INSULATING CONSTRUCTION MATERIALS WITH A BASE OF VEGETAL

ADDITIONS

The invention relates to an insulating construction material with low thermal conductivity comprising vegetal additions, as well as to a process for preparation and to uses of such a material. Such materials may be intended to produce structures cast on site, pre-cast structures or elements of pre-cast structures for buildings and civil engineering structures.

The production of blocks for masonry using vegetal additions incorporated in a lime-based binder matrix (for example hemp used to produce Chanvribloc™ blocks) is a known process.

However, this type of material requires very long hardening times, several weeks in the case of hemp-based materials. Moreover, vegetal additions tend to retard the setting of hydraulic binders, and in particular the setting of Portland cements is delayed.

Therefore, the problem which the invention seeks to resolve is to propose a new material comprising a vegetal addition the hardening time of which is from a few hours to a few days.

Surprisingly, the inventors have shown that it is possible to use trivalent cations mixed with the vegetal additions to obtain a material having low thermal conductivity.

With this aim the invention proposes an insulating construction material with low thermal conductivity comprising vegetal additions and trivalent cations.

The materials according to the present invention have one or more of the following characteristics:

Advantageously, the material according to the invention may be poured on site on the jobsite, or prepared at a concrete batching plant and transported in a mixer truck;

Advantageously, the material according to the invention may be prepared in a pre-cast plant to produce construction elements;

Advantageously, the material according to the invention can harden in a few hours, and in a maximum of a few days;

Advantageously, the material according to the invention has thermal conductivity less than 0.3 VW(m.K) at 23°C and 50% relative humidity; Advantageously, the material according to the invention is sufficiently rigid to at least support its own weight; Advantageously, the hardened material according to the invention has low density in the dry state, comprised from 150 kg/m ³ to 1 000 kg/m ³ , preferably 450 kg/m ³ to 750 kg/m ³ ; the dry state is generally to be understood as having a constant mass, once generally it has spent a sufficient time in an oven.

Advantageously, biomass is incorporated in the material according to the invention making it thus possible to store C0 ₂ and reduce the C0 ₂ impact of the material,

Advantageously, the material according to the invention uses vegetal additions. These vegetal additions are renewable vegetation.

The present invention relates to a material with a density of 150 to 1 000 kg/m ³ when the hardened material is in the dry state, said material comprising

- a hydraulic binder;

- a vegetal addition from annual plants, the mass ratio of the dry vegetal addition/hydraulic binder being comprised from 0.05 to 2;

- from 0.01 to 1 .2 equivalent moles of trivalent cations per kg of dry vegetal addition from a source of soluble trivalent cations in an aqueous medium;

- from 0.001 to 2 % of a foaming agent, the percentage being expressed by mass relative to the mass of binder; and

- water, the water/binder mass ratio being comprised from 0.3 to 2.5.

The material according to the invention comprises a hydraulic binder, a source of soluble trivalent cations in an aqueous medium, a vegetal addition, a foaming agent, water, optionally a fluidizer and optionally a setting accelerator of the hydraulic binder.

A hydraulic binder is a material which sets and hardens by hydration. Preferably, the hydraulic binder is or comprises a Portland cement.

The hydraulic binder of the material according to the invention may be selected from Portland cement, Fondu ^® cements, sulfoaluminous cements, calcium aluminate cements, cement obtained from the clinker described in patent application WO 2006/018569, hydraulic lime, aerated lime, calcium sulphate, hemihydrate calcium sulphate, anhydrous calcium sulphate and mixtures thereof.

The hydraulic binder of the material according to the invention may comprise cement.

The suitable cement for the material according to the invention is preferably the cement described according to the European NF EN 197-1 Standard of February 2001 . The suitable cement for the material according to the invention may be the CEM I, CEM II, CEM III, CEM IV or CEM V types of cement.

Preferably, the suitable cement for the material according to the invention is selected from the types of cement:

- CEM I or CEM II, optionally mixed with mineral additions, or

- CEM III, CEM IV or CEM V.

The preferred suitable hydraulic binder for the material according to the invention is the Portland CEM II or III cement, alone or combined with other cements, for example those described according to the NF EN 197-1 Standard of February 2001 .

According to a variant of the invention, the hydraulic binder of the material according to the invention comprises at least one cement of type CEM I or CEM II, combined with additions of slag and/or fly ash and/or silica fume and/or pozzolanic materials and/or metakaolin. These may make it possible to replace the CEM ll/A, CEM ll/B, CEM Ill/A, CEM lll/B, CEM 11 I/ , CEM IV/A, CEM IV/B, CEM V/A or CEM V/B types of cement cements blended with slags and/or fly ash .

