Material based on natural colloids and naturally derived wax with liquid-solid phase change

Abstract

The present invention relates to a composition for 3D printing of construction materials comprising: - a mineral colloidal matrix composed of water and granular inclusions, water representing 30 to 50% of the mass of the granular inclusions, and - 1 to 30%, preferably 3 to 20%, and even more preferably 5 to 10% by mass relative to the mass of the granular inclusions of natural wax, it also relates to a 3D printing process implementing this composition and to rigidified construction materials obtained by this process.

Description

Title of the invention: Material based on natural colloids and wax of natural origin with liquid-solid phase change Technical field

[0001] The present invention relates to a composition for 3D printing of construction materials, its printing method as well as the printed construction material, and in particular to a composition based on a mineral colloidal matrix composed of water and granular inclusions for 3D printing of construction materials and its printing method. Prior art

[0002] A building material is a material used for construction purposes, for example, for the construction of buildings. Wood, cement, metals, bricks, concrete, clay are the most commonly used types of building materials today. The choice of these materials is generally based on their cost-effectiveness for construction projects. Many naturally occurring substances, such as clay, sand, wood, and rocks, and even plant fibers and plant aggregates have been used to construct buildings. In addition to natural materials, many more or less synthetic, man-made products are used.

[0003] Construction materials can generally be classified into two categories: natural materials and materials derived from the petrochemical industry, which can be referred to as synthetic materials. Natural materials are those that are not or only slightly processed by industry, such as wood, cork, stone. Natural materials are more respectful of the environment and the health of living beings because they do not release hazardous substances into the construction environment. Few materials available on the international market are 100% natural. Synthetic materials are manufactured in industrial facilities after extensive human manipulation, such as petroleum-based plastics and paints. Most often, these materials are derived from virgin resources that are not renewable.

[0004] Today, the state of the art includes all sorts of building materials, but the most common are brick, concrete, metal, glass, and clay. A brick is a block made of a kiln-fired material, usually clay or shale. Clay bricks are formed in a mold or more commonly by extrusion through a die and then cutting them with wire to the appropriate size in commercial manufacturing. Concrete is a composite building material made from The combination of aggregates and a hydraulic binder such as cement. The most common form of concrete is Portland cement concrete, which consists of mineral aggregates, usually gravel and sand, Portland cement, and water. Concrete is not a renewable material and its environmental impact is very significant.

[0005] In recent years, more and more high-rise buildings are being built from wood worldwide due to the technical qualities of this material and modern technical possibilities of shaping, its low cost, ease of maintenance, low embodied energy, and renewable nature. In addition, wood is not a hazardous waste.

[0006] Modern construction is a multi-billion dollar industry, and the production of raw materials for construction purposes occurs on a global scale. It is often a key governmental and commercial point of contact between nations. Environmental concerns are also becoming a major global topic regarding the availability and sustainability of certain materials and the extraction of such large quantities necessary for human habitation. The construction sector is the third most polluting sector in the world, responsible for 40% of energy consumption, produces 36% of the CO2 released into the air, uses 50% of raw materials and 21% of the world's drinking water.

[0007] Today, many people are choosing to use eco-friendly building materials when building or renovating their homes. An eco-friendly building material is one that reduces energy consumption and reduces the impact on human well-being and the environment. There are many different materials that can be used in the construction industry that are eco-friendly; from foundations to insulation, interior and exterior wall cladding, flooring, and countertops.

[0008] An eco-friendly building material is a product that has been designed to cause the least possible harm to the environment. A material in itself can be eco-friendly, for example, wood. Or even conventional materials can become eco-friendly depending on the construction technique used. The various characteristics that eco-friendly materials and techniques have are: renewal, reuse of waste, local availability, reduction of pollution (air, land, water), biodegradability, durability and energy efficiency. It is difficult to obtain a material that has all these properties.

[0009] Building materials based on natural colloids are ecological building geomaterials. These are raw materials available in large quantities, such as clay, fine silt, mud, sedimentary alluvium. These natural colloids, such as clay, require the presence of water to be shaped. They are considered sticky and viscous after the addition of water and are therefore difficult to handle and malleable. However, clays have a major defect related to drying: the volume of water within the material decreases, leaving empty spaces, leading to a significant volume shrinkage of the material, making it fragile when used as a construction material. In addition, these materials have the disadvantage of taking several days to dry at room temperature, making their use as construction materials disadvantageous compared to cement or concrete, which stiffen quickly and allow for a high construction rate. These geomaterials also have a high sensitivity to water, leading to a significant loss of mechanical strength: this control of water sensitivity is a key aspect for considering their use as construction materials on a large scale.

