1/2/2007 1 Low Cracking - High Performance Concrete (LC-HPC) Bridge Decks By David Darwin University of Kansas 56th Annual Concrete Conference University of Minnesota December 7, 2006
1/2/2007 1
Low Cracking - High Performance Concrete (LC-HPC)
Bridge Decks
ByDavid Darwin
University of Kansas56th Annual Concrete Conference
University of MinnesotaDecember 7, 2006
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Research supported by:
15 State DOTs: Delaware, Kansas, Idaho, Indiana, Michigan, Minnesota, Mississippi, Missouri, Montana, New Hampshire, North Dakota, Oklahoma, South Dakota, Texas, WyomingFHWA
Lead state – Kansas
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Outline
BackgroundExperiencesLaboratory work
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20 Low-Cracking High Performance Concrete (LC-HPC) Bridges
So far –13 planned for Kansas 2 planned for South Dakota1 planned for Minnesota1 planned for Missouri
Project Scope
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Selection of Bridges
Composite steel girder bridgesFull-depth slabsRemovable formsMatching bridges to serve as a control
where possible
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Background
Why we use LC-HPC
Specifications for LC-HPC decks
1/2/2007 10Off cracks76 mm (3 in.)
0.0
0.6
1.2
1.8
2.4
3.0
3.6
4.2
4.8
5.4
6.0
6.6
7.2
0 24 48 72 96 120 144 168 192 216 240
Age, months
Chl
orid
e C
onte
nt, k
g/m
3Conventional Overlay5% Silica Fume Overlay7% Silica Fume OverlayMonolithicLinear (20%)Linear (All)
20% U
20% L
1/2/2007 11On cracks76 mm (3 in.)
0.0
0.6
1.2
1.8
2.4
3.0
3.6
4.2
4.8
5.4
6.0
6.6
7.2
0 24 48 72 96 120 144 168 192 216 240
Age, months
Chl
orid
e C
onte
nt, k
g/m
3
Conventional Overlay5% Silica Fume Overlay7% Silica Fume OverlayMonolithicLinear (20%)Linear (All)
20% U
20% L
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Crack Surveys
Composite steel girder bridges3 deck types
MonolithicConventional OverlaySilica Fume Overlay
3 studies – over 11 years76 bridges160 individual concrete placements139 surveys
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Factors
AgeBridge Deck TypeMaterial EffectsSite Conditions - Temperature Date of Construction
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Age
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0.00
0.20
0.40
0.60
0.80
1.00
1.20
0 25 50 75 100 125 150 175 200 225 250 275
Bridge Age, months
Cra
ck D
ensi
ty, m
/m2
Monolithic
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Bridge Deck Type
MonolithicConventional OverlaySilica Fume Overlay
Overlay decks evaluated based on the properties of the subdeck
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0.51 0.490.44
0.33
0.000.100.200.300.400.500.600.700.800.90
7% SFO 5% SFO CO MONO
Bridge Deck Type
Cra
ck D
ensi
ty, m
/m2
Age
Cor
rect
ed
Number of Bridges
(9) (18) (30) (16)
Number of Surveys
(9) (36) (52) (32)
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Material Effects
Concrete Mixture ProportionsWater contentCement contentVolume of cement paste
SlumpCompressive StrengthAir content
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Water content
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0.14
0.37
0.73
0.000.100.200.300.400.500.600.700.800.90
147 (248) 156 (263) 165 (278)
Water Content, kg/m3 (lb/yd3)
Cra
ck D
ensi
ty, m
/m 2
Age
Cor
rect
ed
Number of Placements
Number of Surveys
(15) (13) (5)
(29) (26) (11)
Monolithic
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Cement content
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0.17
0.69
0.000.100.200.300.400.500.600.700.800.90
358 (603) 379 (639)
Cement Content, kg/m3 (lb/yd3)
Cra
ck D
ensi
ty, m
/m 2
Age
Cor
rect
ed
Number of Placement
Number of Surveys
(24) (8)
(47) (16)
Monolithic
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Volume of cement paste
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0.19 0.16
0.680.73
0.000.100.200.300.400.500.600.700.800.90
26 27 28 29
Percent Volume of Water and Cement, %
Cra
ck D
ensi
ty, m
/m 2
Age
Cor
rect
ed
Number of Placements
Number of Surveys
(8) (16) (4) (5)
(16) (31) (8) (11)
Monolithic
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Slump
1/2/2007 27Monolithic
0.18
0.31
0.51
0.87
0.11 0.15 0.19 0.22
0.000.100.200.300.400.500.600.700.800.90
38 (1.5) 51 (2.0) 64 (2.5) 76 (3.0)
Slump, mm (in.)
