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ENCI 579 81 Superior Performing Asphalt Pavements zPerformance based design system ytesting and design procedures simulate closer to the actual loading.

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Presentation on theme: "ENCI 579 81 Superior Performing Asphalt Pavements zPerformance based design system ytesting and design procedures simulate closer to the actual loading."— Presentation transcript:

1 ENCI Superior Performing Asphalt Pavements zPerformance based design system ytesting and design procedures simulate closer to the actual loading and climatic conditions yperformance graded asphalt binders yaggregate specifications yhot mix asphalt design and analysis system xLevel 1 material selection and volumetric design xLevel 2 Level 1 design + performance testing xLevel 3 Level 1 design + more performance testing yEnhanced mix performance xPermanent deformation xFatigue Cracking and Low temperature cracking

2 ENCI Superpave zSHRP established yrs. zBinder specs in use by 100% of US, Ont., Quebec in Canada zLevel 1 Mix design - partial use zStill to come ysimple performance tests yperformance prediction models

3 ENCI Superpave Mixture Design yKey features are laboratory compaction and performance testing yLaboratory compaction xSuperpave gyratory compactor (SGC) xcompacts test specimens to simulate actual pavement and loading conditions xprovides information about the compactability of a particular mixture xdesign mixtures that do not exhibit tender mix behavior and do not densify to low air voids under traffic

4 ENCI Superpave Mixture Design zPerformance testing and performance prediction models ydetailed predictions of actual pavement performance in terms of ESAL’s ySuperpave Shear tester (been replaced by triaxial) yIndirect Tensile tester zShort term aging protocol xperformance of HMA immediately after construction is influenced by mix properties from hot mixing and compaction xoven aged mix at 135 C 4 hours to simulate delays that can occur during construction

5 ENCI Superpave Mixture Design

6 ENCI Level 1 Mix Design zVolumetric mix design zSelect asphalt and aggregate materials zdevelop several aggregate trial blends (3) that meet Superpave aggregate specs zblend asphalt, compact, analyze zuse best blend with several asphalt contents to determine the design asphalt content at 4% air voids and compare to other criteria

7 ENCI Gyratory Compactor zBetter simulates field compaction than hammer zCompacts specimen but also measures density during compaction zMeasures compactibility so tender mixes are identifies zLarger size aggregate blends can be used (50 mm max size) because of larger mold sizes

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9 zAmount of compaction depends on traffic and climate zN des is the design number of gyrations used for volumetric properties zN max < 98%, N ini < 89% of max. density - used to indicate compactibility zLog N max = 1.1 Log N des zLog N ini =.45 Log N des

10 ENCI Trial Blends zThe available aggregate stockpiles are combined in varying percentages, 3 blends are usually considered zAggregate properties are determined (either on blends or estimated from individual aggregates) zCompact each blend and estimate volumetric properties

11 ENCI Trial Blends zFor each aggregate trial blend: zAsphalt binder grade selected zMixing temperature (non modified) yviscosity Pa-s (150 – 190 mm2/s) zCompaction temperature yviscosity = Pa-s (250 – 310 mm2/s) zPrepare aggregates y2 specimens for each trial blend : 2 x 4700g for compaction y1 approx. 2000g for max density (uncompacted mix) y1 x 3700 g for moisture sensitivity

12 ENCI Trial Blends zHeat, mix with asphalt and short term age for 4 hours at 135°C representing possible delays in the field zCompact specimens for N max gyrations, recording height

13 ENCI Data Analysis zMeasure density at N max, using volume of cylinder calculate estimated density at N max, N ini, N des zErrors in estimated densities due to surface irregularities of briquette are corrected using ratio of measured to estimated density at N max zMeasure Max. theoretical density of the uncompacted mix zCalculate air voids, VMA, VFA at N des

14 ENCI Data Analysis zWhen you calculate your air voids you want to be at 4%……….. zEstimate asphalt content at 4% using P b,est = P bi - (.4x(4-AV%)) zCalculate corrected values of design VMA and VFA for 4% air voids using yVMA est = VMA initial +C x (4-AV%) where C =.1 if AV% 4% yVFA est = ( VMA est - 4) / VMA est

15 ENCI Blend Selection zCheck blend properties against design criteria yVMA VFA meets table 6-14,6-15 in text yN ini < 89%, N max < 98% of max density ypasses moisture sensitivity (T283) x80 % minimum indirect tensile strength ydust content (% passing mm sieve divided by effective asphalt content) between.6 and 1.2 zChoose best blend - new samples ( 2 compaction 2 max density) are made and checked yP 4% AV yone at 0.5% less y2 more at 0.5% and 1% higher xvolumetric properties calculated at each a/c content xa/c content at 4 % chosen other criteria checked

