La Nueva AASHTO Guia de Diseno de Pavimentos Hormigon

Transcription

1 La Nueva AASHTO Guia de Diseno de Pavimentos Hormigon Michael I. Darter Emeritus Prof. Civil Engineering, University of Illinois & Applied Research Associates, Inc. USA October 2012 Cordoba, Argentina

2 Current AASHTO vs. Current Needs Wide range of structural and rehabilitation designs 50+ million loads Limited structural sections 1.1 million load reps AASHO Road Test AASHTO Design Guide 1 climate/2 years 1 set of materials All climates over years New and diverse materials

3 1996: AASHTO Decided New Design Needed : Development of new AASHTO design procedure. 2007: AASHTO Interim Mechanistic-Empirical Pavement Design Guide approved. 2011: New software DARWin-ME. Implementation by many States, Canadian Provinces, & Others since

4 Definitions Mechanistic-Empirical Pavement Design Guide, or MEPDG (DARWin-ME). Fundamental engineering mechanics as basis for modeling (stress, strain, deformation, fatigue, cumulative damage, etc.). Empirical data from field performance. M-E Marriage of theory and data. 4

5 AASHTO Interim MEPDG Version April 2007 on Transportation Research Board web site: AASHTO Interim MEPDG Manual of Practice

6 Climate Traffic Materials & Construction Structure,Joints, Reinforcement Comprehensive DG Inputs System DG Process Axle load (lb) DG Outputs Damage Distress Field Distress Mechanistic Response Time Damage Accumulation Damage Distress Prediction & Reliability 6

7 Pavement Characterization For Each Layer: Physical properties Thermal properties Hydraulic properties Base Concrete Base Subbase Subgrade 7

8 New Or Reconstructed JPCP Joint spacing = 4 m Dowel Dia. = 27 mm JPCP Reconstructed Aggregate, Lean Conc., Asphalt Dense Aggregate Compacted Subgrade CTE, Shrinkage, MR, E c E c, friction Mr, gradation, Atterberg, thermal, & hydraulic properties Natural Subgrade 8

9 Composite Pavement, Phoenix, AZ 25 mm New HMA E*, other inputs 25 cm New JPCP CTE, MR, E c, shrink HMA or Unbound Aggregate Base E*, E c, Mr, friction Unbound Aggregate Natural Subgrade Mr, gradation, Atterberg, thermal, & hydraulic properties 9

10 Concrete Pavement Restoration Restoration of joint load transfer, slab replacement (past damage), tied PCC shoulder, diamond grinding 10

11 JPCP Overlay JPCP Overlay 5 cm HMA Separation Old PCC Slab (C&S) CTE, MR, E c, shrink E*, other inputs Aggregate Base Natural Subgrade Bedrock 11

12 MEPDG Analysis Results Uniform (2 lanes) JPCP Overlay Milled exist HMA layer Aggregate Base Aggregate Subase 4 m joint spacing 33 mm dowels 3.9 m outer lane width 12

13 Design for Performance JPCP: Models IRI= f(iri i, faulting, cracking, spalling, soil( P -200 ), age, FI ) Transverse Crack= f(loads, slab, base friction, subgrade, jt space, climate,shoulder, lane width, built-in temp grad, PCC strength, Ec, shrink, ) Joint Faulting= f(loads, dowels, slab, base, jt space, climate, shoulder, lane width, zero-stress temp, built-in gradient, ) 13

14 Slab Dimensions & Base Friction Slab thickness: 15 to >40-cm Slab width: conventional, widened Tied shoulders: load transfer Slab/Base friction: Full (typical) 14

15 Slab Thickness Vs. Cracking 80 Slabs cracked % Data: AASHO Road Test plus I years, 12 million trucks MEPDG Slab thickness, in 15

16 Impact of Slab Width/Edge Support 0.5 m 16

17 Transverse Joints Need for dowels. Benefit of larger dowels. Transverse joint spacing. 17

18 Need for Dowels & Diameter Joint faulting, in Without dowels in dowel diameter in dowel diameter Heavy trucks (millions) 18

