WO2017098482A1

WO2017098482A1 - Construction elements

Info

Publication number: WO2017098482A1
Application number: PCT/IB2016/057533
Authority: WO
Inventors: Michael Windsor Symons
Original assignee: Zetland Technologies Limited; Van Der Walt, Louis, Stephanus
Priority date: 2015-12-11
Filing date: 2016-12-12
Publication date: 2017-06-15

Abstract

The invention provides a construction element comprising an artefact obtained by pressing, cold or at ambient temperature, a non-sticky free-flowing granular cementitious or gypsum-based precursor composition, causing the granules of the precursor composition to cohere and form the artefact.

Description

CONSTRUCTION ELEMENTS

FIELD OF THE INVENTION

THIS INVENTION relates to construction elements. The invention provides a construction element. The invention also provides a fixed construction assembly. The invention further provides a method of erecting a fixed construction. The invention extends to precursor compositions for producing a construction element and to a method of producing a precursor for construction element. The invention also extends to a method of producing a construction element.

SUMMARY OF THE INVENTION

In this specification, "dry mass" means the mass of the concerned substance as measured on a dry basis for that substance. For example, an aqueous solution of polyvinyl alcohol that comprises 10% dry mass polyvinyl alcohol, comprises 10g of dry polyvinyl alcohol per 100g of solution.

IN ACCORDANCE WITH ONE ASPECT OF THE INVENTION IS PROVIDED a construction element comprising an artefact obtained by pressing, cold or at ambient temperature, a non-sticky free-flowing granular cementitious or gypsum-based precursor composition, causing the granules of the precursor composition to cohere and form the artefact. The artefact may be a planar board. The construction element may comprise a core element and two of the planar boards, the planar boards being adhered to the core element at locations opposite each other, thus providing a composite, layered construction element. In other words, the construction element typically comprises two outer boards, contiguous with a core element that space the boards from each other.

The construction element may have at least one recess in its periphery, which recess is bordered by the two planar boards and by the core element, in which recess a spline can be received to spline the construction element to another construction element.

The construction element may include a spline that projects from the periphery of the construction element and can be received by a complementally shaped recess of another construction element, to spline one construction element to the other construction element.

Two splines and two recesses are, preferably, provided by a rectangular core element which is off-set from peripheral edges of identically sized boards adhered to it. Thus are defined recesses where the core element is inwardly off-set and splines where it the core element is outwardly off-set.

Preferably, generally speaking, the construction element is layered, rectangular, and has grooves in two cornering edges thereof and splines in two other cornering edges thereof, thereby allowing for the construction element to be interlocked, as a construction assembly, with another such element, by interlocking one spline of one element with the recess of another element. Typically, one construction element can so interlock with four other such construction elements.

In one embodiment of the invention, in which the precursor composition is cementitious, the precursor composition may comprise

Portland cement;

a cement extender;

water;

one or a combination of guar gum and a fully hydrolysed polyvinyl alcohol; and a gelling agent that reacts with the guar gum and/or the polyvinyl alcohol, thus rendering the precursor composition into free-flowing non-sticky granular form.

Preparing the precursor composition may include blending the Portland cement, the extender, at least some of the water, the guar gum and/or fully hydrolysed polyvinyl alcohol and, optionally, the synthetic fibre, pulp fibre and/or lignocellulosic fibre referred to hereinafter. Thereafter, the gelling agent may be introduced.

An alternative approach is to blend the gelling agent with the guar and/or polyvinyl alcohol, and optionally also with the fibres mentioned below, and thereafter adding the Portland cement and the extender.

While not wishing to be bound by theory, the Applicant understands that reaction of the gelling agent with the guar and/or the polyvinyl alcohol gels or cross-links the guar and/or the polyvinyl alcohol, thus gelling the precursor composition and resulting in the precursor composition being rendered into the granular form. As mentioned above, pressing the precursor composition causes the granules thereof to coalesce, thereby forming a homogenous artefact. After pressing, the artefact may still be wet, and may therefore be subjected to drying in providing the construction element.

Before pressing the granules to cohere and form the artefact, the granules may be spread out on a surface in a desired configuration. Optionally, reinforcing members such a steel bars, mesh, fibre, polymer-coated fibreglass crinette and the like, and/or functional components such as conduits, may also be arranged between the granules, to be included in the artefact.

The guar gum may be an aqueous solution of guar gum, comprising guar gum in a concentration of from 0.5 to 3% dry mass, and wherein the fully hydrolysed polyvinyl alcohol is an aqueous solution of fully hydrolysed polyvinyl alcohol, comprising fully hydrolysed polyvinyl alcohol in a concentration of from 2.5 to 7% dry mass.

The precursor composition may comprise water in an amount of from 50% to 80% by mass based on the dry mass of the Portland cement. The water of the precursor composition may be the water of the one or combination of the aqueous solution of guar gum and the aqueous solution of polyvinyl alcohol.

The precursor composition may comprise from 20 to 70%, more preferably 30 to 60% dry mass of the Portland cement, based on the combined mass of the Portland cement and the cement extender. The precursor composition may comprise from 30 to 80%, more preferably 40 to 80% dry mass of the cement extender, based on the combined mass of the Portland cement and the cement extender. The cement extender may be selected from one or a combination of any two or more of sugar cane bagasse, fly ash, micronized silica, silica flour, and silica-based sand.

The cement extender may comprise an aggregate, typically as 20 to 35% dry mass based on the combined mass of the cement extender and the aggregate. The aggregate may typically be of a particle size in the range of 2 to 8mm diameter. The aggregate may, for example, be stone.

The gelling agent may be an aqueous solution of borax comprising 1 to 8%, more preferably 2 to 6% dry mass borax.

The precursor composition may comprise from 5 to 15%, more preferably from 5 to 10% by mass of the gelling agent, as the aqueous solution of borax, based on the mass of the one or combination of the aqueous solution of guar gum and the aqueous solution of polyvinyl alcohol.

In another embodiment of the invention, in which the precursor composition is gypsum- based, the precursor composition may comprise

gypsum, preferably in the form of beta hemi-hydrate calcium sulphate;

water;

The following statements relate to the gypsum-based precursor composition.

Preparing the precursor composition may include blending the gypsum, at least some of the water, the guar gum and/or fully hydrolysed polyvinyl alcohol and, optionally, the synthetic fibre, pulp fibre and/or lignocellulosic fibre referred above and hereinafter. Thereafter, the gelling agent may be introduced.

An alternative approach is to blend the gelling agent with the guar and/or polyvinyl alcohol, and optionally also with the fibres referred to above and hereinafter, and thereafter adding the gypsum. While not wishing to be bound by theory, the Applicant understands that reaction of the gelling agent with the guar and/or the polyvinyl alcohol has the same effect in the case of the gypsum-based precursor as in the case of the cementitious precursor.

