GB2218453A - Fabricating structures - Google Patents

Abstract

A method for the construction of civil engineering structures in which a membrane 32, for example of flexible material, is supported by water, air or similar pressure P or by other supporting structure and a ferrocement laminate is constructed on the membrane, by successive application of material. After the laminate structure has been built up to sufficient strength, the pressure P may be removed, together with the membrane so that the structure is self-supporting for subsequent layers. The illustrated laminate comprises an unreinforced gel layer 2, followed by five reinforced layers 3 to 6 and 33, and a final top coat layer 7. The reinforced layers may be fabricated by applying a layer of mortar and, while still wet, pushing reinforcement such as expanded metal, into the mortar. A web of reinforcement wires or rods may be provided before the ferrocement is applied. In embodiments, a sequential casing arrangement is described. When the membrane 32 is floated on water, floating docks, pontoons, barges, or caissans may be constructed. <IMAGE>

Description

"METHOD AND SYSTEM FOR CONSTRUCTION" This invention relates to a method and system for the construction of civil engineering and similar structures such as buildings, bridges, dome structures, pipes, channels, tanks and similar forms.

The invention utilises the ferrocement laminating process in which a plurality of relatively thin layers of reinforced concrete material are used to fabricate the required structure. The process is described in relation to the fabrication of marine structures in British Patent No. 1347587. In the method described in this patent, a first or gel coat of cementitious material is applied to a rigid mould and is allowed to harden. The subsequent layer or layers have reinforcing material pressed into them while they are still in the plastic state.

The present invention is directed to a new method of building structures, particularly civil engineering structures such as large spans of a bridge or large domes with the minimum use of mechanical cranes, rigid support systems and labour.

According to a first aspect, the method of the invention involves initially erecting a light membrane structure having the general form of the structure to be fabricated and thence sequentially laminating onto said membrane a plurality of layers of concrete or other laminatable material, no layer being added until the previous layers are strong enough te hold them. In this way, by starting off with a very light structure, an immensely strong structure can be built up gradually - laminating continues until the required thickness and reinforcing materials are embodied in the structure, and in order to satisfy the. design criteria and also make the structure self-supporting.

The membrane may initially be supported by air, gas, water or other fluid, or may simply be supported by its own strength in tension. The membrane may alternatively be supported by mechanical means such as a web of cables or bars over which the membrane is stretched or which, in a preferred embodiment, carry a moveable shutter which itself carries the membrane.

In all cases the membrane is relatively light and would be easily distorted or otherwise damaged by a great weight of material on top of them. Therefore the method of the invention involves applying thin and light weight layers of fluid base materials, e.g.

mortar, concrete, plastic and plastic foams or similar materials of a type which harden with age and/or temperature, and which by their nature become firm, rigid and able to support their own weight with assistance from the support membrane. The base materials and reinforcing materials are laminated in layers which will support their own weight and yet be light enough not to distort the required form, as defined by the membrane. The resulting material, when hardened and cured to a sufficient state, will then be able to support an even greater weight of similar laminated materials and the process repeated sequentially until the required strength, weight, dimensions and content of reinforcement in any crosssection has been achieved to satisfy any given design.

The base materials are normally supplied to the membrane by a spraying process or a splattering process or by an even spreading and compacting in thin layers.

In some instances the base material may be brush painted onto a textile membrane to stiffen that membrane.

The base materials may incorporate reinforcing fibres of metal, plastic or organic means.

The base material may consist of mortar, concrete, plaster, plastic polymers, plastic foams or similar materials and is supplied to the membrane in a fluid or plastic state.

The base materials may be modified with additives which alter the basic properties of the materials i.e. quick setting and chemical resistant mortars/cements, various polymers and/or lubricating or plastisizing agents as required by design. Size and type of aggregates in mortar and concrete may be modified by design.

The base material may be further reinforced by applying strips or sheets of flexible pervious materials of steel or plastic meshes of welded or woven form, of expanded metals or expanded plastics meshes or combinations of both. The reinforcing materials may include course and open weave textiles of any type and may include steel reinforcing bars, plates and strip materials, as required.

