Download - Best Practices in Bridge Deck Construction
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Best Practices in Bridge Deck
Construction
Robert J. Frosch, Ph.D., P.E.
Professor of Civil Engineering
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Bridge Deck Cracking
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Types of Cracking
• Transverse
• Longitudinal
• Map
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Transverse Cracking
• Appear before or shortly after opening
– Typically less than 28 days
• Full depth
• Through plane of reinforcement
• Spaced 3 to 10 ft apart
• Concrete and steel superstructures
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Transverse Cracking
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Stay-in-place Forms
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Wood Forming
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Impact
Full Depth
Transverse
Crack
Corrosion of
Reinforcement
Delamination
in Deck
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Longitudinal Cracking
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Construction Detail
7 7
/8”
W36x150
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Map Cracking
Typically observed in Overlays
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General Experience
• Monolithic Concrete Structures
– Least cracking
• Steel Superstructures
– Most cracking
– Restraint
• Composite action
• Stay-in-place steel forms
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Field Instrumentation
I65 over SR25
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Deck Instrumentation
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Temperature
40
50
60
70
80
90
100
110
120
8/15 8/20 8/25 8/30 9/4
Date (2000)
Tem
per
atu
re (
o F
)
Ambient Temperature
Deck Temperature
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Longitudinal Reinforcing Strain
-500
0
500
1000
1500
2000
2500
3000
8/15 8/20 8/25 8/30 9/4
Date (2000)
Mic
rost
rain
s
Traffic
(C)
(T)
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Stress Transfer 7 7
/8”
12”
@ 19 days
#4 Top & #5 Bottom
Long. Bars @ 11 13/16”
psi f c 600 , 5 ' =
c cr f f '
6 =
Tc = Ts
psi f s 800 , 81 =
( ) ( psi 450 ) s f in in in . 52 . 0 . 7 . 12
2 8
7 = * ( (
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Field Instrumentation Findings
• Transverse cracking at 19 days
• Longitudinal reinforcement yielded
• Cracking not influenced by live loads
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Field Investigations
• 4 bridges
– I-65 (Standard Design)
– SR 18 (Empirical Designs)
– Thayer Road Bridge (FRP)
– SR 23 (HPC & Purdue Empirical)
• Instrumentation
– Strain Gauges
– Thermocouples
• Crack Mapping
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Field Study Findings
• Field Investigation
– Low shrinkage concrete decreases cracking
– Reinforcement affects cracking
– Thermal effects contribute to cracking
– Crack Growth
• Maximum cracks 5x initial
– Reinforcement may yield
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Restrained Shrinkage
• Eliminate Restraint
– Composite action
– Pan forms
• Eliminate Shrinkage
– Concrete shrinks
• Eliminate Cracking
– Minimize cracking
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Laboratory Composite Models
As Built
Free Shrinkage
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Shrinkage Investigation
4’-4”
7 7/8”
2’-9 1/2”
Direction
Of Shrinkage
Measurement
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Specimen Variables
• Wood Forms
• SIP Forms
Transverse
Longitudinal
#5 Bars #4 Bars
• Reinforcement
• Thickness
Unsealed
Sealed
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Effect of Sealing
0 300 -300
Micro Strains
Sealed Unsealed
Top of Deck
7-7/8”
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Deck Pan Stiffness
0 300 -300
Micro Strains
0 300 -300
Micro Strains
Longitudinal Orientation Transverse Orientation
No Pan
(Sealed)
Deck Pan
(Sealed)
Top
Bottom
9 7
/8”
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Concrete shrinkage & curing
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Low Shrinkage Concrete
• Reduced cement and water content
• Increased sand, addition of fly ash
0
1000
2000
3000
4000
5000
6000
0 5 10 15 20 25 30
Time (days)
Com
pre
ssiv
e S
tren
gth
(p
si)
Low Shrinkage
Class C
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Shrinkage Behavior
0
100
200
300
400
500
0 10 20 30 40
Time (days)
Str
ain
(µ
ε)
Wet Cure Drying Shrinkage
Thermal expansion
and shrinkage
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Effect of Concrete Mix
• Long term effects
– Low shrinkage mix: decreased total shrinkage
-550
-500
-450
-400
-350
-300
-250
-200
1 3 5 7 10 14 21 28 V-1 V-2
Wet curing duration (days)
Sh
rin
ka
ge
(µε)
-550
-500
-450
-400
-350
-300
-250
-200
1 3 5 7 10 14 21 28 V-1 V-2
Wet curing duration (days)
Sh
rin
ka
ge
(µε)
Class C Low Shrinkage
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Reinforcement Stress at Time of
Cracking
6t cf f=
cT F=
'6 c
g
y
f
f =
6c c cF f A=
T=As fs
(6 )c c s sA f A f=
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Reinforcement
15’-6”
3’ 8”
8’ 2’ 2’
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Maximum Crack Width
Black
6 mils 12 mils
18 mils
0
10
20
30
40
50
60
0 5 10 15 20 25 30
Crack Width (mils)
Ste
el S
tress (
ksi)
70
9” Spacing
1.3 Factor
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18” Spacing, #4 bar
4” Spacing, #4 bar
Minimum Maximum ρg
Reinforcement Layout
1.25%
0.27%
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Specimen Construction
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Strain - # 4 Bars
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Control Cracking
Design Construction
Materials
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Recommendations
• Curing is Essential
– Minimum 7 day wet cure
• Minimize drying shrinkage
– Mix design
– Minimize concrete strength
• Alternative forming system
– Flat forms
– Remove forms
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Recommendations
• Additional reinforcement required
– Above Shrinkage and Temperature
–
– Max spacing 9 in. for Epoxy Coated
Reinforcement
g
y
c
s Af
fA
'6=