FIG. 21. FIG 25.

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.