The process requires the application in sequence of base material and reinforcing materials one upon the other to form a laminate.

The materials may be applied by manual or mechanical means. The rate of application of both materials, base and reinforcing, being always compatible with the stiffness and pressure on the underside of the support membrane and the ability of that membrane to support material without distortion from the designed parameters.

The process requires that the reinforcing materials be laid upon and embedded into the base materials in such a manner that the base materials are forced to pass through the perforation or interstices of the reinforcing materials, thus ensuring the complete penetration of the base materials around the reinforcing materials and vice versa.

Preferably any excess material is removed fr-om the top of the reinforcing material to prevent unnecessary weight. The process of embedding reinforcing materials into the base material can be aided by the use of a roller and trowel of suitable design. The process may also be mechanised. The membrane may or may not be removed after casting, as required by design.

The membrane may be used to support insulating material, for example, polystyrene sheet, foamed glass, polyurethane foam etc., onto which the laminate materials may be applied. These insulating materials may thus be encapsulated within the section of the structure as required by the design.

The dimensions of the support membrane may be determined by means of guy wires, diametral or circumferential wires, levels and guides as is normal practice in civil engineering.

By membrane casting on water a flat and level base may be constructed on which may be added the constituent part of a much larger structure.

By membrane casting onto an air supported structure 2 containment dome of any size may be constructed. A system of casting in opposed segments of the required dome, in a sequential pattern, would allow the construction of very large domes, as will be explained hereinafter.

Stiffness of structure can be achieved by inducing corrugation or box section or curved surfaces into the membrane surface by applying precast lightweight sections, or by restraint wires/cables which shape the surface of the membrane.

The membrane onto which the process is carried out, may be formed from any suitable sheet materials which may be joined by stitching, glueing or welding or taping together to form air or watertight membranes.

Examples are polythene or vinyl sheet materials, canvas or plastic canvas materials or other textiles.

By casting the laminated materials on and around the suspension cables or restraint cables of a membrane structure, these cables may be thus encapsulated in the structure.

The process of laminating layer upon layer of mortar and steel meshes produces ferrocement. This technique allows for a high proportion of reinforcement to be concentrated within a small cross-section and the ferrocement laminate produced has a very high strength to weight ratio when compared with conventional concrete practice. The use of this laminated material in conjunction with the membrane system allows the building of very large unsupported spans and structures.

The laminating process allows for the design of a cross-section with different materials within that section. The properties of the base materials may be varied within any cross-section.

In most cases the laminate thickness would be between 2 and 2" and would be built up in approximately 211 increments. Once a laminate of say 12 1l to 2" is constructed a further substantial load may be applied and in this case one has created a further support - a concrete formwork to support mass concrete.

A laminate of approximately q" may be sufficient in most cases to support the weight of operatives to allow the ongoing lamination process on a structure. These dimensions are given for example only and would in practice be determined by design relative to the whole structure.

A second aspect of the invention provides a web-like structure of self-supporting steel rods or cables around which the concrete or other laminatable material is cast, using the sequential laminating technique described above. High tensile steel cables and rods are commonly used in civil engineering and advantage is taken of their ability to retain a high degree of elastic memory. Alternatively, standard steel reinforcement bars could be used.

Initially, the cables are formed both vertically and horizontally into a "web", which when erected is self-supporting. Then the voids of the web are filled by spraying and laminating perforated material into the membrane which is attached relative to the web and preferably spaced therefrom.

In an embodiment of the invention a very light weight travelling shutter is suspended from the web cables and carries with it the membrane onto which the process of laminating is carried out, thus filling the web void areas. The structure is built up in sections, moving the shutter between sections to gradually build up the structure. Each section is laminated with a sufficient number of layers to be strong enough to support subsequently- fabricated sections.

Stiffening webs or plates may be provided at right angles to the plane of structure. These allow the construction of several skins of structure, which can be sub-divided as required by the design. The subdivisions may be regarded as permanent shuttering and can be filled at any stage with concrete or other materials as required.

