JP2024501615A - Production of plaster moldings on a cycle press machine using grinding waste - Google Patents

Abstract

The present invention is a method for producing a gypsum molded body, comprising the steps of (i) providing a mixture containing a) grinding waste obtained from a gypsum fiber product, b) fibers, and c) water; (ii) putting the mixture or a part thereof into a mold and pressing the mixture with a press to form a gypsum molded body; (iii) drying the formed gypsum molded body; a) The total weight of the grinding waste and b) recycled paper fibers is 80% to 100% by weight of the solid weight of the mixture, and the mass ratio of a) grinding waste to b) recycled paper fibers in the mixture is (a:b) ) is in the range of 25:1 to 5:1. The invention also relates to the mixture used in the method, the gypsum moldings obtainable by the method, and the use of the grinding waste for the production of gypsum moldings.

Description

The present invention relates to a method for producing gypsum moldings, in particular gypsum fiberboard, in which grinding waste of gypsum fiber products is used. The invention furthermore relates to the mixture used in the method, the gypsum moldings obtainable by the method, and the use of the grinding waste for the production of gypsum moldings.

The production of gypsum fiber products often results in the formation of grinding debris as a waste product. This grinding debris is generated, for example, when a gypsum product is subjected to finishing that includes surface grinding and/or sawing. Until now, grinding debris has mostly been disposed of as waste in landfills.

A method of manufacturing a gypsum molded body using a cycle press machine is a conventional technique. Generally, hydratable gypsum, derived from gypsum raw materials, is used as a binder in these methods.

U.S. Pat. No. 5,632,848 describes an apparatus for continuous processing of board-like products containing gypsum, such as fiberboard and wallboard, in which waste-type material is considered the source of calcium sulfate. ing. As an example, US Pat. No. 5,632,848 mentions the conversion of scrap gypsum wallboard by grinding and baking to obtain a suitable starting material.

European Patent No. 0490160 (A1) describes a method for manufacturing a plate-shaped or block-shaped gypsum building material with a pore structure, in which calcium sulfate α-type hemihydrate, water and Optionally, additives are mixed in to form a pourable slurry, which is then subjected to a suitable molding process. Grinding waste from the production of gypsum building materials can be reused for the production of slurry.

German Patent Application No. 41 27 932 (A1) describes a method for producing fiber-reinforced gypsum board in a multilayer continuous filtration process by adding a suspension of gypsum and wet-processed fibers, preferably from waste paper. and related to equipment. The grinding waste obtained in this process can be reused by feeding the grinding waste to a sintering plant, where the grinding waste is converted into reusable material.

WO 2017/098482 (A1) describes the production of molded articles, such as slabs, by pressing non-stick, free-flowing granular cementitious or gypsum-based precursor compositions. The gypsum-based precursor composition includes calcium sulfate hemihydrate, water, guar gum and/or hydrolyzed polyvinyl alcohol, and a gelling agent. Since the binder system is organic based, no separate drying step is required. A hydraulic press machine is used for pressing.

WO 2019/001677 (A1) refers to a method of manufacturing a gypsum slurry and a method of manufacturing a gypsum product such as a gypsum board using the gypsum slurry. The gypsum slurry may include a wet ground gypsum paper component and stucco, and the solids content of the wet ground gypsum paper component relative to the stucco may be from 0.5% to 10% by weight.

The drawbacks of traditional methods for preparing gypsum products, considering the use of wastes generated during the production of gypsum products such as grinding waste, are that the grinding waste is subjected to energy-consuming calcination for activation. It is something that can be done. In other methods, only a relatively small proportion of the grinding debris is added to the new raw material, such as stucco, for example, the grinding debris produced in the process is added directly for reuse. As a result, most of the generated grinding debris has traditionally been disposed of as waste in landfills.

It is therefore an object of the present invention to provide a method for preparing gypsum products in which a large part of the grinding waste of the gypsum fiber products can be recycled without requiring a prior energy-intensive calcination treatment. there were.

