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NPCA Precast Show – Internal Curing Page 1 of 40
Jason Weiss, [email protected] March 2020
NPCA Show - Improving the Performance of Concrete with Internal Curing Slide 1 of 120
Improving the Performance of
Concrete with Internal Curing
Internally Cured Concrete – Jason Weiss - [email protected]
Objectives
Concrete
Problems
Defining Internal
Curing
Science of
Internal Curing
Internal Curing
Applications
NPCA Show - Improving the Performance of Concrete with Internal Curing Slide 2 of 120
Objectives
• Understand difference between external
and internal curing
• Understand why the
use of internal curing
is needed today
• Understand the
science of internal curing
• Understand which properties of concrete
can be improved with internal curing
• Examine recent steps the industry is
taking to implement internal curing
Objectives
Concrete
Problems
Defining Internal
Curing
Science of
Internal Curing
Internal Curing
Applications
NPCA Show - Improving the Performance of Concrete with Internal Curing Slide 3 of 120
Concrete Problems
• American’s spend 4.2 billion hours a
year stuck in traffic
• Bridges (>25%) are structurally deficient
or functionally obsolete
• Highways (>33%) are in poor
or mediocre
condition
• Cracked and
spalling concrete
• Corroding steel
reinforcement
Objectives
Concrete
Problems
Defining Internal
Curing
Science of
Internal Curing
Internal Curing
Applications
NPCA Precast Show – Internal Curing Page 2 of 40
Jason Weiss, [email protected] March 2020
NPCA Show - Improving the Performance of Concrete with Internal Curing Slide 4 of 120
Concrete Opportunities
• Reducing unwanted cracking in
concrete, especially in higher
performance concrete
• Improving construction schedule when
long curing times are needed
• Improving rapid repairs and patches
• Making concrete less susceptible to
thermal cracking at early ages
• VALUE ADDED PRODUCT …..
Objectives
Concrete
Problems
Defining Internal
Curing
Science of
Internal Curing
Internal Curing
Applications
NPCA Show - Improving the Performance of Concrete with Internal Curing Slide 5 of 120
Curing
• When concrete is placed it is sensitive and can
be easily damaged if not treated properly
• We want to maintain appropriate temperature
and moisture during the first few weeks
• Proper curing enables concrete to hydrate
(chemically react) developing potential strength
and durability
• Proper curing reduce
stress and cracking
potential due to
drying or temperature
changes
• Important but frequently overlooked step
Objectives
Concrete
Problems
Defining Internal
Curing
Science of
Internal Curing
Internal Curing
Applications Photo
C.
DiB
ella
NPCA Show - Improving the Performance of Concrete with Internal Curing Slide 6 of 120
External Curing
• Conventional curing works by treating
the ‘outside’ of concrete after placement
– Placing water
(water curing) on the
concrete surface
– Placing a curing
compound that
helps to reduce water
loss to evaporation
Objectives
Concrete
Problems
Defining Internal
Curing
Science of
Internal Curing
Internal Curing
Applications
NPCA Precast Show – Internal Curing Page 3 of 40
Jason Weiss, [email protected] March 2020
NPCA Show - Improving the Performance of Concrete with Internal Curing Slide 7 of 120
Challenges with External Curing
• External curing has worked for centuries,
why is something different needed now?
• In an effort to make concrete less
permeable (i.e., HPC) we use more low
w/c systems with supplementary cement
• While reduced porosity is good for
durability, it can limit water movement
limiting the effectiveness of water curing
• Supplementary cementitious materials
requires longer curing times (slower
reactions) and have more chemical
shrinkage with hydration
Objectives
Concrete
Problems
Defining Internal
Curing
Science of
Internal Curing
Internal Curing
Applications
NPCA Show - Improving the Performance of Concrete with Internal Curing Slide 8 of 120
Internal Curing
• Internal curing - process by which the
hydration of cement occurs when internal
reservoirs provide additional water that is
not part of
the mixing
water
• Allows curing
to be well
distributed
• Allows curing
as needed
Objectives
Concrete
Problems
Defining Internal
Curing
Science of
Internal Curing
Internal Curing
Applications
NPCA Show - Improving the Performance of Concrete with Internal Curing Slide 9 of 120
How Does Internal Curing Work?
• Water can be lost due to drying
• Water can be consumed by hydration
resulting in self desiccation
Objectives
Concrete
Problems
Defining Internal
Curing
Science of
Internal Curing
Internal Curing
Applications
NPCA Precast Show – Internal Curing Page 4 of 40
Jason Weiss, [email protected] March 2020
NPCA Show - Improving the Performance of Concrete with Internal Curing Slide 10 of 120
How Does Internal Curing Work?
• Porous lightweight aggregate
is ‘prewetted’ before mixing
• Water moves from the ‘pores’
in LWA to the paste on demand as needed
• This movement is due to fact that smaller
pores want to remain ‘water filled’
Conceptual
Model
of Pores In
Concrete
Conventional Concrete Internally Cured Concrete
LWA
Radlin
ska
et al. 2
007
Objectives
Concrete
Problems
Defining Internal
Curing
Science of
Internal Curing
Internal Curing
Applications
NPCA Show - Improving the Performance of Concrete with Internal Curing Slide 11 of 120
Internal Curing Applications
• NYDOT using internal curing in bridge
decks (map showing bridges as of 2012)
• General experience is positive
• Reduced cracking with no problems to
contractor or supplier
Objectives
Concrete
Problems
Defining Internal
Curing
Science of
Internal Curing
Internal Curing
Applications
Streeter et al. 2012
NPCA Show - Improving the Performance of Concrete with Internal Curing Slide 12 of 120
Internal Curing Applications
• RR intermodal facility
– 250,000 yd3 of low slump IC material
• CRC Paving for TxDOT
– 6 months 1 crack, 5.5 years minor drying or
plastic shrinkage cracking
Objectives
Concrete
Problems
Defining Internal
Curing
Science of
Internal Curing
Internal Curing
Applications
Friggle et al. 2008
NPCA Precast Show – Internal Curing Page 5 of 40
Jason Weiss, [email protected] March 2020
NPCA Show - Improving the Performance of Concrete with Internal Curing Slide 13 of 120
Internal Curing Applications
• Two bridge decks were cast in 2010 at the
same time in Monroe Co (Bloomington) IN
• Internally cured bridge: similar workability,
higher strength, lower transport and no
cracking (3 cracks in the plain bridge)
• Additional bridges being constructed
Objectives
Concrete
Problems
Defining Internal
Curing
Science of
Internal Curing
Internal Curing
Applications Photo
Cre
dit D
iBella
NPCA Show - Improving the Performance of Concrete with Internal Curing Slide 14 of 120
Internal Curing Applications
• Building large slabs
is complex
• Denver Water 10-
Million Gallon Lone
Tree Tank No. 2
• Negligible
differences in
placing & finishing
• Opinion – less
cracking and
maintainence
Objectives
Concrete
Problems
Defining Internal
Curing
Science of
Internal Curing
Internal Curing
ApplicationsBates et al. 2012
NPCA Show - Improving the Performance of Concrete with Internal Curing Slide 15 of 120
Summary
• US infrastructure is aging & deteriorating:
IC offers one approach to extend the
service life of concrete
• LWA can be used as a reservoir to ‘hide
water’ throughout the cross section that
can be used during hydration
• Internal curing can reduce shrinkage and
shrinkage induced cracking
• Internal curing is being implemented, with
examples shown, in practice and showing
great potential
Objectives
Concrete
Problems
Defining Internal
Curing
Science of
Internal Curing
Internal Curing
Applications
NPCA Precast Show – Internal Curing Page 6 of 40
Jason Weiss, [email protected] March 2020
NPCA Show - Improving the Performance of Concrete with Internal Curing Slide 16 of 120
NPCA Show - Improving the Performance of Concrete with Internal Curing Slide 17 of 120
Internal Curing Concept, Mixture
Proportioning, and Aggregate
Objective
Concept
Internal and
External Curing
Proportioning
Principles
Example
Aggregate
Properties
Internally Cured Concrete Series – [email protected]
NPCA Show - Improving the Performance of Concrete with Internal Curing Slide 18 of 120
Objectives
• To understand what is meant
by the term internal curing
• To understand the principles
that are used to proportion
internally cured mixtures: 1) chemical shrinkage volume
2) aggregate spacing
3) aggregate properties
• To understand the tests that are
used to quantify aggregate performance
Objective
Concept
Internal and
External Curing
Proportioning
Principles
Example
Aggregate
Properties
NPCA Precast Show – Internal Curing Page 7 of 40
Jason Weiss, [email protected] March 2020
NPCA Show - Improving the Performance of Concrete with Internal Curing Slide 19 of 120
What is Curing
• Describes the process by which
hydraulic-cement concrete matures
and develops hardened properties
over time
• Continued
hydration of the
cement in the
presence of
sufficient water
and heat.