The suitable hydraulic binder for the material according to the invention may be a calcium aluminate cement. It is generally a cement comprising a C ₄ A ₃ $, CA, Ci ₂ A _7, C ₃ A or CnA ₇ CaF ₂ mineralogical phase or mixtures thereof, for example Fondu ^® cements, sulfoaluminous cements, calcium aluminate cements according to the European NF EN 14647 Standard of December 2006, cement obtained from the clinker described in patent application WO 2006/018569, cement obtained from the clinker described in patent application WO 2013/023731 , cement obtained from the clinker described in patent application WO 2013/023729, or mixtures thereof.

The suitable hydraulic binder for the material according to the invention may be selected from Fondu ^® cements, sulfoaluminous cements, calcium aluminate cements and mixtures thereof.

The suitable hydraulic binder according to the invention may be an ettringite, cement, for example a sulfoaluminous cement with an addition of calcium sulphate or a calcium aluminate cement with an addition of calcium sulphate.

The suitable hydraulic binder according to the invention may be hydraulic lime, aerated lime by itself or in a mixture.

The suitable cement for the material according to the invention is preferably a fine cement or micro fine cement. Preferably, the suitable cement for the material according to the invention has a specific Blaine surface from greater than or equal to 3300 cm ² /g, more preferably greater than or equal to 3500 cm ² /g, even preferably greater than or equal to 3800 cm ² /g. Preferably, the suitable cement for the material according to the invention has a specific Blaine surface from 3300 cm ² /g to 9000 cm ² /g, more preferably from 3500 cm ² /g to 7000 cm ² /g, even more preferably from 3500 cm ² /g to 6000 cm ² /g.

The material according to the invention is produced using a source of soluble trivalent cations in an aqueous medium.

The material according to the invention comprises from 0.01 to 1 .2 equivalent moles of trivalent cations from a source of soluble trivalent cations in an aqueous medium per kg of dry vegetal addition. Preferably the material according to the invention comprises 0.1 to 1 .2, and more preferably 0.3 to 1 equivalent moles of trivalent cations from the source of soluble trivalent cations in an aqueous medium per kg of dry vegetal addition.

The source of soluble trivalent cations in an aqueous medium may be selected from one or more soluble salts.

The source of soluble trivalent cations in an aqueous medium may be selected from iron salts or aluminium salts or mixtures thereof.

When the source of soluble trivalent cations in an aqueous medium is a soluble iron salt in an aqueous medium, it may be iron nitrite (III), iron nitrate (III), iron chloride (III), iron sulphate (III), iron nitrite (II), iron nitrate (II), iron chloride (II), iron sulphate (II) or mixtures thereof.

When the source of soluble trivalent cations in an aqueous medium is a soluble aluminium salt in an aqueous medium, it may be aluminium nitrite, aluminium nitrate, aluminium hydroxide, aluminium sulphate, aluminium chloride of mixtures thereof.

According to a variant, the material according to the invention comprises aluminium salts mixed with calcium sulphate, in particular anhydrous calcium sulphate.

These salts may, in particular be used as prior treatment of the vegetal addition,

The material according to the invention may optionally comprise a setting accelerator of the hydraulic binder, in particular from 0.01 to 5 % percentage by mass relative to the hydraulic binder.

The setting accelerator of the hydraulic binder in the material according to the invention may be selected from anhydrous calcium sulphate, calcium sulphate hemi- hydrate, calcium hydroxide, calcium chloride, calcium nitrite, calcium nitrate, sodium nitrate, lithium carbonate, lithium chloride, lithium hydroxide, lithium nitrite, lithium nitrate, lithium sulphate and mixtures thereof.

The material according to the invention may optionally comprise mineral additions. The suitable mineral additions are generally materials which can be used to partially substitute the cement.

The suitable mineral additions for the material according to the invention may be selected from pozzolanic materials, silica fume, slags, calcined shale, materials containing calcium carbonate, siliceous additions, fly ash, zeolites, ash resulting from the combustion of plants, calcined clays and mixtures thereof.

The suitable mineral additions used according to the invention may be pozzolanic materials (for example, as defined in the European NF EN 197-1 Standard of February 2001 , paragraph 5.2.3), silica fume (for example, as defined in the European NF EN 197-1 Standard of February 2001 , paragraph 5.2.7), slags (for example, as defined in the European NF EN 197-1 Standard of February 2001 , paragraph 5.2.2), calcined shale (for example, as defined in the European NF EN 197- 1 Standard of February 2001 , paragraph 5.2.5), materials containing calcium carbonate, for example limestone, (for example, as defined in the European NF EN 197-1 Standard of February 2001 , paragraph 5.2.6), siliceous additions (for example, as defined in the French NF P 18-509 Standard of December 1998, paragraph 5), fly ash (for example, as described in the European NF EN 197-1 Standard of February 2001 , paragraph 5.2.4), or mixtures thereof.

The mineral additions used according to the invention may also be ash coming from the combustion of plant, for example ash coming from the combustion of rice husk.

The mineral additions used according to the invention may also be zeolites. Fly ash is generally pulverulent particles comprised in fume from thermal power plants which are fed with coal. It is generally recovered by electrostatic or mechanical precipitation.

