a PG 58-34 • mix temp = 165 to 172°C • compaction temp = 151 to 157°C • 5 stockpiles - measure bulk and apparent specific gravities ENCI 579 8

  19. Measure 4 consensus properties • can measure blends but will use individual in this case to estimate blend properties which has an advantage in choosing blends • final design blends must meet criteria not individual stockpiles ENCI 579 8

  20. 3 blends are produced • 1 - Intermediate, 2 - Coarse, 3 - Fine ENCI 579 8

  21. Blends are checked against gradation requirements and for consensus properties - all 3 pass ENCI 579 8

  22. Trial asphalt content • absorption water calculated from bulk and apparent specific gravities of aggregate blends • Absorption water % = 100 (1/Gsb-1/Gsa) • Blend 1 = .9% water absorption • Blend 2 = 1.0%, Blend 3 = .9% • From table 6-12 in text, initial binder content is 4.4% for all 3 blends • Two samples of each blend are compacted using Nini = 8, Ndes = 109, Nmax = 174 (from design table table 6-13 text) • Maximum and bulk specific gravities (RD) (Gmm, Gmb) are measured and compactor data obtained ENCI 579 8

  23. Trial Blend 1 ENCI 579 8

  24. Trial Blend 1 ENCI 579 8

  25. Trial Blend 2 ENCI 579 8

  26. Trial Blend 2 ENCI 579 8

  27. Trial Blend 3 ENCI 579 8

  28. Trial Blend 3 ENCI 579 8

  29. The % max density at Nini , Ndes, Nmax is calculated from an average of the two samples of each blend • Calculated air voids and VMA at Ndes • AV = 100 - %Gmm • 1 = 100-96.2 = 3.8%, 2 = 4.3%, 3=4.8% • %VMA = 100 - (%Gmm x Gmm x (1 - Pbi))/Gsb • 1 = 100-(96.2x2.563x.956)/2.699 = 12.7% • 2 = 13.0% • 3 = 13.5%

  30. Estimate properties @ 4% air voids • Pb,est = Pbi - (.4 x(4-AV)) • 1 = 4.4-(.4x(4-3.8)) = 4.3% • 2 = 4.5% • 3 = 4.7% • VMAest = VMAinitial + C x (4 - AV) • 1 = 12.7 + (.1 x (4.0 - 3.8)) = 12.7% • 2 = 13.0 + (.2 x (4.0 - 4.3)) = 13.0% • 3 = 13.5 + (.2 x (4.0 - 4.8)) = 13.4% • %VFAest = 100x (VMAest - 4)/VMAest • 1 = 100 x (12.7 - 4.0)/12.7 = 68.5% • 2 = 69.2% • 3 = 70.1% ENCI 579 8

  31. Estimate properties at 4% Air Voids • %Gmm,est @ Nini = % Gmm,trial - (4-Av,trial) • 1 = 87.1-(4-3.8) = 86.9% • 2 = 85.9% • 3 = 87.1% • Similarly for Nmax • 1 = 97.4% • 2 = 97.7% • 3 = 97.3% • Results for 4% air voids for 3 blends: ENCI 579 8

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  33. ENCI 579 8

  34. Dust ration = P0.75/Pbe,est • 1 = 3.1/3.6 = .86 • 2 = 2.9/3.7 = .78 • 3 = 3.5/4.0 = .88 • All pass with values between .6 and 1.2 • Blend 1 fails VMA, blend 2 just meets VMA, therefore select blend 3 • If no blends were acceptable start over with new stockpile ratios • Evaluate blend 3 as before by mixing 2 specimens with 4.2%, 4.7%, 5.2% and 5.7% AC contents • Note: this time aggregate consensus properties must be measured on the blends and not calculated from stockpile values ENCI 579 8

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  41. Calculating mix volumetric properties (not estimating) for the final blend use: • Calculated air voids, VMA, VFA at Ndes%AV = 100 - %Gmm%VMA = 100 - (%Gmm x Gmm x (1 - Pbi))/Gsb%VFA = 100 x ((VMA - AV)/VMA) ENCI 579 8

  42. ENCI 579 8

  43. Blend is tested for moisture sensitivity and has tensile strength ratio of 82.6% which exceed the 80% minimum requirement • This blend meets all required design criteria and is approved for use! ENCI 579 8

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