Raw earth construction material, based on a mixture of raw earth, cellulose and starch

Abstract

Raw earth construction material, resulting from the addition of cellulose and starch to a clay material and the mixing therewith, the ratio of the weight of amylopectin to the weight of amylose in the added starch being greater than 3.

Description

[0001] Raw earth construction material, based on a mixture of raw earth, cellulose and starch

[0002] Technical field and state of the art

[0003] The invention relates to the reinforcement of the mechanical resistance of raw earth materials having clay materials by biopolymers, for raw earth construction.

[0004] By "clay materials" we mean here a clay mineral or a group of clay minerals, as well as rocks composed mainly of these minerals.

[0005] By "clay mineral" we mean a phyllosilicate, in particular kaolinite, illite or montmorillonite.

[0006] 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).

[0007] Clay minerals are weathering and detrital minerals. Depending on the parent rock being weathered, the climatic conditions, and the topography, different clay minerals will form.

[0008] 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 lattice, the fourth vertex being connected to an octahedral layer. In a tetrahedral layer, the central cation of the tetrahedron (Si 4+ , or substituted by Al 3+ ) is coordinated with four oxygen atoms or hydroxyl groups. In an octahedral O layer, the central cation (Al 3+ , or substituted by Mg 3+ , or Fe 3+ ) is coordinated with oxygen atoms or hydroxyl groups.

[0009] The distance between each layer defines the interlayer space. The layer and the interlayer space form the structural unit of the clay mineral.

[0010] Under normal temperature and pressure conditions, clay materials contain water in their structure, the term hydrated phyllosilicate being used to represent this reality. Phyllosilicates can be classified in various ways, the classification used here taking into account the basic structure of the sheets. By "kaolinite" is meant a mineral from a family of clay minerals with the general formula AI2Si2O5(OH)4, comprising a TO chain, which is defined by a tetrahedral SiO4 layer and an octahedral AlOe 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 repetition 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 one sheet and the O of the tetrahedral layer of the next 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 pseudo-hexagonal platelets, which can be stacked in the form of books or vermicules up to 50 to 100 μm thick. "Kaolinite" also refers to other, rarer clay minerals of the same family, including dickite and nacrite, which are polytypes, and halloysite, which is a polymorph and has a tubular structure with a structural unit of 10 Å when hydrated.

[0012] Kaolinite is the main component of kaolin, a rock resulting from the weathering 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 kaolin clay.

[0013] By "illite" we mean here a clay mineral of general formula (Si3.4AI0.6) (Al2) OI O(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, oxygens are mainly present. Illite particles are generally composed of 5 to 10 sheets. Illite is a clay mineral that is much less used than kaolinite.

[0014] By "montmorillonite" we mean here a clay mineral of the smectite family, with the general formula (Al2- x Mg x )Si4(Oio)(OH)2(CEC) x, the term "CEC" designating cation exchange capacity. Smectites exhibit a TOT-type layer chain, 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 layer chain is stabilized by hydrated cations such as Ca 2+ , Mg 2+ and Na +. These cations have a high 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, oxygen is mainly present. Montmorillonite particles are composed of about 5 layers, and their organization is close to an interconnected network.

[0015] Montmorillonites are the main constituents of swelling clays. The use of swelling clays in raw earth construction is delicate. While 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). Clay minerals, and in particular their porosity, must 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).The general properties of kaolinite, illite and montmorillonite are as follows:

[0016] By "raw earth" we mean 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.

[0017] 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. 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.

[0018] State of the art

[0019] 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).

[0020] 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).

[0021] Adobe consists of molding and drying in the sun a mixture of raw earth and 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 compressed earth block). 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 FR31 1 7483 (I n Situ Lab, 2022) describes a construction material comprising dried seaweed mixed with clayey soil. Reference may also be made to document FR31 15721.

[0022] Rammed earth consists of compacting a mixture of raw earth with a smaller amount of water than adobe, between formwork, layer by layer. For example, see document FR2861 010.

[0023] 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).

[0024] Coal 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. Coal is often framed with wooden elements.

[0025] Kaolinite is sold in dry powder form as a binder for the preparation of plasters, cob, rammed earth or raw earth bricks (adobe).

[0026] 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.

[0027] By "biopolymers" we mean 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 contain a significant quantity of amylopectin.

[0028] Biopolymers can, for example, be derived from waste from agriculture or the food industry.

[0029] By "mechanical resistance" we mean here in particular the mechanical resistance to compression.