The chemical composition of a fly ash mainly depends on the chemical composition of the unburned carbon and on the process used in the thermal power plant where it came from. Its mineralogical composition also depends on the same factors. The nature of the fly ash used according to the invention may be siliceous or calcic.

Preferably, the fly ash used according to the present invention is selected from fly ash described in the European NF EN 197-1 Standard of February 2001.

Slags are generally obtained by rapid cooling of molten slag resulting from the melting of iron ore in a blast furnace. The slags used according to the present invention may be selected from granulated blast-furnace slags according to the EN 197-1 Standard of February 2001 , paragraph 5.2.2.

Silica fume used according to the present invention may be a material obtained by the reduction of very pure quartz using coal in electric arc furnaces used for the production of silicon and alloys of ferrosilicon. Silica fume generally comprises spherical particles comprising at least 85% by mass of amorphous silica.

Preferably, the silica fume used according to the present invention may be selected from silica fume according to the European NF EN 197-1 Standard of February 2001 , paragraph 5.2.7.

The pozzolanic materials used according to the present invention may be natural siliceous and/or silico-aluminous substances or a combination thereof. Natural pozzolans are an example of pozzolanic materials. Natural pozzolans are generally materials of volcanic origin or sedimentary rocks; calcined natural pozzolans, are materials of volcanic origin, clays, shale or thermally-activated sedimentary rocks. The pozzolanic materials used according to the present invention may be selected from pumice, tuff, scoriae or mixtures thereof.

Preferably, the pozzolanic materials used according to the present invention may be selected from the pozzolanic materials according to the European NF EN 197- 1 Standard of February 2001 paragraph 5.2.3.

Preferably, the mineral additions used according to the invention may be materials containing calcium carbonate, for example, limestone and/or fly ash and/or silica fume.

Preferably, the mineral additions used according to the invention may be silica fines and/or a limestone filler.

The calcined clays used according to the present invention may result from the calcination of a clay, in particular, kaolinite clay, associated with different minerals (phyllosilicates, quartz, iron oxides) in variable proportions depending on the deposits. They may be obtained either by calcination followed by grinding or by grinding followed by calcination in production units with rotating kilns, plateaux kilns or, for example, by calcination called « flash » calcination. They are essentially composed of particles of amorphous alumina silicate.

Preferably, the calcined clays used according to the present invention may be selected from the metakaolins according to the preliminary project of the PR NF P 18- 513 Standard of December 201 1 . The material according to the invention is produced using vegetal additions from annual plants. Annual plants are generally plants which only live for one season, which germinate, develop and die during one year. They are to be differentiated from perennial plants. All or part of annual plants may be used as vegetal additions (grains, stems, leaves) according to the invention. Annual plants are generally to be understood as including biannual plants or short life cycle plants.

The suitable vegetal additions for the material according to the invention are solid materials of vegetal origin or ground vegetal waste. Preferably, the vegetal additions are not liquid extracts of vegetal or plant resins. The vegetal additions may be vegetal fibers.

The suitable vegetal additions for the material according to the invention may be porous and rich in organic materials (cellulose, hemicellulose, lignin, etc), derived from plants via industrial production processes (e.g. shredding, crushing, grinding, separating).

Examples of vegetal additions from annual plants comprise, for example vegetal additions of hemp origin, hemp straw, hemp chaff, maize straw, maize cob, sorghum, flax straw, flax shives, miscanthus (elephant grass), rice straw, rice husks, sugarcane bagasse, cereal straws, sunflower straw, kenaf, coconut, olive nuts, bamboo, Balsa wood, poplar, wood pellets (for example shredded spruce), wood chips, barley straw, wheat straw, rey straw, millet straw, oat straw, fonio straw, corn straw, reed, jute, sisal, abaca, henequen, sunflower pith, rape seed straw, soya straw, manioc straw, cassava straw, castor-oil plant, red pimpernel plant, forget-me-not plant, borage plant, cosmos plant, French marigold plant, annual Poppy plant, fescue and mixtures thereof.

Preferably, the vegetal addition from annual plants may be hemp chaff.

Preferably, the vegetal addition from annual plants may be rice husk. Rice husk derive from the threshing of rice, which is generally used for human food consumption. Rice husk are constituted by an assembly of bracts or glumes which enclose the grain and protect it during its growth.

Threshing is generally carried out by a mechanical fractioning process, after beating, using a machine generally equipped with two horizontal discs coated with an abrasive material to separate the grains from the bracts and glumes. It is also possible to use rubber cylinder threshing machines, at variable revolution speeds, to thus reduce the risk of breaking the grains of rice.

The proportion of rice husk resulting from rice threshing fluctuates between 17 and 23 % (percentage by mass) depending on the variety of rice. The obtained product has a brown-beige colour and a hard consistency. Its apparent density generally varies from 1 10 to 140 kg/m ³ . Rice husk are practically rot-proof and insect-proof. The content of cellulose represents 35 to 45 % of the mass. The ash, composed almost completely of silicon dioxide (silica), represents approximately 15 to 20% of the mass of rice husk. The content of amorphous silica represents 85 to 93 % of the mass of the ash.