As in the case of the cementitious precursor composition, pressing the gypsum-based precursor composition causes the granules thereof to coalesce and thereby form a homogenous artefact. After pressing, the artefact may still be wet, and may therefore be subjected to drying in providing the construction element.

Also as in the case of the cementitious precursor composition, before pressing the granules to cohere and form the artefact, the granules may be spread out on a surface in a desired configuration. Optionally, reinforcing members such a steel bars, mesh, fibre, polymer-coated fibreglass crinette and the like, and/or functional components such as conduits, may also be arranged between the granules, to be included in the artefact.

The gypsum may be present in the precursor compound from 80 to 95% dry mass.

As in the case of the cementitious precursor composition, the guar gum may be an aqueous solution of guar gum, comprising guar gum in a concentration of from 0.5 to 3%, more preferably 1 to 2% dry mass, and wherein the fully hydrolysed polyvinyl alcohol is an aqueous solution of fully hydrolysed polyvinyl alcohol, comprising fully hydrolysed polyvinyl alcohol in a concentration of from 2.5 to 7% dry mass.

The precursor composition may comprise water in an amount of from 70% to 1 10% by mass based on the dry mass of the calcium sulphate. The water of the precursor composition may be the water of the one or combination of the aqueous solution of guar gum and the aqueous solution of polyvinyl alcohol.

The following statements apply to both abovementioned embodiments of the precursor composition.

The precursor composition may include one or a combination of any two or more of synthetic fibre, pulp fibre and lignocellulosic fibre. In the case of synthetic fibre, the precursor composition may include 1 to 8% dry mass, more preferably 2 to 6% dry mass synthetic fibre. In the case of pulp fibre of lignocellulosic fibre, the precursor composition may include 6 to 8% dry mass of the lignocellulosic fibre.

When the artefact is a board, the board may have a thickness of from 4 to 100mm, more preferably from 30 to 40mm.

Furthermore, the board may have a dry density of from 0.7 to 1 .9 g/cc, more preferably from 0.75 to 1 .6 g/cc, more preferably from 1 to 1 .4 g/cc, e.g. 1 .2 g/cc. In the case of the cementitious precursor composition, the density may be from 0.7 to 1 .9 g/cc, more preferably from 0.75 to 1.7 g/cc. In the case of the gypsum-based precursor composition, the density may be from 0.7 to 1 .7 g/cc.

In the case of the gypsum-based precursor composition, the precursor composition may be pressed for from 5 to 25 seconds.

The core element may be of a polymeric foam material, e.g. Neopor by BASF, or polystyrene or phenolic or polyurethane or monofilament glass or rockwool reinforced gypsum foam. The following modifiers may also be included in the precursor composition:

- thermoplastic emulsion resins incorporated at up to 15%, more preferably up to 8% dry mass, e.g. acrylics and styrene isobutylene rubber;

- perlite at up to 30%, more preferably up to 20%, to control density and ease of cutting or machining; - exfoliated micron size vermiculite at up to 30%, more preferably up to 20% dry mass, further to control density and workability; and

- any of the volume extenders described in the detailed description of the invention below, to control density and ease of cutting or machining.

IN ACCORDANCE WITH ANOTHER ASPECT OF THE INVENTION IS PROVIDED

an assembly comprising two or more of the construction elements as hereinbefore described, the construction elements being splined together. IN ACCORDANCE WITH A FURTHER ASPECT OF THE INVENTION IS PROVIDED

a method of erecting a construction, the method including splining together two or more of the construction elements as hereinbefore described.

THE INVENTION EXTENDS, AS SEPARATE ASPECTS THEREOF, to the respective precursor compositions as described above in relation to the construction element aspect of the invention, for producing a construction element.

THE INVENTION ALSO EXTENDS, AS FURTHER SEPARATE ASPECTS THEREOF, to methods of producing precursor compositions as described above in relation to the construction element aspect of the invention, for producing a construction element.

THE INVENTION FURTHER EXTENDS, AS YET A FURTHER SEPARATE ASPECT THEREOF, to a method of producing a construction element, which method includes producing an artefact by subjecting, respectively, the precursor compositions herein described, in granular form, to pressing, thus causing the granules to cohere.

The method may include drying the cohered granules, e.g. by temperature treatment, thus obtaining the artefact.

The method may further include adhering two of the artefacts to a core element, as hereinbefore described, to provide the construction element. DETAILED DESCRIPTION OF THE INVENTION

THE INVENTION WILL NOW BE DESCRIBED in more detail, with reference to a process for implementing a method of producing a construction element, as illustrated diagrammatically in accompanying Figure 1 , and exemplary embodiments of construction elements of and obtainable in accordance with the invention.

Process

The following description is to be read in conjunction with the summary of the invention above, and features described in relation to the process 10 are, in more detail, as described in relation to the aspects of the invention set out in the summary of the invention.

Referring to the drawing, reference numeral 10 generally indicates a process for implementing a method of producing a construction element in accordance with the invention. The process 10 includes a variety of feedstocks, some of which are optional depending on how the process is desired to operate. The feedstocks include Portland cement 12, fly ash or siliceous fines 14, perlite 16, vermiculite 18, solution A (as described below) 20, and polypropylene fibrillated fibre 26.

The process 10 also includes a first mixer 24, a weigh cell 22, a second mixer 28, and a granule-receiving hopper 32 having an auto weight discharge powered by an auger.

The process 10 further includes a frame and edge restraint assembly 30, a granule spreading and levelling stage 34, a frame stacking and cleaning stage 36, and a filled frame layup and press feed 38.

Still further, the process 10 includes a hydraulic press 40, a pressed frame stacker 46, a curing chamber 48, and a trolley parking zone 44.

The process 10 also includes a trolley exit zone 50 and a board removal and spline location stage 52.

Still further, the process 10 includes a calibration sanding stage 58 and a sizing stage 56.

Further, the process 10 includes a Neopor plant 59, a Neopor cutting stage 60, a glue application stage 62, a glue reservoir 64, cement and resin feedstocks 80, 82, and lamination presses 66, 68, 70. Further still, the process includes cutting stages 74, 76.

Finally, the process 10 includes a curing and spline grout setting stage 78, and dispatch from there.

In use, the feedstocks Portland cement 12, fly ash or siliceous fines 14, perlite 16, vermiculite 18, solution A 20, and polypropylene fibrillated fibre 26 are fed into the second mixer 28 via the weigh cell 22. Before such feeding, solution A is mixed with the polypropylene fibrillated fibre 26 in the first mixer 24.