[0030] By "water resistance" we mean resistance to degradation by liquid water, in particular capillary water and rainwater.

[0031] The mechanical resistance to compression of raw earth-based construction materials is very modest, in the techniques of the prior art.

[0032] The document Morel et al. {Mechanical performance of adobe, 3rd transdisciplinary exchanges on raw earth constructions, 2009) describes the manufacture of molded or pressed earth blocks 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 M Pa.

[0033] 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. 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).

[0034] 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).

[0035] Traditional recipes are used with raw earths that vary greatly. As a result, the mechanisms leading to the improvement of the properties of raw earths by adding biopolymers are not precisely known.

[0036] This is particularly the case with the influence of the addition of biopolymers on the mechanical and water resistance of raw earth.

[0037] It is known in the prior art to add biopolymers to raw earth to increase the mechanical resistance to compression of a clay material comprising mainly kaolinite and possibly another clay mineral.

[0038] 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 K earth is a synthetic earth formulated from industrial kaolin and sand, a natural R earth includes kaolinite and illite, and a natural S earth includes kaolinite, illite, vermiculite.

[0039] 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 clay-limestone fines (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.

[0040] 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 soil containing kaolinite. The addition of cow dung results in 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.

[0041] The paper 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 to a mixture of sand and kaolinite on the one hand, and to a natural earth comprising kaolinite, illite and smectite, with a dispersant (hexamethaphosphate) being used during mixing. The compressive strength of materials made from natural earth is about 8 MPa, and is not changed by the addition of alginate. The addition of alginate increases the compressive strength of materials made from kaolin.

[0042] Reference may also be made to the document Ouedraogo et al. {Physical, thermal and mechanical properties of adobes stabilized with fonio (Digitaria exilis) straw. J Build Eng 23:250-258, 2019).

[0043] Most raw earths, however, contain little or no kaolinite. This is particularly the case for natural earths containing swelling clays, rich in smectites.

[0044] In some publications, compressive strength tests are presented for building materials formed from a mixture of raw earth and an organic binder, the raw earth not containing kaolinite or containing little kaolinite.

[0045] The Ouedraogo document {Stabilizer of sustainable and ecological building materials based on raw earth by 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. 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 the addition of a biosourced molecule on the compressive strength of a natural raw earth mixed with sand, the natural raw earth comprising mainly illite (7%) and also including 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).

[0046] Objectives of the invention

[0047] The invention aims to strengthen the mechanical resistance and advantageously the water resistance of a raw earth base material with clay minerals by biopolymers and cellulose fibers, for raw earth construction.

[0048] Increasing the water resistance of raw earth elements improves the acceptability of this material on the construction market.

[0049] A load-bearing construction material or one acting as a dividing wall must in fact resist immersion in water if it is placed at the base of a wall (in the event of flooding or water damage), as well as possible water erosion (rain).

[0050] The invention aims to enable construction in raw earth from raw earth containing 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.

[0051] 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.

[0052] The invention aims in particular to increase the mechanical resistance to compression of raw earth which may contain a variety of clay materials, and which is reinforced via the addition of starch combined with the addition of cellulose fibers.

[0053] 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 an important barrier for construction in urban areas where multi-story construction is necessary.

[0054] The invention aims in particular to increase the mechanical resistance to compression of a wide spectrum of raw earths, containing kaolinite and / or montmorillonite.

[0055] Biopolymers are advantageously sourced from a local resource, close to the construction site.

[0056] Raw earth also advantageously comes from a local resource.

[0057] 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 benefits by considerably increasing the gray energy emitted, and by making the recyclability of the material more difficult.

[0058] The use of biopolymers differs from the use of dispersing agents, such as superplasticizers used in the manufacture of concrete, as these superplasticizers can have disadvantages for the environment.

[0059] General presentation of the invention

[0060] For these purposes, the invention relates, according to a first aspect, to a material for construction in raw earth, having a base material which comprises a raw earth, the raw earth being a mixture of aggregates such as pebbles, gravel, sand and silt, and a binder formed by clay minerals and water, the clay minerals having at least smectite and another clay mineral chosen from kaolinite or illite, the material for construction in raw earth comprising mixed with the raw earth: polymers of natural plant origin which are cellulose fibers and at least one starch, the starch added to the base material having a ratio between the weight of amylopectin and the weight of amylose greater than 3.

[0061] Advantageously, the material for raw earth construction comprises, in relation to its total dry mass, at least 2% by weight of cellulose.