Objective
Concept
Internal and
External Curing
Proportioning
Principles
Example
Aggregate
Properties
NPCA Show - Improving the Performance of Concrete with Internal Curing Slide 20 of 120
Conventional Curing (ACI 308)
• Measures taken to limit the loss of
water, heat, or both, from the
concrete, or by externally providing
moisture and heat.
• Action taken to maintain moisture
and temperature conditions in a
freshly placed cementitious mixture
to allow hydraulic-cement hydration
and, if applicable, pozzolanic
reactions to occur
Objective
Concept
Internal and
External Curing
Proportioning
Principles
Example
Aggregate
Properties
NPCA Show - Improving the Performance of Concrete with Internal Curing Slide 21 of 120
External Curing
• Conventional
concrete is done
to the outside of
the concrete
• Can think of
this a little like
a crab/lobster
exoskeleton http://express.howstuffworks.com/exp-exoskeleton.htm
Objective
Concept
Internal and
External Curing
Proportioning
Principles
Example
Aggregate
Properties
NPCA Precast Show – Internal Curing Page 8 of 40
Jason Weiss, [email protected] March 2020
NPCA Show - Improving the Performance of Concrete with Internal Curing Slide 22 of 120
• Water Ponding, Sprinkling, Burlap:
Supply Additional Water
• Curing Membranes:
Reduce Loss of
Water to the
Environment
Most Common Types of
External Curing
Objective
Concept
Internal and
External Curing
Proportioning
Principles
Example
Aggregate
Properties
NPCA Show - Improving the Performance of Concrete with Internal Curing Slide 23 of 120
Are There Other Options
• Exoskeleton vs Endoskeleton
• Can we look inside the concrete
• Can we supply water from inside
http://science.howstuffworks.com/environmental/earth/geology/dinosaur-bone-age.htm
Objective
Concept
Internal and
External Curing
Proportioning
Principles
Example
Aggregate
Properties
NPCA Show - Improving the Performance of Concrete with Internal Curing Slide 24 of 120
Internal Curing (IC)
• IC works
from the
inside of
concrete
• IC uses
reservoirs
of water
that hide water before set to get a
dense structure and make the water
available after set for hydration
Ca
str
o e
t a
l. 2
01
0
Objective
Concept
Internal and
External Curing
Proportioning
Principles
Example
Aggregate
Properties
NPCA Precast Show – Internal Curing Page 9 of 40
Jason Weiss, [email protected] March 2020
NPCA Show - Improving the Performance of Concrete with Internal Curing Slide 25 of 120
Where Do We ‘Hide’ IC Water ?
• Porous Inclusions - a solid body
that contains pores for gas or liquid
to be enclosed within the mass of a
mineral.
• Lightweight aggregate
has pores that enable
it to absorb water that
can be released after setting
Objective
Concept
Internal and
External Curing
Proportioning
Principles
Example
Aggregate
Properties
NPCA Show - Improving the Performance of Concrete with Internal Curing Slide 26 of 120
Why IC and Why Now?
• HPC are ‘dense’ and remove and
disconnect large pores
• While this is good for durability it
makes it more difficult for curing
water to move into concrete
• Concrete also self-desiccates (i.e.,
dries from inside without water loss)
• Self-desiccation increases in low
w/c & with supplementary materials
Objective
Concept
Internal and
External Curing
Proportioning
Principles
Example
Aggregate
Properties
NPCA Show - Improving the Performance of Concrete with Internal Curing Slide 27 of 120
What is Self-Desiccation
• Simply – it’s like internal drying
without water loss
• A reduction in
internal relative
humidity (RH)
occurs when
pores are emptied
• What causes these pores to empty?
• Does the size of the pore matter?
Objective
Concept
Internal and
External Curing
Proportioning
Principles
Example
Aggregate
Properties
NPCA Precast Show – Internal Curing Page 10 of 40
Jason Weiss, [email protected] March 2020
NPCA Show - Improving the Performance of Concrete with Internal Curing Slide 28 of 120
Proportioning Principles
• Aggregate Spacing – the LWA
need to be well-spaced to allow
water to reach all the paste
• How much LWA/water is needed –
The majority of uses are performed
based on replacing chemical
shrinkage of the hydrating paste
• Properties of the Aggregate – The
aggregate needs to be able to
absorb and release the water
Objective
Concept
Internal and
External Curing
Proportioning
Principles
Example
Aggregate
Properties
NPCA Show - Improving the Performance of Concrete with Internal Curing Slide 29 of 120
Proportioning Principles
• Aggregate Spacing – the LWA
need to be well-spaced to allow
water to reach all the paste
• How much LWA/water is needed –
The majority of uses are performed
based on replacing chemical
shrinkage of the hydrating paste
• Properties of the Aggregate – The
aggregate needs to be able to
absorb and release the water
Objective
Concept
Internal and
External Curing
Proportioning
Principles
Example
Aggregate
Properties
NPCA Show - Improving the Performance of Concrete with Internal Curing Slide 30 of 120
Chemical Shrinkage
• Le Chatelier
• 1850-1936
• Volume of reactants
larger than volume
of the products
• Chemical Shrinkage
+ =
+ =
Objective
Concept
Internal and
External Curing
Proportioning
Principles
Example
Aggregate
Properties
NPCA Precast Show – Internal Curing Page 11 of 40
Jason Weiss, [email protected] March 2020
NPCA Show - Improving the Performance of Concrete with Internal Curing Slide 31 of 120
Mixture Proportioning for IC
• Concept of proportioning mixtures
for internal curing is simple
• Demand – Space created by
chemical shrinkage (or other loss)
• Supply – Water stored in the LWA
Supply Demand
Objective
Concept
Internal and
External Curing
Proportioning
Principles
Example
Aggregate
Properties
NPCA Show - Improving the Performance of Concrete with Internal Curing Slide 32 of 120
Mixture Proportioning for IC
• How much lightweight aggregate
should we use ?
