Portland cement concrete if made with a non-porous aggregate is
impervious to moisture, and yet at the same time, if not hydraulically
compressed, will take up a sufficient quantity of moisture from the air
to prevent condensation upon the surface of the walls. It not only
resists the disintegrating influences of the atmosphere, but becomes
even harder with the lapse of time. It may also be made in several
different colors, and can be finished off to nearly a polished surface
or can be left quite rough. Walls built of this material may be made so
hard that a nail cannot be driven into them, or they can be made
sufficiently soft to become a fixing for joinery, and, if a non-porous
aggregate be used, no damp course is required. Further than this, if
land be bought upon which there is sufficient gravel, or even clay that
can be burnt, the greatest portion of the building material may be
obtained in excavating for the cellar; and in seaside localities, if the
(salt) shingle from the beach be used, sound and dry walls will be
obtained. The use of concrete as a material for building will be found
to meet all the defects set forth by practical people, as it may be made
fire-proof, vermin-proof, and nail-proof, and in dwellings for the poor
will therefore resist the destructive efforts of the "young barbarian."
Nothing, therefore, can be better as a building material. The system
ordinarily employed to erect structures in concrete consists of first
forming casings of wood, between which the liquid concrete is deposited,
and allowed to become hard, or "to set." The casings are then removed,
the cavities and other imperfections are filled in, and the wall
receives a thin facing of a finer concrete. If mouldings or other
ornament be required, they are applied to this face by the ordinary
plasterer's methods. This system finds favor in engineering
construction, and also in very simple forms of architectural work, but
with very complicated work the waste in casings is very great. Besides
this, however, the face is found sometimes to burst off, especially if
it has been applied some time after the concrete forming the body of the
wall has set, and the method of applying ornament is not economical.
[Illustration: 1.-18.]
A system of building in concrete has recently been invented by Messrs.
F. & J.P. West, of London, illustrations of which we now present. To
this system Messrs. West have given the name of "Concrete Exstruction,"
from the Latin "exstructio," which they consider to be a more
appropriate word than "constructio," as applied to concrete building in
general. In Messrs. West's system of building in concrete, instead of
employing wood casings, between which to deposit the concrete or beton,
and removing them when the beton has become hard, casings of concrete
itself are employed. These casings are not removed when the beton has
set, but they become a part of the wall and form a face to the work. In
order to form the casings, the concrete is moulded in the form of slabs.
Figs. 1 to 18 of our engravings show various forms of the slab, which
may be manufactured with a surface of any dimensions and of rectangular
(Fig. 1), triangular, hexagonal (Figs. 2, 14, and 15), and indeed of any
other form that will make a complete surface, while for thickness it may
be suited to the work to which it is to be applied, that used for heavy
engineering work differing from that employed in house construction. It
is found that the most convenient height for the rectangular slab (Fig.
1) is 12 inches and the breadth 18 inches, as the parts of a structure
built with slabs of these dimensions more often correspond with
architectural measurements. The hexagonal slab (Fig. 2) is made to
measure 12 inches between its parallel sides. Where combinations of
these slabs will not coincide with given dimensions, portions of slabs
are moulded to supply the deficiency. The moulds in which the slabs are
made are simple frames with linings having a thin face of India-rubber
or other suitable material, by the use of which slabs with their edges
as shown, and also of the greatest accuracy, can be manufactured. That
portion of the back of the slab which is undercut is formed by means of
soft India-rubber cores. The moulds for making portions of the slabs
have a contrivance by which their length may be adjusted to suit given
dimensions.
During the process of casting the slabs, and while they are in a plastic
state, mouldings (if required) or other ornaments, having a suitable
key, are inserted in the plastic surface, which is finished off to them
(Figs. 7, 8, and 10). The slabs may also be cast with ornaments, etc.,
complete at one operation (Fig. 11), but it is more economical to have
separate moulds for the mouldings and other ornaments, and separate
moulds for the slabs, and to apply the mouldings, etc., during the
process of casting the slab. Corbels (Fig. 9), sets off (which would be
somewhat similar to the plinth course slab No. 10), and other
constructive features may also be applied in a similar way, or may be
provided for during the casting of the slab. A thin facing of marble or
other ornamental solid or even plastic material may be applied to the
face of the slabs during the process of casting, thus enabling the work
to be finished as it is carried up, or a key may be formed on the face
of the slab to enable the structure to be plastered afterward.
