WO2016051085A1 - Insulating concrete block containing plant aggregates - Google Patents

Abstract

The invention relates to an insulating, load-bearing concrete block comprising plant aggregates and mineral aggregates. It also relates to the method for producing such a concrete, by mixing the plant aggregates and the mineral aggregates in determined respective proportions.

Description

 INSULATING CONCRETE BLOCK AND BASED ON VEGETABLE GRANULATES

The invention relates to a method of manufacturing a low thermal conductivity concrete, to this concrete, and to building elements comprising this concrete. The invention also relates to concrete blocks both carrier, lightweight and having good thermal resistance.

 It is known to manufacture blocks using plant aggregates incorporated in a binder matrix based on lime (for example hemp to make blocks such as Chanvribloc ™). However, this type of material requires very long drying times, several weeks in the case of materials based on lime. In addition, plant aggregates tend to delay the setting of hydraulic binders, and in particular to delay the setting of Portland cements. In addition, this type of block, although insulating, is weakly carrying and does not allow the realization of supporting structures. By definition, it is understood that the supporting structure is based on the foundations.

 It is also known to manufacture concrete blocks using mineral aggregates, but devoid of plant aggregates. Generally, this type of block, although carrier is weakly insulating and does not contribute to the insulation of the building, unless using light mineral aggregates. However, the use of light mineral aggregates has several disadvantages, especially the fact that these aggregates require a significant transport from their place of extraction, place sparse and very localized, to the production site (for example pumice comes from Greece). Also the carbon footprint associated with these light mineral aggregates is often unfavorable.

 There is therefore a need for insulating concrete blocks and carriers based on plant aggregates. Indeed, the vegetable aggregate has the advantage of being a local resource, so requiring little transport to the place of transformation.

 Also the problem to be solved by the invention is to propose a new concrete comprising plant aggregates and allowing the realization of concrete blocks both carrier, light and having a high thermal resistance.

 Surprisingly, the inventors have demonstrated that it is possible to use plant aggregates and inorganic aggregates in respective proportions determined to produce a concrete for manufacturing lightweight concrete blocks with good thermal resistance.

For this purpose, the invention provides a method for producing a lightweight, low thermal conductivity carrier concrete comprising aggregates of plant origin and inorganic aggregates. The invention also relates to the concrete obtained from this process. The concrete and / or the process according to the present invention have one or more of the following characteristics:

 advantageously, the concrete according to the invention may be prepared in a prefabrication plant for producing construction elements, in particular concrete blocks;

 advantageously the concrete according to the invention can cure in 24 hours, and at most in 7 days;

 advantageously the concrete according to the invention has a thermal conductivity at 23 ° C and 50% relative humidity less than 0.7 W / (m.K); advantageously the concrete according to the invention is respectful of the environment;

advantageously, the incorporation of the biomass in the concrete according to the invention makes it possible to store C0 ₂ and thus reduce the impact C0 ₂ of the material;

 advantageously the concrete according to the invention uses plant aggregates which are renewable materials,;

 advantageously the concrete according to the invention uses plant aggregates which are waste to date, and generally incinerated;

advantageously the concrete according to the invention uses all types of plants which allows the use of local resources and avoid the transport of materials. The present invention relates to a method for manufacturing a concrete whose density (d) in the dry state is from 800 to 1500 kg / m ^3, comprising the following steps:

 (i) mix

 • 100 to 300 kg of cement;

 • water with a Water / Cement (E / C) mass ratio of 0.3 to 0.9;

• 10 to 80 kg of identical or different plant aggregates (M _gv ), this mass being calculated from the following formula: M _gv = [d - (0.75 X m _gm ) - ( _1.17 XC)] / [1 - (0.75 X k X (m _gm / m _gv ))] where:

_Mgv , d, C and E are respectively the mass in kg of plant aggregates, the target density in kg / m ³ of dry concrete, the mass in kg of cement and the mass in kg of water,

m _gv is the arithmetic mean of the real densities in kg / m ³ of the plant aggregates, weighted by the volume proportions of the plant aggregates, rrigm is the arithmetic mean of the real densities in kg / m ³ of the mineral aggregates, weighted by the volume proportions of the mineral aggregates,

 k is an adjustment coefficient of 0.8 to 4;

