CEMENT BOARD

Abstract

A cement board includes a lightweight core between a first covering layer and a second covering layer, wherein the lightweight core results from the curing of an aqueous cementitious composition including, based on the total dry matter, 20 to 90 wt % of a reactive binder mixture and 10 to 80 wt % of fillers, wherein the reactive binder mixture includes, based on the total dry matter of the reactive binder mixture: 15 to 25 wt % hydraulic cement, 50 to 65 wt % calcium sulphate hemihydrate, and 10 to 35 wt % pozzolanic material; and at least one of the first and second covering layers includes a glass fibre-based sheeting, the sheeting being fully or partially embedded in a cementitious matrix.

Claims

1. A cement board comprising a lightweight core between a first covering layer and a second covering layer, wherein the lightweight core results from the curing of an aqueous cementitious composition comprising, based on the total dry matter, 20 to 90 wt % of a reactive binder mixture and 10 to 80 wt % of fillers, wherein said reactive binder mixture comprises, based on the total dry matter of the reactive binder mixture: 15 to 25 wt % hydraulic cement, 50 to 65 wt % calcium sulphate hemihydrate, and 10 to 35 wt % pozzolanic material; and at least one of the first and second covering layers (11, 12) comprises a glass fibre-based sheeting, said sheeting being fully or partially embedded in a cementitious matrix.

2. The cement board according to claim 1, wherein a weight ratio of the calcium sulphate hemihydrate to pozzolanic material is less than 2.5.

3. The cement board according to claim 1, wherein a weight ratio of the hydraulic cement to pozzolanic material is less than 2.

4. The cement board according to claim 1, wherein the pozzolanic material is selected from silica fumes, fly ash, metakaolin, or mixtures thereof.

5. The cement board according to claim 1, wherein the reactive binder mixture comprises, based on the total dry matter of the reactive binder mixture: 17 to 20 wt % hydraulic cement, 52 to 63 wt % calcium sulphate hemihydrate, and 15 to 30 wt % pozzolanic material.

6. The cement board according to claim 1, wherein the aqueous cementitious composition comprises 25 to 70 wt. % of the reactive binder mixture and 30 to 75 wt. % of fillers.

7. The cement board according to claim 1, wherein the fillers are selected from aggregates, lightweight fillers, and fibres.

8. The cement board according to claim 1, wherein the cementitious matrix in which the glass fibre-based sheeting is embedded results from the curing of an aqueous cementitious composition comprising a reactive binder mixture having the same composition as the reactive binder mixture of the core.

9. The cement board according to claim 1, wherein the glass fibre-based sheeting is coated with a resin material on one or both of its sides.

10. A process for manufacturing the cement board according to claim 1, comprising mixing a cementitious slurry, pouring the cementitious slurry onto a conveyor, in which a first covering layer carried by the conveyor is covered with the cementitious slurry, the latter forming a lightweight core of the cement board, extruding and cutting the first covering layer covered in cementitious slurry, into a cement board of the desired dimension and curing the lightweight core of the cement board.

11. A process for manufacturing the cement board according to claim 10, wherein before the extruding, a second covering layer (12) is put on top of the cementitious slurry covering the first covering layer.

12. A process for manufacturing the cement board according to claim 11, wherein before being put on top of the cementitious slurry covering the first covering layer, the second covering layer is covered with cementitious slurry.

13. The cement board according to claim 1, wherein the glass fibre-based sheeting is a scrim, a mat or a fabric.

14. The cement board according to claim 6, wherein the aqueous cementitious composition comprises 30 to 50 wt. % of the reactive binder mixture and 50 to 70 wt. % of fillers.

15. The cement board according to claim 7, wherein the aggregates include sand or calcium carbonate.

16. The cement board according to claim 7, wherein the lightweight fillers include expanded clay or hydrophobic expanded perlite.

17. The cement board according to claim 7, wherein the fibres include glass fibres, synthetic fibres or natural fibres.

Description

[0037] FIG. 1 is a schematic view of a cement board manufacturing process;

[0038] FIG. 2 is a table of the components used to manufacture a cement board according to the invention;

[0039] FIG. 3 is a cross-section view of a cement board according to the invention;

[0040] FIG. 4 is a cross-section view of the cement board according to a specific embodiment of the invention, with a partially embedded sheeting;

[0041] FIG. 5 is a cross-section view of the cement board according to another embodiment of the invention, with a partially embedded sheeting;

[0042] FIG. 6 is a cross-section view of the cement board according to the embodiment of FIG. 4, the sheeting being fully embedded;

[0043] FIG. 7 is a cross-section view of the cement board according to the embodiment of FIG. 5, the sheeting being fully embedded.

