Clay material comprising a mixture of cellulose and starch for earthen construction

Abstract

Raw earth construction material, obtained by adding and mixing cellulose and starch into a clay material, characterized in that the ratio of amylopectin to amylose by weight in the added starch is greater than 3. Figure 14

Description

Title of the invention: Clay material comprising a mixture of cellulose and starch for raw earth construction Technical field and state of the art

[0001] The invention relates to the reinforcement of the mechanical resistance of clay materials by biopolymers, for construction in raw earth.

[0002] By "clay materials" is meant here a clay mineral or a set of clay minerals, as well as rocks composed essentially of these minerals.

[0003] By “clay mineral” is meant here a phyllosilicate, in particular kaolinite, illite or montmorillonite.

[0004] For a general presentation of clays and clay minerals, one can refer for example to Meunier (Clay, ISBN 3-540-21667-7, 2005), Velde et al. (The origin of clay minerals in soils and weathered rocks, ISBN 978-3540756330, 2008), Bergaya et al. (Handbook of clay science, ISBN 978-0-08-098258-8, 2013), Lloyd et al. (Handbook of clay minerals, ISBN 978-1632393814, 2015).

[0005] Clay minerals are weathering and detrital minerals. Depending on the parent rock that is weathered, the climatic conditions and the topography, different clay minerals will form.

[0006] Phyllosilicates comprise sheets corresponding to the stacking of tetrahedral T layers and octahedral O layers. In phyllosilicates, the tetrahedra share three out of four vertices by the basal oxygen atoms, which form a hexagonal network, the fourth vertex being connected to an octahedral layer. In a tetrahedral layer, the central cation of the tetrahedron (Si4+, or substituted by Al3+) is coordinated with four oxygen atoms or hydroxyl groups. In an octahedral O layer, the central cation (Al3+, or substituted by Mg3+, or Fe3+) is coordinated with oxygen atoms or hydroxyl groups.

[0007] The distance between each layer defines the interlayer space. The layer and the interlayer space form the structural unit of the clay mineral.

[0008] Under normal conditions of temperature and pressure, clay materials contain water in their structure, the expression hydrated phyllosilicate being used to represent this reality.

[0009] Phyllosilicates can be classified in various ways, the classification used here taking into account the basic structure of the layers.

[0010] By "kaolinite" is meant here a mineral from a family of clay minerals of general formula Al2Si2O5(OH)4, comprising a TO chain, which is defined by a tetrahedral SiO4 layer and an octahedral A1O6 layer with a structural unit of 7Å. The electrically neutral TO sheets are linked to each other by hydrogen bonds, of the type -Al-OH—O-Si-, and Van der Waals forces. The repeat distance between the sheets is 7 Å, measurable by X-ray diffraction. In the interlayer space of kaolinite, strong hydrogen bonds between the OH of an octahedral layer of a sheet and the O of the tetrahedral layer of the following sheet prevent the insertion of water between the sheets. Kaolinite is neutral, with some charge defects at the particle edges. Kaolinite particles are generally composed of 50 to 100 sheets.

[0011] Most commonly, kaolinite occurs as micron-sized pseudohexagonal platelets, which can be stacked in the form of books or vermicules reaching 50 to 100 qm in thickness.

[0012] By "kaolinite" we also designate here the other clay minerals of the same family, which are rarer, in particular dickite, nacrite which are polytypes, and halloysite which is a polymorph and has a tubular structure with a structural unit of 10 Å when it is hydrated.

[0013] Kaolinite is the main component of kaolin, a rock resulting from the alteration of acid rocks (granite, granodiorite, pegmatite). When meteoric or hydrothermal degradation products remain in place, a primary or residual kaolin is formed. When the degradation products are transported before deposition, a sedimentary or secondary kaolin is obtained, sometimes called kaolinic clay. Kaolinite or kaolin is most often mined in open pits. Secondary deposits are generally richer in kaolinite (up to 85-95%) than primary deposits, and represent more than two-thirds of world production and about three-quarters of world reserves. The main producers of kaolin in France are Imerys, Sibleco and the Armorican kaolin company SOKA. Kaolinite is a noble clay mineral, used as a mineral filler in the paper industry, for paints, rubbers, and plastics.Kaolinite is used in the manufacture of ceramics and refractory materials, food packaging. In clays, which are rocks containing more than 50% clay minerals, clays containing mainly kaolinite are noble clays.

[0014] By "illite" is meant here a clay mineral of general formula (Si3,4Alo,6) (Al2) Oio(OH)2, 0.6K+, formed of TOT type sheets. The substitution of Si by Al, in the tetrahedral layer, induces charge defects conducive to the presence of potassium in the interlayer space. This is housed in the hexagonal ring formed by the oxygens, inducing a strong ionic interlayer bond. This strong ionic bond prevents the presence of water in the interlayer space and therefore limits swelling. The interlayer distance is 10 Å. The hydroxyl groups are present between the tetrahedral and octahedral layers and are therefore inaccessible. On the surface of the particles are mainly oxygen. Illite particles are generally composed of 5 to 10 layers. Illite is a clay mineral that is much less used than kaolinite.

[0015] By "montmorillonite" we mean here a clay mineral of the smectite family, of general formula (Al2xMgx)Si4(Oi0)(OH)2(CEC)x, the term "CEC" designating the cation exchange capacity. Smectites have a sequence of TOT-type sheets, like illite. On the other hand, in addition to the substitutions of Si by Al in the tetrahedral layer, there are also substitutions of Al by Mg in the octahedral layer, inducing a greater charge defect than for illite. Thus, the sequence of sheets is stabilized by hydrated cations such as Ca2+, Mg2+ and Na+. These cations have a significant hydration energy and allow water to easily access the interlayer space. Montmorillonite is a swelling clay with an interlayer distance of 50 to 100 Å. Like illites, hydroxyl groups are present between the tetrahedral and octahedral layers and are therefore inaccessible.On the surface of the particles are mainly oxygens. Montmorillonite particles are composed of about 5 layers, and their organization is close to an interconnected network.

[0016] Montmorillonites are the main constituents of swelling clays. The use of swelling clays in raw earth construction is delicate. Although it is known to add swelling inhibitors (saponin, polypropylene glycol, amines) to these clays, the use of these inhibitors can have a negative effect on the compressive strength properties, as shown by Masson (Reduction of the swelling of a montmorillonite under hygric stress by the use of organic molecules, application to raw earth construction, 2021).

[0017] Clay minerals, and in particular their porosity, are to be considered at different scales: that of the sheet (and the interlayer space), that of the assembly of sheets forming particles, that of the assembly of particles forming aggregates (with spaces between the particles), and that of the assemblies of aggregates (with spaces between the aggregates).

