concrete pavements

7/30/2019 Concrete Pavements

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Concrete Pavements

John HarveyUniversity of California, Davis


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Overview

Concrete Pavement Types How Concrete Pavements Fail

Concrete Pavement Design Concrete Materials for Pavements

Construction, Traffic, Delay, Money


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What is the Objective of

Pavement Engineering andManagement?

Provide adequate serviceability at

minimum cost Provide best serviceability possible with

funds available

Maximum mobility at minimum cost


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Rigid Pavements - Jointed Plain

Concrete Pavement

Hydraulic Concrete Slabs

Base/Subbase Layers

Subgrade

Portland Cement Concrete

Fast Setting Hydraulic

Cement Concrete

Lean Concrete Base

Treated Permeable BasesAggregate Bases

Asphalt Concrete Base

Cement Treated BasesCompaction

Fabrics

Mineral Admixtures

Chemical Admixtures

Slab dimensions designed

to not crack


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Other Rigid Pavement Types

Jointed Reinforced Concrete Pavement (JRCP)

reinforcing steel in slabs steel holds cracks tightly together

longer slabs than for plain concrete

Continuously Reinforced Concrete Pavement

(CRCP)

no sawed joints

Prefabricated/Post-Stressed Concrete Pavement

Pre-Stressed Concrete Pavement


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Pavement Performance (Life)

Curve

Ride Quality

Structural

Capacity

Traffic Repetitions(=Years?)

Unacceptable

Field Maintenance

Capital Maintenance


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Full-ScaleTesting

(months)

Laboratory Testing(weeks)

Computer Analysis

(days)

Time& Cost

Reliability

of answers

Long-Term

Monitoring(10-30 years)


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HVS on SR14 near Palmdale


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Side View of HVS


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Where is Caltrans Pavement

Network in its Life Cycle?

When was it built, how long was it

designed for?

Mostly deployed Mostly maintenance and rehabilitation

Some new lanes, realignments Beginning reconstruction


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What Causes Pavement

Distress?

Traffic Environment

Interaction of traffic/environment,construction quality, materials, design


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Environment = Water, Temperature

Increase in water content

decreases soil stiffness decreases soil shear strength

decreases resistance to erosion, pumping

Temperature

asphalt concrete stiffness/strength high at low

temperatures, low at high temperatures

temperature changes cause expansion/contraction

stresses in all asphalted and cemented materials


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Traffic Variables

Its the trucks Loads

Tire pressures Speeds

Dynamics (interaction with roughness) Which are most important?


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Big Truck - 1960


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Big Truck - 1960


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Big Truck - 2001


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Super Single Tires


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Trucks areHeavier,

Faster,More

Numerous

DifferentSuspension,

Different Tires


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An Approximate Load

Equivalence Factor Equation Standard axle load = 80 kN single axle

Caltrans current LEF equation forESALs:

ESALs = (Lsingle/80kN)4.2

ESALs = 2*(0.5*Ltandem/80kN)4.2

ESALs = 3*(0.33*Ltridem/80kN)4.2

Current California legal load limits:

single axle: 89 kN tandem axle: 151 kN


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Rigid Pavement OverviewConcrete slabs, carry

nearly all load stress

Load transfer between

slabs important

Base must provide uniform, continuous support

to slabs, often stabilized with cement or asphalt

Granular sub-base to provide support to base and

slabs, without pumping, expansion/contractionCompacted subgrade, must not expand or contract

to provide uniform support to layers above


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Slab Dimensions

Concrete slabs have engineered length andwidth

Longer slabs are more prone cracking due toshrinkage, curling and warping

Shorter slabs require more joints, which costmore to build and maintain, and can result in

rougher ride

Typical slab width is 3.7 m (12 ft) = one lane

Slab length is a design variable

Caltrans joint spacing has varied over the years


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Environment and Loading

Tensile stresses crack concrete slabs

Environment-related mechanisms causing

tensile stresses

shrinkage and warping

curling

Load related mechanisms

load mass

load location on slab

Environment and load stresses are additive


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Shrinkage and Warping

Base

Concrete Slab

Self-weightTension

Warping of slab:Top of slab cures faster, drier, shrinks more than bottom

Concrete typically shrinks when curing

Uniform shrinkage causes some tensile stresses

Non-uniform shrinkage causes warping,higher tensile stresses

Cool and moist below

Hot and dry above


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Shrinkage Crack (Top-Down)

Slab core laid on its side

Top-Down crack


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Base

Concrete Slab

Self-weight

Curling of slab: caused by temperature differencebetween top and bottom of slab

Night - cooler on top

Base

Tension

Tension

Day - hotter on top

Concrete Slab

Self-weight

Curling


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Desert4 mm

High Desert/

Mountain

South Coast

Bay Area

North

Coast

2500 mm

Central

Valley


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Average

Maximum Air

Temperatures,

April-September

24-29 C

29-35 C

35-41 C

18-24 C


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Average

Minimum Air

Temperatures,

October-March

-1.5 to -3.5 C

3.5 to 8.5 C8.5 to 13.5 C

-6.5 to -1.5 C

Sl b Si d E i t l


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Slab Size and Environmental

Region Effects Longer slabs result in greater

shrinkage stresses warping stresses

curling stresses

Thicker slabs have larger temperature

gradients; bending resistance, weight cancel

Shrinkage, warping, curling worst where largeday-night temperature changes

desert central valley


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Top-Down Thermal/Shrinkage

Cracking at Palmdale


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Load Transfer

Load Transfer:

load on one slab partially carried by

adjacent slabs

reduces tensile stresses in slab

reduces deflections at joints

Load transfer comes from:

aggregate interlock

tie bars (rough steel bars)

dowels (smooth steel rods)