• Three Basic Methods
– Rule of Thumb
7 lbs per 100 lbs cementitious
– Simple Calculation: Supply vs Demand
– More Complicated Features
Objective
Concept
Internal and
External Curing
Proportioning
Principles
Example
Aggregate
Properties
NPCA Show - Improving the Performance of Concrete with Internal Curing Slide 33 of 120
Simple Rule of Thumb
• 7 lbs water per 100 lbs cementious
• 6 bag mixture – 564 lb/yd3
• IC Water = 7*564/100 = 39.5 lb/yd3
• Assume Aggregate with 15%
Absorption
• MassLWA-OD = 39.5/15% = 263 lb/yd3
• Very Good First Approximation
Objective
Concept
Internal and
External Curing
Proportioning
Principles
Example
Aggregate
Properties
NPCA Precast Show – Internal Curing Page 12 of 40
Jason Weiss, [email protected] March 2020
NPCA Show - Improving the Performance of Concrete with Internal Curing Slide 34 of 120
Conventional Concrete
• SG Cement = 3.15; SG C. Agg = 2.68
• SG F. Agg = 2.75; SG LWA = 1.52
• Density = SG * 62.4 lb/ft3
• Volume = Mass/Density
Conventional Density Volume
lb/yd3 lb/ft3 ft3
Cement 564.0 196.6 2.87
Water 203.0 62.4 3.25
Coarse Aggregate 1750.0 171.6 10.20
Fine Aggregate 1514.9 167.2 9.06
Lightweight Aggregate ~ 94.8 ~
Air ~ ~ 1.62
Objective
Concept
Internal and
External Curing
Proportioning
Principles
Example
Aggregate
Properties
NPCA Show - Improving the Performance of Concrete with Internal Curing Slide 35 of 120
Example for One Yard of Concrete
With Internal Curing
• MassLWA = 263 lb
• VolLWA = 263/(1.52*62.4) = 2.78 ft3
• VolF. Agg = 9.05 – 2.78 = 6.28 ft3
• MassF. Agg = 6.28*2.68*62.4= 1051 lb
Conventional Internally Cured
lb/yd3 lb/yd3
Cement 564.0 564.0
Water 203.0 203.0
Coarse Aggregate 1750.0 1750.0
Fine Aggregate 1514.9 1050.8
Lightweight Aggregate ~ 263.2
Objective
Concept
Internal and
External Curing
Proportioning
Principles
Example
Aggregate
Properties
NPCA Show - Improving the Performance of Concrete with Internal Curing Slide 36 of 120
Volume Proportions
Objective
Concept
Internal and
External Curing
Proportioning
Principles
Example
Aggregate
Properties
NPCA Precast Show – Internal Curing Page 13 of 40
Jason Weiss, [email protected] March 2020
NPCA Show - Improving the Performance of Concrete with Internal Curing Slide 37 of 120
Mixture Proportioning for IC
• How much lightweight aggregate
should we use ?
• Three Basic Methods
– Rule of Thumb
7 lbs per 100 lbs cementious
– Simple Calculation: Supply vs Demand
– More Complicated Features
Objective
Concept
Internal and
External Curing
Proportioning
Principles
Example
Aggregate
Properties
NPCA Show - Improving the Performance of Concrete with Internal Curing Slide 38 of 120
Demand Equation
• Demand – Volume created when cement
reacts (hydrates) – this is known as
chemical shrinkage
• The product of three terms– Cf – Cement Factor – The amount of Cement
in the concrete
– CS – the chemical shrinkage of the cement
(est 0.064 ml/g)
– aMax is the expected maximum degree of
hydration (0 to 1)
Objective
Concept
Internal and
External Curing
Proportioning
Principles
Example
Aggregate
Properties
NPCA Show - Improving the Performance of Concrete with Internal Curing Slide 39 of 120
Supply Equation
• Supply – the amount of water that is
supplied by the light weight aggregate.
This is the water stored in the aggregate.
• The product of three terms
– MLwa – Mass of the lightweight aggregate
– f – the volume of water absorbed by the
lightweight aggregate (absorption) - refers to
the water absorbed at a particular time
– S – the saturation factor
Objective
Concept
Internal and
External Curing
Proportioning
Principles
Example
Aggregate
Properties
NPCA Precast Show – Internal Curing Page 14 of 40
Jason Weiss, [email protected] March 2020
NPCA Show - Improving the Performance of Concrete with Internal Curing Slide 40 of 120
Example
• Determine the mass of LWA for a cubic
yard of concrete if one uses internal curing.
• The plain mixture has a cement content of
560 lb/yd3, Chemical shrinkage of 0.07
ml/gcem, and a LWA with 15% porosity
(determined from 24 hr absorption)
• Assume amax = 1 and S = 1
Objective
Concept
Internal and
External Curing
Proportioning
Principles
Example
Aggregate
Properties
NPCA Show - Improving the Performance of Concrete with Internal Curing Slide 41 of 120
Example of Spreadsheet
• Developed an automated
spreadsheet to perform the
calculations that you just did by
hand
• The goal is to go from an existing
mixture design to an internally
cured mixture design using the
properties of the lightweight
aggregate
Objectives
Principles
Aggregate
Spacing
Simple
Example
Bentz
Equation
Example
Automation
Batching
Discussion
NPCA Show - Improving the Performance of Concrete with Internal Curing Slide 42 of 120
Step 1: Begin with Information from
the Conventional Mixture
• This information can generally be
obtained from the ready mix
supplier as shown in orange cellsLegend
Target Air, % 6.5% Ready Mix Input
w/c 0.366 LWA Input
Materials Weight SG (SSD) Volume, ft3
Cement 564 3.15 2.869
GGBFS 115 2.99 0.616
Fly Ash 0 2.64 0.000
Silica Fume 25 2.2 0.182
Sand 1210 2.623 7.393
Coarse Aggregate 1 1700 2.763 9.860
Coarse Aggregate 2 0 2.763 0.000
Water 258 1 4.135
Air 0 0 1.755
Σ 3872 - 26.810
Plain Mixture Design
Objectives
Principles
Aggregate
Spacing
Simple
Example
Bentz
Equation
Example
Automation
Batching
Discussion
NPCA Precast Show – Internal Curing Page 15 of 40
Jason Weiss, [email protected] March 2020
NPCA Show - Improving the Performance of Concrete with Internal Curing Slide 43 of 120
Step 2: Add LWA Information
• We will now enter information
about the LWA being used
• We will show how to obtain these
values later today, for now assume
they are known
• These are obtained
experimentally for
your LWA material
• As shown in
the green cells
LWA Absorption: 15.0%
LWA Desorption: 85.0%
LWA Specific Gravity 1.750
Cement Factor 704
Chemical Shrinkage: 0.065
Degree of Hydration 1
SSD LWA Replacement 413
SSD Sand Replaced 619
Internal Curing Properties
Objectives
Principles
Aggregate
Spacing
Simple
Example
Bentz
Equation
Example
Automation
Batching
Discussion
NPCA Show - Improving the Performance of Concrete with Internal Curing Slide 44 of 120
Step 3: Obtain IC Mixture
Proportions (Automatically)
Materials Weight SG (SSD) Volume, ft3
Cement 564 3.15 2.869
GGBFS 115 2.99 0.616
Fly Ash 0 2.64 0.000
Silica Fume 25 2.2 0.182
Sand 591 2.623 3.613
Lightweight Aggregate 413 1.750 3.780
Coarse Aggregate 1 1700 2.763 9.860
Coarse Aggregate 2 0 2.763 0.000
Water 258 1 4.135
Air 0 0 1.755
Σ 3666 - 26.810
IC Mixture Design
Objectives
Principles
Aggregate
Spacing
Simple
Example
Bentz
Equation
Example
Automation
Batching
Discussion
NPCA Show - Improving the Performance of Concrete with Internal Curing Slide 45 of 120
Objectives
Principles
Aggregate
Spacing
Simple
Example
Bentz
Equation
Example
Automation
Batching
Discussion
NPCA Precast Show – Internal Curing Page 16 of 40
Jason Weiss, [email protected] March 2020
NPCA Show - Improving the Performance of Concrete with Internal Curing Slide 46 of 120
Step 3: What Happened
• The equation is applied to
determine the mass of lwa knowing
absorption, desorption, cement
factor (sum of cementitious
materials), DOH, and chemical
shrinkage
• With this mass of LWA the volume
of LWA is determined and an equal
volume of sand is removed.
