Note: Descriptions are shown in the official language in which they were submitted.
10;~679~
1 This invention relates to a method of manufacturing
pre-cast concrete building slabs or panels, and relates partic-
ularly though not exclusively to a method of manufacturing pre-
cast concrete building panels for use as wall cladding.
There are a number of pre-cast concrete building slabs
and panels commercially available at the present time, and these
known slabs and panels come in a variety of sizes and designs.
For example, it is known to provide a building slab or panel with
cavities in order to reduce the overall weight of the panel, and
to improve its insulation properties. However, in providing such
cavities there is a tendency for the panel or slab to lose some
of its rigidity and strength, and if it is a smaller panel of a
nature which can be carried manually and readily, then the panel
thickness must be maintained at a minimum thickness, but with
wire reinforcement if the panel is to have sufficient strength.
Therefore, on the one hand, it is desirable to reduce
the thickness of the slab or panel to the minimum in order to
save costs, but this reduction in thickness has the effect of
reducing the strength, and on the other hand, therefore, care
must be taken to ensure that the panel strength is not so im-
paired as to make the slab or panel unusuable.
It is known to include wire reinforcement in a panel
to improve the strength, but this has the disadvantage of in-
creasing the thickness of the panel to provide the necessary
cover to the steel therefore increasing the weight of the panel
and increasing its cost.
One solution which I have already proposed to overcome
the problem is to reinforce the rear of a thin concrete skin
with hardboard or the like sheet material, and this solution has
given improved results. The present invention provides a method
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10367g7
1 for the manufacture of such panels so that the results are
improved even further, and the panels produced thereby are of
even and higher strength, without the weight being increased.
In accordance with the method and the present invention,
a pre-cast concrete panel is manufactured in the following steps:
a) a reinforcing sheet of hardboard or the like is soaked
in water;
b) it is supported substantially horizontally in a mould;
c) the hardboard or the like is covered with a thin skin
of concrete whilst the hardboard or the like is still wet;
d) a cavity in the mould extending peripherally of the
hardboard or the like is filled with concrete, before or after
applying the concrete skin to the hardboard so that hardboard
edge regions become embedded in the concrete; and
e) the concrete and hardboard or the like are caused or
allowed to dry sufficiently to enable the panel to be removed
from the mould.
It has been found, using this method, that the hardboard
is firmly anchored to the skin of concrete when dry and gives
the panel, in the region of the concrete and hardboard, consider-
able strength, sufficient that, for normal wall cladding uses,
no reinforcement is required in the concrete skin.
Furthermore, the section of the panel defined by the
hardboard and concrete skin has surprising ductility and behaves
more like a ductile metal than a concrete laminate. This effect
is achieved due to the fact that the hardboard shrinks as it
dries out, and during initial shrinkage of the hardboard, the
concrete, being still wet and having virtually no inherent
strength, moves with the hardboard. After an initial period,
however, the concrete sets sufficiently to resist the continuing
~0;~67g7
1 hardboard shrin~age, and the hardboard becomes tensioned, and
the concrete compressed, and hence pre-stressed. Thus, when the
panel is loaded on the concrete skin, and the skin and hardboard
deflect, the effect is not to tension one side of the skin as
might be expected but only to release the pre-stressing, and the
skin remains in compression; it is well known that concrete is
very strong in compression and hence thQ reason why the panel has
more strength than would be expected.
It may be desirable to locate wire or rod reinforcement
in the cavity which is filled with concrete to reinforce the
concrete placed therein, which forms a peripheral rib to the
finished panel.
In a preferred case, the skin is faced by tamping
aggregate thereinto whilst it is still wet.
The aggregate also adds to the strength of the panel,
and contributes to the fact that the skin can be made of a
minimum thickness whilst maintaining a high strength also
contributing to the fact that it is not necessary for the skin
to have any wire reinforcement therein. Indeed, in some examples
the skin will be so thin that it would not be possible to insert
any wire reinforcement.
