HYDROPHOBIC MORTAR COMPOUND

Description

Technical field of the invention

[0001] The present invention relates to an additive for gypsum-based binder systems for reducing water absorption in set systems. State of the art

[0002] Gypsum-based binders were used primarily in mortar and screed applications from the early Middle Ages onward. Unlike today, their application was not limited to interior use, but also included use in exposed masonry. Many historic buildings constructed of calcium sulfate-based building materials in Germany are located in the immediate vicinity of gypsum deposits, such as the Harz Mountains, the Thuringian Basin, Franconia, and the limestone mountains near Lüneburg in Lower Saxony and Bad Segeberg in Schleswig-Holstein. This is described, for example, in: Tesch, V: Structure-optimized repair mortars based on calcium sulfate for outdoor use, Building Materials and Solid Construction Series, Issue 6, Dissertation, Kassel, 2006 .

[0003] Particularly critical when using gypsum binders in construction is the high solubility of 2.14 g / l (at 20°C) compared to other mineral building materials (as described in: https: / / www.salzwiki.de / index.php / Gips, accessed 07.01.2021). This property actually precludes the use of gypsum binders outdoors, but historical gypsum mortars nevertheless exhibit enormous durability, exceeding that of today's mortar systems. Unfortunately, no documentation on the production and formulations of these historical systems has survived. Only comparative SEM images were taken as part of a dissertation. These show a clear difference in the microstructure of the historical and contemporary gypsum mortars. The historical mortar has much coarser gypsum crystals than today's mortar.

[0004] Despite their greater durability, even the historic gypsum binders require repair over time, as moisture can penetrate the masonry through gaps and cracks. This leads to increased loosening, which can quickly compromise the stability of the structure.

[0005] During the last century, the reaction mechanism of subsequent ettringite formation was still unknown, so cementitious binder systems were routinely injected into gypsum-containing masonry. This ettringite formation can be chemically described as follows: 3CaO • Al 2 O 3 • 6H 2 O + 20H 2 O + 3(CaSO 4 • 2H 2 O) → 3CaO • Al 2 O 3 • 3CaSO 4 • 32H 2 O Calcium aluminate hydrate (cement) + water + gypsum → ettringite

[0006] This reaction is accompanied by a volume increase of approximately 4.8%, which causes lasting damage to the masonry instead of repairing it. If the systems were fully integrated into the existing building, not only is the structural stability compromised, but in most cases the building can hardly be renovated and only at enormous expense and time. A well-known example of improper repair is the Runneburg Castle in Weissensee (Thuringia, Germany). Due to the consequences of subsequent ettringite formation, the residential tower had to be secured with a steel corset (see: Eckart, A.: Findings / Damage to Historical Building Structures: Natural Walls / Historical Bricks, lecture notes, Weimar, 2017). ).

[0007] In addition to the formation of ettringite, thaumasite can also form in the simultaneous presence of cement and gypsum. However, this reaction is more problematic in a cementitious building material system, as the strength-forming CSH phases of the cement paste are decomposed, potentially weakening the entire component and significantly compromising its stability. Nevertheless, this phenomenon must also be considered when renovating gypsum-containing masonry, especially if incompatible cementitious binders were used in the past. Thaumasite forms preferentially at temperatures below 15 °C, whereas ettringite remains stable at temperatures up to 70 °C. In addition to cement and gypsum, carbonate reactants are also necessary for the formation of thaumasite (see: Eckart, A.: Findings / Damage to Historical Building Structures: Natural Walls / Historical Bricks, lecture notes, Weimar, 2017). ):3CaO • 2SiO 2 • 3H 2 O + 24H 2 O + 2CaSO 4 • 2H 2 O + 2CaCO 3 → 2(CaSiO 3 • CaSO 4 • CaCO 3 ) • 15H 2 O + Ca(OH) 2 CSH phase (cement) + water + gypsum + lime → thaumasite

[0008] Exact data on the number of historic buildings constructed of gypsum masonry is currently unavailable. However, there are approximately 1.3 million listed buildings in Germany, of which at least a third are estimated to be endangered or in need of renovation. Presumably, about 10% of these are made of gypsum (this figure is based on the area-related gypsum deposits across Germany). Therefore, it can be assumed that approximately 130,000 listed buildings in Germany are made of gypsum. In addition, there are other historic buildings that are not listed as historical monuments. It would be assumed that the total number of historic buildings constructed of gypsum masonry in Germany amounts to approximately 250,000 to 400,000.

