Bridge Deck Cracking

David DarwinUniversity of Kansas

National Concrete Consortium

Columbus, OHApril 27, 2016

Research Sponsors

OutlineScopeFindings SpecificationsField ExperienceTechnologies Under Active StudyConclusions

Scope of WorkBeginning in 1991

Initiated bridge deck crack surveys using standardized methods (150+ decks)

Established principal factors controlling cracking

Scope of WorkBeginning in 2005

Constructed 25 bridge decks under Low Cracking High-Performance Concrete (LC-HPC) specifications (17 in Kansas)

Most bridges in study have steel girders

Findings

What’s not a major concernMoment region and load-induced stresses in the deck

8

Moment region

7% Silica Fume Overlay

9

Moment region

Conventional Overlay

10

Moment region

Monolithic

11

Moment region

Monolithic

Factors

Age Bridge Deck Type Material Effects Site Conditions – Temperature Curing Date of Construction

Monolithic

Age

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

Cra

ck D

ensi

ty, m

/m2

Bridge Age, months

14

Bridge Deck Type

MonolithicConventional OverlaySilica Fume Overlay

Bridge Deck Type

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)

Material EffectsConcrete Mixture Proportions

Water contentCement contentVolume of cement paste

SlumpCompressive strengthAir content

Paste Content

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

/m2

Age

Corre

cted

Number of Placements

Number of Surveys

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

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

Monolithic

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

edUncorrectedAdjusted for Water Content

Number of Placements

Number of Surveys

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

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

Slump

Monolithic

Settlement Cracking

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

Corre

cted

Number of Placements

Number of Surveys

(7) (12) (10)

(13) (24) (23)

Monolithic

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)

Air Content

Monolithic

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)

Crac

k Den

sity,

m/m

2

Age C

orre

cted

Number of Placements

Number of Surveys

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

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

High Air Temperature

Monolithic

5/3/2016 23

Date of Construction

0.16

0.50

0.000.100.200.300.400.500.600.700.800.90

1984-1987 1990-1993

Date of Construction

Crac

k Den

sity,

m/m

2

Age-

Corre

cted

Number of Bridges

(6) (7)

Number of Surveys

(12) (16)

Date of Construction - Monolithic

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

Crac

k Den

sity,

m/m

2

Age C

orre

cted

(6) (36) (6)

(6) (17) (3)Number of BridgesNumber of Surveys

Date of Construction - Conventional 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

Crac

k Den

sity,

m/m2

Age C

orre

cted

(6) (20) (16) (10)

(2) (10) (8) (10)Number of BridgesNumber of Surveys

Date of Construction - Silica Fume Overlays

Control of early evaporation and improved curing

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#)

Crac

k Den

sity,

m/m2

Age C

orrec

ted

(6) (8) (10) (18) (10)

(2) (4) (5) (9) (10)Number of BridgesNumber of Surveys

Control of early evaporation and improved curing -Silica Fume Overlays

Why increased cracking?

Cement finenessConcrete slumpPlacing equipmentFinishing equipment

1

2

3

4

5

6

7

8

9

10

1984 1986 1988 1990 1992 1994 1996 1998 2000 2002 2004 2006 2008

Slum

p, in

.

Placement Date

MONO

CO Subdecks

5% SFO Subdecks

7% SFO Subdecks

Overall ApproachWork to reduce plastic, settlement, thermal

and drying shrinkage cracking

Low cement & water contentsLow slumpModerate, not high, strengthControl concrete temperatureMinimum finishingEarly start and extended curing

LC-HPC Specifications Optimized Aggregate Gradation Low-absorption Aggregate 1 inch Max Size Aggregate Cement Content ≤ 540 lb/yd3

w/c ratio = 0.43 – 0.45 Air Content of 8 ± 1½% Designated slump 1½ – 3 in. (3½ in. max) Controlled temperature (55 – 70°F) Improved curing

Thermal Cracking

Rule of Thumb: Cracking will result when temperature of plastic concrete in deck exceeds temperature of girders by more than 36° F (20° C).

