NH-2 ALLAHABAD BYPASS PQC PAVEMENTS (ABP-2 & ABP-3)

ABP CONSTRUCTION REVIEWEARLY PERFORMANCE ON NH-2

& PQC REPAIR METHODS

Shiraz TayabjiConsultant, The World Bank

NHAI/World Bank Workshop on National Highway Rigid Pavements

Allahabad – October 9, 2007 The World Bank

Presentation OutlinePresentation objectivesFundamentals of PQC pavements – brief overviewBest Construction PracticesSummary of June/October 2004 discussions &

recommendationsMarch 2006 site visits overview & observations Overall 2006 recommendations

Design & construction practicesMaintenance & repair practices

ABP 2 & 3 Site Visit & ObservationsDiscussion

Pavement Terminology

cracking Pavement thickness

Transverse joint

Dowel bars

Concrete Slab

SubgradeBase & subbase

Longitudinal joint

Tie bars

And, shoulders – PCC or AC

Outside/truck lane may be widened

Joint Faulting

Pavement Function► Provide acceptable long-term (30 to 40+

years) service life with a low level of M&RFunctional (smoothness, safety, noise)Structural (distress, structural response)

► Components of pavement performance (affected by design features & construction quality)

Initial condition (construction)Premature distress (design and/or construction)Fatigue related distress (construction/materials))Durability related distress (ASR)

Concrete Pavement Types► Jointed concrete pavement (most popular) ► Continuously reinforced concrete pavement► Jointed reinforced concrete pavement (not used)► Roller compacted concrete pavement► Prestressed concrete pavement (experimental)► Precast concrete pavement► Whitetopping (resurfacing of distressed asphalt

pavement)► Pervious concrete

6

Key PCCP Types►JPCP

14 to 16 ft joint spacing (mostly 15 ft)t = 6 in (streets) to 8 to 10 in (secondary roads) to 11 to 14 in (primary and interstate systems)Dowels & stabilized base for medium/heavy volume of truck traffic

►CRCPSteel: 0.65 to 0.80%Cracking at 3 to 6 ft, very tight cracksTerminal joints at structures

JPCP

14 to 16 ft

Transverse Joints(with or without dowels)

Longitudinal Joint (with tiebars)

PLANVIEW14 to 16 ft

CRCP

Longitudinal Joint (with tiebars)

PLANVIEW

Typical Crack Spacing(3 to 8 ft)

Continuous Longitudinal Reinforcement

(Deformed Bars)(0.65 to 0.8%)

Widened Slab/Tied Shoulder

► Widened LaneSlab paved 0.6 m wider than usualLane striped at normal 3.65 width Reduces edge and corner stress/deflections

► Tied cement concrete shoulderReduces edge stress/deflectionsReduces moisture infiltrationEmergency/future traffic lane

0102030405060708090

1stQtr

2ndQtr

3rdQtr

4thQtr

EastWestNorth

Concrete Properties► Strength

Flexural: 4 to 4.5 MPa (each 50 psi ~ 1 in)Compressive: ~ 28 MPa

► Stiffness/Modulus - E: ~ 28,000 MPa► Durability

Free of Materials Related Distress (eg., ASR, etc)

How do Concrete Pavements Fail?

TransverseCracking

Early age & in-service

Smoothness (IRI)Construction & in-service

FaultingAnd, localized distresses (spalling) and materials related distresses (not an issue in India)

Some longitudinal cracking – typically early age

Pavement Performance

Time or Traffic

Serv

icea

bilit

y

Long Life Design & ConstructionStandard

Deficient Design & Construction

Threshold Level

Service Life► At end of service life

40+ years for primary system 20+ years for secondary system (??)

Distress ValueCracked Slabs, % 10 - 15 Faulting, mm 6 Smoothness (IRI), m/km 2.5 to 3.0Spalling Minimal?Materials Related Distress None

Asphalt Layer

How Pavements Carry Loads

Concrete’s rigidness spreads the load over a large areaand keeps pressures on the subgrade low.

Concrete PavementStresses & Deflections

Early Age Behavior (first ~72 hours)•Affected by slab curling, warping and volume changes due to temperature changes and drying shrinkage

In-service Behavior•Affected by traffic loadings, slab curling, and warping (a little bit)

Sources of Slab Stresses

►Traffic Loads►Thermal Curling (day & night)►Moisture Warping (early age)►Shrinkage (early age)►Contraction and Expansion from

Temperature Changes (affected by frictional restraint/bond to base) – early age

Traffic Loading►Major source of stresses in pavements►Traffic load results in bending stress

(tensile stress at top or bottom of the slab)

►Repeated applications can result in fatigue cracking & joint faulting

►Critical location for traffic loading is generally along outside slab edge

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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

Basics of Thickness Design(Edge Stress & Fatigue)

►Compressive strength: ~ 30 Mpa (4000 psi)

►Flexural strength: ~ 4.5 MPa (650 psi)

T

C

Basics of Thickness Design Corner Deflection / Erosion (pumping)/Faulting

► Higher k-value (stiffer support) will lower deflections

► Load transfer (dowel bars) will lower deflections► Non-erodible base much better

Slab Stress Computation

►Stress and deflection for three loading conditions

Interior (not important)EdgeCorner

PCC SlabSubbaseSubgrade

PCC SlabSubbase

PCC SlabBase/Subbase

PCC SlabPCC SlabPCC Slab

K value

Typical Load Stress Values(Axle Load = 90 kN, p = 690 kPa)