In the research underlying the present invention, it was unexpectedly found that these objects could be achieved by a method for producing plaster moldings by using a mold press and grinding waste of a specific composition.

The invention therefore relates to the method according to claim 1, as well as the mixtures used therein, the corresponding gypsum moldings obtainable by the method according to the invention, and the use according to the further independent claims. Preferred embodiments of the invention are set out in the dependent claims.

Therefore, the present invention is a method for manufacturing a gypsum molded body, comprising:
(i)
a) Grinding waste obtained from gypsum fiber products;
b) fiber;
c) providing a mixture comprising water;
(ii) placing the mixture or a portion thereof in a mold and pressing the mixture with a press to form a gypsum molded body;
(iii) a step of drying the gypsum molded body,
In the mixture provided in step (i),
The total weight of a) grinding waste and b) fibers is 80% to 100% by mass of the solid weight of the mixture,
the mass ratio (a:b) of a) grinding waste to b) fibers is in the range of 25:1 to 5:1;
Regarding the method.

An advantage of the invention is that the grinding waste of fiber gypsum products can be recycled to a large extent without requiring a prior energy-intensive firing process. Waste disposal can be avoided. This is environmentally friendly and advantageous from an economic point of view. In addition, a further improved flexural tensile strength could be unexpectedly observed for the plates produced by the method of the invention compared to plates obtained by conventional methods.

The method of the present invention is for producing a gypsum molded body. The gypsum molding may be any article known to those skilled in the art. Each of the manufactured plaster moldings is preferably a gypsum fiberboard, in particular a gypsum fiberboard for raised floors or raised floor elements.

The dimensions of the plaster molding can vary depending on the intended use. As standard dimensions for gypsum fiberboard (or gypsum plasterboard), for example, the following ranges can be given: thickness 10 mm to 42 mm, width 1000 mm to 1250 mm, length 1500 mm to 3000 mm. The width and length of the raised floor element are generally small, for example both independently in the range 300mm to 800mm, preferably 620mm, more preferably 600mm, and the thickness can be in the range 28mm to 45mm. . If required, smaller (eg 20 mm) or larger dimensions are of course possible.

The method of the present invention comprises (i)
a) Grinding waste obtained from gypsum fiber products;
b) fiber;
c) providing a mixture comprising water;

Mixtures are obtained by mixing the essential components and optionally further components with each other. Any suitable mixing equipment can be used. Preference is given to using high performance mixers, such as Eirich mixers or forced mixers. A forced mixer is preferred because it provides a stronger granulation effect. Furthermore, the mixing time can be shortened and the homogeneity of the mixture is improved.

The order of addition of the components is arbitrary. Generally, the grinding waste and fibers are mixed in a mixer until a homogeneous premixed dry mixture is obtained (for example, a duration of 1 to 3 minutes), followed by the addition of water to achieve a suitable dispersion. Further mixing (for example for a duration of about 1 minute to 5 minutes depending on the mixer used) is suitable. One or more further additives, particularly retarders, may be added to the system in dry or liquid form at any suitable point in the mixing operation.

The mixture is preferably mixed until a soil wet consistency is achieved, ie the mixture is preferably a soil wet mixture. The term "soil wet consistency" is not clearly defined, but is known to those skilled in the art. Those skilled in the art know that the correct addition of water is important for processing properties and for obtaining the required properties of the cured mixture, such as flexural tensile strength. Soil wet consistency can therefore be tested with a simple and practical test, the so-called snowball test. This test can be performed by forming a snowball-like clod in your hand. If such clods cannot form, the mixture may be too wet. The snowballs should not collapse when you open your hand, if they do, the mixture is too dry. A slight adhesion of the mixture should remain on the hands. A snowball may exhibit a slight sheen on its surface due to a thin film of liquid.

