Asphalt Concrete Mix Design

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Asphalt Concrete Mix Design. Superpave. Superpave Volumetric Mix Design. Goals Compaction method which simulates field Accommodates large size aggregates Measure of compactibility Able to use in field labs Address durability issues Film thickness Environmental. Specimen Preparation.
Transcript
Asphalt Concrete Mix DesignSuperpaveSuperpave Volumetric Mix Design
  • Goals
  • Compaction method which simulates field
  • Accommodates large size aggregates
  • Measure of compactibility
  • Able to use in field labs
  • Address durability issues
  • Film thickness
  • Environmental
  • Specimen Preparation
  • Mechanical mixer
  • 0.170 Pa-s binder viscosity
  • Short term oven aging
  • 4 hours at 135°C
  • 2 hours at 135°C (optional)
  • Mixing/Compaction TempsViscosity, Pa s1051.5Compaction Range.3.2Mixing Range.1100110120130140150160170180190200Temperature, C150 mmSpecimen Preparation
  • Specimen Height
  • Mix Design - 115 mm (4700 g)
  • Moisture Sens. - 95 mm (3500 g)
  • Loose Specimen for Max. Theor. (Rice)
  • varies with nominal max size
  • 19 mm (2000 g)
  • 12.5 mm (1500 g)
  • MixingPlace pre-heated aggregate in bowl and add hot asphaltMixingPlace bowl on mixer and mix until aggregate is well-coatedShort Term AgingEmpty mix into pan and place in oven to simulate short term aging2 hours for low absorption aggregates4 hours for high absorption aggregatesShort Term Aging Important
  • Allows time for aggregate to absorb asphalt
  • Helps minimize variability in volumetric calculations
  • Most terms dependent upon volumes which change with changes in the amount (volume) of absorbed asphalt
  • CompactionPlace funnel on top of mold and place mix in mold.Take care not to allow the mix to segregate.CompactionPlace another paper on top of mix and place mold in compactor.CompactionExample of typical full-size compactors.CompactionKey Components of Gyratory Compactorheightmeasurementcontrol and dataacquisition panelreactionframeloadingrammoldtilt barrotatingbaseCompaction
  • Gyratory compactor
  • Axial and shearing action
  • 150 mm diameter molds
  • Aggregate size up to 37.5 mm
  • Height measurement during compaction
  • Allows densification during compaction to be evaluated
  • Ram pressure600 kPa1.25oCompactionAfter aging, take mix and preheated mold from oven. Place paper in bottom of mold.CompactionOnce compaction is finished, extrude sample from mold.CompactionRemove the paper and label samples.SGC Results% Gmm10 100 1000Log GyrationsThree Points on SGC Curve% GmmNmaxNdesNini10 100 1000Log GyrationsDesign Compaction
  • Ndes based on
  • average design high air temp
  • traffic level
  • Log Nmax = 1.10 Log Ndes
  • Log Nini = 0.45 Log Ndes
  • % GmmNmaxNdesNini10 100 1000Log GyrationsData Presentation% Gmm10098Nmax = 17496Ndes = 10994Nini = 892Specimen 190Specimen 288Average86841101001000Number of GyrationsSuperpave Mix Design AnalysisSuperpave Testing
  • Specimen heights
  • Mixture volumetrics
  • Air voids
  • Voids in mineral aggregate (VMA)
  • Voids filled with asphalt (VFA)
  • Mixture density characteristics
  • Dust proportion
  • Moisture sensitivity
  • Superpave Mix Designgw Vmx
  • Gmb (estimated) = Wm
  • Where: Wm = mass of specimen, g Vmx = volume of compaction mold (cm3) gw = density of water, g/cm3Assumption: specimen is smooth-sided cylinderSuperpave Mix Design
  • However, surface irregularities cause the volume of the specimen to be slightly less than volume of cylinder
  • Actual bulk specific gravity measurement of compacted sample used to determine correction factor, C:
  • Gmb (measured)Gmb (estimated)C = % Gmm = Gmb (estimated) C / Gmm (measured)Superpave Mix Design
  • Determine mix properties at NDesign and compare to criteria
  • Air voids 4% (or 96% Gmm)
  • VMA See table
  • VFA See table
  • %Gmm at Nini < 89%
  • %Gmmat Nmax < 98%
  • Dust proportion 0.6 to 1.2
  • SGC Results% GmmIncreasing asphalt cement content96% (4% Voids)NdesNmaxNini10 100 1000Log GyrationsEach line = avg. of two samplesSuperpave Mix Design
  • VMA requirements:
  • Nominal max agg size Min. VMA
  • 9.5 mm 15
  • 12.5 mm 14
  • 19 mm 13
  • 35 mm 12
  • 37.5 mm 11
  • Superpave Mix Design
  • VFA requirements:
  • Traffic (millions of ESALs) Range of VFA
  • < 0.3 70 to 801 to 3 65 to 78> 3.0 65 to 75% weight of - 0.075 material% weight of effective asphalt0.6 << 1.2Superpave Mix DesignEffective asphalt content is asphalt on surface of aggregate(asphalt not absorbed by aggregate)Superpave Mix Design
  • Moisture Sensitivity
  • Prepare set of 6 specimens
  • 6 to 8% voids
  • Represents anticipated in-service voids
  • Determine tensile strength of 3 of specimens
  • Condition remaining 3 in water bath (60oC, 24 hr.)
  • Option for freeze cycle
  • Bring to test temperature (25oC) and determine wet (conditioned) tensile strength
  • Moisture SensitivityAASHTO T 283
  • Measured on proposed aggregate blend and asphalt content
  • Reduced compactive effort to increase voids
  • 3 Conditioned Specimens3 Dry SpecimensVacuum saturate specimensSoak at 60oC for 24 hoursSoak at 25oC for 2 hoursAvg. wet tensile strengthTSR = Avg. dry tensile strengthMoisture SensitivityAASHTO T 283Determine the tensile strengths of both sets of 3 specimensCalculate the Tensile Strength Ratio (TSR)Minimum of 80% needed Moisture SensitivityAASHTO T 283Indirect tensile strength apparatus for 100 mm specimensExample of Superpave Mix DesignTrial Gradations19.0 mm Nominal Mixture100.090.080.070.0Trial Blend 3Trial Blend 160.050.0% PASSING40.0Trial Blend 230.020.010.00.00.0752.36 19.0Sieve Size (mm) raised to 0.45 power Aggregate Consensus Properties
  • Blended Aggregate properties are determined
  • Property Criteria Blend 1 Blend 2 Blend 3Coarse Ang. 95%/90% min. 96%/92% 95%/92% 97%/93%Fine Ang. 45% min. 46% 46% 48%FLat/Elong. 10% max. 0% 0% 0%Sand Equiv. 45 min. 59 58 54Combined Gsb n/a 2.699 2.697 2.701Combined Gsa n/a 2.768 2.769 2.767Compaction Characteristics%Gmm
  • Blend %AC Nini Ndes Nmax
  • 1 4.3% 86.9% 96.0% 97.4%
  • 2 4.5% 85.9% 96.0% 97.7%
  • 3 4.7% 87.1% 96.0% 97.3%
  • Volumetric Properties Blend %AC %Air %VMA %VFA DP1 4.3% 4.0% 12.7% 68.5% 0.862 4.5% 4.0% 13.0% 69.2% 0.783 4.0% 4.0% 13.5% 70.1% 0.88VFABlend 3% binderVa% binder% binder%Gmm at NiniDP%Gmm at Nmax% binder% binderSelection of Design Asphalt Binder ContentVMA% binderQuestions - ?
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