• That’s all
Objectives
Principles
Aggregate
Spacing
Simple
Example
Bentz
Equation
Example
Automation
Batching
Discussion
NPCA Show - Improving the Performance of Concrete with Internal Curing Slide 47 of 120
Step 4: Mixture Design
• This is likely a good place to start
for your trial batch if they have
made this concrete before
• This will let you check the
workability and the air content
• Remember orange boxes likely
come from the ready mix producer
and the green properties are for the
lwa you are using
Objectives
Principles
Aggregate
Spacing
Simple
Example
Bentz
Equation
Example
Automation
Batching
Discussion
NPCA Show - Improving the Performance of Concrete with Internal Curing Slide 48 of 120
Aggregate Testing
• Gradation (spacing, paste content)
• Specific gravity (mixture proportioning)
• Absorption: how much water can be held
– Absorption during the first 72 hours
– 24 hour absorption, using cone and paper
towel method
• Desorption: how much water will be
released back to the mixture
– Curve of desorption during drying
– Thermo Gravimetrical Analyzer, Q5000
Objective
Concept
Internal and
External Curing
Proportioning
Principles
Example
Aggregate
Properties
NPCA Precast Show – Internal Curing Page 17 of 40
Jason Weiss, [email protected] March 2020
NPCA Show - Improving the Performance of Concrete with Internal Curing Slide 49 of 120
0 6 12 18 24 30 36 42 48
Time (h)
0
4
8
12
16
20
24
28
32
36
No
rma
lize
d A
bs
orp
tio
n,
%(M
as
s W
ate
r/M
as
s O
ve
n D
ry S
am
ple
)
LWA #1 to #15
• Rapid initial absorption, slows over time
• 24 hour absorption values between 6 to 30%
• Magnitude depends on the source
LWA Absorption over time
Castro et al. 2009
Objective
Concept
Internal and
External Curing
Proportioning
Principles
Example
Aggregate
Properties
NPCA Show - Improving the Performance of Concrete with Internal Curing Slide 50 of 120
0 6 12 18 24 30 36 42 48
Time (h)
0.0
0.2
0.4
0.6
0.8
1.0
1.2
No
rma
lize
d A
bs
orp
tio
n "
S",
(Ma
ss
Wa
ter/
24
h W
ate
r A
bs
orp
tio
n)
LWA #1 to #15
AtS
• When absorption is normalized by 24 hour
absorption, they show a relatively uniform
behavior described by the power equation
LWA Absorption Over Time
Castro et al. 2009
Objective
Concept
Internal and
External Curing
Proportioning
Principles
Example
Aggregate
Properties
NPCA Show - Improving the Performance of Concrete with Internal Curing Slide 51 of 120
Surface Dry (SD) Condition:
Paper Towel Method (ASTM 1761)
• LWA is oven dried, cooled,
and soaked for 24 hours(or an alt. time, ASTM 72 hours)
• Excess water is removed
• Free moisture on the surface of LWA is dried by placing it under air current until it reaches surface dry (SD) condition
• Free moisture is monitored by placing a paper towel on LWA. If water is not seen on the towel and LWA did not stick to the paper towel, SD condition was reached.
Objective
Concept
Internal and
External Curing
Proportioning
Principles
Example
Aggregate
Properties
NPCA Precast Show – Internal Curing Page 18 of 40
Jason Weiss, [email protected] March 2020
NPCA Show - Improving the Performance of Concrete with Internal Curing Slide 52 of 120
Centrifuge Test
• Wetted aggregates
were placed in the
centrifuge
• The sample is spun
to remove excess
surface moisture
• The mass of the
spun sample and the
mass of the spun
sample after oven drying
are used to determine the absorbed moisture
• Good correlation with paper towel test (fast, less
subjective, measures surface moisture)
Miller et al. in progress
Objective
Concept
Internal and
External Curing
Proportioning
Principles
Example
Aggregate
Properties
NPCA Show - Improving the Performance of Concrete with Internal Curing Slide 53 of 120
Alternative to the Centrifuge is the
Paper Towel Method
Testing Method Average Duration (minutes)
Standard Deviation (minutes)
Paper Towel 42 13.2
Centrifuge 12 5.0
Paper Towel Method
LWA Source Average
Absorption (%)
Standard Deviation
(%)
Coefficient of
Variation
Buildex Marquette 21.26 2.26 0.106
Stalite 10.51 4.91 0.467
Utelite 21.75 5.34 0.246
Pooled Standard Deviation (%) 4.51 -
Average Coefficient of Variation
- 0.273
Centrifuge Method
LWA Source Average
Absorption (%)
Standard Deviation
(%)
Coefficient of
Variation
Buildex Marquette 20.18 0.56 0.028
Stalite 8.47 0.27 0.032
Utelite 18.96 0.47 0.025
Pooled Standard Deviation (%) 0.45 -
Average Coefficient of Variation - 0.028
Paper Towel
COV 0.273
Centrifuge
COV 0.028
Objectives
Principles
Centrifuge &
Paper Towel
Absorption
Surface
Moisture
Relative
Density
Desorption
Gradation
Summary
Mil
ler
et a
l 2
01
4
NPCA Show - Improving the Performance of Concrete with Internal Curing Slide 54 of 120
ASTM C1761 Desorption
• The previous slides show an approach
that measures the mass loss for each RH
• ASTM C1761 measures the mass loss
between prewetted surface dry (SD)
aggregate and the aggregate when its
stored over a specific saturated salt (94%
RH)
• Benefit is it is a test that is easy to
perform as a check step
Objective
Concept
Internal and
External Curing
Proportioning
Principles
Example
Aggregate
Properties
NPCA Precast Show – Internal Curing Page 19 of 40
Jason Weiss, [email protected] March 2020
NPCA Show - Improving the Performance of Concrete with Internal Curing Slide 55 of 120
Desorption of Expanded LWA
80 82 84 86 88 90 92 94 96 98 100
Relative Humidity (%)
0.0
0.2
0.4
0.6
0.8
1.0
Mo
istu
re C
on
ten
t, %
(Ma
ss
Wa
ter/
24
h W
ate
r A
bs
orp
tio
n)
LWA #1 to #15
Average
• ESCS LWA release a large portion of their moisture
at high humidities. Commercial materials shown.
This is desirable for internal curing.
85 to 98%
moisture
released
Castro et al. 2009
Objective
Concept
Internal and
External Curing
Proportioning
Principles
Example
Aggregate
Properties
NPCA Show - Improving the Performance of Concrete with Internal Curing Slide 56 of 120
Aggregate Summary
• All the important properties for the
lightweight aggregate are
summarized on the summary tab
LWA Absorption:
LWA Desorption:
LWA Specific Gravity:
Surface Moisure:
Objectives
Principles
Centrifuge &
Paper Towel
Absorption
Surface
Moisture
Relative
Density
Desorption
Gradation
Summary
NPCA Show - Improving the Performance of Concrete with Internal Curing Slide 57 of 120
Aggregate Properties
(From Published Literature)Objectives
Principles
Centrifuge &
Paper Towel
Absorption
Surface
Moisture
Relative
Density
Desorption
Gradation
Summary
LWA name24 h centrifuge
absorption, %
24 h centrifuge
desorption, %
24 h PSD Relative
Density (SG)
Gravelite (Riverlite LA) 16.4 92.4 1.502
Livlite (Riverlite AL) 30.0 97.5 1.430
TXI (Trinity) Frazier Park 17.5 95.2 1.633
Buildex Marquette 18.8 96.2 1.723
Buildex New Market 14.9 98.3 1.724
Haydite AX 12.4 97.5 1.753
Haydite A 13.5 98.7 1.743
Haydite DiGeronimo 17.1 97.3 1.639
Hydrocure 17.3 96.4 1.771
Norlite 17.4 95.7 1.620
TXI (Trinity) Boulder 19.0 89.8 1.737
TXI (Trinity) Streetman 20.1 88.0 1.777
Utelite 19.7 90.6 1.784
Solite LLC 16.4 97.1 1.886
Stalite 9.1 97.5 1.647
NPCA Precast Show – Internal Curing Page 20 of 40
Jason Weiss, [email protected] March 2020
NPCA Show - Improving the Performance of Concrete with Internal Curing Slide 58 of 120
Aggregate Conditioning
• Conventionally
• Prewet the lightweight aggregate for 24 to
48 hours with sprinkling
• Alternatively
• Materials can be used without prewetting
however very high level information is
needed about the absorption
Objective
Concept
Internal and
External Curing
Proportioning
Principles
Example
Aggregate
Properties
NPCA Show - Improving the Performance of Concrete with Internal Curing Slide 59 of 120
Placing and Finishing
Objective
Concept
Internal and
External Curing
Proportioning
Principles
Example
Aggregate
Properties
NPCA Show - Improving the Performance of Concrete with Internal Curing Slide 60 of 120
Placing and Finishing
Objective
Concept
Internal and
External Curing
Proportioning
Principles
Example
Aggregate
Properties
NPCA Precast Show – Internal Curing Page 21 of 40