Into the laminate cross-section may be embedded any type of pervious materials to form reinforcement of the structure. The base materials of the laminate may be varied in density, chemical resistance, and may be modified with polymers or special cements, as requireg Tubes, channels and void formers of whatever type may be set into the laminate during the course of construction. Insulating and other sheet materials may be incorporated into the laminate. Any additional reinforcement materials of rod, or strip or perforated plate may be embedded into the laminate during the construction, as required. If required, texture and or colour may be added to the structure under construction as is known in the construction and engineering field.

The methods described above may be used for tug construction of large domes with several skins of laminate material and sub-divided to give the required stiffness. The sub-divisions may be regarded as permanent shuttering for the containment of more materials. The same methods may be adapted to the construction of bridges and similar constructions and forms.

We will now consider our novel ferrocement laminate manufacturing process, as used in the present invention.

It is known in civil engineering practice that concrete and mortar materials may be applied by a spraying process called either the "gunite" or "shotcrete" method. There are certain disadvantages in the presently used system which can be obviated by th laminating process. In the presently used methods the reinforcements are placed and fixed into position prior to the application of the concrete or mortar. The desire to include the maximum amount of steel wire or rod reinforcement in a given cross-section often produces a barrier to the penetration of the materials into the section with a resulting loss of quality. The spraying application often produces a quantity of what is termed "rebound material" which is wasteful in many ways and produces a detrimental environment.The gunite and shotcrete methods usually relate to crosssections in excess of two inches, whereas ferrocement usually relates to sections of less than two inches.

The ratio of steel content to concrete content is low in gunite and shotcrete systems. The steel to mortar ratio of ferrocement is high by comparison and is even higher in a ferrocement laminate cross-section.

The high strength to weight ratio of ferrocement laminated material and thin cross section permits the material to be used to advantage in the manufacture of products and panels, or for the construction of permanent formworks as are understood in the civil engineering field. The accepted practice for the manufacture of ferrocement is to apply by hand plastering the mortar into a armature or cage of reinforcement which is already fixed in the required position.

In my advantageous process ferrocement is produced by a process of laminating layers of reinforcement one upon the other into a fluid or plastic mortar and embedding the same reinforcement completely into the mortar. By this process the reinforcements are placed as close as possible within the mortar and the matrix produced is completely free of voids and thus a monolithic material is produced.

It is first required to prepare a suitable surface on which the process may be carried out or applied. In the case of product manufacture this would be the preparation of a mould, involving its cleaning, setting, oiling with release agent, positioning of guides and stops, all as is normal practice in the glass reinforced plastic, glass reinforced cement and the concrete casting trade. In the case of applying the process to renovate or strengthen an existing structure, the surface to which the ferrocement laminate is to be applied must be cleaned and prepared to receive the material This can be done by pressure washing or sand/grit blasting in order to provide a clean and "keyed" surface as is normal practice in the trade.

An initial "gel" coating is applied to the mould or onto said membrane. As mentioned above, this may be carried out by a process of spraying, splattering, or by other means of spreading or applying a thin layer of material. It is preferable to allow this first layer to harden a little or to apply small and suitable spacing pieces prior to the application of the subsequent layers of base materials and reinforcements. A further layer of base material is now applied and a first layer of reinforcing material is incorporated. The reinforcement is applied to and embedded into the fluid or plastic base materials or mortar. A light pressure may be impressed upon the reinforcement material to ease the reinforcement into the base material.

Hand tools of special design may be used to assist the manual method of carrying out the process.

Such a tool may for example consist of a suitable roller system mounted upon a short cr long handle as required. The roller may have several wheels mounted in a shaft and the diameter of the wheels may be variable. The bearing or "tread" of the wheels will be kept to a minimum, consistent with the stiffness required to keep the wheel rigid. The wheels may for example range from approximately 4" to 18" in diameter and in tread thickness from 1/8th" to 4". The wheels may be made of any suitable materials including steel and plastic.

A further form of tool is a trowel, similar to a plastering trowel, but with protrusions at right angles to the surface of the trowel. The depth, length and width, and spacing of these protrusions being variable to suit the particular applications.