[0062] Advantageously, the material for raw earth construction comprises, in relation to its total dry mass, at least 4% by weight of cellulose.

[0063] In certain implementations, the material for raw earth construction comprises, relative to its total dry mass, at least 6% by weight of cellulose, advantageously at least 7% by weight of cellulose.

[0064] According to various implementations, the mass of amylopectin in the added starch is greater than 80%, advantageously greater than 90%.

[0065] In some implementations, the starch is selected from the group comprising rice starch, wheat starch, and waxy maize starch. Waxy maize refers to a hybrid maize whose grain starch is almost entirely composed of amylopectin. In some implementations, the hybrid maize is a variety resulting from genetic modification, for example CRISPR.

[0066] It could also be considered to use remains or residues of cassava, banana, potato or others, whose starches advantageously have amylopectin / amylose ratios greater than 3.

[0067] Advantageously, the added starch is rice starch or waxy maize starch and / or wheat starch.

[0068] Advantageously, the average length of the cellulose fibers is between 1 and 10 mm.

[0069] 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 (SlIBK), bleached hardwood kraft fibers (H BK).

[0070] Advantageously, the base material is excavated natural earth or construction site residue or previously crushed and ground rock.

[0071] In some implementations, the second clay mineral has illite, and the material has as starch wheat starch (W), rice starch (R), or waxy maize starch (Ap).

[0072] In some implementations, the second clay mineral has kaolinite, and the material has rice starch (R) or waxy maize starch (Ap) as starch.

[0073] In various implementations, the material for raw earth construction comprises, in relation to its total dry mass: between 10% and 40% by weight of clay mineral, less than 90% by weight of aggregates such as sand, gravel, silts, 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.

[0074] Advantageously, the raw earth contains kaolinite and montmorillonite, and rice starch and cellulose fibers, the material having a mechanical compressive strength greater than 4 M Pa.

[0075] In some implementations, the naturally occurring polymers are present in plant fibers, or in plant extracts, and / or the naturally occurring polymers are derived from agricultural or food industry waste.

[0076] Advantageously, the material for raw earth construction is recyclable and without hydraulic binders, such as lime and cement.

[0077] Advantageously, the material for raw earth construction is without limestone or dolomitic filler.

[0078] By "filler" is meant a powdery material having a volume particle size distribution such that the value of d90 is less than 250 pm. Preferably, the value of d50 is less than 20 pm, in particular 10 pm. The particle size distribution can be determined by laser particle size analysis.

[0079] Limestone is composed mainly of calcium carbonate (calcite) and dolomite of calcium and magnesium carbonate (dolomite). Preferably, the limestone filler, respectively dolomitic, comprises at least 80% by weight, in particular at least 90% by weight, of calcite, respectively dolomite.

[0080] Advantageously, the material for raw earth construction is recyclable and free from dispersing agents, such as superplasticizers.

[0081] Advantageously, cellulose fibers and starch are without chemical transformation.

[0082] Advantageously, the material has at least 5% of aggregates whose largest dimension is greater than 1 mm.

[0083] Advantageously, the cellulose fibers and starch are chosen so that the compressed material following a shape retains the same shape when immersed in water for at least 12 hours.

[0084] Advantageously, the material for raw earth construction is recyclable, includes montmorillonite, and is free from anti-swelling agents.

[0085] In various implementations, the base material also includes sand.

[0086] Advantageously, the raw earth is sieved.

[0087] A second aspect is a compressed brick made from the material presented above.

[0088] Advantageously, the brick has a material having a mechanical resistance greater than 2 M Pa, advantageously greater than 4 MPa.

[0089] Advantageously, the brick comprises before drying a water content between 10% and 16% of the total dry mass, and after drying a water content less than or equal to 5%.

[0090] In another aspect, an extruded brick made from the material presented above is proposed.

[0091] Another aspect of the invention is an adobe made with the material presented above.

[0092] According to another aspect, it is proposed to use a building material as presented above, in which 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-story constructions.