Component a) is grinding waste obtained from gypsum fiber products. The fibers in the gypsum fiber product are paper fibers, recycled paper fibers, glass fibers, chopped glass fibers, cellulose fibers, wood fibers, mineral fibers, plastic fibers, or combinations thereof, preferably paper fibers, recycled paper fibers, or these. It may be a combination of The grinding debris may be waste products generated in the manufacture of gypsum fiber products. The gypsum fiber product from which the grinding waste is derived may be a paper fiber reinforced gypsum product, preferably a gypsum fiberboard, ie the grinding waste is preferably obtained from the production of gypsum fiberboard.

Gypsum fiberboard can generally be gypsum board with fibers. Fibers include all types of fibers, such as paper fibers, recycled paper fibers, glass fibers, chopped glass fibers, cellulose fibers, wood fibers, mineral fibers, plastic fibers, or combinations thereof, preferably paper fibers, recycled paper fibers. , or a combination thereof.

In a preferred embodiment, the grinding chips are obtained from surface grinding and/or sawing of gypsum fiber products, in particular gypsum fiberboard. Surface grinding includes grinding the surface and/or edges of a product. Grinding and/or sawing operations are typically performed during the finishing step during manufacturing after the gypsum fiber crude product has been formed. Surface grinding may be suitable, for example, to smooth the surface and/or to remove defects such as burrs. Sawing may be suitable, for example, to cut the product into desired dimensions and/or configurations.

The grinding chips used can be obtained from surface grinding (grinding chips) or from sawing (grinding chips) or a mixture thereof. Preferably, 60% to 100% by weight, preferably 90% to 100% by weight of the grinding waste is (grinding waste) obtained from surface grinding of gypsum fiber products. It is more preferable that the grinding waste is obtained from surface grinding (grinding waste).

Grinding waste from gypsum fiber products has the composition of the gypsum fiber product from which it is derived. Since gypsum fiber products harden during manufacture, the specific composition may also depend on the point at which the grinding debris is produced.

It is also clear that the grinding chips are added to the mixture, ie in uncalcined form. As known to those skilled in the art, calcination is the dehydration of gypsum primarily into calcium sulfate hemihydrate (also called plaster or stucco), which involves heating the gypsum, usually at a temperature of at least 120°C. It involves evaporating most of the water of crystallization. Here, calcination of the grinding chips is not necessary since calcium sulfate hemihydrate is produced during the drying process (to remove excess water) of the gypsum fiber product from which the grinding chips are derived. Preferably, during the drying process of the gypsum fiber product from which the grinding debris is derived, calcium sulfate hemihydrate is formed on the surface of the gypsum fiber product. Therefore, the hemihydrate content in the grinding chips obtained from surface grinding may be higher than the hemihydrate content in the grinding chips obtained from sawing.

In a preferred embodiment, the grinding waste contains 40% to 90% by weight, preferably 60% to 80% by weight of calcium sulfate, based on the weight of the grinding waste excluding the weight of fibers contained in the grinding waste. Contains hydrates.

The term "based on the mass of the grinding waste excluding the mass of the fibers contained in the grinding waste" means that the fibers contained in the grinding waste are not taken into account. For example, in the case of grinding waste containing 10% by mass of fibers, the remaining 90% serves as the basis for calculation (100%).

Due to the above-mentioned high proportion of hardenable calcium sulfate hemihydrate, energy-intensive calcinations are no longer necessary in the inventive production method for gypsum moldings such as raised floor elements. A high proportion of hemihydrate also improves the flexural tensile strength of the product. The production of gypsum moldings according to the invention is therefore not only cheaper than traditional methods, but also environmentally friendly due to the elimination of energy-intensive firing steps.

The grinding waste contains fibers, preferably paper fibers, especially recycled paper fibers. In a preferred embodiment, the grinding waste comprises from 6% to 15% by weight, preferably from 8% to 13% by weight, based on the total weight of the grinding waste, of fibers, preferably paper fibers, especially recycled paper fibers.

