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Evaluation of Concrete Curing
Effectiveness
Muhammad Ehsanul Bari
Dan Zollinger, Phd, PEPeizhi Sun
Zachry Department of Civil Engineering
Texas A&M University
14 April, 2013
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OUTLINE Present Technology
ASTM C 156 New Approach
Curing Indexing Index Validation and Testing
Conclusions
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Present Testing Technology Time of Curing
Low surface concrete strength Delamination and spalling
Duration (rate) of Curing Set Gradient
Liquid membrane-forming curing compounds Only represented by total moisture loss
No attention paid to a design rate of application
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New Approach Laboratory Test for Evaluating Curing
Compound
Relative humidity (RH) measurement
Moisture loss measurement Concrete surface abrasion test
Propose an Evaluation Index
Relate Index to Performance
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Relative Humidity Measurement ACMM device to collect RH data
RH data Ambient temperature
Wind speed
Solar radiation
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Relative Humidity Measurement Sealed chamber
Collect RH data near perfect curing conditions Filtered chamber
Collect RH data just below the concrete curing surface
7Top ViewSide View
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Relative Humidity Measurement screen is place over a plate for the filter
chamber thin mortar layer on the screen
curing compound is applied on the mortar
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After placing curing compound , place the ACMM device on the housings inthe plate
Relative Humidity Measurement
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Relative Humidity Measurement
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same procedure is applicable for field condition to
collect RH data
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Relative Humidity Measurement
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Example of RH Data Curing compound 1600
225 ft2/gal application rate
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Indexes for Evaluating Curing Evaluation Index
based on maturity or equivalent age of concrete
Curing Index
through modeling curing as moisture diffusion
process
based on time dependent diffusion coefficient
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Evaluation Index (EI) Equivalent Age (t) of Concrete
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( ) ( )4
0 00 0
1
1 (7.5 7.5 )
t to o
i H
rm rm
T T T T t t t
T T RH T T
= =
+
[ ] 14)5.75.7(+1= HH
where
H = the moisture modification factorRH = the humidity of concrete
ti = equivalent age of concrete
i = sealed, filtered, and ambient conditions
T = the average temperature of the concrete during time interval t
T0 = the datum temperature with a value of -10 C
Trm
= room temperature 21C
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Evaluation Index (EI) EI is defined as:
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as
af
tt
ttEI
=
where
tf= the equivalent age of the filtered curing condition
ts = the equivalent age of the sealed curing conditionta = the equivalent age of the ambient curing condition
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0 0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
00.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9 1
10/11/12 12:00 PM
10/12/12 12:00 AM
10/12/12 12:00 PM
10/13/12 12:00 AM
10/13/12 12:00 PM
10/14/12 12:00 AM
10/14/12 12:00 PM
10/15/12 12:00 AM
Evaluation Index
Relative Humidity, %/100
Date-
Time
Re
sinCure
sealedrh
filter
edrh
AmRH
EI
0 0 0 0 0 1 1
0.00
0.10
0.20
0.30
0.40
0.50
0.60
0.70
0.80
0.90
1.00
Relative Humidity, %/100
Date-Time
LithiumCure
Exam
ples(
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Curing Index
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Curing process can be represented by the following
differential equation:
2
2
u u
t z
=
where
u = suction in concrete (pF)
= Diffusion coefficient (cm2/sec)
t = time (sec)
Suction in pF = log (capillary pressure)
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Curing Index
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c
b
w
where
current diffusion coefficient
best possible diffusion coefficient
worst possible diffusion coefficient
=
=
=
, w c
w b
Curing Index CI
=
Diffusion Coefficient Curing Index
exp( )cCI a b t = Modeled CI with with R2 = 0.92
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Dielectric Constant (DC) Apply a thin layer of concrete mortar on top of the cap and spray curing
compound on it
Take off the cap and insert the probe into the cylinder when measuringthe DC readings
Let the bottom surface of the probe
fully contact with the concrete surface and read the reading
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( )
=t
et ,,,
is related to the curing compound application rate. The higher is, better the
curing quality is.
is related to curing compound quality. The higher is, it is more likely that
curing compounds would diminish more quickly.
is related to the effective duration of the curing compound.