· 150 to 1300 kg of identical or different mineral aggregates (M _gm ), this mass being calculated from the following formula: M _gm = 0.75 X m _gm X [1 - (k X (M _g Jm _gv )) ], or :

M _gm is the mass in kg of mineral aggregates;

 0 to 3% by weight relative to the mass of cement of a hardening accelerator;

 • 0.1 to 30% by weight relative to the mass of plant aggregates of an inertant which is a source of soluble trivalent cations in an aqueous medium;

 (ii) vibrate the mixture obtained in step (i), and optionally squeeze this mixture. The process according to the invention may comprise a stage of pretreatment of the plant aggregates by the source of trivalent cations, preferably iron salts or aluminum salts. In this case, the source of trivalent cations is added to the prewetting water of the vegetable additions.

 According to one variant, the method of manufacturing a concrete according to the invention comprises: a step of pre-wetting the plant aggregates with the water containing the source of soluble trivalent cations in an aqueous medium; and

 a mixing step between the pre-wetted plant aggregates and the mineral aggregates, the cement, the water and possibly the hardening accelerator.

 Preferably, in step (i) of the process according to the invention, the coefficient k is between 1 and 3. The coefficient k makes it possible to adjust the value of the real density obtained with the value of the target density. (d), that is, the one targeted by the operator. Those skilled in the art will be able to determine the coefficient k by calibration of the concrete formulation. For example, the coefficient k is a predetermined adjustment coefficient of the degree of compaction of concrete that depends on several parameters, including:

 the apparatus used in step (ii);

 the form factor of plant aggregates; and

 volume ratio of plant aggregates and mineral aggregates.

 The method according to the invention may comprise a preliminary step of determining the coefficient k.

This is a preliminary step where a test batch is made, where the coefficient k is adjusted so that the target density is equal to the value of the mass. real volume obtained with this tempered. A new determination of the coefficient k is necessary as soon as the difference between the target density and the real density obtained varies substantially, for example more than 10%.

 Preferably, in step (ii) of the process according to the invention, the mixture can be vibrated and pressed simultaneously.

 To achieve step (ii), it may be envisaged to use a shock table, a vibrating table or any other industrial tool such as a block press, a layer.

 According to a variant of the process according to the invention, it is possible to add a third cure step of the concrete obtained. For example, the material can be maintained in an atmosphere whose residual humidity varies from 60 to 100% for a few hours to several days.

 According to another embodiment of the method according to the present invention, it is possible to add each of the constituents mentioned in step (i) separately.

Preferably, step (i) of the process according to the invention is calculated for 1 m ³ of concrete.

 The invention also relates to a concrete that can be obtained according to the method described above.

Preferably the concrete according to the invention has a density (d) in the dry state of from 950 to 1400 kg / m ³ , more preferably from 900 to 1300 kg / m ³ , still more preferably from 850 to 1200 kg / m ³ .

 The concrete and the process according to the invention can be implemented from hydraulic binder, vegetable aggregates, inorganic aggregates, a source of trivalent cations soluble in aqueous medium, water, optionally an accelerator. curing.

 A hydraulic binder is a material that picks up and hardens by hydration. Preferably, the hydraulic binder is or comprises a Portiand cement.

 The cement suitable for the concrete according to the invention or the mixture of step (i) of the process according to the invention is preferably the cement described in accordance with European Standard NF EN 197-1 of February 2001. The cement suitable for concrete according to the invention may be of the CEM I, CEM II, CEM III, CEM IV or CEM V type.

 Preferably, the cement suitable for concrete according to the invention or the mixture of step (i) of the process according to the invention is CEM I or CEM III type cement and mixtures thereof.

The preferred cement suitable for the concrete according to the invention or the mixture of step (i) of the process according to the invention is Portiand cement CEM I or III, alone or mixed with other cements for example those described in accordance with European Standard NF EN 197-1 of February 2001.

 It should be noted that the cement suitable for the concrete according to the invention or the mixture of step (i) of the process according to the invention can be a reconstituted cement, that is to say a mixture of cement CEM I or CEM II with mineral additions such as those described in the European standard NF EN 197-1 of February 2001.