[0018] The general properties of kaolinite, illite and montmorillonite are as follows: Kaolinite Illite Montmorillonite Sheet type TO TOT TOT Interlayer cation None K+ Ca2+ Mg2+ Na+ Interlayer distance 7 10 50-100 leaflet (in angstroms) Number of leaflets per particle 50-100 5-10 5 Specific surface area (m2 / kg) 8-30 67-150 600-800 CEC (Cmole+ / kg) 1-20 10-40 120-200

[0019] By "raw earth" is meant here a material found under the topsoil, and resulting from natural processes of chemical and physical alteration of a parent rock, raw earth being a mixture of clay minerals, silts, sands, gravels and pebbles, raw earth being building earth.

[0020] Raw earth is a granular mineral material, composed of solid, liquid and gaseous matter. The solid fraction can be made up of grains: pebbles, gravel (from 20 mm to 5 mm), sand (5 mm to 0.06 mm), silt (0.06 mm to 2 pm), clay, which are platelets rather than grains (size less than 2 pm) and metal oxides which have coloring properties (size also less than 2 pm). The liquid fraction is made up of water and organic and mineral bodies dissolved in this water. The gaseous fraction is made up of nitrogen, oxygen, carbon dioxide, as well as gases resulting from the life present in the earth (hydrogen, methane, etc.). The liquid and gaseous fractions undergo very rapid changes.

[0021] Essentially composed of aggregates (pebbles, gravel, sand and silt) and a binder (the paste formed by clays and water), raw earth is part of the concrete family ("earth concrete"), alongside cement concrete.

[0022] Raw earth is used in construction using different techniques: adobe, rammed earth, earth-straw, cob, clay, compressed earth block (CEB). Different techniques for compressing raw earth are also known (shaped, compressed, compacted, extruded earth).

[0023] For a presentation of earth construction techniques, one can refer for example to the Houben document (Treatise on earth construction, ISBN 2-86364-161-1, 2006).

[0024] Adobe consists of molding and drying in the sun a mixture of raw earth, a high quantity of water to form a plastic paste, often amended with straw. Adobe also refers to the raw earth bricks obtained by this molding and drying. In the compressed earth technique, the raw earth is compressed in a metal mold to obtain earth blocks (BTC block of compressed earth). The compressed earth block technique is sometimes presented as a modern version of adobe. Document EP2633131 (Terraco, 2013) describes a compressed raw earth construction element comprising a smectite chosen from montmorillonite or bentonite. Document FR3117483 (In Situ Lab, 2022) describes a construction material comprising dried seaweed mixed with clayey soil. Reference may also be made to document FR3115721.

[0025] Rammed earth consists of compacting a mixture of raw earth with a smaller quantity of water than adobe, between formwork, layer by layer. We can refer for example to document FR2861010.

[0026] Cob consists of a mixture of raw earth, water and natural fibers, such as straw, hay, horsehair, cow dung, to cover the wattle and daubs by coating them, or by applying pressure to the laths of timber-framed houses. For example, see document FR2970475 (Jolie terre, 2012).

[0027] Cob consists of a mixture of raw earth with straw or other fibers, the resulting material being shaped into large balls, placed on top of each other and compacted with the feet or hands to form walls. Cob is often framed by wooden elements.

[0028] Kaolinite is marketed in dry powder form as a binder for the preparation of plasters, cob, rammed earth or raw earth brick (adobe).

[0029] The invention allows at least the reinforcement of the mechanical resistance and advantageously of the water resistance of clay materials by biopolymers, for construction in raw earth.

[0030] By "biopolymers" is meant here polymers of natural origin, biosourced, in particular of high molecular weight, such as present in plant or animal fibers, or in plant extracts. Biopolymers are in particular starches extracted from rice, corn, wheat or other (potato, cassava, etc.), which have a significant quantity of amylopectin.

[0031] Biopolymers can, for example, be derived from agricultural or food industry waste. Biopolymers also refer to lipids here.

[0032] By “mechanical resistance” is meant here in particular the mechanical resistance to compression.

[0033] By “water resistance” we mean here the resistance to degradation by liquid water, in particular capillary water, rainwater.

[0034] The mechanical resistance to compression of raw earth-based construction materials is very modest, in the techniques of the prior art.

[0035] The document Morel et al. (Mechanical performance of adobe, 3rd transdisciplinary exchanges on raw earth constructions, 2009) describes the manufacture of block of earth compressed from raw earth whose clay is mainly kaolinite, smectite being a minority, the compressive strength of the material obtained being between 2 and 4.5 MPa.

[0036] This mechanical compressive strength decreases when the water content of the material decreases. The mechanical compressive strength depends on the implementation, and it is generally accepted that the compressive strength of the building material increases with the compaction rate, starting from a minimum value for adobe or cob, to an intermediate value for the rammed earth technique, the highest resistance values ​​being obtained for compressed earth blocks.

[0037] It is known empirically, in traditional recipes, to add polysaccharides, lipids, proteins to raw earth, to improve its properties. We can refer for example to the document Vissac et al. (Clays & Biopolymers. Natural stabilizers for earth construction, 2017). We can also refer to the document Losini et al. (Natural additives and biopolymers for raw earth construction stabilization - a review, 2021).

[0038] In these traditional recipes, the molecules added to the raw earth are contained in an unprocessed natural product (for example cow dung or horse manure, containing cellulose, or algae containing carrageenans), or the molecules are contained in a complex mixture extracted from a natural product (oils, waxes or butter, for example linseed oil, shea butter, gum arabic).

[0039] Traditional recipes are used with raw earths that vary greatly between them. As a result, the mechanisms leading to the improvement of the properties of raw earths by adding biopolymers are not precisely known.

[0040] This is particularly the case with the influence of the addition of biopolymers on the mechanical resistance of raw earths.

[0041] It is known in the prior art to add biopolymers to raw earth to increase the mechanical resistance to compression of a clay material mainly comprising kaolinite and possibly another clay mineral.

[0042] The Guiheneuf document (Formulation and reinforcement of earth material blocks for structural use, 2020) describes the addition of polysaccharides (xanthan gum, alginates), or lipids (linseed oil), tannins, casein, sodium hexametaphosphate, to three earths, all containing kaolinite as the main clay mineral. A first earth K is a synthetic earth formulated from industrial kaolin and sand, a natural earth R includes kaolinite and illite, and a natural earth S includes kaolinite, illite, vermiculite.

[0043] The Alhaik document (Influence of starch on the rheological, mechanical and multiphysical properties of earth-straw formulations, 2017) describes the use of starch as an additive to kaolinite on the one hand or to fine clay-limestone FAC on the other hand, the FAC comprising kaolinite and illite, the FAC being derived from the washing of aggregates in quarries. The addition of starch increases the compressive strength of kaolinite and FAC.

[0044] Millogo et al. (Earth blocks stabilized by cow-dung, Mater Struct 49:4583-4594, 2016) describes the effect of adding cow dung to a lateritic earth containing kaolinite. The addition of cow dung allows a slight increase in compressive strength, from 2.1 to 2.8 MPa. The authors hypothesize that the addition of cow dung causes a reaction with kaolinite, producing an amine that reduces the porosity of the adobe.

