OA22019A - Solid, concrete-like material containing natural Combretum gum. - Google Patents

Abstract

The present invention relates to a novel, carbon-negative, concrete-like solid material obtained by compacting and heat-treating a composition comprising combretum gum, clay, sand and/or a sand-clay mixture, and water; a manufacturing process for said solid material; and its use in various applications, particularly in the field of construction materials. The material of the invention exhibits improved mechanical strength and/or water resistance compared to prior art materials that aim to eliminate the use of cement and replace it with other binders. Furthermore, its mechanical strength is comparable to that obtained with cement-based concrete-type materials, while ensuring a lower environmental impact in terms of carbon footprint, recyclability, use of renewable materials, toxicity, etc., for the production of sustainable, healthy, and ecological housing.

Description

Solid, concrete-like material containing natural combretum gum

The present invention relates to a new solid material of the type of concrete with a negative carbon balance obtained by compaction and heat treatment of a composition comprising at least a natural combretum gum, clay, sand and/or a mixed sand-clay material, and water, a process for manufacturing said solid material as well as its use in various applications, and in particular in the field of construction materials.

Concrete is one of the most widely used manufactured materials in the world. It has the advantage of good compressive strength, ranging from 20 to 100 MPa. It is primarily composed of aggregates (gravel, crushed stone), mixed with cement, sand, and water. Annual aggregate consumption in France is 350 million tons, or 6 tons per capita per year and 17 kg per capita per day. Projections show that the demand for aggregates continues to rise, particularly for the construction of new buildings. Natural aggregates are generally obtained by exploiting alluvial, terrestrial, or marine sand and gravel deposits. Natural aggregates are not a renewable resource, and although technically unlimited, they are becoming increasingly scarce for societal and environmental reasons. It is becoming increasingly difficult to open new quarries to meet the demand for natural aggregates, as these operations cause nuisances for nearby residents (noise, dust, increased traffic, etc.). Furthermore, the calcination of natural limestone mineral resources needed for cement production is responsible for nearly half of the CO2 emissions associated with concrete manufacturing, making it one of the most CO2-intensive materials produced by humans. The RE2020 environmental regulations are expected to be imposed on construction material producers within the next two to three years.

Solutions have been proposed to reduce the environmental impact (particularly in terms of carbon footprint) of concrete, such as using terracotta bricks. However, their production generates significant energy consumption and large quantities of CO2.

Raw earth-based materials have also been described. However, their compressive strength remains low (around 5 MPa), and their water resistance is also poor, limiting the construction of buildings to a maximum of one or two stories. In some countries, such as Burkina Faso, raw earth is currently the most widely used building material because these countries do not produce cement, and its importation is very expensive. However, in tropical regions, raw earth building materials are vulnerable to torrential rains that destroy people's homes every year.

To improve the performance of raw earth, cement- or lime-based binders have been studied. However, as explained above, these binders have a significant environmental impact. Other binders with a low environmental impact have been described, such as starch, chitosan, rice straw, glutinous rice, or alginate. However, the resulting materials do not fully meet expectations in terms of mechanical properties and/or water resistance.

The aim of the present invention is therefore to overcome the drawbacks of the prior art, and in particular to provide building materials with mechanical strength close to that of cement concrete but with a lower environmental impact in terms of carbon footprint, recyclability, use of renewable materials, toxicity, etc., in order to produce sustainable, healthy, and ecological housing. Another aim of the invention is to improve water resistance, particularly suited to the low-cost construction market. A further aim of the invention is to provide a manufacturing process for the aforementioned materials that is simple, scalable, uses abundant raw materials, and is environmentally beneficial.

The present invention therefore has as its first object a solid material based on sand and/or clay, characterized in that it is obtained by compaction and heat treatment of a composition comprising a) sand, clay, and/or a mixed sand-clay material, b) combretum gum, and c) water.

The material of the invention exhibits improved mechanical strength and/or water resistance compared to prior art materials that aim to eliminate the use of cement and replace it with other binders. Furthermore, its mechanical strength is comparable to that obtained with cement-based concrete materials, while guaranteeing a lower environmental impact in terms of carbon footprint, recyclability, use of renewable materials, toxicity, etc., to produce sustainable, healthy, and ecological housing.

The material is obtained from a composition comprising a) sand, clay and/or a mixed sand-clay material, b) combretum gum, and c) water.

a) sand, clay and/or mixed sand-clay material

The composition comprises (as component a)) sand, clay and/or a sand-clay mixture, preferably sand and optionally a sand-clay mixture, and particularly preferably sand and a sand-clay mixture.