Solution A is in the form of a cementitious precursor composition, in accordance with the invention.

The mixing that occurs in the second mixer 28 produces a granular precursor composition, as provided for in accordance with the invention.

The granular precursor composition is fed to the granule-receiving hopper 32 and is automatically discharged, based on predetermined weight parameters, by the auger. The frame and edge restraint assembly 30 feeds an empty frame and edge restraint to the granule spreading and levelling stage 34, the frame having been cleaned in the cleaning stage 36. The empty frame is then filled with granular precursor composition, and is transferred via filled frame layup and press feed 38 to the hydraulic press 40. In the hydraulic press 40, the granular precursor is pressed such that the granules cohere, providing a homogenous cohered, but still wet, artefact, in the form of a board, held in the frame. The frame carrying the artefact is passed to the filled frame stacker 46, from where it is transferred to a curing chamber 48. In the curing chamber 48 the artefact is subjected to heat treatment, and thus is cured to form a cured artefact, or board, in the frame. The trolley carrying the now cured artefact is rolled to the trolley exit zone 50. From there the board in the frame is removed from the trolley and transferred to the board removal and spline location stage 52, while the trolley is moved back to the trolley parking zone 44, for availability to the filled frame stacker 46. After having been removed from the frame, splines are located and attached to two cornering edges of the board.

The removed board is transferred, sequentially, to the calibration sanding stage 58 and sizing stage 56, being subjected to sanding and sizing, e.g. by sawing.

The Neopor plant 59 produces foamed core element material, which is cut to foamed core elements in the Neopor cutting stage 60. Glue is applied to a core element in the glue application stage 62, being fed from the glue reservoir 64, cement and resin feedstocks 80, 82. The board is then adhered to glued surfaces of the core elements, thereby providing construction elements in accordance with the invention, which are passed to the lamination presses 66, 68, 70 for lamination. Lamination may alternatively or additionally be of the core elements, as such, and/or the boards, as such. From the lamination presses 66, 68, 70., the construction element, or core elements or boards, is transferred to cutting stages 74, 76, in which further sizing is effected.

Finally, the process 10 includes a curing and spline grout setting stage 78. After curing and spine grout setting, the completed construction element is dispatched.

Construction elements of or obtainable in accordance with the invention

Specific embodiments of construction elements, core materials and boards manufactured by the process of the invention from the cementitious precursor composition of the invention, are shown in Figure 2 and Figure 3, some including steel rebar reinforcing elements, which are cut to width and length.

Further embodiments of construction elements of and obtainable in accordance with the invention, and their use in providing fixed constructions in accordance with the invention, are illustrated in Figures 4 to 13, respectively showing the following:

In Figure 4, numerals 1 and 2 show the pressed precursor compositions of the invention, i.e. the artefacts obtainable in accordance with the invention, laminated to a core element, identified as "Neopor by BASF," in the form of a Neopor graphitic expanded polystyrene or polyurethane or phenolic foam by BASF or Momentive. Numeral 3 shows a joint member or spline measuring typically 45mm x 12mm, with steel reinforcing.

Numeral 4 shows joining of the panels as shown, which may be adhesively secured, preferably with a resin modified cement slurry.

Numeral 4B shows an alternative embodiment, in which no joint members are used and the components fit flush and are glue bonded, for example with a polyurethane or epoxy adhesive or cement/polymer slurry.

In Figure 5, various embodiments of posts, as construction elements of the invention, are illustrated.

Reference numeral 5 shows a 3-way post with optional reinforcing 6 composed of pressed and then machined precursor compound.

Reference numeral 7 shows a 2-way inline post with a typical reinforcement.

Reference numeral 8 shows a 4-way post.

Finally, reference numeral 9 shows a 2-way corner post.

In Figure 6 is shown, by reference numeral 10, a bottom section of a wall comprising a construction element according to the invention, comprising outer boards contiguous with a core element. The construction element is the element of Figure 1. The construction element is received in a u-track floor runner 1 1 which is secured to a concrete base with expanded bolts, such as rawl or Hilti (not shown).

In Figure 7 is shown the top of a typical wall section, showing reinforcing steel 14, a top ring beam 12 adhesively secured to a wall 13, preferably using a cement with thermoplastic emulsion resin modification. Alternatively the top ring beam may be replaced by a u-section galvanized typically 1 .2mm gauge steel.

Figure 8 shows conventional staggered block-laying, comprising conventional bricks and the like. Block sizes up to 900 kg long and 600 kg high.

Panel construct is less practical without mechanical assistance, because weight may be excessive and dangerous. A cross section of the brick or block is shown. Figure 9 shows a construct with joint continuous vertical lines.

Figure 10 shows laminated cement boards for posts. Access for services provision is facilitated by engineering a vertical space. Figure 11 shows, from top to bottom, three stages of assembly of a splined assembly.

Figure 12 shows foam core offsetting to provide tongue and groove formations assembly. Exposed polymeric foam is coated appropriately to improve resistance to damage in transport and assembly. Figure 13 shows assembly of a construction element of the invention with a spline through adhesive bonding, thus minimizing any chance of miss-alignment, and the need for skill in rapid assembly. Fixed constructions of or obtainable in accordance with the invention

A typical fixed construction in accordance with the invention would typically comprise of a strip foundation or a raft designed by a professional structural engineer, taking account of the weight of the super structure, or top structure and on the advice of a geotechnical expert concerning the condition of the ground.

A steel u-track of 0.8 to 1 .2mm gauge floor runners are now placed in position and secured to the concrete with expanding bolts at 30mm centers.

Wall sections comprising construction elements in accordance with the invention, e.g. comprising of pressed cement/ash or geopolymer sheets or boards optionally with woven wire, glass fibre or textile fabric reinforcing laminated either side of a Neopor or EPS core and optionally with joint apertures to receive the jointing strips in place, are placed in the floor runners and are secured with tex screws at 300mm centres, to this steel u-section floor track. Successive panels or bricks are positioned and secured to each other adhesively with the aid of locator splines or keys which are grouted in position and to each other with a cement/thermoplastic resin or polymeric adhesive such as urethane or epoxy.

Features of the invention as implemented by the process 10 In this section, features of the invention implemented by the process 10 of Figure 1 are described in more detail and, where inconsistent with the description of Figure 1 as read with the summary of the invention, present alternatives to features described in the description of Figure 1 and the summary of the invention. All percentages are by dry mass of the cementitious precursor composition, unless otherwise indicated.

