Evening star. [volume] (Washington, D.C.) 1854-1972, 1914-09-05
ELECTRICITY
WILL EFFECT CONCRETE
Tests Of Building Material Con-
Quoted by Bureau of
Standards.

II is usually difficult to determine the
direct cause of failure Of reinforced con-
crete structures and it will therefore be
OF interest to those engaged in this class
Of work to know that the United States
bureau Of standards has made an elab-
crate series Of experiments to deter
mine the effect Of electrolysis on REIN
forced concrete. There has been con-
siderable discussion as to the means en-
ployed to prevent damage by stray cleo
trio currents to underground cables and
pipes. and while experts have long
known to a limited extent that this dam
age also extends to reinforced concrete
work no definite information was avail
able on this very important question.
These experiments. which were started
in 1910. proposed first to determine the
nature and cause of the phenomena pro-
duced by the passage of electric cur
rents; second, to investigate the probable
practice and the conditions under which
trouble is likely to occur. and third, to
find means of mitigating the trouble due
to electrolysis leading to specific recon-
mendations.
Theory Fully Established.
OF the numerous theories that have
been advanced for the cracking of re-
inforced concrete due to electric cur
rents. that one which attributes it to
oxidation of the iron following electricity
tic corrosion has been fully established.
The oxides formed occupy % times as
great a volume as the original iron, and
the pressure resulting from this increase
Of volume causes the concrete to crack.
The mechanical pressure developed at
the surface Of the iron has been meas
ured in a number of cases. and has been
found to reach values as high as 400
pounds per square inch, a value more
ing of the concrete. Corrosion of iron.
even in wet concrete. is very slight when
the voltage of the stray current does not
exceed fifteen volts. but the corrosion
becomes rapid when the voltage exceeds
f1ftv volts Therefore, in order to in
sure safety of reinforced concrete from
electrolysis the investigation shows that
the voltage Of stray currents must be
kept low, and this is especially true
wherever the concrete is exposed to the
action of salt water. The voltage of
stray currents may be kept below the
danger point by observing the following
precautions.
Great Precaution Needed.
In wiring a. concrete building with di-
rect current circuits 1t ts Of the greatest
importance that the construction be such
as to preclude the possibility of either
side of the circuit coming in contact with
the concrete The insulation should be
of the best grade and the wires should
be inclosed in continuous metal conduit.
When practical periodic tests should be
made on the insulation and any defects
remedied. All pipes entering the concrete
building should be provided with insu-
lating points where the pipes enter the
building ead-covered cables coming
into buildings should be insulated from
the concrete structure by supporting them
on wood or other similar material.
In case of new structures OF reinforced
concrete salt should be omitted altogeth-
er II there is the slightest probability that
they may ever be subjected to the action
Of electric currents. Calcium chloride is
quite as bad as sodium chloride, it being
the chloride that, does the harm A good
deal can be accomplished also by the
proper construction of the basement
foundations and footings of the building.
II beneath the foundation and outside the
basement walls a layer of insulating ma
terial be placed 1t will prevent the access
Of electric current through the building
foundations.
Painting May Help.