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Internal Curing Using Prewetted Lightweight Aggregates
Presented to:
LA DOTD Transportation Conference
February, 2013
Jeff Speck, P.E., FACI
V.P. Sales & Marketing
Big River Industries, Inc.
Improving Concrete Durability and
Sustainability Using Internal Curing
Curing is one of seven essential
procedures “that make concrete capable
of providing decades of service with
little or no maintenance.”
[ACI 201 2R-08, Guide to Durable Concrete]
INTERNAL CURING USING PREWETTED LIGHTWEIGHT AGGREGATE
ACI: Internal Curing: “supplying water
throughout a freshly placed cementitious
mixture using reservoirs, via pre-wetted
lightweight aggregates, that readily release
water as needed for hydration or to replace
moisture lost through evaporation or self-
desiccation [1]”
INTERNAL CURING USING PREWETTED LIGHTWEIGHT AGGREGATE
What is LWA? • Expanded shale, clay and
slate (ESCS)
• Structural, ceramic aggregate produced in a rotary kiln
• Less than half the unit weight of ordinary aggregate
• Complies with
ASTM C-330 and C-331
• Use fine aggregate to distribute water
• Help satisfy increased water demand from SCM’s
• Works even at moderate 0.40 – 0.48 w/cm
INTERNAL CURING USING PREWETTED LIGHTWEIGHT AGGREGATE
INTERNAL CURING USING PREWETTED LIGHTWEIGHT AGGREGATE
It’s All About the Distribution
Henkensiefken (2008)
Coarse
LWA
Fine LWA
Hydration Age Estimated Travel
Distance for Water
< 1 day 20 mm
1 day to 3 days 5 mm
3 days to 7 days 1 mm
> 28 days 0.25 mm
Clogging the Capillaries
With Products of Hydration Restricts the Flow of Water
Bentz, D., Koenders, S., Monnig, S., Reinhardt, H., van Breugel, K ., Ye, G.
INTERNAL CURING USING PREWETTED LIGHTWEIGHT AGGREGATE
• Benefits • Less shrinkage, less cracking
• Improved fluid transport properties
• lower water absorption
• lower chloride permeability & penetration
• More hydration & SCM reaction
• less cement or more strength
• Results • More durable structures achieving extended
service life
• Improved economics
• Increased sustainability
INTERNAL CURING USING PREWETTED LIGHTWEIGHT AGGREGATE
Extensive Lab Research
INTERNAL CURING USING PREWETTED LIGHTWEIGHT AGGREGATE
121 Citations as of December 2011
Stress Development Mechanisms
INTERNAL CURING USING PREWETTED LIGHTWEIGHT AGGREGATE
Why Does Concrete Crack?
Restraint + Volume Change = Stress
Occurs When Tensile Stress Exceeds
Tensile Capacity
Stress Development Mechanisms
INTERNAL CURING USING PREWETTED LIGHTWEIGHT AGGREGATE
• Early-Age Volume Change Occurs Because of
• Thermal effects
• Temperature changes due to hydration
• Coefficient of thermal expansion
• Decrease of internal relative humidity
• Drying due to atmospheric conditions
• Self-desiccation (autogenous shrinkage)
The “Bentz Equation”
𝑀𝐿𝑊𝐴 =𝐶𝑓 ∗ 𝐶𝑆 ∗ α𝑚𝑎𝑥
𝑆 ∗ 𝝓𝐿𝑊𝐴
~ 7 lb of internal curing water needed per 100 lb
cement
INTERNAL CURING USING PREWETTED LIGHTWEIGHT AGGREGATE
Mixture Proportions of the Fine Aggregate In a Yard of Concrete
Natural Sand
10-25% LWAS 75-90% Natural Sand
For Internal Curing Replace a Portion of Natural Sand
With Lightweight Aggregate Sand (LWAS)
LWAS
Cement Paste Cement Paste LWA
Sealed - SRA
Unsealed - Plain Unsealed - SRA
Sealed - LWA
Unsealed - LWA
Sealed - Plain Sealed - SRA
Unsealed - Plain Unsealed - SRA
Sealed - LWA
Unsealed - LWA
Sealed - Plain
0.1 1.0 10.0 100.0 1000.0
Kelvin Radius (nm)
30
40
50
60
70
80
90
100
Rela
tiv
e H
um
idit
y (
%)
= 72 x 10-3 N/m (Plain)
= 36 x 10-3 N/m (~5% SRA)
20 40 60 80 100
Relative Humidity (%)
-5000
-4000
-3000
-2000
-1000
0
Sh
rin
kag
e S
train
()
w/c = 0.30
w/c = 0.30+5%SRA
Menisci Radius (nm)
r1 r1 r2
r3 r3 r4
Sealed - SRA
Unsealed - Plain Unsealed - SRA
Sealed - LWA
Unsealed - LWA
Sealed - Plain Sealed - SRA
Unsealed - Plain Unsealed - SRA
Sealed - LWA
Unsealed - LWA
Sealed - Plain
0.1 1.0 10.0 100.0 1000.0
Kelvin Radius (nm)
30
40
50
60
70
80
90
100
Rela
tiv
e H
um
idit
y (
%)
= 72 x 10-3 N/m (Plain)
= 36 x 10-3 N/m (~5% SRA)
20 40 60 80 100
Relative Humidity (%)
-5000
-4000
-3000
-2000
-1000
0
Sh
rin
kag
e S
train
()
w/c = 0.30
w/c = 0.30+5%SRA
Menisci Radius (nm)
r1 r1 r2
r3 r3 r4
• Largest pores will empty first
• The saturated LWA provides water to the paste and keeps
a large pore full
Why can LWA be used for IC?
