Construction panel and method of manufacturing thereof

Abstract

The construction panel comprises a porous cured core material having a density in the range of 0.75 to 0.95 kg / dm3 and provided with a composition comprising a set inorganic binder and cured cement powder, wherein the cured cement powder is present in an amount of at least 20wt% based on dry weight of the composition, and a fiber reinforcement embedded in the core material. It is manufactured in a method comprising the steps of providing an aqueous composition and providing a fiber reinforcement, for instance in the form of a fiber mat; casting the composition into a mould, with the reinforcement being embedded therein; and curing the composition into a core material of the construction panel, for instance by means of air-curing.

Description

[0001] Construction panel and method of manufacturing thereof

[0002] FIELD OF THE INVENTION

[0003] The invention relates to a construction panel comprising: a core material provided with a composition comprising a set inorganic binder, and a fiber reinforcement, for instance in the form of a first and a second fiber mat. The invention further relates to a method of manufacturing such a construction panel.

[0004] BACKGROUND OF THE INVENTION

[0005] Such cement-based construction panels that are reinforced with fiber mats are known in the market, such as under the tradename Aquapanel®. The panels are known to be fire-resistant and insensitive for humidity. Typically, they are used outdoor behind a decorative panel or inside. As a consequence, the exposure to weather conditions is less, and hence the requirements on flexural strength and dimensional stability are not as high as those for fiber cement facade panels, such as for instance sold under the trade name Equitone®. This leads thereto that the density of the product is also lower.

[0006] EP1981826B2 discloses a construction panel of the type mentioned in the opening paragraph. The core material herein comprises a lightweight component and a filler. The binder is Portland cement. The lightweight component is expanded perlite, in the form of grains embedded in the binder, which is furthermore hydrophobized with silicone oil. The filler is limestone flour. The first and second reinforcement are embedded in cover layers of Portland cement. The density of the resulting construction panel is in the range of 0.3 to 1.2 kg / dm3. Based on the examples in the patent, the overall content of limestone flour is 60wt% based on dry weight (thus excluding any remaining humidity), Portland cement 27wt%, hydrophobized expanded perlite 12% and glass fiber mat 2%.

[0007] It is a disadvantage of the known construction panel that its mechanical properties are limited, while the density is still significant. Tests performed on commercially available Aquapanel-boards with a density of 1.06 kg / dm3gave a flexural strength of 8.0 MPa and a bending strength of 1.2 J / m2. It would be desirous to provide construction panels with a lower density, with equal or higher flexural strength and improved bending strength. In fact, a lower density will result in lower transport cost and energy consumption. Typically, however, a decrease in density implies higher porosity or lower content of cement. The particle density of cement is about 3.2 kg / dm3, the bulk density around 1.5 kg / dm3. A reduction of the cement content will reduce the strength, as the cement is the binder that keeps the board together.

[0008] SUMMARY OF THE INVENTION

[0009] It is therefore a first object of the invention to provide a construction panel of the type mentioned in the opening paragraph, which has equal or better mechanical properties that existing construction panels on the market and still has lower density.

[0010] It is a further object of the invention to provide a manufacturing method for such panel.

[0011] According to a first aspect, the invention provides a construction panel comprising

[0012] - a porous cured core material having a density in the range of 0.75 to 0.95 kg / dm3 and provided with a composition comprising a set inorganic binder and cured cement powder, wherein the cured cement powder is present in an amount of at least 20wt% based on dry weight of the core material, and - a fiber reinforcement embedded in the core.

[0013] According to a second aspect, the invention provides a method of manufacturing a construction panel having a density in the range of 0.75 to 0.95 kg / dm3, comprising the steps of:

[0014] - providing a composition comprising an inorganic binder and cured cementitious powder and a foaming agent, wherein the cured cementitious powder is present in an amount of at least 20wt% based on dry weight of the core material, and

[0015] - providing a fiber reinforcement, for instance in the form of a fiber mat;

[0016] - casting the composition into a mould, with the first and the second reinforcement being embedded therein;

[0017] - curing the composition into a core material.

