restrained shrinkage cracking: self-curing concrete made...

CBC 2008 May 4-7, 2008 Slide 1 of 26

School of Civil Engineering

Purdue University

Restrained Shrinkage Cracking:

Self-Curing Concrete Made using

Saturated Lightweight Aggregate

Ryan Henkensiefken, Purdue University

Tommy Nantung, INDOT

Jason Weiss, Purdue University

Prepared and Presented for the 2008 National Concrete Bridge Conference

St. Louis, Missouri, by Ryan Henkensiefken

CBC 2008 May 4-7, 2008 Slide 2 of 26

Outline

• Cracking in Bridge Decks

• Causes of Autogenous Shrinkage

• How LWA helps Mitigate the Problem

• Objectives

• Difference between Sealed and Unsealed Curing Conditions as it relates to autogenous shrinkage

• Experimental Measurements

• Experimental Results

• Conclusion

CBC 2008 May 4-7, 2008 Slide 3 of 26

Cracking in Bridge Decks

• Increase in the use of high-performance concrete in bridge decks because of improved durability

• HPC tends to have increased autogenous shrinkage in sealed conditions

Initial Specimen

Autogenous

Shrinkage Effect

Initial Bridge Deck

Length

Restraint Effect Reconnect Deck

Disconnect Deck

CBC 2008 May 4-7, 2008 Slide 4 of 26

Outline




• Objectives




• Conclusion

CBC 2008 May 4-7, 2008 Slide 5 of 26

Causes of Autogenous Shrinkage

• Hydration

product volume

is smaller than

cement and water

volume

• Not problematic with higher w/c mixtures

Cement

Water

Hydration

products

Chemical

shrinkage

1 Vol

1 Vol

1.8

Vol

CBC 2008 May 4-7, 2008 Slide 6 of 26

• Chemical Shrinkage

creates vapor filled

space

• Pressure Difference

between fluid and

vapor

• Pressure Difference

is the cause of

shrinkage


Jensen, 2005

CBC 2008 May 4-7, 2008 Slide 7 of 26


• Autogenous shrinkage

is the shrinkage of the

bulk system

• Before set - No stress

development due to

autogenous shrinkage

• After set - Can have

significant stress

development due to

autogenous shrinkage

Jensen, 2005

CBC 2008 May 4-7, 2008 Slide 8 of 26


0 1 2 3 4 5 6 7

Time (Days)

0

0.01

0.02

0.03

0.04

0.05

Po

re V

olu

me (

ml/

gcem)

Chemical Shrinkage

Autogenous Shrinkage

Open Void Space

CBC 2008 May 4-7, 2008 Slide 9 of 26

Outline




• Objectives




• Conclusion

CBC 2008 May 4-7, 2008 Slide 10 of 26

80 82 84 86 88 90 92 94 96 98 100

Relative Humidity (%)

0

10

20

30

40

50

60

70

80

90

100

Pe

rcen

t o

f A

bso

rbe

d

Wate

r R

em

ain

ing

(%

)

LWA

How LWA helps Mitigate the Problem

• Water is given up at

high relative

humidities

• Water leaves the

largest pore first

• Pores of the LWA are

larger than the pores

of the paste

Radlinska et al, 2007

CBC 2008 May 4-7, 2008 Slide 11 of 26


• Initial consumption

of water

• Replenish system

with water from

LWA

Jensen, 2005

CBC 2008 May 4-7, 2008 Slide 12 of 26


0 1 2 3 4 5 6 7

Time (Days)

0

0.01

0.02

0.03

0.04

0.05

Po

re V

olu

me (

ml/

gcem)

Chemical Shrinkage

Autogenous Shrinkage

Open Void Space

CBC 2008 May 4-7, 2008 Slide 13 of 26

Outline




• Objectives




• Conclusion

CBC 2008 May 4-7, 2008 Slide 14 of 26

Objectives

• Discuss the difference

between sealed and

unsealed curing

conditions

• Provide experimental

measurement of

shrinkage performance

of mortars with varying

LWA volume

replacements.

