Wood concrete and its manufacturing process

Abstract

The invention relates to a concrete comprising a binder (1), and wood particles (2) coated in a metakaolin (3), the volume content of the wood particles (2) in the concrete being greater than or equal to 30%. The invention also relates to a method for manufacturing a concrete according to the invention. This method is particular in that it comprises the following steps: - mixing the wood particles (2) with the metakaolin (3), in order to obtain a coating of the wood particles (2) by the metakaolin (3), - mixing the wood particles (2) with at least one binder (1) and water. Figure for abstract: Fig 1

Description

Title of the invention: Wood concrete and its manufacturing process Technical field

[0001] The present invention relates to the field of construction. It relates more particularly to a wood concrete, and its manufacturing process. The invention makes it possible in particular to obtain a low-carbon concrete that is not very sensitive to variations in hygrometric conditions. Prior art

[0002] Wood concrete now offers a low-carbon alternative to conventional concrete. It is a concrete in which the aggregates are replaced by wood particles, resulting in a material offering high mechanical and thermal performance while being lighter than conventional concrete.

[0003] One of the problems posed by wood concrete is its sensitivity to variations in hygrometric conditions. Indeed, when wood is in contact with particularly humid air, it tends to absorb moisture, which leads to an increase in its volume, or swelling. When the air becomes dry again, the wood releases this moisture into the air, which leads to a decrease in its volume, or shrinkage. This phenomenon can generate cracks in construction elements made of wood concrete.

[0004] Document FR2677295 proposes to solve this problem by coating the wood particles with silica fume. This solution is not satisfactory, silica fume having a high cost and posing supply difficulties due to its scarcity. Statement of the invention

[0005] The present invention aims to overcome these drawbacks by proposing a concrete comprising a binder and wood particles, the volume content of the wood particles in said concrete being greater than or equal to 30%. This concrete is particular in that the wood particles are coated in a metakaolin.

[0006] Thanks to these provisions, the concrete according to the invention has a reduced carbon footprint thanks to the presence of wood, while having a mechanical resistance making it compatible with construction, and an increased sensitivity to variations in hygrometry thanks to the use of metakaolin, an inexpensive, very available material with a low carbon footprint.

[0007] The total mass of the metakaolin coating said wood particles can be between 15 and 60% of the total mass of the wood particles, which allows effective coating of the wood particles and effective sealing of their microporosity.

[0008] The total volume of metakaolin coating said wood particles may be greater than or equal to 4% of the total volume of the wood particles, which allows effective coating of the wood particles and effective sealing of their microporosity.

[0009] Said concrete may comprise sodium silicate, the mass of sodium silicate being between 5 and 15% of the mass of wood particles, which makes it possible to effectively fix the metakaolin on the wood particles.

[0010] The present invention also relates to a method for manufacturing concrete according to the invention, characterized in that it comprises the following steps: - mixing the wood particles with the metakaolin, in order to obtain a coating of the wood particles with the metakaolin, - mixing wood particles with at least one binder and water.

[0011] Thanks to these provisions, the concrete according to the invention can be obtained in a simple and efficient manner.

[0012] Said manufacturing method may comprise a step of drying the wood particles to a humidity level of less than 50% before mixing the wood particles with the metakaolin, which allows more effective coating of the wood particles with the metakaolin by mixing.

[0013] Said manufacturing method may comprise a step of mixing the wood particles together before mixing the wood particles with the metakaolin, which makes it possible to obtain a homogeneous mass of wood particles, and thus a more homogeneous coating by the metakaolin by mixing.

[0014] Said manufacturing method may comprise the following steps: - addition of sodium silicate to the wood particles coated with metakaolin, in order to fix the metakaolin on the surface of the wood particles, - drying of wood particles coated with metakaolin and sodium silicate, to a humidity level below 50%.

[0015] In this way, the metakaolin coating remains fixed on the surface of the wood particles, and does not dilute in the other elements entering into the composition of the concrete when the wood particles are mixed with it. The metakaolin can therefore effectively play its role of sealing the microporosity of the wood particles.

[0016] The fixing step may consist of vaporizing a sodium silicate solution in a mixer in which the dried wood particles and the metakaolin have been mixed, which is a simple and effective embodiment of the invention.