[0044] The present invention will now be described more fully hereinafter with reference to the accompanying drawings, in which some, but not all embodiments of the invention are shown. Indeed, the invention may be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; on the contrary, these embodiments are provided so that this disclosure will satisfy applicable legal requirements.

[0045] Like numbers refer to like elements throughout drawings.

[0046] As shown in FIG. 1, the cement board manufacturing process 1 which is used to manufacture cement boards 4 according to the invention is a continuous process. Such manufacturing process comprises at least a tank 2, in which components for a cementitious slurry 10 are continuously mixed. This cementitious slurry 10 is an aqueous cementitious composition whose components are described hereinafter. The cementitious slurry 10 is poured on a conveyor 3, this conveyor 3 carrying a first covering layer 11. This first covering layer 11 is thus covered with the cementitious slurry 10, the latter forming a lightweight core of the cement boards 4. In some embodiments, the conveyor 3 comprises vibrating components which help spread out the cementitious slurry 10 with its vibrations. The cement boards 4 may also comprise a second covering layer 12, which will be described in relation to FIGS. 3 to 7. Once the cementitious slurry 10 has been poured on the first covering layer 11, they go through an extruder and a cutting station, not shown on FIG. 1, where they are cut into cement boards 4 of desired dimensions. The cement boards 4 can then be stored for a curing process.

[0047] As shown in the table of FIG. 2, the components mixed in the tank 2 are, according to the invention, a reactive binder mixture comprising 15 to 25 wt. % of hydraulic cement, 50 to 65 wt. % of calcium sulphate hemihydrate and 10 to 35 wt. % of pozzolanic material, as well as fillers. The reactive binder mixture as a whole makes up 20 to 90 wt. % of the components of the aqueous cementitious composition while the fillers make up the remaining 10 to 80 wt. %. These percentages are based on the solid weight ratio between the component and (wt.) the total dry matter. In some embodiments, the percentages of each component are complementary, meaning if there is 15 wt. % of hydraulic cement and 50 wt. % of calcium sulphate hemihydrate, then there must be 35 wt. % of pozzolanic material, as the total of the percentages must be equal to 100. Another example of a composition covered by the invention would be to have 20 wt. % of hydraulic cement, 60 wt. % of calcium sulphate hemihydrate and 20 wt. % of pozzolanic material.

[0048] According to a preferred embodiment of the invention, the reactive binder mixture comprises 17 to 20 wt. % hydraulic cement, 52 to 63 wt. % calcium sulphate hemihydrate, and 15 to 30 wt. % pozzolanic material. According to an embodiment, the aqueous cementitious composition comprises 25 to 70 wt. %, preferably 30 to 50 wt. %, of the reactive binder mixture and 30 to 75 wt. %, preferably 50 to 70 wt. %, of fillers, as a complement of the aqueous cementitious composition.

[0049] The pozzolanic material may be selected from silica fumes, fly ash, metakaolin, or mixtures thereof, whereas the fillers can be chosen from aggregates such as sand or calcium carbonate, lightweight fillers such as expanded clay or hydrophobic expanded perlite, and fibres such as glass fibres, synthetic fibres or natural fibres. These fillers are effectively inert materials, which do not significantly react with the reactive binder mixture. The aqueous cementitious composition may also comprise additives or admixtures, e.g., retarders, accelerators, plasticisers or foaming agents. Such additives can be used to alter or enhance the properties of the reactive binder mixture and to improve the quality of the cement board 4.

[0050] Preferably, the weight ratio of the calcium sulphate hemihydrate compared to the pozzolanic material is less than 2.5. Similarly, the weight ratio of the hydraulic cement compared to the pozzolanic material is preferably less than 2.

[0051] FIGS. 3 to 7 illustrate cross-section views of different embodiments of a cement board 4 according to the invention. The cement board 4 comprises a lightweight core 13 made of cementitious slurry 10 of the aforementioned composition, as well as a first covering layer 11 and a second covering layer 12. The lightweight core 13 lies between these covering layers 11 and 12. According to the invention, at least of one of the first covering layer 11 and second covering layer 12 comprises a glass fibre-based sheeting 14. This sheeting 14 can either be partially embedded in a cementitious matrix 15, as shown in FIGS. 3 to 5, or fully embedded in the cementitious matrix 15, as in FIGS. 6 and 7. The cementitious matrix 15 is thus the part of the cement board 4 in which the glass fibre-based sheeting is embedded. This cementitious matrix 15 can be made of a reactive binder mixture having the same composition as the reactive binder mixture of the lightweight core 13 described hereinbefore, or it can be made of a reactive binder mixture having a different composition. In the embodiments illustrated on the figures, the cementitious matrix 15 is represented as having the same composition as reactive binder mixture of the lightweight core 13.