[Illustration: FIG. 19. FIG 20.]
In Fig. 20, the structure from the bottom of the trenches is shown with
the sides of the trenches removed. It will be seen that the footings are
constructed in the most economical manner by not being stepped. As no
damp-course is required in concrete work, when the aggregate is of a
non-porous material, one is not shown. Upon the top of the footings is
generally laid a horizontal slab, called the wall-base slab, the special
feature of which is that it enables the thickness of the wall to be
gauged accurately, and also provides a fixing for the first course of
slabs. Figs. 4 and 5 show such slabs for internal and external angles,
and Fig. 6 shows one for straight work. The use of a wall-base slab is
not essential, although it is the more accurate method of building, for
in cases where it is desirable to economize labor, or from other causes,
the slabs forming the first course may be made with a thicker base, and
may be fixed by a deposition of concrete, which is allowed to set behind
them. The second course of slabs is laid upon the first course with
breaking joints of half-slab bond, each course being keyed to the other
by means of a quick-setting cementing material poured into the key-holes
provided in the edges of the slab for that purpose, a bituminous cement
being preferred. The key-holes are made in several ways, those shown in
the illustrations being of a dovetail shape; circular, square, or indeed
holes of any other shape formed in the edges of the slab and in an
oblique direction are also employed. Special slabs for cants, or
squint-quoins (Figs. 17 and 18) and angles (Figs. 12, 13, 14, 15, and
16) are manufactured, the angle occurring (if we omit the hexagonals and
take the 18 inch slab) at three-quarters the length of each slab. This
gives a half-slab bond to each course, as on one face of the quoin in
one course will appear a quarter slab and in the course above a
three-quarter slab superimposed upon it, or _vice versa_. Thus are the
walls in Figs. 19 and 20 built up. For openings, the jambs and lintels
(and in window-openings the sill) are made solid with a provision for a
key-hole to the mass of concrete filling behind them. That portion of
the jambs against which the slabs butt has a groove coinciding with a
similar one in the edge of the slab, for the purpose of forming a joggle
joint by squeezing the bedding material into them or by joggling them in
with a cement grout. All the slabs are joggled together in a similar
way.
[Illustration: FIG. 21.-FIG 25.]
The plastic concrete filling or beton which the shells are made to
contain may be deposited between the slabs when any number of courses
(according to convenience) have been built up, and when set practically
forms with the solid work introduced a monolith, to which the face slabs
are securely keyed. With over-clayed Portland cements, which are known
to contract in setting, and with those over-limed cements which expand
(both of which are not true Portland cements), the filling in is done in
equal sections, with a vertical space equal to each section left between
them until the first sections have become thoroughly hard, and these are
then filled in at a second operation. In order to provide for flues,
air-passages, and ways for electric installations, and for gas and
water, pipes (made of an insulating material if required) or cores of
the required shape are inserted in the plastic beton, and where
necessary suitable openings are provided on the face of the work.
Provision is also made for fixing joinery by inserting, where required,
slabs made or partly made of a material into which nails may be driven,
such as concrete made with an aggregate of burnt clay, coke, and such
like. Hollow lintels are also made of the slabs keyed together at their
vertical joints, and when in position these are filled in with beton.
This system, however, is only recommended for fire-place openings
instead of arches.