More Hydration
0.40 0.425 0.45 0.475 0.50
Degre
e o
f hydra
tion
(%
)
█ Mixture with
internal curing
█ Mixture without
internal curing
0%
2
0%
4
0%
6
0%
8
0%
Water / cement ratio
Espinoza-Hajazin (2010)
Degree of hydration of cement @ 90 days, cured @ 50%
RH
Higher Compressive Strength
- Portland Cement Mortar @ 0.30 & 0.50 w/c
Sealed Curing 50% RH Curing
Golias (2011)
Less Shrinkage; Less Cracking
Schlitter (2010)
Plain 0.30 Concrete
0.6 mm wide crack
observed @ 12 days
IC 0.30 Concrete
0.4 mm wide crack
observed @ 43 days
0 20 40 60 80
Time to Cracking, hours
Control IC
Delayed Cracking
- Summer curing temp. profile for expanded shale
IC mix
Byard (2010)
Lower Chloride Permeability
0.40 0.425 0.45 0.475 0.50
Charg
e p
assed (
cou
lom
bs)
█ Mixture with
internal curing
█ Mixture without
internal curing
0
water / cement ratio
1200
2400
3600
Espinoza-Hajazin (2010)
Chloride ion permeability @ 90 days, cured @ 50%
RH
Internal Curing vs. No Internal Curing
Denver Water Test Slabs – 92oF ambient, 20% RH
No conventional curing
Internal Curing No Internal Curing
Denver Water – 10 million gallon tank
– 1300 yard slab pour
Change Order to include walls and columns
Denver Water – 10 million gallon tank
– Contractor requested change order to use IC mix
for ring girder, columns and walls
INTERNAL CURING USING PREWETTED LIGHTWEIGHT AGGREGATE
Denver Water - Conclusions
• Using IC resulted in an 80% reduction in
shrinkage cracks compared to similar size
tanks built previously
• Based on the Lonetree Basin project
success, IC will be used for:
• 2 more 10 MG tanks will be built this
year
• Three 15 MG tanks are planned for 2014
Paving in Texas
UP RR Intermodal Facility Constructed 2005
250,000 yd3 IC project low slump pavement
Visual inspections At 6 months one crack At 5.5 yrs minuscule plastic or drying shrinkage cracks
NY: 16 built or under construction as of 2012
IN: 33 bridges
INTERNAL CURING USING PREWETTED LIGHTWEIGHT AGGREGATE
Bridges in New York & Indiana
INTERNAL CURING USING PREWETTED LIGHTWEIGHT AGGREGATE
Indiana Bridges NE of Bloomington
• Replacement of two bridges ¼ mile apart
• Prestressed concrete box beams
• Composite RC deck
• 8” thick at centerline, 4½” thick at edge
INTERNAL CURING USING PREWETTED LIGHTWEIGHT AGGREGATE
Indiana Bridges NE of Bloomington
InDOT 2010
Standard External Curing
(wet burlap) – Both Bridges
INTERNAL CURING USING PREWETTED LIGHTWEIGHT AGGREGATE
Indiana Bridges NE of Bloomington
InDOT 2010
Plain Concrete Deck at
One Year
INTERNAL CURING USING PREWETTED LIGHTWEIGHT AGGREGATE
Indiana Bridges NE of Bloomington
Plain Concrete Deck at
One Year
Longitudinal and
Transverse crack
INTERNAL CURING USING PREWETTED LIGHTWEIGHT AGGREGATE
Indiana Bridges NE of Bloomington
IC Concrete Deck at
One Year
No Cracks
Texas State Highway 121
1300 CY, 5 miles of CRCP, Class P
INTERNAL CURING USING PREWETTED LIGHTWEIGHT AGGREGATE
SR-121
Crack Spacing of IC Section at 10 months
INTERNAL CURING USING PREWETTED LIGHTWEIGHT AGGREGATE
Conclusions
INTERNAL CURING USING PREWETTED LIGHTWEIGHT AGGREGATE
• The use of saturated LWA for internal curing delays the occurrence of early-age cracking in bridge deck and pavement applications
• This is because the use of LWA for IC:
• Decreases or eliminates stresses due to autogenous shrinkage effects
• Decreases the modulus of elasticity
• Decreases the coefficient of thermal expansion
• This improved cracking performance may be in the form of: reduced number of cracks and/or decreased crack widths.