[0009] In order to increase the durability and weathering resistance of gypsum mortars and stucco plasters, various methods are known in the state of the art.

[0010] Previous solutions rely, on the one hand, on the subsequent surface application of hydrophobic agents. WO 95 / 25706 describes a method for treating buildings constructed with mineral materials, to which a hydrophobic substance based on silanone and / or siloxanes is applied.

[0011] EP 2 240419 describes a mixture of a mineral binder based on calcium sulfate and at least one additive which imparts hydrophobic properties to the mineral binder based on calcium sulfate. This binder mixture contains a mineral binder based on calcium sulfate and at least one mixture of fatty acid salts of at least two different metal cations or two different ammonium cations or a mixture of at least one metal cation and at least one ammonium cation, wherein the metal cations are selected from the group consisting of alkali metals, alkaline earth metals, zinc, aluminum and rare earths and wherein the proportion of fatty acid salts of fatty acids having 8 to 17 C atoms, based on the total amount of fatty acid salts in the fatty acid salt mixture, is 20% by weight or more than 20% by weight, or the proportion of fatty acids having 8 to 14 C atoms is 10% by weight or more than 10% by weight.-%, based on the total amount of fatty acid salts in the fatty acid salt mixture, or both. Construction materials according to the invention that are obtainable from a binder mixture according to the invention can be, for example, plasterboard, gypsum blocks, or other molded parts, in particular plasterboard.

[0012] A building material composition containing at least one hydrophobic powder is described in DE 100 49 072, wherein the powder contains at least one carboxylic acid residue.

[0013] DE 195 42 443 C2, DE 100 49 127 C2, and DE 44 02 408 A1 describe a process for polymerizing mineral coating and binder compositions using water-redispersible powder. In one described embodiment, a portion of a protective colloid is added to a dispersion powder composition, with casein being mentioned as a suitable protective colloid.

[0014] The use of Lycopodium in combination with calcium sulfate is known from DE 101 33 399 A1, where special wax-based compositions are specified which can form the basis for cosmetic products and can be used in particular for impregnating and wetting wipes for personal cleansing and care.

[0015] A powdered surface protection system is described in DE 102 39 071 A1 that can be applied to surfaces such as plastic films, metal, painted metal, ceramics, paper, leather, wood, but also fibers and yarns, as well as building materials such as masonry, concrete, bricks, plaster surfaces and the like. The powder can be inorganic or organic in nature. Examples of suitable particulate materials are organic powders, e.g. polymer powders such as polyethylene powder, polypropylene powder, polytetrafluoroethylene powder, and bioorganic powders such as lycopodium. Inorganic powders can be, for example, those based on silicon dioxide or silicates such as silicic acid powder, e.g. precipitated silica, diatomaceous earth, pyrogenic silica, porosils and silica gel powder, clay minerals, quartz powder, glass powder, e.g. glass spheres, furthermore aluminum oxide, zeolites, titanium dioxide; it is also possible for oxidic powders to be hydrophobized with fluoroorganic silanes.The powder can be applied using a pressure-sensitive adhesive followed by sprinkling and blowing off, or using a photo-crosslinkable adhesive or a curable varnish.

[0016] Compositions and methods for waterproofing damp structures made of water-permeable or water-corrodible building materials are described in DE 689 23 137 T2, wherein the basic composition contains C8 to C18 fatty acids.

[0017] An admixture for mineral binder compositions, in particular mortar or concrete, for improving frost resistance and resistance to de-icing salt is described in WO 2021 / 037996. It comprises a reducing agent, a thickener, an air-entraining agent, and at least one solvent. The thickener can be, for example, gelatin and / or casein.

