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

Current AASHTO vs. Current Needs

AASHTO Design Guide

AASHO Road Test

50+ million loads

1.1 million load reps

Wide range of structural and

rehabilitation designs

Limited structural sections

1 climate/2 years

All climates over 20-50 years

1 set of materials

New and diverse materials

3

1996: AASHTO Decided New Design Needed

1998-2007: 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 2004.

4

Definitions

Mechanistic-Empirical Pavement Design Guide,

or MEPDG (now named 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.

AASHTO Interim DARWin-ME

AASHTO Interim DARWin-ME Manual of

Practice

6

DG Inputs

Axle load (lb)

Materials & Construction

Structure,Joints,

Reinforcement

Climate

Damage

Dis

tre

ss

DG Process

Distress Prediction & Reliability Mechanistic Response Damage Accumulation

Time

Da

ma

ge

DG Outputs

Field Distress

Comprehensive System

Traffic

7

Pavement Characterization

For Each Layer:

Physical properties

Thermal properties

Hydraulic properties

Concrete

Base

Subbase

Subgrade

Base

8

New Or Reconstructed JPCP

Dense Aggregate

JPCP Reconstructed

Aggregate, Lean Conc., Asphalt

Compacted Subgrade

Natural Subgrade

CTE, Shrinkage, MR, Ec

Ec, friction

Mr, gradation,

Atterberg, thermal, &

hydraulic properties

Joint spacing = 4 m

Dowel Dia. = 27 mm

9

Composite Pavement, Phoenix, AZ

Unbound Aggregate

25 cm New JPCP

HMA or Unbound Aggregate Base

Natural Subgrade

CTE, MR, Ec, shrink

Mr, gradation,

Atterberg, thermal, &

hydraulic properties

E*, Ec, Mr, friction

25 mm New HMA E*, other inputs

10

Concrete Pavement Restoration California

Restoration of joint load transfer, slab replacement (past damage),

tied PCC shoulder, diamond grinding

11

JPCP Overlay Georgia

JPCP Overlay

5 cm HMA Separation

Old PCC Slab (C&S)

Aggregate Base

Natural Subgrade

Bedrock

CTE, MR, Ec,

shrink

E*, other inputs

12

4 m joint spacing

33 mm dowels

3.9 m outer lane width

JPCP Overlay of Existing Asphalt

Milled exist HMA layer

JPCP Overlay

Aggregate Subase

Aggregate Base

Kansas Turnpike

13

Joint Faulting= f(loads, dowels, slab,

base, jt space, climate, shoulder, lane

width, zero-stress temp, built-in

gradient, …)

IRI= f(IRIi, 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, …)

Design for Performance JPCP: Models

14

Slab Dimensions & Base Friction

Slab thickness: 15 to >40-cm

Slab width: conventional, widened

Tied shoulders: load transfer

Slab/Base friction: Full (typical)

15

Slab Thickness Vs. Cracking

Data: AASHO Road Test

plus I-80 16 years,

12 million trucks

80

60

40

20

0

8 9 12 11 10 13

Slab thickness, cm

Sla

bs c

racked

%

DARWin-ME

20 cm 25 cm 30 cm

16

Impact of Slab Width/Edge Support

0.5 m

17

Transverse Joints

Need for dowels.

Benefit of larger dowels.

Transverse joint spacing.

18

Need for Dowels & Diameter

Joint faulting, in

Heavy trucks (millions) 0 5 10 15 20 25

0

0.02

0.04

0.06

0.08

0.10

32 mm dowel diameter

25 mm dowel diameter

Without dowels

19

Joint Spacing Effect: CA Project

Pavement Age, years

0

20

40

60

80

100

0 5 10 15 20 25 30 35

Percent Slabs Cracked

5.9 m

3.8 m

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.

21

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

Temperature & Moisture Effects

Winter

Unbound Aggregate Base Mr Vs Month

0

50

100

150

200

250

1 2 3 4 5 6 7 8 9 10 11 12

Month

Res

ilie

nt

Mo

du

lus

, k

si

Winter

23

Concrete Slab/Base Contact Friction

Concrete Slab (JPCP, CRCP)

Base Course (agg., asphalt, cement)

Subbase (unbound, stabilized)

Compacted Subgrade

Natural Subgrade

Bedrock

Slab/Base

Friction

Slab & Base Thick

Joint spacing

Tied shoulder, widened

Friction slab/base

Concrete Slab & Structure Inputs Flex & Comp Strength

Modulus Elasticity

Str. & Mod. gain w/time

Poisson’s Ratio

Coef. Thermal Expan.

