Transactions of the American Society of Civil Engineers, vol. LXX, Dec. 1910 | Page 2

weather,
the placing of the caissons promised to be a simple matter. Therefore,
detailed plans were prepared for this structure.
An effort was made to preserve some element of the yachting idea in
the design, and bow-string trusses, being merely enlarged gang planks,
were used to connect the caissons.
The pier was originally laid out as a letter "L," with a main leg of 300 ft.
and a short leg of 36 ft. The pier head consisted of eight caissons in
close contact, and was intended to form a breakwater, in the angle of
which, and protected from the wave action, was to be moored the float
and boat landing. After the first bids were received, the owner wished
to reduce the cost, and every other caisson in the pier head was omitted,
so that, as built, the pier contains eight caissons and five 53-ft. trusses.
The caissons supporting the trusses are 8 ft. wide and 12 ft. long, and
those in the pier head are 12 by 12 ft. On account of the shoal water and
the great height of the outer caissons in comparison with their
cross-section, it seemed advisable to mould them in two sections. The
reinforcement in the side walls consisted of round 1/2-in. rods
horizontally, and 3/8-in. rods vertically, spaced as shown on Fig. 1,
together with cross-diaphragms as indicated.
The caissons were reinforced for exterior pressures, which were to be
expected during the launching and towing into position, and also for
interior pressures, which were to be expected at low tide, when the
water pressure would be nothing, but the filling of the caissons would
be effective. The corners were reinforced and enlarged. In order to
secure a proper bedding into the sand foundation, a 12-in. lip was
allowed to project all around the caisson below the bottom. In the
bottom there was cast a 3-in. hole, and this was closed by a plug while
the lower section was being towed into place.
The question of the effect of sea water on the concrete was given much
thought. The writer is unable to find any authoritative opinions on this
subject which are not directly controverted by equally authoritative
opinions of a diametrically opposite nature. He thinks it is a question

that this Society might well undertake to investigate promptly and
thoroughly. There can be no question that there are many distressing
instances of failures due to the action of sea water and frost on concrete,
and that many able and experienced engineers in charge of the
engineering departments of the great transportation companies have
simply crossed concrete off their list of available materials when it
comes to marine construction. It is a subject too large in itself to be
discussed as subsidiary to a minor structure like the one herein
described, and though many have rejected concrete under these
conditions, other engineers equally conservative are using it freely and
without fear.
The writer consulted with his partner and others at some length, and,
considering all the advantages to accrue by the use of these concrete
caissons, decided to do so after taking all known precautions.
[Illustration: FIG. 1.]
These precautions consisted in:
First, the use of cement in which the chemical constituents were limited
as follows:
It was specified that the cement should not contain more than 1.75% of
anhydrous sulphuric acid (SO_{3}) nor more than 3% of magnesia
(MgO); also that no addition greater than 3% should have been made to
the ingredients making up the cement subsequent to calcination.
Secondly, to secure by careful inspection the most completely
homogeneous mixture possible, with especial care in the density of the
outer skin of the caissons.
Thirdly, a prolonged seasoning process before the new concrete should
be immersed in the sea water.
In addition to these well-known precautions, it was decided to try the
addition to the cement of a chemical element that should make with the
free lime in the cement a more stable and indissoluble chemical

combination than is offered by the ordinary form of Portland cement.
This was furnished by the patent compound known as "Toxement,"
which is claimed by the inventor to be a resinate of calcium and silicate
of alumina, which generates a resinate of lime and a silicate of alumina
in crystalline form. It is further claimed that each of these materials is
insoluble in sodium chloride and sodium sulphate, 3% solution. It was
used in all the caissons, excepting Nos. 1 and 2, in the proportions of 2
lb. of Toxement to each 100 lb. of cement. The first two caissons were
not thus treated, and will be held under close observation and
comparison with the others, which were treated with this compound.
The mixture used was one of cement (Pennsylvania brand), two of sand,
and four of gravel.