[0018] WO 2007 / 036324 describes a water-redispersible additive for reducing efflorescence in hydraulically set systems, which is particularly suitable as an additive for addition to dry mortars. The water-redispersible powder consists of at least one organic component and at least one water-soluble organic polymeric protective colloid, and optionally further additives, wherein the organic component contains at least one compound with a cyclic group that is fully or partially saturated, has a melting point of approximately -20°C to 250°C and a molecular weight of approximately 100 to 10,000, and forms a stable dispersion in water with the water-soluble organic polymeric protective colloid, wherein the weight ratio of the organic component to the water-soluble organic polymeric protective colloid is approximately 95:5 to 5:95.The additive according to the invention can be used in hydraulically setting compounds, in particular in concrete, gypsum and / or lime and / or cement plasters, repair and / or full thermal insulation mortars, jointing and / or tile adhesives, leveling and / or filler compounds, sealing slurries and / or as an additive for concrete coatings and for adhesives.

[0019] WO 2006 / 058655 describes a hydrophobizing additive in the form of a water-redispersible powder or an aqueous dispersion which comprises one or more water-insoluble, film-forming base polymers based on homopolymers or copolymers of one or more monomers from the group comprising vinyl esters of unbranched or branched alkylcarboxylic acids having 1 to 15 C atoms.

[0020] These solutions have the disadvantage that siloxane / silane-based hydrophobic agents are usually suitable for cementitious systems, since calcium sulfate-based systems lack the silicon component required for their effectiveness or crosslinking. By subsequently applying silanes to the finished surface structure, a dense film is achieved on the component surface.

[0021] Other hydrophobic gypsum binder systems are based on the use of fatty acid salts, carboxylic acid-containing powders, or cellulose fibers. The effectiveness of these products is only sufficient for indoor use. Powders containing carboxylic acids are prone to hydrolysis (splitting by water), so the effectiveness of the hydrophobic treatment is significantly reduced after this reaction. The use of cellulose fibers, on the other hand, severely impairs the processability of the binder, requiring either a significant increase in the water / binder ratio, which in turn leads to a reduction in compressive strength and durability, or counteracting this with additional additives. The use of casein is also state of the art, although it is usually added in the range of 30% to 50% of the solids content.It causes an increase in the formation of long needle-shaped gypsum crystals (15-30 µm), which, due to their size, have a higher water resistance but are nevertheless only suitable for indoor use.

[0022] Document US 1 048 695 A discloses a water-repellent composition for gypsum comprising Chinese tung oil, calcium stearate, casein, a preservative therefor and water. Description of the invention

[0023] The object of the invention is therefore to provide a hydrophobic calcium sulfate mortar compound based on bioadditives, which further improves the durability and weathering resistance of gypsum mortars and stucco plasters.

[0024] This object is achieved by a hydrophobizing agent for calcium sulfate binders and calcium sulfate-containing binders having the features of claim 1. Advantageous embodiments are described in the subclaims.

[0025] Bioadditives from the lycopodium group, such as club moss spores, are used in combination with casein to achieve internal hydrophobicity. This functionalization of the mortar enables its use outdoors and for the repair of existing buildings containing gypsum.

[0026] Clubmoss (Lycopodium clavatum) is a vascular spore plant native primarily to Northern and Central Europe and widespread in America, Asia, and Russia. The plant's spores are approximately 34 µm in size and have a very high A / V ratio (ratio of surface area A to volume V), making them highly flammable and used for pyrotechnic effects. Furthermore, due to their structure and high oil content, they are very hydrophobic, so they are used in pharmaceuticals as a tablet coating to prevent tablets from sticking together, for example. Clubmoss spores have microfine structures, creating a so-called "lotus effect." Water molecules cannot penetrate this structure. The surface energy of the building material is reduced. However, water has a very high surface tension, which means these molecules are repelled and no longer attracted.Applied to the building material, this means that liquids can no longer penetrate the interior because the surface energy of the solid is reduced. Since water has a very high surface tension, this type of hydrophobic treatment no longer attracts water, but rather repel it.

