Description

Title: Additive manufacturing of insulating element

The invention relates to the field of construction.

It relates more particularly to the manufacture of insulating elements by an additive manufacturing technique.

In addition to its advantages in terms of comfort and economy, the thermal insulation of buildings, both under construction and renovation, is a key issue in the fight against global warming. It is therefore essential that the construction elements have the lowest possible thermal conductivity. To respond to this problem, a large number of technical solutions have been proposed, which implement various insulating elements (mineral wool, organic foams, etc.) associated with structural elements (walls, roofs, etc.).

The invention aims to propose new techniques for manufacturing construction elements having improved thermal insulation.

Additive manufacturing techniques are currently experiencing promising developments in a large number of technical fields. Also called

"3D printing", additive manufacturing is a method in which a computer-controlled robot manufactures three-dimensional objects by continuously depositing material layer after layer. These techniques make it possible in particular to manufacture objects having complex shapes.

Additive manufacturing has, for example, been used to manufacture structural elements such as concrete walls.

The additive manufacturing of construction elements, for example in concrete or mortar, makes it possible to integrate the design, planning and construction processes and to automate and rationalize the latter. Other advantages of this technology include a reduction in labor costs, a reduction in waste and material consumption, the elimination of formwork and a reduction in the duration of projects and investments. In the present text, concrete or mortar is understood to mean a material comprising a hydraulic binder and aggregates.

In known technologies, a wet mortar, obtained by mixing a dry mortar and mixing water, is pumped and conveyed to a printing head attached to a robot or a gantry whose movement is controlled by computer. . A layer of wet mortar is deposited over a layer of mortar previously deposited, generally by being extruded through a nozzle. The print head is continuously moved in a predetermined pattern to produce the final object.

The invention proposes a different way to obtain insulating construction elements by this type of technique.

To this end, the subject of the invention is a process for obtaining an insulating element made of mineral foam by additive manufacturing, in which layers of a paste of superimposed mineral foam are successively deposited, said mineral foam having, after hardening, a mass volume of at most 200 kg/m 3 .

The invention also relates to a method for obtaining a construction element comprising at least one structural element and at least one insulating element made of mineral foam, said method comprising a step of obtaining said insulating element made of mineral foam by process of the invention.

Another object of the invention is an insulating element made of mineral foam, or a construction element, capable of being obtained by one of these methods.

The invention therefore applies additive manufacturing techniques not to construct the structural or carrier element of the construction element, but on the contrary to construct the insulating element. The printing of the insulating element makes it possible in particular to benefit from the advantages of additive manufacturing while complying, with regard to the manufacture of structural elements, with certified and recognized conventional processes, which do not require specific authorizations.

The construction element will most often be a wall or a wall element, in particular for a facade or shear wall. It can also be a floor element. The element will generally be intended to be integrated into the structure of a building.

The term “mineral foam” means a cellular or cellular mineral material. The cells or cells are preferably filled with air. The size of the cells or cells is preferably at most 400 μm, in particular at most 250 μm. The proportion by volume of air in the foam is preferably between 10 and 80% (not taking into account the air included in any porous light aggregates described later in the text).

The mineral foam preferably comprises at least one hydraulic binder.

Obtaining the mineral foam paste preferably comprises mixing with an aqueous solution of a dry composition comprising at least one hydraulic binder, then mixing the mineral paste thus obtained.

By dry composition is meant a powder mixture. After setting and hardening, the final foam can be called hardened foam, or alternatively cement foam, mortar foam or concrete foam. The aqueous solution can be simply water, or alternatively water comprising in solution, in dispersion or in suspension one or more additives, in particular organic, for example surfactants, or alternatively mineral, for example silica nanoparticles.

The hydraulic binder is chosen in particular from Portland cements, aluminous cements, sulphoaluminous cements, hydrated lime, crushed granulated blast furnace slags, fly ash and mixtures thereof.

