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Basics of Concrete Pavement Thickness Design

Basics of Concrete Pavement Thickness DesignConcrete Pavement Design Geometrics Thickness (es) Joints MaterialsConcrete Pavement Design Geometrics Thickness (es) Joints MaterialsMost Often Influence Cost& Selection of ProjectsCOSTC oncrete Pavement Design Geometrics Thickness (es) Joints MaterialsMost Often InfluenceReal-world PerformancePERFORMANCEC oncrete Pavement DesignPerformance FactorDesign AreaBlow-upsRandom crackingFaultingPumpingSpallsJointing & SubbaseMaterials Selection &ProportioningASRD-crackingFreeze-ThawSc alingSkid ResistanceThickness (Slab)Fatigue CrackingPrinciples of DesignLoad stressesVolume change stressesCurling/Warping stressesJointing orReinforcingThicknessThickness Design Procedures Empirical Design Procedures Based on observed performance AASHO Road Test Mechanistic Design Procedures Based on mathematically calculated Pavement responses PCA Design P

PAVEMENT DESIGN NCHRP 1-26 Phase II Final Report Pavement design is an a priori process. The new pavement will be built in the future, on subgrades often not yet exposed or accessible; using materials not yet manufactured from sources not yet identified; by a contractor who submitted the successful "low dollar" bid, employing unidentified

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Transcription of Basics of Concrete Pavement Thickness Design

1 Basics of Concrete Pavement Thickness DesignConcrete Pavement Design Geometrics Thickness (es) Joints MaterialsConcrete Pavement Design Geometrics Thickness (es) Joints MaterialsMost Often Influence Cost& Selection of ProjectsCOSTC oncrete Pavement Design Geometrics Thickness (es) Joints MaterialsMost Often InfluenceReal-world PerformancePERFORMANCEC oncrete Pavement DesignPerformance FactorDesign AreaBlow-upsRandom crackingFaultingPumpingSpallsJointing & SubbaseMaterials Selection &ProportioningASRD-crackingFreeze-ThawSc alingSkid ResistanceThickness (Slab)Fatigue CrackingPrinciples of DesignLoad stressesVolume change stressesCurling/Warping stressesJointing orReinforcingThicknessThickness Design Procedures Empirical Design Procedures Based on observed performance AASHO Road Test Mechanistic Design Procedures Based on mathematically calculated Pavement responses PCA Design Procedure (PCAPAV) Pavement DESIGNNCHRP 1-26 Phase II Final ReportPavement Design is an a priori new Pavement will be built in the future, on subgrades often not yet exposed or accessible; using materials not yet manufactured from sources not yet identified.

2 By a contractor who submitted the successful "low dollar" bid, employing unidentified personnel and procedures under climatic conditions that are frequently less than ideal. Thickness Design Considerations: Traffic Loads and Traffic Growth Subgrade and Subbases Drainage Concrete Properties Load Transfer ReliabilityDesign of Concrete PavementsAASHTO Design ProceduresAASHTO Guide for Design of Pavement Structures -1993 AASHO Road Test(1958-1960) Third Large Scale Road Test Maryland Road Test (1950-51)Rigid Pavements Only WASHO Road Test (1952-54)Flexible Pavements only Include both Rigid and Flexible Designs Include a wide range of axle loads and Pavement cross-sectionsAASHO Test LayoutAASHO Test Layout368 rigid test sections 468 flexible test sectionsMax Single AxleMax Tandem AxleAASHO Test TrafficAASHO Road Test PerformanceSurviving SectionsLoop (36 Sect)Asphalt (4 Sect)Loop ApplicationsServiceabilityLoop ApplicationsServiceabilityConcrete (38 Sect)Asphalt (10 Sect) Concrete (39 Sect)Asphalt (11 Sect) Concrete (47 Sect)Asphalt (17 Sect)

3 AASHTO Design Procedures & Changes1961-62 AASHO Interim Guide for the Design of Rigid and Flexible Pavements1972 AASHTO Interim Guide for the Design of Pavement Structures -19721981 Revised Chapter III on Portland Cement Concrete Pavement Design1986 Guide for the Design of Pavement Structures1993 Revised Overlay Design Procedures1998 Revised Portland Cement Concrete Pavement DesignLog(ESALs) Z*s+ *Log(D+1) ()+ + *10D7 + Normal DeviateOverallStandard DeviationDepth()+ *[]()LogS' *J* 025.**Change in ServiceabilityTerminal ServiceabilityDrainageCoefficientLoad TransferModulus ofRuptureModulus of ElasticityModulus ofSubgrade Reaction1986-93 Rigid Pavement Design EquationAASHTO Design TrafficESAL s or E-18 s The number and weight of all axle loads from the anticipated vehicles expected during the Pavement Design life -expressed in 18-kip (80kN) Equivalent Single Axle Loads for each type of Pavement .

4 Rigid ESAL s or E-18 s Flexible ESAL s or E-18 sAASHTO Design Traffic -ESALsEquivalent Number of 18k Single Axle LoadsESALs GENERATED BY DIFFERENT VEHICLES/DAYVEHICLENUMBERRIGIDESALsFLEXI BLEESALsSingle Units 2 Trailer 3 Trailer 4 Trailer 5 , Pickup, DESIGNT rafficLoad Equivalence Factor (LEF) The Ratio of the Effect (Damage) of a Specific Axle Load on Pavement Serviceability to the Effect Produced by an 18-kip Axle Load at the AASHO Road for each: Pavement TypeThicknessTerminal DESIGNT rafficLoad Equivalence Factor (LEF) No. of repetitions of 18-k SAL Load causing given PSI No.

