瀝青混凝土配合比設計聯(lián)邦公路管理局PPT課件

1、1Specimen Preparation Mechanical mixer0.170 Pa-s binder viscosity Short term oven aging4 hours at 135C 2 hours at 135C (optional)第1頁/共40頁2 Compaction RangeMixing RangeMixing/Compaction Temps第2頁/共40頁3Specimen Preparation Specimen HeightMix Design - 115 mm (4700 g)Moisture Sens. - 95 mm (3500 g) Loose

2、 Specimen for Max. Theor. (Rice)varies with nominal max size19 mm (2000 g)12.5 mm (1500 g)第3頁/共40頁4Place pre-heated aggregate in bowl and add hot asphaltMixing第4頁/共40頁5MixingPlace bowl on mixer and mix until aggregate is well-coated第5頁/共40頁6Empty mix into pan and place in oven to simulate short term

3、 aging2 hours for low absorption aggregates4 hours for high absorption aggregatesShort Term Aging第6頁/共40頁7Short Term Aging ImportantAllows time for aggregate to absorb asphaltHelps minimize variability in volumetric calculationsMost terms dependent upon volumes which change with changes in the amoun

4、t (volume) of absorbed asphalt第7頁/共40頁8CompactionPlace funnel on top of mold and place mix in mold.Take care not to allow the mix to segregate.第8頁/共40頁9CompactionPlace another paper on top of mix and place mold in compactor.第9頁/共40頁10Example of typical full-size compactors.Compaction第10頁/共40頁11react

5、ionframerotatingbaseloadingramcontrol and dataacquisition panelmoldheightmeasurementtilt barKey Components of Gyratory CompactorCompaction第11頁/共40頁12Compaction Gyratory compactor Axial and shearing action 150 mm diameter molds Aggregate size up to 37.5 mm Height measurement during compaction Allows

6、densification during compaction to be evaluated1.25oRam pressure600 kPa第12頁/共40頁13After aging, take mix and preheated mold from oven. Place paper in bottom of mold.Compaction第13頁/共40頁14Once compaction is finished, extrude sample from mold.Compaction第14頁/共40頁15CompactionRemove the paper and label sam

7、ples.第15頁/共40頁16SGC Results% GmmLog Gyrations101001000第16頁/共40頁17Three Points on SGC Curve第17頁/共40頁18Design Compaction Ndes based onaverage design high air temptraffic level Log Nmax = 1.10 Log Ndes Log Nini = 0.45 Log Ndes% GmmLog Gyrations10 100 1000NiniNdesNmax第18頁/共40頁19Data Presentation第19頁/共40

8、頁20Superpave Mix Design Analysis第20頁/共40頁21Superpave TestingSpecimen heightsMixture volumetricsAir voidsVoids in mineral aggregate (VMA)Voids filled with asphalt (VFA)Mixture density characteristicsDust proportionMoisture sensitivity第21頁/共40頁22 Gmb (estimated) = Wm Superpave Mix Designgw VmxWhere:Wm

9、 = mass of specimen, gVmx = volume of compaction mold (cm3)gw = density of water, g/cm3Assumption: specimen is smooth-sided cylinder第22頁/共40頁23 However, surface irregularities cause the volume of the specimen to be slightly less than volume of cylinder Actual bulk specific gravity measurement of com

10、pacted sample used to determine correction factor, C:Superpave Mix DesignC = Gmb (measured)Gmb (estimated)% Gmm = Gmb (estimated) C / Gmm (measured)第23頁/共40頁24Superpave Mix Design Determine mix properties at NDesign and compare to criteria Air voids 4% (or 96% Gmm) VMA See table VFA See table %Gmm a

11、t Nini 89% %Gmmat Nmax 98% Dust proportion 0.6 to 1.2第24頁/共40頁25SGC Results% GmmLog Gyrations101001000Increasing asphalt cement contentEach line = avg. of two samplesNiniNdesNmax96% (4% Voids)第25頁/共40頁26 VMA requirements: Nominal max agg sizeMin. VMA 9.5 mm15 12.5 mm14 19 mm13 35 mm12 37.5 mm11Super

12、pave Mix Design第26頁/共40頁27 VFA requirements: Traffic (millions of ESALs) Range of VFASuperpave Mix Design 3.065 to 75第27頁/共40頁28% weight of - 0.075 material% weight of effective asphalt0.6 1.2Effective asphalt content is asphalt on surface of aggregate(asphalt not absorbed by aggregate)Superpave Mix

13、 Design第28頁/共40頁29 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 (conditi

14、oned) tensile strengthSuperpave Mix Design第29頁/共40頁30Moisture SensitivityAASHTO T 283Measured on proposed aggregate blend and asphalt contentReduced compactive effort to increase voids3 Conditioned Specimens3 Dry SpecimensVacuum saturate specimensSoak at 60oC for 24 hoursSoak at 25oC for 2 hours第30頁

15、/共40頁31Calculate the Tensile Strength Ratio (TSR)Minimum of 80% needed Moisture SensitivityAASHTO T 283Determine the tensile strengths of both sets of 3 specimensTSR = Avg. wet tensile strengthAvg. dry tensile strength第31頁/共40頁32Moisture SensitivityAASHTO T 283Indirect tensile strength apparatus for

16、 100 mm specimens第32頁/共40頁33Example of Superpave Mix Design第33頁/共40頁34Trial GradationsSieve Size (mm) raised to 0.45 power % PASSING0.010.020.030.040.050.060.070.080.090.0100.019.02.36 0.07519.0 mm Nominal MixtureTrial Blend 1Trial Blend 2Trial Blend 3第34頁/共40頁35Aggregate Consensus PropertiesBlended

17、 Aggregate properties are determinedPropertyCriteriaBlend 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 2.767第35頁/共40頁36 Blend %AC NiniNdes Nmax1 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%Compaction Characteristics第36頁/共40頁37 Blend %AC %Air %VMA %VFA DP1 4.3% 4.0% 12.7% 68.