1- analysis & design of pccp - shiraz
TRANSCRIPT
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IMCYCSeminar on Design and Construction
of Concrete Pavements
Mexico City, Mexico
October 22, 2004
Seminar Outline
Welcome, Introductions, Workshop Objectives
Part 1 Analysis & Design of PCCP
Part 2 Concrete Pavement Construction
Part 3 Evaluation of PCCP
Part 4 PCCP Maint., Repair & Rehabilitation
Part 5 New Concrete Pavement Technologies
Analysis and Design of Concrete
Pavements and Overlays
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Concrete Pavement
Fundamentals
Pavement Terminology
crackingPavement thickness
Transverse joint
Dowel bars
Concrete Slab
Subgrade
Base & subbase
Longitudinal joint
Tie bars
And, shoulders PCC or AC
Joint Faulting
PCCP Types
JPCP 14 to 18 ft joint spacing
t = 6 in (streets) to 8 to 10 in (secondaryroads) to 11 to 14 in (primary and interstatesystems)
Dowels & stabilized base formedium/heavy volume of truck traffic
CRCP
Steel: 0.65 to 0.80%
Cracking at 3 to 6 ft, very tight cracks
Terminal joints at structures
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JPCP
(14 to 18 ft)
Transverse Joints
(with or without dowels)
Longitudinal Joint
(with tiebars)
PLAN
VIEW(14 to 18 ft)
CRCP
Longitudinal Joint
(with tiebars)
PLAN
VIEW
Typical Crack Spacing
(3 to 8 ft)
Continuous LongitudinalReinforcement
(Deformed Bars)(0.65 to 0.8%)
Concrete Properties
Strength Flexural: 550+ psi (each 50 psi ~ 1 in)
Compressive: 4,000+ psi
Stiffness/Modulus - E: 4,000,000+ psi
Durability
Free of MRD (eg., ASR, etc)
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Sources of Slab Stresses
Traffic Loads
Thermal Curling (day & night)
Moisture Warping
Shrinkage (early age & later)
Contraction and Expansion from
Temperature Changes (affected by
frictional restraint/bond to base)
Traffic Loading
Major source of stresses in pavements
Traffic load results in bending stress
(tensile stress at top/bottom of the slab)
Repeated applications can result in
fatigue cracking & joint faulting
Critical location for traffic loading is
generally along outside slab edge
Traffic Load Stresses
At slab edge:
Traffic load creates a tensile stress at
bottom of slab
At slab corner
Traffic load creates a tensile stress at top
of slab
Repeated applications can result in fatigue
cracking
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Slab Stress Computation
Stress and deflection for three loading
conditions
Interior
Edge
Corner
PCC Slab
Subbase
Subgrade
PCC Slab
Subbase
PCC Slab
Base/Subbase
PCC SlabPCC SlabPCC Slab
K value
Typical Load Stress Values(Axle Load = 20,000 lb, p = 100 psi)
170240125500/stiff10
200290145100/soft10
12518090500/stiff12
240340180500/stiff8
Corner
Stress,
psi
Edge
Stress,
psi
Interior
Stress,
psi
k, pciSlab t, in.
1
1312
11109
8765
432
Truck Loading (1993Guide):
Truck factors
ESALs
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Temperature Effects
Differentialtemperatures at the
top and bottom of the
PCC slab result in
slab curling Temperature
differentials are
usually expressed as
linear temperature
gradients
Depth,i
n
52 56 60 64 68 72
Temperature, oF
Top of PCC Slab
0
6
3
9
6 AM 11 AM7 PM
3 PM
Linear idealization
of 3 PM gradient
Effect of Temp. Gradients in
PCC Slabs (Curling)
Warmer at top
Cooler at top
TENSION
Slab displacementfor positivegradient
COMPRESSION
Temperature
De
pth
Temperature
Depth
Slab displacementfor negativegradient
Curling Stresses
Positive gradients producetensile stresses at the bottom ofthe pavement slab
Critical when wheel load atslab edge
Negative gradients producetensile stresses at the top of thepavement slab
Critical when wheel load atslab corner
Magnitude depends on slabproperties, support conditions,and thermal gradient
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Typical Curling Stress
Values For long slabs, t = 10 in., a = 0.000005 in./in./F,
E = 4,000,000 psi, temp. diff = 30 F,
then, Edge Curling Stress = 300 psi
For slabs, 12 ft wide & 20 ft long,
then, Edge Curling Stress = 270 psi (long.)
and Edge Curling Stress = 100 psi (trans.)