[0045] The document Perrot et al. (Strategies for optimizing the mechanical strengths of raw earth-based mortars. Constr Build Mater 167:496-504, 2018) describes the addition of alginate in a mixture of sand and kaolinite on the one hand, and in a natural earth comprising kaolinite, illite and smectite, a dispersant (hexamethaphosphate) being used during mixing. The compressive strength of the natural earth is approximately 8 MPa, and is not modified by the addition of alginate. The addition of alginate increases the compressive strength of the kaolin.

[0046] Reference may also be made to the document Ouedraogo et al. (Physical, thermal and mechanical properties of adobes stabilized withfonio (Digitaria exilis) straw. J Build Eng 23:250-258, 2019).

[0047] However, most raw earths do not contain or contain little kaolinite. This is particularly the case for natural earths containing swelling clays, rich in smectites.

[0048] In some publications, compressive strength tests are presented for construction materials formed from a mixture of raw earth and an organic binder, the raw earth not comprising kaolinite or comprising little kaolinite.

[0049] The Ouedraogo document (Stabilizer of sustainable and ecological construction materials based on raw earth using organic and / or mineral binders with low environmental impacts, 2019) describes the addition of ovalbumin in two natural earths, a first natural earth comprising illite, chlorite and a little montmorillonite, a second natural earth comprising mainly kaolinite, and illite.

[0050] The document Tourtelot et al. (Influence of Biopolymers on the Mechanical Behavior of Earth-Based Building Materials. Recent Prog Mater 3, 2021) describes the effect of adding a bio-sourced molecule on the compressive strength of natural raw earth mixed with sand, the natural raw earth mainly comprising illite (7%) and also comprising chlorite, kaolinite and traces of smectites. The bio-sourced molecule is chosen from the group comprising polysaccharides (cellulose, lignin, pectin, sodium alginate, wheat starch), a lipid (linseed oil), a protein (casein) and a complex molecule (tanic acid). The addition of a molecule from a first group leads to a decrease in compressive strength or has no notable effect on compressive strength (pectin, lignin, casein, tannic acid, linseed oil). The addition of a molecule from a second group leads to an increase in compressive strength (cellulose, wheat starch). With regard to the elastic modulus in compression, the addition of tannic acid, linseed oil, or casein leads to a sharp decrease in the elastic modulus. Objectives of the invention

[0051] The invention aims to reinforce the mechanical resistance and advantageously the water resistance of clay materials by biopolymers, for construction in raw earth.

[0052] Increasing the water resistance of raw earth elements helps improve the image of this material on the construction market.

[0053] A load-bearing construction material or one acting as a dividing wall must in fact withstand immersion in water (in the event of water damage), as well as possible water erosion (rain).

[0054] The invention aims to enable construction in raw earth from a variety of clay materials, with minimal impact on the environment, the implementation steps being few in number, avoiding sorting and the multiplication of earth characterizations before use.

[0055] By using mainly, and preferably only, local materials, the invention aims to provide a construction material reducing the transport of raw materials, and developing the use of local secondary materials in eco-construction.

[0056] The invention aims in particular to increase the mechanical resistance to compression of a wide variety of clay materials.

[0057] Indeed, currently, raw earth is mainly used for filling and partitions. Obtaining high mechanical resistance for raw earth would allow structural use (load bearing), which is a major obstacle for construction in urban areas where multi-story construction is necessary.

[0058] The invention aims in particular to increase the mechanical resistance to compression of a wide spectrum of raw earths, containing kaolinite and / or montmorillonite.

[0059] The biopolymers are advantageously derived from a local resource, close to the construction site.

[0060] Raw earth also advantageously comes from a local resource.

[0061] The use of biopolymers differs from the known use of hydraulic binders, such as lime and cement. The addition of lime or cement to the raw earth material makes raw earth construction lose some of its environmental interest by considerably increasing the gray energy emitted, and by making the recyclability of the material more difficult.

[0062] The use of biopolymers differs from the use of dispersing agents, such as superplasticizers used for the manufacture of concrete, these superplasticizers being able to present disadvantages for the environment.

[0063] The invention also aims at stabilizing a variety of soils comprising clay materials.

[0064] Soil stabilization is an important issue in urban planning. Indeed, the volume of excavated earth (tunnels, building foundations) is very large. This earth is mostly considered waste, while very large volumes of earth are also required for land development (for example for road infrastructure embankments). The stabilization of this excavated earth is part of a circular economy scheme: the excavated earth loses its status as waste and becomes a resource used locally. General presentation of the invention

[0065] For these purposes, the invention relates, according to a first aspect, to a material for raw earth construction, resulting from the addition and mixing of polymers of natural plant origin which are advantageously cellulose fibers and at least one starch, in a base material which comprises a clay material having at least one clay mineral chosen from the group comprising: kaolinite, illites and smectites including montmorillonites, the starch added to the base material having a ratio between the weight of amylopectin and the weight of amylose greater than 3.

[0066] According to various implementations, the weight of amylopectin in the added starch is greater than 75%, advantageously greater than 80%, advantageously greater than 90%.

[0067] In certain implementations, the starch is selected from the group comprising rice starch, wheat starch, and / or waxy maize starch. Waxy maize here refers to a hybrid maize whose grain starch is almost entirely composed of amylopectin. In certain implementations, the hybrid maize is a variety resulting from genetic modification, for example CRISPR.

[0068] It could also be envisaged to use remains or residues of cassava, banana, potato or others, the starches of which advantageously have amylopectin / amylose ratios greater than 3.

[0069] Advantageously, the cellulose is in the form of fibers, the average length of the fibers being between 1 and 10 mm.

[0070] According to various implementations, the cellulose is chosen from the group comprising high purity celluloses containing more than 96% cellulose (SP), bleached kraft celluloses (SBK), unbleached kraft fibers (SUBK), bleached hardwood kraft fibers (HBK).

[0071] In some implementations, the base material is a raw earth which is a mixture of aggregates such as pebbles, gravels, sands and silts, and a binder formed by the clay material and water.

[0072] In various implementations, the clay material comprises several different clay minerals selected from kaolinite, illites and smectites including montmorillonites.

[0073] Advantageously, the base material is excavated natural earth or construction site residue or previously crushed and ground rock.

[0074] In various implementations, the material for raw earth construction comprises, in relation to its total dry mass:

[0075] - between 20% and 40% by weight of clay mineral,

[0076] - less than 80% by weight of aggregates such as sand, for example between 40% and 80% by weight of aggregates, and

[0077] - between 0.2% and 3% by weight of starch, advantageously between 0.3% and 1.5% by weight of starch.