[0017] The fixing step may consist of soaking the metakaolin-coated wood particles in a sodium silicate solution, which allows efficient distribution of the sodium silicate over the entire surface of the wood particles. Brief description of the drawings

[0018] The present invention and its advantages will appear better in the following description of several embodiments given as non-limiting examples, with reference to the appended drawings, in which:

[0019] [Fig-1] [Fig.l] is a schematic view of a concrete according to one embodiment preferred of the invention. Description of the embodiments

[0020] The concrete according to the invention, represented in [Fig.l], comprises a binder 1, and wood particles 2 coated in a metakaolin 3.

[0021] The binder is preferably a mineral binder chosen from the group comprising, for example, cement, Portland cement, CEM II cement, another cement meeting the cement standard EN 197-1, blast furnace slag, metakaolin, calcined clays or a combination of at least two of these components.

[0022] One or more fillers can be added to the cement, such as siliceous or calcareous fillers meeting the NF P18-508 standard.

[0023] Sand can be added in addition to the binder to form a mortar and improve the strength of the wood concrete.

[0024] The metakaolin used for the coating is for example a flash metakaolin.

[0025] The wood particles may be coated exclusively with metakaolin, or with a mixture of metakaolin and one or more other products, for example a CEM IV cement. The metakaolin, if not used alone for the coating, may constitute at least 50% by weight of the coating products, and preferably at least 70 to 80%.

[0026] The wood particles may be in the form of chips, wafers, granules, or any other form, for example. The wood particles may have a particle size of between 1 mm and 50 mm, preferably between 2 mm and 14 mm. The wood may be of any species, for example pine, spruce, fir, beech, oak, bamboo, a mixture of at least two of these species, or other.

[0027] The volume content of wood particles in the concrete according to the invention may be greater than or equal to 30%, preferably greater than or equal to 50%, for example between 60 and 75%.

[0028] The quantity of metakaolin coating the wood particles, in terms of mass, is for example between 15 and 60%, preferably between 35 and 55% of the quantity of wood particles. Thus, if the volume content of the wood particles in the concrete is 70%, the quantity of metakaolin coating the wood particles is preferably between 80 and 125 kg per m3.

[0029] The quantity of metakaolin coating the wood particles, in terms of volume, is for example greater than 4%, preferably between 6 and 10% of the quantity of wood particles.

[0030] In a preferred embodiment, the concrete comprises sodium silicate, the function of which is to fix the metakaolin on the wood particles, and to prevent it from mixing with the other constituents of the wood concrete, for example the binder, when they are mixed with the wood particles. The mass of sodium silicate is for example between 5 and 15%, preferably between 8 and 12% of the mass of the wood particles.

[0031] As an alternative to sodium silicate, other alkaline activators such as sodium carbonate or sodium hydroxide can be used to fix the metakaolin to the wood particles.

[0032] In the concrete according to the invention, the particularly fine particles of metakaolin seal the micropores of the wood particles. This not only reduces the dimensional variation of these particles with variations in hygrometry, but also increases their mechanical strength and durability.

[0033] The concrete according to the invention can be manufactured according to a process comprising the following steps: - preferably, drying the wood particles to a moisture content of less than 50%, preferably less than 30%. This moisture content can be measured by completely drying the wood particles in an oven and calculating the difference in mass between the current mass of the particles and the mass of the completely dry particles divided by this dry mass.This drying step can be carried out in the open air, in a drying tank, in a fluidized bed, or by any other means, - preferably, mixing the wood particles together, for example in a mixer, in order to obtain a homogeneous mass of wood particles, for a duration for example of between 30 and 90 seconds, preferably between 50 and 70 seconds, - mixing the wood particles with the metakaolin, for example in a mixer which can be identical to the mixer used in the previous step, in order to obtain a coating of the wood particles by the metakaolin, for a duration for example of between 30 and 120 seconds, preferably between 50 and 90 seconds. A portion of the binder, for example from 0 to 30% of the total weight of the binder, can be incorporated during this mixing step, possibly from the start. Preferably, in this mixture, at least 70% of the mass consists of wood and metakaolin, . - mixing wood particles with at least one binder and water, and where appropriate with other elements entering into the composition of the concrete such as one or more fillers, and fillers such as sand.

[0034] It should be noted that part of the binder can be mixed with the wood particles from the step of mixing the wood particles with the metakaolin. A step of mixing the wood particles with the metakaolin and with part of the binder is then obtained, for example from 10 to 30% by weight of the total quantity of binder.