Portland cement of an MPa rating from 32 - 52 or higher and constituting between 28% and 80% of the cementitious precursor composition by mass, optionally reinforced with synthetic fibres, such as polyvinyl alcohol, surface modified orfibrillated polypropylene, nylon, acrylic, aramid, polyethylene teraphthalate, or by cellulose fibres such as pulp or even papermill sludge, or splinters or chips of wood or sugar cane bagasse or other biomass fibrous material of high aspect ratio.

Synthetic fibres are used at percentages by mass of from 0.025% to 8% and the biomass when used from 7% to 30% dry mass. The cement is extended with inorganic particles such as ground silicas and slags, silica sand, fly-ash, wollastonite, pumice or other inorganics free from carbon, salinity, clay and organic matter, and preferably high in the oxides of silica, aluminium and iron, contributing to pozzolanic properties, such as sugar cane bagasse ash or fly-ash with a silica percentage greater than 70% and containing iron 3%, aluminium 9% and other oxides.

The inorganic cement extenders are used in a proportion of 20% to 80% in a dry format. All of these dry components are first blended thoroughly. Density modifiers may be used, such as expanded perlite, or exfoliated vermiculite, hollow glass balloons, foamed silicas or glass, pumice and diatomaceous earth, in order to control the density of the final product, and promote workability, such as sawing, profiling or sanding. In those products that do not need to be sawn or worked to profile, aggregates in the size range 2 to 8 mm may be included.

A solution of guar in water is added to the dry components, such that the water to cement ratio is in the range 35% - 105% of the cementitious precursor composition the solution containing between 0.5% and 3% by dry mass of guar gum in water. Polyvinyl alcohol having a molecular weight in the range 100 000 - 170 000 and a degree of hydrolysis of 98 to 99 mol% and viscosity typically of a 4% solution at 20°C being in the range 18 - 30 CPs may be used instead of guar or other hydrated polysaccharide colloids or in combination.

Resins may be added to contribute to water resistance, toughness, flexibility and propagating the interfacial bond between fibres and steel reinforcing and the matrix. Examples of these resins are the thermoplastic emulsions, such as styrenated acrylics, pure acrylics, styrene butadiene rubbers, synthetic latexes and similar. Resins incorporated at from 0% to 15%, more usually 0% to 5% of thermoplastic emulsions.

The entire mix is thoroughly blended to form a uniform slurry.

To the slurry is added a gelling agent which reacts with guar to cause gelling. The gelling agent is preferably in the form of a solution of a metallic ion in water, the preferred being borax, which is a disodium tetra borate deca- or penta-hydrate, added at a concentration in water of between 1 % and 7%, more preferably in the range 2% to 5% and typically on a mass basis between 5% and 15% of the guar solution. The mix is thoroughly blended and with increasing shear, the entire mass breaks into granules or small particles of a non-sticky nature. An aggregate may be blended with the granules, such as in rail road ties.

The composition is laid up for processing on platens or on moving belts at a specific mass per unit area, suitable to the density of the final product and its thickness. At the right positions in this mass may be laid up reinforcing, preferably steel bar the surface of which has been distressed or ribbed or coated to ensure grip, or alternatively steel wire or mesh. However steel rods, flats, angles, or tubes are preferred and are cleaned of rust and preferably have been wetted with an adhesion promoter such as such with a thermoplastic emulsion binder, ensuring interfacial adhesion and optionally may be pre-stressed by applying tension to the bars whilst they are located in a press molding box.

The mass proceeds through a hydraulic press which may be multi-daylight, single- daylight, or continuous, where the composite is pressed at room temperature at a pressure of between 7 - 50kg/cm² for between 5 - 25 seconds, preferably of the order of 7 - 15 seconds, whilst under pressure, whereupon the entire mass becomes a cohesive solid, or mass without dimensional instability or spring back, by which is meant volume increase on the release of pressure and no fissuring, parting, or cohesion loss. These sheets now proceed from the pressing station to a cure area, where cement hydration can commence and subsequent to which the flat sheets are converted into elongate members by sawing or cutting between the reinforcing steel bars, to make structural components of specific dimensions, density, reinforcement and mass. These sheets, with or without steel reinforcing, may also be bonded to a polymeric foam core, the sheets being from 10mm to 80mm thick, more usually from 20mm to 50mm thick, the foam core being more usually 20mm to 100mm thick, the foam core being more usually 20mm to 90mm thick, as blocks or as wall panels 90mm to 160mm thick or as composites or boards of from 6mm to 80mm thick as building boards. Examples of metal reinforced components or un-reinforced cross-sectional dimension used in housing would be typically the width of the wall thickness and of a thickness from 12mm - 50mm, laminated as posts. Beams and rafters, lintels, purlins and piles and would be of a section appropriate to the strength, and the handling and the assembly of the components. Dry densities would be of the order of 700 to 2 000kg/m³, more usually in the range 800 to 1 ,250 kg/m³, saving between 50% and 80% of the mass of an equivalent cast structure of cement with aggregate.

The principal binder in the product is Portland cement. The term hydration is used to describe reactions in which water is chemically combined. This gives rise to the term hydraulic binder. Cement is basically manufactured from shale, limestone and iron ore stockpiles. The raw materials are ground and fed into a rotary kiln with lime. Cement contains between 63% and 68% lime, 19% and 24% silica, 4% and 7% alumina and 1 % to 4% iron. These materials are blended with coal or other energy producing materials to generate the temperature, which by the end of the process reaches a temperature of 1 ,450°C and hence the criticism of Portland cement being a CO2 generator. However it is a unique binder essential to the building industry. It is classified in South Africa into three grades; 32.5; 42.5 and 52.5, with the suffix R referring to rapid setting, otherwise the suffix N being normal and these numbers refer to the final strength after 28 days in mPa compressive strength. When water is added to cement, the process of hydration commences forming a tri-calcium silicate, which is the major contributor of strength and which is the major utiliser of lime and which is 45 - 65% of the set cement by mass. The second major component is di-calcium silicate making up 10% to 35%, which forms the initial gel and which has a strong influence on final porosity. Finally tri-calcium aluminate and tetra-calcium alumino ferrite make up between 5% and 10% in each case. The water to cement ratio is very important and this depends on the extenders used. If the water to cement ratio for a given mix can be accurately controlled, the highest possible quality cement results with a minimum of capillarity and pore spaces and minimum need for drying. Those substances that are added to cement in the composition of the product are preferably those that can react with the lime in cement and which can be termed pozzolanic material, by which is meant that compounds of silica, alumina, iron and calcium may be formed and examples of these are granulated blast furnace slags, fly ash, burnt shale and silica fume and sugar cane bagasse ash of a silica percentage greater than 70%. These extenders as they are called, may retard the speed of setting but increase the later age strength, reduce pore permeability, can prevent alkali silica reactions and they combine chlorides and reduce chloride induced corrosion of embedded steel, and they can increase strength materially. High performance structural components should be based on a strength class of 42.5N or higher cement. Fly ash is extracted by electrostatic precipitators from the flue gasses of power stations fired with pulverized coal which is the case in South Africa. Fly ash particle size can be as low as 10μ and usually round in shape and may contain 45 - 50% silica, 25 - 30% alumina, 4 - 8% calcium and 9 - 1 1 % iron. It is preferable in the structural elements, as well as in the foamed lightweight bricks to use a minimum of 30% by mass of fly ash, up to 70%. Condensed silica fume, which is a byproduct of the silica smelting operations, has 92% silica and relatively small percentages of iron and aluminium. It promotes density. Granulated blast furnace slag in fact when activated either by water or especially by lime, gives rise to reactions very similar to those occurring in cement. It is therefore a very good additive to cement and when, at the right particle size, is a very beneficial contributor. Silica fume as a function of its minute particle size; i.e. 20 000 m²/kg of specific surface, has very valuable properties of minimizing porosity and improving cohesion, which is particularly important in the structural product. A water to cement ratio of over 1 is common. The reason is the requirement of wetting of the extenders and creating an optimum foaming consistency in the case of the foamed cement bricks.