Concrete temperature control

55 – 70°F50 – 75°F if approved by Engineer

Cold-weather concreting

Maintain temperature of both girders and deck

Alternatives to Pumping

Concrete Buckets Conveyor Belts

PlacingAir cuff/bladder valve on pump or limit drop with conveyorFilling end walls and diaphragms ahead of slab

Consolidation RequirementsVertically mounted internal gang vibrators

Concrete Finishing

General Rule:Less is More

Pan or burlap dragBullfloatingNo finishing aids!

Curing

Presoaked burlapTimely placementConstantly wet Spray hoses Soaker hoses 14 days

Presenter

Presentation Notes

Same crew must be used

Curing

14 days wet cure with burlap, soaker hoses, and plastic

Followed by curing compound to slow the rate of evaporation

Field Experience

0

0.2

0.4

0.6

0.8

1

1.2

0 12 24 36 48 60 72 84 96 108 120

Cra

ck D

ensi

ty (m

/m2 )

Bridge Age (Months)

Control

LC-HPC

Bridges 1 and 2

0.0

0.2

0.4

0.6

0.8

1.0

1.2

0 12 24 36 48 60 72 84 96 108 120 132

Cra

ck D

ensi

ty (m

/m2 )

ControlLC-HPC

Bridge Age (Months)

Control-1/2 - P2Control-1/2 - P1

LC-HPC-1 - P2LC-HPC-1 - P1

LC-HPC-2

Bridges 11 and 13

0.0

0.2

0.4

0.6

0.8

1.0

1.2

0 12 24 36 48 60 72 84 96 108

Cra

ck D

ensi

ty (m

/m2 )

Bridge Age (Months)

Control-11

LC-HPC-13

Control-13

LC-HPC-11

Bridge 4

0.0

0.2

0.4

0.6

0.8

1.0

1.2

0 12 24 36 48 60 72 84 96 108

Cra

ck D

ensi

ty (m

/m2 )

Bridge Age (Months)

Control-4

LC-HPC-4 - P1

LC-HPC-4 - P2

High Air Temperature

KU11

KU 5 KU3

KU6

KU7

KU9

KU4-p2

KU13

KU2 KU 1-p1KU1-p2

0.00

0.10

0.20

0.30

0.40

0.50

0.60

0.70

0.80

0.90

56 60 65 69 71 78 78 79 84 87 88

Cra

ck D

ensi

ty, m

/m2

at 3

6 m

onth

s

Daily High, °F

Technologies Under Active Study

Internal curing with pre-wetted lightweight aggregate combined with slag cement and silica fumeShrinkage reducing admixturesShrinkage compensating admixturesRheology modifying admixturesSynthetic fibers

Reducing shrinkage cracking using:

Internal curing with pre-wetted lightweight aggregate combined with slag cement and silica fume

Internal Curing Shrinkage

-100

0

100

200

300

400

500

600

700

0 50 100 150 200 250 300 350

Aver

age

Free

Shr

inka

ge (m

icro

stra

in)

Drying Time (days)

Control

10% LWA

10% LWA,30% Slag

10% LWA,30% Slag, 3%SF

Reducing settlement cracking using:

Rheology modifying admixtures

Synthetic fibers

Control mixture

Synthetic fibers

Rheology modifying admixture

Conclusions

Material properties and construction procedures are the principal factors controlling cracking in bridge decks

ConclusionsLow-slump, moderate-strength concrete results in less cracking than high-slump, high-strength concrete

Conclusions

Best performance requires adherence to all aspects of the specifications

The University of Kansas

David Darwin, Ph.D., P.E.

Deane E. Ackers Distinguished Professor and ChairDept. of Civil, Environmental & Architectural Engineering2150 Learned HallLawrence, Kansas, 66045-7609785 864-3827 Fax: 785 864-5631

daved@ku.edu