According to one embodiment, the composition comprises from 5 to approximately 95% by mass of sand, relative to the total mass of the composition. Preferably, the composition comprises at least approximately 50% by mass of sand, and particularly preferably from 65% to 90% by mass of sand relative to the total mass of the composition (corresponding to the total sand content, i.e., from the sand and the mixed material).

The sand preferably has a grain size of 2 mm or less, and particularly preferably less than 2 mm.

According to one embodiment, the composition comprises from 0.01 to approximately 90% by mass of clay, relative to the total mass of the composition. Preferably, the composition comprises at most approximately 50% by mass of clay, particularly preferably from 0.5% to 25% by mass of clay, and more particularly preferably from 1% to 15% by mass of clay, relative to the total mass of the composition (corresponding to the total clay content, i.e. from the clay and the mixed material).

Clay typically includes phyllosilicates such as kaolinite, muscovite, smectites, illites, and/or chlorites; quartz; iron oxides and/or hydroxides such as goethite, hematite; carbonates such as calcite and/or dolomite; and/or other types of silicates such as certain feldspars (e.g. albite and/or orthoclase).

The clay preferably has a particle size less than or equal to 2 pm, and particularly preferably less than 2 pm.

The sand-clay mixture is preferably a raw clayey soil. The raw clayey soil can thus provide the clay in the composition of the invention.

In a preferred embodiment, the composition includes sand, raw clayey earth (as a mixed sand-clay material), combretum gum, and water.

According to this embodiment, the composition comprises approximately 65% to 85% by mass of sand, and approximately 0.1% to 20% by mass of raw clayey earth, relative to the total mass of the composition.

Raw clay soil may comprise from 0.01 to 50% by mass approximately of clay and from 50 to 99.9% by mass approximately of sand, relative to the total mass of raw clay soil, and preferably from 15 to 40% by mass approximately of clay and from 60 to 85% by mass approximately of sand, relative to the total mass of raw clay soil.

In a particularly preferred embodiment, sand and raw clay are present in the composition in a sand/raw clay mass ratio ranging from approximately 0.1 to 50, and preferably from approximately 3 to 10. This results in materials with improved performance in terms of compressive strength and water resistance.

The solid material

The material obtained from the composition is a solid material. Such a material can be in the form of a block, a brick, or any other solid element.

In other words, the material of the invention is in a non-powdery form.

b) combretum gum

The composition also includes combretum gum.

Combretum gums are gums extracted from certain trees or plants of the Combretum family, and in particular from trees of the species Combretum mgricans. They are abundant natural resources found in tropical Africa.

In one embodiment, combretum gum represents at least 0.1% by mass approximately, preferably from 1% to 20% by mass approximately, particularly preferably from 1.5% to 15% by mass approximately, and more particularly preferably from 2% to 10% by mass approximately, relative to the total mass of the composition.

c) water

The composition preferably comprises no more than approximately 30% water by mass, particularly preferably approximately 1 to 20% water by mass, and even more particularly preferably approximately 2 to 10% water by mass, relative to the total mass of the composition. This allows for optimal compaction of the material (preferably having a dry density greater than 2000 kg/ ^m³ ).

Compaction

Compaction can be carried out at a pressure of at least approximately 0.5 MPa, preferably at a pressure ranging from approximately 1 MPa to 50 MPa, and particularly preferably from approximately 5 MPa to 25 MPa. The use of such pressure ranges makes it possible to obtain a compact material (preferably with a dry density greater than 2000 kg/ ^m³ ) and thus, high compressive strength.

Compaction can be carried out with a hydraulic press.

Thermal treatment

Thanks to heat treatment, good mechanical strengths are obtained.

Heat treatment is preferably carried out at a temperature of at least approximately 30°C, particularly preferably at a temperature ranging from approximately 35°C to 65°C, and even more particularly preferably at a temperature ranging from approximately 40°C to 60°C. The use of such temperature ranges results in improved performance in terms of compressive strength and water resistance.

Heat treatment can be carried out in an oven or in ambient air (e.g. in the sun).

The heat treatment is preferably carried out at atmospheric pressure.

The heat treatment can last at least 4 days, preferably at least 7 days, and particularly preferably from 21 to 28 days.

The invention also has as a second object a method for manufacturing a solid material conforming to the first object of the invention, characterized in that it comprises at least the following steps:

i) preparation of a composition comprising a) sand, clay, and/or a mixed sand-clay material, b) combretum gum, and c) water, ii) compaction of the composition to form a compacted solid product, and iii) heat treatment of the compacted solid product.