CBC 2008 May 4-7, 2008 Slide 15 of 26

Outline




• Objectives




• Conclusion

CBC 2008 May 4-7, 2008 Slide 16 of 26

Sealed and Unsealed Curing

Conditions

• Interior Voids

are created

due to self-

desiccation

• Surface Voids

are created due to drying

• Sealed curing experiences internal voids only

• Unsealed curing experiences both internal and external voids

liquid solid vapor

(a) Sealed (b) External Drying Only (c) Unsealed

Drying Drying Sealed

Radlinska et al, 2007

CBC 2008 May 4-7, 2008 Slide 17 of 26

Outline




• Objectives




• Conclusion

CBC 2008 May 4-7, 2008 Slide 18 of 26

Experimental Measurements

• As more LWA is added more water is available

• Aggregate volume remained constant at 55%

0% 728 218 1418 0 0

3.8% 728 218 1319 60 6

7.3% 728 218 1230 114 12

11.0% 728 218 1135 172 18

14.3% 728 218 1050 223 23

18.3% 728 218 950 283 30

25.3% 728 218 808 369 39

29.3% 728 218 667 455 48

33.0% 728 218 567 525 54

Additional Water

Provided by LWA (kg/m3)

Cement

(kg/m3)

Water

(kg/m3)

Fine Aggregate

(kg/m3)

LWA

(kg/m3)

CBC 2008 May 4-7, 2008 Slide 19 of 26

Experimental measurements

• Internal Relative

Humidity

• Free Shrinkage

C157 with first 24 hours

• Restrained Shrinkage

C1581

Moon et al., 2004

Sant, 2007

CBC 2008 May 4-7, 2008 Slide 20 of 26

Outline




• Objectives




• Conclusion

CBC 2008 May 4-7, 2008 Slide 21 of 26

Internal Relative Humidity

• Equation relating RH to pore size

• Equation relating pore size to shrinkage

0 1 2 3 4 5 6 7

Time (Days)

80

82

84

86

88

90

92

94

96

98

100

Rela

tive H

um

idit

y (

%)

33.0% LWA

29.3% LWA

25.3% LWA

18.3% LWA

14.3% LWA

7.3% LWA

0.0% LWA

sp

pKKr

S 112

3

RT

V

RHr m

)ln(

)cos(2

Henkensiefken et al., 2008

CBC 2008 May 4-7, 2008 Slide 22 of 26

Sealed Free Shrinkage

0 7 14 21 28

Time (Days)

-400

-300

-200

-100

0

100

200

300

400

Str

ain

()

33.0% LWA

29.3% LWA

25.3% LWA

18.3% LWA

14.3% LWA

11.0% LWA

7.3% LWA

0.0% LWA


CBC 2008 May 4-7, 2008 Slide 23 of 26

Sealed Restrained Shrinkage

0 2 4 6 8 10 12 14 16 18 20 22

Time (Days)

-60

-50

-40

-30

-20

-10

0

10

Str

ain

()

25.3% LWA

14.3% LWA

11.0% LWA

7.3% LWA

3.8% LWA

0.0% LWA


CBC 2008 May 4-7, 2008 Slide 24 of 26

Unsealed Free Shrinkage

0 7 14 21 28

Time (Days)

-800

-700

-600

-500

-400

-300

-200

-100

0

100

200

300

Str

ain

()

33.0% LWA

29.3% LWA

25.3% LWA

18.3% LWA

14.3% LWA

11.0% LWA

7.3% LWA

0.0% LWA


CBC 2008 May 4-7, 2008 Slide 25 of 26

Unsealed Restrained Shrinkage

0 2 4 6 8 10 12 14

Time (Days)

-60

-50

-40

-30

-20

-10

0

10

Str

ain

()

33.0% LWA

29.3% LWA

25.3% LWA

14.3% LWA

11.0% LWA

7.3% LWA

0.0% LWA


CBC 2008 May 4-7, 2008 Slide 26 of 26

Conclusions

• Specimens with a larger replacement

volume of LWA maintained a higher internal

humidity

• Specimens with a larger volume of LWA

showed a reduction in rate of shrinkage and

absolute shrinkage

• The time to cracking is prolonged for

mixtures with an increasing replacement

volume of LWA

CBC 2008 May 4-7, 2008 Slide 27 of 26

Acknowledgements

• This work was supported in part by the Joint Transportation Research Program administered by the Indiana Department of Transportation and Purdue University

• Dale Bentz

– National Institute of Standards and Technology

• John Roberts

– Northeast Solite Corporation

• Jack Spaulding

– Hydraulic Press Brick Company

CBC 2008 May 4-7, 2008 Slide 28 of 26

Questions

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