AU2014200044A1

AU2014200044A1 - Lightweight Building Member

Info

Publication number: AU2014200044A1
Application number: AU2014200044A
Authority: AU
Inventors: Catherine Mary Inglis; Philip Morey
Original assignee: BRICKWORKS BUILDING PRODUCTS Pty Ltd
Current assignee: BRICKWORKS BUILDING PRODUCTS Pty Ltd
Priority date: 2013-01-07
Filing date: 2014-01-06
Publication date: 2014-07-24
Also published as: AU2014200044A2; AU2014101579A4

Abstract

The present invention relates to lightweight building member of cementitious material for use in buildings or in another applications and to methods of forming lightweight building members. The building member is produced from a mixture including cement, water, a superplasticiser, a lightweight aggregate, a wood material and a bonding agent. The method includes placing the mixture in a mould and curing the mixture to form a lightweight building member. 'N K' N :; "": rThCN CN N 'K * ~ A~ * :; N 42' ' \ "A ~ 'N" "''' ""' ':; A ~~:v' "N "'A N" '' ~ A 'N.' N ~ ~ ' -' ' s :;'~ ' . ~ 'IN. t " "N N ~ 'K:; ~N"'S ~ A "N' N X 'K ~ '' " A N". N'

Description

1 Lightweight Building Member Field of the Invention The present invention relates to lightweight building member of cementitious material 5 for use in buildings or in another applications and to methods of forming lightweight building members. Background of the Invention Lightweight building members are sometimes used in building construction for use as 10 exterior and/or interior wall panels of the building structure. Existing lightweight building members are sometimes produced from autoclaved aerated concrete (AAC). AAC is a lightweight, building member material that is used to form building members such as wall, floor and roof panels or blocks that are typically not used as load bearing structural members. AAC is typically produced by creating a mixture of 15 aluminium powder, sand, lime and/or cement and water as a binding agent and then placing the mixture into forms. Chemical reactions take place in the mixture that give the AAC its lightweight and other properties. Typically, the aluminium powder included in the mixture reacts with calcium hydroxide and water to form hydrogen gas bubbles in the mixture of up to 3mm in diameter. 20 After the mixture is placed in forms it is allowed to cure. When the mixture has cured, the forms are removed and the cured mixture is then typically cut into blocks or panels and placed in an autoclave chamber. The autoclave applies a steam pressure hardening process which causes a further chemical reaction in the mixture whereby 25 the sand reacts with calcium hydroxide to form calcium silicahydrate which provides the AAC material with strength characteristics and other properties. Autoclaves used to produce AAC members are typically very large and expensive devices that consume significant amounts of energy and water for their operation. 30 Lightweight building members formed from AAC are presently utilised in the construction of buildings. AAC building members are mainly used as non-load bearing wall panels and have limited structural capacity due to their low compressive strength. AAC building members cannot be left exposed to environmental conditions, e.g. debris, water, etc. as this may damage the cellular structure of the building members. SPEC-955731.docx 2 The porosity of AAC means that it is particularly subject to capillary action, i.e. vapour transmission. As a result, most commonly, AAC building members are not used as structural elements but used as infill or internal walls only. The requirement to submit AAC building members to an autoclave process means that the capital costs to 5 establish an AAC building member production facility are high and the ongoing energy and water consumption of such devices is significant. Where building members such as structural elements, infill or internal walls may be required to meet acoustic performance requirements. Such acoustic performance 10 requirements can include the sound insulation performance of a building member which relates to the extent to which sound power incident on the building member is transmitted through the building member. Good acoustic performance by building members, such as walls, can be achieved by increasing the inherent mass of the building members. Where the density of the building member is reduced, such as in 15 the case of AAC building members, the acoustic performance is typically inferior to the acoustic performance of relatively more dense building members, such as building members produced with ordinary (non-lightweight) concrete. Accordingly, a need exists for lightweight building members and a method of producing lightweight building members without requiring an autoclave process and 20 that can be produce lightweight building members faster and at less cost than traditional AAC building members. A need also exists for lightweight building members that have comparable or greater structural rigidity than traditional AAC building members. A need also exists for lightweight building members that do not include relatively large gas filled voids and associated porosity and permeability. A 25 need also exists for lightweight building members for use as structural elements, infill or internal walls that have comparable or greater acoustic performance than traditional AAC building members. Summary of the Invention 30 In a first aspect, the present invention provides a method of forming a lightweight building member for use in construction, including: * preparing a mixture including i. cement; <filename> 3 ii. water; iii. a superplasticiser; iv. a lightweight aggregate; v. a wood material; and 5 vi. a bonding agent, and placing the mixture in a mould and curing the mixture to form a lightweight building member. The cement can be ordinary Portland cement or blended cement. 