12 ft
20 ft
Warping Stresses
Moisture difference between top and bottom
of slab
Greater moisture at top of slab results in
downward warping and vice versa
Moisture contents through slab in:
Wet climates fairly constant
Dry climates top is drier that bottom
Warping Stresses
Slab top wetter than bottom
Slab bottom wetter than top
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Drying Shrinkage Stresses
Loss of moisture in hardened concrete leads
to shrinkage of slab
Shrinkage resisted by friction of the base
Slab contractiondue to moisture loss
Base frictional forces
Temperature Shrinkage
Stresses
Daily/seasonal temperature changes cause
PCC slab to expand/contract
Frictional force between slab and base
creates stresses in slab
Slab contractiondue to low temps
Base frictional forces
Shrinkage Stresses (Axial)
(Important for early age)
Frictional force between slab and base
creates stresses in slab
Introduction of joints in slab reduces
magnitude of shrinkage stresses
Joints need to be provided as early as
possible
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Axial Tensile Stresses
(base/subgrade drag)
= (f L )/2
Where: = slab frictional stress, psi
f = slab/base frictional factorL = slab length, ft
PCC Fatigue Damage
Determination of N
log N =f(applied stress level, PCC strength)
Log N
Stress
Level
N1 N2
1
2
Materials characteristic curve
PCCP Deflection/Load Transfer
Load-transfer => abilityto transfer load across
joint/crack
Poor load transferleads to:
Corner Cracking
Pumping of Fines
Faulting
Initial LT ~ 90+%
Need LT > 75 % inservice
Load Transfer = 100% (Good)
L= x
U= 0
Load Transfer = 0% (Poor)
L= x U= x
LT,% = Unloaded/Loaded *100
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Early Age Behavior
Concerns with early age cracking
PCCP Performance Issues
Structural Performance - Ability to
withstand traffic and environmental
loadings over time (30+ years)
Distress types, extent, & severity
Deflection response
Functional Performance - Providing
users safe and comfortable ride
Ride (IRI), Friction, Noise
Operational Issues
Minimal maintenance/repairs for
high volume highways
Functional Pavement
Performance
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Functional Pavement
Performance
Ability of pavement to provide smooth, safe
ride to users
Roughness/Serviceability
Texture/Friction Texture/Noise
Roughness/Smoothness Definitions
Deviations in pavement surface that affect ridequality
Caused by:
Built-in surface irregularities
Distress (traffic, environment, materialproblems)
Smoothness - Lack of roughness
Road Users - I know it when I feel it !!
PCCP Profile Measurement
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Pavements that are Built Smoother
Pavements that are built smoother remain
smoother over time and last longer
0.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
4.0
0 5 10 15 20 25 30
Pavement Age (Years)
IRI(m
/km
)
Achieving Ride
Initial ride (controlled by specification)
In-service changes in ride (controlled by design &specification)
Requirements
Initial ride (Profile Index/IRI)
Profile Index < 12 in./mile
IRI < 75 in./mile
Low rate of degradation in ride quality overtime
IRI increase/year < 3 in./mile (av. over 20years)
Surface Texture
Influences surface friction and noise
Consists of:
Microtexture
Fine scale roughness contributed byfine aggregate in mortar
Macrotexture
Small surface channels, grooves, orindentations formed or cut
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Texturing Methods PCC
Transverse tine
Longitudinal tine
Turf drag
Burlap drag
Diamond grinding
Longitudinal grooving
Exposed aggregate
Surface Friction
Force developed at
pavement-tire interface that
resists sliding
Influenced by:
Surface texture
Surface drainage (cross-
slope)
Locked-wheel trailer tester(f = ??)