[0010] New techniques are thus being sought to counteract the defects inherent in the use of materials based on natural colloids, in particular long drying times and the alteration of properties upon contact with water. Such modernization will thus allow the use of materials based on natural colloids in different ways, whether as bricks, as prefabricated elements or as construction materials. There is also a need to modernize construction techniques, in order to adapt construction methods to these new materials, for example through the use of 3D printing, also called additive manufacturing by extrusion, or by dynamic molding via a suitable heating extrusion device.

[0011] Patent application WO2019 / 155143Al describes, for example, a method for producing a construction material that can be used in 3D printing construction. More specifically, the document discloses a method comprising mixing a clay product with water. The mixture is then heated and mixed with an organic acid, phytic acid, in order to complex the metal ions present inside the clay. The mixture is then neutralized by providing a base, sodium hydroxide, to condense the metal ion-based complexes. Wax is added to the mixture as a thermo-reactive product and the mixture is heated so that the thermo-reactive product is liquid. The mixture is then printed by extrusion and the hardening of the thermo-reactive product allows the geometric characteristics of the printed material to be maintained.

[0012] Patent application EP3778238A1 describes a system and method for preparing ecological building elements. More specifically, the document discloses a system composed of clay, water, cement, filler based on waste from the rice production industry and additives. The system allows the production of building elements by a method comprising making the system based on waste from the rice production industry. This mixture is then extruded through a nozzle in a predefined 3D coordinate system. This process allows walls to be printed layer by layer, with each layer being deposited after the previous one has dried. The additives present in the system make it possible to provide additional properties to the printed building element. For example, the addition of wax to the system makes the building element impermeable and water-resistant.

[0013] There is therefore still a need for a composition based on products of totally natural origin allowing the 3D printing of ecological materials that are simple to produce and handle and that have excellent mechanical properties, that are insensitive to water and breathable, so that the printed material can be used as a construction material while having a positive environmental balance. Summary

[0014] The present invention therefore proposes, according to a first aspect, a composition for 3D printing of construction materials comprising: - a mineral colloidal matrix composed of water and granular inclusions, and - from 1 to 30%, preferably from 3 to 20%, and more preferably still from 5 to 10% of wax of natural origin by mass relative to the mass of the granular inclusions.

[0015] According to another aspect, there is provided a method of 3D printing of construction materials comprising the following steps: - the incorporation of the composition according to the first aspect of the present invention into a 3D printing device, - heating the mixture to a temperature below 100°C and above or equal to the melting temperature of the wax of natural origin, and - printing the material in a predefined 3D coordinate system.

[0016] According to another aspect, there is provided a stiffened construction material based on a colloidal matrix of water and granular inclusions comprising from 1 to 30%, preferably from 3 to 20%, and even more preferably from 5 to 10% by mass relative to the mass of the granular inclusions of wax of natural origin.

[0017] According to another aspect, there is provided a building element printed according to the method of the second aspect of the present invention. Brief description of the drawings

[0018] Other characteristics, details and advantages will appear on reading the detailed description below, and on analyzing the attached drawings, in which:

[0019] [Fig. 1] shows a printed material according to one embodiment

[0020] [Fig.2] shows the evolution of the shear threshold as a function of the temperature of materials printed according to one embodiment.

[0021] [Fig.3] shows the evolution of the deterioration of mechanical properties due to the presence of water, of materials printed according to an embodiment depending on the quantity of wax of natural origin. Detailed description

[0022] The present invention relates to a composition for 3D printing of construction materials comprising: - a mineral colloidal matrix composed of water and granular inclusions, and - from 1 to 30%, preferably from 3 to 20%, and more preferably still from 5 to 10% by mass relative to the mass of the granular inclusions of wax of natural origin.

[0023] The mineral colloidal matrix composed of water and granular inclusions represents the majority of the composition according to the present invention. By "majority" is meant at least 50% by mass of the total mass of the composition. It is composed of water as well as granular inclusions. The respective quantity of water and granular inclusions may vary depending on the type of granular inclusions used, their physicochemical activity and their specific surfaces.