[0093] List of Figures 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: Figure 1 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 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 5% by weight for the histogram bars with hatching and at 1% by weight for the other histogram bars, the clay mineral being kaolinite; Figure 2 is a histogram similar to Figure 1, the clay mineral being an illite; Figure 3 is a histogram analogous to Figure 1, the clay mineral being a montmorillonite;Figure 4 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 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 relative to the total dry mass (clay, sand, additive) for the histogram bars with hatching and at 0.3% by weight relative to the total dry mass for the other histogram bars, the clay mineral being kaolinite; Figure 5 is a histogram similar to Figure 4, the clay mineral being an illite; Figure 6 is a histogram analogous to Figure 4, the clay mineral being a montmorillonite;Figure 7 is a histogram showing the compressive strength values ​​in MPa of a clay mineral-based mortar (Ref), and clay mineral-based mortars to which 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 (SlIBK) or recycled cellulose pulp (RP) is added, the clay mineral being kaolinite; Figure 8 is a histogram analogous to Figure 7, the clay mineral being illite; Figure 9 is a histogram analogous to Figure 7, the clay mineral being montmorillonite;Figure 1 0 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 (H BK), or unbleached kraft fiber (SU BK) or recycled cellulose pulp (RP), the clay mineral being kaolinite; Figure 1 1 is a histogram analogous to Figure 10, the clay mineral being an illite; Figure 12 is a histogram analogous to Figure 10, the clay mineral being a montmorillonite; Figure 13 represents the initial state, the state after 10 minutes and the state after 30 minutes of a control sample from natural soil, without the addition of cellulose and without the addition of starch, immersed in water;Figure 14 represents the initial state, the state after 10 minutes, the state after 30 minutes and the state after 12 hours of a sample from a natural earth with the addition of cellulose and starch, immersed in water; Figure 1 5 is a histogram showing the compressive strength values ​​in M ​​Pa 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; Figure 1 6 is a histogram showing the compressive strength values ​​in MPa of a mixture of kaolinite and sand (Reference), and of this same mixture with the addition of rice starch, wheat starch, corn starch, amylopectin, amylose, and of a mixture comprising rice starch and cellulose fibers;Figure 1 7 is a histogram showing the compressive strength values ​​in MPa of a mixture of montmorillonite, kaolinite and sand (reference), and of this same mixture with the addition of rice starch and cellulose fibers; Figure 1 8 is a histogram showing the compressive strength values ​​in MPa of a mixture of montmorillonite and sand (Reference), and of this same mixture with the addition of different mass percentages of medium-length cellulose fibers.;

[0094] Detailed description of embodiments

[0095] Embodiments will be described by way of examples, with reference to the drawings.

[0096] In the histograms, the vertical bars correspond to the 95% confidence intervals.

[0097] Examples of starch addition in mortars based on illite, kaolinite or montmorillonite

[0098] Three clay minerals were tested: kaolinite (SOKA, France), illite (ARVEL, France), and montmorillonite (ABM, Italy). The identification of clay minerals was confirmed by X-ray diffraction.

[0099] 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 Science and Technology of Lille 1, 1985). Kaolinite contains 1.6% 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.

[0100] Five starches were tested, from corn (M), wheat (W), rice (R), waxy corn (Ap) and corn with a high amylose content (Am). These starches are marketed by the company Sigma-Aldrich.

[0101] The weight percentages of amylose and amylopectin in the five starches used are shown in the table below.

[0102] 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.

[0103] 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.

[0104] To form mortars, sand was added to the clay mineral for 30 seconds, then starch and distilled water were introduced into the sand / clay mineral mixture in a planetary mixer at a constant rotation speed of 62 rpm for one minute. The resulting product was recovered and mixed again at a constant speed of 93 rpm for 30 seconds. The resulting mortar was kept in a sealed beaker for 48 hours.

[0105] 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).

[0106] After compaction, the product obtained was removed from the mold and dried at 20°C in an environment of 50% relative humidity, until a constant mass was obtained.

[0107] 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. Then, for each of these three clays and for each of the five starches tested, two test materials, comprising respectively 1% by weight of starch, and 5% by weight of starch.

[0108] The compressive strength and elastic modulus of the mortars were evaluated using a compression test performed with a Shimadzu Autograph AGS-X press, equipped with a 300 kN load cell. The surfaces of the dried specimens were flattened using a wood file, to form horizontal and parallel surfaces. 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 strain 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 strain.

[0109] 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).

[0110] Figures 1 to 3 show the average compressive strength in MPa of the mortars tested.

[0111] Starch-free compositions are considered as references (Ref). Reference mortars based on illite or montmorillonite have a similar compressive strength, around 1 M Pa, while the kaolinite-based reference mortar has the lowest compressive strength, around 0.5 M Pa.

[0112] Montmorillonite-based mortar is poorly 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.

[0113] 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.