International Friction Index
Achieving Safety By specification
Materials (e.g., concrete)
Finishing operations
Requirements
Initial friction characteristics (eg. FN > 50?)
Long-term friction characteristics (eg., FN > 35?)
Minimize hydro-planning potential
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Texture and Noise
Motor and exhaust control noise levels for
vehicles under 35 mph
Tire-pavement interaction primary source at
greater speeds
Mainly a concern in urban areas
Factors affecting noise
Tine or groove depth
Width
Spacing
Orientation
PCC typically 3 dB(A) > AC
Proposed Texture Guidelines
Tining
3mm width
3mm depth
Random transverse spacing
10/14/16/11/10/13/15/16/11/10/21/13/10
24/27/23/31/21/34
19mm longitudinal
Concrete Pavement
Design Considerations
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Concrete Pavement
Performance Requirements
Structural performance
Long life - no major distresses
Functional performance
Safety very few wet weather accidents Smoothness good ride
( A well constructed pavement with the best
materials WILL fail early if it is not designed
correctly)
Pavement Performance
Time or Traffic
Serviceability
Enhanced
Design
Standard
Design
Performance
Benefit vs.
Incremental Cost
Deficient
Design &
Constructio
nThreshold
Level
Pavement Design
Considerations Minimize failure conditions & costs
Understand typical failure mechanisms
How does a concrete pavement crack?
How does a concrete pavement fault?
How does a concrete pavement get rough?
Are there other local failure conditions that
need to be addressed?
Understand impact of design features
Minimize costs by optimizing design features
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How do Concrete Pavements Fail?
Transverse
Cracking
Smoothness
(IRI)
FaultingAnd, localized
distresses (spalling)
and materials
related distresses
Allowable Distress
At end of service life
40 years for primary system (US)
20+ years for secondary system (US)
2.5 to 3.0Smoothness (IRI),
m/km
6 7Faulting, mm
10 - 15Cracked Slabs, %
ValueDistress
Concrete Pavement Design Elements
Pavement system Slab geometry & boundary conditions
Jointing and load transfer
Pavement layers (slab, base/subbase, subgrade)
Material characteristics (strength, stiffness)
Loading
Truck loading (a wide range of truck traffic & axleloadings)
Environmental (slab temp. & moisture effects)
Climatic (seasonal variations & drainage needs)
Ability to consider applicable failure modes
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Developing Failure (Design) Models
- Early Testing of PCCP 1920s
Developing Failure (Design) Models
- AASHO Road Test (late 1950s)
The AASHO Road
Test equations &
design procedure
used for > 30 years,but are no longer
considered suitable
for current levels of
heavy truck traffic
conditions
Accelerated Testing &Instrumented Test Highways
Instrumented Test Sections to
calibrate/validate analysis
models >>
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CC Pavement Analysis1920s to 1950s
Prof. Westergaard established techniques for
computing slab stresses & deflections
Equations developed for curling stresses due
to temperature gradients in the slab
(Bradburys chart)
Current -- 2D Finite Element Analysis
Deflections
0.0535
0.0512
0.0477
0.0442
0.0407
0.0371
0.0336
0.0301
0.0266
0.0231
0.0196
0.0161
0.0126
0.0091
0.0079
Flat Slab Condition, Tridem Axle Loading
Stresses in Y-direction
360.2
340.7
311.5
282.2
253.0
223.8
194.5
165.3
136.0
106.8
77.6
48.3
19.1
-10.1
-19.9
Load Transfer Considerations inDesign
Load-transfer is a slabs
ability to transfer part of its
load to the adjacent slab
Poor load transfer leads to:
