Concrete Shrinkage Testing and Challenges– All shrinkage methods require tight climate controls....
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Concrete Shrinkage Testing and Challenges Presented by Jafar Allahham MS student University of Utah NC2 Meeting April 26 th , 2017 Little America Hotel
Transcript of Concrete Shrinkage Testing and Challenges– All shrinkage methods require tight climate controls....
Concrete Shrinkage Testing and Challenges
Presented by Jafar AllahhamMS student
University of Utah
NC2 Meeting April 26th, 2017Little America Hotel
Acknowledgements• Others at Univ. of Utah Assisting on Project:
• Amanda Bordelon, Ph.D., P.E. (PI on project) • Catalina Arboleda (PhD student)• Min Ook Kim (PhD student)• Lingkun Li (MS student) • Siddartha Rayaprolu (MS student)
• Set-up of Restrained Ring Apparatus Funded by:– Utah Department of Transportation (Project Grant No. 14.402)
• Thomas Hales• Bryan Lee• Scott Strader• Scott Nussbaum• Nicholas Clark• Vincent Liu
– Department of Civil and Environmental Engineering at University of Utah
Concrete Shrinkage
• 4 types of shrinkage– Autogenous– Plastic– Carbonation– Drying
• Other volumetric changes– Creep– Thermal Expansion
and Contraction
Why Concrete Shrinkage is a Problem
http://builtconstructions.in/
Common Factors Affecting Shrinkage in Concrete
• Temperature of the environment.• Relative humidity and curing method.• Water-to-Binder ratio and paste content.• Aggregate size and air content.• Specimen size.
PCA Manual
0
200
400
600
800
1000
1200
1400
1600
0 5 10 15 20 25 30
Free
shrin
kage
(mic
rost
rain
)
Age of concrete (days)
0.54 w/c 0.49 w/c 0.43 w/c 0.38 w/c 0.33 w/c 0.28 w/c
all 28% cement volume content
stored in humidity chamber environment
Aggregate Size and Air Content
• Aggregates’ volume remains constant as the concrete dries restrains paste less net shrinkage.
• Air entrained mixtures exhibit higher shrinkage due to higher overall paste content.
Specimen Size
• Concrete thickness• Thinner – earlier cracking
0
20
40
60
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0 1 2 3 4 5 6 7
Age
of c
rack
ing
(day
s)
Concrete thickness (inches)
Delatte et al. 07Weiss et al. 02Allahham et al. 16
Concrete Shrinkage Testing
Shrinkage TestingASTM C157 Un-restrained (free) Shrinkage Test
• 1” to 4” rectangular prism sizes possible (depends on max aggregate size)– 1” prism most common for mortar– 3” prism for 1” coarse aggregate– 4” prism for 2” coarse aggregate
• Standard recommends moist curing for 28 days to minimize variation.
• After initial curing, samples stored in controlled environment (same as all shrinkage test methods)
Additional Factors Studied Free Shrinkage
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0 10 20 30 40 50 60
Shri
nkag
e (1
0-6
in/in
)
Time (Days)
RefrigeratorHumidity ChamberStorage Room 130CUDOT LabFog Room
University of Utah Lab
RH (%) Temperature (∘C)Location Min Max Average Min Max Average
Refrigerator 0.0 12.0 4.5 7.0 15.0 11.2Humidity Chamber 50.0 50.0 50.0 23.0 23.0 23.0University of Utah 26.0 68.5 53.7 15.0 26.5 23.5
UDOT 32.5 55.5 44.3 23.3 27.8 25.4Fog Room 75.5 104.0 99.9 17.5 25.0 21.9
Specimen Size EffectFree Shrinkage
• Even with same aggregate size (here sand only)• Smaller samples shrink more (more surface area per volume
leads to more drying)• Similar trend as restrained (smaller concrete sample = more
shrinkage)
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0 5 10 15 20 25 30 35 40 45 50 55 60Shri
nkag
e (1
0-6
in/in
)
Time (Days)
1x1x10" prism2x2x10" prism3x3x10" prism
Ring Test Methods
ASTM C1581
AASHTO T334
Outer diameter of concrete 16”
Outer diameter of steel 13”
Outer diameter of concrete 18”
Outer diameter of steel 12”
Height 6”
Height 6”
Steel inside ring 0.5” thick
Concrete 3” thick
Concrete 1.5” thick
Pro and Cons of the Test Methods Pros Cons+ Relatively simple
setup.+ Can be used as a mix
design quality control.
− Not correlated to actual field performance Concrete is usually restrained.
− Requires control of temperature and humidity in sample storage room.
+ Simulates restrained conditions.
+ Mixtures can be evaluated in 28 day timeframe.
+ Can study concrete pavement mixtures or bridge deck mortar.
− Steel must be custom made.− Requires control of temperature
and humidity in sample storage room.
− High testing setup cost.− Concrete may never crack.
Free Shrinkage
Restrained Shrinkage
Ring Shrinkage Test Set-up Requirements
Data Fluctuation
-200
-150
-100
-50
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50
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0 3 6 9
Aver
age
Stra
in a
fter
Tem
pera
ture
C
ompe
nsat
ion
(10^
-6 in
/in)
Age (days)
Trial 1 both 2” rings failed between 3 and 7 days
Trial 2 both 2” rings failed at 8 days
Environmental Controls• Temperature 73 +/- 3 F and relative humidity 50% +/- 4%.
– We found room humidifier not producing 50% nor maintaining consistent RH levels
– Temperature fluctuations reduced with humidifier, but still too high each day
30
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70
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78
4/13 4/13 4/14 4/14 4/15 4/15 4/16
Rel
ativ
e H
umid
ity
(%)
Tem
pera
ture
(F)
Fahrenheit(ｰF) Humidity(%rh)
Room Environment Fluctuation
50
60
70
80
9010
/710
/21
11/4
11/1
812
/212
/16
12/3
01/
13
Tem
pera
ture
(F)
50
60
70
80
90
10
30
50
70
10/7
10/2
111
/411
/18
12/2
12/1
612
/30
1/13
Rel
ativ
e H
umid
ity
(%)
10
30
50
70
Before humidifier After humidifier
Summary of Ring Test Challenges• High dependability on the surrounding environment
– All shrinkage methods require tight climate controls.
• At minimum, need to visually monitor the restrained rings– Poor quality of the strain gauge software can cause problems.– Strain gauges can be temperature-compensating.
• AASHTO T334 ring test method is not a favorable method to compare mix designs – May never crack
• ASTM C157 free shrinkage method preferred – Can be used to compare different mixtures and environmental
conditions.
Questions?
Report of this work can be found at:
Jafar Allahham, Amanda Bordelon, Lingkun Li, and Siddartha Rayaprolu. “Review and Specification for Shrinkage Cracks of Bridge Decks”, Utah Department of Transportation Report No. UT-16.17, December 2016.