(Axle Load = 20,000 lb, p = 100 psi)

Slab t, mm

k, kPa/mm

Interior Stress,

kPa

Edge Stress,

kPa

Corner Stress,

kPa

20013.5/stiff(500 pci)

1240(180 psi)

2340(340 psi)

1650(240 psi)

250 13.5/stiff 860 1650 1170

300 13.5/stiff 620 1240 860

250 2.7/soft 1000 2000 1380

Temperature Effects

Differential temperatures at the top and bottom of the PCC slab result in slab curlingTemperature differentials are usually expressed as linear temperature gradients

Dep

th, i

n

52 56 60 64 68 72

Temperature, oF

Top of PCC Slab0

6

3

9

6 AM 11 AM7 PM

3 PM

Linear idealizationof 3 PM gradient

Effect of Temp. Gradients in PCC Slabs (Curling)

Warmer at top (positive gradient)

Cooler at top (negative gradient)

TENSION

Slab displacement for positive gradient

COMPRESSION

TemperatureDepth

TemperatureDepth

Slab displacement for negative gradient

Thermal Stresses

Stiff base results in higher stressesmore risk of cracking

Self weight (early age)

Cooler at top

Base

Moisture Warping (more important for early age behavior)

►Moisture difference develops between top and bottom of slab (top surface drier)

Early age – excessive surface moisture loss due to poor curing can lead to built-in slab warping – not recoverable In service – top 20 to 50 mm is typically drier that rest of slab

Slab bottom usually wetter than top

Warping

Self weight (early age) and traffic load (later)

Slab surface drying

Axial Tensile Stresses(important for early age behavior)

►Slab contractionLoss of moisture in concrete leads to shrinkageTemperature drop causes slab to contract

►Slab contraction resisted by base friction► Frictional force between slab and base

creates tensile stresses in slabSlab contractiondue to moisture loss

Base frictional forces

Temperature Contraction & Concrete Drying - Strains and Stresses

Drying Drying

Friction

DryingRestraintRestraint

Axial Tensile Stresses (Important for early age)

►Introduction of joints in slab reduces magnitude of tensile stresses

►Joint sawing needs to be done as early as possible – before large stresses develop

FOR BOTH TRANSVERSE & LONGITUDINAL JOINTS

Early Age Behavior► Concerns with early age cracking due to high

curling, warping, and axial restraint stresses

Restraint Stresses

PCC Fatigue Damage

• Allowable no. of repeated loadslog N = f (applied stress level, PCC strength)

Log N

StressLevel

N1 N2

σ1

σ2

Material’s characteristic curve

Allowable N is very high if stress/strength < 0.5

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Faulting & Pumping

Corner loading produces critical pavement deflections

Transverse joint

PCCP Deflection Response

Typical Deflection Values(slab t = 250 mm, JS = 4.65 m, k = 8 kPa/mm)

(slab t = 10 in., JS = 15 ft, k = 300 pci)► Corner/joint deflections most critical► Corner Deflections

18,000 kg TAL at corner ~ 1 mm (no dowels); ~ 0.5 mm (doweled)

18,000 kg TAL 0.6 m from corner ~ 0.5/0.25 mm► Night-time curling (uplift at corner from a flat

condition) – no dowelsFor 5.5 C differential temp. ~ 0.4 mm

► Possible built-in slab curling (at time of set) at corner – no dowels – not fully recoverable

Equal to 5.5 C differential temp. ~ 0.4 mm

0.04 in. = 1 mm

Load Transfer at Joints

► Load-transfer is a slab’s ability to transfer part of its load to the adjacent slab

► Poor load transfer leads to: Pumping & Faulting

► Initial LT ~ 90+%► Need LT > 70 - 75 % in

service

► Need to consider dowel bearing stresses

Dowel looseness over timeDowel size, embedment, concrete quality & cover very important

Load Transfer = 95 to 100% (new)

L= xU= 0

Load Transfer = 0% (Poor)

L= x U= x

Critical dowel P > 14 kN (3,000 lb) (millions of applications)

Conventional Dowel Layout(divided highway)

Outer Traffic LaneInner Traffic Lane

12 dowels @ 300 mm cc

12 dowels @ 300 mm cc

TrafficTraffic

Need dowel bars in widened portion of outside lane

Outer 4 dowels very critical

Should not compromise effectiveness of these 4 dowels

Dowel Loads Across a Joint

3,000 lb = 13.5 kN, 300 pci = 8 kPa/mm)

40,000 lb = 18,000 kg

Critical Dowel LoadNeed to consider dowel bearing stresses

Affects dowel looseness over timeDowel size, embedment & cover very importantConcrete consolidation around dowels very important

Critical dowel P > 14 kN (3,000 lb), millions of applications

QA/QC - Dowel Bar Alignment► Typical specs

Skew: 6 mm per 300 mm.Hori.:+ 25 mm ; Long.: + 25 mmVert.: + 25 mm (+ 50 mm for thicker pavements OK)

► Pre-placed baskets – measured before concrete placement or in hardened concrete (GPR, MIT SCAN)

► Inserted dowels – measured in hardened concrete (GPR, MIT SCAN)

Pavements that are Built Smoother…

Pavements that are built smoother remain smoother over time and last longer

Thank YouThank You