[0024] According to one embodiment, the granular inclusions can be chosen from clay, limestone, silt, sedimentation mud, sedimentary alluvium and their mixture.

[0025] Clay is a natural rock material based on silicates or aluminosilicates with a grain structure of less than one micrometer. Limestone is a sedimentary rock mainly composed of calcium carbonate readily soluble in water which can be reduced to powder, with a grain size range of up to 100 micrometers, preferably up to 50 micrometers. Silt is a sedimentary formation with a grain structure of more than one micrometer and less than one hundred micrometers. Sedimentation sludge is a mixture of water and fine sedimentary particles of silt and clay, often from the aggregate production industry. These materials are easily accessible because they are present in the form of natural deposits but also in the form of waste, industrial waste and co-products of the construction industry mainly.They can therefore be taken directly from nature or reused for recycling and waste recovery purposes, thus reducing the ecological impact of industries producing these materials as waste.

[0026] According to one embodiment, the clay may be kaolin.

[0027] Kaolin is a natural, white, loosely cohesive clay composed of kaolinite, a mineral species based on hydrated aluminum silicate. Kaolin is a clay that is used in many industries, including the paper, medical, and and cosmetics. Kaolin is thus present in its natural state in the form of deposits or as industrial waste in large quantities. It thus has the advantage of being available in its natural state and of being able to be recycled when it is in the form of industrial waste for the purpose of recycling and waste recovery.

[0028] The composition according to the invention also comprises from 1 to 30% by mass, preferably 3 to 20% by mass, more preferably 5 to 10% by mass relative to the mass of the granular inclusions of wax of natural origin.

[0029] Wax is an organic compound with long carbon chains. There are two types of wax, waxes of natural origin and synthetic waxes. Waxes of natural origin, animal or vegetable, consist mainly of esters of fatty acid and alcohol or glycol while mineral waxes derived from petroleum are mainly extracted from solid hydrocarbon residues. In the present invention the term wax of natural origin covers waxes of vegetable and animal origin. This type of wax is malleable at room temperature, hydrophobic and has a melting point above 30°C varying depending on the wax chosen.

[0030] Hot wax has a low viscosity and therefore allows the viscosity induced by the clay to be significantly reduced. Pumping and extrusion difficulties encountered with clays are frequently caused by excessive viscosity and therefore difficult flow to obtain. We can also notice a sticky effect induced by this high viscosity: the wax reduces this effect and greatly facilitates the extrusion / pumping of the material.

[0031] The wax of natural origin makes it possible to formulate a liquid-solid phase change composition and to give this composition the ability to stiffen rapidly at room temperature, thus allowing shaping by 3D printing of the composition according to the first aspect of the invention. Since 3D printing is carried out by successive deposition of layers one above the other, it is necessary that when deposition of a layer n, the layer n-1 located directly below is already sufficiently stiffened to support the weight of the layer n and that the whole does not collapse. The stiffening speed of the composition is directly linked to the mass percentage of wax in the composition. 1% by mass relative to the mass of the granular inclusions of wax of natural origin is sufficient for the composition to be usable for 3D printing.Beyond 30% by mass relative to the mass of granular inclusions of wax of natural origin, the relationship between final mechanical resistance and speed of thermal setting becomes irrelevant.

[0032] The mechanical properties decrease proportionally to the amount of natural wax added to the composition. For small amounts of wax of natural origin, the mechanical properties of the material resulting from the composition are close to those of the mineral colloidal matrix alone and for large amounts of wax of natural origin, the material resulting from the composition has reduced mechanical properties.

[0033] The wax of natural origin also makes it possible to make the stiffened material based on the composition insensitive to water. Since the wax is hydrophobic, mixing the wax with the mineral colloidal matrix based on water and granular inclusions makes it possible to make the latter resistant to water after solidification. Since the mineral colloidal matrix, such as clay, is particularly sensitive to water, its use alone as a construction material poses numerous problems with regard to waterproofing, service life, alteration of the structure and its mechanical properties. The use of a wax makes it possible to solve these problems. 1% by mass relative to the mass of the granular inclusions of wax of natural origin is sufficient to significantly reduce the sensitivity of the material to water.