The mineral foam and/or the dry composition can also comprise aggregates, in particular light aggregates, that is to say having an apparent density of less than 200 kg/m 3 . The lightweight aggregates are chosen in particular from perlite, vermiculite, expanded glass beads, expanded polystyrene beads, cenospheres, expanded silicates, aerogels and mixtures thereof. The mineral foam can also comprise aggregates other than light aggregates, but preferably in a weight content of at most 20%, in particular at most 15%, or even at most 10% or at most 5% (after curing) .

The maximum size of the aggregates is preferably at most 3 mm, in particular at most 2 mm and even at most 1 mm, taking into account the reduced section of the pumping device and the nozzle of the head of impression. To ensure good stability of the foam, the maximum size of the aggregates is even advantageously at most 0.1 mm. The maximum size can be checked for example by sieving.

The dry composition preferably comprises at least one additive, chosen in particular from superplasticizers, thickeners, accelerators and retarders. The dry mortar advantageously comprises inorganic thickeners, for example swelling clays, capable of increasing the elastic limit at rest of the wet mortar. The accelerators and retarders make it possible to adjust the time required for the setting and hardening of the hydraulic binder.

The mineral foam paste can be obtained by various techniques, which have in common the fact that a gas, in particular air, is introduced into the paste. The gas can in particular be generated or introduced during the mixing of the mineral paste, or even provided by an aqueous foam or by a solution containing a gas-generating agent, added to the paste after mixing.

According to one embodiment, the dry composition and/or the aqueous solution comprises an air-entraining agent capable of trapping air within the mineral paste during mixing. In this case the mineral foam paste is formed during mixing. Such an agent is preferably a surfactant. It may in particular be an anionic surfactant. The anionic surfactant is advantageously chosen from alkyl sulphates, alkyl sulphonates, alkyl ether sulphates, alkylarylsulphates and surfactants produced from proteins or amino acids, for example N-acylglutamates and N-acylsarcosinates. The air-entraining agent can also be polyvinyl alcohol.

In this embodiment, the dry composition preferably comprises at least 40%, or even at least 60% by weight of light aggregates, a hydraulic binder comprising a sulfoaluminate cement and/or an aluminous cement, an air-entraining agent, a content by weight of at least 0.3%, in particular at least 0.5%, and optionally a thickening agent, in particular chosen from polyvinyl alcohols, starch ethers, cellulose ethers, guar ethers and clays. The lightweight aggregates preferably have an average diameter of at most 80 μm.

According to another embodiment, the dry composition and/or the aqueous solution comprises a gas-generating agent capable of generating gas bubbles within the mineral paste during its mixing. Such an agent is for example a metallic powder (for example of aluminium, zinc, silicon, etc.) capable of reacting with water and hydroxides. It can also be a peroxide, for example hydrogen peroxide, capable for example of reacting with manganese salts.

Alternatively, the gas-generating agent can be added to the mineral paste (after kneading). For example, obtaining the mineral foam paste may comprise a step of adding to the kneaded paste an aqueous solution comprising this agent. This addition can be made just before the print head.

According to yet another embodiment, obtaining the mineral foam paste further comprises a step of obtaining an aqueous foam and then a step of mixing said aqueous foam with the mineral paste. In this case, the mineral foam is obtained by mixing the kneaded mineral paste and the aqueous foam. The aqueous foam is for example obtained by mixing water and a foaming agent (or a foam stabilizing agent) then by introducing a gas, in particular air, by agitation, bubbling or injection under pressure. The median diameter of the bubbles of the aqueous foam is preferably at most 400 mpi, in particular at most 250 μm.

The foaming agent is for example a surfactant. According to a preferred example, it is a surfactant derived from proteins or amino aids.