[0018] It was found in experiments leading to the invention that the addition of cured cementitious powder in sufficient amount enabled embedding the fiber reinforcement into the same core material. Hence, there is no need anymore for separate outer layers. Moreover, the cured cement powder turns out to have a lower density than fresh cement and still may be integrated into the core material by virtue of reactions with fresh cement during curing. It was surprisingly found that the resulting core material is moreover homogeneous, as visible with the human eye, and that the pores in the core material turn out to be of the closed cell-type. Preferably at least 80%, more preferably at least 90%, even more preferably at least 95% of the pores are closed cell pores.

[0019] In one preferred embodiment, the amount of cured cement powder is at least 25wt% (i.e. weight per cent) based on dry weight of the core material. More preferably the amount of cured cementitious powder is in the range of 30 to 50 weight%. Good results were obtained with about 40wt%.

[0020] For sake of clarity, the composition referred to hereinabove and in the claims relates to the dry composition as specified prior to curing. Water will be added so as to enable curing. As known to the skilled person, such curing comprises hydration reactions to obtain certain calcium silicates, wherein water is adopted into the cement matrix.

[0021] In a further implementation, the cured cement powder comprises fibers and / or fibrous material. Such cured cement powder particularly originates from fiber cement products and is for instance based on waste generated during production and / or installation. The provision of fibrous material is deemed beneficial in view of its relatively low density, as compared to inorganic powders. The concentration of fibers and / or fibrous material is for instance in the range of 2-10 weight%, based on the dry weight of the cured cement powder. More preferably, the concentration is in the range of 2-6 wt%, such as 3-6 wt%, optionally 4-5 wt%. A higher concentration of fibrous material in the cured cement powder tends to decrease flowability and processability of the cured cement powder during production. Therewith, it limits the maximum amount of cured cementitious powder. The concentration of fibers and / or fibrous material in the cured cement powder may be limited by means of separation steps, especially in combination with grinding steps.

[0022] In an alternative or further embodiment, the core material comprises a first cured cementitious powder comprising fibers and / or fibrous material and a second cured cementitious powder. The second cured cement powder may comprises fibers and / or fibrous material or may be free of fibers and / or fibrous material. Preferably it contains less fibers and / or fibrous material than the first cured cement powder. This second cured cementitious powder may further have a different cement composition than the first cured cement composition. In one further implementation, such second cured cementitious powder may be a cured calcium silicate material, such as tobermorite, vermiculite, xonotlite.

[0023] Preferably, the cured cement powder has a particle size distribution with a d90-value of at most 100 pm as measured by air jet sieving, and a d25 value of at least 4 pm. Said particle size distribution is found appropriate for incorporation of the cured cement powder into the fresh cement matrix formed during curing.

[0024] More preferably, the porous core material has a porosity in the range of 10-20%, more preferably at least 11% by volume. Such a porosity is higher than porosities disclosed for other ways of forming porous cement particles, such as in WO2012 / 149421A1. In the latter prior art, a specific porosity of 9.2 % by volume is reported. In the present technology, a porosity of 13% was detected experimentally. Furthermore, the average pore radius is in the range of 100-140 pm, whereas the prior art specifies an average pore diameter between 20 and 60 pm. This distinct porosity and pore sizes leads to a significantly lower density with an enhanced flexural modulus (SMOR).

[0025] In a suitable embodiment, the composition comprises cement as a binder in an amount in the range of 30-70wt%, preferably 40-60wt%, based on dry weight of the composition. The cement is preferably chosen from calcium sulfoaluminate cement and Portland cement, and more preferably is Portland cement. The use of cement as a binder in combination with cementitious cured powders was found beneficial. For sake of clarity, it is observed that the composition and its weight percentages refer to the composition used for preparation of the core material, and hence prior to curing. In the curing reaction, hydratation of cement occurs and hence water is incorporated into the core material.

