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Internal Curing Concrete
Dr Peter Taylor
With thanks to:
John Ries, ESCSIDale Bentz, NIST
Jason Weiss, Purdue
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Internal Curing
Why?
How?
So What? Where Next?
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Internal Curing - Why
Curing is:
Provision of moisture and temperature
to allow hydration and minimizedimensional change
Keep it wetKeep it warm
Start early
stay late
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Without curing we will increase risk of
Cracking
Scaling
A soft surface
What about strength?
Internal Curing - Why
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Internal Curing - Why
Time
Pro
perty
Continuous cure
Curing stops
Elevated temperature curing
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Water
Unhydratedcement
Capillarypores
HCP
W/C = 0.40 W/C = 0.75 W/C = 0.25
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Internal Curing - Why
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Internal Curing - Why
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Material should
Hold sufficient water
Hold the water until needed and not
effect w/c
Give up water at high RH (desorption)Not adversely effect
the concrete quality
Internal Curing - How
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Internal Curing - How
Super Absorbent Polymers
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Internal Curing - How
Desorption
- Virtually all moisture available at 94% RH
Castro 2011
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Water Moving From Aggregate
Paste
LWA
Interface
0.0 mm 0.5 mm0.0 mm 0.5 mm
Detector
X-ray Source
Cement Paste
LWA
Water Can Move ~2 mm after sometime
Schlitter(2010)
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Internal Curing - How
Its All About the Distribution
Henkensiefken (2008)
Coarse
LWAFine LWA
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How Much?
LWA
f
LWAS
CSCM
*
**max
where
MLWA
= mass of (dry) LWA needed per unit volume of concrete (kg/m3
or lb/yd3);Cf= cement factor (content) for concrete mixture (kg/m3 or lb/yd3);
CS= chemical shrinkage of cement (mass of water/mass of cement);
max = maximum expected degree of hydration of cement (0 to 1);
For ordinary Portland cement, the maximum expected degree of
hydration of cement can be assumed to be 1 forw/c0.36 and tobe given by [(w/c)/0.36] forw/c< 0.36.
S= degree of saturation of aggregate (0 to 1);
LWA
= desorption of lightweight aggregate from saturation down to
93 % RH (mass water/mass dry LWA).
Bentz & Snyder (1999), Bentz, Lura, & Roberts (2005):
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Simple IC Mixture Design
Need 7 lbs of IC water per 100 lbs of
cementitious
600 lbs cementitious = 42 lbs of IC water
Assume 18% LWA absorption in the field Assume LWA at 55 lbs/cf
55 x .18 = 9.9 lb/cf water at 90% desorption 8.9
Need 42 lbs IC water / 8.9 = 4.7 cf of LWA 4.7 cf x 55 lb/cf = 259 lbs of LWA aggregate
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NY State DOT Specifications
Proper amount of water
30% replacement of fine aggregate Minimum 15% absorbed
moisture
Place under sprinklerfor minimum of 48 hours
Allow stockpiles to drain
for 12 to 15 hoursimmediately prior to use
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Internal Curing - How
Can we do without this?
Nope
Still have tokeep the
surface
hydrating
Thats where
the abusehappens
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Internal Curing - So What
Benefits
Better hydration & SCM reaction
Improved durability Less cement
Less shrinkage, warping, cracking
Extended service life Improved economics
Increased
sustainability
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Internal Curing - So What
More Hydration
0.40 0.425 0.45 0.475 0.50
Degreeofhyd
ration(%)
Mixture with
internal curing
Mixture without
internal curing
0%
20%
40%
60%
80%
Water / cement ratio
Espinoza-Hajazin (2010)
Degree of hydration of cement @ 90 days, cured @ 50% RH
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Internal Curing So What
Less Shrinkage (Sealed)
Henkensiefken (2009)
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Internal Curing So What
Less Shrinkage; Less Cracking
0 20 40 60 80
Time to Cracking, hours
Control IC Byard (2010)
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Internal Curing So What
Reduced Warping
Wei (2008)
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Internal Curing So What
Lower Absorption
Henkensiefken (2009)
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Internal Curing So What
Reduced Conductivity
Castro (2011)
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Internal Curing So What
Lower Chloride Permeability (90 days)
0.40 0.425 0.45 0.475 0.50
Chargepassed(cou
lombs)
Mixture with
internal curing
Mixture
without
internal curing
0
water / cement ratio
1200
2400
3600
Espinoza-Hajazin (2010)
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Internal Curing - So What
Higher Compressive Strength
- Portland Cement Mortar
0.30 & 0.50 w/c50% RH Curing
Golias (2010)
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Internal Curing - How
Looks too easy
Need an extra stockpile
It has to be wet Not produced in IA
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Internal Curing So What
Service Life Prediction
Cusson (2010)
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Internal Curing So What
Initial & Life Cycle Cost
Cusson (2010)
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Paving in Texas, Bridges in New York & Indiana
UPRRIntermodalFacilityConstructed2005
NY: 9 built or under construction, 7
in design
IN: 33 bridges
Examples
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Buchanan County - Bridge
Three span bridge at Pine Creek
One half conventional (both lanes) Other half using Internal Curing Concrete
About 20% of fine aggregate replaced withlight weight aggregate
Other mix proportions unchanged
Internal Curing Whats Next
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Buchanan County - Bridge
176 feet long, 40 wide
Three spans
Instrument two external spans
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Similar mixtures Control Test
Unit weight 143 138
Slump 4.25 5.00 Air 6.5 6.8
Set time 276 272
7-day strength 4,760 4,820 28-day strength 5,910 7,070
28-day flex 660 715
Shrinkage 0.028 0.023
Buchanan County - Bridge
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Task 1 - Test aggregate and mixture in ISU
lab and during construction
Fresh properties Mechanical properties over time
Cracking potential
Permeability
Hydration rates Moisture contents
Corrosion in the deck
Buchanan County - Bridge
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Task 2 - Live Load Testing
After construction Prior to traffic
One year post-construction
Strain transducers installed on the bottom of thedeck and the girders
Loaded with a fully loaded tandem axle dump
truck to evaluate the live load performance of the
structure
Buchanan County - Bridge
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Concrete overlay
40-ft panels!
Hoping to monitor Warping
Cracking
Buchanan County - Pavement
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Fundamental concept makes sense
Lab data is promising
Field data looking good
Closing