[0078] Advantageously, the material for raw earth construction comprises, in relation to its total dry mass: less than 10% by weight of cellulose, advantageously less than 7.5% by weight of cellulose.

[0079] In various implementations, the clay material comprises at least two clay minerals, kaolinite and montmorillonite, and wherein the base material comprises, relative to its total dry mass:

[0080] - between 20% and 40% by weight of clay mineral,

[0081] - less than 80% by weight of aggregates such as sand, for example between 40% and 80% by weight of aggregates,

[0082] - between 0.2% and 3% by weight of starch, advantageously between 0.3% and 1.5% by weight starch, and

[0083] - less than 10% by weight of cellulose, advantageously less than 7.5% by weight of cellulose.

[0084] In certain particular implementations, the naturally occurring polymers comprise lipids.

[0085] In some implementations, the material for raw earth construction comprises polymers of natural animal origin.

[0086] In various implementations:

[0087] - polymers of natural origin are present in plant fibers or animal, or in plant extracts, and / or

[0088] - polymers of natural origin are derived from agricultural waste or the food industry.

[0089] Advantageously, the material for raw earth construction is recyclable and without hydraulic binders, such as lime and cement.

[0090] Advantageously, the material for raw earth construction is recyclable and free from dispersing agents, such as superplasticizers.

[0091] In certain advantageous implementations, the material is recyclable, includes montmorillonite, and is free of anti-swelling agents.

[0092] According to a second aspect, there is provided a method of manufacturing a material for construction as presented above, the method comprising a step of mixing water, starch and cellulose fibres in a base material which comprises a clay material, the mass percentage of water being between 20% and 45%.

[0093] Advantageously, the base material is a raw earth which is a mixture of aggregates such as pebbles, gravel, sand and silt, and a binder formed by the clay material and water.

[0094] Advantageously, the base material comprises sand, or alternatively sand is added to the mixture, to form a mortar, the mortar is then advantageously molded, in particular advantageously compressed or compacted, before drying.

[0095] According to a third aspect, it is proposed to use a material for raw earth construction as presented above, the base material being raw earth.

[0096] In various implementations, the construction material is used either as filling or for the production of compressed bricks or other materials, for example for partitions or structural elements in order to take up mechanical loads, particularly for multi-story constructions. List of figures

[0097] Other objects and advantages of the invention will appear in the light of the description of embodiments, given below with reference to the appended drawings in which:

[0098] [Fig-1] is a histogram showing the compressive strength values ​​in MPa of a clay mineral-based mortar (Ref), and of clay mineral-based mortars to which high amylose corn starch (Am), corn starch (M), wheat starch (W), rice starch (R), and high amylopectin waxy corn starch (Ap) are added, the starch being added at 5% by weight for the hatched histogram bars and at 1% by weight for the other bars of histograms, the clay mineral being kaolinite;

[0099] [Fig.2] is a histogram analogous to [Fig.l], the clay mineral being an illite;

[0100] [Fig.3] is a histogram analogous to [Fig.l], the clay mineral being a mont- morillonite;

[0101] [Fig.4] is a histogram showing the elastic modulus values ​​at the com pressure in MPa of a mortar based on a clay mineral (Ref), and mortars based on a clay mineral to which is added a corn starch with a high amylose content (Am), a corn starch (M), a wheat starch (W), a rice starch (R), and a waxy corn starch (Ap) with a high amylopectin content, the starch being added at 1.5% by weight for the histogram bars with hatching and at 0.3% by weight for the other histogram bars, the clay mineral being kaolinite;

[0102] [Fig.5] is a histogram analogous to [Fig.4], the clay mineral being an illite;

[0103] [Fig.6] is a histogram analogous to [Fig.4], the clay mineral being a mont- morillonite;

[0104] [Fig.7] is a histogram showing the compressive strength values ​​in MPa of a mortar based on a clay mineral (Ref), and mortars based on a clay mineral to which cotton cellulose (CC) is added, or high purity cellulose containing more than 96% cellulose (SP), or bleached kraft cellulose (SBK), or bleached hardwood kraft fiber (HBK), or unbleached kraft fiber (SUBK) or recycled cellulose pulp (RP), the clay mineral being kaolinite;

[0105] [Fig.8] is a histogram analogous to [Fig.7], the clay mineral being an illite;

[0106] [Fig.9] is a histogram analogous to [Fig.7], the clay mineral being a mont- morillonite;

[0107] [Fig. 10] is a histogram showing the values ​​of elastic modulus under compression in MPa of a mortar based on a clay mineral (Ref), and mortars based on a clay mineral to which is added cotton cellulose (CC), or high purity cellulose containing more than 96% cellulose (SP), or bleached kraft cellulose (SBK), or bleached hardwood kraft fiber (HBK), or unbleached kraft fiber (SUBK) or recycled cellulose pulp (RP), the clay mineral being kaolinite;

[0108] [Fig. 11] is a histogram analogous to [Fig. 10], the clay mineral being an illite;

[0109] [Fig.12] is a histogram analogous to [Fig.10], the clay mineral being a montmorillonite;

[0110] [Fig. 13] represents the initial state, the state after 10 minutes and the state after 30 minutes of a control sample, without addition of cellulose and without addition of starch, immersed in water;

[0111] [Fig. 14] represents the initial state, the state after 10 minutes, the state after 30 minutes and the state after 12 hours of a sample with the addition of cellulose and starch, immersed in water;

[0112] [Fig. 15] is a histogram showing the compressive strength values ​​in MPa of a montmorillonite (Reference), and of this montmorillonite with the addition of short, medium and long cellulose fibers, or with the addition of medium cellulose fibers and rice starch;

[0113] [Fig. 16] is a histogram showing the compressive strength values ​​in MPa of a kaolinite (Reference), and of this kaolinite with the addition of rice starch, wheat starch, corn starch, amylopectin, amylose, and a mixture comprising rice starch and cellulose fibers;

[0114] [Fig. 17] is a histogram showing the compressive strength values ​​in MPa of a mixture of montmorillonite and kaolinite (reference), and of this same mixture with the addition of rice starch and cellulose fibers. Detailed description of embodiments

[0115] Embodiments will be described by way of examples, with reference to the drawings.

[0116] In the histograms, the vertical bars correspond to the 95% confidence intervals.

[0117] Examples of adding starch to mortars based on illite, kaolinite or montmorillonite

[0118] Three clay minerals were tested: kaolinite (SOKA, France), illite (ARVEL, France), and montmorillonite (ABM, Italy). The identification of the clay minerals was confirmed by X-ray diffraction.

[0119] The tested products are of industrial purity, evaluated according to a semi-quantitative method described by Holtzapffel (Clay minerals. Preparation. Diffractometric analysis and determination. University of Sciences and Techniques of Lille 1, 1985). Kaolinite contains 16% illite, as well as quartz, as impurities. Illite contains 5% kaolinite, as well as quartz and carbonates, as impurities. Montmorillonite contains 0.7% illite, and quartz as impurities.