[0026] According to an advantageous embodiment, the composition further comprises a cellulose ether, such as hydroxyethylmethylcellulose. Alternative cellulose ethers, such as other hydroxyalkyl alkyl celluloses, wherein alkyl is preferably Ci-C4-alkyl and more preferably Ci-C4-n-alkyl are not excluded. Examples include hydroxymethylmethylcellulose, hydroxypropylmethylcellulose, hydroxyethylethylcellulose, hydroxyethylpropylcellulose, hydroxypropylpropylcellulose. Cellulose ethers are known to retain water and therewith in use to increase the viscosity. The beneficial results of the present technology may be facilitated by the use of the cellulose ether, in that the water retention leads to slower curing and hence extended incorporation of the cured cement powder into the fresh cement matrix. The cellulose ether is suitably present in an amount of at least 1.0 wt%, preferably at least 1.5 wt%, more preferably at least 2.0 wt% based on dry weight of the composition. This concentration is higher than amounts reported for dry construction mixes, such the maximum of 0.75 wt% reported in Yu. Kovalenko et al, Eastern- European Journal of Enterprise Technologies, 105(2020), 28-33.

[0027] It is highly preferred that the present construction board is manufactured by using a foam technology. Thereto, the composition comprises a foaming agent, such as an anionic surfactant. A variety of foaming agents is known per se and furthermore discussed in WO2012 / 149421, which is incorporated by reference for that respect. In addition to a foaming agent, water is used in an amount that exceeds the typical water / cement ratio known for hydratation. Preferably, the water / cement ratio is in the range of 1 to 1.5. Herein, the ratio is a mass ratio. Furthermore, the mass of the cured fiber cement is not included in the cement mass.

[0028] According to a further embodiment, the curing of the core material occurs by means of air-curing. Therewith, the need of transporting the casted uncured (i.e. green) panel to an autoclave, and the high- temperature treatment in the autoclave is avoided. However, autoclave-curing is not excluded, in which case the composition would include both cement and a source of silica such as quartz in appropriate ratios as known per se.

[0029] The fiber reinforcement present in the construction panel is preferably a fiber matt. More preferably, use is made of a glass fiber matt, as known per se. More preferably, a first and a second fiber matt are present in the construction panel, so as to strengthen the panel on both outer sides. This use of fiber matts is deemed to provide an acceptable strengthening at an acceptable price. Nevertheless, it is not excluded that another type of fiber reinforcement is applied in the present technology.

[0030] These and other aspects of the invention will be further elucidated with reference to the Examples and to the Figures. It is observed for clarity that any of the embodiments discussed hereinabove or hereinafter with respect to one aspect of the invention are also applicable to any other aspect of the invention.

[0031] In the Figures:

[0032] Fig. 1 is an optical microscopic picture of a cross-section through the porous core material of the present invention. The x- and y-axis indicate the dimensions of the sample.

[0033] Fig. 2 is a histogram of the pore radius of the pores, as measured using a porosimeter.

[0034] EXAMPLES

[0035] Example 1 - Manufacture

[0036] A test composition was prepared comprising cement, recycled and cured fiber cement powder, a foaming agent, a dispersing agent and a water retention compound. Portland cement (type I) was used as the cement. The cured fiber cement powder was an autoclave-cured fiber cement powder, comprising between 6 and 8 wt% of cellulose fiber. Additionally, the powder was a reaction product from a reaction of quartz with cement in a weight ratio of approximately 1:1, with some addition of aluminum oxide, such as kaolin. The cured fiber cement powder had a particle size entirely or at least substantially below 100 pm, as defined by sieving. 91.0 wt% passed a sieve with 90 pm sieve aperture, 85.2wt% passed a sieve with 63 pm sieve aperture, and 76.9 wt% passed a sieve with 40 pm sieve aperture. Median (50volume%) lies at 26 pm and the 10%-limit at 2.5 pm (check, 90% is in the graph of Kristof report at 200 pm, quite different from the report of Joyce). Bulk density of the fiber cement powder was 0.57 kg / dm3.1The foaming agent is a mix of anionic surfactants, commercially available as a liquid air entrainer for concrete and other cement based systems, with recommended use level of 0.01- 0.5wt%. The dispersion agent is an admixture based on modified polycarboxylic ether (PCE) polymers, obtained from BASF as Masterglenium 51. The water retention compound was a cellulose ether. In this

[0037] 1Data from report R2019032959 annexes (J. Mareels) example, use was made of a modified hydroxyethyl methyl cellulose (HEMC) obtained from Dow as Walocel with a viscosity of 50000 mPa.s and a neutral pH. The experimental composition is shown in Table 1.