 Preferably the mixture of step (i) of the process according to the invention or the concrete according to the invention comprises from 150 to 250 kg of cement, more preferably from 180 to 225 kg.

 Preferably, the mixture of step (i) of the process according to the invention or the concrete according to the invention comprises water with a Water / Cement (E / C) mass ratio of between 0.4 and 0.8. more preferably between 0.55 and 0.65.

 The term "water" should be understood as the effective water required for the hydration of a hydraulic binder and the implementation of a hydraulic composition in the fresh state. This effective water is to be distinguished from the total water present in the mixture (at the time of mixing), which generally comprises the effective water and the water absorbed by the aggregates and the vegetable additions (pre-wetting water).

 The mixture of step (i) of the process according to the invention or the concrete according to the invention uses plant aggregates, which are identical or different. Advantageously, the plant aggregates make it possible to lighten the concrete, compared to a concrete without plant aggregates having comparable mechanical performances.

 Vegetable aggregates are materials of plant origin or crushed vegetable waste.

 It can be natural materials or aggregates porous natural and rich in organic matter (cellulose, hemicelluloses, lignins ...). from plants via industrial manufacturing processes (shredding, crushing, grinding, separation). All types of plants may be suitable as a source of plant aggregates.

 Vegetable aggregates include, for example, chenevotte (hemp), corn cob, sorghum, flax shives, miscanthus (elephant grass), rice husks (rice husk), bagasse of cane, cereal straw, rapeseed straw, sunflower straw, maize straw, kenaf, coconut, olive kernel, bamboo, wood pellets (eg shredded spruce) ), wood chips and their mixtures.

Preferably, the mixture of step (i) of the process according to the invention or the concrete according to the invention uses plant aggregates chosen from the granules of hemp (hemp), corn cob, sorghum flax, miscanthus (elephant grass), rice husks, cane bagasse, cereal straw, rape straw, sunflower straw, corn straw, kenaf, coconut, olive kernels, bamboo, wood pellets (eg shredded spruce), wood chips and mixtures thereof.

 Preferably, the plant aggregates may be chenevotte or wood chips.

 Preferably, the vegetable aggregates may be the rice husk. The rice husk comes from husking rice, which is generally used in human nutrition. The rice husk is made up of all the bracts or lemmas that enclose the grain and protect it during its growth.

 The shelling is generally carried out by a mechanical fractionation process, after threshing, using a machine generally equipped with two horizontal disks coated with an abrasive material for separating the grain from the bracts and lemmas. It is also possible to use rubber roll mills, rotating at varying speeds, thus reducing the risk of breaking the grain of rice.

The proportion of rice husks resulting from shelling of rice varies between 17 and 23% (percentage by weight) depending on the variety. The product obtained is of a brown-beige color, of hard consistency. Its bulk density generally ranges from 1 to 140 kg / m ³ . The rice husk is practically rot-proof and unassailable by insects. The cellulose content represents from 35 to 45% of the mass. The content of amorphous silica represents from 13 to 19% of the mass. Ashes, composed almost entirely of silicon oxide (silica), represent about 15 to 20% of the mass.

 The plant aggregates suitable for concrete according to the invention can be treated so as to reduce their water absorption capacities and their release capacities of water-soluble organic substances (products potentially retarding the setting of the hydraulic binder) in water or in the cementitious medium, by different techniques:

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

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

 For example, the plant aggregates may be charcoal derived from the pyrolysis of biomass.

For example, the treated plant aggregates may have been subjected to mixing or spraying with a compound which confers on them a particular property, especially the hydrophobic properties. For example, a water-repellent treatment with hydrocarbons, silicones, latices, vegetable oils, fatty alcohols, fatty acids or mixtures thereof. The water-repellent treatment may be an attachment of (C2-C30) alkyl groups to the OH group of the biomass by esterification and / or etherification.

 According to one variant, the mixture of stage (i) of the process according to the invention or the concrete according to the invention comprises at least treated plant aggregates. According to another variant, all the plant aggregates used according to the present invention are treated.

 Preferably the mixture of step (i) of the process according to the invention or the concrete according to the invention comprises from 20 to 65 kg of plant aggregates, more preferably from 25 to 55 kg.