[0120] Five starches were tested, from corn (M), wheat (W), rice (R), a waxy corn (Ap) and a corn with a high amylose content (Am). These starches are marketed by the company Sigma-Aldrich.

[0121] The weight percentages of amylose and amylopectin in the five starches used are shown in the table below. Amylose (% by mass) Amylopectin (% by mass) Am 72 28 M 27 73 W 17 83 R 13-25 75-87 Ap 1 99

[0122] Two starch solutions were prepared with a rate of 2.25% by weight and 10.36% by weight respectively. These two solutions were used to prepare a clay mineral + starch mixture comprising respectively 1% by weight and 5% by weight of starch, relative to the mass of clay.

[0123] The water / clay mineral ratio is 13.6% by weight for kaolinite, 13.5% by weight for illite and 29.0% by weight for montmorillonite.

[0124] To form mortars, sand was added to the clay mineral for 30 seconds, starch and distilled water then being introduced into the sand / clay mineral mixture, in a planetary mixer, with a constant rotation speed of 62 rpm, for one minute. The product obtained is recovered and is mixed again at a constant speed of 93 rpm for 30 seconds. The mortar obtained was kept for 48 hours in a sealed beaker.

[0125] The obtained mortar was molded in a cylindrical mold with a height of 40 mm and a diameter of 20 mm, and was compacted under a uniaxial pressure of 44 kPa at a displacement speed of 1 mm / minute, using an Instron machine (Merlin 5500).

[0126] After compaction, the product obtained is removed from the mold and drying at 20°C in an environment of 50% relative humidity was carried out, until a constant mass is obtained.

[0127] The following materials were formed: three reference materials (Ref) comprising 30% by weight of clay mineral (kaolinite, or illite, or montmorillonite) and 70% by weight of sand, and not containing starch, and for each of the five starches tested, two test materials, comprising respectively 1% by weight of starch, and 5% by weight of starch.

[0128] The compressive strength and elastic modulus in compression of the mortars were evaluated using a compression test carried out with a Shimadzu Autograph AGS-X press, equipped with a 300 kN force sensor.

[0129] The surfaces of the dried specimens were flattened using a wood file to form horizontal and parallel surfaces. The specimens were compressed at 0.5 mm / min. The equipment provided the displacement and force. The stress was calculated as the ratio of the force to the horizontal area of ​​the specimens. The compressive strength was considered as the maximum stress relative to to the deformation of the sample. Finally, the elastic modulus was considered as the stress slope between 30% and 60% of the maximum stress on the linear part of the deformation.

[0130] In Figures 1 to 6, the results obtained for the material comprising 1.5% by weight of starch relative to the total dry mass (clay, sand, additive), with 28.5% by weight of clay mineral relative to the total dry mass (clay, sand additive) are presented with hatching in the histograms, compared to the results obtained for the material comprising 0.3% by weight of starch, relative to the total dry mass (clay, sand, additive).

[0131] Figures 1 to 3 show the average compressive strength in MPa of the mortars tested.

[0132] Starch-free compositions are considered as references (Ref). Reference mortars based on illite or montmorillonite have a similar compressive strength, around 1 MPa, while the kaolinite-based reference mortar has the lowest compressive strength, around 0.5 MPa.

[0133] Montmorillonite-based mortar is not very mechanically reinforced by starches. The compressive strength of montmorillonite mortar remains between 1 and 2 MPa for all starches tested, and for both starch concentrations.

[0134] The illite-based mortar is consolidated mainly by wheat (W) and rice (R) starches, as well as by amylopectin (Ap). The compressive strength of the illite-based material is quadrupled with the addition of rice starch or the addition of amylopectin.

[0135] The kaolinite-based mortar is reinforced solely by rice starch (R) or amylopectin (Ap). At 1% by weight, the compressive strength is increased twofold with amylopectin (Ap) and fourfold with rice starch (R). At 5% by weight, amylopectin (Ap) reinforces the kaolinite-based mortar up to 4.5 MPa. Thus, the compressive strength of the kaolinite-based mortar is increased three to fourfold with rice starch (R) and almost ninefold with amylopectin (Ap). It can be noted that although corn and rice starches have similar amylose / amylopectin ratios, they do not have the same impact on the compressive strength of the kaolinite-based mortar.

[0136] The compressive strength of illite and kaolinite mortars is increased four to ninefold with wheat starch (W), rice starch (R) and amylopectin (Ap).

[0137] For effective reinforcement of the mortar, the increase in compressive strength is advantageously combined with an increase in the elastic modulus. The mortar obtained then has low deformation before rupture.

[0138] The elastic moduli in compression are presented in Figures 4 to 6 (y-axis in MPa).

[0139] For the montmorillonite-based mortar, results similar to those obtained for compressive strength are observed, the elastic modulus of 60 MPa remaining substantially constant with the addition of starch tested and the % by weight of starch added.

[0140] The elastic modulus of the illite-based mortar increases with the addition of starch, from 150 MPa for the reference (Ref) to 450 MPa with 5% by weight of amylopectin (Ap).

[0141] For the kaolinite-based mortar, similar results to those obtained for the compressive strength are observed, a significant increase in the elastic modulus being observed with the addition of starch, from 95 MPa to 280 MPa with 0.3% by weight of rice starch (R) and 760 MPa with 1.5% by weight of amylopectin (Ap) relative to the total dry mass (clay, sand, additive).

[0142] The study of dried mortar mixtures at the macroscopic scale highlights that starches have varied impacts on mechanical properties, depending on the nature of the clay and starch. It can be noted that kaolinite and illite present the greatest disparity in mechanical behavior, depending on the nature of the starches. Mortars based on kaolinite and illite are mainly reinforced by rice starch (R) and amylopectin (Ap).

[0143] Examples of adding cellulose to mortars based on illite, kaolinite or montmorillonite

[0144] Seven celluloses were tested. Merck's cotton cellulose (CC) was used for its near 100% cellulose purity. The other six celluloses were supplied by the French Forestry Commission (FCBA). Three softwood celluloses were used: a high-purity cellulose containing more than 96% cellulose (SP), a bleached kraft cellulose (SBK), and an unbleached kraft fiber (SUBK). A bleached hardwood kraft fiber (HBK) was also used for its length difference with softwood celluloses. Finally, two application celluloses were selected: a recycled pulp (RP) and a microcellulose (MC).

[0145] All celluloses differ in their morphologies. Three celluloses can be considered pure fibers: cotton cellulose (CC), pure cellulose (PS), and microcellulose (MC). Cotton cellulose is pure due to its botanical source, while the other two are pure due to the mechanical and chemical treatments of the initial wood fibers.