The suitable vegetal additions for the material according to the invention may be in the form of needles or chips, the length of which generally varies from 1 mm to 4 cm, the width varies from 0.5 mm to 1 cm and the thickness varies from 0.5 mm to 0,5 cm.

The suitable vegetal additions for the material according to the invention may be treated, in order to reduce their water-absorption capacities and their releasing capacities in water or in the cement medium of organic water-soluble substances (potential setting retarders for the hydraulic binder). Different techniques may be used:

- leaching in water with a neutral or basic pH at a temperature of 20 to 100°C,

- polymerization of the organic water-soluble substances of the biomass by thermal treatment (cross-linking or pyrolysis) at high temperature (from 80 to 220 °C), or by ionisation or plasma treatment or UV.

For example, the treated vegetal additions may have been mixed or sprayed with a compound giving them a particular property, in particular hydrophobic properties. For example, a water-proof treatment with hydrocarbons, silicons, latex, vegetable oils, fatty alcohols, fatty acids or mixtures thereof. The waterproof treatment may be a bond of alkyl groups (C2 to C30) on the OH group of the biomass by esterification and/or etherification.

According to a variant, the material according to the invention comprises at least one treated vegetal addition. According to another variant, all vegetal additions used according to the present invention are treated.

Preferably, the material according to the invention comprises 10 to 1 000 litres of vegetal addition per m ³ of material.

Preferably, the material according to the invention has a mass ratio of dry vegetal addition/binder comprised from 0.02 to 1 , preferably from 0.1 to 1 .0. A dry vegetal addition is generally to be understood as having been dried at 105°C for 24 hours.

The material according to the invention is produced using a foaming agent.

The foaming agent used according to the invention may be selected from ionic, anionic, non-ionic, amphiphilic or amphoteric foaming agents and used alone or in mixtures. By way of ionic surfactants, the following non-limiting examples may be mentioned: alkylethersulfonates, hydroxyalkylethersulfonat.es, alphaolefinesulfonat.es, alkylbenzenesulfonat.es, alkylester sulfonates, alkylethersulphates, hydroxyalkylethersulphat.es, alphaolefinesulphates, alkylbenzenesulphates, alkylamide sulphates, as well as their alkoxylated derivatives (in particular ethoxylated derivatives (EO) and/or propoxylated derivatives (PO)), the corresponding salts or mixtures thereof.

By way of ionic surfactants, the following non-limiting examples may also be mentioned: saturated or insaturated fatty acid salts and/or their alkoxylated derivatives, in particular (EO) and/or (PO) (for example sodium laurate, sodium palmitate or sodium stearate, or sodium oleate), methyl laurate alpha sulfonated, sodium laurate alpha sulphonated, alkylglycerol sulfonates, sulfonated polycarboxylic acids, paraffin sulfonates, N-acyl N-alkyltaurates, alkylphosphates, alkylsuccinamates, mono or di alkylsulfosuccinamates, alkylsuccinates, mono or di alkylsulfosuccinates, sulphates of alkylglucosides.

By way of non-ionic surfactants, the following non-limiting examples may be mentioned: ethoxylated fatty acids, alkoxylated alkylphenols or arylphenols (in particular (EO) and/or (PO)), aliphatic alcohols more particularly C8-C22 linear or branched, products resulting from the condensation of ethylene oxide or propylene oxide with propylene glycol or ethylene glycol, products resulting from the condensation of ethylene oxide or propylene oxide with ethylene diamine, amides of alkoxylated fatty acids (in particular (EO) and/or (PO)), alkoxylated amines (in particular (EO) and/or (PO)), alkoxylated amidoamines (in particular (EO) and/or (PO)), amine oxides, alkoxylated terpenic hydrocarbons (in particular (EO) and/or (PO)), alkylpolyglucosides, polymers or amphiphilic oligomers, ethoxylated alcohols, esters of sorbitan or esters of ethylated sorbitan.

By way of amphoteric surfactants, the following non-limiting examples may be mentioned: betaines, derivatives of imidazoline, polypeptides or lipoaminoacids. More particularly, suitable betaines according to the invention may be selected from cocoamidopropyl betaine, dodecylic betaine, hexadecylic betaine and octadecylic betaine, phospholipids and their derivatives, esters of amino acids, water-soluble proteins, esters of water-soluble proteins and mixtures thereof.

By way of cationic surfactants, the following non-limiting examples may be mentioned: alkyl ammonium, aryl ammonium, amino alkyl oxide e.g. amino-laurate oxide or amino propyl cocoate oxide, alkyl amphocarboxyl glycinate e.g. caprylamphocarboxyl glycinate.

According to a particular embodiment of the invention, the non-ionic foaming agent may be associated to at least one anionic or cationic or amphoteric foaming agent.

