60 | CONCRETO & Construções | Ed. 93 | Jan – Mar • 2019
and alkali-aggregate reaction (AAR)).
Current techniques are also unable
to predict damage in elements aris-
ing from loading, fatigue, acciden-
tal impact and unavoidable stress
concentrations.
Structural health monitoring (SHM)
using fibre optic sensors (FOSs) stra-
tegically integrated into structural sys-
tems is part of an effective approach
towards infrastructure management.
The same has been studied and ap-
plied to numerous structures in Cana-
da (the Safe Bridge, near Duncan, BC,
for example, and the Gentilly Nuclear
Reactor in Quebec, see Fig. 5) and
abroad. Unfortunately, FOSs are pro-
hibitively expensive and are not able
to sense changes in the chemical en-
vironment in concrete that lead to du-
rability and deterioration concerns. A
number of novel sensors are now in
development.
3. CONCRETE USED
AS A SENSOR
Recently, a new type of concrete
has been developed at the Univer-
sity of British Columbia (UBC) which
can not only sense changes in its
stress condition and temperature,
but also detect the presence of
cracking and other damaged states,
changes in the chemical environ-
ment, chloride content and onset
of steel corrosion, moisture content
and loss of strength. As opposed
to other sensors, their cementitious
nature allows them to be integrat-
ed better into the parent structure
where they develop a natural bond
and have similar physical and trans-
port properties (Fig. 6). When in-
stalled strategically as tiny sensors
in the structure, these elements can
interact wirelessly over the internet
and provide the engineer with con-
tinuous data on the overall health of
the structure they form part of (Fig.
8). These can easily be integrated in
both new and old structures and can
be interrogated continuously or peri-
odically depending on the need.
Concrete by nature is a poor con-
ductor of electricity and, hence, a poor
sensor. The only requirement for con-
crete to start sensing is that it should
be a good conductor of electricity and
must show a variation in its resistiv-
ity when the conditions are altered. A
detectable response may emerge as
a result of changes in the strain/stress
field (a property often called piezore-
sistivity, see Fig. 7) or to changes in
the chemical environment (a property
u
Figure 5
Sensors on Gentilly Nuclear Reactor in Quebec
(Courtesy: Professor, ISIS Canada)
u
Figure 6
Left: cement composite with carbon fibre at 100X magnification
Right: MWCNT bridging hydration products at 5000X magnification