In an important embodiment there is provided guar gum which is extracted from the endosperm of guar beans. The guar plant is similar to soya in appearance and is drought resistant. It is a leguminous shrub, cyanopsis tetragonoloba. Guar gum consists of 36.0% galactose anhydride and 63.1 % mannose anhydride referred to as galactomannan, of molecular weights 220,000 and is a linear anisodimensional carbohydrate polymer. Guar is in fact a long chain polyalcohol with 1 - 2 diol gronpings capable of complexation. It is non ionic or cationic or anionic. It binds water through hydrogen bonding, as free hydroxyl groups, its film is resistant to oils and greases and it is stable across a wide range of Ph. Guar with polyvinyl alcohol in ranges 60 guar to 40 polyvinyl alcohol is preferred but for dust suppression a guar solution of 0.2% to 0.4% of a 5,000 viscosity, combined with 1 .25% polyvinyl alcohol solution is effective. Wide combinations of different concentrations in water are possible. Guar with polyvinyl alcohol, complexed by Boron B(OH)4 - forms rigid three dimensional polyvalent metal crosslinks. Guar may be complexed on its own in the same way to granulate cement or gypsum or calcium aluminate slurries for boards, damp milled grains, fertilizer constituents, lignocellulosic fibres, for boards, coal fines, mineral fines, carpets, textiles or inorganic fibres for pressed products and others variously described above. As a dust suppressant at a solution concentration of a 5,000 viscosity specification at 0.15% to 0.35% complexation may occur in situ with reaction with elements in the dust or substrate. Guar of molecular weights of 100,000 to 3 million may be used at concentrations of 0.15% to 3% and be crosslinked at 0.001 % to 0.5%, more preferably between 0.01 % to 0.25%, examples being sodium or potassium permanganate or the compounds or elements mentioned previously. Guar's principal functions in the invention applications is as a binder, hydrocolloid and gel agent. Its use as a thickener and fracturing agent are well known in other applications. Typical crosslinks are depicted below.

The polyvinyl alcohol optionally used in the methipd of the invention with a gipar solution as a mix together which is to convert a slurry into flowable granules, and which on compression instantly form a cohesive sheet or board product optionally with the necessary reinforcement integral is the fully hydrolysed grades such as Moliol 20/98 by Clariant, or Goshenol N types NH18, NH20, NH300 by Nippon Goshei with molecular weights in the range 125 000 to 160 000 g/mol and viscosities of 4% solution at 20°C in the range 16 - 30 MPa.s with a degree of hydrolysis or saponification mol% between 97 and 99.5 and an ester value of 20 ± 5mgKOH/g but molecular weights from 100 000 can be suitable. A most favourable grade is Poval 1 17 by Kururay. These grades must be dissolved in water by first dispersing them cold, and then raising the temperature of the dissolution water to 95°C causing the dissolution of the polyvinyl alcohol, which is now in a molecular separated suspension in water capable of imposing considerable water resistance on the other constituents of the product. Further waterproofness may be imposed by the use of dimethylol urea or acids such as orthophosphoric or certain salts such as ammonium chloride or sodium/ammonium bichromate, typically being added at 5% by mass on the polyvinyl alcohol in a dry format. A further attribute is that the higher the drying temperature if used of the end product, the greater the insolubility of the polyvinyl alcohol. The concentration in water of the polyvinyl alcohol my mass is in the range 2 - 20%, more preferably in the range 4 - 15% and still more preferably in the range 5 - 12% and the solution mixed with the dry components of the composition acts as the gauging water for the Portland cement. A gelling agent, which increases the viscosity or causes the partial or complete gelling or precipitation of the hydraulic binder slurry is key to the method of this invention. The regularly arrange hydroxyl groups of the guar or other hydrated polysaccharide colloid chain can form chemically more or less stable complex compounds or associates with certain substances. In addition when the guar gels, it loses all tack and becomes non- sticky. In addition the guar or polyvinyl alcohol or a blend envelopes the other components of the hydraulic binder slurry, including the Portland cement and extenders as an integral part of the gel, giving it considerable cohesive properties and allowing the formed sheet to be pressed in such a way that no breakage, friability, parting or fissures result and no spring back or volume increase after pressing. The pressing need only be for a few seconds, but certainly in the range 5 - 25 seconds, whereupon a cohesive sheet is formed which is stable, smooth and which can be platen stacked to allow the chemistry of the cement and its extenders to go to completion. The classic complex formed from guar is its reaction with boric acid or one of the borates. Boric acid gives the monodiol complex, which in turn forms a poly- electrolite and didiol complex. The gelation particularly suitable to the method is the precipitation of the guar by borax in solution which is Na2B₄05(OH)₄.8H20 referred to as disodium tetraborate decahydrate. The pentahydrate is also satisfactory.

Borax partially hydrolyes boric acid and this acts as a buffered gelling agent. In the method, the borax is dissolved in water to give a solution concentration of between 1 - 8% by mass, more preferably in the range 2 - 5%. This solution when blended with the guar solution, in the cement slurry is used in the range 1 - 5% borax by mass on the mass of the polyvinyl alcohol, more preferably in the range 1 .5 - 3%. Other possible gelation agents are elements of the sub-groups 1 v-v1 on the periodic table and also manganese, or certain other metal ions. The preferred gelling agent on the grounds of performance is borax, which results in near precipitation of the guar or guar with polyvinyl alcohol joint solution, to form free flowing, non-sticky granules on mechanical shear which can then be spread to a specific mass per unit area to give the end product, with its reinforcement at whatever thickness and position is appropriate. Density is modified by the extenders and the choice imposed by application needs. However, the calcium in the cement also is a potent gel former with guar and the need or otherwise of an additional gel agent is process dependent.