For example, they may be of about 1/8th" thick, about 2" long and spaced about 2" apart.

The roller is used to assist the embedding of reinforcement into the base materials and the trowel is used to guage the depth of base materials.

The process requires the sequential repartition of the application of matrix or base materials and reinforcements one upon the other until the required depth of cross-section and number of layers of reinforcements of whatever type have been applied to satisfy any given design requirements.

This process is particularly suited to the manufacture/application of ferrocement laminate but not exclusively. The process may be applied to the manufacture and application of similar materials by the laminating technique.

The base or matrix material may be mortar, concrete, plastic or plastic foam materials or similar, or a type which may be applied in a fluid or plastic state and which harden with age and/or temperature. In the case of mortar or concrete, these may be modified by the application of additives and/or special cements to enhance their properties. The mixing of these materials is variable by design. The manufactured products may be cured by the application of heat, of steam and of water as required by design of the material.

The reinforcement materials may consist of any pervious materials of steel or plastic meshes of welded, woven or expanded form. They may also consist of expanded metals and expanded plastic meshes in sheet or strip form. The reinforcement materials may also comprise various types of textiles of an open weave form. The mortar base or matrix materials may contain fibres of steel, plastic or organic means.

The laminate material may be further enhanced and strengthened by the embedding of further reinforcement materials being steel or plastic rod or strip materials. These materials being embedded into the first placed matrix materials as previously explained.

The size and placing/orientation of these reinforcements may be determined by design.

The matrix or base materials may be varied throughout any cross-section by design i.e. a chemical resistant matrix may be applied to the "gel" or outer layer of the laminate and a less expensive, or material of a different density may be applied in the subsequent laminate.

A further feature of this process is the ability to apply and include in the total crcss-section other materials including void formers and insulation materials in block or sheet or aggregate form. These may include plastic void formers, polystyrene blocks or sheets, and/or similar materials or urethane foams, glass foam or cork or other suitable materials.

The mechanical, structural, and insulation values can be varied as required by design. The dimensions of plan and cross-section of any element or laminate may be determined by design.

The process may be mechanised for use in mass production of products by this process. The mechanisation of the process may also be applied to the manufacture of and the repair of structures.

In order that the invention may be better understood, several embodiments thereof will now be described by way of example only and with reference to the accompanying drawings in which: Figure 1 is a cross-section of a typical ferrocement laminate construction; Figures 2 and 3 are views similar to Figure 1, showing alternative constructions; Figure 4 is a perspective view of the panel of Figure 3; Figure 5 is a side view of a representative dome structure to which a ferrocement laminate has been applied for strengthening; Figures 6A and B are horizontal and vertical cross-sections respectively of a building panel made by ferrocement laminating techniques; Figure 7 is a perspective view of a hand roller for use in the laminating process; Figures 8 and 9 are end and side views respectively of a further hand tool for use in the laminating process;; Figure 10 is a cross-section cf a typical laminate applied to a membrane; Figure 11 is a diagrammatic side view of a typical membrane casting over water; Figure 12 is a sectional view of an inflated dome membrane for supporting a ferrocement laminate structure; Figure 13 is a perspective view of a cable reinforced inflated membrane for supporting a ferrocement laminate structure; Figure 14 is a sectional view of the side of the cable reinforced membrane of Figure 13; Figures 15, 16 and 17 each show a sectional view cf a valley over which a bridge is to be built, and illustrate the sequence of construction; Figures 18 and 19 are plan views of the valley of Figure 15 to 17, showing different stages of construction of the bridge; Figures 20 and 21 are plan and side views of a shutter assembly suitable for casting the bridge;; Figure 22 is a section 22-22 of Figure 20; Figure 23 is an enlarged view of part of Figure 22; Figures 24 and 25 are plan and side views respectively of a cable arrangement for supporting a dome shape web structure; and Figure 26 is a side view of the erected web of the dome structure of Figures 24 and 25.