[0052] According to an embodiment, the glass fibre-based sheeting 14 does not need to have a strong alkali protection, as the composition of the lightweight core 13 has a low pH which has a positive impact on the dissolution of the sheeting 14.

[0053] On the cross-sections of FIGS. 4 and 6, the cement board 4 is represented with a first covering layer 11 comprising a sheeting 14 comprising both a scrim 16 and a mat 17, and a second covering layer 12 comprising only a scrim 16. These figures illustrate a possible embodiment of the cement board 4, but the invention also intends to cover embodiments in which both the first and the second covering layers 11 and 12 comprise both a scrim 16 and a mat 17, in which both the first and the second covering layers 11 and 12 comprise only a scrim 16, and in which the first covering layer 11 comprises a scrim 16 and the second covering layer 12 comprises both a scrim 16 and a mat 17.

[0054] The shape of the sheeting 14 follows the surface 40 of the cement board 4. The scrim 16 being made of a woven grid, sections 160 of this grid are visible. The grid extends both in a longitudinal direction and in a transverse direction, these longitudinal and transverse directions being the directions in which the cement board 4 mainly extends. The grid defines openings 161 in the scrim into which the cementitious matrix 15 can flow, thus creating a mechanical interaction with the scrim 16. These openings 161 in the scrim 16 must be sufficiently large so that the cementitious matrix 15 can penetrate inside the scrim 16. The mat 17 is placed over the scrim 16 according to a stacking direction S of the lightweight core 13 and the first and second covering layers 11 and 12. The mat 17 thus sits between the scrim 16 and the surface 40 of the cement board 4. The scrim 16 is here made of glass fibres, but it could also be made of a metallic material.

[0055] On the cross-sections of FIGS. 5 and 7, which are other embodiments of the invention, the cement board 4 is represented with a first covering layer 11 comprising a mat 17, for example of glass fibre, this mat being coated with a resin material 18. The resin material 18 can be a thermoplastic resin, e.g., polyethylene terephthalate (PET). This resin material 18 covers both sides of the mat 17, these sides being defined according to the stacking direction S of the lightweight core 13 and the first and second covering layers 11 and 12. As an alternative not shown here, the resin material 18 can cover only one of the two sides of the mat 17.

[0056] The resin material 18 makes the cement board 4 waterproof, preventing water from reaching the lightweight core 13. This lightweight core 13 is thus protected from humidity, which is advantageous for use in highly humid environments, such as swimming pools and humid climates.

[0057] As explained above, the glass fibre-based sheeting 14 can either be partially or fully embedded in the cementitious matrix 15.

[0058] When the glass fibre-based sheeting 14 is partially embedded in the cementitious matrix 15, as is the case in FIGS. 3, 4 and 5, the sheeting 14 is visible on the surface 40 on the cement board 4 as it sits at this surface 40 of the cement board 4. In this case, the cementitious matrix 15 seeps into the sheeting 14 from a first of its ends 140 but does not go through to a second of its ends 141. In other words, the cementitious matrix 15 penetrates the sheeting 14 but does not go fully through its thickness T, such thickness T being defined by the distance from the first end 140 to the second end 141 of the sheeting 14, measured along the stacking direction S of the lightweight core 13.

[0059] On the other hand, when the glass fibre-based sheeting 14 is fully embedded in the cementitious matrix 15, as is the case in FIGS. 6 and 7, this cementitious matrix 15 penetrates it from its first end 140 to its second end 141, meaning that the cementitious matrix 15 goes through the sheeting 14. As a result, the glass fibre-based sheeting 14 is does not form the surface 40 of the cement board 4 and is fully immersed inside the cementitious matrix 15.

[0060] The glass fibre-based sheeting 14 can be fully embedded during the cement board manufacturing process 1 explained relative to FIG. 1, and in this case the composition of the cementitious matrix 15 is identical to the composition of the cementitious slurry 10 of the lightweight core 13. Alternatively, the glass fibre-based sheeting 14 can be coated or impregnated beforehand with a cementitious slurry. This cementitious slurry may be identical or different from the cementitious slurry 10 forming the lightweight core 13 of the cement board 4.

[0061] Any modifications and other embodiments of the invention set forth herein will come to mind to one skilled in the art to which the invention pertains having the benefit of the teachings presented in the foregoing descriptions and the associated drawings. Therefore, it is to be understood that the invention is not to be limited to the specific embodiments disclosed and that modifications and other embodiments are intended to be included within the scope of the appended claims. Although specific terms are employed herein, they are used in a generic and descriptive sense only and not for purposes of limitation.