19 Joint Spacing Effect: CA Project Percent Slabs Cracked 100 Measured (12-ft) 80 Measured (19-ft) 60 Predicted (12-ft) Predicted (19-ft) Pavement Age, years 19

20 Base & Subbase Materials, Thickness Base types: unbound aggregate, asphalt, cement/lean concrete. Base modulus, thickness, friction with slab. Subbase(s): unbound aggregate, lime treated soils, cement treated soils, etc. 20

21 Material Characterization Material modulus is a key property of each layer Resilient Modulus Mr of Unbound Materials & Soils Dynamic Modulus E* of HMA base Static Modulus of Concrete Slab & Cement-Treated Base 21

22 Subgrade / Embankment / Bedrock Soil types: all AASHTO classes with defaults for gradation, PI, LL, resilient modulus. Subgrade resilient modulus: changes due to temperature & moisture over year. Lime and cement treated soils. Thick granular layers. Bedrock layer. 22

23 5.Review computed outputs Unbound Aggregate Base Mr Vs Month Resilient Modulus, ksi Winter Month 23

24 Concrete Slab/Base Contact Friction Concrete Slab (JPCP, CRCP) Base Course (agg., asphalt, cement) Subbase (unbound, stabilized) Slab/Base Friction Compacted Subgrade Natural Subgrade Bedrock 24

25 Concrete Slab & Structure Inputs Coef. Thermal Expan. Thermal Conductivity Specific Heat Built-In Thermal Grad. Flex & Comp Strength Modulus Elasticity Str. & Mod. gain w/time Poisson s Ratio Thermal Structural Mix Properties Fatigue Capacity Design Cementitious Mat ls W/C Shrinkage (drying) Unit weight Slab Thick Joint spacing Tied shoulder, widened Friction slab/base

26 Concrete Properties Elastic Modulus, E ASTM C 469 Change over time Flexural Strength, modulus of rupture Third point loading test ASTM C 78 Change over time Concrete coefficient of thermal expansion AASHTO TP60-00 Concrete shrinkage ASTM C 157 Change over time 26

27 Concrete Coefficient of Thermal Expansion Percent slabs cracked Limestone 6.5x10-6 /F Granite, Sandstone, Quartzite 6.0x10-6 /F 5.5x10-6 /F 5.0x10-6 /F Age, years 27

28 Climate (temperature, moisture, solar rad., humidity, wind) Integrated Climatic Model (ICM) User identifies local weather stations (851 available in US): Hourly temperature, Precipitation Cloud cover, Relative ambient humidity Wind speed. User inputs water table elevation. ICM Computes temperatures in all pavement layers and subgrade. ICM Computes moisture contents in unbound aggregates and soils. ICM Computes frost line. 28

29 Climatic Factors Slab Curling/Warping Positive temp. gradient Negative temp. gradient & shrinkage of surface Bottom Up Cracking Top Down Cracking 29

30 Slab Built-In temperature gradient during construction at time of set (solar radiation) 30

31 Impact of Traffic Loading Vehicle volume, growth & classification Single, tandem, tridem, quad axle load distributions Monthly vehicle distribution Hourly load distribution Lateral lane distribution Tire pressure Tractor wheelbase 31

32 Vehicle Class Distribution Level 1 Utah sitespecific distribution Level 2 Utah distribution for given highway class Level 3 DARWin- ME Truck Traffic Class (TTC)

33 Axle Configuration Factors Wheelbase Tire Pressure (hot inflation OR measured under operating conditions) Axle Spacing Dual Tire Spacing Axle Width 33

34 Traffic Wander Pavement Shoulder Truck Wander Direction of traffic x Typical Values X (mean) = 457 mm (18 in) X (SD) = 254 mm (10 in) 34