In Fig. 25, circular construction is exhibited as applied to the apsidal
end of a church, slabs similar to those shown in Fig. 21 being employed
for that purpose, while Figs. 22, 23, and 24 show forms of slabs
suitable for constructing cylinders with horizontal axes and domes. In
Fig. 19, which is the upper part of Fig. 20, is shown a system of
constructing floors of these slabs. It is only necessary to explain that
the slabs are first keyed to the lower flange of the iron joist by means
of a cement (bituminous preferred), and the combination is then fixed in
position, the edges of the slabs adhering to, or rather supported by,
the iron joist being rebated so as to receive and support intervening
slabs, the heading joints of which are laid to break with those of the
slabs supported by the joists. For double floors the iron joists are
made with a double flange on their lower edge, and are fitted to iron
girders, which cross in the opposite direction. This provision secures
the covering of the cross girders on their undersides by the ceiling
slabs. The concrete having been deposited upon the slabs, its upper
surface may be finished off in any of the usual ways, while the ceiling
may be treated in any of the ways described for the walls. This system
does not exclude the ordinary methods of constructing floors and roofs,
although it supplies a fireproof system. Where required, bricks, stone,
and, in fact, any other building material, may be used in conjunction
with the slabs.
The system of building construction is intended, as in the case with all
concrete, to supersede brickwork and masonry in the various uses to
which they have been applied, and, at the same time, to offer a more
perfect system of building in concrete. Hitherto slab concrete work has
never been erected in a perfectly finished state (i.e., with mouldings,
etc., complete), but has either been left in a rough state or without
ornament, or else has been constructed so as never to be capable of
receiving good ornamental treatment. Hitherto the great difficulty in
constructing concrete walls of concrete and other slabs has been to
prevent the slabs from being forced outward or from toppling over by the
pressure of the plastic filling-in material from the time of its
deposition between the slabs until it has become hard enough to form,
with the slabs, a solid wall. Besides the system of forming the slabs of
L (vertical or horizontal) section, or with a kind of internal buttress
and shoring them up from the outside, or of supporting the slabs upon
framing fixed against the faces of the wall, several devices have been
used to obviate this difficulty.
In the first place, temporary ties, or gauges, connecting the slabs
forming the two faces of the wall, have been used, and as soon as the
plastic filling-in material has set or become hard (but not before),
these have been removed. Secondly, permanent ties or cramps have been
used, and, as their name implies, have been allowed to remain in the
wall and to be entirely buried in the plastic filling-in material. These
permanent transverse ties or cramps have been of two kinds: those which
were affixed as soon as the slabs were placed in position, and those
which were made to form part of the manufactured slab, as, for instance,
slabs of Z or H horizontal section. Thirdly, a small layer of the
plastic filling-in material itself has been made to act as a transverse
tie by depositing it, when plastic, between the slabs forming the two
parallel faces of each course, allowing it (before filling in the
remaining part) to set and to thus connect together the slabs forming
each face of the wall, a suitable hold on the slabs, in some cases,
being given to the tie by a portion of the slab being undercut in some
way, as by being dovetailed, etc. As the slabs in this latter system
generally have wide bases, they may also be bedded or jointed in cement,
and, provided temporary ties be placed across their upper edges to
connect the slabs forming each face of the wall together, the space
between the faces of the wall may then be filled in with the plastic
concrete.
All these devices, however, are not of permanent utility; they are only
temporarily required (i.e., up to the time that the beton has become
hard and formed a permanent traverse tie between the two faces of the
wall), for it is manifest that the ultimate object of all slab concrete
construction is: (a) To retain and to mould the plastic concrete used in
forming the wall; (b) to key or fix the slabs to the mass which they
themselves have moulded; and (c) to form a facing to the wall. When
these objects shall have been accomplished, there is no further need of
any tie whatever beyond that which naturally obtains in a concrete wall.
In West's system, however, where the slabs are keyed course to course,
any kind of transverse tie to be used during the process of
construction, except that used in the starting course, is entirely
dispensed with, and the courses of slabs above depend solely upon the
courses of slabs below them for their stability and rigidity up to the
time that the plastic filling-in has been deposited and become hard
between both faces of the wall.