[0034] The wax of natural origin makes it possible to make the stiffened material based on the composition according to the invention breathable. A breathable material is a material capable of evacuating moisture through it. This property is particularly advantageous for construction materials because it allows them to evacuate the moisture present inside the construction to the outside. Materials based on natural colloids naturally have a porous structure. The incorporation of the wax of natural origin makes it possible to make this network of porosity thermally dependent. The temperature influences the viscosity of the wax and the surface tension between the wax and the granular inclusions. The quantity of wax used is adapted according to the size of the porosities of the material, the temperature of use and the viscosity of the wax at this temperature of use, as well as the target water vapor diffusion factor.

[0035] By choosing the nature and the mass proportion of wax of natural origin in the composition according to a first aspect of the invention, it is possible to modify the stiffening speed and the mechanical properties of the material obtained from the composition. Thus, it is possible to adapt the mass proportion and the nature of wax according to the rate and the type of construction material that one wishes to print or extrude. For example, a structure requiring a material with a very rapid stiffening speed and good mechanical properties with a gravitational force unfavorable to the holding of the structure, during and after construction, such as vaults or cantilevers, will therefore need a significant mass proportion of wax of natural origin, greater than 10% and less than 30% by mass relative to the mass of the granular inclusions, preferably greater than 10% and less than 20%.On the other hand, a structure requiring a material with a stiffening speed that is not necessarily rapid, less demanding mechanical properties and with a gravitational force that is not unfavorable to the structure's stability. such as a house wall, may require a low mass proportion of natural wax, greater than 1% and less than 10% by mass relative to the mass of granular inclusions.

[0036] There are many types of materials based on natural colloids and very large geographical disparities. Natural colloids therefore do not have the same structure and the same properties depending on the geographical areas. Thus, the mass proportion of wax necessary to achieve the properties required for the use that will be made of the composition can also vary due to these disparities. It will be understood by those skilled in the art that the mass proportion of wax can be adapted according to the type of natural colloid that will be used as the base of the composition. For example, for the use of kaolin, a range of 1 to 5% of wax of natural origin relative to the mass of kaolin may be sufficient to obtain mechanical and water resistance properties suitable for construction.

[0037] According to one embodiment, the wax of natural origin can be chosen from soy wax, rapeseed wax, hemp wax, sunflower wax, palm wax, camuba wax, coconut wax, candelia wax, beeswax and their mixture.

[0038] According to one embodiment, the composition according to the invention does not comprise any hardening agent other than wax.

[0039] A hardening agent is a compound that allows a construction material to be stiffened more quickly and to protect it against water shrinkage during stiffening, which can lead to the creation of cracks in the material, thus weakening the structure. Hardening agents are generally synthetic compounds used for concrete and cement in the construction field. In the composition according to the present invention, the wax of natural origin, which is a natural and ecological product, acts as a hardening agent while providing additional properties to the material, in particular insensitivity to water and thermo-dependent perspiration. Thus, the fact of not using an additional hardening agent makes it possible to obtain a composition that is simple to produce, with few different ingredients, ecological, recyclable and reusable, while retaining the advantages of using a hardening agent.

[0040] According to one embodiment, the composition of the invention does not comprise rice-based materials.

[0041] Rice-based materials such as rice straw or rice plait are residues from the rice production industry and can be used as filler in a building material. However, residues from the rice production industry are not readily available materials. Indeed, rice production is very unevenly distributed throughout the world. Since the composition according to the invention has the advantage of being able to be produced in any location, it appears advantageous and ecological not to include in the composition components not available in a nearby environment.

[0042] According to one embodiment, the composition of the invention further comprises a filler of mineral or plant origin, said filler being chosen from sand, gravel, wood chips, flax fibers or hemp shiv and their mixture.

[0043] The colloidal matrix consists of granular inclusions and coarser particles having a particle size greater than 0.2 μm depending on the nature and variability of the starting material used. The use of coarser particles, outside the natural composition of the starting material used, may be considered for economic reasons. These coarser fillers may be of mineral origin, such as sand or gravel, or derived from biomass, such as wood chips, flax fibers or hemp shiv. The dosage of the filler will be determined by analysis of the mechanical gain and the economic potential linked to their use. The mass quantity of filler may be up to three times the mass of the granular inclusions, preferably twice, preferably once. Beyond this quantity, the mechanical strength may be greatly affected.The person skilled in the art will be able to determine the quantity of filler which ensures continuity of the matrix so as not to induce phenomena of local decohesion of the material.