[0114] Kaolinite-based mortar is reinforced solely with 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 kaolinite-based mortar up to 4.5 M Pa. Thus, the compressive strength of 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 kaolinite-based mortar.

[0115] The compressive strength of illite and kaolinite mortars is increased four to ninefold with wheat starch (W), rice starch (R) and amylopectin (Ap).

[0116] For effective mortar reinforcement, increasing the compressive strength is advantageously combined with increasing the elastic modulus. The resulting mortar then exhibits low deformation before failure.

[0117] The elastic moduli in compression are presented in Figures 4 to 6 (y-axis in MPa).

[0118] For the montmorillonite-based mortar, similar results to those obtained for compressive strength are observed, with the elastic modulus of 60 M Pa remaining substantially constant with the addition of starch tested and the % by weight of starch added.

[0119] The elastic modulus of 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).

[0120] For the kaolinite-based mortar, similar results to those obtained for 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 wt% rice starch (R) and 760 MPa with 1.5 wt% amylopectin (Ap) relative to the total dry mass (clay, sand, additive).

[0121] 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). of cellulose in mortars based on illite, kaolinite or montmorillonite. Seven celluloses were tested. Cotton cellulose (CC) from Merck was used for its cellulosic purity close to 100%. 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 due to its length difference with softwood celluloses. Finally, two application celluloses were selected: a recycled pulp (RP) and a micro-cellulose (MC).

[0122] 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.

[0123] The average fiber lengths and diameters are shown in the table below. 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.

[0124] Depending on their length and diameter, celluloses have varying stiffness. 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.

[0125] 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 sheets (SP, SBK, SUBK, RBK).

[0126] The dispersions were therefore dried in a first step, while the leaves were prepared as follows. First, the leaves 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 evolved visually. Finally, the dispersed celluloses were pressed by hand and dried.

[0127] 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 applications.

[0128] Celluloses are incorporated into clay / sand mixtures at a rate of 7.5% of the total dry mass.

[0129] For cellulose mixtures, the water content was determined for each type of clay in order to achieve a flow threshold in the fresh state equal to that of cotton cellulose, around 20 kPa.

[0130] The water content is 22.6% by weight with kaolinite, 26.6% by weight with illite and 43.5% by weight with montmorillonite.

[0131] For the cellulose-free mortar mixes, the water content was decreased to achieve a yield strength of approximately 20 kPa. The water content was 13.6 wt%, 13.5 wt%, and 29.0 wt% for kaolinite, illite, and montmorillonite, respectively.

[0132] All samples were prepared using 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.

[0133] The resulting material was recovered and a third mixing was carried out at a constant speed of 93 rpm for 25 minutes.

[0134] Finally, the mortar mixes were kept in airtight beakers for at least 48 hours.

[0135] 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).

[0136] After compacting and demolding the molded mortars, drying at 20°C and 50%RH was carried out until a constant mass was obtained.

[0137] The compressive strength and elastic modulus of the samples were evaluated using only a compression test. The test was performed using a Shimadzu® AUTOGRAPH AGS-X press equipped with a 300 kN load cell.

[0138] The surfaces of the dried samples were flattened using a wood file, to obtain samples with horizontal and parallel surfaces.

[0139] 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.

[0140] The influence of celluloses on dried mortar mixes was evaluated by a compression test.

[0141] The reference results presented in figures 7 to 12 concern mortar mixtures prepared with a water content lower than that of celluloses, to have an elastic limit of 20 kPa as with cotton cellulose.

[0142] For kaolinite-based mortars, the compressive strength is not increased by the presence of cellulose and, in some cases, it decreases, especially 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 about 0.5 M Pa, 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. Regarding the evolution of the elastic modulus for kaolinite-based mortars, a significant decrease is observed with the same celluloses, from 95 MPa to 8 M Pa.

[0143] In illite-based mortars, the compressive strength tends to increase slightly with the presence of cellulose, from 1 M Pa to 3 M Pa. The elastic modulus is not increased, or even decreases, in the presence of cellulose, from 146 MPa to 35 M Pa.

[0144] For montmorillonite-based mortars, an increase in compressive strength is observed with all celluloses, from 1 MPa up to 7 M Pa. This increase is more significant for the addition of pure softwood cellulose (SP), bleached and unbleached kraft softwood (SBK, SlIBK) and bleached kraft hardwood (HBK), up to 7 M Pa. The same trend is found for the elastic modulus, which increases for all celluloses, from 62 to 271 M Pa. This last observation must be qualified by the size of the confidence intervals, which are wide.