In a preferred embodiment, the grinding waste is based on the mass of the grinding waste excluding the mass of fibers contained in the grinding waste.
60% by mass to 80% by mass of calcium sulfate hemihydrate;
10% by mass to 30% by mass of calcium sulfate dihydrate,
7% by mass to 12% by mass of anhydrite.

The grinding waste may also contain calcite (CaCO ₃ ) and/or quartz, usually both in trace amounts.

Component b) is a fiber.

The fibers are paper fibers, recycled paper fibers, glass fibers, chopped glass fibers, cellulose fibers, wood fibers, mineral fibers, plastic fibers, or combinations thereof, preferably paper fibers, recycled paper fibers, or combinations thereof. good.

The total weight of a) grinding waste and b) fibers is from 80% to 100% by weight, preferably from 90% to 10% by weight of the solid weight of the mixture.

The mass ratio (a:b) of a) grinding debris to b) fibers in the mixture ranges from 25:1 to 5:1, preferably from 15:1 to 7:1. It should be noted that the fibers contained in the grinding waste belong to component a) and are assigned to component a) with respect to this proportion.

Component c) is water.

In order to obtain a favorable mixture in step (i) with a specific soil wet consistency, fairly small amounts of water are suitable. In a preferred embodiment, the mass ratio ((a+b)/c) of the total mass of a) grinding waste and b) fibers to the mass of c) water is between 0.3 and 0.9, preferably between 0.4 and 0. The range is 8.

Due to the low water content of the mixture, a correspondingly reduced drying energy is required, which is a further advantage of the invention.

In the method according to the invention, the mixture may optionally contain one or more additives known to the person skilled in the art. Examples of optional additives are retarders, blowing agents, accelerators, and/or further plaster types such as stucco and/or from different sources.

In a preferred embodiment, at least one retarder is added to the mixture. Examples of suitable retardants are protein sources containing amino acid oligomers or synthetic compounds mimicking them, chelates such as DTPA and EDTA, or polyacrylic acid compounds. An example of a commercially available product is Retardan® P from Sika, which is a Ca salt of polycondensed amino acids.

The total amount of additives, preferably at least one retarder, is preferably less than 20% by weight, more preferably less than 10% by weight, based on the solids weight of the mixture.

The method of the present invention includes the steps of (ii) placing the mixture provided in step (i) or a portion thereof in a mold and pressing the mixture with a press to form a gypsum molded body.

In particular, the process is a discontinuous process, ie each plaster molding is formed one after the other. The mixture may be prepared in an amount sufficient to prepare one gypsum molding or two or more gypsum moldings. In the latter case, of course, only part of the mixture is used to prepare the shaped body.

The mold used obviously depends on the shape and dimensions of the shaped body to be produced. Generally, a simple box, for example a metal box, is suitable. The mold is arranged in cooperation with the press used. The mixture or a portion thereof is placed into a mold, for example by pumping or injection. It is appropriate to uniformly distribute the mixture in the mold before pressing.

The mixture placed in the mold is then pressed by a press to form a plaster molding. The press may be a hydraulic press. The press is preferably a cycle press, especially a hydraulic cycle press. Suitable hydraulic cycle press manufacturers are, for example, Bussmann or Siempelkamp.

Generally, the pressing process with a press, especially a cycle press, is carried out by pressing a movable ram from above onto a fixed support surface. The mold can be attached to a support surface. Suitable discharge means may be fitted to enable drainage of water that may escape from the press body during the pressing process.

For example, a plastic plate can be attached both to the underside of the ram and to the top of the support surface, this plastic plate being provided with rectangular depressions as drainage channels. Water can collect in these depressions, and the water may be actively drawn into the depressions by the applied negative pressure and supplied to the water circuit of the production line via a drain pipe.

The press is preferably at sufficiently high pressure to achieve compaction or compaction of the formed gypsum compact. As a result, increased bulk density is obtained.