Cra
ck D
ensi
ty, m
/m2
Age
Cor
rect
edUncorrected
Adjusted for Water Content
Number of Placements
Number of Surveys
(5) (20) (5) (1)
(10) (40) (11) (3)
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Compressive Strength
1/2/2007 30Monolithic
0.160.26
0.49
0.000.100.200.300.400.500.600.700.800.90
31 (4500) 38 (5500) 45 (6500)
Compressive Strength, MPa (psi)
Cra
ck D
ensi
ty, m
/m2
Age
Cor
rect
ed
Number of Placements
Number of Surveys
(7) (12) (10)
(13) (24) (23)
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Air content
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0.37 0.38
0.13
0.000.100.200.300.400.500.600.700.800.90
4.5 5.5 6.5
Air Content, %
Cra
ck D
ensi
ty, m
/m2
Age
Cor
rect
ed
Number of Placements
Number of Surveys
(7) (19) (5)
(14) (40) (10)
Monolithic
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Site Conditions - Temperature
1/2/2007 34Monolithic
0.19
0.330.37
0.44
0.00
0.10
0.20
0.30
0.40
0.50
0.60
0.70
0.80
0.90
5 (41) 15 (59) 25 (77) 35 (95)
High Air Temperature, C (F)
Cra
ck D
ensi
ty, m
/m2
Age
Cor
rect
ed
Number of Placements
Number of Surveys
(4) (15) (9) (4)
(8) (31) (17) (9)
1/2/2007 35Monolithic
0.14
0.30
0.44
0.00
0.10
0.20
0.30
0.40
0.50
0.60
0.70
0.80
0.90
4 (7) 12 (22) 20 (36)
Daily Temperature Range, C (F)
Cra
ck D
ensi
ty, m
/m2
Age
Cor
rect
ed
Number of Placements
Number of Surveys
(2) (20) (10)
(4) (42) (19)
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Date of Construction
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0.16
0.50
0.000.100.200.300.400.500.600.700.800.90
1984-1987 1990-1993Date of Construction
Cra
ck D
ensi
ty, m
/m 2
Age
Cor
rect
ed
Number of Bridges
(6) (7)
Number of Surveys
(12) (16)
Monolithic
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0.24
0.53
0.81
0.000.100.200.300.400.500.600.700.800.90
1985-1987 1990-1992 1993-1995
Date of Construction
Cra
ck D
ensi
ty, m
/m 2
Age
Cor
rect
ed
Number of Bridges
(6) (17) (3)
Number of Surveys
(6) (36) (6)
Conventional Overlays
1/2/2007 39Silica Fume Overlays
0.87
0.55
0.420.48
0.000.100.200.300.400.500.600.700.800.90
1990-1991 1995-1996 1997-1998 2000-2002
Date of Construction
Cra
ck D
ensi
ty, m
/m2
Age
Cor
rect
ed
(6) (20) (16) (10)
(2) (10) (8) (10)Number of BridgesNumber of Surveys
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Control of Early Evaporation
1/2/2007 41Silica Fume Overlays
0.87
0.58 0.61
0.390.48
0.000.100.200.300.400.500.600.700.800.90
NONE R1, R2 R3 R4, R5, R6 R8, R9
Special Provision, (R#)
Cra
ck D
ensi
ty, m
/m2
Age
Cor
rect
ed
(6) (8) (10) (18) (10)
(2) (4) (5) (9) (10)Number of BridgesNumber of Surveys
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Specifications
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Overall Approach
Low cement & water contentsLow slumpHigh strength is not always goodLow evaporation rateConstruction methods and materials
matterMore early cracking means more
total cracking
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LC-HPC1 inch Max Size AggregateOptimized Aggregate GradationCement Content < 535 lb/yd3
Air Content of 8 ±11/2%Max w/c ratio of 0.42Improved curingControlled temperature
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Thermal Cracking
Rule of Thumb: Cracking will result when the temperature of the concrete deck exceeds the temperature of the girders by more than 20° C (36° F).
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Thermal Cracking
PennDOT1 15° C (27° F)
KDOT 14° C (25° F)
1 Pennsylvania Department of Transportation, “Prevention of Cracks in Concrete Bridge Decks – Summary Report,” Report No. 89-01, March 1996.