5 Of repetitions of X-k Y-Axle Load for a same PSI Change for each: Pavement TypeThicknessTerminal Given Stress or Strain:LOAD EQUIVALENCY FACTORSFOR A GIVEN Pavement STRUCTURES tress or Strain of X-kip Load on Axle Type Y Stress or Strain of 18-kip Load on a Single AxleFor a Given Serviceability Loss:LOAD EQUIVALENCY FACTORSFOR A GIVEN Pavement STRUCTURE# of Repetitions of X-kip Load on Axle Type Y # of Repetitions of 18-kip Load on a Single AxlePSIPSIC oncreteResponseAsphaltResponseSince Pavement responses are different, the equivalency factors (LEFs) are different. When multiplying the traffic by the different equivalencies, you get different ESALsAASHTO Design TrafficSubgrade and Subbases Subbase Layer of material directly below the Concrete Pavement .

6 Subgrade Natural ground, graded, and compacted on which the Pavement is SectionSubgrade / SubbaseStrengthModulus of Subgrade Reaction, kReactionStacked PlatesHydraulic JackPressure GaugeDeflection Dial at 1/3 Pointsk (psi/in) = unit load on plate / plate deflection Subgrade and SubbasesDesign Subgrade strength is nota critical element in the Thickness Design . Has little impact on Thickness . Need to know if Pavement is on: Subgrade (k 100 psi/in.), Granular subbase (k 150 psi/in.), Asphalt treated subbase (k 300 psi/in.) Cement treated/lean Concrete subbase (k 500 psi/in.). AASHTO DESIGNS ubgrade StrengthTypical Soil RelationshipsSoil TypeStrengthk-value(psi / in.)

7 Mr(psi)CBRS ilts / ClaysVery Low50-1001000-1900<3 Fine soilsHigh220-2504300-4850> ,000+> ,000+>12 Subgrade and SubbasesPerformance Proper Design and construction are absolutely necessaryif the Pavement is to perform. Must be uniformthroughout Pavement s life. Poor subgrade/subbase preparation can not be overcome with Thickness . Any Concrete Pavement , built of any Thickness , will have problems on a poorly designed and constructed subgrade or subbase. UNIFORMITY:The KeyTo GOOD Pavement PERFORMANCED esign for Uniform Support Expansive soils Frost susceptible soils Pumping (loss of Support) Cut-fill transitions Poorly compacted excavations Utility work CulvertsSources of Non-Uniform SupportPAVEMENT DESIGNS ubbase EffectsThe current Design does not model the contribution of bases the AASHO Road Test, it was found that the Concrete pavements with granular bases could carry about 30% more traffic.

8 The current Design procedures allows Concrete pavements built with granular bases to carry about 5 -8% more Strength (S c) DeterminationHead of Testing MachineL/3 Span Length = Ld=L/3 Span Length = LL/2 Third-point LoadingCenter-point LoadingConcrete PropertiesConcrete Propertiesf c= Compressive Strength (psi)S c= Flexural Strength (psi)S c= 8-10 f cHead of Testing MachineCylinder DepthCompressive Strength f cConcrete PropertiesUse average, in-field strength for Design (not minimum specified)If specify minimum flexural strength at 28-day of 550 psi & allow 10% of beams to fall below minimum:STEP 1 Estimate SDEV.

9 9% for typical ready = 550 * = 50 psiSTEP 2S c Design = S c minimum+ z * SDEVS c Design = 550 + * 50S c Design = 614 psiDrainageConditions for Pumping Subgrade Soil that will go into Suspension Free water between Slab and Subgrade Frequent Heavy wheels loads / Large DeflectionsDrainage Major Conclusions For Doweled PCC Pavements, Drainage has little affect on Faulting Does reduce D-cracking Drainage significantly reduces fatigue cracking and rutting in AC Pavements Day lighted drainage works best with permeable basesNCHRP 1-34: Subsurface Drainage for PavementsLoad Transfer A slabs ability to share its load with neighboring slabs Dowels Aggregate Interlock Concrete Shoulders Tied Concrete , curb & gutter, and extended lane have same xU= 0 Poor Load TransferLoad TransferGood Load TransferL= x/2U= x/2 Aggregate InterlockShear between aggregate particlesbelow the initial saw cutAggregate InterlockDowel bars Lengths from 15-18 in.

10 In. min. embedment length Diameter in. for roads in. for airports Epoxy or other coating used in harsher climates for corrosion protectionDeflections in Concrete Pavement12 ft LanesOutside Pavement Edge (free edge)Longitudinal Centerline(acts as tied Concrete shoulder)Undoweled transverse JointDoweled transverse Joint2Di~ Di5Di~ DiDiDiLoad TransferAASHTO DESIGNE ffect of Dowels and + + + + +07789101112 ThicknessAllowable ESALsDowels & ShouldersDowels & No ShouldersNo Dowels & ShouldersNo Dowels & No ShouldersConcrete Pavement Design Exclude dowels if: Slab Thickness < in Include dowels if.


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