By way of amphiphilic surfactants, the following non-limiting examples may be mentioned: polymers, oligomers or copolymers which are at least miscible in the aqueous phase.

The amphiphilic polymers or oligomers may have a statistic distribution or a multi- block distribution.

The amphiphilic polymers or oligomers used according to the invention are selected from block polymers comprising at least one hydrophilic block and at least one hydrophobic block, the hydrophilic block being obtained from at least one non-ionic and/or anionic monomer.

By way of example, the following amphiphilic polymers or oligomers may be mentioned: polysaccharides having hydrophobic groups, in particular alkyl groups, polyethylene glycol and its derivatives.

By way of example, the following amphiphilic polymers or oligomers may also be mentioned: three-block polyhydroxystearate - polyethylene glycol - polyhydroxystearate polymers, branched or non-branched acrylic polymers, or hydrophobic polyacrylamide polymers.

Non-ionic amphiphilic polymers, and more particularly alkoxylated polymers (in particular (EO) and/or (PO)), are more preferably selected from polymers, wherein at least one part (at least 50 % by mass) is miscible in water.

By way of examples of this type of polymer, the following polymers may be mentioned among others: three-block polyethylene glycol / polypropylene glycol / polyethylene glycol polymers.

The foaming agent used according to the invention may be a protein, in particular a protein of animal origin, more particularly keratin or keratin hydrolysate, or a protein of plant origin, more particularly a water-soluble protein of wheat, rice, soya or cereals. By way of example, mention may be made of wheat protein hydrolysate or oat protein hydrolysate.

Preferably, the foaming agent used according to the invention is a protein with a molecular weight of 300 to 50 000 Daltons. According to a variant of the invention, the foaming agent comes from the vegetal addition itself used in the material according to the invention. In this case, the foaming agent is freed or released by the vegetal additions. The foaming agent may be tannins, polyphenols, latex, wax, triglycerides, terpenes or mixtures thereof. In this particular case, no external foaming agent is added in the material according to the invention outside the foaming agent freed or released by the vegetal additions itself.

The foaming agent is used according to the invention at a concentration of 0.001 to 2 %, preferably from 0.01 to 1 %, more preferably from 0.005 to 0.3 % by mass of foaming agent relative to the mass of binder. Preferably, the concentration of foaming agent is at least 0.01 %, by mass relative to the mass of binder. More preferably, the concentration of foaming agent is at least 0.1 % by mass relative to the mass of binder.

Preferably, the material according to the invention comprises a hydraulic binder comprising 0.01 to 0.3 % of a foaming agent, percentage by mass relative to the mass of binder.

The material according to the invention may comprise a water-reducer, a plasticizer or a superplasticizer, the mass ratio of the water-reducer/binder being comprised from 0.001 to 0.02.

The material according to the invention may, for example comprise one of the admixtures described in the European NF EN 934-2 Standard of September 2002, the European NF EN 934-3 Standard of November 2009 or the European NF EN 934-4 Standard of August 2009. Advantageously, the material according to the invention comprises at least one admixture for a hydraulic composition: an accelerator, an air- entraining agent (or a foaming agent), a viscosity-modifying agent, a plasticizer and/or a superplasticizer. In particular, it is useful to use a superplasticizer of the polycarboxylate type, in particular from 0.05 to 1.5 %, preferably from 0.1 to 0.8 %, by mass of the binder.

According to a variant, the material according to the invention comprises a superplasticizer.

The term superplasticizer as used in the present description and the accompanying claims is to be understood as including both water reducers and superplasticizers as described in the Concrete Admixtures Handbook, Properties Science and Technology, V.S. Ramachandran, Noyes Publications, 1984.

A water reducer is defined as an admixture which reduces the amount of mixing water of a concrete for a given workability by typically 10-15%. Water reducers include for example, lignosulphonates, hydroxycarboxylic acids, glucides and other specific organic compounds, for example glycerol, polyvinyl alcohol, sodium alumino-methyl- siliconate, sulfanilic acid and casein.

Superplasticizers belong to a new class of water reducers which are chemically different to ordinary water reducers and are capable of reducing water contents by approximately 30% by mass. The superplasticizers have been broadly classified into four groups: sulphonated naphthalene formaldehyde condensate (SNF) (generally a sodium salt); sulphonated melamine formaldehyde condensate (SMF); modified lignosulfonates (MLS); and others. More recent superplasticizers include polycarboxylic compounds such as polycarboxylates, for example, polyacrylates. A superplasticizer is preferably a new generation superplasticizer, for example a copolymer containing polyethylene glycol as graft chain and carboxylic functions in the main chain such as a polycarboxylic ether (PCP). It may be a PCP with a differed effect. Sodium polycarboxylate-polysulphonates and sodium polyacrylates may also be used. Phosphonic acid derivatives may also be used. The amount of superplasticizer required generally depends on the reactivity of the cement. The lower the reactivity, the lower the amount of superplasticizer required.