10 The superplasticiser can be polysulphonated naphthalene or a polycarboxylate. The lightweight aggregate may be lightweight beads. 15 The lightweight aggregate can be lightweight polymer beads. The lightweight aggregate includes expanded polystyrene beads. The lightweight beads can have a density of between about 3kg/M 3 and about 20 6kg/M 3 . The lightweight beads can each have a diameter of about 2mm to about 6mm. In some embodiments, about half of the lightweight beads have a diameter of about 25 3mm and about half of the lightweight beads have a diameter of about 5mm. In some embodiments, the wood material comprises 5 to 20 percent by volume of the mixture. 30 In some embodiments, the wood material comprises 8 to 12 percent by volume of the mixture. The wood material includes wood fibre, wood flour saw dust or a combination thereof. <filename> 4 The bonding agent can include ethylene vinyl acrylate. The method of the invention can further include one or more additives that act as rheology modifying agents. 5 The additive can be a cellulose derivative. The method of the invention can further include providing reinforcement to form a lightweight reinforced building member. 10 The reinforcement can include internal and/or external building member reinforcement. In some embodiments of the invention, a ratio of components of the mixture includes 15 one or more of: i. between about 30 kg and about 100 kg of the cement; ii. between about 20 litres and about 60 litres of the water; iii. between about 200 mL and about 1000 mL of the superplasticiser; 20 iv. between about 80 litres to about 160 litres of the lightweight aggregate in the form of beads and having a density of between about 3kg/M 3 to about 6 kg/M 3 and each of the beads having a diameter of between about 2 mm and about 6 mm; and v. between about 100 grams and about 1000 grams of the bonding 25 agent. A ratio of components of the mixture can include one or more of: i. between about 50kg to about 70kg of cement; ii. between about 20 litres and about 30 litres of the water; 30 iii. about 500 mL of the superplasticiser; iv. between about 100 litres and about 120 litres of the lightweight aggregate in the form of beads and having a density of between about 3kg/M 3 to about 6 kg/M 3 and each of the beads having a diameter of between about 3 mm and about 5 mm; and <filename> 5 v. between about 500 grammes and about 700 grammes of the bonding agent. The method can further include providing one or more fibre-cement panels in the 5 mould. A surface of the fibre-cement panel can be coated with the bonding agent. In some further embodiments of the invention, the method includes providing one or 10 more channels or strips in the mould. In another aspect, the present invention provides a lightweight building member for use in construction, formed from a material including: i. cement; 15 ii. water; iii. a superplasticiser; iv. a lightweight aggregate; v. a wood material; and vi. a bonding agent. 20 Preferably, the wood material includes wood fibre, wood flour saw dust or a combination thereof. Preferably, the lightweight building member has a density of about 0.75 kg/ m 3 25 The building member can have dimensions of between about 2400 and 4200 mm height, between about 300 and 900 mm width and between about 60 to 70 mm depth or thickness. 30 The building member can have dimensions of between about 2400 and 4200 mm height, between about 300 and 900 mm width and 60, 65 or 70 mm depth or thickness. <filename> 6 The building member can include one or more external surfaces covered by a fibre cement sheeting panel. The building member can include a channel or strip in one or more ends or sides of 5 the lightweight building member. Brief Description of the Drawings The present invention will now be described with reference to the accompanying drawings, which illustrate particular preferred embodiments of the present invention, 10 wherein: Figure 1 illustrates a perspective view of a lightweight building member, in particular a wall panel, for use in construction, wherein the panel includes channels in the form of furring channels along opposite lateral edges thereof according to an embodiment of 15 the invention; Figure 2 illustrates a perspective view of a lightweight building member in accordance with another embodiment of the invention, in particular a wall panel, for use in construction, wherein the panel includes an internal reinforcement structure; 20 Figure 3 illustrates a lightweight building