CONCRETE MOULDS.
73
the shoot, at the top of which the water supply is added. The concrète,
however, does not actually becorne wetted until it reaches the fifth row of
pins, the process prior to this being that of dry mixing. A gate, or valve,
at the foot of the shoot, regulates the discharge if not required to be
continuons.
The machine has been used in England at the Liverpool Docks, the
London and India Docks, and at Chatham Dockyard. At the Canada
Branch Dock (No. 2 contract), Liverpool, it proved capable of discharging
rather less than 100 cubic yards per day when fed continuously. This
represents a much more moderate output than those of the machines
previously described, but the concrete was of a very satisfactory quality.
The advantages possessed by a mixer of this type, when used in undertakings
not necessitating a rapid supply, are lightness, mobility, and economy.
Concrete Moulds.—Closely connected with concrete mixers are the tem-
porary wooden moulds within which the fluid concrete is deposited.
For the back of a dock or quay wall, which is usually designed in a series
of horizontal offsets, ordinary deals on edge form a sufficient and satisfactory
enclosure. The offsets are rarely more than a few planks in height; these
are stiffened by short verticals at the back, and the whole rests upon the
ledge next below. The same method, with a slight modification, may be
adopted for the altar courses of a graving dock. The profile is rounded and
the face of the mould carefully planed (fig. 36).
For the front of a dock or quay wall, the moulds are prepared in uniform
sizes of any convenient dimensions. Two methods of supporting them are
illustrated.
In the first case the moulds (fig. 37) rest upon short cantilevers project-
ing from the wall. These cantilevers (fig. 38) are of timber, about 4 by 3
inches section, with their ends laid upon the previously completed work