Preferably, the material according to the invention has a water/binder mass ratio comprised from 0.3 to 2.5.

Preferably, the material according to the invention has a water/binder mass ratio comprised from 0.5 to 2.1 , more preferably from 0.7 to 1.9.

The term « water » is to be understood as the totality of the water present in the mix (at the time of mixing) and it generally comprises the effective water and the water absorbable by the aggregates and the vegetal additions (pre-wetting water). The effective water is the water required to hydrate a hydraulic binder and to provide fluidity of a hydraulic composition obtained in the fresh state.

The material according to the invention may be a ready-mix concrete, a projected concrete, a concrete pre-cast on the jobsite, or a concrete produced in a production plant of pre-cast elements. Ready-mix concrete is generally a concrete having sufficient open workability time to allow for the transport of the concrete to the jobsite where it will be poured. Preferably, the open workability time of ready-mix concretes can be from 15 minutes to 3 hours.

Preferably, the material according to the invention is a concrete produced in a production plant of pre-cast elements, that may need in some cases a step of curing the material or a step of heating the material. According to a variant of the invention, the material according to the invention is a ready-mix concrete that do not need any step of curing the material or any step of pressuring the material or any step of heating the material.

The materials according to the invention associate a sufficiently high compressive strength and reduced thermal conductivity compared to those of concretes usually available in the field. The compressive strength is generally from 0.1 to 4 MPa at 28 days. Moreover, these formulations are simple and easy to use. Finally, the cost of the constituents used is relatively low and they are easily available. This makes these formulations particularly useful in the industry.

Preferably, the material according to the invention has thermal conductivity less than 0.3 W/m.K, preferably less than 0.2 W/m.K, and more preferably less than 0.1 W/m.K at 23°C and 50% relative humidity.

Thermal conductivity (also called lambda (λ)) is a physical value characterising the behaviour of materials during heat transfers by conduction. Thermal conductivity represents the quantity of heat transferred per surface unit and per time unit for a temperature gradient. In the international system of units, thermal conductivity is given in watts per metre per Kelvin, (W-m ^"1 -K ^"1 ). Conventional concretes have thermal conductivity from 1 .3 to 2.1 at 23°C and 50 % relative humidity. Conventional structural lightweight concretes have thermal conductivities generally greater than 0.8 W/m.K at 23°C and 50 % relative humidity.

Thermal conductivity is to be understood according to the invention as thermal conductivity at 23°C and 50% relative humidity, determined according to the following procedure:

measurement of dry thermal conductivity according to the guarded hot plate method according to the ISO 8302 Standard of August 1991 , after complete drying of the sample,

determination of thermal conductivity from values measured in reference temperature and humidity conditions, given for a determined fractile and confidence level and corresponding to a usage time considered to be reasonable in ordinary conditions, according to the European NF EN ISO

10456 Standard of June 2008.

The invention also relates to a process for preparation of a material according to the invention, said process comprising the mixing of a hydraulic binder, a source of soluble trivalent cations in an aqueous medium, a vegetal addition, a foaming agent, water and optionally a mineral addition and a setting accelerator of the hydraulic binder.

The process according to the invention may comprise a step of prior treatment of the vegetal additions by the source of trivalent cations, preferably iron salts or aluminium salts. In this case, the source of trivalent cations is added to the pre-wetting water of the vegetal additions.

The invention also relates to a process for preparation of a material according to the invention which generally comprises:

- a first step of pre-wetting the vegetal additions;

- a second step of mixing the pre-wet vegetal additions and the hydraulic binder, and the mixing water containing the foaming agent, optionally a water reducer and inorganic additives in the quantities described herein above for the material according to the invention.

In this pre-wetting step, water (the pre-wetting water) and the source of trivalent cations (other than the hydraulic binder) are combined with the vegetal additions, before the second step.

In this pre-wetting step, the vegetal addition could be used as such, with its normal humidity. Generally, it's not necessary to dry the vegetal addition before use.

According to a variant of the process according to the invention, it is possible to add a third step, to cure the obtained material. For example, the material may be maintained in an atmosphere with a residual humidity varying from 60 to 100% generally at room temperature for several hours to a few days.

According to another embodiment of the process according to the present invention, it is possible to add each of the constituents described above separately.

The material according to the present invention may be cast to produce, after hydration and hardening, an object cast for the construction field. The invention also relates to such a cast object which comprises the material as described herein above. The objects cast for the construction field include, for example, a floor, a screed, a wall, a partition wall, a ceiling, a work top, a pillar, a masonry block of concrete, a heat- resistant pipe, a panel, a cornice, a mould, a surfacing (for example of a road or a wall), an insulating element (acoustic and/or thermal), an element to fill in cavities (filling or back filling underground galleries).

In the present description, including the accompanying claims, unless otherwise specified, percentages are by mass. The invention also relates to use of a material according to the invention as construction material.

The invention also relates to an object produced with the material according to the invention.