Jason Weiss, [email protected] March 2020
NPCA Show - Improving the Performance of Concrete with Internal Curing Slide 61 of 120
Placing and Finishing
Objective
Concept
Internal and
External Curing
Proportioning
Principles
Example
Aggregate
Properties
NPCA Show - Improving the Performance of Concrete with Internal Curing Slide 62 of 120
Placing and Finishing
Objective
Concept
Internal and
External Curing
Proportioning
Principles
Example
Aggregate
Properties
NPCA Show - Improving the Performance of Concrete with Internal Curing Slide 63 of 120
Placing and Finishing
Objective
Concept
Internal and
External Curing
Proportioning
Principles
Example
Aggregate
Properties
NPCA Precast Show – Internal Curing Page 22 of 40
Jason Weiss, [email protected] March 2020
NPCA Show - Improving the Performance of Concrete with Internal Curing Slide 64 of 120
Summary
• Internal curing uses porous inclusions
(LWA) to supply curing water
• Aggregate needs to be well spaced, ESCS
FLWA provides good spacing
• Important LWA properties – Grading,
specific gravity, absorption and desorption
• Proportioning Principles - LWA (Supply);
chemical shrinkage (Demand)
• In general, 7lb of water is needed for every
100 lb of cement (good rule of thumb)
• Desorption of aggregate is a ‘newer’
property but it is easy to measure with salt
Objective
Concept
Internal and
External Curing
Proportioning
Principles
Example
Aggregate
Properties
NPCA Show - Improving the Performance of Concrete with Internal Curing Slide 65 of 120
NPCA Show - Improving the Performance of Concrete with Internal Curing Slide 66 of 120
Internal Curing Module:
Shrinkage and Shrinkage Cracking
Presented by Jason Weiss, [email protected]
Objectives
Causes of
Shrinkage
Cracking
Influence of
Low w/c & HSC
Chemical and
Autogenous
Shrinkage
IC Review
IC and
Shrinkage
Plastic
Shrinkage
NPCA Precast Show – Internal Curing Page 23 of 40
Jason Weiss, [email protected] March 2020
NPCA Show - Improving the Performance of Concrete with Internal Curing Slide 67 of 120
Objectives
• To understand how shrinkage relates to
stress development and how stress
development relates to cracking
• To understand the different types of
shrinkage and their causes
• To understand why low
w/cm are prone to cracking
• To understand how IC can
reduce the potential for cracking
• To review data that compares the
cracking behavior of plain and IC concrete
Objectives
Causes of
Shrinkage
Cracking
Influence of
Low w/c & HSC
Chemical and
Autogenous
Shrinkage
IC Review
IC and
Shrinkage
Plastic
Shrinkage
NPCA Show - Improving the Performance of Concrete with Internal Curing Slide 68 of 120
Introduction
• Cracking frequently
observed
• Transverse cracking
in 100,000+ bridges
• 62% of DOT’s
consider cracking as
a problem (NCHRP)
• Cracks shorten
service life, increase
maintenance cost,
and accelerate
corrosion
Ph
oto
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p:/
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reg
ate
rese
arc
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eckcra
ckin
g.p
df
Objectives
Causes of
Shrinkage
Cracking
Influence of
Low w/c & HSC
Chemical and
Autogenous
Shrinkage
IC Review
IC and
Shrinkage
Plastic
Shrinkage
NPCA Show - Improving the Performance of Concrete with Internal Curing Slide 69 of 120
Early Age Stress Development
• Concrete shrinks (reduces volume)
due to moisture loss or temperature
reduction
• If this volume
reduction is not
restrained, the
sample will shrink
and get smaller
• If restrained, tensile stresses develop
that can result in cracking
SHRdE
dtd ,
Initial Specimen
Shrinkage Effect
Restraint Effect
Objectives
Causes of
Shrinkage
Cracking
Influence of
Low w/c & HSC
Chemical and
Autogenous
Shrinkage
IC Review
IC and
Shrinkage
Plastic
Shrinkage
NPCA Precast Show – Internal Curing Page 24 of 40
Jason Weiss, [email protected] March 2020
NPCA Show - Improving the Performance of Concrete with Internal Curing Slide 70 of 120
• Fortunately, concrete is an aging visco-
elastic material, stresses “relax” and reduce
Early Age Stress Development
Objectives
Causes of
Shrinkage
Cracking
Influence of
Low w/c & HSC
Chemical and
Autogenous
Shrinkage
IC Review
IC and
Shrinkage
Plastic
Shrinkage
NPCA Show - Improving the Performance of Concrete with Internal Curing Slide 71 of 120
Autogenous Shrinkage
Henkensiefken et al. (2008)
Sealed
33.0%k
29.3%k
25.3%k
18.3%k
14.3%k
11.0%k
7.3%k
0.0%
• As LWA replacement volume increases,
autogenous shrinkage decreases
• 25.3% accounts for the CS volume
Objectives
Causes of
Shrinkage
Cracking
Influence of
Low w/c & HSC
Chemical and
Autogenous
Shrinkage
IC Review
IC and
Shrinkage
Plastic
Shrinkage
NPCA Show - Improving the Performance of Concrete with Internal Curing Slide 72 of 120
22
22
2
22
2 ICOC
ICOC
OS
ISOSSSteelRrConcrete
RR
RR
R
RREtt
IC
Weiss and Furgeson 2001
Hossain and Weiss, 2002
Restrained Shrinkage
Objectives
Causes of
Shrinkage
Cracking
Influence of
Low w/c & HSC
Chemical and
Autogenous
Shrinkage
IC Review
IC and
Shrinkage
Plastic
Shrinkage
NPCA Precast Show – Internal Curing Page 25 of 40
Jason Weiss, [email protected] March 2020
NPCA Show - Improving the Performance of Concrete with Internal Curing Slide 73 of 120
Restrained Shrinkage Cracking
(Sealed Samples)
• The age of
cracking is
plotted as a
function of
LWA addition
• As the volume
approaches
the CS
replacement
(25%) no
cracking is
observed
0 5 10 15 20 25 30 35
Percent Lightweight Aggregate (%)
0
5
10
15
20
25
30
Ag
e o
f S
pecim
en
(D
ays)
Time of cracking (sealed) Mixtures did not crack
No
Cracking
Is Seen
For Higher
Volumes
Henkensiefken et al. (2008)
Objectives
Causes of
Shrinkage
Cracking
Influence of
Low w/c & HSC
Chemical and
Autogenous
Shrinkage
IC Review
IC and
Shrinkage
Plastic
Shrinkage
NPCA Show - Improving the Performance of Concrete with Internal Curing Slide 74 of 120
0 5 10 15 20 25 30 35
Percent Lightweight Aggregate (%)
0
5
10
15
20
25
30
Ag
e o
f S
pecim
en
(D
ays)
Time of cracking (sealed)
Time of cracking (unsealed)Mixtures did
not crack
Restrained Shrinkage Cracking
(Unsealed Samples)
• As before we
see that
increasing the
LWA volume
decreases the
potential for
cracking
• Unsealed
samples
require a
higher volume
No
Cracking
Is Seen
For Higher
Volumes
Henkensiefken et al. (2008)
Objectives
Causes of
Shrinkage
Cracking
Influence of
Low w/c & HSC
Chemical and
Autogenous
Shrinkage
IC Review
IC and
Shrinkage
Plastic
Shrinkage
NPCA Show - Improving the Performance of Concrete with Internal Curing Slide 75 of 120
Thermal Effects
• Dual ring test used to capture expansion
and contraction, Invar rings (low COTE)
• Coil system used to regulate sample
temperature from 60˚C to -10˚C
Schlitter et al. 2010
Objectives
Causes of
Shrinkage
Cracking
Influence of
Low w/c & HSC
Chemical and
Autogenous
Shrinkage
IC Review
IC and
Shrinkage
Plastic
Shrinkage
NPCA Precast Show – Internal Curing Page 26 of 40
Jason Weiss, [email protected] March 2020
NPCA Show - Improving the Performance of Concrete with Internal Curing Slide 76 of 120
Temperature Required to Crack
• Internally cured systems are more robust
Schlitter et al. 2010
Objectives
Causes of
Shrinkage
Cracking
Influence of
Low w/c & HSC
Chemical and
Autogenous
Shrinkage
IC Review
IC and
Shrinkage
Plastic
Shrinkage
NPCA Show - Improving the Performance of Concrete with Internal Curing Slide 77 of 120
Robustness at Early Ages
• IC has greater load or temp. capacity
Schlitter et al. 2010
Objectives
Causes of
Shrinkage
Cracking
Influence of
Low w/c & HSC
Chemical and
Autogenous
Shrinkage
IC Review
IC and
Shrinkage
Plastic
Shrinkage
NPCA Show - Improving the Performance of Concrete with Internal Curing Slide 78 of 120
Review of Main Topics
• Concrete is susceptible to cracking when it
is restrained from shrinking
• The cracking potential
increases with lower w/c
higher strength concrete
• Chemical shrinkage occurs as cement
hydrates, can result in autogenous shr.