Preferably, the rib will have bolt holes to enable
securing bolts to be passed therethrough for the fixing of the
slab or panel either to an adjacent slab or panel or to a struc-
tural beam or the like. Wooden or other fixing fillets may be let
into the rib during casting to provide suitable nailing or
screwing surfaces for example for an interior lining to be
secured to the rib so as to overlie the hardboard or the like sheet.
Also, according to the invention, there is provided a
pre-cast panel formed in accordance with the method as aforesaid.
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103679q
1 An embodiment of the invention will now be described,
by way of example, with reference to the accompanying drawings,
wherein:
Fig. 1 is an elevation of a slab or panel constructed
in accordance with the invention;
Fig. 2 is a fragmentary sectional view of a slab or
panel constructed in accordance with the invention, showing the
panel in its mould,
Fig. 3 is a fragmentary sectional side view showing
how two similar panels each formed in accordance with the method
of the invention may be constructed simultaneously; and
Fig. 4 is a pian view of the arrangement shown in Fig~
3.
Referring to the drawings, and in particular to Figure
2, the slab or panel comprises a pre-cast concrete skin which
defines a major face of the panel, and on its inner face the skin
is reinforced by means of a sheet of hardboard or the like
material 1. The slab or panel illustrated may be approximately
8' x 3'4" x 3" so as to be capable of being carried by one man
or certainly by two men. The slab or panel has a peripheral rib
2 which is of approximately 2" square section. The thickness of
the concrete skin 3 which is reinforced b~ the hardboard or like
panel 1 may be in the region of 3/4". This is a very thin skin,
and because of the thinness of the skin there is no steel rein-
forcement therein. The reinforcement is provided by the hard-
board or the like sheet 1, and aggregate which is tamped into
the outer surface of the skin 3 in performing the method of the
invention which will be explained hereinafter.
In order to manufacture the panel shown in Figure 1,
a mould is constructed. This has a base plate Ml, side pieces
1036797
1 M2 and a recess former M3. The former M3 is smaller than the
internal dimensions of side pieces M2 so that a peripheral
cavity C is formed in the mould. Circular rods R are pushed
through aligned holes in the former M3 and side pieces M2 to de-
fined bolt holes 7 in the finished panel as shown in Figure 3.
Metal wire rod or bar 6 reinforcement is located in the
cavity C as shown and the hardboard 1, after being thoroughly
soaked in water is placed on former M3 as shown. Concrete is
vibrated into the cavity ~ to fill sa~e and next the concrete is
skimmed over the hardboard 1, whilst it is still wet, to form
the concrete skin 3. The concrete skin may be laid on the hard-
board before cavity C is filled with concrete, if desired. Whilst
the concrete of the skin is still wet, further surface treatment
is carried out by laying the desired type of aggregate 4, by
machine or by hand as desired, and in the desired layout, and
subsequently tamping in the aggregate with a broad timber or the
like, to the depth and distribution required. The aggregate, in
addition to contributing to the strength, presents an attractive
surface finish. As the hardboard and concrete dry out, so the
~ hardboard binds to the concrete skin 3 and pre-stresses the same
as explained hereinbefore.
In efect, it will be seen that the slab or panel is
hollowed to the rear or has a rear recess 5 as shown in Fig. 3.
This makes the panel light in weight, and its strength is main-
tained as explained herein by the provision of the hardboard or
the like sheet 1.
The peripheral rib 2 is reinforced by means of the
metal wire or rod 6 and is also provided with the bolt holes or
slots 7 to enable securing bolts to be passed therethrough. In
addition, the peripheral rib may be provided with wooden or
103679 7
1 other fixing fillets during the casting of same for the attachment
of additional components or sheets to the rib as desired.
In Figures 3 and 4, two panels or slabs each as
described in the above, are shown joined together by a peripheral
concrete joint 8 provided with air gaps 9, the entity forming a
hollow block which may be used for partition building or wall
building. Heavier reinforcement may be incorporated in the rib
to make the units more load bearing and the inner suxace of the
recess 5 of each panel or slab may have a coating of plaster
applied thereto.
In soaking the hardboard with water, it may be desirable
to introduce additives with the water in order to achieve
improved bonding between the hardboard and concrete skin.
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