For example, the mineral foam paste preferably comprises 10 to 70% water; from 30 to 75%, in particular from 40 to 60%, of cement, in particular of Portland cement; from 10 to 70%, in particular from 15 to 40%, of fillers, in particular limestone fillers, the median diameter of which (for a volume distribution) is at most 5 μm, in particular between 1 and 4 μm; up to 10%, in particular between 1 and 7%, of fine particles whose median diameter is at most 1 μm; and optionally additives (water-reducing agents, plasticizers, superplasticizers, retarding or accelerating agents, thickening agents, foaming agents, etc.). All the contents indicated are contents by weight. The mixing of the aqueous foam with the mineral paste is preferably carried out by means of a static mixer, in particular of the helical type.

According to another example of this embodiment, the aqueous foam comprises the mixture of a cationic surfactant which is a salt (in particular a halide) of quaternary ammonium and an anionic surfactant which is a salt (in particular an alkaline salt) of C10-C24 carboxylic acid, for example potassium stearate. The hydraulic binder is then preferably Portland cement, in particular of the CEM I 52.5 type. The mineral foam paste preferably comprises a latex, chosen in particular from vinyl and/or acrylic (co)polymers, for example styrene-acrylic copolymers.

According to yet another example of this embodiment, the aqueous foam comprises nanoparticles, in particular of silica, which have the property of stabilizing the foams. Such foams are called "Pickering foams". The silica nanoparticles can themselves be stabilized by surfactants. The density of the mineral foam after hardening (in particular after 28 days) is preferably between 40 and 200 kg/m 3 , in particular between 50 and 180 kg /m 3 , or even between 60 and 150 kg/m 3 , or even between 80 and 120 kg/m 3 .

Due to the presence of a large quantity of gas, in particular air, trapped in a mineral matrix, the foam has low thermal conductivity, in particular by reducing heat transfer by convection and by conduction. The thermal conductivity of the mineral foam after hardening (in particular after 28 days) is preferably at most 60 mW.m _1 .K _1 .

The process comprises the successive deposition of superimposed layers of mineral foam paste.

After it has been obtained, the mineral foam paste is preferably pumped (in particular using a pump) and conveyed, generally in a pipe, to the print head of a printer. The print head notably comprises a nozzle through which the paste is extruded. The extrusion nozzle is preferably located less than 100 mm from the underlying layer. The printer is for example an industrial robot or a gantry, carrying the print head, and whose movement is controlled by a computer. The computer comprises in particular a recording medium in which is stored a set of data or 3D model as well as instructions, which when executed by the computer lead the latter to control the movement (trajectory, speed, etc.). ) from the head of

The printing speed is typically 30 to 1000 mm/s, in particular 50 to 300 mm/s. The thickness (or height, since it is a question here of the dimension in the vertical direction) of the layers of dough is preferably between 5 and 40 mm, in particular between 10 and 20 mm. The width of the dough layers is preferably between 10 and 300 mm, in particular between 20 and 100 mm.

In the embodiment described above, comprising the mixing of an aqueous foam and the mineral paste, this mixing is preferably carried out by means of a static mixer. The addition of the aqueous foam is preferably carried out between the pump and the print head, ideally as close as possible to the print head in order to preserve the structure of the foam. The quantity of aqueous foam relative to the quantity of mineral paste is preferably adjusted automatically, in particular according to the desired density. The ratio between the volume of aqueous foam added and the volume of mineral paste is preferably between 5 and 12. For example, for a density after hardening of 100 kg/m 3, the ratio between the volume of aqueous foam added and the volume of mineral paste is typically around 10.

The method preferably comprises adding to the mineral foam paste, before deposition, a setting and/or hardening accelerator or a rheology modifying agent. The addition can in particular take place at the level of the nozzle or close to the nozzle, therefore just before extrusion. Alternatively, the accelerator or the rheology modifying agent can be added immediately after the deposition, on the surface of the layers. The setting accelerator is for example an aluminum sulphate or a lithium salt, depending on the type of hydraulic binder used. The rheology modifying agent makes it possible, for example, to impart a thixotropic character to the paste. The addition of a setting accelerator or a rheology modifying agent makes it possible to quickly consolidate the layers of mineral foam,

Obtaining the construction element comprising at least one structural element and at least one insulating element made of mineral foam can be achieved in different ways.