• Internal curing is simply using LWA as a
reservoir to ‘hide water’, reduce self-desc.
• Internal curing reduces shrinkage and
shrinkage cracking
Objectives
Causes of
Shrinkage
Cracking
Influence of
Low w/c & HSC
Chemical and
Autogenous
Shrinkage
IC Review
IC and
Shrinkage
Plastic
Shrinkage
NPCA Precast Show – Internal Curing Page 27 of 40
Jason Weiss, [email protected] March 2020
NPCA Show - Improving the Performance of Concrete with Internal Curing Slide 79 of 120
Review of Main Topics
• Internally cured mixtures hide water in the
LWA, this water is released after setting to
increase the pore saturation
• If the pores are more full, the
meniscus in the pore is larger
& resulting shrinkage is smaller
• IC concrete is less susceptible
to restrained shrinkage
cracking than plain concrete
• Plastic shrinkage cracking can be reduced but stored water is used and not available
Objectives
Causes of
Shrinkage
Cracking
Influence of
Low w/c & HSC
Chemical and
Autogenous
Shrinkage
IC Review
IC and
Shrinkage
Plastic
Shrinkage
NPCA Show - Improving the Performance of Concrete with Internal Curing Slide 80 of 120
NPCA Show - Improving the Performance of Concrete with Internal Curing Slide 81 of 120
Internal Curing Module:
Mechanical and Transport Properties
Presented by Jason Weiss, [email protected]
Objectives
Influence of
Internal Curing
Sample
Conditioning
Mechanical
Properties
Durability
Case Studies
NPCA Precast Show – Internal Curing Page 28 of 40
Jason Weiss, [email protected] March 2020
NPCA Show - Improving the Performance of Concrete with Internal Curing Slide 82 of 120
Objectives
• Review the concept of internal curing (IC)
• To understand changes
that occur in
concrete due to IC
• To understand the role
of sample conditioning
• To understand the influence of IC on
mechanical properties
– strength, modulus, density, volume change
• To understand the influence of IC on
durability - transport, FT, corrosion
Objectives
Influence of
Internal Curing
Sample
Conditioning
Mechanical
Properties
Durability
Case Studies
NPCA Show - Improving the Performance of Concrete with Internal Curing Slide 83 of 120
Concrete Curing
• Before discussing internal curing, let’s
review the basics of concrete curing
• ACI-308 – describes “curing” as action
taken to maintain moisture & temperature
in freshly placed cementitious mixture
• This allows hydraulic-cement hydration,
and pozzolanic reactions
to occur so potential
properties of the
mixture may develop
• Increase SCM reaction
Objectives
Influence of
Internal Curing
Sample
Conditioning
Mechanical
Properties
Durability
Case Studies
NPCA Show - Improving the Performance of Concrete with Internal Curing Slide 84 of 120
Curing and Hydration
• Cement and SCM require water to react
• Initial water-filled pore space ‘fills in’
• Reduced porosity: strength transport
• If water is not available, reaction stops
Objectives
Influence of
Internal Curing
Sample
Conditioning
Mechanical
Properties
Durability
Case Studies
NPCA Precast Show – Internal Curing Page 29 of 40
Jason Weiss, [email protected] March 2020
NPCA Show - Improving the Performance of Concrete with Internal Curing Slide 85 of 120
Review of Internal Curing
• The pores in a cementitious
matrix have different sizes
• Water moves out of the
biggest pores first
• Internal curing with LWA
is based on two items
1) water is stored in
LWA pores
2) most pores are larger
than pores in paste
• This water can react
Objectives
Influence of
Internal Curing
Sample
Conditioning
Mechanical
Properties
Durability
Case Studies
Conventional
Concrete
Internally Cured Concrete
LWA
Radlinska et al. 2007
NPCA Show - Improving the Performance of Concrete with Internal Curing Slide 86 of 120
Review of Internal Curing
• Internal curing causes more cement to react
(and more heat to be given off)
• At 3 days we see a difference between an
internally cured and conventional mortar
• Internal
curing
increases
reaction
• IC increases
with curing
time and
increases at later ages for higher w/c
Objectives
Influence of
Internal Curing
Sample
Conditioning
Mechanical
Properties
Durability
Case Studies0.25 0.30 0.35 0.40 0.45 0.50
w/c
Internal Curing
Sealed
0.4
0.5
0.6
0.7
De
gre
e o
f H
yd
rati
on
at
72
h(H
ea
t /
Ma
xim
um
th
eo
reti
ca
l h
ea
t)
Castro et al. 2010
NPCA Show - Improving the Performance of Concrete with Internal Curing Slide 87 of 120
Sample Conditioning
• When additional water is not provided,
the water activity (RH) decreases
• The water activity (RH) decreases the
cement reaction slows or ceases
Objectives
Influence of
Internal Curing
Sample
Conditioning
Mechanical
Properties
Durability
Case Studies
Relative Humidity (Rel. Vapor Pres.)
