SHRINKAGE AND CRACKING BEHAVIOR OF HPC USED FOR

BRIDGE DECK OVERLAYS

By Hasitha Seneviratne

Iowa State University, 2013

INTRODUCTION Objective

To examine the shrinkage and cracking potential of HPC concrete overlay mixes

Different cements Supplementary materials Shrinkage cracking potential

RESEARCH APPROACHShrinkage and Cracking Behavior of HPC Used for Bridge Deck Overlays

Materials Proportions

Experimental work Modeling

εauto εsh εringE, Fc &

Fsplitεsh Creep

Stress analysis

σ Split tensile σ t =Ec εsh σ t ring σ t creep

Cracking Behavior

LITERATURE REVIEW Types of shrinkage

Chemical Autogenous Plastic Drying

Effects of constituent materials Cementitious material Aggregates Admixtures

Factors affecting restrained shrinkage behavior Creep prediction models

B3 Modified NCHRP 496 model

LITERATURE REVIEWPlastic shrinkage

Chemical shrinkage

pore

Capillary Force

Water evaporatesDrying shrinkageAutogenous shrinkage

Factors affecting shrinkage Influence on shrinkage Reference

Autogenous shrinkage

Cement C3A, C4AF increases observed shrinkage

Tazawa (1997)

Fly Ash Reduces autogenous shrinkage

Nakarai (2009)

SlagNo clear evidence of

increasing or decreasing effect, depends on source

and fineness

Whiting (2000)

MetakaolinSimilar shrinkage to control

up to 10% replacement, significant reduction at 15%

replacement

Brooks (2001)

Free Shrinkage

Cement Higher fineness cements increases shrinkage

Deshpande

(2007)Fly Ash Reduces free shrinkage Nakarai

(2009)

SlagFineness influences

performance. Fine ground slag reduces shrinkage

Jianyong (2001),

Miyazawa (2009)

MetakaolinBoth total and pure free

shrinkage are reduced by metakaolin

Brooks (2001)

MATERIALS Cement

Type IP, I/II and I Fly Ash : Class C Fly Ash (Headwaters

Resources) GGBFS (Holcim) Metakaolin : Davison Catalysts Coarse aggregates

Crushed Limestone (2 gradations), Crushed Quartzite Fine aggregates – River Sand Admixtures

Air Entraining Agent: Daravair 1000, Retarder: Daratard 17, Mid-range Water Reducer (MRWR): Mira 62, Standard Water Reducer (NRWR): WRDA 82

MIX PROPORTIONS

EXPERIMENTAL WORK Test methods of concrete shrinkage

Autogenous shrinkage (ASTM C157) Free Drying shrinkage (ASTM C157) Restrained ring shrinkage (ASTM C1581)

Test methods of mechanical properties Elastic modulus (ASTM C469) Compressive strength (ASTM C39) Split tensile strength (ASTM C496)

Shrinkage displayed by cements were as follows Type IP < Type I/II < Type I

Autogenous shrinkage has a high correlation to the amount of cementitious material

Free shrinkage has a strong linear correlation to the mass loss Coarser coarse aggregate displayed lesser restrained shrinkage

SUMMARY OF RESULTS

DISCUSSION Strength Parameters

Concrete mixtures with supplementary cementitious material display late age strength development

Elastic modulus is highly dependent on the amount of cementitious material used

Fly ash improved the strength parameters Slag and combination of MK and fly ash had no

significant impact on strength parameters Combination of fly ash and slag reduced the early

age strength but the strength grew with time. Split tensile strength was greater with coarser

aggregates while elastic modulus was greater with quartzite.

DISCUSSION Free drying stress calculated from the

Hooke’s law and the stress calculated for the strain recorded on the steel ring display a linear relationship.