In certain circumstances, the gel agent may be added to the guar or polyvinyl alcohol, or a blend, before this is mixed with the furnish, depending mainly upon viscosity and intimate wetting.

Thermoplastic polymer dispersion in water can be added to the guar or guar polyvinyl alcohol blend solution. These add desired properties including resistance to ultra-violet light and water, contribution to strength, impact resistance and toughness. Flexual strength is improved and the interfacial bind between the reinforcing and the matrix improved. Some of these polymers have considerable coalesced flexibility. These polymer dispersions are characterized by solid percentage in water of between 40 - 70% more generally of the range 50 - 65%. Examples are vinyl polymers and polymers of acrylates and methacrylates. Several monomers are used in the manufacture, particularly the acrylates and methacrylates, but styrene and vinyl acetates can also be used. Co-polymers or any two or more of these polymers can then be employed, acrylate and methacrylate polymers have long lasting properties, including alkali resistance. Synthetic latex polymers have contributive properties such as styrene butadiene copolymer latexes, such as Synthomer 29Y40, an example of a SBR or a styrene butadiene rubber.

By a combination of all or some of these aspects, low cost, fire proof, thermally efficient, logistically efficient, attractive houses can be built for rural populations, proximate to sugar mills, or power stations, or buildings for any size or purpose. Very rapid and precise assembly of wall components is provided for by offsetting of the foam core or providing a splined assembly, the whole being adhesively assembled.

Volume extenders

The choice of fillers high in oxides of silica, iron and alumina, of very low bulk density to add volume and therefore influence final density, but which may also bond with the highly alkaline sodium or potassium silicate as a form of geopolymer includes hollow glass or siliceous micro cells or balloons. Some of these are synthetic or expanded Perlite, others are by-products such as high silica fractions of micronized coal burnt in power stations which are recovered, including fly ash. Examples are Cenolite by Ash Resources of South Africa or Filite of Runcorn in Kent, UK. However a preferred filler is a refined mineral by Silbrico Corporation called Sil-Cell which is a glass micro cellular filler comprising of hollow glass particles whose shapes vary to combine different geometries, both spherical and irregular. These shapes present the advantage of not only low final product density but reinforcement and impact resistance. Due to the irregular shape of the particles greater tensile strength is derived and a mechanical key in packing occurs during the processing operation. Each particle consists of multiple minute cells of micro bubbles and the effective specific gravity is in the range 0.18 or 180kg/m³. The properties of the material are as follows:

CHEMICAL PROPERTIES

Silicon Dioxide 73%

Aluminium Oxide 17%

Potassium Oxide 5% Sodium Oxide 3%

Calcium Oxide 1 %

Plus Trace Elements

TYPICAL PARTICLE SIZE DISTRIBUTION

(U.S. Sieve) % Wt. Sil-32 Si I -42 Sil-35 Si I -43

+ 50 Mesh 2 Trace 0 0

-50 + 100 15 5 Trace Trace

-100 + 200 33 25 12 5

-200 50 70 88 95 Other hollow glass micro spheres are those by Glaverbel of Belgium. These are boro silicate glass micro bubbles with wall thicknesses of 1 to 3μ filled with an odourless non toxic gas. These have the registered name Microcel and grade M28 consists of 73% silicon dioxide, having been surface treated with a silane coupling agent and have a bulk density of 0.17, a particle size as low as 5μ, a softening temperature of 800°C, a compressive strength of 140 bar and a thermal conductivity of 0.055.

A further candidate is Cenolite which is a lightweight vitreous hollow sealed sphere produced as a by-product from pulverised coal burnt in power stations. These have a silicone dioxide percentage of 51 and an aluminium oxide percentage of 40. The bulk density at 450g/£ is high for the purpose of the invention, but they have a melting point of 1250°C which is at the high end of the melt spectrum due to the high aluminium oxide percentage. Filite of Runcorn, Cheshire of the U.K. is a similar product. Particle sizes of these spheres tend on average to be larger than glass micro balloons, but range from as low as 3μ up to 300, with a mean in the range 50 to 200.

A further hollow glass bubble by 3M is bubble type C15-250 with a nominal average particle density of 0.015mm and an average bulk density in the range 0.06 to 0.012 and a compressive strength of 17 bar. These are a sodium boro silicate glass with a softening point in excess of 700°C. Another example of a glass micro balloon are those by Dicapearl of California such as the 512 grade, suitable for the method of the invention.

A further lightweight glass balloon is that by Dennert under the trademark Poraver. These beads are of a wide range of diameters and densities. Those suitable for the method of the invention are of a diameter of below 1 mm up to 8mm. They have the further advantage of being alkali resistant, are chemically inert and highly compression stable. For example, granules of Poraver in the size range 2mm to 4mm have a bulk density of 190g/£, have an average pressure value in kN of 14 and a pH value in the range 9 to 12. Particle sizes as small as 40μ are available. Poraver is pure glass which is generated from recycling. They have a softening point of 700°C and in the case of those with the lowest bulk densities have thermal insulation properties appropriate to the invention. Another suitable extender is expanded Perlite. Perlite refers to a siliceous rock. This is a form of volcanic glass which when heated to approximately 800°C or more expansion occurs due to the release of water inside the semi-molten rock. If the expansion is done carefully a closed cell results at a density as low as 90kg/m³, the diameter of which depends on the particle size before expanded. If the rock is milled to a small enough particle size, then it is possible to produce the expanded version in particle sizes appropriate for the method of the invention i.e. 200μ or smaller. Properties of Perlite are as follows:

Typical Chemical Analysis * Typical Product Data

Silicon 33.8 Colour White

Aluminium 7.2 G.E. Brightness, % 70-80

Potassium 3.5 Refractive Index 1 .47

Sodium 3.4 Specific Gravity 2.2-.2.4

Iron 0.6 Apparent or Bulk Density, 5-15

lb/ft³ .08-.24 gm/cc

Calcium 0.6 PH Neural

Magnesium 0.2 Oil Absorption 120-240^*

Traces 0.2 Softening Point, °F 1800

°C 980

Oxygen (by difference) 47.5 Moisture, % <1 .0

Net total 97.0 Water Absorption 195-350^*

Bound Water 3.0 Ignition Loss, 3hr 1700°F 1 .5%

(930C) max^**

Total, % 100. Mean Particle Diameter,

0 Microns

As small as 10^***

^* All analysis are shown in ^*lbs (kgs) oil or water/100 lbs

elemental form. (kgs)