member in accordance with another embodiment of the invention, in particular a wall panel, for use in construction, wherein the panel includes opposite major surfaces covered by fibre-cement panels; 25 Figure 4 illustrates a channel in the form of a furring channel that is incorporated into the lightweight panel illustrated in Figure 1; Figure 5 illustrates a mould apparatus for use in a method for forming a plurality of lightweight panels in accordance with an embodiment of the invention; 30 Figure 6 illustrates the mould apparatus of Figure 5 wherein the mould apparatus has been filled with a mixture for forming a plurality of the lightweight panels; <filename> 7 Figure 7 illustrates the mould apparatus of Figure 5 wherein the mixture contained in the mould has cured and the mould apparatus is opened to remove lightweight panels formed in accordance with an embodiment of the invention. 5 The present invention will now be described in more detail below with reference to the preferred embodiments of the invention illustrated in the figures. Detailed Description The present invention relates to a method of forming a lightweight building member, 10 such a lightweight building panel 100 as illustrated in Figure 1, or another embodiment of a building panel 200 as illustrated in Figure 2 or yet another embodiment of a building panel 300 as illustrated in Figure 3. Accordingly, although the present invention is illustrated herein with reference to preferred embodiments in the form of lightweight building panels used, typically, as lightweight infill wall panels, 15 it is to be appreciated that the present invention may provides lightweight building members in other forms. Such other forms may include lightweight panels used for other purposes or lightweight blocks for use in construction. In particular, the method of the invention includes a step of preparing a mixture that includes cement, such as ordinary portland cement, water, a superplasticiser, a lightweight aggregate; wood 20 material and a bonding agent. The method further includes a step of placing the mixture in a mould and curing the mixture to form a lightweight building element. The present invention can provide advantages over existing methods of forming lightweight building members as the present invention can provide a method of 25 producing lightweight building members without requiring an autoclave process and that can be produced faster and at less cost than traditional AAC building members. The present invention can also provide advantages in that the resulting lightweight building member does not include the relatively large gas filled voids associated with AAC building members and, therefore, is less porous and is less susceptible to 30 damage if left exposed to weather. The present invention can also provide advantages in that it can provide a lightweight building member having comparable or greater structural rigidity than existing AAC building members. <filename> 8 In the method of the present invention, cement, such as ordinary Portland cement may be used. However, a blended cement may be used that includes Portland cement, gypsum, calcium oxide, fly ash, ground granulated blast furnace slag, limestone and crystalline silica. The method of the present invention also includes the 5 addition of a superplasticiser to the mixture. The superplasticiser may be polysulphonated naphthalene or a polycarboxylate. It is to be appreciated, however, that another superplasticiser may be chosen based on its suitability to the type and/or composition of the cement that is to be used in the mixture. The amount of the superplasticiser used in the mixture should be an amount sufficient to ensure that the 10 cement forms a fluid paste capable of coating the lightweight aggregate. The method of the present invention also features the inclusion of a bonding agent into the mixture. The bonding agent is preferably ethylene vinyl acrylate (EVA) which may be provided to the mixture in powder form. The amount of the bonding agent 15 employed in the mixture shall be an amount sufficient to act as a bonding agent between the aggregate and the cement matrix. The amount of the bonding agent used is determined as a function of the total surface area of the aggregate included in the mixture. 20 The method of the present invention also includes the addition of the lightweight aggregate, such as a plurality of lightweight beads, into the mixture. The plurality of lightweight beads are preferably lightweight polymer beads such as expanded polystyrene beads. The polystyrene beads will preferable have a density of between about 3kg/M 3 to about 6kg/M 3 . The plurality of lightweight beads each have a 25 diameter of between about 2mm to about 6mm. Preferably about half of the plurality of lightweight beads have a diameter of about 3mm and about half of the plurality of lightweight beads have a diameter of about 5mm. In another embodiment, the lightweight aggregate may include perlite or another low density filler material. The lightweight aggregate may include perlite or other low density fillers either alone or in 30 combination with lightweight beads such as expanded polystyrene beads. A lightweight aggregate or filler is employed to reduce the amount of cement used in the mixture and also to reduce the density of the mixture and the resulting lightweight building member. <filename> 9 The method of the present invention may also include the use of one or more additives that act as a rheology modifying agent. In an embodiment, the rheology modifying agent that may be added to the mixture is a cellulose derivative. 