Corner Cracking
Pumping & Faulting
Also, need to consider dowel
bearing stresses
(dowel looseness
concerns?) >>>
Load Transfer = 100% (Good)
L= x
U= 0
Load Transfer = 0% (Poor)
L= x U= x
P (
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Mechanistic-Empirical
Design Procedures (US)
PCA (1984)/IRC:58-2002
200X Design Guide (Future US
AASHTO)
(New M-E procedures allow consideration of a
broad range of design features)
PCA Thickness Design
Procedure (1984)
Mechanistic stress
analysis
Calibrated to field tests,
test roads
Control criteria are:
Fatigue (cracking)
Erosion (pumping)
Windows-based computer
program (Streetpave)
Fatigue (IRC also)
Midslab loading away
from transverse joint
produces critical edge
stresses
Erosion
Corner loading
produces critical
pavement deflections
Transverse joint Transverse joint
Critical Loading Positions
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Basics of Thickness Design(PCA Edge Stress & Fatigue)
Compressive strength: ~ 280
kg/cm2(4000 psi)
Flexural strength: ~ 45 kg/cm2 (650 psi)
T
C
Basics of Thickness Design (PCA)Corner Deflection / Erosion (pumping)/Faulting
Higher k-value (stiffer support) will lowerdeflections
Load transfer (dowel bars) will lowerdeflections
Non-erodible base much better
The 200X M-E Design Process
ClimateTraffic
Materials
Structure
DistressResponse
Time
Damage
Damage
Accumulation
Iterations
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200X Design Inputs(3 Main Categories & 3 Levels)
Traffic
Volume
Axle load distribution
Axle configuration Climate (site specific)
Latitude, longitude, elevation, etc.
Structure
Layers, thicknesses, and materialproperties
Features joint spacing, shouldertype, layer interface, etc.
Distress Types Considered
Faulting
Transverse Cracking
Edge Punchout in CRCP
IRI for Rigid Pavements [=f(distresses)]
IRI prediction accuracy depends upon
predictive accuracy of all other Distress
Smoothness/IRISmoothness/IRI
Joint FaultingJoint Faulting
TransverseTransverse
CrackingCracking
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Design Parameters Over Pavement Life
Incremental Damage Concept
Time, years
Traffic
PQC Modulus
Granular BaseModulus
DLC Modulus
Each loadapplication
2 8640
SubgradeModulus
Typical 200X Design Guide Results
Allowable 200X Guide Distress
At end of service life 40 years for primary system (US)
20+ years for secondary system (US)
2.5Smoothness (IRI)
6 7 mmFaulting
10 - 15 %Cracked Slabs
ValueDistress
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Joint Spacing
0.33 0.34
0.70
0.83
0.93 0.95
0.0
0.2
0.4
0.6
0.8
1.0
1.2
1.4
Joint 15' Joint 17'
Design Variables
DistressRati
o
(to
Reference)
Cracking
Faulting
IRI
Reference Design
Joint Spacing = 20 ft
Cracking = 18.1%, Faulting = 0.23 in.,IRI = 192.1 in/mile
PCC Properties
0.41
3.86
1.0 1.0 1.05
1.45
0.971.18 1.08
1.60
5.52
2.00
0.0
1.0
2.0
3.0
4.0
5.0
6.0
MOR 700psi MOR 500psi Poisson's Ratio
0.2
Siliceous Gravel
(CTE=7e-6/F)
Design Variables
DistressRatio(toReference) Cracking
Faulting
IRI
Reference Design
28day MOR= 600 psi
Poisson's Ratio= 0.15
Aggregate: Limestone (CTE=5.5e-6/F)
Slab Thickness
0.35
1.23
0.80
1.37
0.87
5.00
0.0
1.0
2.0
3.0
4.0
5.0
Slab Thickness 10" Slab Thickness 14"
Design Variables
DistressRatio
(to
Reference)
CrackingFaulting
IRI
Reference DesignSlab Thickness = 12"
Cracking = 18.1%
Faulting = 0.23 in.
IRI = 192.1 in/mile
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Some Recommendations
Establish national goals for NHS PCC pavements
Service life 40 years (low maintenance)
Smoothness (IRI, m/km) New:
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Review & QuestionsReview & Questions