[0044] According to a second aspect, there is provided a method for 3D printing of construction materials comprising the following steps: - the incorporation of the composition according to the first aspect of the present invention into a 3D printing device, - heating the mixture to a temperature below 100°C and above or equal to the melting temperature of the wax of natural origin, and - printing the material in a predefined 3D coordinate system

[0045] The first step consists of incorporating the composition according to the present invention into a 3D printing device. The composition is thus produced upstream of the process and integrated into the 3D printing device. A 3D printing device is a device for shaping a material composed of the composition according to the invention. A 3D printing device consists of a reservoir containing the composition to be printed and an extrusion device for depositing the composition.

[0046] The second step consists of heating the composition to a temperature below 100°C and greater than or equal to the melting temperature of the natural wax. By heating the mixture, the natural wax mixed with the mineral colloidal matrix composed of water and granular inclusions liquefies. The heated mixture has a pasty, viscous and slightly sticky consistency. This consistency makes it easy to handle and shape the composition.

[0047] The third step consists of printing the material in a predefined 3D coordinate system. By predefined 3D coordinate system is meant the coordinates in a three-dimensional plane of the material to be printed. For example, for printing a straight wall section, the predefined 3D coordinate system will correspond to a rectangular volume whose dimensions are those of the wall section that one wishes to print. Printing is carried out layer by layer. That is to say that the composition is deposited in the predefined 3D coordinate system in the form of a succession of layers of predefined thickness. This thickness ranging, in order of magnitude, from one centimeter to ten centimeters.

[0048] Exposure of the heated composition to room temperature allows the mineral colloidal matrix and the naturally occurring wax to cool. Upon cooling, the naturally occurring wax distributed throughout the material solidifies and allows the entire material to stiffen while maintaining the geometric characteristics of the deposited layer. Thus, when the entire layer is deposited and the printing device deposits the next layer, the deposited layer will already be stiffened, thus supporting the next layer and preventing the structure from collapsing.

[0049] The cohesion between the layers is greatly improved by the wax, there is no appearance of cold joints between two successive printed layers of the composition according to the invention. A cold joint is a discontinuity between two successive layers leading to the weakening of the material and the reduction of its cohesion. In addition, the addition of wax makes it possible to avoid the appearance of cracks which traditionally form in earth constructions due to the shrinkage of water during drying.

[0050] Finally, it is interesting to note that a lubricating effect on the walls of the printing device induced by heating the wax of natural origin reduces the sticky effect. The greater the heating, the more the sticky effect is reduced. This reduction in the sticky effect therefore allows better pumpability of the heated composition according to the first aspect of the invention and a better surface appearance of the printed material.

[0051] According to one embodiment, the 3D printing device is easily movable horizontally and vertically in order to be able to print large materials, such as wall elements.

[0052] According to one embodiment, the 3D printing device is an extrusion device, a controlled flow pump, or even a projection lance.

[0053] According to one embodiment, the 3D printing device may be a mobile extrusion device supplied with material by a controlled flow pump.

[0054] An extrusion device is a device comprising a heated cylindrical barrel in which a screw and a nozzle rotate. The heated cylindrical barrel allows the composition to be heated and the screw to mix and transport of the composition to the nozzle. The nozzle is sized to suit the material to be printed, specifically the geometric dimensions of the layer to be deposited in the predefined 3D coordinate system and the maximum size of the particles present in the material.

[0055] According to one embodiment, the step of printing the material may comprise cooling the heated composition by a liquid nitrogen-based cooling device at the outlet of the 3D printing device, an active air cooling system such as a fan or a forced heat exchange cooling system.

[0056] As explained above, structural elements having a very unfavorable gravity force during construction such as vaults or cantilevers require a significant mass proportion of wax of natural origin, generally greater than 10% by mass relative to the mass of the granular inclusions in order to stiffen very quickly and to have mechanical properties allowing the structure to be maintained. It is however possible to use a liquid nitrogen-based cooling device at the output of the 3D printing device in order to immediately stiffen the deposited composition. Since liquid nitrogen is at a temperature below -195.79°C, contact of the deposited layer with the liquid nitrogen results in immediate solidification of the wax and cooling of the mineral colloidal matrix.This immediate stiffening thus makes it possible to counteract the gravity which is unfavorable for the printing of this type of structure and thus avoid its collapse.