[0145] Celluloses mainly reinforce montmorillonite-based mortars, and to a lesser extent illite-based mortars. The mechanisms leading to these reinforcements of mechanical properties are not precisely known; the inventors present the following hypotheses.

[0146] 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.

[0147] 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, with the movement of these components requiring more energy or more pore water.

[0148] In this regard, it is worth noting 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. The size differences between celluloses and grains in clay mortar mixtures are correlated with the compressive strength results and porosity values ​​of the mortars.

[0149] Examples of adding cellulose and starch to mortars based on natural earth

[0150] The following formulation was tested:

[0151] The mechanical compressive strength of the resulting mortar is 7.2 MPa. Figures 13 and 14 illustrate the increase in water resistance.

[0152] Figure 13 shows 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.

[0153] Figure 14 shows 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.

[0154] Example of adding different quantities of cellulose to montmorillonite-based mortars, initially comprising 70% sand and 30% montmorillonite on the sample without fibers.

[0155] Figure 18 shows that there is a minimum percentage of fibers in the mixture to achieve this effect. Three percentages (expressed as mass of fibers relative to the total dry mass of the mixture - %ms) of medium length fibers are compared to the reference (montmorillonite-sand mixture).

[0156] It is noted that the mixtures containing 0.75% and 2.5% of fibers in the mixture have a better mechanical resistance than the reference, but that the multiplication by 6 of the mechanical resistance to compression described previously requires a high percentage of fibers (7.5% ms).

[0157] Example of adding cellulose and starch fibers to a mixture comprising pure montmorillonite and sand

[0158] In order to determine the optimal length of cellulose fibers in a mortar formulated from montmorillonite, the following formulations were produced, the compressive strength results in M ​​Pa for these different formulations being shown in figure 1 5.

[0159] In the table above, the proportions indicated are defined as a percentage of the total dry mass.

[0160] The average lengths of the added cellulose fibers are specified in the table below. The mechanical performance of the formulations was evaluated by measuring the compressive strength of molded cylindrical samples, 20 mm in diameter and 40 mm in height.

[0161] It can be seen from Figure 1 5 that each of the additions of cellulose fibers to an earth formulated from pure montmorillonite makes it possible to improve the mechanical resistance.

[0162] 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 M Pa against 1 MPa for the reference without additives.

[0163] The optimal order of magnitude of the fibers added to the soil mixture is therefore a few millimeters.

[0164] 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.

[0165] Thus, it is observed that the addition of a combined additive (rice starch and medium fibers) neither improves nor degrades the mechanical resistance of the mixture compared to the medium fiber alone, which allows the starch to be used with earths presenting, in addition to montmorillonite, other clays which need starch to be mechanically and / or hydrously reinforced.

[0166] Example of adding cellulose and starch fibers to a mixture comprising pure kaolinite and sand

[0167] The following formulations were carried out, the compressive strength results in M ​​Pa for these different formulations being represented in figure 16.

[0168] In the table above, the proportions indicated are defined as a percentage of the total dry mass.

[0169] The percentages of amylose and amylopectin in the tested additives are presented in the following table:

[0170] The mechanical performance of the formulations was evaluated by measuring the compressive strength of molded cylindrical samples, 20 mm in diameter and 40 mm in height.

[0171] It can be seen from Figure 1 6 that each of the additions of starch with a high amylopectin content to a soil formulated from pure kaolinite improves the mechanical resistance of the samples tested.

[0172] 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 M Pa compared to 0.5 MPa for the reference without additives.

[0173] The minimum proportion of amylopectin in a starch chosen as an additive for a kaolinite is 80%.

[0174] 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. Example of addition of cellulose fibers and starch in a mixture comprising pure kaolinite, pure montmorillonite and sand

[0175] In order to verify that a combination of additives, each targeted towards a clay, is capable of reinforcing a mortar formulated from the two clays, the following formulations were produced, the compressive strength results in M ​​Pa for these different formulations being represented in figure 17.

[0176] In the table above, the proportions indicated are defined as a percentage of the total dry mass.

[0177] It can be observed from Figure 1 7 that for a soil 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 the mechanical resistance. It increases from 1 M Pa on average for the reference samples to 4.8 Ma on average for the samples with additive.

[0178] 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.

[0179] A bio-sourced additive is thus proposed which is capable of reinforcing a variety of natural soils containing kaolinite and / or montmorillonite in significant proportions.