Figures 1 to 3 show sections through typical sections of ferrocement laminate. Referring firstly to Figure 1, there is shown a mould surface 1 on which is initially cast a gel or first coat 2 of matrix material. On top of this are cast four reinforced coats 3 to 6 followed by a top or covering coat 7. Each of the reinforced coats comprises a base coat of mortar or concrete into which is embedded a reinforcement, for example of expanded metal or similar. The method of building up the layers is described fully above. A typical total thickness would be ".

In Figure 2, the laminate comprises two layers 8,9 and 10,11 on each side of a system of circular voids 12. The voids are surrounded by an unreinforced material 13 such as mortar, concrete or an insulation material.

Figures 3 and 4 show two views of a thermally insulating ferrocement laminate panel. The insulation is provided by insulation blocks 14, for example of polystyrene. On each side of the insulation layers are two reinforced layers 8,9 and 10,11 incorporating mesh reinforcement. Spaces 19 are incorporated in order to assist in the positioning of the blocks during assembly and additional steel bar reinforcement 15 is provided.

Figure 5 shows a bridge, tunnel or sewer structure 20 made for example of brick, which has been reinforced by a supporting ferrocement laminate 21.

This provides strength, and also renovates the internal surface.

Figures 6A and B show two views of a building or similar structural panel to which has been applied a square pattern laminate of reinforcement 22 and foam block insulation materials 23 in an overlapping pattern. Outer layers 24,25, which may or may not be reinforced, complete the assembly.

Figure 7 shows a roller hand tool comprising a handle 26 holding six wheels 27 mounted on a common shaft 28 to which the handle is attached at a central point. The usage of the tool is described above.

A further tool for use in the lamintating process is illustrated in Figures 8 and 9. The tool is basically similar to a steel plasterer's trowel, comprising a steel plate 29 on which is mounted a handle 30. On the undersurface of the plate 29 are formed a plurality of narrow protrusions 31 spaced at regular intervals along the undersurface. When the underside of the plate 29 is wiped across the surface of wet base material, the protrusions ensure that the reinforcing layer is situated a minimum distance, approximately equal to the depth of protrusions, below the surface.

Figure 10 is a view similar to Figure 1, but in which the laminate is built up on the surface of a flexible membrane 32 which is supported by air, water or similar pressure, represented by the arrows P. Five reinforced layers are shown: 3 to 6, as in Figure 1, and 30. The membrane 32 may alternatively be supported by mechanical means, not shown, such as plastic or metal mesh or similar, or may even be supported under its own tension, provided it is strong enough.

Figure 11 shows a laminate of the type illustrated in Figure 10, applied over water 16. The membrane 32 is suspended between a pontoon 34 and a quay 35. A bridge 36 provides a walkway over the work area from which the operatives 37 can apply materials to the membrane in the manner described above. The dotted line 38 shows the position of the membrane prior to the introduction of material. As the membrane is forced down under the weight of applied material the membrane 32 sinks lower and becomes supported by the water.

Figure 12 shows an inflated dome 39 onto which a ferrocement laminate (not shown) may be cast. For a large structure, the dome may be covered in sections, for example as shown at 40,41, etc., of a size which can conveniently be handled during a working period.

Figures 13 and 14 are views of a structure comprising an inflated membrane 32 reinforced by exterior restraint cables 42. Laminate is applied over the exterior surface in the manner described above and eventually embeds the cable 42. The dotted line 43 in Figure 14 represents an exemplary outer surface of a finished laminate layer. In the structure cf Figures 13 and 14, work can proceed in sections as described above. However, with all such shapes, it is advantageous to commence work simultaneously on two sections: one on each side of the structure so that distortion of the structure caused by weight on one side only will be reduced. If only one section can be done at a time, then the work should proceed alternately on opposite sides to reduce distortion.

There will now be described the building up of a ferrocement laminate structure, in sections, using a shutter assembly which carries the membranes on which the laminate is cast. The structure to be described is a bridge, to be built across a valley. A section of the- valley, complete with river 44, is illustrated in Figures 15 and 18. The bridge is to be built between points A and B.