The following examples are provided for the invention purely for illustrative and non-limiting purposes.

Examples of embodiments of the invention

Determination of the density of the fresh material:

The density of the fresh material was determined according to the European NF EN 12350-6 Standard of December 1999. Determination of the density of the hardened material in the dry state:

The density of the hardened material in the dry state was determined according to the European NF EN 12390-7 of September 2001 .

Determination of the compressive strength:

Measurements of the compressive strength were carried out on 10cm x 10cm x

10 cm cubes or 4cm x 4cm x 16 cm specimens according to the European NF EN 12390-3 Standard of February 2003. The weight and mechanical strength of the cubes and specimens of material were measured at the 1 -day, 7-day and/or 28-day time periods using a ZWICK press for the 10cm x 10cm x 10 cm cubes or using the 32 press for the 4cm x 4cm x 16 cm specimens supplied by the company, Recherche Realisation Remy.

Determination of the thermal conductivity:

Thermal conductivity was determined for the dry material according to the hot plate method according to the ISO 8302:1991 Standard of August 1991 , after complete drying of the sample using a CT-metre supplied by the company, Alphis-Ere.

Thermal conductivity was measured on dried 10 cm x 10 cm x 10 cm cubes with a constant weight at 45 °C.

List of the raw materials: The Portland cement n°1 is a CEM I 52.5N cement, with a density of 3150 kg/m ³ . This cement is the CEM I cement and is in the 52.5 strength class. It comes from the Lafarge plant of Le Havre.

The Portland cement n°2 is a CEM I 52.5R cement, with a density of 3140 kg/m ³ and a Blaine specific surface of 3870 cm ² /g. This cement is the CEM I cement and is in the 52.5 strength class. It comes from the Lafarge plant of Le Teil.

The Portland cement n°3 is a cement, with a density of 3120 kg/m ³ and a Blaine specific surface of 6770 cm ² /g. This cement is in the 52.5 strength class. It comes from the Lafarge plant of Saint Pierre La Cour.

The Portland cement n°4 is a cement, with a density of 31 10 kg/m ³ and a Blaine specific surface of 8270 cm ² /g. This cement is in the 52.5 strength class. It comes from the Lafarge plant of Saint Pierre La Cour.

The Fondu ^® cement is supplied by KERNEOS.

The hydraulic lime is the NHL 3.5 Natural ^® hydraulic lime from Lafarge.

The calcium hydroxide, Ca(OH) ₂ is supplied by Sigma-Aldrich.

The iron chloride, FeCI ₃ is supplied by Sigma-Aldrich.

The aluminium chloride, AICI ₃ .6H ₂ 0 is supplied by Sigma-Aldrich.

The anhydrous calcium sulphate, CaS0 ₄ is supplied by Lafarge Le Havre.

The calcium chloride, CaCI ₂ (93 % purity) is supplied by Sigma-Aldrich.

The calcium chloride, CaCI ₂ (75 % purity) is supplied by Brentag.

The iron nitrate, Fe(N03) ₃ is supplied by Sigma-Aldrich.

The sodium nitrate, NaN0 ₃ (99% purity) is supplied by Sigma-Aldrich.

The limestone filler is DURCAL, supplied by OMYA.

The sands in the following list were used and all came from Lafarge quarries (in this list the ranges of aggregates are given in the form of d/D wherein « d » and « D » are as defined in the XPP 18-545 Standard of February 2004):

0/1.6 Cassis sand: calcareous sand from the Lafarge quarry of Cassis;

3/6 Cassis sand: calcareous sand from the Lafarge quarry of Cassis.

The foaming agent is either:

sodium oleate supplied by BASF under the brand name, Microair 104; 4.47 % dry extract;

supplied by COGNIS-BASF under the brand name, Glucopon 600 CSUP; 10.34% dry extract; supplied by Stepan Europe under the brand name Stepanol ALS 25 (24,7% dry extract).

The superplasticizer is either:

PolyCarboxylate Polyethylene glycol (PCP): supplied by BASF under the brand name, Glenium 27: 21 % dry extract;

PolyCarboxylate Polyethylene glycol (PCP) without an anti-foaming agent supplied by CHRYSO and resulting from a commercial admixture under the brand name Optima 203, Base OPTIMA 203: 49.96 % dry extract.

The vegetal addition is either:

Rice husk n°1 from France supplied by Societe Les Silos de Sizeranne - COTRADA in France; water content: 1 1 % (percentage by mass), and density: 105 kg/m ³ (formulations 1 , 2 and 3);

- Rice husk n°2 from Vietnam supplied by Lafarge Concretes in Vietnam; water content: 8.6 % (percentage by mass), and density: 1 10 kg/m ³ (formulation 4 and 5);

Rice husk n°3 from France supplied by Societe Les Silos de Sizeranne - COTRADA in France; water content: 10 % (percentage by mass), and density: 120 kg/m ³ (formulation 5.2).