5 The method of the present invention also includes the addition of a wood material into the mixture. Preferably the wood material is wood fibre, wood flour or saw dust or a combination thereof. The wood material may be a recycled or a virgin wood material. In an embodiment, the amount of the wood material that is added to the mixture comprises 5 to 20 percent by volume of the mixture. In another embodiment, the 10 amount of the wood material that is added to the mixture comprises 8 to 12 percent by volume of the mixture. In another embodiment, the amount of the wood material that is added to the mixture comprises about 8 percent by volume of the mixture. In another embodiment, the amount of the wood material that is added to the mixture comprises about 9 percent by volume of the mixture. In another embodiment, the 15 amount of the wood material that is added to the mixture comprises about 10 percent by volume of the mixture. In another embodiment, the amount of the wood material that is added to the mixture comprises about 11 percent by volume of the mixture. In another embodiment, the amount of the wood material that is added to the mixture comprises about 12 percent by volume of the mixture. 20 It has been found that the addition of wood material to the mixture enhances the acoustic performance of the resulting building member without having a significantly deleterious effect on other characteristics of the building member such as its weight and structural rigidity. Building members, such as structural members, infill or internal 25 wall panels have natural frequencies at which they will resonate and thereby transmit sound at those frequencies at undesirably high levels. It has been found that the inclusion of wood material such as wood fibre, wood flour or saw dust in the mixture of embodiments of the invention has the effect of altering resonant frequencies of the building member. Accordingly, building members can be produced that have an 30 enhanced ability to absorb and reduce transmission of sound at frequencies that are audible to humans. It is believed that the inclusion of wood material to the mixture reduces the negative ratio of transverse to axial strain ('poisson's ratio') of the material comprising the resulting building member from about 0.30 to about 0.25. By <filename> 10 altering the poisson's ratio, the resonant frequencies of the resulting building member can be altered. In a preferred form of the method of the invention the mixture is formed by creating a 5 slurry of the cement, water and superplasticiser. The slurry is checked for consistency and when it is determined that the consistency of the mixture is adequate the lightweight aggregate, such as polystyrene beads, are then added to the slurry along with the EVA bonding agent. The mixture is allowed to mix until the matrix become homogeneous. The mixture may be mixed by any suitable means, such as in a 10 cement or concrete mixing drum or in any other suitable apparatus. The mixture is then poured into a mould such as the mould illustrated in Figures 5 to 7 relatively quickly before the thixotropic character of the mixture changes significantly from a less viscous state achieved during the mixing process to a more viscous state after mixing has stopped. If the mixture is not poured into the mould relatively quickly after 15 mixing has stopped the mixture may become too viscous and may not effectively pour into the mould. Referring to Figures 5 to 7, an embodiment of the mould 50 is illustrated. However, it is to be appreciated that forms of mould other than the embodiment of the mould 50 20 illustrated in Figures 5 to 7 and described herein may be employed in the method depending on the nature and purpose of the lightweight building members that are to be formed. Accordingly, any mould shape, size or configuration may be employed that is capable of providing one or more mould cavities that are capable of holding and forming a quantity of the abovementioned mixture into a desired shape or 25 configuration. Such moulds could include moulds capable of forming lightweight building members such as wall, floor and roof panels or blocks that are typically not used as load bearing structural members. In the preferred embodiment of the mould 50 illustrated in Figures 5 to 7, the mould 30 50 includes a base plate 52, a plurality of mould walls 53 upstanding from the base plate 52, a fixed side wall 54 also upstanding from the base plate 52 and a pair of end walls 56, 57 that are upstanding from and removably mounted to opposite ends of the base plate 52 and the mould panels 53. The mould panels 53 are each pivotally coupled along a lower edge thereof to the base plate 52 via a pivotal coupling 51 