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17 ENCI Level 2 & 3 Design zPerformance tests for permanent deformation fatigue cracking and low temperature cracking ySuperpave Shear Tester (SST) ( been replaced by triaxial) yIndirect Tensile Tester (IDT) zLab testing has not yet been validated with field results and is still in experimental stage zCurrent expectations are that Level 2 & 3 will be combined into one and Level 1 will include an additional simplified stability test zAt present research - triaxial testing for rutting and fatigue and indirect tension test for thermal cracking - presently being evaluated

18 ENCI Example - Level 1 zInterstate 43 in Milwaukie, Wisconsin zNominal max aggregate size = 19mm zDesign ESALs = 18,000,000 ythis would actually require a level 3 design

19 ENCI zSelect a PG ymix temp = 165 to 172°C ycompaction temp = 151 to 157°C z5 stockpiles - measure bulk and apparent specific gravities

20 ENCI zMeasure 4 consensus properties ycan measure blends but will use individual in this case to estimate blend properties which has an advantage in choosing blends yfinal design blends must meet criteria not individual stockpiles

21 ENCI z3 blends are produced y1 - Intermediate, 2 - Coarse, 3 - Fine

22 ENCI zBlends are checked against gradation requirements and for consensus properties - all 3 pass

23 ENCI zTrial asphalt content yabsorption water calculated from bulk and apparent specific gravities of aggregate blends yAbsorption water % = 100 (1/Gsb-1/Gsa) yBlend 1 =.9% water absorption yBlend 2 = 1.0%, Blend 3 =.9% zFrom table 6-12 in text, initial binder content is 4.4% for all 3 blends zTwo samples of each blend are compacted using N ini = 8, N des = 109, N max = 174 (from design table table 6-13 text) zMaximum and bulk specific gravities (RD) (G mm, G mb ) are measured and compactor data obtained

24 ENCI Trial Blend 1

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26 ENCI Trial Blend 2

27 ENCI Trial Blend 2

28 ENCI Trial Blend 3

29 ENCI Trial Blend 3

30 zCalculated air voids and VMA at N des yAV = %G mm x1 = = 3.8%, 2 = 4.3%, 3=4.8% y%VMA = (%G mm x G mm x (1 - P bi ))/G sb x1 = 100-(96.2x2.563x.956)/2.699 = 12.7% x2 = 13.0% x3 = 13.5% The % max density at N ini, N des, N max is calculated from an average of the two samples of each blend

31 ENCI zEstimate 4% air voids yP b,est = P bi - (.4 x(4-AV)) x1 = 4.4-(.4x(4-3.8)) = 4.3% x2 = 4.5% x3 = 4.7% yVMA est = VMA initial + C x (4 - AV) x1 = (.1 x ( )) = 12.7% x2 = (.2 x ( )) = 13.0% x3 = (.2 x ( )) = 13.4% y%VFA est = 100x (VMA est - 4)/VMA est x1 = 100 x ( )/12.7 = 68.5% x2 = 69.2% x3 = 70.1%

32 ENCI zEstimate properties at 4% Air Voids Nini = % Gmm,trial - (4-Av,trial) x1 = 87.1-(4-3.8) = 86.9% x2 = 85.9% x3 = 87.1% ySimilarly for Nmax x1 = 97.4% x2 = 97.7% x3 = 97.3% yResults for 4% air voids for 3 blends:

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35 ENCI zDust ration = P0.75/Pbe,est x1 = 3.1/3.6 =.86 x2 = 2.9/3.7 =.78 x3 = 3.5/4.0 =.88 xAll pass with values between.6 and 1.2 zBlend 1 fails VMA, blend 2 just meets VMA, therefore select blend 3 zIf no blends were acceptable start over with new stockpile ratios zEvaluate blend 3 as before by mixing 2 specimens with 4.2%, 4.7%, 5.2% and 5.7% AC contents zNote: this time aggregate consensus properties must be measured on the blends and not calculated from stockpile values

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42 ENCI Calculating mix volumetric properties (not estimating) for the final blend use: zCalculated air voids, VMA, VFA at N des %AV = %G mm %VMA = (%G mm x G mm x (1 - P bi ))/G sb %VFA = 100 x ((VMA - AV)/VMA)

43 ENCI

44 ENCI zBlend is tested for moisture sensitivity and has tensile strength ratio of 82.6% which exceed the 80% minimum requirement zThis blend meets all required design criteria and is approved for use!


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