Hemp chaff n°1 supplied by Chanvriere de I'Aude; water content: 12 % (percentage by mass), and density: 1 10 kg/m ³ ; (formulations 6 to 19, except 12);

Hemp chaff n°2 supplied by Chanvriere de I'Aude; water content: 15 % (percentage by mass), and density: 1 10 kg/m ³ ; (formulation 12).

The water is tap water.

Process for production of the material according to the invention:

Method 1 :

The batches of reference material or material according to the invention were prepared using a KENWOOD mixer (Series « Chef Classique KM400/410 » 4.3-litre stainless steel bowl; planetary movement with a whip) in a temperature-regulated room at 20°C according to the following procedure:

Introduce the vegetal addition in the bowl of the mixer, then mix for one minute at the lowest speed of the mixer;

- Introduce the pre-wetting water and the source of trivalent cations other than the Portland cement in the bowl of the mixer, then mix for one minute at the lowest speed of the mixer;

Interrupt the mixing for ten minutes;

Introduce the cement and all the other constituents of the formulation in the bowl of the mixer, then mix for one minute at the lowest speed of the mixer;

Introduce the mixing water containing the foaming agent and the superplasticizer, when present, in 20 to 30 seconds whilst mixing at lowest speed of the mixer, then mix everything for one minute at speed 3 of the mixer; Measure the density of the fresh material by weighing the paste in a 0.75-litre bowl using the CONTROLS aerometer (Series 1954),

Pour the rest of the paste into polystyrene moulds (4 cm x 4 cm x 16 cm specimens or 10 cm x 10 cm x 10cm cubes). Keep the specimens or cubes in their moulds at 20 °C and 100 % residual humidity,

After 48 hours, de-mould the specimens and cubes and keep them at 20 °C and a residual humidity varying from 60 to 100 %.

Method 2:

The batches of reference material or material according to the invention were prepared using a mixer provided by VMI Rayneri (Model PH602, N°121025, 30-litre stainless steel mould; planetary movement) in a temperature-regulated room at 20°C according to the following procedure:

Introduce the hemp chaff or rice husk, the pre-wetting water and the FeCI ₃ or AICI ₃ in the mixer,

- Mix the mixture continuously for ten minutes at a speed of 26 rpm,

Introduce the Portland cement and when present the hydraulic lime, the limestone filler and the anhydrous calcium sulphate in the mixer, then mix for 1 minute at 26 rpm, Introduce the mixing water, the foaming agent when present, and the superplasticizer when present, in the mixer in 20 to 30 seconds and mix for five minutes at 26 rpm,

Stop the mixing, measure the density of the fresh material by weighing the paste in a 0.75-litre bowl using the CONTROLS aerometer (Series 1954),

Pour the rest of the paste into 10 cm x 10 cm x 10cm cubes. Keep the cubes in their moulds at 20 °C and 100 % residual humidity,

After 24 hours, de-mould the cubes and keep them at 20 °C and residual humidity varying from 60 to 100 %.

The material according to the invention is exemplified by the embodiments described below.

Example 1 : Materials according to the invention comprising rice husk

The materials 1 to 5 and the controls 1 and 2 were produced according to Method 1 . The material 5.2 was produced according to Method 2.

The materials 1 to 5.2 and the controls 1 and 2 had the following compositions:

* Binder = Cements + Ca(OH)2 + Limestone filler;

** Total water = water in the vegetal addition + water of the organic additives (foaming agents, plasticizers) + water from stabilizers (solution of FeCk) + pre-wetting water + mixing water;

5 ***D = Density;

****Cs = Compressive strength;

"n.m.= not measured. Example 2: Materials according to the invention comprising hemp chaff

The materials 6 to 10 were produced according to Method 1 . Control 3 and Material 1 1 to 19 were produced according to Method 2.

The materials 6 to 1 1 and control 3 had the following compositions:

* Binder = Cements + Ca(OH)2 + hydraulic lime + Limestone filler;

** Total water = water in the vegetal addition + water of the organic additives (foaming agents, plasticizers) + water from stabilizers (solution of FeCk) + pre-wetting water + mixing water;

***D = Density;

****Cs = Compressive strength;

nn.m.= not measured. The materials 12 to 16 and control 16 had the following compositions:

* Binder = Cements + Ca(OH)2 + Limestone filler + Anhydrous calcium sulphate;

** Total water = water in the vegetal addition + water of the organic additives (foaming agents, plasticizers) + water from stabilizers (solution of FeCk, AICI ₃ if not anhydrous) + pre-wetting water + mixing water;

***D = Density;

****Cs = Compressive strength;

nn.m.= not measured. The materials 17 to 19 had the following compositions:

* Binder = Cements + Anhydrous calcium sulphate;

** Total water = water in the vegetal addition + water of the organic additives (foaming agents, plasticizers) + water from stabilizers (solution of FeCk, AICI ₃ if not anhydrous) + pre-wetting water + mixing water;

***D = Density;

****Cs = Compressive strength.