as <filename> 11 shown in Figure 5 in particular. As illustrated in Figure 5, the pivotal coupling of the plurality of mould panels 53 to the base 52 via the pivotal couplings 51 facilitates preparation of the mould apparatus 50 for receiving a batch of the mixture. As illustrated in Figure 5, in an open position each of the mould panels 53 may stand at 5 an incline of substantially less than 90 degrees relative to the base plate 52. Preparation of the mould apparatus 50 may involve coating the mould panels with a lubricant, such as oil, and then closing the mould panels 53 such that they each stand substantially upright from the base plate 52. Where the base plate 52 is laid horizontally the mould panels 53 stand substantially vertically when in the closed 10 position illustrated in Figure 6. A channel, such as a furring channel 110 illustrated in Figure 4, or another form of channel such a C channel having a C shaped section, may be inserted into the base of each mould cavity 55 formed between adjacent mould panels 53 or between a 15 mould panel 53 and the side wall 54, as illustrated in Figure 5. The furring channel 110 may take any suitable form but in the embodiment illustrated in Figure 5, the furring channel 110 is an elongated metal strip including a planar web portion 112 with a pair of opposing lateral side wall members 113, 115 upstanding from lateral edges of the web 112. Lateral flange members 114, 116 extend outwardly from an 20 upper edge of each of the lateral side wall members 113, 115. In an embodiment in which the channel is a C channel (not shown), the channel includes a metal strip with a pair of opposing lateral side wall members upstanding from lateral edges of the web. 25 As illustrated in Figure 6, when the mould panels 53 are closed and stand substantially upright from the base plate 52, the end panels 56 and 57 are connected to the mould apparatus 50 at opposite ends thereof to enclose opposite ends of the mould cavities 55. The mixture 59 may than be poured into the mould cavities 55 until the mould cavities 55 are filled as illustrated in Figure 6. Another channel such as 30 another one of the furring channels 110, or a C channel or another suitable form of channel, may be placed in each of the mould cavities 55 after the mixture has been placed within the mould cavities 55. The mixture is then allowed to cure within the mould cavities 55. After the mixture has cured, the mould apparatus 50 is opened as illustrated in Figure 7 to enable the removal of the end plates 55, 56 and the pivoting <filename> 12 of subsequent mould panels 53 as illustrated in Figure 7 to enable the formed panels 100 to be removed from the mould apparatus 50. As illustrated in Figure 1, the resulting lightweight building member in the form of a panel 100 is a lightweight cementitious panel that, in the embodiment of the panel 100 illustrated in Figure 1, 5 includes furring channels 110 on opposite lateral edges thereof to provide reinforcement. The furring channels 110 also operate to support and/or lock the lightweight panel 100 in position in a structure. As mentioned above, other forms of channels other than the furring channels 110 illustrated in Figure 1 may be adopted for the purpose of providing reinforcement and/or for supporting and/or locking the 10 lightweight panel 100 in position in a structure. Such other forms of channels include but are not limited to C channels. As illustrated in Figure 2, another embodiment of the lightweight building member in the form of a lightweight panel 200 may be formed with internal reinforcement. The 15 embodiment of the lightweight panel 200 illustrated in Figure 2 is formed by inserting a reinforcement structure 210 into each of the mould cavities 55 before or after, but preferably after, the mixture has been poured into the mould cavities 55. In the embodiment illustrated in Figure 2, the reinforcement structure 210 is a steel reinforcement structure that is formed in a grid pattern and includes a plurality of 20 longitudinal reinforcement bars 212 and a plurality of transverse reinforcement bars 214 that are interconnected with the longitudinal reinforcement bars 212. The transverse reinforcement bars 214 are, in a preferred form, provided with a bend 216 at a midpoint along each of the transverse reinforcement bars 214. Thus, the resulting reinforcement structure 210 has a triangular shaped profile. The inclusion of the 25 internal reinforcement structure 210 provides the lightweight panel 200 with additional tensile strength and ductility so as to resist cracking and/or structural failure. The lightweight panels 200 may also be provided with channels such as the furring channels 110 as illustrated in Figures 1 and 4 or another form of channel such as a C channel. 