The pressure applied to the mixture in the mold by the press may be in the range, for example, from 0.9 kg/mm ² to 4.0 kg/mm ² , preferably from 1.1 kg/mm ² to 2.0 kg/mm ² .

The duration of pressure application may range from 20 seconds to 240 seconds. Longer or shorter durations are also possible.

The bulk density of the resulting gypsum molded body, in particular gypsum fiberboard, may be, for example, in the range 1100 kg/m ³ to 1900 kg/m ³ , preferably in the range 1200 kg/m ³ to 1700 kg/m ³ . According to a preferred embodiment, the gypsum molding or the gypsum fiberboard are respectively raised floor elements. Due to high loads during pressing, compressed gypsum fiberboard with a high bulk density, for example in the range 1400 kg/m ³ to 1700 kg/m ³ , preferably in the range 1500 kg/m ³ to 1650 kg/m ³ , suitable as a raised bed.

After completion of the pressing operation, the (formed) gypsum molded body is dried in step (iii). Drying results in hardening or hardening of the product.

The (formed) plaster molding can be removed from the mold before, during or after the drying process. The drying step may be carried out at ambient conditions, for example at a temperature of 15° C. to 40° C. and an air atmosphere. Heating is possible if desired. In order to obtain a product of uniform quality, it may be appropriate to dry the shaped plaster body under standardized conditions with respect to temperature, atmosphere and humidity. Preferably, the plaster molding is dried to constant weight. Dryers adapted or designed to provide relatively low residual moisture in the shaped gypsum body are preferred.

An optional further step may be (iv) finishing the prepared plaster molding. Finishing preferably includes grinding of the surface and its edges, ie surface grinding and/or sawing. The grinding waste obtained in step (iv) can be reused as the grinding waste in step (i). The finishing process is common to these products. Finishing may be performed after step (iii).

The present invention also provides a mixture for producing a gypsum molded body, comprising:
a) Grinding waste gypsum fiber products;
b) fiber;
c) contains water;
The total weight of a) grinding waste and b) fiber is 80% to 100% by weight of the solid weight of the mixture, and the mass ratio (a:b) of a) grinding waste to b) fiber is 25 : in the range of 1 to 5:1,
Concerning mixtures.

The present invention also relates to a gypsum molded body obtainable by the above-described method of the present invention.

The invention also relates to the use of grinding waste of fiber gypsum products as starting material for the production of gypsum moldings, in which case the grinding waste is used in uncalcined form.

All method steps, materials, characteristics and descriptions relating to the above-mentioned method apply equally to the mixture according to the invention, the gypsum molding according to the invention and the use according to the invention, to which reference is made, if applicable. .

In the following, the invention is further illustrated by examples, which should not be construed as limiting the scope of the present application in any way.

General procedure for the manufacture of the panels The press used is a hydraulic cycle press from the manufacturer Bussmann. The press ram can apply a maximum press pressure of 87 kg/ ^cm2 . To form the panel, a steel forming box is attached to the support surface. The internal dimensions of the molding box are 610-610-200 ^mm3 . In order to drain any water that may leak from the press body during the pressing process, a plastic plate is installed both on the underside of the ram and on the top of the support surface, and this plastic plate has a rectangular depression as a drainage channel. including. Water collects in these depressions, is actively drawn into the depressions by the applied negative pressure, and is supplied to the water circuit of the production line via drain pipes.

Grinding debris produced in the manufacture of gypsum fiberboard can be used during surface polishing of the board surface. The polishing waste includes, for example, about 60% to 80% by weight of calcium sulfate hemihydrate, 10% to 30% by weight of calcium sulfate dihydrate, and 7% to 12% by weight of calcium sulfate anhydrous. It may contain gypsum and trace amounts of calcite (CaCO ₃ ) and quartz. The percentages given are based on the total weight of the grinding waste excluding the mass of paper fibers contained in the grinding waste. In this regard, the grinding waste contains about 10% by weight of recycled paper fibers, based on the total weight.