Am
ou
nt
of
Wate
r
in H
yd
r. R
eacti
on
0.4
0.32
0.24
0.16
0.08
0.0
0 0.2 0.4 0.6 0.8 1.0
Non-Evaporable Water
Total Water
Hydration Stops
Aft
er
Bro
wn
yard
an
d
Po
we
rs 1
94
2
NPCA Precast Show – Internal Curing Page 30 of 40
Jason Weiss, [email protected] March 2020
NPCA Show - Improving the Performance of Concrete with Internal Curing Slide 88 of 120
Curing and Strength
Objectives
Influence of
Internal Curing
Sample
Conditioning
Mechanical
Properties
Durability
Case Studies
Go
lias
et
al. 2
011
Water Curing Drying
• Comparing the strength of a water cured
and dried system
• Internal curing is similar for wet cured,
much improved for drying
NPCA Show - Improving the Performance of Concrete with Internal Curing Slide 89 of 120
Mechanical Properties
• LWA concrete has
been widely used for
nearly a century
• Hibernia – Offshore in
Newfoundland
• 10,000 -13,000 psi
concrete was used
Objectives
Influence of
Internal Curing
Sample
Conditioning
Mechanical
Properties
Durability
Case Studies
NPCA Show - Improving the Performance of Concrete with Internal Curing Slide 90 of 120
Mechanical Properties
• Begin by considering that concrete is a
composite that consists of three main
phases at the ‘mm-scale’
– Paste
– Aggregate
– Interfacial Transition
Zone (ITZ)
Objectives
Influence of
Internal Curing
Sample
Conditioning
Mechanical
Properties
Durability
Case Studies
NPCA Precast Show – Internal Curing Page 31 of 40
Jason Weiss, [email protected] March 2020
NPCA Show - Improving the Performance of Concrete with Internal Curing Slide 91 of 120
Interfacial Transition Zone (ITZ)
• In conventional mixtures, the ITZ with
LWA is better than with NWA (Holm 1984)
– The alumina/silica surface
of the LWA reacts with CH
– The modulus between the
LWA and the matrix is
more similar, therefore
there is less cracking
– Less bleed water at
surface of the aggregate
– The surface is not as ‘well
defined’ so CH can enter
the aggregate
Objectives
Influence of
Internal Curing
Sample
Conditioning
Mechanical
Properties
Durability
Case Studies
Smaller Interface with LWA
NPCA Show - Improving the Performance of Concrete with Internal Curing Slide 92 of 120
Elastic Modulus of Concrete
Objectives
Influence of
Internal Curing
Sample
Conditioning
Mechanical
Properties
Durability
Case Studies
• For paste with the same level degree of
hydration, the influence of internal curing is
shown below for a typical bridge deck
mixture using
a shale LWA
• IC mixtures
have a lower
modulus than
a NWA
• Deformations
in the LWA are
more similar to paste Golias et al. 2011
NPCA Show - Improving the Performance of Concrete with Internal Curing Slide 93 of 120
Elastic Modulus
Objectives
Influence of
Internal Curing
Sample
Conditioning
Mechanical
Properties
Durability
Case Studies
• Elastic modulus is higher for all
conventional mixtures
• Greater difference for the lower w/c
mixtures since paste is stronger Golias et al. 2011
Water Curing Sealed Curing
NPCA Precast Show – Internal Curing Page 32 of 40
Jason Weiss, [email protected] March 2020
NPCA Show - Improving the Performance of Concrete with Internal Curing Slide 94 of 120
Durability of LW Concrete
• USS Selma (1919) – 7,500 ton ship exposed
to sea water
– Low permeability, low corrosion
– 28 day f’c greater than 4000 psi
– Tested in the 1980s f’c in excess of 8000 psi
• Sister ship in Powell River, BC (5ksi, 8.7ksi)
Objectives
Influence of
Internal Curing
Sample
Conditioning
Mechanical
Properties
Durability
Case Studies
NPCA Show - Improving the Performance of Concrete with Internal Curing Slide 95 of 120
Main Principles of Internal Curing
Objectives
Influence of
Internal Curing
Sample
Conditioning
Mechanical
Properties
Durability
Case Studies
• Additional internal
curing water
reacts more
binder to
densify the
system
• LWA has a
reduce ITZ
and reduces
percolation
• At low w/c the
capillary pores depercolate
NPCA Show - Improving the Performance of Concrete with Internal Curing Slide 96 of 120
BSE/SEM Plain (top) and Internally
Cured (bot) (Bentz and Stutzman 2008)
• asdfObjectives
Influence of
Internal Curing
Sample
Conditioning
Mechanical
Properties
Durability
Case Studies
NPCA Precast Show – Internal Curing Page 33 of 40
Jason Weiss, [email protected] March 2020
NPCA Show - Improving the Performance of Concrete with Internal Curing Slide 97 of 120
Frequent Question
• But LWA particles are porous, do they not
lead to increased transport (permeability) ?
• Zhang and Gjorv (1991) reported
permeability of high-strength LWC is more
dependent on cement paste than LWA
• Pyc et al. (2008) data suggests that once the
pores in LWA empty they are not easily
resaturated, even upon complete immersion
of the specimen
• Henkensiefken et al. (2009)
confirmed it is difficult to resaturate
low w/c IC except for high vacuum
Objectives
Influence of
Internal Curing
Sample
Conditioning
Mechanical
Properties
Durability
Case Studies
NPCA Show - Improving the Performance of Concrete with Internal Curing Slide 98 of 120
Transport Tests
• Ionic diffusion – concentration
driven, diffusion of ionic species
• Capillary sorption – filling of a
dry material mainly due to
capillary effects
• Permeation – driven by
pressure gradient
• Wick action – drying
on one side
of element
Objectives
Influence of
Internal Curing
Sample
Conditioning
Mechanical
Properties
Durability
Case Studies
NPCA Show - Improving the Performance of Concrete with Internal Curing Slide 99 of 120
0 25 50 75 100
Amount of LWA from Equation 1 (%)
0
20
40
60
80
Init
ial
So
rpti
vit
y (
10
-4 m
m3 w
ate
r /
mm
2 s
urf
ac
e/ s
ec
0.5)
w/c = 0.45
w/c = 0.42
w/c = 0.36
w/c = 0.30
a) 65% RH
0 25 50 75 100
Amount of LWA from Equation 1 (%)
0.0
1.0
2.0
3.0
4.0
Wa
ter
Ab
so
rpti
on
at
8 d
ays
(m
m3 w
ate
r / m
m2 s
urf
ac
e) w/c = 0.45
w/c = 0.42
w/c = 0.36
w/c = 0.30
a) 65% RH
Water Absorption
Castro et al. 2011
• The plots below show how internal curing
reduces absorption for several w/c
• 100% LWA has enough water to be equiv. to
the chemical shrinkage volume
Objectives
Influence of
Internal Curing
Sample
Conditioning
Mechanical
Properties
Durability
Case Studies
LWA
f
LWAS
CSCM
f
a
max
NPCA Precast Show – Internal Curing Page 34 of 40
Jason Weiss, [email protected] March 2020
NPCA Show - Improving the Performance of Concrete with Internal Curing Slide 100 of 120
Water Absorption
Objectives
Influence of
Internal Curing
Sample
Conditioning
Mechanical
Properties
Durability
Case Studies
• The IC with a w/c of 0.3
behaves like a w/c of 0.23
• This can be explained by the
increase in hydration and reduction in porosity
NPCA Show - Improving the Performance of Concrete with Internal Curing Slide 101 of 120
Durability Related to Transport
Cover
Reinforcing
Bar
Deicing Salt
• Salt can be
absorbed or can
diffuse in the
pores
• When chloride
reaches the rebar
(at sufficient
concentration) it
can depassivate
the steel and
leads to
corrosion
Objectives
Influence of
Internal Curing
Sample
Conditioning
Mechanical
Properties
Durability
Case Studies
NPCA Show - Improving the Performance of Concrete with Internal Curing Slide 102 of 120
How Long Does it Take for
Corrosion to Start ?