30 Figure 3 illustrates another embodiment of the lightweight building member in the form of a lightweight panel 300 which includes fibre-cement board panels 310, 320 on opposite major facing surfaces of the panel 300. Applying the fibre-cement panels 310, 320 to the lightweight panel 300 involves inserting both of the fibre-cement <filename> 13 panels 310, 320 into each one of the mould cavities 55 of the mould apparatus 50 prior to pouring the mixture into the mould cavities 55. Prior to pouring the mixture into the mould cavities the fibre-cement panels 310, 320 are coated on one surface with a bonding agent emulsion which may preferably include ethylene vinyl acrylate (EVA) to 5 ensure that the fibre-cement panels 310, 320 adhere to the mixture when the mixture cures. After the mixture cures the lightweight panels 300 are removed from the mould cavities 55 with the fibre-cement panels 310, 320 adhered to the major facing surfaces of the lightweight panel 300. The resulting lightweight panel 300 has external surfaces that are pre-finished and ready for use as internal and/or external, 10 wall panels of a building structure without requiring an additional step of applying a finishing material, such as plaster, thereto. The lightweight panels 300 are, therefore, ready for painting. The lightweight panel 300 illustrated in Figure 3 may also be provided with the internal reinforcement structure 210 as illustrated in Figure 2 and/or channels such as the furring channels 110 as illustrated in Figures 1 and 4 or another 15 form of channel such as a C channel. The following is an example of the method of the invention being carried out to form a plurality of the lightweight panels 100 using the mould apparatus 50 illustrated in Figures 5 to 7 above. The following example provides quantities of constituents of the 20 mixture used for the production of a single one of the panels 100 having the dimensions of 2700 mm height, 600 mm width and 65 to 70 mm depth or thickness (such as any one of 60, 65 or 70 mm depth or thickness) and a mass of approximately 79kg and a density of about 0.75kg/M 3 and a water absorption characterised as less than about 5%. It is to be appreciated that for n number of 25 panels 100 to be produced then approximately n times the following quantities of constituents of the mixture would be used. In the following example, reinforcement in the form of 28mm furring channels were adopted and were inserted into the mould cavities 55 to be incorporated into both lateral edges of the panels 100. The resulting panel was tested to have a lateral load capacity of greater than 100kg. The resulting 30 panel 110 also had an acoustic performance of Rw 40 to 50 (bare panel) and a pull out strength of greater than 80 kilograms when utilising 8 gauge, 25mm screws. In the example, the mixture was produced using Portland cement, water and a superplasticiser. The amount of cement that was used was between 30kg and 100kg, <filename> 14 but preferably between 50 and 70kg. A superplasticiser in the form of polysulphonated naphthalene was included in an amount of about 500ml but could be between 200ml and 1 litre depending on the superplasticiser used. Potable water was included of between 20 and 30 litres but could be as much as 60 litres. The cement, 5 water and plasticiser were placed in an agitator, such as a concrete agitator, to form a slurry. The lightweight aggregate in the form of polystyrene bead and the bonding agent were then added to the slurry to form the mixture. The amount of the polystyrene 10 bead used was between 80 to 160 litres, and preferably between 100 and 120 litres, wherein each of the beads has a diameter between 2 and 6mm and preferably a 50:50 mixture of 3mm and 5mm diameter beads. The bonding agent was a dispersible block copolymer such as EVA but any similar type of water dispersible bonding agent could be used that may also include other additives that can act as 15 rheology modifying agents including cellulose derivatives or other similar chemicals. The amount of the bonding agent added to the mixture was between 100 grams and 1000 grams but is preferably within the range of 500 to 700 grams. In the example, wood material was added to the mixture. The wood material was a 20 recycled wood material and the amount of the wood material that was added to the mixture comprised 8 to 12 percent by volume of the final mixture. The mixture was then inspected to ensure good hydration of the cement and of the mixture and, if necessary, more water could be added, to allow the mixture to flow into 25 the mould cavities 55 of the mould apparatus 50 so as to minimise air bubbles in the mixture. The mixture was mixed in the agitator for about 10 mins. The mould cavities 55 were each fitted with a channel in the form of a 28mm furring channel in the base of each 30 mould cavity 55 to act as an edge stiffener. The mixture was then poured from the agitator into the oiled mould cavities 55. A channel in the form of a 28mm furring channel was then placed in the top of each mould cavity 55 on top of the mixture therein. The mixture was then allowed to cure after which the mould panels 53 where <filename> 15 pivoted about the pivotal couplings 51 thereof to the base plate 52 to enable release of consecutive lightweight panels 100 from the mould apparatus 50. It is to be understood that various alterations, modifications and/or additions may be 5 made to the method and/or to the lightweight building member without departing from the ambit of the present invention as disclosed herein. <filename>

