Underground Construction - January 2022 - 36

CIGMAT Report
for the smart cement and 25 percent for the 3 percent polymer
slurry, as shown in FIGURE 6.
For hardened cement, the trends were opposite. With added
pressure, resistivity increased by 80 percent, for compressive stress
of 700 psi (FIGURE 3), but with the gas leak, resistivity reduced by
-35 percent, as shown in FIGURE 7. Th is is a clear indication of the
sensing characteristic of smart cement.
In smart cement with 3 percent polymer, the maximum resistivity
change was -12 percent. By monitoring the resistivity change,
the gas migration in cement can be detected and quantifi ed.
Th e Vipulanandan correlation model was used to relate the discharge
velocity (V = average discharge per unit area) to the change
in resistivity as follows, in Equation (6):
V= x /(A3
+ B3 × x)
where x = Piezoresistive Axial Strain (∆ρ /ρo
) percent.
Th e model parameters A3 (sec percent/mm) and B3
summarized in TABLE 4.
(sec/mm) are
TABLE 4. Correlation model parameters for discharge velocity
and the change in resistivity
A3
Curing Time
1 Hour Curing
Smart Cement (SC)
3% PMSC1
24 Hour Curing
Smart Cement (SC)
3% PMSC1
(sec %/mm)
1.13
0.96
0.83
0.59
B3
(sec/mm)
-0.01
-0.02
0.016
0.006
R2
0.96
0.98
0.99
0.99
RMSE
(mm/s)
5.97
3.39
1.17
0.62
TABLE 5: Properties of two silane coatings and one latex coating
Silane Material
Physical
State
Silane-1
Silane-2
Coating Material
Coating-1 (Latex Based)
* V.O.C = volatile organic carbon
Liquid
Liquid
Physical
State
Liquid
Density
(kg/m3
)
1000
760
Density
(kg/m3
)
1365
Silane
Content (%)
100
40
V.O.C.*
(gm/L)
104
Conclusions
Based on the experimental and analytical study on smart cement
without and with 1 percent and 3 percent SBR polymer addition,
the following conclusions are advanced:
1. Adding SBR polymer increased the resistivity of the smart
cement: 4 percent with the 1 percent polymer; 12 percent with
3 percent polymer. Hence, resistivity could be a good quality
control parameter in the fi eld. Th e Vipulanandan curing model
predicted the trends very well.
2. Addition of polymer increased the compressive strength
of smart cement, after 24 hours of curing, by 32 percent
with the 3 percent polymer.
(6)
3. Th e polymer addition made the smart cement piezoresisitive.
With 3 percent polymer, the resistivity change at peak
stress was more than 100 percent after 24 hours of curing.
Vipulanandan p-q Piezoresisitive Model predicted the
behavior very well.
4. Addition of polymer reduced the gas leak. Smart cement
resistivity changes were highly sensitive to the gas leak and
can be used to detect and quantify gas leaks.
COMPOSITE COATINGS TO PROTECT
REINFORCED CONCRETE IN
SALT-WATER ENVIRONMENT
Corrosion in reinforced concrete structures is raising increasing
concern because it requires immediate repairs and rehabilitation to
extend the service life of the structures.
One of the methods to stop the ingress of corrosion-causing
Flash Point
(°C)
77
>100
Solids by
Weight (%)
53.50
FIGURE 7: Resistivity change with gas leak for 24-hour cured smart
cement without and with 3 percent SBR
FIGURE 6: Resistivity change with gas leak for 1-hour cured smart
cement without and with 3 percent SBR
36 JANUARY 2022 | UCONonline.com
FIGURE 8: Specimens being dried for measuring the weight change
during the drying cycle
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