The mixture of step (i) of the process according to the invention or the concrete according to the invention uses mineral aggregates. Mineral aggregates are generally standard mineral materials whose density is greater than or equal to 2000 kg / m ³ , or light whose density is less than 2000 kg / m ³ . Mineral aggregates are usually natural mineral materials, but can also be recycled materials.

 The inorganic aggregates that are suitable according to the invention can be those described in European Standard NF EN 12620 of August 2003.

 Mineral aggregates suitable according to the invention may include sand (whose particles generally have a maximum size (Dmax) less than or equal to 4 mm), and chippings (whose particles generally have a minimum size (d min) greater than 4 mm and preferably a size Dmax less than or equal to 20 mm). Each granulate is characterized by two digits: the first corresponds to the "d" as defined in the standard XPP 18-545 of February 2004 and the second corresponds to the "D" as defined in the standard XPP 18-545 of February 2004.

 Mineral aggregates may include calcareous, siliceous and silico-calcareous materials. They include natural, artificial materials, waste and recycled materials.

 The light inorganic aggregates that are suitable according to the invention can be those described in European Standard NF EN 13055-1 of December 2002.

Light mineral aggregates include natural or artificial aggregates. Natural lightweight aggregates of mineral origin have generally not undergone any transformation other than mechanical and are generally derived from volcanic rocks. These natural aggregates are for example pozzolans (pumice), silicates (vermiculite or perlite). Light artificial aggregates of mineral origin result from an industrial process including thermal or other modifications. These artificial aggregates are, for example, clays (expanded clays), schists (expanded shales, expanded slates) or silicates (expanded vermiculite or expanded perlite) or expanded glass granulates.

 The calcined shales used according to the present invention may be a material produced in a special oven at a temperature of about 800 ° C mainly comprising dicalcium silicate and monocalcium aluminate. (see European Standard NF EN 197-1 of February 2001 section 5.2.5)

 The clays used according to the present invention may be phyllosilicates. The clays according to the invention may be chosen from kaolinite, smectites (generic term used to designate swelling clays, including montmorillonite), illite, muscovite, chlorites, or mixtures thereof.

 The calcined clays used according to the present invention may be clays which have undergone a heat treatment.

 Preferably the mixture of step (i) of the process according to the invention or the concrete according to the invention comprises from 250 to 1200 kg of mineral granules, more preferably from 400 to 1100 kg.

 The mixture of step (i) of the process according to the invention or the concrete according to the invention may optionally comprise a curing accelerator of the hydraulic binder, in particular from 0.01 to 2.5%, this percentage being expressed by mass. compared to the mass of cement.

 The accelerator for curing the cement that is suitable according to the invention may be chosen from anhydrous calcium sulphate, calcium sulphate hemihydrate, calcium hydroxide, calcium chloride, calcium nitrite and calcium nitrate. and their mixtures.

 The mixture of step (i) of the process according to the invention or the concrete according to the invention uses an inert which is a source of trivalent cations soluble in aqueous medium.

 The mixture of step (i) of the process according to the invention or the concrete according to the invention comprises from 0.1 to 30% by weight relative to the mass of plant aggregates of a source of trivalent cations soluble in medium aqueous, preferably from 0.2 to 25%, and even more preferably from 0.5 to 20% by weight relative to the mass of plant granules, from the source of soluble trivalent cations in an aqueous medium.

The source of soluble trivalent cations in an aqueous medium can be chosen from one or more soluble salts. The source of soluble trivalent cations in an aqueous medium may be selected from iron salts, aluminum salts and 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 (III) nitrite, iron (III) nitrate, iron (III) chloride, iron (III) sulphate, iron (II) nitrite, iron (II) nitrate, iron (II) chloride, iron (II) sulphate or mixtures thereof.

 When the source of water-soluble trivalent cations is an aqueous soluble aluminum salt, it may be aluminum nitrite, aluminum nitrate, aluminum hydroxide, sodium sulfate, and the like. aluminum, aluminum chloride or their mixtures.

 These salts can in particular be used in the preliminary treatment of plant aggregates.