The grinding waste (approximately 90% by weight) and the waste paper fibers (approximately 10% by weight) are predried in a high-performance mixer (for example an Eirich mixer or a forced mixer) until a homogeneous mixture is obtained (duration approximately 120 seconds).

The retarder can be added to the system in dry or liquid form. After subsequent addition of water (water-solids value approximately 0.6), the mixture is mixed until the specified soil wet consistency is achieved (approximately 2 to 3 minutes depending on the mixer used).

This material is pressed into panels using a cycle press machine. For this purpose, the material is placed in a forming box of 610 x 610 x 200 mm ³ , distributed evenly and pressed at a pressure of 0.87 kg/mm ² (corresponding to the maximum capacity of the used press machine 300 bar) . After the pressing process, the boards were dried under air in the laboratory or test factory.

For production on an industrial scale, the manufacturing process may be modified accordingly, in particular with respect to the finishing of the stampings (eg grinding of surfaces and edges).

The following examples are performed according to this general procedure, unless corrections or more precise specifications are indicated below.

Sample Grinding chips are generated during the manufacture of gypsum fiberboard, surface grinding chips are obtained from surface grinding, and sawing chips are obtained from sawing. The HH ratio refers to the amount of calcium sulfate hemihydrate in the grinding waste, based on the mass of the grinding waste excluding the mass of paper fibers contained in the grinding waste. Differences in the amount of hemihydrate in the grinding chips are due to the different products from which the grinding chips are derived, the different thicknesses of the surfaces to be ground on these different products, the different drying conditions, and the amount of grinding obtained from surface grinding. This is due to the (undetermined) mixing ratio between the scraps and the grinding chips obtained from sawing.

The following starting materials are used to prepare the panels.

Stucco: Stucco manufactured by Knauf Gips KG GD1: Mixture of surface grinding waste and sawing waste, HH ratio 44.5% by mass.
GD2: Mixture of surface grinding waste and sawing waste, HH ratio 34.6% by mass.
GD3: Mixture of surface grinding waste and sawing waste, HH ratio 6.7% by mass.
Vinnapas EP 3360 Aqueous polymer dispersion prepared from vinyl acetate and ethylene Retardan P Ca salt of polycondensed amino acids, Sika

The following formulations shown in Table 1 are used to prepare the panels.

Sample 2 is according to the invention. Samples 1, 3 and 4 are reference examples. The drying temperature was 40°C. Sample 1 is a typical formulation according to the prior art.

The sample 1 mixture shows a significant granulation effect. One test plate of Sample 1 was destroyed during demolding.

The mixtures of samples 2 and 3 show a significant granulation effect, but the granules are homogeneously moistened.

Panels were prepared according to the general procedure described above. Two test plates (600 x 600 x 20 mm ² ) were prepared for each formulation, two small pieces (400 x 300 mm ² ) were cut from each of these test plates and the samples (for the formulation of sample 1: sample 1_1 , 1_2, etc.). The parameters shown in Tables 2 and 3 below were determined according to EN 15283-2:2009-12. Table 2 contains values for specimens based on Samples 1 and 2 (invention), and Table 3 contains values for specimens based on Samples 3 and 4.

The flexural tensile strength of both samples 1 and 2 meet the requirements of the standard (≧5.5 N/mm ² ), and the flexural tensile strength of inventive sample 2 is higher than that of reference sample 1. The cause of this unexpected result is unknown. The flexural tensile strengths of both samples 3 and 4 do not meet the requirements of the standard.

The flexural tensile strength of plates prepared using grinding chips appears to depend on the proportion of HH contained in the grinding chips.

Surface Grinding Analysis Ten samples of grinding debris obtained from surface grinding were collected in a plant manufacturing gypsum fiberboard on different products. The hemihydrate content of the samples was determined by X-ray diffraction. For the values given in Table 4 below, paper fibers contained in the samples were not taken into account.