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Load Transfer Locations

Dowels

Dowels

Dowels

Dowels

Dowels

Dowels

Dowels

Dowels

Dowels

Dowels

Dowels

Dowels

Dowels

Dowels

Dowels

Dowels

Dowels

Dowels

Ties

Ties

Ties

Ties

Ties

Ties

Ties

Ties

Aggregate interlock wherever joint sawed in larger slab

Longitudinal joints

Transversejoints


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Load Transfer

Devices

Sawed transverse joint Dowel Aggregate interlock

Sawed longitudinal joint Tie Bar Aggregate interlock


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Joint Saw Cut with Aggregate Interlock


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Dowel BarBasket

Alternative:

Dowel BarInserters


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Tie Bars in Longitudinal Joint


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Load Transfer Efficiency (LTE)

LTE = deflection at Bdeflection at A

when load is at A

A B

A B

LTE vs Repetitions


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LTE vs Repetitions

Dowelled and Undowelled HVS Sections

0.00

0.10

0.20

0.30

0.40

0.50

0.60

0.70

0.80

0.90

1.00

0.0

E

+00

1.0

E

+05

2.0

E

+05

3.0

E

+05

4.0

E

+05

5.0

E

+05

6.0

E

+05

7.0

E

+05

8.0

E

+05

9.0

E

+05

Load Repetitions

LoadTran

sferEfficien

cy

Dowel(90kN)

Nodowels(70kN)

h = 200 mmm

CTB = 100 mm

L d T f Q i


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Load Transfer Questions

Why are dowels smooth? permits slabs to shrink and thermally contract with

small tensile stresses

What happens if too many lanes are tied

together?

shrinkage, temperature contraction can cause a crack

same when slabs are too long

Is there aggregate interlock and loadtransfer

with asphalt shoulders? No

with cold joints between adjacent lanes?No


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Base Erosion

Mechanisms:

Water enters joints and cracks, erodes base material

Vertical deflections of truck loads create hydraulic

pumping action

Primarily occurs at transverse joints,corners

locations of largest deflections if poor load transfer

efficiency

Also occurs at longitudinal joints and

transverse cracks


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Faulting

Base material moves from B to A

Slabs become tilted, creates step-offFaulting development controlled by:

load transfer efficiency

erodability of base

A B

Severely effects ride quality

thump, thump, thump


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Pumping, Voids

A B

Base

Water and large

verticaldeflection pump base,

subbase and subgradematerial out, leave void

Voids result in less

support to slab, higher

tensile stresses under

load, and cornercracking


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Concrete Cracking

Traffic and environmental loads cause

tensile stresses Higher stresses result in fewer

repetitions before cracking (fatigue)

Types of cracking:

transverse

longitudinal

corner


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Fatigue Life Calculation

1. = f(E, k, h, L, P)

= slab bending stress

E = concrete elastic modulus

k = subgrade support value

h = concrete thickness

L = slab length

2. Stress Ratio = /MR

MR = concrete flexural strength

3. Plot /MR versus Repetitions to Failure

FSHCC F ti R i t R lt


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FSHCC Fatigue Resistance Results

0.00

0.40

0.80

1.20

1.60

1.E+00 1.E+02 1.E+04 1.E+06 1.E+08

Repetitions to Failure

Stre

ssRatio

BeamPCA CurvePCC Slab

FSHCCAASHO

Pumping

Did not fail


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Transverse Cracking

Critical load conditions:

heavy single axle at mid-slab at edge

day-time curl (additive with load)

no load transfer at edge

Stresses reduced by:

shorter joint spacing thicker slab (Eh3)

stronger flexural strength of concrete

load transfer at edge (tied shoulder, wide lane)

T C k


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Transverse Cracks

Corner Cracking


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Corner Cracking

Critical load conditions: heavy tandem axle at corner

night-time curl (additive with load) warping

no load transfer at edge and transverse joint

erosion of base under corner


thicker slab (Eh3)


load transfer at joint and edge (dowels, tiedshoulder, wide lane)

C C k


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Corner Cracks


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Longitudinal Cracking

Critical load conditions:

heavy single axle at mid-slab about 0.5 mfrom edge

night-time curl

warping


thicker slab (Eh3)


Longitudinal Crack


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Longitudinal Crack

Wide-Truck Lane and Lane


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Wide Truck Lane and Lane

Striping Critical (worst) load location for

transverse and corner cracking

wheels along slab edge

best location is down middle of slabs

For outside truck lane can use widelane (4.3 m instead of 3.7 m)

put stripe at 3.7 m to get trucks off edge potential alternative to tied shoulder

Always try to keep trucks off edge andcorners

Wide Truck Lane (with


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Wide Truck Lane (withdowels)

This is a test section!