0 500 1000 1500 2000 2500 30000

200400600800

10001200

f(x) = 0.384535035575493 x + 62.2560617351607R² = 0.69395051435333

Free Drying Stress, psi

Ring

Str

ess,

psi

6 7 4 10 9 5 8 11 1 2 305

10152025303540

Mix ID

Aver

age

Stre

ss R

ate,

psi/

day

Moderate-highModerate-low

Low

Mix

Total cementitious

material content/pcy

Strain Rate α, (μstrain/day)

Cracking time tr, (days)

Stress Rate q, (psi/day) Average

Stress Rate, S

(psi/day)

Rank

ASTM C 1581 Cracking Potential RatingS1 S2 S3 S1 S2 S3 S1 S2 S3

1 665 24.0 23.7 24.2 - - - 24 23 23.6 24 9 Moderate-Low2 650 19.2 20.6 19.5 - - - 19.0 20.4 19.2 20 10 Moderate-Low3 575 12.9 16.8 20.7 - - - 12.8 16.6 20.5 17 11 Moderate-Low4 710 23.8 24.1 27.3 - 13 17 23.5 36.4 35.8 32 3 Moderate-High5 625 26.8 24.7 22.6 11 - - 26.6 24.5 35.7 25 4 Moderate-High6 825 26.7 28.9 32.2 16 16 18 32.9 37.6 41.5 37 1 Moderate-High7 695 34.2 36.6 37.2 - - - 33.8 36.2 36.8 36 2 Moderate-High8 670 22.3 28.5 23.7 - - - 22.0 28.2 23.4 25 7 Moderate-High9 590 19.7 29.6 33.0 - - - 19.5 29.3 32.7 27 6 Moderate-High

10 675 27.2 29.8 27.2 - - - 26.9 29.5 26.9 28 5 Moderate-High11 590 24.1 27.8 21.5 - - - 23.9 27.5 21.3 24 8 Moderate-Low

Mixes 4, 5 and 6 have high cracking potential, Mixes 1, 7, 8, 9 and 10 have medium cracking potential and Mixes 2, 3 and 11 have low cracking potential

Mix No.

σfree = E*εfree

(psi)σ free/(1+φ) ,psi (σfree/1+φ)/Fsp  

Cracking Potential

Peak (σring/1+φ)/Fsp

, (psi/psi)

Cracking Potential

Average Stress Rate, S (psi/day)

ASTM Cracking Potential Rating

14 day 28day 14 day 28day 14 day 28day Rank

1 1351 1766 363 513 1.07 1.22 7 Medium 0.77 Medium 23.6 Moderate-Low

2 1350 1656 395 508 1.12 1.19 8 Low 0.56 Low 19.675 Moderate-Low

3 933 1246 243 343 0.71 0.89 11 Low 0.55 Low 16.6 Moderate-Low

4 1441 1876 414 560 1.37 1.74 3 High 1.00 High 31.9 Moderate-High

5 1989 2344 542 678 1.71 1.93 1 High 0.85 High 24.9 Moderate-High

6 1571 2253 516 766 1.32 1.74 2 High 0.89 High 37.3 Moderate-High

7 1647 2028 466 600 1.19 1.36 6 Medium 0.69 Medium 35.6 Moderate-High

8 1297 1744 315 490 1.09 1.37 4 Medium 0.77 Medium 24.5 Moderate-High

9 1238 1539 277 396 0.99 1.03 10 Low 0.60 Medium 27.1 Moderate-High

10 1509 1771 457 558 1.13 1.11 9 Low 0.76 Medium 27.7 Moderate-High

11 1900 2092 479 575 1.29 1.36 5 Medium 0.52 Low 24.2 Moderate-Low

CONCLUSION AND RECOMMENDATION

Concrete mixes with high shrinkage values may not always crack first and it is the combined effect of shrinkage and mechanical properties (elastic modulus, creep, and strength) that determines concrete cracking potential.

20% fly ash which reduces shrinkage and 25% GGBFS which has little effect on the shrinkage and are recommended to be used in bridge deck overlay concrete either as singular replacements or in combination.

Type I/II Cement may be preferred over Type I cement and Type IP is preferred over Type I/II cement for the consideration of the shrinkage cracking resistance.

Type IP < Type I/II < Type I

CONCLUSION AND RECOMMENDATION

Since free drying shrinkage and mass loss have a strong correlation, mass loss can be used as a good indicator for free drying shrinkage.

Compressive strength is a good indicator to evaluate elastic modulus and split tensile strength.

Controlling the paste volume in concrete to maintain minimum paste volume is highly recommended. Cautions shall be taken when total cementitious material content in concrete of over 700lb/ft3 is used for bridge decks.

Results of the finite element analysis reveals that the mixes would not display cracking within the 56 day period of study.

THANK YOU!QUESTIONS?