[0035] At the end of this last step, the composition obtained can be cast in a molding bench, then put under mechanical pressure, at a pressure level of, for example, between 80 and 150 kN / m2, in order to obtain a prefabricated construction panel.

[0036] In a preferred embodiment of the invention, the method further comprises the following steps, after coating the wood particles with the metakaolin, and before mixing these particles with the binder and water: - fixing the metakaolin coating the wood particles on the surface of the wood particles. This fixing is preferably achieved using sodium silicate. A sodium silicate solution may be sprayed onto the wood particles, for example directly in the mixer used for coating, or onto a conveyor transporting the wood particles after they have been coated. Alternatively, the wood particles coated with metakaolin may be dipped in a sodium silicate solution, which has the advantage of a more homogeneous distribution of the sodium silicate on the particles, - drying the wood particles coated with metakaolin and sodium silicate, to a humidity level below 50%, preferably 30%. This drying step can be carried out in the open air, in a drying tank, in a fluidized bed, or by any other means.

[0037] Here is an example of the composition of a concrete according to the invention, for 1 m3 of compacted concrete: - binder (mixture of cement, blast furnace slag, limestone filler, cement representing at least 40% of the total mass): 270 to 310 kg, - sand, grain size between 0 and 4 mm: 342 kg, - treated wood particles, grain size between 4 and 8 mm: 670 to 710 liters, - water: 210 to 250 kg.

[0038] In this composition, the treated wood particles consist of the following elements, according to the respective mass contents: - wood: between 64 and 66%, - metakaolin: 30%, - sodium silicate: between 6 and 8%.

[0039] One of the concretes whose composition is listed above was tested according to standard NF EN 772-14, in order to examine its sensitivity to humidity in terms of dimensional variations. Its performance was compared to a control concrete whose composition was identical, but in which the wood particles were not coated in metakaolin. The tests showed that the dimensional variations of the concrete according to the invention are half as significant as the dimensional variations of the control concrete without pretreatment.

[0040] Mechanical compressive strength tests according to standard NF EN 12390-3 were also carried out with an average strength greater than 4 mega Pascal at 28 days.

[0041] The present invention is of course not limited to the embodiments described but extends to any modification and variant obvious to a person skilled in the art within the limits of the appended claims. Furthermore, the technical characteristics of the different embodiments and variants mentioned above may be, in whole or in some cases, combined with each other.

Claims

Claims

1. Concrete comprising a binder (1), and wood particles (2), the volume content of the wood particles (2) in said concrete being greater than or equal to 30%, characterized in that the wood particles (2) are coated in a metakaolin (3).

2. Concrete according to claim 1, wherein the total mass of the metakaolin (3) coating said wood particles (2) is between 15 and 60% of the total mass of the wood particles (2).

3. Concrete according to one of claims 1 to 2, wherein the total volume of metakaolin (3) coating said wood particles (2) is greater than or equal to 4% of the total volume of the wood particles (2).

4. Concrete according to one of claims 1 to 3, comprising sodium silicate, the mass of sodium silicate is between 5 and 15% of the mass of wood particles (2).

5. Method for manufacturing a concrete according to one of claims 1 to 4, characterized in that it comprises the following steps: - mixing the wood particles (2) with the metakaolin (3), in order to obtain a coating of the wood particles (2) with the metakaolin (3), - mixing the wood particles (2) with at least one binder (1) and water.

6. Manufacturing method according to claim 5, characterized in that it comprises a step of drying the wood particles (2) to a humidity level of less than 50% before mixing the wood particles (2) with the metakaolin (3).

7. Manufacturing method according to one of claims 5 to 6, characterized in that it comprises a step of mixing the wood particles (2) together before mixing the wood particles with the metakaolin (3).

8. Manufacturing method according to one of claims 5 to 7, characterized in that it comprises the following steps: - adding sodium silicate to the wood particles (2) coated with metakaolin (3), in order to fix the metakaolin (3) on the surface of the wood particles (2), - drying the wood particles (2) coated with metakaolin (3) and sodium silicate, to a humidity level of less than 50%.

9. Manufacturing method according to claim 8, characterized in that the fixing step consists of vaporizing a sodium silicate solution in a mixer in which the dried wood particles (2) and the metakaolin (3) have been mixed.

10. Manufacturing method according to claim 8, characterized in that the fixing step consists of soaking the wood particles (2) coated with metakaolin (3) in a sodium silicate solution.

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