The composition is as defined in the first object of the invention.

The compaction is as defined in the first object of the invention.

The heat treatment is as defined in the first object of the invention.

The invention also has as its third object the use of a solid material conforming to the first object of the invention or obtained according to a process conforming to the second object of the invention, as a building material, in particular for the production of habitats.

I

Brief description of the drawings

The attached drawings illustrate the invention:

[Fig. I] Figure 1 illustrates a solid material according to the invention.

Other features and advantages of the present invention will become apparent from the description of examples presented below, to which the invention is not, however, limited.

Examples

Example 1: Preparation of a solid material M1 according to the invention and comparison with materials not according to the invention MA and MB

The combretum gum used in the present invention was extracted from the bark of trees or shrubs of the species Combretum nigricans in Burkina Faso as follows: harvesting takes place between January and April before the first rains. The combretum gum is directly collected by hand from the tree bark. The gum can also be collected by making incisions in the tree to increase production yields.

The extracted gum is in the form of a very hard and fragile resin, similar to glass.

The type of soil used in the examples is:

- a raw clayey earth from the Nagen brickworks in France containing quartz, calcite, goethite, smectite, chlorite and albite (hereinafter referred to as Nagen earth). This contains 22.5% by mass of clay (particles < 2 mm) relative to the total mass of the raw earth, the remainder being comparable to sand with a maximum size < 2 mm, or

- a raw clayey earth from the Bouisset brickworks in France comprising quartz, orthoclase, muscovite, illite and kaolinite (hereinafter referred to as Bouisset earth). This contains 32% by mass of clay (particles < 2 pm) relative to the total mass of the raw earth, the remainder being comparable to sand with a maximum size < 2 mm.

The sand is a CEN-certified sand conforming to EN 191-1 and ISO 679:2009. It is supplied by Société Nouvelle du Littoral, a French company located in Leucate, in the south of France, near the ports of Barcelona and Marseille. It has a grain size of 0/2 mm (hereinafter referred to as Leucate sand).

The extracted gum is ground into a fine powder with a particle size of less than 1.25 mm.

The ground gum is mixed with raw earth, sand, and water to form a composition 1 comprising 3.6% by mass of combretum gum, 11.3% by mass of Nagen soil (comprising 2.5% by mass of clay and 8.8% by mass of sand), 78.9% by mass of Leucate sand, and 6.2% by mass of water. The composition is then compacted using a hydraulic press sold by IGM at a pressure of 15 MPa to form a brick, which is then heat-treated at a temperature of approximately 50°C for about fifteen days using an oven to form a material M1. The resulting brick is analyzed for compression (compressional strength) using a device sold under the trade name Universal Press 100 kN by IGM.

The results are given in Table 1 and compared with those obtained with additions of lime or cement (dry compressive strength).

Composition A, which is not in accordance with the invention, comprises 3.3% by mass of lime, 82.3% by mass of Nagen earth (comprising 18.5% by mass of clay and 63.8% by mass of sand), and 14.4% by mass of water. Composition B, which is not in accordance with the invention, comprises 3.3% by mass of cement, 84.1% by mass of Bouisset earth (comprising 26.9% by mass of clay and 57.2% by mass of sand), and 12.6% by mass of water. After compaction and heat treatment as described above for composition 1, the materials not in accordance with the invention, MA and MB, are obtained, respectively.

The water resistance of the bricks is also measured. To do this, the bricks are immersed in water for two hours and then kept for 24 hours in a waterproof bag. After this time, the compressive strength is measured as determined above (wet compressive strength).

[Table 1]

M1 MAU MBU Dry compressive strength (MPa) 17.3 5.3 9.2 Wet compressive strength (MPa) 2.5 1.0 2.3

i‘i Materials not forming part of the invention

The results in Table 1 show that combretum gum gives much better results than with additions of lime or cement in similar proportions.

The presence of sand in composition 1 helps to avoid or reduce the occurrence of cracking during heat treatment.

Figure 1 represents the material Ml as prepared in Example 1.

Example 2: Preparation of solid materials according to the invention M2a, M2b, M3a, and M3b

Several materials according to the invention have been prepared from a combretum gum as described and extracted in Example 1.

The extracted gum is prepared according to one or the other of the methods described below: - by dry method, as in example 1. Grinding is carried out dry to obtain a fine powder with a particle size of less than 1.25 mm;

- in liquid form, the gum is then dissolved in water.