Building commences by stretching a pair of spaced ropes or wires 45 across the valley from point A to point B. A frame 46 is suspended on the ropes 45 from slip rings 47 so as to be moveable backwards and forwards along the ropes. This frame is used in the next stage of construction in which a plurality of cable or bars 48, for example of steel, are erected over the valley in such a way that they are attached and supported at their ends in foundations C and D.

The frame 46 acts as a jig to hold the bars 48 in position as they are lowered and secured into the foundations. The frame 46 can also be left in place during the construction in order to hold the bars in position until construction has advanced far enough for the structure to have gained its own stability.

Sideways movement of the cables may also be prevented by means of guy ropes 49,50 taken to ground anchorages at E,E1, and F,F1. Additional restraints may be necessary, depending upon the size of the structure and local conditions.

The number of bars 48 depends upon the circumstances and, in particular the required width of the bridge. In the present example, there is described a bridge with 8 bars, spaced at 1 foot centres.

Typically the bar is 25-40mm in diameter.

The start of construction proper is illustrated in Figures 16 and 19. It will be seen that the arch formed by the bars 48 has been divided into sections numbered from the foundation points C,D towards the middle. Each section is intended to represent a work period, for example, a day. Thus, on day 1, the two sections numbered 1 on each side are constructed, then the two sections 2 are constructed, and so on. This method of construction relieves distorting loads on the bars. Figure 16 shows sections 1 and 2 already constructed and section 3 about to start. Construction is carried out by a pair of travelling shutters 51.

Each shutter comprises a first part 52 which is slidably mounted on the bars 48 and a second part 53 in the form of a support membrane which is attached at one end to the first part 52 and extends under the bars 48 for the full length of the section to be constructed.

The membrane 53 defines a well into which concrete can be cast. The use and construction of the shutter will be described in more detail below.

When all five sections have been completed on each side, the arch is then built up in layers to the designed thickness and then webs or columns 54 built upwards from the arch to support the roadway 55 (see Figure 17). The exact construction will be dictated by the requirements of the design.

In an alternative method of construction (not shown) work proceeds in stages, as before, but from the centre of the arch simultaneously towards each of the foundations C,D. This method may be preferable in some circumstances.

The use and construction of each of the shutters 51 is shown in more detail in Figures 20 and 21. Part 52 comprises a platform 56 on which personnel may stand during construction. The platform is supported by members 57 which are themselves slidably supported on the bars 48. Supported on the members 57 beneath the bars 48, and spaced therefrom, typically by 1" to 4", is an arcuate platform 58 of the same radius of curvature as that of the bars 48. The platform extends beyond the platform 58 to form the aforesaid membrane 53 and defines, with the existing structure 17, a mould 59 into which concrete can be cast to create the next section. The edge of the existing structure 17 is chamfered to improve the support of the newly-cast section.

Figure 22 is a section through a completed section 17 and shows the bars 48 completely enclosed by upper and lower laminated layers 60,61. As shown in the more detailed view of Figure 23, each layer 60,61 itself comprises a plurality of laminated layers of reinforced ferrocement, made up in the manner described above. The central part of the section - between bars 48 - may be filled with filler such as concrete, mortar, or polystyrene foam, and/or may be provided with lateral stiffening, as required by the specification. Typically, the total thickness will be 4", with each of the laminated layers taking up 1", made up of four ," layers, and the central section 2".

Figures 24 to 26 illustrate stages in the construction of a dome shaped structure using the shutter technique described above. Six cables 62 are arranged radially from a central base member 63. The cables are affixed to a swivel connection at the boss to allow the cable strand to rotate. Positioned at equally radially spaced intervals about the boss and spaced therefrom are winching or jacking points 64 through each of which one of said cables 62 passes. A plurality of horizontal cables 65 complete a web structure which is used to support a shutter or shutters (not shown). The horizontal cables extend circumferentially, with the boss member 63 at their centre. Joints are provided at each intersection between radial cables 62 and circumferential cables 65.

Those joints must be such as to allow the radial cables freedom to rotate. The circumferential cables may be held in position by other lighter cables (not shown) until the web of cables is in the required position.