Claims

1. A method of forming a lightweight building member for use in construction, including: 5 e preparing a mixture including i. cement; ii. water; iii. a superplasticiser; iv. a lightweight aggregate; 10 v. a wood material; and vi. a bonding agent, placing the mixture in a mould and curing the mixture to form a lightweight building member. 15

2. The method of claim 1, wherein the cement is ordinary Portland cement or blended cement.

3. The method of claim 1 or claim 2, wherein the superplasticiser is polysulphonated naphthalene or a polycarboxylate. 20

4. The method of any one of the preceding claims, wherein the lightweight aggregate may be lightweight beads.

5. The method of claim 4, wherein the lightweight beads includes lightweight polymer beads. 25

6. The method of claim 4 or claim 5, wherein the lightweight beads includes expanded polystyrene beads.

7. The method of claim 5 or claim 6, wherein the lightweight beads have a density of between about 3kg/M 3 and about 6kg/M 3 . 30

8. The method of any one of claims 5 to 7, wherein the lightweight beads each have a diameter of about 2mm to about 6mm. <filename> 17

9. The method of any one of claim 5 to 8, wherein about half of the lightweight beads have a diameter of about 3mm and about half of the lightweight beads have a diameter of about 5mm. 5

10. The method of any one of the preceding claims, wherein the wood material comprises 5 to 20 percent by volume of the mixture.

11. The method of any one of the preceding claims, wherein the wood material comprises 8 to 12 percent by volume of the mixture. 10

12. The method of any one of the preceding claims, wherein the wood material includes wood fibre, wood flour, saw dust or a combination thereof.

13. The method of any one of the preceding claims, wherein the bonding agent 15 includes ethylene vinyl acrylate.

14. The method of any one of the preceding claims, further including one or more additives that act as rheology modifying agents. 20

15. The method of claim 14, wherein the additive is a cellulose derivative.

16. The method of any one of the preceding claims, further including providing reinforcement. 25

17. The method of claim 16, wherein the reinforcement includes internal and/or external reinforcement.

18. The method of any one of the preceding claims, wherein a ratio of components of the mixture includes: 30 i. between about 30 kg and about 100 kg of the cement; ii. between about 20 litres and about 60 litres of the water; iii. between about 200 mL and about 1000 mL of the superplasticiser; <filename> 18 iv. between about 80 litres to about 160 litres of the lightweight aggregate in the form of lightweight beads having a density of between about 3kg/M 3 to about 6 kg/M 3 and each of the beads having a diameter of between about 2 mm and about 6 mm; and 5 v. between about 100 grammes and about 1000 grammes of the bonding agent.

19. The method of any one of the preceding claims, wherein a ratio of components of the mixture includes: 10 i. between about 50kg to about 70kg of cement; ii. between about 20 litres and about 30 litres of the water; iii. about 500 mL of the superplasticiser; iv. between about 100 litres and about 120 litres of the aggregate in the form of lightweight beads having a density of between about 15 3kg/M 3 to about 6 kg/M 3 and each of the beads having a diameter of between about 3 mm and about 5 mm; and v. between about 500 grammes and about 700 grammes of the bonding agent.

20 20. The method of any one of the preceding claims, further including providing one or more fibre-cement panels in the mould.

21. The method of claim 20, wherein a surface of the fibre-cement panel is coated with the bonding agent. 25

22. The method of any one of the preceding claims, further including providing one or more channels or strips in the mould.

23.A lightweight building member for use in construction, formed from a material 30 including: i. cement; ii. water; iii. a superplasticiser; iv. a lightweight aggregate; <filename> 19 v. a wood material; and vi. a bonding agent.

24. The lightweight building member of claim 23, wherein the wood material 5 includes wood fibre, wood flour, saw dust or a combination thereof.

25. The lightweight building member of claim 23 or claim 24, wherein the building member has a density of about 0.75 kg/ M 3 . 10

26. The lightweight building member of any one of claims 23 to 25, wherein the building member has dimensions of between about 2400 and 4200 mm height, between about 300 and 900 mm and between about 60 to 70 mm depth or thickness. 15

27. The lightweight building member of any one of claims 23 to 25, wherein the building member has dimensions of between about 2400 and 4200 mm height, between about 300 and 900 mm width and 60, 65 or 70 mm depth or thickness.

28. The lightweight building member of any one of claims 23 to 27, wherein the 20 lightweight building member includes one or more external surfaces covered by a fibre-cement panel.

29. The lightweight building member of any one of claims 23 to 28, wherein the lightweight building member includes a channel or strip in one or more ends or 25 sides of the lightweight building member. <filename>