[0146] The average fiber lengths and diameters are shown in the table below. Average length Length (microns) Average diameter (microns) (microns) CC 20 3 20 SP 2346 37.1 672 SBK 1752 30.6 672 SUBK - - HBK 807.0 16.3 672 RP 1172.5 21.25 672 MC - -

[0147] The longest celluloses are from pure softwoods (SP) with more than 2000 pm, while the shortest are those from cotton (CC) with a length one hundred times shorter.

[0148] Depending on their length and diameter, celluloses have variable rigidity. Indeed, the shortest cellulose, cotton cellulose (CC), has an effective length equal to the average length, while the longest cellulose, pure cellulose (SP), has an effective length one-third shorter than its average length.

[0149] Cotton cellulose (CC) was received in powder form and could be used without prior treatment. This was not the case for the other six celluloses, which were in aqueous dispersion (RP and MC) or in sheet form (SP, SBK, SUBK, RBK).

[0150] The dispersions were therefore dried in a first step while the sheets were prepared as follows. First, the sheets were cut into small pieces of less than 1 cm. In a second step, the pieces were immersed in distilled water and mixed until the dispersion no longer visually evolved. Finally, the dispersed celluloses were pressed by hand and dried.

[0151] All mortar mixes are composed of a clay / sand ratio of 30 / 70 by mass. In these mortar mixes, the sand is used to structure the clay and not to design a mortar for construction application.

[0152] Celluloses are incorporated into the clay / sand mixtures at a rate of 7.5% by weight.

[0153] For cellulosic mixtures, the water content was determined for each type clay in order to reach an elastic limit equal to that of cotton cellulose, around 20 kPa.

[0154] The water content is 22.6% by weight with kaolinite, 26.6% by weight with illite and 43.5% by weight with montmorillonite.

[0155] For the cellulose-free mortar mixes, the water content was decreased to achieve a yield strength of about 20 kPa. The water content was 13.6 wt%, 13.5 wt% and 29.0 wt% for kaolinite, illite and montmorillonite, respectively.

[0156] All samples were prepared according to the same procedure. First, clay and sand were mixed in a planetary mixer at a constant speed of 62 rpm for 30 s. Then, the prepared celluloses and distilled water were poured into the powder mixture and mixed at a constant speed of 62 rpm for 5 minutes.

[0157] The material obtained was recovered and a third mixing was carried out at a constant speed of 93 rpm for 25 minutes.

[0158] Finally, the mortar mixes were cured in airtight beakers for at least 48 hours.

[0159] The mortar mix was molded into a cylindrical shape of 20 mm diameter and 40 mm length. The compaction strength was approximately 44 kPa at a travel speed of 1 mm / min using an Instron® testing machine (Merlin 5500).

[0160] After compacting and demolding the molded mortars, drying at 20°C and 50% RH was carried out until a constant mass was obtained.

[0161] The compressive strength and elastic modulus of the samples were evaluated using only a compression test. The test was carried out using a Shimadzu® AUTOGRAPH AGS-X press equipped with a 300 kN load cell.

[0162] The surfaces of the dried samples were flattened using a wood file, to obtain samples having horizontal and parallel surfaces.

[0163] The samples were compressed at 0.5 mm / min. The equipment provided the displacement and force. The stress was calculated as the ratio of the force to the horizontal area of ​​the samples. The compressive strength was considered as the maximum stress versus the deformation of the sample. Finally, the elastic modulus was considered as the stress slope between 30% and 60% of the maximum stress on the linear deformation part.

[0164] The influence of celluloses on dried mortar mixes was evaluated by a compression test.

[0165] The reference results presented in Figures 7 to 12 concern mortar mixtures prepared with a water content lower than that of celluloses, to have a yield strength of 20 kPa as with cotton cellulose.

[0166] For kaolinite-based mortars, the compressive strength is not increased by the presence of cellulose and, in some cases, it decreases, notably with bleached softwood kraft cellulose (SBK), bleached hardwood kraft cellulose (HBK) and recycled pulp (RP). The compressive strength of the reference kaolinite-based mortar is approximately 0.5 MPa, while with the addition of bleached softwood kraft cellulose (SBK), bleached hardwood kraft cellulose (HBK) or recycled pulp (RP), the compressive strength decreases to 0.2 MPa. As regards the evolution of the elastic modulus for kaolinite-based mortars, a significant decrease is observed with the same celluloses, from 95 MPa to 8 MPa.

[0167] In illite-based mortars, the compressive strength tends to increase slightly with the presence of cellulose, from 1 MPa to 3 MPa. The elastic modulus is not increased, or even decreases, in the presence of cellulose, from 146 MPa to 35 MPa.

[0168] For montmorillonite-based mortars, an increase in compressive strength is observed with all celluloses, from 1 MPa up to 7 MPa. This increase is more significant for the addition of cellulose from pure softwoods (SP), bleached and unbleached kraft softwoods (SBK, SUBK) and bleached kraft hardwoods (HBK), up to 7 MPa. The same trend is found for the elastic modulus, which increases for all celluloses, from 62 to 271 MPa. This last observation must be qualified by the size of the confidence intervals, which are wide.

[0169] Celluloses mainly reinforce montmorillonite-based mortar, and to a lesser extent illite-based mortars.

[0170] The mechanisms leading to these reinforcements of mechanical properties are not known precisely, the inventors present the following hypotheses.

[0171] The mechanical reinforcement observed at the macroscopic scale would result both from a modification of the granular arrangement and the pore space and from a chemical interaction between the molecules of the biopolymers with the surface of the clay minerals.

[0172] The water absorption capacity of celluloses could decrease the amount of water available for grain movement in mortar mixes. The addition of celluloses could increase the number of contacts between the different components, the movement of these components requiring more energy or more pore water.

[0173] In this regard, it is noted that short cellulose (cotton cellulose - CC) has approximately the same size as clay particles and is shorter than the median diameter of sand, while other celluloses are ten times longer than sand grains. Size differences between celluloses and grains in clay mortar mixtures are correlated with compressive strength results and porosity values ​​of mortars.

[0174] Examples of adding cellulose and starch to mortars based on illite, kaolinite or montmorillonite

[0175] The following formulation was tested: Starch 5.25 g Cellulose 26.5 g Starch water 102.2 g Cellulose water 48.8 g Moist soil 512.3 g Soil water 13.74 g Dry soil 498.5 g Sand 176.8 g Addition bucket 9.8 g

[0176] The mechanical compressive strength of the mortar obtained is 7.2 MPa. Figures 13 and 14 illustrate the increase in water resistance.

[0177] In [Fig. 13] are represented the initial state, the state after 10 minutes and the state after 30 minutes of the control sample (without addition of cellulose and without addition of starch) immersed in water.

[0178] In [Fig. 14] are represented the initial state, the state after 10 minutes, the state after 30 minutes and the state after 12 hours of a sample with the addition of cellulose and starch, immersed in water.