[0057] According to a third aspect, the invention relates to a stiffened construction material based on a colloidal matrix of water and granular inclusions comprising from 1 to 30%, preferably from 3 to 20%, and even more preferably from 5 to 10% by mass relative to the mass of the granular inclusions of wax of natural origin.

[0058] As explained above, the addition of wax to a colloidal matrix of water and granular inclusions makes it possible, after stiffening the composition, to give the material obtained advantageous properties in terms of shaping and durability, allowing it in particular to be used as a construction material.

[0059] According to one embodiment, the stiffened construction material based on a colloidal matrix of water and granular inclusions may have at least one of the following properties: a compressive strength greater than 4MPa, insensitivity to water or a breathability property.

[0060] After stiffening, the composition of the colloidal matrix based on water and granular inclusions and from 1 to 30%, preferably from 3 to 20%, and even more preferably from 5 to 10% by mass relative to the mass of the granular inclusions of wax of natural origin no longer comprises almost any water. The addition of wax of natural origin thus allows, during the withdrawal of water during stiffening, to control the shrinkage of the stiffened material and therefore the appearance of cracks. The absence of cracks and therefore of weaknesses within the material thus allows it to have sufficient mechanical properties for its use as a construction material. The addition of wax of natural origin therefore gives the stiffened material based on the colloidal matrix made up of water and granular inclusions sufficient mechanical properties for its use as a construction material, in particular a mechanical compressive strength greater than 4 MPa. For comparison, a class B40 concrete block has a compressive strength of 4 MPa. The wax therefore makes it possible to overcome one of the problems inherent in mineral colloidal matrices based on water and granular inclusions during their stiffening.The proportion of wax can be adapted to obtain the desired mechanical properties.

[0061] Furthermore, as explained above, mineral colloidal matrices based on water and granular inclusions, and more particularly based on clay, are materials which, after stiffening, are particularly sensitive to water. That is to say, these stiffened materials see their properties significantly altered in the presence of water. This problem therefore makes it difficult to use these materials as construction materials because contact with water, for example during bad weather, floods or periods of high humidity, can weaken the internal structure of this stiffened material. Thus, the use of this material as a basic material in the field of construction is not possible without additional protection to protect it from water.The presence of 1 to 30%, 3 to 20%, and even more preferably 5 to 10% by mass relative to the mass of granular inclusions of wax of natural origin makes it possible to make the stiffened material very insensitive to water and meets the requirements for use as a construction material.

[0062] Finally, the presence of 1 to 30% by mass relative to the mass of granular inclusions of wax of natural origin in the stiffened material based on the mineral colloidal matrix of water and granular inclusions makes it possible to advantageously confer on it the property of perspiration. As explained previously, a perspiring material is a material that easily wicks away moisture. This property thus makes it possible to make the stiffened material based on the mineral colloidal matrix of water and inclusions particularly suitable for its use as a construction material, and more specifically as a single-component wall.

[0063] According to a fourth aspect, there is provided a building element printed according to the method according to the second aspect of the present invention.

[0064] The method according to the second aspect of the invention thus allows the printing of a complete construction element from the composition according to the first aspect of the invention. By construction element is understood a complete assembly which can be, for example, a wall element, a vault, a ceiling, an overhang or a complete construction such as a house. The building element is composed of the stiffened material according to the third aspect of the invention and will therefore possess the advantageous properties thereof. It will be understood by those skilled in the art that the proportion of wax can be adapted according to the printed building element so that the building element has the properties necessary to maintain the structure. Examples

[0065] Example 1: Preparation of a stiffened construction material ([Fig.l]).

[0066] A composition according to the invention is prepared by mixing: 1 kg of kaolinite from the Imérys Ploemeur quarry (France) 45% by mass relative to the total mass of water kaolinite, and 5% by mass relative to the mass of soy wax kaolinite with a melting point of 52-54°C marketed by ADC. The composition is integrated into a specific extruder designed for double-walled ECT brand ceramic materials. The mixture is kneaded using a mixer integrated into the extruder and a temperature between 70 and 80°C is maintained. A material of dimensions 2x12x7cm is printed by successively depositing 6 continuous layers. A printed material is obtained as shown in [Fig.l].