Say premium for IC is $10/CY (assumption)
Assume 9” deck
Compute premium per SF of bridge deck:
$10/CY (0.75 CF/SF) (1CY/27CF) = $0.28/SF
Compare to Fed Aid unit costs for entire bridge:
Avg = $156/SF 0.28/156 = 0.18%
Max = $558/SF 0.28/558 = 0.05%
Min = $57/SF 0.28/57 = 0.49%
The cost of IC, compared to total bridge cost, is very minor – less than ½ of 1%, at worst!
Cost of Internal Curing
Summary:
• Less shrinkage, less cracking
• More hydration & SCM reaction
• Improved transport properties
• Lower water absorption
• Lower chloride permeability & penetration
• Increased durability
• Significant increase in service life
• Significant life cycle cost reduction
• Increased sustainability
Researchers
Dale Bentz Chemical Engineer
National Institute of Standards &
Technology
100 Bureau Drive Stop 8615
Gaitherburg, MD 20899
(301) 975-5865
http://concrete.nist.gov/bentz
Jason Weiss Professor
Purdue University – School of Civil
Engineering
550 Stadium Mall Drive
West Lafayette, IN 47907
(765) 494-2215
http://cobweb.ecn.purdue.edu/~wjweiss
Anton Schindler HRC Director/Associate Professor
Auburn University
238E Harbert Engineering Center
Auburn, AL 36849
(334) 844-6263
References
Byard, B. & Schindler, A. (2010). Cracking Tendency of Lightweight
Concrete, Research Report. Auburn University: Highway Research
Center.
Castro, J. (2011). Moisture Transport in Cement-Based Materials:
Application to Transport Tests and Internal Curing, Ph.D. Thesis. West
Lafayette: Purdue University.
Cusson, D., Lounis, Z., & Daigle, L. (2010). Benefits of Internal Curing
on Service Life and Life-Cycle Cost of High-Performance Concrete
Bridge Decks – A Case Study. Cement and Concrete Composites, 32.
Espinoza-Hajazin, G., & Lopez, M. (2010) Extending Internal Curing
To Concrete Mixtures With W/C Higher Than 0.42. Construction &
Building Materials, Elsevier Ltd.
Golias, M. (2010). The Use of Soy Methyl Ester-Polystyrene Sealants
and Internal Curing to Enhance Concrete Durability, M.S. Thesis. West
Lafayette: Purdue University.
References (cont’d)
Henkensiefken, R. (2008). Volume Change and Cracking in Internally
Cured Mixtures Made with Saturated Lightweight Aggregate Under
Sealed and Drying Conditions, Presented at ACI Fall Convention, St.
Louis, MO.
Henkensiefken, R., Bentz, D., Nantung, T., & Weiss, J. (2009). Volume
Change and Cracking in Internally Cured Mixtures Made with
Saturated Lightweight Aggregates under Sealed and Unsealed
Conditions. Cement and Concrete Composites , 31 (7), 426-437.
Schlitter, J., Kenkensiefken, R., Castro, J., Raoufi, K., Weiss, J., &
Nantung, T. (2010). Development of Internally Cured Concrete for
Increased Service Life. Joint Transportation Research Program. West
Lafayette: Purdue University.
Wei, Y., & Hansen, W. (2008). Pre-soaked Lightweight Fine Aggregates
as Additives for Internal Curing in Concrete. In D. Bentz, & B. Mohr
(Ed.), Internal Curing of High-Performance Concretes: Laboratory and
Field Experiences (pp. 35-44). Farmington Hills: American Concrete
Institute.
In the words of Jason Weiss
IC is “ready to go, NOW!”
“The research has been done; it’s time to
stop talking about it and start making use of
it.”
- – Jason Weiss at TRB, January, 2013