[0179] Example of adding cellulose and starch fibers to a mixture comprising pure montmorillonite and sand

[0180] The following formulations were produced, the compressive strength results in MPa for these different formulations being shown in [Fig.15]. Formulation name Clay: Montmorillonite Sand Additive Water REFERENCE 30% ms 70% ms - 43.5% ms SHORT FIBERS 27.75% ms 64.75% ms 7.50% ms cotton microfibers 43.5% ms MEDIUM FIBERS 27.75% ms 64.75% ms 7.50% ms bleached softwood kraft fibers 43.5% ms FIBERS 27.75% ms 64.75% 7.50% ms fibers of 51.77% LONG ms cotton long ms MEDIUM FIBERS + RICE STARCH 27.47% ms 64.75% ms 7.50% ms bleached softwood kraft fibers + 0.28% ms rice starch 53.95% ms

[0181] In the table above, the proportions indicated are defined as a percentage of the total dry mass.

[0182] The average lengths of the added cellulose fibers are specified in the table below. Name Detail Average Length SHORT FIBERS Cotton Microfibers 0.02 mm MEDIUM FIBERS Bleached Softwood Kraft Fibers 1.8 mm LONG FIBERS Long Cotton Fibers 17.9 mm

[0183] The mechanical performance of the formulations was evaluated by measuring the compressive mechanical strength of molded cylindrical samples, 20 mm in diameter and 40 mm in height.

[0184] It can be seen from [Fig. 15] that each of the additions of cellulose fibers to an earth formulated from pure montmorillonite makes it possible to improve the mechanical resistance.

[0185] But we observe above all that the medium fibers, with an average length of 1.8 mm, are more efficient than the short fibers and the long fibers for this class of clay: the medium fibers make it possible to obtain a mechanical resistance of 6 to 7 MPa against 1 MPa for the reference without additives.

[0186] The optimal order of magnitude of the fibers added to the soil mixture is therefore a few millimeters.

[0187] It is observed that for the addition of a combined additive (rice starch and medium fibers), the mechanical resistance of the mixture is close to the resistance for the medium fiber alone.

[0188] Example of adding cellulose and starch fibers to a mixture comprising pure kaolinite and sand

[0189] The following formulations were produced, the compressive strength results in MPa for these different formulations being shown in [Fig.16]. Formulation name Clay: Kaolinite Sand Additive Water REFERENCE 30% ms 70% ms - 22.6% ms RICE STARCH 29.7% ms 70% ms 0.3% ms rice starch 22.6% ms WHEAT STARCH 29.7% ms 70% ms 0.3% ms wheat starch 22.6% ms CORN STARCH 29.7% ms 70% ms 0.3% ms corn starch 22.6% ms AMYLOPECTIN E 29.7% ms 70% ms 0.3% ms amylopectin (waxy corn starch) 22.6% ms AMYLOSE 29.7% ms 70% ms 0.3% ms amylose (corn starch) 22.6% ms RICE STARCH + MEDIUM FIBER 28.59% ms 67.37% ms 0.29% ms rice starch + 3.75% ms bleached softwood kraft fiber 28.4% ms

[0190] In the table above, the proportions indicated are defined as a percentage of the total dry mass.

[0191] The percentages of amylose and amylopectin in the tested additives are presented in the following table: Name Detail Percentage of Amylose Percentage of Amylopectin Amylose Corn variety containing a high proportion of amylose 72% 28% Corn starch 27% 73% Wheat starch 17% 83% Rice starch 13-25% 75-87% Amylopectin Waxy maize 1% 99%

[0192] The mechanical performance of the formulations was evaluated by measuring the compressive mechanical strength of molded cylindrical samples, 20 mm in diameter and 40 mm in height.

[0193] It can be seen from [Fig.16] that each of the additions of starch with a high amylopectin content to an earth formulated from pure kaolinite improves the mechanical resistance of the samples tested.

[0194] Thus, the addition of 1% by mass of rice starch relative to the dry mass of clay makes it possible to obtain a mechanical resistance of 1.8 MPa compared to 0.5 MPa for the reference without additives.

[0195] The minimum proportion of amylopectin in a starch chosen as an additive for a kaolinite is 80%.

[0196] It is observed that for the addition of a combined additive (rice starch and medium fibers), the mechanical resistance of the mixture is close to the resistance for rice starch alone.

[0197] Example of adding cellulose and starch fibers to a mixture comprising pure kaolinite, pure montmorillonite and sand

[0198] The following formulations were produced, the compressive strength results in MPa for these different formulations being shown in [Fig. 17]. Formulation name Clay Sand Additive Water REFERENCE 15% dm kaolinite +15% dm montmorillonite 70% dm - 33.05% dm RICE STARCH + MEDIUM FIBERS 14.03% dm kaolinite +14.03% dm montmorillonite 66.15% dm 0.28% dm rice starch 5.5% dm bleached softwood kraft fibers 40.51% dm

[0199] In the table above, the proportions indicated are defined as a percentage of the total dry mass.

[0200] It is observed, in view of [Fig. 17], that for an earth formulated from pure kaolinite and pure montmorillonite in equal proportions, the addition of a combined additive (rice starch and medium-sized cellulose fibers), interacting with both kaolinite and montmorillonite, increases mechanical strength. It increases from 1 MPa on average for the reference samples to 4.8 Ma on average for the samples with additive.

[0201] Tests on a mixture comprising pure kaolinite and pure montmorillonite, mixed with sand, have thus made it possible to establish that a combination of cellulose and starch (advantageously with a choice of fibre length and a minimum amylopectin content), makes it possible to significantly strengthen the mixture of the two types of clay.

[0202] A bio-sourced additive is thus proposed capable of reinforcing a variety of natural soils containing kaolinite and / or montmorillonite in significant proportions.

[0203] This additive is advantageously formulated as follows:

[0204] In a first step, the total proportion of clays (in dry mass) in the earth to be reinforced is determined.

[0205] In a second step, the water content of the soil to be reinforced is determined.

[0206] In a third step, a starch is added, advantageously at 1% (by mass per relative to the dry mass of clay), the starch advantageously comprising at least 80% amylopectin.

[0207] In a fourth step, a replacement, advantageously at 7.5%, of the dry mass is carried out with cellulose fibers, preferably of average size of the order of a few mm.

[0208] If a percentage of 7.5% in dry mass is not achievable during mixing or during implementation, this percentage can advantageously be reduced to 4-5%.

[0209] The invention has numerous advantages.

[0210] The invention proposes combinations of bio-sourced materials, of plant origin, making it possible to reinforce a broad spectrum of natural earths, and allowing their use as raw earths for construction, these natural earths comprising in particular kaolinite and montmorillonite.

[0211] The invention aims to enable the uses in construction of a wide variety of clay materials, mainly comprising illite, or kaolinite or montmorillonite, in particular for the manufacture of elements such as adobe or compressed, compacted or extruded earth blocks.

[0212] The mechanical resistance to compression of raw earth is significantly increased.