35 Design Reliability Design life: 1 to 100 years. Select design reliability: 50 to 99 percent Transverse cracking Joint faulting Smoothness, IRI Standard error based on prediction error of distress & IRI from hundreds of field pavement sections. 35

36 Field Calibration Concrete Sections 36

37 Example Prediction of Transverse Fatigue Cracking 37

38 LTPP , FL Percent Slabs Cracked Pavement Age, years Measured Predicted 38

39 Example Project Joint Faulting 39

40 Example: Wisconsin JPCP, US cm JPCP, CTE=11/C, Width=4-m Random Jt Space: 4 to 6-m No Dowels 10-cm Unbound Aggregate Base (2.3% fines) Natural Subgrade Bedrock 40

41 WS JPCP Measured Vs Predicted 14 years, 5.5 million trucks Distress Slab cracking Joint faulting Existing JPCP 4-m = 0% 6-m = 38% 1.75-mm IRI 2.3 m/km 41

42 What If... Modify the JPCP Design? If we could go back and modify the original design, what would we do? Add 27-mm diameter dowel bars at transverse joints. Use of 5-m uniform joint spacing rather than 4-6-m random spacing. 42

43 WS JPCP Measured Vs Predicted 14 years, 5.5 million trucks Distress Existing JPCP MEPDG Prediction Slab cracking 4-m = 0% 6-m = 38% 4-m = 0% 6-m = 60% Joint faulting 1.75-mm 2.0-mm IRI 2.3 m/km 2.3-m 43

44 Examples Of Concrete Pavement Design Process Software sold by AASHTO. 44

45 GENERAL INFO ANALYSIS PARAMETER S EXPL ORER WINDO W PAVE MENT STRUC TURE ERROR LIST LAYER PROPERTIES RUN PROG RESS

46 Rigid Pavement Design Process 1. Trial design selection 2. Estimate inputs 3. Run software 4. Review computed outputs 5. Compare distresses & IRI with criteria 6. Design Reliability met? 7. Modify trial design as needed 46

47 Compare output distress & IRI IRI, in/mile IRI at 95% IRI at 50% Pavement age, years 47

48 Does design meet performance criteria? Performance Criteria Distress Target Reliability Target Distress Predicted Reliability Predicted Acceptable Terminal IRI (in/mi) Transverse Cracking (% slabs cracked) Mean Joint Faulting (in) Fail Pass Fail 48

49 LTPP 0214 SPS2, W of Phoenix, MP 109, 32 Million Trucks

50 Design Reliability Reliability design methodology in ME-PDG is practical to use (not complicated). But, requires consideration of more than thickness for JPCP. JPCP: thickness, dowel diameter, & joint spacing must be considered together. Other factors may be varied as well. 50

51 Reliability Level Impact for JPCP Project Design Reliability Vs Slab Thickness Slab Thickness, in Design Reliability 51

52 Recommended Design Reliability Criteria: Arizona Performance Criteria Divided Highways, Freeways, Interstates NonDivided, NonInterstate, 10,000+ADT ,000ADT 5012,000 ADT <500 ADT Design Reliability 97% 95% 90% 80 75

53 Modify Trial Design as Needed Here is where experience and knowledge of fundamental concepts of pavement behavior and performance counts! Examples: Too high joint faulting? Increase dowel diameter Too high cracking? Increase thickness, shorter joint spacing, add tied PCC shoulders Too high IRI? Reduce distress, specify smoother construction 53

54 MEPDG Analysis Capabilities Design & Rehabilitation: many alternatives What if questions Evaluation: forensic analysis Construction deficiencies: impacts on life, $ Truck size and weight: cost allocation Acceptance quality characteristics: impact on performance, $ 54

55 Key Benefits of M-E M E Design Allows design for longer life pavements (checks for early distress) Allows designer to quantify costs & benefits Allows designer to optimize the design (biggest bang for $) IRI (IRI i, fault, crack, spall) Faulting Cracking 55