In order to erect the web, the boss member 63 is first lifted above the level of the jacking points 64. The jacking points 64 are then operated to push the radial cables 62 towards the centre, thus raising the boss member 63 - see Figure 25. The jacking points 64 should be such as to operate at the same rate to force the dome-shaped web upwards.

Figure 26 shows the fully erected frame. Many more cables could be used both radially and circumferentially, as dictated by the circumstances.

The spaces between the cables are filled by the process of laminating either onto a membrane covering the web, or onto a membrane incorporated into a shutter. In either case, work should proceed in sections at opposite sides, as explained above.

By means of the above described techniques, a rigid structure may be built, onto an air or water supported membrane.

By these methods a floating structure may be constructed on water, without the slipways or dry docks or floating docks usually required. The methods may be used to construct floating docks, pontoons, barges, caissons and similar structures of any size.

By these methods a self-supporting structure may be constructed without the use of rigid mechanical support systems.

The methods may be used to build large spatial structures, domes, bridges, culverts, hyperbolic paraboloids, double curved shells and barrel vault roofs etc.

Claims (19)

1. A method of construction comprising initially erecting a light membrane structure having the general form of a structure to be fabricated and thence sequentially laminating onto said membrane a plurality of layers of concrete or other laminatable material, the layers being added as the strength of the existing structure permits.

2. A method as claimed in Claim 1 wherein the membrane is made of flexible material and is supported by fluid pressure to the desired shape.

3. A method as claimed in Claim 1 wherein a web of rods or wires is assembled, and the membrane is supported by said web.

4. A method as claimed in Claim 3 wherein the membrane is draped over the web and is supported thereon by gravity.

5. A method as claimed in Claim 3 wherein the membrane is supported against said web by fluid pressure.

6. A method as claimed in Claim 3 wherein the membrane is attached to a moveable shutter which shutter is moved about the web to enable the structure to be fabricated in sections.

7. A method as claimed in any one of Claims 3 to 6 wherein the concrete or other laminatable material is applied in such a way as to completely embed the web of rods or wires within the finished structure.

8. A method as claimed in any one of the preceding claims wherein the laminating is carried out in sections to cover the whole required area of the membrane.

9. A method as claimed in Claim 8 wherein work proceeds on two sections simultaneously, said two sections being positioned on corresponding opposite sides of the structure, such that imbalance does not distort the overall shape of the membrane as construction proceeds.

10. A shutter for carrying out the method of Claim 6, said shutter comprising a first section which is moveably mounted on said web and a second section extending under the web to define said membrane on which a laminate can be built up to embed the web.

11. A shutter as claimed in Claim 10 wherein said first section includes a work platform positioned to enable personnel to carry out the laminating onto the membrane.

12. A laminate material for use in the method as claimed in any one of Claims 1 to 9, said material comprising a plurality of layers of reinforced material, each layer comprising a base material which is initially of a fluid nature and which is capable of becoming hardened by time and/or temperature and into which is pressed, while the base material is still fluid, a reinforcing material.

13. A laminate as claimed in Claim 12 including an additional unreinforced gel coat adjacent the membrane.

14. A laminate as claimed in either one of Claims 12 or 13 wherein said base material is centitious material.

15. A method of construction comprising erecting a web of rods or bars to a shape having the general form of a structure to be fabricated, mountin on said web so as to be supported thereby, a membrane, and thence sequentially laminating onto said membrane a plurality of layers of concrete or other laminatable material.

16. A method as claimed in Claim 15 wherein the laminated layers are such as to completely embed the web in the finished structure.

17. A method as claimed in either one of Claims 16 or 17 wherein said membrane has an area which is small in relation to the total area to be laminated, and wherein the laminating is carried out in sections.

18. A method as claimed in Claim 17 wherein the membrane is attached to a shutter assembly which is mounted on said web in such a way as to be moveable from section to section as construction proceeds.

19. A method as claimed in Claim 18 wherein said shutter comprises a first section which is moveably mounted on said web and a second section extending under the web to define said membrane.