The crushed or dissolved gum is then mixed with raw earth, sand, and water to form:

- a composition 2 comprising 5.2% by mass of combretum gum, 10.9% by mass of Nagen earth (comprising 2.5% by mass of clay and 8.4% by mass of sand), 76.1% by mass of Leucate sand, and 7.8% by mass of water (composition 2a comprising the gum obtained by dry method and composition 2b comprising the gum obtained by liquid method); and - a composition 3 comprising 5.3% by mass of combretum gum, 11% by mass of Bouisset earth (comprising either 3.5% by mass of clay and 7.5% by mass of sand), 77.2% by mass of Leucate sand, and 6.5% by mass of water (composition 3a comprising the gum obtained by dry method and composition 3b comprising the gum obtained by liquid method).

Compositions 2a, 2b, 3a, and 3b are then compacted using a hydraulic press sold by IGM at a pressure of 15 MPa to form bricks. These bricks are then heat-treated at approximately 50°C for twenty-eight days in an oven to form materials M2a, M2b, M3a, and M3b, respectively. The resulting bricks are analyzed for compression (compressional strength) using a device sold by IGM under the trade name Presse Universelle 100 kN (dry compressive strength).

The compressive strengths are given in Table 2.

[Table 2]

M2a M2b M3a M3b Dry compressive strength (MPa) 39 36 45 38

The results in Table 2 show that the compressive strengths obtained on the two compositions according to the invention with a combretum gum prepared by dry or liquid means are high and much higher than those listed in the Part 1.

Example 3: Preparation of a solid material as defined in the invention

Several materials according to the invention have been prepared from compositions 2b and 3b as described in Example 2.

Compositions 2b and 3b were then compacted using a hydraulic press sold by IGM at a pressure of 15 MPa to form bricks which were then heat-treated at a temperature of 50°C for 7 days, 14 days, 21 days or 28 days in an oven to form materials M2b-T7, M2b-T14, M2b-T21, and M2b-T28 and materials M3b-T7, M3b-TI4, M3b-T21, and M3b-T28 respectively.

The resulting bricks were analyzed for compression (compressional strength) using a device sold under the trade name Presse Universelle 100 kN by the company IGM. The compressive strengths of bricks heat-treated at 50°C for varying durations were compared to that of a brick obtained from the same compositions 2b and 3b dried at 20°C, i.e., not having undergone heat treatment at 50°C (materials M2b-ST and M3b-ST). The results are given in Table 3.

[Table 3]

Dry compressive strength (MPa) M2b-ST‘) 11 M2b-T7 31 M2b-T14 32 M2b-T21 33 M2b-T28 36 M3b-STG 12 M3b-T7 32 M3b-T14 32 M3b-T21 34 M3b-T28 38

<’> Materials not forming part of the invention

The results in Table 3 show that without heat treatment the compressive strength remains low.

Claims (9)

DEMANDS l. Solid material based on sand and/or clay, characterized in that it is obtained by compacting and heat-treating a composition comprising a) sand, clay, and/or a mixed sand-clay material, b) combretum gum, and c) water. 2. Solid material according to any one of the preceding claims, characterized in that the composition comprises from 5 to 95% by mass of sand, and preferably from 65% to 90% by mass of sand, relative to the total mass of the composition. 3. Solid material according to any one of the preceding claims, characterized in that the composition comprises from 0.01% to 90% by mass of clay, and preferably from 0.5% to 25% by mass of clay, relative to the total mass of the composition. 4. Solid material according to any one of the preceding claims, characterized in that the composition comprises sand and raw clayey earth, combretum gum and water. 5. Solid material according to claim 4, characterized in that sand and raw clayey earth are present in the composition in a sand/raw clayey earth mass ratio ranging from 0.1 to 50. 6. Solid material according to any one of the preceding claims, characterized in that the heat treatment is carried out at a temperature of at least 30°C, and preferably at a temperature ranging from 35°C to 65°C. 7. Solid material according to any one of the preceding claims, characterized in that the compaction is carried out at a pressure of at least 0.5 MPa, and preferably at a pressure ranging from 1 MPa to 50 MPa. 8. Solid material according to any one of the preceding claims, characterized in that the combretum gum represents at least 0.1% by mass relative to the total mass of the composition, and preferably from 1% to 20% by mass, relative to the total mass of the composition. 9. A method for manufacturing a solid material as defined in any one of the preceding claims, characterized in that it comprises at least the following steps: i) preparation of a composition comprising a) sand, clay and/or a mixed sand-clay material, b) combretum gum, and c) water, ii) compaction of the composition to form a compacted solid product, and iii) heat treatment of the compacted solid product. I 10. Use of a solid material as defined in any one of claims 1 to 8, as a building material, in particular for the production of habitats