Low Cracking - High Performance Concrete (LC-HPC) Bridge...

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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 Surveys

(8) (16) (4) (5)

(16) (31) (8) (11)

Monolithic

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Slump

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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 Surveys

(5) (20) (5) (1)

(10) (40) (11) (3)

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Compressive Strength


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 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 Surveys

(7) (19) (5)

(14) (40) (10)

Monolithic

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Site Conditions - Temperature


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 Surveys

(4) (15) (9) (4)

(8) (31) (17) (9)


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 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


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


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

[email protected]

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