^* Samples were collected at different times.

The hemihydrate content is high and the variation is relatively small (63.7% to 79.3%), with minimal variation within the same product. Significantly more Contains HH. The variation between different products is significantly low.

Hemihydrate proportions of up to 90% have even better results, since the hemihydrate acts as a binder in the system (by reacting with water to form calcium sulfate dihydrate). is expected and therefore a higher stability (eg flexural tensile strength) of the plaster molding is expected.

Claims (15)

A method for producing a gypsum molded body, the method comprising:
(i)
a) Grinding waste obtained from gypsum fiber products;
b) fiber;
c) providing a mixture comprising water;
(ii) placing the mixture or a portion thereof in a mold and pressing the mixture with a press machine to form the gypsum molded body;
(iii) drying the gypsum molded body,
In the mixture provided in step (i), the total weight of a) the grinding waste and b) the fibers is 80% to 100% by weight of the solid weight of the mixture, and a) the grinding waste b) the mass ratio (a:b) of the fibers is in the range of 25:1 to 5:1;
Method. The method of claim 1, wherein the press is a cycle press. The grinding waste is obtained from surface grinding and/or sawing of the gypsum fiber product, and 60% to 100% by weight, preferably 90% to 100% by weight of the grinding waste is on the surface of the gypsum fiber product. 3. A method according to claim 1 or 2, preferably obtained from grinding, and wherein the grinding debris is more preferably obtained from surface grinding. The grinding waste contains 40% to 90% by weight of calcium sulfate hemihydrate, preferably 60% to 80% by weight, based on the mass of the grinding waste excluding the mass of the fibers contained in the grinding waste. % by weight of calcium sulfate hemihydrate, and/or the grinding waste contains from 6% to 15% by weight, preferably from 8% to 13% by weight, based on the total weight of the grinding waste, Process according to any one of claims 1 to 3, preferably comprising paper fibres, in particular recycled paper fibres. The grinding waste contains 60% to 80% by mass of calcium sulfate hemihydrate and 10% to 30% by mass, based on the mass of the grinding waste excluding the mass of the fibers contained in the grinding waste. of calcium sulfate dihydrate and 7% to 12% by weight of anhydrite. Claim: The gypsum fiber product from which the grinding waste originates is a gypsum fiberboard, and/or the gypsum molded body produced is a gypsum fiberboard, in particular a gypsum fiberboard for raised floors. The method according to any one of 1 to 5. In the mixture provided in step (i), the mass ratio ((a+b)/c) of the total mass of a) the grinding waste and b) the fibers to c) the mass of water is between 0.3 and 0.9. , preferably in the range from 0.4 to 0.8. said mixture further comprises one or more additives, preferably at least one retarder, the total amount of additives being less than 20% by weight, preferably less than 10% by weight, based on the solid weight of said mixture The method according to any one of claims 1 to 7. A method according to any one of claims 1 to 8, wherein the grinding waste is added to the mixture in uncalcined form. The method according to any one of claims 1 to 9, further comprising the step of (iv) finishing the plaster molding comprising grinding and/or sawing of the surface and edges of the prepared plaster molding. A mixture for the production of gypsum moldings, comprising:
a) Grinding waste of gypsum fiber products;
b) fiber;
c) contains water;
The total weight of a) the grinding waste and b) the fiber is 80% to 100% by weight of the solid weight of the mixture, and the mass ratio (a:b) of a) the grinding waste to b) the fiber is , in the range of 25:1 to 5:1,
blend. A mixture according to claim 11, wherein the mixture is as described in any one of claims 3 to 9. A gypsum molded body obtained by the method according to any one of claims 1 to 10. Use of grinding waste of gypsum fiber products as starting material for the production of gypsum moldings, wherein said grinding waste is used in uncalcined form. Use according to claim 14, wherein the grinding waste is as described in any one of claims 3 to 6.