 Advantageously, the mixture of step (i) of the process according to the invention or the concrete according to the invention does not comprise foaming agent.

 Advantageously, the mixture of step (i) of the process according to the invention or the concrete according to the invention does not comprise any mineral additions, other than those already present in compound cements, for example of the CEM III type, or other than those that can be used to make a recomposed cement from a CEM I or CEM II.

 The mixture of step (i) of the process according to the invention or the concrete according to the invention may comprise a water-reducing agent, a plasticizer or a superplasticizer, the weight ratio of water-reducing agent / binder being comprised of 0.001 to 0.02.

 The mixture of step (i) of the process according to the invention or the concrete according to the invention may for example comprise one of the adjuvants described in the European standards NF EN 934-2 of September 2002, NF EN 934-3 of November 2009 or NF EN 934-4 of August 2009. Advantageously, the mixture of step (i) of the process according to the invention or the concrete according to the invention can comprise at least one adjuvant for hydraulic composition: a carrier agent of air, a viscosity agent, a plasticizer and / or a superplasticizer.

 According to one variant, the mixture of step (i) of the process according to the invention or the concrete according to the invention may comprise at least one superplasticizer.

The term "superplasticizer" as used in the present specification and accompanying claims is to be understood to include both water reducers and superplasticizers as described in the book entitled "Concrete Admixtures Handbook, Properties Science". and Technology, "VS Ramachandran, Noyes Publications, 1984. A water reducer is defined as an adjuvant which typically reduces the amount of mixing water of a concrete by 10 to 15% for a given workability. Water reducers include, for example, lignosulfonates, hydroxycarboxylic acids, carbohydrates and other specialized organic compounds, for example glycerol, polyvinyl alcohol, sodium alumino-methyl-siliconate, sulfanilic acid and casein.

 Superplasticizers belong to a new class of water reducers, chemically different from normal water reducers and able to reduce water amounts by about 30%. Superplasticizers were broadly classified into four groups: sulfonated condensates of naphthalene formaldehyde (SNF) (usually a sodium salt); sulphonated condensates of melamine formaldehyde (SMF); modified lignosulfonates (MLS); And the 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 a polyethylene glycol as grafted chain and carboxylic functions in the main chain as a polycarboxylic ether (PCP). It may be a deferred PCP. Sodium polycarboxylate polysulfonates and sodium polyacrylates can also be used. Phosphonic acid derivatives can also be used. The required amount of superplasticizer usually depends on the reactivity of the cement. The lower the reactivity, the lower the required amount of superplasticizer.

 The concrete according to the invention may be a precast concrete on site, or a concrete manufactured in a factory for the production of prefabricated elements.

 The concretes according to the invention combine a sufficiently high compressive strength with a reduced thermal conductivity compared with those concretes usually available in the field. The compressive strength is generally 1 to 15 MPa at 7 days. In addition, these formulations are simple and easy to put into practice. Finally the constituents used are relatively low cost and readily available. This makes these formulations particularly useful in the industry.

 Preferably, the concrete according to the invention has a thermal conductivity of less than 0.7 W / (mK), preferentially less than 0.6 W / (mK), and even more preferably less than 0.5 W / (mK). .

Thermal conductivity (also called lambda (λ)) is a physical quantity that characterizes the behavior of materials during conductive heat transfer. Thermal conductivity is the amount of heat transferred per unit area and a unit of time under a temperature gradient. In the international system of units, the thermal conductivity is expressed in watts per meter Kelvin, (W / (mK)). Ordinary concretes have a thermal conductivity generally between 1, 3 and 2.1.

 Thermal conductivity according to the invention is termed the thermal conductivity, determined dry according to the hot wire method, after complete drying of the sample.

 The invention also relates to the use of a concrete according to the invention as a construction material.

 The concrete according to the present invention can be shaped to produce, after hydration and hardening, a shaped object for the field of construction. The invention also relates to such a shaped object which comprises the concrete as described above. Objects shaped for the field of construction include, for example, a floor, a screed, a wall, a partition, a ceiling, a pillar, a block, a planelle, a facade panel, a cornice, a mold , an insulating element (acoustic and / or thermal). Objects shaped for the field of construction may optionally be integrated with other objects to make a system, for example a masonry wall.