• The chloride will migrate to the bar over time
• How long does it take to reach a critical level
• Depends on the quality of the concrete and
the depth of the reinforcement
Time
Chloride
at the Bar
Critical Value
Objectives
Influence of
Internal Curing
Sample
Conditioning
Mechanical
Properties
Durability
Case Studies
NPCA Precast Show – Internal Curing Page 35 of 40
Jason Weiss, [email protected] March 2020
NPCA Show - Improving the Performance of Concrete with Internal Curing Slide 103 of 120
Reduced Chloride Ingress
0
2
4
6
8
28 d 56 d 180 d
Exposure to Cl- (d)
Pen
etr
ati
on
dep
th (
mm
)
Control IC
Bentz 2008
Objectives
Influence of
Internal Curing
Sample
Conditioning
Mechanical
Properties
Durability
Case Studies
Bentz 2009
NPCA Show - Improving the Performance of Concrete with Internal Curing Slide 104 of 120
• IC reduces
the overall
conductivity
• An IC with a
w/c of 0.30
behaves like
a w/c of 0.23
• As observed
with absorption
this is due to
hydration and reduced porosity
0.20 0.25 0.30 0.35 0.40
water - cement ratio
0
2
4
6
8
10
12
14
16
18
20
Co
nd
ucti
vit
y,
(10
-3 S
/m) Mortar - 28 d
LWA 12% - 28 d
LWA 24% - 28 d
0.23 0.29
Transport Properties: Electrical
Conductivity in Low w/c Mortars
Castro et al. 2011 Castro et al. 2011 Objectives
Influence of
Internal Curing
Sample
Conditioning
Mechanical
Properties
Durability
Case Studies
NPCA Show - Improving the Performance of Concrete with Internal Curing Slide 105 of 120
Freeze-Thaw Behavior
• Prior studies have shown that drying
can be beneficial for saturated LWC
• Recall, IC with a sufficiently low w/c, where
self-desiccation occurs, pulls water from LWA
• Exposure to F/T at very early ages maybe a
concern but over time the LWA empties
would empty
Objectives
Influence of
Internal Curing
Sample
Conditioning
Mechanical
Properties
Durability
Case Studies
NPCA Precast Show – Internal Curing Page 36 of 40
Jason Weiss, [email protected] March 2020
NPCA Show - Improving the Performance of Concrete with Internal Curing Slide 106 of 120
Freeze-Thaw Behavior
• Performance of lightweight bridge concrete
bridge decks is at least as good as normal
density concrete (Brown et al. 1985)
• Experiments have shown
that plain and internally
cured concrete behave
similarly if they are properly
air entrained
• Use a sufficiently low w/c where self-
desiccation will pull water out of the LWA
Objectives
Influence of
Internal Curing
Sample
Conditioning
Mechanical
Properties
Durability
Case Studies
NPCA Show - Improving the Performance of Concrete with Internal Curing Slide 107 of 120
Typical FT Behavior
• Studies on IC mixtures made with
expanded aggregate are durable with
proper air systems (Jones et al. 2013)
Jones et al. 2013
Background
on IC
LWA vs SAP
Objectives
Experimental
Approach
Mixture
Proportions
Air/Slump
Strength
Freeze-Thaw
Conclusions
NPCA Show - Improving the Performance of Concrete with Internal Curing Slide 108 of 120
Alkali-Silica Reactivity (ASR)
The Mechanisms
Objectives
Influence of
Internal Curing
Sample
Conditioning
Mechanical
Properties
Durability
Case Studies
NPCA Precast Show – Internal Curing Page 37 of 40
Jason Weiss, [email protected] March 2020
NPCA Show - Improving the Performance of Concrete with Internal Curing Slide 109 of 120
Alkali Silica Reaction
• Shin et al. 2010 reported results for 5
systems (reactive, 15 & 28% reactive sand
(m), 15 & 28% non reactive sand (N))
• Internal Curing Pros
– decreases porosity through hydration
– accommodation space allows gel to
form without developing pressure
– dilution (replaces reactive aggregates)
• Internal Curing Cons
– Higher RH/moisture in paste would
enable more ASR reaction to occur
Objectives
Influence of
Internal Curing
Sample
Conditioning
Mechanical
Properties
Durability
Case Studies
NPCA Show - Improving the Performance of Concrete with Internal Curing Slide 110 of 120
Alkali Silica Reaction
• Shin et al. 2010 reported on 5 systems
• Reactive (R) – Most reactive and expansive
• Non Reactive Aggregate Replacement at 15 &
28% (m) – Reduces expansion due to dilution
• Internal Curing – LWA Replacement at 15 & 28%
(N) – more effective even than non-reactive
aggregate
LWA provides
space for
expansive
gel to form
15% replacement
is CS volume
Objectives
Influence of
Internal Curing
Sample
Conditioning
Mechanical
Properties
Durability
Case Studies
NPCA Show - Improving the Performance of Concrete with Internal Curing Slide 111 of 120
Bloomington Indiana
Objectives
Influence of
Internal Curing
Sample
Conditioning
Mechanical
Properties
Durability
Case Studies
NPCA Precast Show – Internal Curing Page 38 of 40
Jason Weiss, [email protected] March 2020
NPCA Show - Improving the Performance of Concrete with Internal Curing Slide 112 of 120
Strength Results
• Similar or slightlyhigher compressivestrength resultsin Bloomington IN(DiBella et al. 2011)
• Similar strength andfresh properties in Tonowanda NY (shown); Lisle NY(Wolfe et al. 2012)
Class HP Class HP-IC
Comp. Str. 7 day 3,040 psi 3,500 psi
Comp. Str. 28 day 4,677 psi 4,683 psi
Comp. Str. 56 day 5,343 psi 5,417 psi
Concrete Density 140.2 pcf 135.2 pcf
Air Content 5.5 % 6.0 %
Slump 5.0” 4.5”
Objectives
Influence of
Internal Curing
Sample
Conditioning
Mechanical
Properties
Durability
Case Studies
NPCA Show - Improving the Performance of Concrete with Internal Curing Slide 113 of 120
Transport Properties
Plain and IC Bridge Decks (Indiana)
Location of the two bridges
IC concrete bridge deck was placed by
means of a bucketPlain concrete bridge deck was pumped
Cement
ContentW/C
Fine
Agg.
Fine
LWA
Coarse
Agg
Mixture
Water
Water in
LWAWR AE
(kg/m3) (kg/m3) (kg/m3) (kg/m3) (kg/m3) (kg/m3) (%)A (%)A
Plain 390 0.39 726 - 1046 152 - 0.22 0.08
Int. Cured 390 0.39 313 270 1046 152 25 0.22 0.08
A percentage referred to the cement weight
Objectives
Influence of
Internal Curing
Sample
Conditioning
Mechanical
Properties
Durability
Case Studies
NPCA Show - Improving the Performance of Concrete with Internal Curing Slide 114 of 120
Rapid Chloride Penetration Test
Objectives
Influence of
Internal Curing
Sample
Conditioning
Mechanical
Properties
Durability
Case Studies
Lisle, NY
NPCA Precast Show – Internal Curing Page 39 of 40
Jason Weiss, [email protected] March 2020
NPCA Show - Improving the Performance of Concrete with Internal Curing Slide 115 of 120
• Plain bridge deck exhibited several cracks
Visual Inspection of the
Plain Bridge Decks after 20 Months
Objectives
Influence of
Internal Curing
Sample
Conditioning
Mechanical
Properties
Durability
Case Studies
NPCA Show - Improving the Performance of Concrete with Internal Curing Slide 116 of 120
Visual Inspection of the
IC Bridge Decks after 20 Months
• The internally cured bridge deck
mixture resulted in no visible cracks.
Internally cured bridge deck
Objectives
Influence of
Internal Curing
Sample
Conditioning
Mechanical
Properties
Durability
Case Studies
NPCA Show - Improving the Performance of Concrete with Internal Curing Slide 117 of 120
Review of Main Topics
• Internal curing is simply using LWA as a
reservoir to ‘hide’ water
• Internal curing hydrates
more cementitous materials
• Internal curing reduces porosity
(due to hydration) and percolated ITZ
• In general, similar compressive strength
observed (coarse aggregate same, part
of fine aggregate replaced)
• Internal curing reduces fluid transport
(absorption/diffusion) reducing corrosion
• Internal curing is being implemented
Objectives
Influence of
Internal Curing
Sample
Conditioning
Mechanical
Properties
Durability
Case Studies
NPCA Precast Show – Internal Curing Page 40 of 40
Jason Weiss, [email protected] March 2020
NPCA Show - Improving the Performance of Concrete with Internal Curing Slide 118 of 120
Conclusions
• Strength -Generally similar due to increased hydration counteracting potentially lower strength aggregate
• Modulus - Lower, but beneficial, as it allows restrained concrete to stretch easier
• Freeze-Thaw - Generally similar to a plain concrete with proper air entrainment
• ASR can be reduced due to dilution
• ASR and sulfate attack reduceddue to space accommodation
• Reduced cracks - Cracks are the Achilies heal of corrosion
Objectives
Influence of
Internal Curing
Sample
Conditioning
Mechanical
Properties
Durability
Case Studies
NPCA Show - Improving the Performance of Concrete with Internal Curing Slide 119 of 120
Conclusions
• Transport Properties – Similar or improved since porosity decreases/ITZ depercolates
– Lower absorption
– Similar or lower diffusivity (Cl-)
– RCPT & electrical properties are similar or up to 30% better
– Artifacts associated with current testing methods such as cut surfaces in samples, vacuum saturation, conductive aggregate
• IC concrete has the ability to reduce the
chloride transport which has implications
on the time to corrosion and service life.
Objectives
Influence of
Internal Curing
Sample
Conditioning
Mechanical
Properties
Durability
Case Studies
NPCA Show - Improving the Performance of Concrete with Internal Curing Slide 120 of 120
Acknowledgements/Disclaimer
• These slides were developed as a part of
a series for the Expanded Shale, Clay
and Slate Institute by Jason Weiss.
• These materials are provided as general
information and do not constitute legal or
other professional advice.
• Any use of this information in the design
or selection of materials for practice
should be approved by the project owner
and engineer-of-record.
Objectives
Causes of
Shrinkage
Cracking
Influence of
Low w/c & HSC
Chemical and
Autogenous
Shrinkage
IC Review
IC and
Shrinkage
Plastic
Shrinkage