[0027] Casein contributes to the hydrophobicity of the invention in two ways. Firstly, the particles act as a filler in the set gypsum mortar system. The casein fills the voids between the calcium sulfate dihydrate crystallites, making it more difficult for moisture to penetrate the mortar, as the overall porosity is reduced. Secondly, the casein attaches itself to the calcium sulfate crystals. This creates a retarding effect, as the water, which reacts with the calcium sulfate crystallites to form calcium sulfate dihydrate during setting, has a harder time "docking" onto the crystals. This results in a few large crystals forming instead of many small crystals. These crystals have a lower solubility than the smaller crystals. The durability of the hardened mortar is thus significantly increased.

[0028] The combination of club moss spores and casein hydrophobizes the mortar system using different reaction mechanisms. The hydrophobic effect achieved by using both sustainable natural products far exceeds that achieved by using the individual components.

[0029] It is understood that the features mentioned above and those to be explained below can be used not only in the combinations indicated, but also in other combinations or in isolation, without departing from the scope of the present invention. Examples of implementation

[0030] The results of the following examples were determined using a test method for measuring the contact angle for determining the surface free energy of a solid surface according to DIN EN ISO 19403-2:2020. In this method, at least three drops of at least two test liquids are dispensed onto a flat sample surface. The surface free energy of the solid is calculated using a suitable model from the averaged contact angles of each liquid, their surface tensions, and their polar and disperse fractions. The result is expressed as the contact angle. See also: DIN EN ISO 19403-2: Paints and varnishes - Wettability - Part 2: Determination of surface free energy of solid surfaces by contact angle measurement (ISO 19403-2:2017); German version EN ISO 19403-2:2020, April 2020.

[0031] For a first embodiment, the contact angle was determined on a stucco composition (beta hemihydrate only) using the method described above for different ratios of club moss spores and casein in the composition of the hydrophobic agent: composition Contact angle Reference (beta hemihydrate) 33,2° 0.1 M% club moss spores + 0.1 M% casein 40,1° 0.4 M% club moss spores + 0.4 M% casein 79,3° 1.2 M% club moss spores + 1.2 M% casein 95,2°

[0032] For a second example, the contact angle was determined on a historical gypsum mortar using the method described above for different ratios of club moss spores and casein in the composition of the hydrophobic agent: composition Contact angle Reference (historical gypsum mortar) not measurable 0.1 M% club moss spores + 0.1 M% casein 79,3° 1.2 M% club moss spores + 1.2 M% casein 112,6°

[0033] In both examples, the specification "M %" refers to the mass fraction of the dry binder.

Claims

1. A hydrophobizing agent for calcium sulfate and calcium sulfate-containing binders comprising a) spores of plants from the family Lycopodiaceae, and b) casein.

2. The hydrophobizing agent according to claim 1, characterized in that the spores of plants from the family Lycopodiaceae are spores of clubmoss (Lycopodium) and / or spores of common clubmoss (Lycopodium clavatum).

3. The hydrophobizing agent according to claim 1, characterized in that the spores of plants from the family Lycopodiaceae are a mixture of different spores from the family Lycopodiaceae.

4. The hydrophobizing agent according to any one of claims 1 to 3, comprising between 0.1 wt.% and 1.2 wt.% clubmoss spores and / or between 0.1 wt.% and 1.2 wt.% casein.

5. The hydrophobizing agent according to claim 4, characterized in that the mass fractions of clubmoss spores and casein are equal.

6. A method for producing a composition of a calcium sulfate binder or a calcium sulfate-containing binder and a hydrophobizing agent, which contains spores of plants from the family Lycopodiaceae and casein, wherein the hydrophobizing agent is added either during the mixing of the dry raw materials of the binder or during the combining of the raw materials of the binder with mixing water.

7. Use of a hydrophobizing agent according to any one of claims 1 to 5 as a component of dry mixtures, preferably in bagged or silo-stored goods.