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
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.