In practice, dowels

should go completelyacross joint

Wide lane

extra 0.6 m

3.7 m lane


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Long-Term Durability

Concrete strength gain Sulfate attack

Alkali-aggregate reaction

Spalling, mechanical abrasion

resistance

S lf t Att k


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Sulfate Attack

Sulfates in soil and water can create a

sulfate (acidic) environment for concrete

slabs Sulfates reduce pH of cement,

degrades some kinds of concretecrystal structures

Controlled by concrete chemistry,

water/cement ratio, access to water

First identified in California, Type I/II

cement usually required

L b M t S l ft S lf t E


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Lab Mortar Samples after Sulfate Exposure

Hydraulic

cement A

Hydrauliccement B


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Alkali-Aggregate Reaction

High pH of cement causes reaction with

aggregates, particularly those with

certain siliceous minerals

Continued reaction (requires water)

creates gel which expands When expansion strain greater than

failure strain, concrete cracks Can completely crack, destroy concrete

First identified in California in 1920s

C t St th G i Ch i l


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Concrete Strength Gain, Chemical

Conversion, Mechanical Abrasion Portland cement

typically continues to gain strength with time hydration products (crystals) are stable

Other cement types (such as FSHCC) may not continue to gain strength after initial

high early strength

may have hydration products that change withtime, reduce strength

Hard aggregate, strong cement needed toresist chipping, spalling, chain wear


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Soils Expansion

Certain clay soils will expand when

have access to source of water Can cause distortion in pavement

Uniform support to slabs is key to goodconcrete pavements

do not use unless completely mitigate risk

of soils expansion

Influence of Materials Selection


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Influence of Materials Selection

and Design on Each Distress Understanding of climate and traffic essential

Materials selection effects on performance: high enough flexural strength for cracking

not such high strength or early strength that shrinkage

cracks occur

Balance in joint spacing, lane tieing: load transfer,

thermal, shrinkage contraction, stresses, ride quality Adequate thickness to resist bending

Base type: non-erodible, accommodate curl, warping

Load transfer: dowels, tie bars, wide lanes


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Typical Properties for QC/QA

1) Fresh Concrete Properties

2) Hardened Concrete Properties

3) Surface Roughness

4) Thickness

5) Surface Friction

Hardened Concrete Properties


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Hardened Concrete Properties

1) Strength Tests

fc, MR

2) Shrinkage Tests

mortar bar

concrete prism

3) Maturity

ASTM C 1074-93

Flexural Strength Apparatus


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Flexural Strength Apparatus( ASTM C 78 - third-point loading)

Calculation of Modulus of


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Calculation of Modulus of

Rupture (MR)

CTM 523 or ASTM C 293:

MR = 1.5PL/(bd2)

ASTM C 78:

MR = PL/(bd

2

)

Why use flexural strength


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y g

test?1) Required for pavement design

2) Most realistic to slab bending action

3) Conservative estimate of slab strength

Cons of flexural beam tests moisture sensitive temperature sensitive size and loading configuration effects


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Maturity Testing

ASTM C 1074 Internal temperature of concrete relates

directly to concrete strength

Develop correlation curve in lab

Precision to baseline cylinders: 5%


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Maturity Testing

Temperature-Time Factor, M(t)

CompressiveStrength(M

Pa)

Co

mpressive

Strength(p

si)

0 100 200 300 400 5000

5

10

15

20

25

30

35

40

0

1000

2000

3000

4000

5000M(t) = (Ta-To) t

M(t) = temperature-time factor

t = time interval

Ta = average concrete temp.

To = datum temp. (-10oC)

Dowel Bar Retrofit


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Dowel Bar Retrofit

Dowel Bar Retrofit of Transverse Joint


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Dowel Bar Retrofit of Transverse Joint

Dowel Bar Retrofit of Transverse Crack


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Dowel Bar Retrofit of Transverse Crack

Completed DBR


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Completed DBR

Rigid Long-Life Strategies


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Rigid Long Life Strategies

Currently Under Investigation

200-225 mm PCC

100 mm CTB

150 mm ASB Remove PCC, Replacewith 200-300 mm

Concrete Slab100 mm CTB or other

base type

(Recompact) ASB

Effect of Pavement Thickness and


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Effect of Pavement Thickness and

Construction Window on Project Duration

20 lane-km project

Const. Window 203 mm 254 mm 305 mm Duration

Cont. (3 shift) 1.4 2.1 2.4 WeeksCont. (1 Shift) 4.0 5.9 6.6 Weeks

Weekend 6.2 10.1 11.4 No. of Weekend

254 and 305 mm slab require new base (more time)

For both AC and Rigid Long-Life Strategies

most critical element controlling constructionduration is reconstruction thickness, which

determines amo nt of old material to be remo ed

concrete pavements

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