[0180] This additive is advantageously formulated as follows: In a first step, the total proportion of clays (in dry mass) in the earth to be reinforced is determined.

[0181] In a second step, the water content of the soil to be reinforced is determined.

[0182] In a third step, a starch is added, advantageously at 1% (by mass relative to the dry mass of clay), the starch advantageously containing at least 80% amylopectin.

[0183] In a fourth step, a replacement is carried out, advantageously at 7.5%, of the dry mass with cellulose fibers, preferably of average size of the order of a few mm.

[0184] 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%.

[0185] Example of rice starch addition in a mixture of natural soil and sand for the production of compressed earth blocks

[0186] Rice starch, containing mainly amylopectin, is here added to a mixture of excavated earth and sand to make compressed earth blocks (CEBs) whose resistance to immersion in water is enhanced by the presence of rice starch.

[0187] Compressed earth blocks (CEBs) are manufactured using a steel mold and an electromechanical press. They are cubes with a side of 10 cm. After manufacture, they dry for 7 days in an enclosure at 40°C to reach a stabilized mass.

[0188] Resistance to immersion in water was tested for 4 reference compressed earth blocks (CEB) (without additive) as well as for 6 compressed earth blocks (CEB) containing 1% rice starch relative to the dry mass.

[0189] The water resistance test protocol is as follows. The compressed earth block (CEB) is placed in an enclosure at 107°C until completely dry. It is then weighed to determine its dry mass. Then, it is suspended from a holding device and immersed to a height of 5 cm in water at room temperature (it is therefore partially immersed), for a predefined period. Depending on its resistance to immersion, parts of the block may detach. Then, it is placed again in the enclosure at 107°C, until completely dry, then its mass is weighed to determine the loss of mass compared to the original block. This loss of mass makes it possible to estimate the resistance to partial immersion in water.

[0190] The table below shows the mass losses of the reference blocks and the blocks containing rice starch, with different immersion times in water.

[0191] It is observed that the reference blocks tend to suffer significant material loss, whereas the blocks prepared from the mixture containing rice starch suffer much lower material losses.

[0192] It can be concluded that this excavated soil to which rice starch is added is more resistant to erosion by immersion under water than the unadjuvanted soil and therefore has a much greater water resistance than the unadjuvanted soil.

[0193] The invention has many advantages.

[0194] The invention proposes combinations of bio-sourced materials of plant origin, making it possible to reinforce a wide spectrum of natural earths, and allowing their use as raw earths for construction, these natural earths comprising in particular kaolinite and montmorillonite. 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 or extruded earth blocks.

[0195] These bricks can be obtained after sieving the raw earth to keep only the particles with the appropriate granulometry. Sand can also be added to make them.

[0196] Raw earth generally contains, apart from clay, mainly aggregates (sand, silt, gravel, etc.).

[0197] Pure sand can be added, in particular taking into account the recommendations of the granulometric ranges for each material (compressed brick, adobe, extruded brick) or the expertise of the builder.

[0198] For example, raw earth may initially contain 5%-40% sand of the total dry mass, and an additional 5% to 40% sand (of the total dry mass of the new mixture to make the building material) may be added depending on the building materials used.

[0199] The mechanical resistance to compression of raw earth is significantly increased.

[0200] The addition of cellulose and starch, particularly amylopectin, helps increase mechanical strength.

[0201] The addition of starch (especially amylopectin) and / or cellulose fibers can strengthen different soils, including illite, kaolinite, or montmorillonite as the main clay mineral. The addition of starch, especially rice starch, and even more specifically amylopectin, interacts mainly with kaolinite and the addition of cellulose with montmorillonite. Illite, on the other hand, is reinforced by both biopolymers.

[0202] For a soil whose clay is of the kaolinite type, the compressive strength of 0.5 M Pa increases to 4.5 MPa with the use of rice starch 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.

[0203] The water resistance of the material is enhanced, particularly by the starch, which would delay the flow of water into its pores. In particular, rice starch from rice bran helps increase water resistance.

[0204] The addition of starch can enhance the water resistance of clay materials such as excavated soils, including both kaolinite and montmorillonite as the main clay mineral. The addition of starch thus allows the production of a raw earth construction material from soils of varying composition, thereby enhancing its mechanical and / or water resistance.