[0038] Table 1; dry test composition.

[0039] In a first example, water was added in a ratio of water to Portland cement of 1.15. In a second example, water was added in a ratio of water to Portland cement of 1.26. The dry test composition and the water were mixed to obtain a homogeneous slurry mixture.

[0040] The resulting slurry was applied in a mould in which a first and a second glass fiber mat were provided on a top and a bottom side. The glass fiber mat was a glass-fiber mesh (scrim) supplied from Chomarat, type Rotatex G1100N. The scrims have a surface weight of 123 g / m2and a mesh size of 2.5mm x 3.0mm. To make the scrims alkali resistant, a PVC coating (70 g / m2) is added to the glass fibre yarn (53 g / m2). The glass fiber matts were arranged in a manner that they are incorporated in the slurry, and at a distance of approximately 1 mm to the bottom and the top surface of the resulting plate. The mould had a top surface of 200 x 240 mm2.

[0041] After casting of the slurry into the mould with the glass fiber matts, the composite is post-compressed using an electrical mechanical press. The post-compression force is adapted to obtain a final sample thickness of ca. 12.5mm.

[0042] Example 2 characterization of mechanical properties

[0043] Tests were performed to identify mechanical properties of the plates manufactured in accordance with Example 1. Results thereof are listed in Table 2. For comparison, a commercially available fiber cement product sold as Aquapanel™ Interior by Knauf Aquapanel GmbH was tested (herein also referred to as Refl). This is a board made in accordance with a so-called semi-dry method and includes a core and two outer layers. The glass mesh is included in the outer layers. The fresh individual layers are herein board is then post-compressed to arrive at a thickness of approximately 12.5. Manufacturing method of such a board is disclosed in EP1981826B1. As mentioned therein, the inner core comprises about 24 weight% of Portland cement, about 10 weight% of hydrophobated expanded perlite with a grain size in the range of 0.1-3 mm and about 50% calcium carbonate (limestone mehl), with remainder being humidity. The outer layer comprises Portland cement and calcium carbonate in a weight ratio of 1:3, with the remainder of the glass fiber matt and humidity. As a further reference (herein referred to as Ref 2), values are taken from WO2012 / 149421A1. The modulus of rupture (MOR, typically expressed in Pa = kg / m2.s) of each of the samples was measured by making use of a UTS / INSTRON apparatus (type 3345, cel = 5000N). The limit of elastic deformation (IMOR, J / m2) were measured by making use of a UTS / INSTRON apparatus (type 3345, cel = 5000N) with software Bluehill by Instron (Norm EN12467 and related norms). Table 2 specifies test results.

[0044] Table 2 - test results

[0045] Example 3 characterization of microstructure

[0046] A characterization on the microstructure was performed using a Keyence 3D Optical Profilometer KEYNCE VR-5000. Thereto, a sample as obtained from Example 1 was cut through to obtain a crosssection. Fig. 1 shows an optical image. The pores are of a closed-cell type, as far as identifiable visually and under a microscope. The pore distribution appears homogeneous, as a consequence of the manufacturing process using a foaming additive. The pore size in a bottom layer is substantially equal (i.e. not much smaller) than pore size of a top layer. This indicates that the foam was stable during manufacture, resulting in a stable mixture such that the foam bubbles did not coagulate and diffuse towards the top of the mixture. This implies that the foam mixture can be used in a casting process.