Dielectric Constant (DC)
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Concrete Surface Abrasion Test Test concrete surface abrasion resistance based on ASTM
C944
By measuring the amount of concrete abraded by a rotating
cutter in a given time period (10 min, under 22 lb. of load inthis study)
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0
2
4
6
8
10
12
14
16
18
20
84 85 86 87 88 89 90
DepthfromSurface(in)
RH (%)
Int 0 Int 5 Int 10 Int 15 Int 20
No Curing Curing
0
2
4
6
8
10
12
14
16
18
20
70 75 80 85 90 95 100
DepthfromSurface(in)
RH (%)
Int 0 Int 5 Int 10 Int 15 Int 20
Set Gradient
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( )L , D-Days l
( )-
1 1
2 2
3 3
C = e
Site
1
2
3
N
Field Performance Calibration
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Performance vs. Climatic
Conditions
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Cracking Calibration
maxC
C
2 2, C
1 1,N C
cfN
( ){ }1 211
10 %k k r
fN Ln C
+= = c
( )3
1 1
cfTo tLog N C
r oR C C
= =
c
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Damage Coefficients (C4, C5)
{ } ( ) ( )
( ) ( ) { }{ } ( ) ( ){ }
( ) { } ( ){ }
5 5
5
5 5
1
4
4
4
5 4 5
4 5 4 5
4 5 5
1% 1
1
11
%1
1%
11
%
11
%
11%
c
c
c
C C
fC
C C
f
f
f
f
C C N N C D
N C N
C
Ln C Ln N Ln C C Ln NC
n Ln C C Ln N Ln N Ln C C Ln DC
Ln Ln C C Ln N C Ln NC
y b mx
y Ln C
= = + +
=
+ = +
= + = +
= +
= +
=
( )
( ) { } { }
5
4 4;fb mLn N
f
x Ln N
m C
b Ln C mLn N C e
+
=
=
= =
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Design Stress Ratio
2
1
3
1 1
10
10
i
Ci
i
ci c i built in C
built in ci C
N
Log D Cr
C C
r r r r r
r r r
=
= =
= +
c
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Built-In Gradient
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{ }&cbuilt in c w set r r r = +
{ }design
Totwls envr r r
MoR
= = +
{ } { }& & &i
i i i c
env
env c w built in c w c w set r r r r r r MoR
= = + = + +
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Curing and Fatigue Damage Therefore, evaluation index or curing index
can be tied to the calibration of cracking andallowable wheel load calculation.
This can help to better predict theperformance of the pavement.
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Test ProgramMaterial and Mixture Design
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Curing Compound
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Test Program (Contd)Experimental Design
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Environmental Condition
Variable Unit Low Level Medium Level High Level
Curing compound A Lithium B
Application Rate Ft2/gallon 220 120
w/c of mixture 0.4 0.43
Wind Speed mph 0 5
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Validation Checking Evaluation of Curing effectiveness between
different curing compounds
Evaluation of Curing effectiveness under
different ambient conditions
w/c ratio = 0.43 for all the results shown inthe presentation
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Lithium/120 Lithium/220 A/120 A/220 B/120 B/220
Moisture loss
Validation Checking
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Lithium A B
EI at 72 hours
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Lithium A B
Weight,lb.
3-day Abrasion weight loss
Sands used in this section are 100% passing through #4
sieve, some of the large variance may due to the
influence of large aggregate particles retaining on #8
sieve.
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Circle----- Curing compound B
Line------ Curing compound ATriangle---- Lithium
Red----120 AR
Green ----220 AR
(some tests were conducted by a few people, lack of consistency)
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Dielectric constant & Water content
Two same mixes applied with high (120 ft2/gal ) and low (220 ft2/gal ) rate of curing compound
Sample with higher application rate (120 ft2/gal ) shows higher DC and water content over time
Water content is predicted using a self consistent model developed by Dr. Sang Ick Lee
w/c Curing compound Type Application rate Fixed ambient condition
0.43 2250 120 ft2/gal & 220 ft2/gal 32C, 50% RH, 5 mph wind
0
0.05
0.1
0.15
0.2
0.25
8.00
9.00
10.00
11.00
12.00
13.00
14.00
15.00
16.00
17.00
18.00
0.00 10.00 20.00 30.00 40.00 50.00 60.00
VolumetricWaterContent
DielectricConstant
Time, hours
Variation of Volumetric Water Content by D.C.
Dielectric constant (120 ft2/gal) Dielectric constant (220 ft2/gal)
water content (120 ft2/gal) water content (220 ft2/gal)
3 51 2 4
1 2 3 4 5
02 2 2 2 2
Aggw h cp uc Air
+ + + + =
+ + + + +
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Model for Comparison of Dielectric constant
0.00
2.00
4.006.00
8.00
10.00
12.00
14.00
16.00
18.00
0.00 10.00 20.00 30.00 40.00 50.00 60.00DielectricC
onstant
Time, hours
Variation of Volumetric Water Content by D.C.
Dielectric constant (120 ft2/gal) Dielectric constant (220 ft2/gal)
Pridicted model (120 ft2/gal) Pridicted model (220 ft2/gal)
y1 = 16.778*(1-exp(-(1/(t*0.013))^0.417)
y2 = 16.47*(1-exp(-(1/(t*0.0171))^0.446)
Weibull accumulative distribution:
where,
= amplifying parameter
= scaling parameter, and
= shift parameter.