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Alternatives to Pumping
Concrete BucketsConveyor Belts
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Consolidation RequirementsVertically mounted internal gang vibrators
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Finishing
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Machine Fogging
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Early Wet Burlap Cure – within 10 minutes
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Curing
14 days wet cure with burlap, soaker hoses, and plasticFollowed by curing compound to slow the rate of evaporation
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Qualification SlabTo demonstrate implementation of the
specialized process and address problems before bridge deck casting.
ProcessContractorReady Mix PlantInspectors
NO SUPRISES
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Selection of Contractors
PrequalifiedMultiple bridge contracts (to gain from
experience)
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Experiences
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Kansas Bridges
1-2
8-10
3-6&7c
7
1312
11&12c
Unless specifically noted, all control bridges are in the same county as LC-HPC bridge.
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Kansas Bridges - TimelineBridge Groups S O N D J F M A M J J A S O N D J F M A M J J A S O N D J F M A M J J A S O N D
12
1-2control3
3control4
4control5
5control6
6control7
7control8*
8-10control*9
9control10*11
11control12
12control13
13control
LET Date * Prestressed-Girder BridgePre-Construction MeetingQualification SlabCast Deck1st Crack Survey
2004 2005 2006 2007
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Construction experiences
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Qualification Slabs 1 and 2 – Fall 2005, Spring 2006 - Kansas City Area
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Burlap placement within 10 min and 10 ft of strike off
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Qualification Slab 7 – June 8, 2006 – Topeka, KS
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Qualification slabs
Contractor learned:Could pump mix
Need two bridges to place burlap, pre-fold
Fogging could not be used as finishing aid (especially in front of roller)
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KsDOT Project Manager: “This proves the value of the trial slab. You can see how much the contractor learned from the beginning to the end of the slab.”
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Cores of deck show that finishing methods leave large coarse aggregate particles close to the upper surface of the deck
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Bridge 1: October & November 2005
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Bridge Placements
Bridge superintendent observed that he preferred working with optimized concrete with cement content of 540 lb/yd3 to traditional mix with cement content of 602 lb/yd3
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Bridge 7 June 24, 2006
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Bridge 2 September 13, 2006
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Bridge Placements
Temperature controlled with ice, place at night in mid-summerPumpable even with 1.5-in. slumpBullfloating worked wellEach contractor needs to work on perfecting the art of placing burlap, keeping wetCure barriers same as deck
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Conclusions - Experiences
Optimized concrete mixes with relatively low cement (paste) contents are very pumpable, placeable, and finishable
Temperature can be controlled using ice
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Techniques can be learned easily and workers can become proficient in a short period of time
Bid prices are dropping as contractors become more familiar with the methods involved
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Laboratory Work - Briefly
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-50
0
50
100
150
200
250
300
350
0 5 10 15 20 25 30Time, Days
Free
Shr
inka
ge, M
icro
stra
in
Type I/II Cement0.45 w/c 7-Day Cure
0.43 w/c 7-Day Cure0.45 w/c 14-Day Cure0.43 w/c 14-Day Cure0.41 w/c 7-Day Cure
0.41 w/c 14-Day Cure
Average Free Shrinkage (Drying Only). 535 lb/yd3 Type I/II Cement
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-50
50
150
250
350
450
0 5 10 15 20 25 30Time, Days
Free
Shr
inka
ge, M
icro
stra
in
Control 7-Day Cure
Control 14-Day Cure
Average Free Shrinkage (Drying Only). 535 lb/yd3 Type I/II Cementw/cm = 0.42, 23.26% paste
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-50
50
150
250
350
450
0 5 10 15 20 25 30Time, Days
Free
Shr
inka
ge, M
icro
stra
in
Class F Fly Ash Replacement
40% Class F FA 14-Day Cure
20% Class F FA 14-Day Cure
Control 14-Day Cure
Average Free Shrinkage (Drying Only). w/cm = 0.42, 23.26% paste
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-50
50
150
250
350
450
0 5 10 15 20 25 30Time, Days
Free
Shr
inka
ge, M
icro
stra
inSRA and GGBFS
Control 14-Day Cure
60% GGBFS (#1) 7-Day Cure
60% GGBFS (#1) 14-Day Cure
SRA 7-Day Cure
SRA 14-Day Cure
Average Free Shrinkage (Drying Only). w/cm = 0.42, 23.26% paste
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Summary
Background
Experiences
Laboratory Work – in brief
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Questions?
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The University of Kansas
David Darwin, Ph.D., P.E.Deane E. Ackers Distinguished ProfessorDirector, Structural Engineering & Materials
Laboratory
Civil, Environmental & Architectural Engineering1530 W. 15th Street, 2142 Learned HallLawrence, Kansas, 66045-7609(785) 864-3827 Fax: (785) 864-5631