[0047] Four different areas of the surface created by cutting were analysed by the profilometer. Each of the areas had a size of 21x27.8 mm (583.8 mm2). The total number of pores in the four areas was 6150. A threshold was set to -0.050 mm, which means that any feature with a depth of less than 50 microns was not included. Pores with a cross-sectional area of less than 0.003 mm2(3000 pm2) were not included either. This setting reduces the noise considerably.

[0048] Porosity was calculated as the sum of the cross-sectional areas measured for each pore divided by the total surface area of the four areas. Since the pore density is random and homogeneous, the porosity in the cutting plane can be assumed to be representative for the overall porosity.

[0049] Pore size distribution was calculated on the basis of the measured maximum pore depth (dmax) and the measured pore volume Vp. This was done for each pore separately. Use was made of the formula for the determination of the radius for a spherical cap: Vp= (l / 3)n(3rb - dmax)dmax2, with R the radius, i.e. half the pore diameter. After reworking, this leads to rb = 1 / 3 * (3 * Vp / (n.dmax2) + dmax)• Herein, dmaxis chosen to be positive rather than negative. The calculation assumes spherical pores.

[0050] Based hereon, a porosity of 13.2 % was found, and an average pore radius of 115 pm. Averaging of the horizontal feret generated by the software of the porosimeter, the average pore radius is 117 pm.

Claims

Claims1. A construction panel comprising- a porous cured core material having a density in the range of 0.75 to 0.95 kg / dm3and provided with a composition comprising a set inorganic binder and cured cement powder, wherein the cured cement powder is present in an amount of at least 20wt% based on dry weight of the composition, and- a fiber reinforcement embedded in the core material.

2. The construction panel as claimed in claim 1, wherein said cured cement powder has a particle size distribution with a d90-value of at most 100 pm as measured by air jet sieving, and a d25 value of at least 4 pm.

3. The construction panel as claimed in claim 1 or 2, wherein said cured cement powder comprises fibrous material in an amount of 2-10wt%, preferably 3-6 wt% based on dry weight of the cured cement powder.

4. The construction panel as claimed in any of the preceding claims, wherein said porous material has a porosity in the range of 10-20%.

5. The construction panel as claimed in claim 1-4, wherein said porous material has an average pore size in the range of 100-140 pm.

6. The construction panel as claimed in any of the preceding claims, wherein the composition comprises cement as a binder in an amount in the range of 30-70wt%, preferably 40-60wt%, based on dry weight of the composition, wherein the cement is preferably chosen from calcium sulfoaluminate cement and Portland cement, and more preferably is Portland cement.

7. The construction panel as claimed in any of the preceding claims, particularly claim 6, wherein the composition comprises cured cement powder in an amount of 30-50wt%, based on dry weight of the composition.

8. The construction panel as claimed in any of the preceding claims, further comprising a cellulose ether, such as hydroxyethylmethylcellulose.

9. The construction panel as claimed in claim 8, wherein the cellulose ether is present in an amount of at least 1.0 wt%, preferably at least 1.5 wt%, more preferably at least 2.0 wt% based on dry weight of the composition.

10. The construction panel as claimed in any of the preceding claims, wherein the core material is aircured.

11. The construction panel as claimed in any of the preceding claims, wherein the reinforcement is provided as at least one fiber mat, preferably comprising glass fibers.

12. Method of manufacturing a construction panel having a density in the range of 0.75 to 0.95 kg / dm3, comprising the steps of:- providing an aqueous composition comprising an inorganic binder, such as cement, and cured cement powder and a foaming agent, wherein the cured cement powder is present in an amount of at least 20wt% based on dry weight of the composition, and- providing a fiber reinforcement, for instance in the form of a fiber mat;- casting the composition into a mould, with the fiber reinforcement being embedded therein;- curing the composition into a core material of the construction panel, for instance by means of aircuring.

13. The method as claimed in claim 12, wherein the foaming agent is an anionic surfactant.

14. The method as claimed in claim 13, wherein water is present in the slurry in a ratio of water to inorganic binder in the range of 1 to 1.5.

15. The method as claimed in claim 12-14, wherein the composition further comprising cellulose ether, preferably in an amount of at least 1.0 wt% based on dry weight of the composition.

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