[0213] The addition of cellulose and starch, in particular amylopectin, makes it possible to increase mechanical resistance.

[0214] The addition of starch (in particular amylopectin) and / or cellulose fibers makes it possible to reinforce different earths, comprising illite, or kaolinite, or montmorillonite as the main clay mineral. The addition of starch, in particular rice starch, and even more particularly amylopectin, interacts mainly with kaolinite and the addition of cellulose with montmorillonite. Illite, on the other hand, is reinforced by the two biopolymers.

[0215] For a soil whose clay is of the kaolinite type, the compressive strength of 0.5 MPa increases to 4.5 MPa with the use of natural rice starch granules and in particular the amylopectin it contains. A reinforcement of the same order of swelling clays of the smectite type with cellulose fibers is measured: the reference compressive strength of 1 MPa increases to 6 MPa with cellulose.

[0216] The water resistance of the material is reinforced, in particular by the starch which would delay the flow of water in its pores.

[0217] The addition of starch makes it possible to strengthen the water resistance of clay materials such as excavated earth, including both kaolinite and montmorillonite as the main clay mineral. The addition of starch thus contributes to the production of a material for raw earth construction, from earths of variable composition, making it possible to strengthen its mechanical and / or water resistance.

[0218] The invention thus allows mechanical reinforcement working for two large families of clay minerals with opposing behaviors.

[0219] The invention thus allows the recovery of raw earths containing a clay mineral considered to be noble (kaolinite) as well as raw earths containing a clay mineral that is not considered economically (illite), or raw earths containing a clay mineral considered to be harmful (montmorillonite). Smectites exhibit swelling upon hydration and shrinkage upon drying, generating numerous problems in buildings.

[0220] Reinforcing raw earth with a combination of starch and cellulose will be effective on the vast majority of earths (from quarries, excavations), and will facilitate the use of raw earth in construction, particularly in the manufacture of compacted earth bricks or extruded earth bricks.

[0221] The invention facilitates the use of excavated earth in new construction or the rehabilitation of old constructions, as well as in soil stabilization.

[0222] The invention facilitates the production of materials for construction in raw earth, from soils of variable compositions, without it being necessary to carry out prior analyses of these soils to characterize them, in particular with regard to their composition in clay minerals.

Claims

Claims

1. Material for construction in raw earth, resulting from the addition and mixing of polymers of natural plant origin which are cellulose fibers and at least one starch, in a base material which comprises a clay material having at least one clay mineral chosen from kaolinite, illites and / or smectites, the starch added in the base material having a ratio between the weight of amylopectin and the weight of amylose greater than 3.

2. Raw earth construction material according to claim 1, characterized in that the weight of amylopectin in the added starch is greater than 75%, advantageously greater than 80%, advantageously greater than 90%.

3. Raw earth construction material according to claim 1 or 2, characterized in that the added starch is chosen from rice starch and / or waxy maize starch.

4. Raw earth construction material according to any one of claims 1 to 2, characterized in that the added starch is wheat starch.

5. Raw earth construction material according to any one of claims 1 to 4, characterized in that the cellulose fibers have average lengths of between 1 and 10 mm.

6. Raw earth construction material according to any one of claims 1 to 5, characterized in that the cellulose is chosen from the group comprising high purity celluloses containing more than 96% cellulose (SP), bleached kraft celluloses (SBK), unbleached kraft fibers (SUBK), bleached hardwood kraft fibers (HBK).

7. Raw earth construction material according to any one of claims 1 to 6, characterized in that the base material is raw earth which is a mixture of aggregates such as pebbles, gravel, sand and silt, and a binder formed by the clay material and water.

8. Raw earth construction material according to any one of claims 1 to 7, characterized in that the clay material comprises several different clay minerals chosen from kaolinite, illites and smectites including montmorillonites.

9. Raw earth construction material according to any one of claims 1 to 8, characterized in that the base material is excavated natural earth or construction site residue or pre- thoroughly crushed and ground.

10. Raw earth construction material according to any one of claims 1 to 9, characterized in that the raw earth construction material comprises, relative to its total dry mass: - between 20% and 40% by weight of clay mineral, - less than 80% by weight of aggregates such as sand, for example between 40% and 80% by weight of aggregates, and - between 0.2% and 3% by weight of starch, advantageously between 0.3% to 1.5% by weight of starch.

11. Raw earth construction material according to any one of claims 1 to 10, characterized in that the raw earth construction material comprises, relative to its total dry mass, less than 10% by weight of cellulose, advantageously less than 7.5% by weight of cellulose.

12. Raw earth construction material according to any one of claims 1 to 11, characterized in that the clay material comprises at least two clay minerals, namely kaolinite and montmorillonite, and in which the base material comprises, relative to its total dry mass: - between 20% and 40% by weight of clay mineral, - less than 80% by weight of aggregates such as sand, for example between 40% and 80% by weight of aggregates, - between 0.2% and 3% by weight of starch, advantageously between 0.3% and 1.5% by weight of starch, and - less than 10% by weight of cellulose, advantageously less than 7.5% by weight of cellulose.

13. Material for raw earth construction according to any one of claims 1 to 12, characterized in that the polymers of natural origin comprise lipids.

14. Raw earth construction material according to any one of claims 1 to 13, characterized in that the raw earth construction material comprises polymers of natural animal origin.

15. Raw earth construction material according to any one of claims 1 to 13, characterized in that: - the polymers of natural origin are present in plant fibers, or in plant extracts, and / or - the polymers of natural origin are derived from agricultural waste or the food industry.

16. Raw earth construction material according to any one of claims 1 to 15, characterized in that the raw earth construction material is recyclable and without hydraulic binder, such as lime and cement.

17. Raw earth construction material according to any one of claims 1 to 16, characterized in that the raw earth construction material is recyclable and free from dispersing agents, such as superplasticizers.

18. A raw earth construction material according to any one of claims 1 to 17, characterized in that the raw earth construction material is recyclable, comprises montmorillonite, and is free of anti-swelling agents.

19. A method of manufacturing a building material as set forth in any one of claims 1 to 18, the method comprising a step of mixing water, starch and cellulose fibers in a base material which comprises a clay material, the mass percentage of water being between 20% and 45%.

20. A method according to claim 19, characterized in that the base material is a raw earth which is a mixture of aggregates such as pebbles, gravel, sand and silt, and a binder formed by the clay material and water.

21. Method according to one of claims 19 to 20, characterized in that the base material comprises sand or in that sand is added to the mixture, to form a mortar, and advantageously, the mortar is molded, and in particular compressed or compacted, before drying.

22. Use of a building material as set forth in any one of claims 1 to 18, the base material being raw earth.

23. Use of the building material according to claim 22, wherein the building material is used either as a filler or for the production of compressed bricks or the like, for example for partitions or structural elements in order to take up mechanical loads, in particular for multi-storey constructions.

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