Thermal Conductivity

Specific Heat

Built-In Thermal Grad.

Cementitious Mat’ls

W/C

Shrinkage (drying)

Unit weight

Thermal Structural

Mix Properties

Design

Fatigue Capacity

25

Concrete Coefficient of Thermal Expansion

0

5

10

15

20

0 5 10 15 20 25 30

Age, years

Perc

en

t sla

bs c

racked

6.5x10-6/F

6.0x10-6/F

5.5x10-6/F

5.0x10-6/F Limestone

Granite, Sandstone,

Quartzite

26

Climate (temperature, moisture, solar rad., humidity, wind)

Integrated Climatic Model (ICM)

User identifies local weather stations:

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.

27

Climatic Factors Slab Curling/Warping

Positive temp. gradient

Bottom Up Cracking

Negative temp. gradient

& shrinkage of surface

Top Down Cracking

28

Slab Built-In

temperature

gradient during

construction at

time of set

(solar radiation)

29

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

Vehicle Class Distribution

Level 1 – Site-

specific distribution

Level 2 – Distribution

for given highway

class

Level 3 – DARWin-

ME Truck Traffic

Class (TTC)

31

Axle Configuration Factors

Axle Width

Axle Spacing

Tire Pressure (hot inflation OR measured

under operating conditions)

Dual Tire Spacing

Wheelbase

32

Traffic Wander

x

Direction of traffic

Pavement Shoulder

x

Direction of traffic

Pavement Shoulder

Typical Values

X (mean) = 45.7 cm

X (SD) = 25.4 cm

Truck Wander

33

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.

34 National Field Calibration Concrete Sections

35

Example Prediction of Transverse Fatigue Cracking

Example Prediction Joint Faulting

36

Example Prediction IRI IR

I, in

/mi

40

80

120

160

200

240

280

320

Age, months

0 24 48 72 96 120 144 168 192 216 240

SHRPID=4_0262

38

DARWin-ME

Software sold by AASHTO

www.aashto.org

GENERAL INFO

RUN PROGRESS

PAVEMENT STRUCTURE

LAYER PROPERTIES

PERFORMANCE

EXPLORER WINDOW

ERROR LIST

40

DARWin-ME 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

41

Compare output distress & IRI

0

40

80

120

160

200

240

280

320

360

400

0 2 4 6 8 10 12 14 16 18 20 22

Pavement age, years

IRI,

in

/mil

e

IRI at 50%

IRI at 95%

42

Does design meet performance criteria?

Distress

Target

Reliability

Target

Distress

Predicted

Reliability

Predicted Acceptable

                         

  172 95 130 83.15 Fail

  15 95 1.6 99.98 Pass

  0.15 95 0.089 93.13 Fail

Transverse Cracking (% slabs cracked)

Mean Joint Faulting (in)

Performance Criteria

Terminal IRI (in/mi)

43

Reliability Level Impact for JPCP Project

Design Reliability Vs Slab Thickness

7

8

9

10

11

12

13

14

15

60 80 90 95 99 99.9

Design Reliability

Sla

b T

hic

kn

ess, in

Recommended Design Reliability Criteria: Arizona

Performance

Criteria

Divided

Highways,

Freeways,

Interstates

Non Divided,

Non Interstate,

10,000+ ADT

2001 –

10,000 ADT

501-2,000

ADT

< 500

ADT

Design

Reliability 97% 95% 90% 80 75

45

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, treated base

Too high IRI? Reduce distress, specify smoother construction

46

DARWin-ME Analysis Capabilities

New Design: several alternatives

Rehabilitation Design: several alternatives

“What if” questions

Evaluation: forensic analysis

Construction deficiencies: impacts on life, $

Truck size and weight: cost allocation

Acceptance quality characteristics: impact on performance, $

47

Key Benefits of DARWin-ME 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 (IRIi, fault, crack, spall) Faulting

Cracking

Directly considers Performance