[0067] Example 2: Influence of the quantity of wax on the admissible shear stress limit as a function of time.

[0068] Based on example 1, 2 types of materials of different consistencies were poured into a container 7 cm in diameter and 3.5 cm in height by varying the mass proportion of water relative to the mass of kaolinite in the composition: Formulation 1: 35% water, Formulation 2: 45% water. These two materials are distinct: the first is relatively firm when hot and the second is more fluid. The thermal setting speed as a function of time has been estimated.

[0069] [Fig.2] shows the evolution of the shear threshold as a function of temperature and time interval after exposure to room temperature, as well as the evolution of the temperature of the material as a function of time. The shear threshold is measured during thermal setting at different temperatures using a vane geometry rheometer with a measuring gap of 4 mm and a ribbed container in order to avoid wall slip induced by the heated wax. These measurements are correlated with those carried out using a cone penetrometer (ISO17892-12 2004). These measurements show a significant stiffening during the first two minutes and a more gradual evolution beyond. The shear threshold after stiffening after 1 hour is respectively 3000 Pa for formulation 1 and 800 Pa for formulation 2.

[0070] Example 3: Influence of the quantity of wax on water resistance.

[0071] Based on example 1, 5 test specimens with dimensions of 4x4x16cm were castings by varying the mass proportion of wax in relation to the mass of kaolinite in the composition: Test tube 1: 0% soy wax, Test tube 2: 2% soy wax, Test tube 3: 4% soy wax, Test tube 4: 7% soy wax, and Test tube 5: 10% soy wax.

[0072] [Fig.3] shows the deterioration of the mechanical properties of the material after complete immersion of the stiffened material after 30 minutes of immersion and after 12 hours of immersion. The introduction of wax makes it possible to significantly reduce the deterioration of the mechanical properties of the stiffened material. The higher the proportion of wax, the lower the deterioration of the mechanical properties.

Claims

Claims

1. Composition for 3D printing of construction materials comprising: - a mineral colloidal matrix composed of water and granular inclusions, the water representing 30 to 50% of the mass of the granular inclusions, and - from 1 to 30%, preferably from 3 to 20%, and more preferably still from 5 to 10% by mass relative to the mass of the granular inclusions of wax of natural origin.

2. Composition for 3D printing of building materials according to claim 1, not comprising a curing agent other than wax.

3. A composition for 3D printing of building materials according to any preceding claim, not comprising rice-based materials.

4. Composition for 3D printing of building materials according to any one of the preceding claims, wherein the granular inclusions are chosen from clay, limestone, silt, sedimentary alluvium, sedimentation mud and their mixture.

5. Composition for 3D printing of construction materials according to claim 4 in which the clay is kaolin.

6. Composition for 3D printing of building materials according to any one of the preceding claims in which the wax of natural origin is chosen from soy wax, rapeseed wax, hemp wax, sunflower wax, palm wax, carnuba wax, coconut wax, candelia wax, beeswax and their mixture.

7. Composition for 3D printing of construction materials according to any one of the preceding claims further comprising a filler of mineral or vegetable origin, said filler being chosen from sand, gravel, wood chips, flax fibers or hemp shiv and their mixture.

8. A method of 3D printing building materials comprising the following steps: - incorporating a composition according to any one of claims 1 to 7 into a 3D printing device, - heating the mixture to a temperature below 100°C and above or equal to the melting temperature of the wax, and - printing the material in a predefined 3D coordinate system.

9. A method of 3D printing building materials according to claim 8 wherein the printing step comprises cooling the heated composition by a liquid nitrogen-based cooling device at the outlet of the 3D printing device, an active air cooling system such as a fan or a forced heat exchange cooling system.

10. A method of 3D printing building materials according to claim 8 or 9, wherein the 3D printing device is an extrusion device.

11. Rigidified construction material based on a mineral colloidal matrix composed of water and granular inclusions comprising: - from 5 to 10% by mass relative to the mass of the granular inclusions of wax of natural origin.

12. Rigidified construction material based on a mineral colloidal matrix composed of water and granular inclusions according to claim 11 characterized in that the material has at least one of the following properties: a compressive strength greater than 4MPa, insensitivity to water or a breathability property.

13. Building element printed according to the method of any one of claims 8 to 10

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