[0205] The invention thus allows mechanical reinforcement working for two large families of clay minerals with opposite behaviors. The invention thus allows the recovery of raw earths containing a clay mineral considered noble (kaolinite) as well as raw earths containing a clay mineral not considered economically (illite), or raw earths containing a clay mineral considered harmful (montmorillonite). Smectites exhibit swelling upon hydration and shrinkage upon drying, generating numerous problems in buildings.

[0206] 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 compressed earth bricks or extruded earth bricks.

[0207] The invention facilitates the use of excavated earth in new construction or the rehabilitation of old buildings, as well as in soil stabilization.

[0208] The invention facilitates the production of raw earth construction materials from soils of varying compositions, without it being necessary to carry out prior analyses of these soils to characterise them, in particular with regard to their clay mineral composition.

Claims

AMENDED CLAIMS received by the International Bureau on March 13, 2025 (13.03.2025) Claims 1. A raw earth construction material, having a base material which is a raw earth, which is a mixture of aggregates such as pebbles, gravels, sands and silts, and a binder formed by clay minerals and water, the clay minerals having at least montmorillonite and a second other clay mineral chosen from kaolinite or illite, the raw earth construction material comprising, mixed with the raw earth: polymers of natural plant origin which are cellulose fibers and at least one starch, the starch added to the base material having a ratio between the weight of amylopectin and the weight of amylose greater than 3, the raw earth construction material being recyclable and without hydraulic binder such as clay and cement.

2. Raw earth construction material according to claim 1, wherein the raw earth construction material comprises, relative to its total dry mass, at least 2% by weight of cellulose.

3. Raw earth construction material according to one of claims 1 to 2, wherein the raw earth construction material comprises, relative to its total dry mass, at least 4% by weight of cellulose.

4. Raw earth construction material according to any one of claims 1 to 3, wherein the raw earth construction material comprises, relative to its total dry mass, at least 6% by weight of cellulose, advantageously at least 7% by weight of cellulose.

5. Material for raw earth construction according to any one of claims 1 to 4, in which the mass of amylopectin in the added starch is greater than 80%, advantageously greater than 90%.

6. Raw earth construction material according to any one of claims 1 to 5, characterized in that the added starch is rice starch.

7. Raw earth construction material according to any one of claims 1 to 5, characterized in that the added starch is waxy maize starch and / or wheat starch.

8. Raw earth construction material according to any one of claims 1 to 7, characterized in that the cellulose fibers have average lengths of between 1 and 10 mm.

9. Raw earth construction material according to any one of claims 1 to 8, characterized in that the cellulose is a high purity cellulose comprising more than 96% cellulose (SP).

10. Material for raw earth construction according to any one of claims 1 to 8, characterized in that the cellulose is chosen from the group comprising bleached kraft celluloses (SBK), unbleached kraft fibers (SlI BK), bleached hardwood kraft fibers (H BK). 1 1. Raw earth construction material according to any one of claims 1 to 10, characterized in that the base material is excavated natural earth or construction site residue or previously crushed and ground rock.

12. Raw earth construction material according to any one of claims 1 to 11, characterized in that the second clay mineral contains illite, and the material contains wheat starch (W), rice starch (R), or waxy maize starch (Ap) as starch.

13. Raw earth construction material according to any one of claims 1 to 11, characterized in that the second clay mineral has kaolinite, and the material has rice starch (R) or waxy maize starch (Ap) as starch.

14. Material for raw earth construction according to any one of claims 1 to 13, characterized in that the material for raw earth construction comprises, relative to its total dry mass: between 10% and 40% by weight of clay mineral, less than 90% by weight of aggregates such as sand, gravel, silts, 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.

15. Raw earth construction material according to any one of claims 1 to 14, characterized in that the raw earth contains kaolinite and montmorillonite, and rice starch and cellulose fibers, the material having a mechanical compressive strength greater than 4 MPa.

16. Raw earth construction material according to any one of claims 1 to 15, characterized in that the raw earth construction material is limestone or dolomite.

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

18. Material for raw earth construction according to one of claims 1 to 17, characterized in that the material has at least 5% of aggregates whose largest dimension is greater than 1 mm.

19. Material for construction in raw earth, according to any one of claims 1 to 18, characterized in that the base material also comprises sand.

20. Compressed or extruded brick, made with the material defined according to any one of claims 1 to 19, the brick having for example a material having a mechanical resistance greater than 2 M Pa, advantageously greater than 4 M Pa.

21. Adobe made with the material defined according to any one of claims 1 to 19.

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