Underground Construction - January 2020 - 43

Conclusions
Smart cement was used as the binder in the concrete to make it
highly bulk sensing; smart grout was developed using the smart
cement with water-to-cement ratio of 0.6.
Based on experimental and analytical study on the behavior of
concrete and grout, the following conclusions are advanced:
* The addition of coarse aggregate and curing time increased the
initial electrical resistivity of the smart cement composite, as
well as its long-term electrical resistivity. The initial electrical
resistivity of smart cement was 1.02 Ω.m, which increased to
3.74 Ω.m. with 75% gravel. After 28 days of curing, the electrical
resistivity of smart cement was 14.14 Ω.m, which increased to
61.24 Ω.m. with 75% gravel. Also, the Vipulanandan Curing
Model predicted the electrical resistivity development in the
concrete very well.
* The piezoresistivity of the smart cement with 0% and 75%
gravel content after 28 days of curing was 204% and 101%,
respectively, at peak compressive stress. The Vipulanandan
Piezoresistivity Model can be used to predict the piezoresistivity
behavior of the smart cement composites very well.
* The failure strain of concrete is 0.3%, hence piezoresisitive
concrete has magniﬁed the monitoring resistivity parameter
by 336 times (33,600%) or more, based on the aggregate
content and making the concrete a bulk sensor.
* The smart cement grouts showed change in sensing property with
applied stress behavior under compressive stress. Piezoresistivity
at peak stress increased from 155% to 179% with curing time.
* The repaired smart cement showed piezo-sensing property,
regaining 84% strength and 42% piezo-sensing property.

ANNUAL CONFERENCE
During CIGMAT's annual Conference and Exhibition, speakers are

18
Grout: Smart cement only
Vipulanandan p-q Piezoresistive model
1 day
7 days
28 days

16
14

Stress, MPa

12
10
8
6
4
2
0

100

Δ / 0, %

150

200

250

FIGURE 11: Piezoresistive responses of the smart cement grout after 1, 7 and
28 days of curing, and using the Vipulanandan p-q Piezoresistive Model.
14
Smart cement grout
12
10
Stress, MPa

Several one-day cured sensing cement specimens (0.38 w/c ratio)
were used for the repair study after failing the specimen under
compression loading. The compressive strength of the one-day
cured sensing cement varied from 10.81 MPa to 12.00 MPa
(TABLE 7). Resistivity change of the one-day cured sensing cement
at peak stress varied from 268% to 300% and data on the repaired
specimens is summarized in TABLE 7.
Sensing cement grout was used to repair the sensing cement
specimen with a strength of 12.00 MPa and 300% changes in
resistivity with applied stress at failure. After submerging the
damaged specimen for 3 hours in the grout, it was cured for one
day and tested under compression load. The percentage weight
change in the repaired specimen was 0.24%. The compressive
strength of the repaired specimen was 10.09 MPa, an 84% strength
recovery, which was the highest strength recovery observed.
Changes in sensing property with applied stress (Δρ/ρ %) at
4 MPa for the repaired sample was 15% compared to the sensing
cement 86%, recovery of 18%. The change in sensing property
at failure (Δρ/ρ %)f for the repaired specimen was 48% at peak
stress of 10.09 MPa. The sensing property change in sensing
cement at 10.09 MPa was 234%. Hence, smart grout repair
resulted in 21% recovery of the change in sensing property
with applied stress behavior (FIG. 12).

8
6
4
Vipulanandan p-q Piezoresistive model
Initial sample-Experiment
Repaired sample-Experiment

2
0

100

150
200
Δ / 0, %

250

300

350

FIGURE 12: Comparing the predicted and measured compressive stressresistivity change relationships for smart cement, before and after repairing
with smart cement grout, following one day of curing.

invited from major cities, transportation authorities and energy
industries around the country to present and discuss projects
and problems in construction, maintenance and rehabilitation.
The well-attended event, "Infrastructures, Energy, Geotechnical,
Flooding and Sustainability Issues Related to Houston and Other
Major Cities," also addresses technical issues related to maintenance and rehabilitation of water and wastewater systems,
nondestructive testing methods, oil wells and pipelines, hydraulic
fracturing, and smart materials for various applications. In addition, geotechnical topics include expansive clays, rapid construction of deep foundations, and ground faulting.
See the variety and quality of presentations by accessing the
Proceedings from past years of the conference, at the CIGMAT
website (http://cigmat.cive.uh.edu).
The 25th Conference and Exhibition, CIGMAT-2020, will be held
on March 6, 2020. Check the CIGMAT website for more information and updates on the event. *
UConOnline.com | JANUARY 2020

http://cigmat.cive.uh.edu http://www.UConOnline.com

Underground Construction - January 2020

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