[Illustration: CONCRETE CONSTRUCTION]
There is, however, a more decided difference between West's system and
those previously in use, for it is marked by the fact that the slabs
composing the shell of the whole structure in many cases may be built up
before the filling-in is deposited between the slabs, and in none of the
other cases can this be done. In fact, only in the first two cases
before mentioned can more than one course of slabs be laid before
filling-in of some kind must be done. Compared with the ordinary method
of building in concrete, this system avoids: 1. The charge for use and
waste of wood casings; 2. finishing the face of the work (both inside
and outside) after the structure is raised, and, therefore, the
bursting-off of the finished face; and 3. the difficulties encountered
in working mouldings and other ornaments on the face of the work by the
ordinary plasterer's methods. It also provides a face of any of the
usual colors that may be obtained in concrete, besides a facing of any
other material, such as marble, etc., and produces better and more
durable work, at the same time showing a saving in cost, especially in
the better classes of work; all of which is effected with less plant
than ordinarily required. For engineering work, such as sea walls, the
hexagonal slabs, made of greater thickness than those employed for
ordinary walling, will answer admirably, especially if the grooves be
made proportionately larger. By the use of these slabs the work may be
built up with great rapidity. For small domestic work, such as the
dwellings of artisans, these slabs; which are of such a form as to
render them easy of transport, may be supplied to the workmen themselves
in order that they may erect their own dwellings, as, on account of the
simplicity of this system and the absence of need of plant, any
intelligent mechanic can do the work.
Any arrangement of independent scaffolding may be employed for this
system, but that invented specially for the purpose by Mr. Frank West,
as shown in Fig. 26 of our engravings, is to be preferred. It not only
supplies the necessary scaffold, but also the necessary arrangements for
hoisting the slabs, as well as for raising the liquid concrete and
depositing it behind the slabs. It is really an independent scaffold,
and may be used wherever a light tramway of contractor's rails can be
laid, which in crowded thoroughfares would of necessity be upon a
staging erected over the footway. The under frame is carried upon two
bogie frames running upon the contractor's rail, by which means it is
enabled to turn sharp curves, a guide plate inside the inner rail being
provided at the curves for this purpose. The scaffold itself consists of
a climbing platform made to travel up or down by means of four posts
which have racks attached to their faces, and which are fixed to the
under frame and securely braced to resist racking strains. A worm
gearing, actuated by a wheel on the upper side of the scaffold, causes
the scaffold to ascend or descend. A railgrip, made to act at the curves
as well as on the straight portions of the rail by being attached to a
radial arm fixed to the under frame, assists the stability of the
scaffold where required, but the gauge of the rails is altered to render
the scaffold more or less stable according to its height. Combined with
the same machine, and traveling up and down one of the same posts used
for the scaffold, is an improved crane. Its action depends upon the
proposition in geometry that if the length of the base of a triangle be
altered, its angles, and therefore its altitude, are altered. A portion
of the vertical post up and down which the crane climbs forms the base
of a triangle, and a portion of the jib, together with the stay, forms
the remaining two sides. Hence, by causing the foot of one or the other
to travel upward, by means of the worm gearing, the upper end of the jib
is either elevated or depressed.
The concrete elevator, which is also combined with the scaffold,
consists of a series of buckets carried upon two parallel endless chains
passing over two pairs of wheels. On the under frame is fixed a hopper,
into which is thrown, either by hand or from a concrete mixer running
upon the rails, the material to be hoisted, and from which it gravitates
into a narrow channel, through which pass the buckets (attached to the
chain) with a shovel-like action. The buckets, a motor being applied to
one pair of wheels, thus automatically fill themselves, and on arriving
at top are made to tip their contents, and jar themselves, automatically
into a hopper by means of a small pinion, keyed to the shaft by which
they are attached to the endless chain, becoming engaged in a small rack
fixed for that purpose. From the upper hopper the material is taken away
to the required destination by means of a worm working in a tube. For
varying heights, extra lengths of chain and buckets are inserted and
secured by a bolt passed through each end link, and secured by a nut. By
using this scaffold, a saving in plant, cartage, and labor is effected.
The elevator may also be used for raising any other material besides
concrete.
Such is the new system of concrete construction and scaffolding of
Messrs. West, which appears to be based on sound and reasonable
principles, and to have been thoughtfully and carefully worked out, and
which moreover gives promise of success in the future. We may add in
conclusion that specimens of the work and a model of a scaffold
are shown by Messrs. West at their stand in the Inventions
Exhibition.--_Iron_.
* * * * *
[Illustration: ALBANY BUILDINGS SOUTHPORT. E.W. JOHNSON, ARCHITECT.]
* * * * *