“Structural element” means an element of the building which satisfies a structural role or which contributes to its reinforcement. The structural element is for example a concrete wall.

According to one embodiment, the insulating element forms a formwork, the method further comprising a step of filling said formwork with a structural element, in particular concrete. By way of example, the insulating element is printed so as to form two walls facing each other and forming a cavity, into which concrete is poured. The walls can be flat or have the most diverse shapes, as allowed by the additive manufacturing technique. A construction element is thus formed comprising a concrete wall surrounded by two outer insulating layers.

According to another embodiment, the layers of mineral foam are deposited against at least one pre-existing structural element. The layers are thus deposited in contact with an element, for example concrete, along at least one of its main surfaces. For example, a concrete wall is obtained having on at least one (optionally on two) of its surfaces an insulating layer.

As part of this embodiment, the layers of mineral foam can be deposited between and in contact with two pre-existing structural elements. Thus, for example, a wall is formed comprising a first and a second concrete wall between which a layer of mineral foam is placed.

The construction elements can be prefabricated elements, intended to be assembled on the construction site, for example by means of a mortar, in order to form the external or internal walls (for example the shear walls) of a building. The elements can also be manufactured directly on the construction site and form the complete wall of the building.

Claims

1. Process for obtaining an insulating element made of mineral foam by additive manufacturing, in which layers of a paste of superimposed mineral foam are successively deposited, said mineral foam having, after hardening, a density of at most 200 kg/ m 3 .

2. Method according to claim 1, in which the mineral foam comprises at least one hydraulic binder, chosen in particular from Portland cements, aluminous cements, sulfoaluminate cements, hydrated lime, crushed granulated blast furnace slags, fly ash and their mixtures.

3. Method according to the preceding claim, in which obtaining the mineral foam paste comprises mixing with an aqueous solution of a dry composition comprising at least one hydraulic binder, then mixing the mineral paste thus obtained.

4. Method according to the preceding claim, in which the dry composition and/or the aqueous solution comprises an air-entraining agent capable of trapping air within the mineral paste during mixing.

5. Method according to claim 3, in which the dry composition and/or the aqueous solution comprises a gas-generating agent capable of generating gas bubbles within the mineral paste during its mixing.

6. Method according to claim 3, in which the obtaining of the mineral foam paste further comprises a step of obtaining an aqueous foam then a step of mixing said aqueous foam with the mineral paste.

7. Method according to one of the preceding claims, in which the size of the cells of the mineral foam is at most 400 mpi, in particular at most 250 μm.

8. Method according to one of the preceding claims, in which the density of the mineral foam after hardening is between 50 and 180 kg/m 3 , in particular between 60 and 150 kg/m 3 .

9. Method according to one of the preceding claims, in which the mineral foam and/or the dry composition comprises light aggregates, chosen in particular from perlite, vermiculite, expanded glass beads, expanded polystyrene beads, cenospheres , expanded silicates, aerogels and mixtures thereof.

10. Method according to the preceding claim, in which the maximum size of the aggregates is at most 1 mm, in particular at most 0.1 mm.

11. Method for obtaining a construction element comprising at least one structural element and at least one insulating element made of mineral foam, said method comprising a step of obtaining said insulating element made of mineral foam by the method of one of previous claims.

12. Method according to claim 11, in which the construction element is a wall or a wall element.

13. Method according to one of claims 11 or 12, wherein the insulating element forms a formwork, said method further comprising a step of filling said formwork with a structural element, in particular concrete.

14. Method according to one of claims 11 or 12, wherein the layers of mineral foam are deposited against at least one pre-existing structural element.

15. Method according to the preceding claim, in which the layers of mineral foam are deposited between and in contact with two pre-existing structural elements.