^** Due to residual combined

water

^*** Varies with product

A still further inorganic volume extender is exfoliated vermiculite. Vermiculite is sourced from iron bearing phlogopite or biotite. At 900 to 1000°C vermiculite exfoliates when inter lamina water is expelled causing exfoliation and volume extension perpendicular to the lamina plates resulting in 6 to 15-fold expansion and decrease in bulk density from 1000kg/m³ down to 60 to 180kg/m³. The micron grade is of 500μ to 1 .5mm in size, and may beneficially be blended with bentonite at up to 2% by mass. Assembly of Structures

The crux of this invention is the cold pressing of cement and/or gypsum compositions into which may optionally be inserted reinforcement, preferably as elongate steel rods, in the correct linear and spatial positions during the furnish lay-up, followed by pressing into cohesive sheets, then sawing the resultant composite to length or into structural strips. The structural elements may be bolted or otherwise adhered together, as appropriate in the structural assembly, such as a house. They may also be used as beams, roof members, lintels, wall plates, door frames and piles. The wall panels or blocks comprise of cementitious boards either side of a polymeric or gypsum foam core to which they are adhered and into which location splines or keys are grouted on two adjacent sides, the other two routed to receive the splines or keys of the adjacent blocks during assembly. The reinforcing steel pressed integral with posts, ring beams, jointing sections and structural components, may be coated with a compatible adhesive such as a styrenated acrylic just prior to pressing integral with the SCBA or fly-ash cement board components, and may be any of rod, angle, tube, flat or other appropriate cross section.

In the method of the invention there is provided the assembly of the structural elements with the lightweight blocks or bricks by grouting posts to the concrete slab or bolting them. The slab may comprise of pressed boards on either side of a polymeric foam on beams, in turn attached to piles made of the structural elements onto which the posts are now affixed, or alternatively the slab may be a conventional concrete poured slab, on which assembly now commences. After the positioning and securing of the posts, the panels are adhesively secured together once each block has been engaged with the grouted spline or key horizontally and vertically to the adjacent blocks and to the posts. Once all of the walls are up, and the wall plates in position with window frames and door frames preferably in position, the entire surfaces of the house, optionally both inside and outside may be covered by a sealer comprising of a thermoplastic emulsion chosen from an acrylic or a styrene butadiene rubber latex solution, with Portland cement and optionally extenders and added water in such a way that the sealer coats the panel described above. This layer is built to a thickness of approximately 1 - 3 mm and which serves as a plaster as well as a waterproof membrane forbidding water penetration. The surfaces are smoothed ready for painting or textured by a roller and also serve to cover the block joint lines. The brick or panel surfaces are more than adequate in all respects, and require only an oxide colourant or ferrous salt or an alkali resistant plaster primer followed by water based paint. Services such as water and electric points may be post inserted by copper or steel tube insertion into the core foam to remove the foam from the tube, before the conduit and/or copper water pipes are inserted, services being reticulated above ceilings and plug, light switch or connection points being cut through the brick or panel liner or sheet as appropriate. Services may also be post assembly installed by routing the appropriate positions.

From the compositions and processes described, all of the following components of a house may be produced:

Roof rafters, trusses and purlins;

Door and window frames; Wall panels or bricks or blocks;

Siding, soffits and eave closures;

Decorative claddings;

Floor and wall tiles;

Ceilings, Wall boards and window cills;

Beams or piles;

Lintils

All the above reinforced, or not, as required and by varied density, surfaces may have pressed into them, such as wood grain pattern, brick or stone simulation or specialized textures, during the actual process. Volumetric extension of the composition allows sufficient compression ratio to allow for detailed surface patterning or profiling. The assembled blocks do not essentially require a sealer coat, which itself can be roller textured. The sides of the blocks are ready for painting.

Background to some aspects of the invention

Sugar cane is a plant belonging to the grass family, reaching a height of 5m, comprised of a composition of celluloses 45% - 50%, sucrose 20% - 25%, lignin 18% - 24%, ash 1 % - 4% and waxes 1 %. Sugar is grown in tropical and subtropical areas in 120 countries. In South Africa the industry is worth R12 billion/year. 120 million tons of sugar is produced in the world, 70% of which is from sugar cane and the balance from sugar beet. The sugar content of the juice is 20% and the cane stem produces 50kg of juice to every 100kg of cane. Growing is seasonal and production is only 20 - 32 weeks in the year, or two to five months. The trash or leaves are generally burnt in situ, whereas the biomass left after the pressing out of the cane juices, is called bagasse. This is used for making boards, paper and animal feeds and has many other uses. Cane does not only produce sugar but also ethanol and cellulose. Furfural is also produced for the synthesis of nylons and other plastics and bagasse can also be used to produce biodegradable plastics and products as diverse as biodegradable dinner plates. In sugar production, the biomass residue after pressing out the cane juices is burnt to generate energy for the sugar mill, and any residual energy is used to generate electricity for the grid. The ash that is produced is pumped into ponds or dams, and is typically comprised of silicon dioxide, 70% - 90%, aluminium 9%, ferric oxide 2.8%, potassium oxide 3.5% and calcium oxide 2.2%. There is therefore a significant percentage of reactive oxides, most particularly silica, which makes it a candidate for geopolymers, using highly alkaline reactants, or as a cement extender.

The sugar industry is characterised by being rural by definition, generally in tropical or sub-tropical areas and often close to the sea or to rivers in environments high in rainfall. There is therefore a need for converting the ash into a useful product that can create jobs and that can also provide shelter for rural populations. The sugar industry is highly contributive in curtailing urbanisation, which is a serious problem throughout the world and is resulting in huge informal settlements in Africa. Fly-ash is the very small particle bi-product of coal firing in power generation. It is produced in very large quantities, is generally free of carbon and is typically high in the oxides of silica, iron and alumina, which may be present in amounts exceeding 70%. Oxides of alkali metals must be tested for their presence which is undesirable because hydration can result in bulking and efflorescence. Good fly-ash is pozzolanic becoming part of cement hydration products contributing to good quality. A further bi-product of coal fired power generation is gypsum produced by flu gas desulphurisation. It may also be sourced from other industrial processes such as acid mine water desalination. Calcining converts the dehydrate to the hemi-hydrate, which is an excellent raw material for fire protection and interior building products. Paper lined boards, referred to as sheet rock in America, can be improved upon. In terms of process and performance, but purity is best over 92% calcium sulphate.

