D aeyoon S cale Industrial C o.,Ltd.
C hloride-M eter D Y -2501B
1
1. Technology Preview
Concrete is a basic material for constructing streets, highways, trail roads, and harbors, but
the chloride in concrete causes internal corrosion of reinforcing steel in concrete structures.
So recently this has become an issue affecting people in many areas.
Concrete has an alkalinity of over pH12. This creates a passive state layer on the surface of
reinforcing steel to protect against corrosion, but the chloride ion partially breaks down this
passive state layer eventually leading to corrosion of the reinforcing steel. Hence, the
corrosion of the aggregates accelerates the corrosion of concrete, decreasing the durability
of any concrete-made structures.
Chloride in hard concrete can be classified into two species. There is the water-soluble
chloride form such as NaCl, KCl, CaCl
2,
which directly affects corrosion of reinforcing steel in
concrete, and the acid-soluble chloride form, 3CaO Al
․
2
O
3
CaCl
․
2
10H
․
2
O, which indirectly affects
corrosion of reinforcing steel in concrete.
In an ion selective electrode (ISE), the potential difference developed between the sensing
and reference electrodes is a measure of the activity of the reactive species. As the activity
of the species reacting at the sensing electrode varies, so does the potential measured
between the two electrodes. As first shown by Nernst, electrode response may be described
by a linear equation:
E = Eo + S log a
where “E” is the measured voltage, “Eo” is a combination of several constants within the
system including reference potentials, “S” is the slope of the electrode, and “a” is the
activity
of
the
measured
species.
By
measuring
the
electrode’s
potential
in
both a
standardizing solution and in a sample solution, it is possible to calculate the unknown
solution’s concentration by using the following form of the previous equation:
Cx = Ci x 10
E/S
△
where “Cx” is the concentration of the unknown solution, “Ci” is the concentration of the
standardizing solution, “
E” is the difference between the observed potentials in the
△
standardizing and sample solutions, and “S” is the electrode slope, the change in electrode
potential per ten-fold change in concentration. All measurement techniques are based upon
some form of this concentration equation. A meter with microprocessor capability is
recommended for all the measurement methods using ion selective electrodes. Meters with a
millivolt readability to ± 0.1 mV may also be used.