( , , , ) . 1
t
W t e
=
1/
120 ft2/gal 16.778 76.923 0.417
220 ft2/gal 16.47 5.848 0.446
Higher 1/ Lower rate of reduction of
moisture Better curing
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Victoria, Tx
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3/26/2013
100 Ft Test SectionSurface
Treatment (1)Lithium Cure (2)
Shrinkage
Reduction (3)Resin Cure (13=4) Notes
1 + NO - Tr - None 200 ft2/galFirst half sprayed with Dayton resin, rest
sprayed with city resin
2 - SB - None + With 200 ft2/gal manually sprayed with city resin
3 - SB - Tr - None 150 ft2/gal manually sprayed with city resin
3/28/2013
100 Ft Test
Section
Surface Treatment
(1)Lithium Cure (2)
Shrinkage
Reduction (3)Resin Cure (13=4) Note
1 + NO + Si + With 150 ft2/gal All the Lithium are sprayed
manually at 200 ft2/gal.
The City Resin cure are sprayed
by using the machine. 150 ft2/gal
goes two passes, 200 ft2/gal goes
one pass.
No City Resin was sprayed on
Section 4, 6, 8, since the Sinak
Lithium sprayed on this section is
already mixed with resin
2 - SB - Tr plus + With 200 ft2/gal
3 + NO + Si + With 200 ft2/gal
4 - SB + Si mix + With
5 + NO - Tr plus + With 150 ft2/gal
6 + SB + Si mix - None
7 + SB + Si - None 150 ft2/gal
8 - NO + Si mix - None
9 - SB - Tr - None 150 ft2/gal
Victoria Test Plan
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Effectiveness Index (EI)
0
0.1
0.2
0.30.4
0.5
0.6
0.7
0.8
0.9
1
Mar 26 (Section
1)
Mar 26 (Section
3)
Mar 28 (Section
3)
Mar 28 (Section
8)
EI
EI at 72 hours Date100 Ft
TestSection
Lithium Cure (200ft2/gal)
Resin Cure
March 26 1 - Transil 200 ft2/gal
March 26 3 - Transil 150 ft2/gal
March 28 3 + Sinak 200 ft2/gal
March 28 8 + Resin-mixedSinak None
Dayton Resin cure were unevenly sprayed on
March 26 Section#1because the thick compound
clogged the spray gun.
The other sections are sprayed with City Resin
cure (except for March 28 Section#8)
0.01
0.1
1
10
100
1/
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Evaluation Index (EI)Test Section 8 at Victoria
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Curing IndexSection 3 and Section 8, Victoria
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T and RH Gradient set gradient around maturity 200 deg C-hr
leads to curled up position
set gradient strain was 510-4
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T and RH gradient of Section 8 at 8.75 hr
0
2
4
6
8
10
12
0 5 10 15 20 25
S
labThicknessfromB
ot
tom(
in)
Temperature (Deg C)
0
2
4
6
8
10
12
0.88 0.9 0.92 0.94 0.96 0.98 1
S
labThicknessfromB
ot
tom(
in)
Relative Humidity (%)
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Curing Effectiveness Can be monitored in laboratory and the field
Can be indexed to strength and setting Moisture Modeling (routinely done)
Examine the factors affect set gradient of concrete
Improved calibration of cracking models
Improved concrete pavement design and
performance prediction
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CODE BRIGHT Computational
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mat1
mat4
mat5
mat3
mat6
mat2
N
M
J
K
L
P O
I
CODE_BRIGHT Computational
Code Coupled analysis in porous media Interaction with the atmosphere(Olivella, 1995;Guimares, 2002; Snchez, 2004)
Finite element in space 1D, 2D and 3D elements
Monolithic coupling
Full Newton-Raphson
Finite difference in time Implicit time discretisation scheme
Automatic time advance
Mass conservative approach for mass
balance equations User-friendly pre/post processing of data
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Date EI %Cracking Cure
Mar 5th 0.814 5.6% WMR
Jun 26th 0.785 WMR- 1g/150 ft2
Jun 15-16 0.734 Lithium Relay 1g/188 ft2
0.971 Lithium Relay 1g/94ft2
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Evaluation of Curing EffectivenessCuring Compound A
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NW: No wind W: With wind NC: No Curing
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Evaluation of Curing Effectiveness
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NW: No wind
W: With wind
NC: No curing
Large aggregate particles
retaining on #8 sieve were
eliminated
all sands used are 100% passing
through #8 sieve
Curing compound A