Throughout the developing world there is a critical shortage of housing, particularly for the poor. As populations densify to urban areas and slums develop, sociological and health issues increase. Crime escalates and human dignity suffers. The reason for the housing shortfall may be attributable to cost, logistics and method. As an example in South Africa there is a backlog of three million low cost housing units and as much as 73% of the population has now moved to urban areas, often in informal settlements.

Brick and mortar is just not delivering and the reasons are logistical. Very often cement is too distant from the point of need, clay deposits suitable for brick making may not be available and neither may be sand or other aggregates that are suitable. There is often a shortage of close to hand water. Transport is the key issue and the availability of skills.

A still further exacerbation is the very high energy consumption of conventional building materials. These have typically a density of 2,200kg/m³ and in the case of cement requires a process temperature of 1 ,450°C and in the case of clay bricks, over 1 ,200°C. Building components are increasingly made from cement and sand in which the cement composition may be between 10% and 15%. Some of the quality is very poor usually as a result of either the addition of too little cement, or the use of unsatisfactory sand or aggregates. Alternative methods of building are becoming increasingly important, not only for delivery but for energy conservation. These are usually based on two frame methods, either steel or timber.

Traditionally in North America and Europe, timber frame was based on indigenous coniferous or deciduous trees that were mature, giving rise to stable high-strength frames. In the tropics or sub-tropics indigenous timbers are sometimes used which can have a serious implication for the environment or alternatively plantation timbers, which are very often used when still immature, giving rise to instability. There are other disadvantages, notably water ingress, warping, attack by insects and micro- organisms, and cost.

In the case of steel frames these suffer a number of disadvantages, the principal one of which is cost, closely followed by a high co-efficient of thermal expansion, resulting in thermal bridging and instability due to the disparate properties of the materials in contact with the steel. This can result in water ingress and structural instability such as cracking.

Another major drawback to alternative building systems is often the lack of acceptability by the people for whom the houses are built, even though they may be poor. There is therefore a need for alternative structures built of homogenous materials thereby avoiding instability as a function of thermal properties, that have a much lower weight per unit footprint, thereby saving not only costs of transport but also energy in component production or original content. There is also a need for an alternative method to be considered, which must be at least the equal of conventional construction but with better thermal performance. Increasingly the use of bi-products, often termed waste, is very important. A carbon neutral product such as sugar cane bagasse ash is a very significant preferred raw material from which can be constructed a complete house.

Claims

1 . A construction element comprising an artefact obtained by pressing, cold or at ambient temperature, a non-sticky free-flowing granular cementitious or gypsum- based precursor composition, causing the granules of the precursor composition to cohere and form the artefact.

2. The construction element according to claim 1 , wherein the artefact is a planar board.

3. The construction element according to claim 2, which comprises a core element and two of the planar boards, the planar boards being adhered to the core element at locations opposite each other, thus providing a composite, layered construction element.

4. The construction element according to claim 3, which has at least one recess in its periphery, which recess is bordered by the two planar boards and by the core element, in which recess a spline can be received to spline the construction element to another construction element.

5. The construction element according to claim 3 or claim 4, which includes a spline that projects from the periphery of the construction element and can be received by a complementally shaped recess of another construction element to spline the construction element to the other construction element.

6. The construction element according to any of claims 1 to 5, wherein the precursor composition is cementitious and comprises

Portland cement;

a cement extender;

water;

7. The construction element according to claim 6, wherein the guar gum is an aqueous solution of guar gum, comprising guar gum in a concentration of from 0.5 to 3% dry mass, and wherein the fully hydrolysed polyvinyl alcohol is an aqueous solution of fully hydrolysed polyvinyl alcohol, comprising fully hydrolysed polyvinyl alcohol in a concentration of from 2.5 to 7% dry mass.

8. The construction element according to claim 6 or claim 7, wherein the precursor composition comprises water in an amount of from 50% to 80% by mass based on the dry mass of the Portland cement.

9. The construction element according claim 7 or claim 7 and claim 8, wherein the water is the water of the one or a combination of the aqueous solution of guar gum and the aqueous solution of polyvinyl alcohol.

10. The construction element according to any of claims 6 to 9, wherein the precursor composition comprises from 20% to 70% dry mass of the Portland cement, based on the combined mass of the Portland cement and the cement extender.

1 1. The construction element according to any of claims 6 to 10, wherein the precursor composition comprises from 30% to 80% dry mass of the cement extender, based on the combined mass of the Portland cement and the cement extender.

12. The construction element according to any of claims 6 to 1 1 , wherein the gelling agent is an aqueous solution of borax comprising 1 to 8% dry mass borax.

13. The construction element according to claim 7 and any of claims 6 or 8 to 12, wherein the precursor composition comprises from 5 to 15% by mass of the gelling agent, based on the mass of the one or combination of the aqueous solution of guar gum and the aqueous solution of polyvinyl alcohol.

14. The construction element according to any of claims 6 to 13, wherein the precursor composition includes one or a combination of any two or more of synthetic fibre, pulp fibre and lignocellulosic fibre.

15. The construction element according to any of claims 6 to 14, wherein the cement extender is selected from one or a combination of any two or more of sugar cane bagasse, fly ash, micronized silica, silica flour, and silica-based sand.

16. The construction element according to any of claims 1 to 5, wherein the precursor composition is gypsum-based and comprises

beta hemi-hydrate calcium sulphate;

water;

17. The construction element according to claim 16, wherein the guar gum is an aqueous solution of guar gum, comprising guar gum in a concentration of from

0.5 to 3% dry mass, and wherein the fully hydrolysed polyvinyl alcohol is an aqueous solution of fully hydrolysed polyvinyl alcohol, comprising fully hydrolysed polyvinyl alcohol in a concentration of from 2.5 to 7% dry mass.

18. The construction element according to claim 16 or claim 17, wherein the precursor composition comprises water in an amount of from 70% to 1 10% by mass based on the dry mass of the calcium sulphate.

19. The construction element according to claim 17 or claim 17 and claim 18, wherein the water is the water of the one or a combination of the aqueous solution of guar gum and the aqueous solution of polyvinyl alcohol.

20. The construction element according to claim 2 and any of claims 3 to 19, wherein the board has a thickness of from 4 to 100mm.

21. The construction element according to claim 20, wherein the board has a thickness of from 30 to 40mm.

22. The construction element according to claim 2 and any of claims 3 to 21 , wherein the board has a dry density of from 0.7 to 1 .9 g/cc.

23. The construction element according to claim 3 and any of claims 4 to 22, wherein the core element is of a polymeric foam material.

24. A fixed construction assembly comprising two or more of the construction elements according to any of claims 1 to 24, the construction elements being splined together.

25. A method of erecting a fixed construction, the method including splining together two or more of the construction elements according to any of claims 1 to 24.