IE46427B1 - Method of manufacturing pre-cast concrete panels - Google Patents

Description

This invention relates to a method of manufacturing precast concrete building slabs or panels, and relates particularly 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 ba 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 coats, but thia reduction in thaik nee a 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 impaired as to make the slab or panel unusable.

St is known to include wire reinforcement in a panel to improve the strength, but this has the disadvantage of increasing the thickness of the panel to provide the - 2 necessary cover to the steel, therefore increasing the weight of the panel and increasing its coat.

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 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 of tha present invention, a pre-cast concrete panel is manufactured by the following steps :a) a flat, reinforcing sheet of hardboard or other moisture absorbent fibrous material having a rigidity similar to that of hardboard soaked in water; b) the soaked reinforcing sheet is supported substantially horizontally in a mould; o) the upper surface of tha supported reinforcing sheet is covered with a skin of concrete in the plastic state whilst the reinforcing sheet is still wet; d) a cavity in the mould at the periphery of the reinforcing sheet is filled with concrete in the plastic state, before or after applying the concrete skin to the reinforcing sheet so that the concrete of the skin and in the cavity become integral an· d the reinforcing sheet edge regions are trapped between - 3 the concrete of the skin and the concrete in the cavity and e) the concrete and reinforcing sheet are caused or allood to dry sufficiently to enable the panel to be removed from the mould.

It has been found using hardboard in 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, considerable 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 i.n achieved due to the fact that fhe 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 hardboard shrinkage, 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 hot 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 the reason why the panel has more strength than would be expected. - 4 4 6 4 27 It may be desirable to locate wire or rod reinforcement in the cavity which is filled with concrete to reinforce tho 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 10 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 15 bolts to be passed therethrough for the fixing of the slab or panel either to an adjacent slab or panel or to a structural beam or the like. Wooden or other fixing fillet 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 Also, according to the invention, there is provided a precast panel formed in accordance with the method as aforesaid - 5 4 6 4 2 7 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 5 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 used together; and Fig. 4 is a pain view of the arrangement shown in Fig. 3.

Referring to the drawings, and in particular to Figure 2, the slab or panel comprises a concrete skin which defines a major face of the panel, and on its inner face the skin is reinforced by means of a moisture absorbent fibroua materiel, in this case a hardboard or the sheet 1, which is flat and rigid.

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 man. 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 by the hardboard 1 may be in the region of This is a very thin — δ — ί 6 4 2 7 skin, and because of the thinness of the skin there is no steel reinforcement; therein. The reinforcement is provided by the hardboard or the like sheet 1, and aggregate which is tamped into the outer surface of the skin 3 in preferred method of tha invention which will be explained hereinafter.

Xn order to manufacture the panel shown in Figure 1, a mould is constructed. This has a base plate Ml, side pieces 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 1θ formed in the mould. Circular rods R are pushed through aligned holes in the former M3 and side pieces M2 so that e. 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 define 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 se shown and the hardboard 1, after being thoroughly soaked in water is placed on former M3 as shown. Concrete in the plastic state is vibrated into the cavity C to fill same and next concrete on the- plastic state is skimmed over the hardboard 1, whilst it is still wet and in the plastic state, to form the concrete skin 3 so that the skin and concrete in cavity C become integral as shown, embedding only the edge regions of the hardboard 1 herein. The concrete skin may ba laid on the hardboard before cavity c is filled with concrete, if --74 6 4 27 desired, aihilst 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. Ihe aggregate, in addition to contributing to the strength, presents an attractive surface finis) 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 effect, it will be seen that tbe slab or panel is hollowed to fee rear or has a rear recess 5 as shown in Pig. 3. This sakes the panel light in weight, and its strength is maintained as explained herein by the provision of the hardboard sheet 1.

The peripheral rib 2 is reinforced by means of the metal wire os 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 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 desribed in the above, are shown joined together by a peripheral concrete 4642' joint 8 provided with air gaps 9, the entity forming a hollow blocs 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 surface c 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 introudce additives with the water in order to achieve improved bonding between the hardboard and concrete skin.

Claims (5)

1. Ά method of manufacturing a pre-cast concrete panel comprising the following steps :a) a flat reinforcing sheet of hardboard or other moisture 5 absorbent fibrous material having a rigidity similar to that of hardboard soaked in water? b) the soaked reinforcing sheet is supported substantially horizontally in a mould? c) the upper surface of the supported reinforcing sheet 10 is covered with a skin of concrete in the plastic state whilst the reinforcing sheet is still wet? d) a cavity in the mould at the periphery of the reinforcing sheet is filled with concrete in the plastic state before or after applying the concrete skin to the reinforcing sheet so 15 that the concrete of the skin and in the cavity become integral and the reinforcing sheet edge regions are trapped between concrete of the skin and the’poncreta in the cavity? and e) the concrete and reinforcing sheet are caused or allowed to dry sufficiently to enable the panel to be removed 20 from the mould,

2. Ά method according to Claim 1, including the additional step of tamping aggregate into the concrete skin whilst it is still wet so as to form an aggregate facing surface. - lo

3. .. method according to Claim 1 or 2, wherein metal reinforcing wire or rod is located in tee cavity before it is filled witn concrete.

4. A method of manufacturing a pre-cast building panel 5. Substantially as hereinbefore described.

5. A pre-cast building panel manufactured in accordance with the method of any of the preceding claims.