 The invention also relates to the use of a concrete according to the invention to manufacture blocks or panels.

 The invention also relates to a block comprising the concrete according to the invention.

 By block is meant in the sense of the present invention, masonry blocks, blocks to stick, planelles, bushels, lintels, blocks to bancher, chaining blocks.

 The block according to the present invention has one or more of the following characteristics:

 advantageously the block according to the invention can be carrier, that is to say generally having a compressive strength of at least 2.5 MPa according to the French standard NF EN 771 -3 CN of March 2012;

 advantageously the block according to the invention can be filled with an insulator so as to improve its thermal resistance, in this case the good thermal performance of the block can significantly reduce the thickness of insulation required and therefore the thickness of the finished wall ;

 advantageously the block according to the invention can be light.

In the present description, including the accompanying claims, the percentages are by weight unless otherwise specified.

The following examples are non-limiting and illustrate the invention. Examples of embodiments of the invention

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 European Standard NF EN 12390-7 of September 2001

Determination of the compressive strength:

 The compressive strength measurements were carried out on three cubes of 10cm according to the European standard NF EN 12390-3 of February 2003. The mechanical strength of the concrete cubes was measured at the expiry of 7 days with the aid of a mechanical press. The ramp rate is 2kN / s.

Determination of thermal conductivity:

 The thermal conductivity is determined in the dry state according to the hot wire method, after complete drying of the sample at 105 ° C., using a CT-meter apparatus supplied by Alphis-Ere.

List of raw materials:

The cements used are CEM I 52, 5R cements with a density of 3150 kg / m ³ (Lafarge du Teil plant) and CEM III 52, 5L with a density of 2990 kg / m ³ (Lafarge du Havre plant).

Vegetable aggregates are granules of Chenevotte supplied by the company Chanvrière de l'Aube; the water content of Chènevotte was 13% (percentage by mass), and its bulk density was 1 10 kg / m ³ .

 The mineral aggregates are limestone aggregates and pumice aggregates.

The limestone aggregates are a combination of three particle sizes (0-1, 6 mm, 1, 6-3 mm, 3-6 mm) and come from Lafarge de Cassis quarry. The pumice aggregates have a particle size of 0-6mm and come from the Lafarge quarry of the island of Lava in Greece.

The inertant is iron chloride FeCl ₃ provided by Sigma-Aldrich in 45% aqueous solution.

The curing accelerator is calcium chloride CaCl ₂ is supplied by Sigma-Aldrich.

 Water is the water of the network.

Process for manufacturing the concrete according to the invention Various tempered tests were carried out according to the following protocol:

 Mix for 10 min in a concrete mixer the plant aggregates and a solution containing water and the inertant.

 - Mix in a 10-liter Rayneri mixer the concrete according to the following procedure:

 1. Moisten the bowl with a sponge,

 2. Introduce the mineral and vegetable aggregates into the bowl and a quantity of pre-wetting water corresponding to 4% of the mass of mineral aggregates,

 3. Mix for one minute, then let stand for 4 minutes,

4. Introduce the cement into the mixer and knead for 1 minute,

5. Introduce in 30 seconds a solution comprising the addition of water and the previously dissolved hardening accelerator and knead for 2 minutes.

The mass required to obtain one liter of wet concrete after compaction was weighed. This quantity of concrete was then poured into a cubic metal mold of 10cm side provided with a riser and a counter mold of a mass of 14 kg. The mold was fixed on a vibrating table and vibrated at 50 Hz with an amplitude of 2 mm. The whole was vibrated until the against-mold comes into contact with the mold. The 1-liter cube thus obtained is demolded and then moisturized for 24 hours, then stored in a regulated room at 20 ° C / 100% RH. Following this protocol, different spoils were made and are described below in the table. For the examples below, the pre-wetting water of the plant aggregates is adjusted to reach a water content of 100%. The dosage inerting (FeCl ₃ ) is set at 0.3 mol / kg of dry plant aggregates and the hardening accelerator dosage (CaCl ₂ ) is set at 1% by mass of cement. The references Ex.1 to Ex.5 correspond to formulas according to the invention. References Ref 1 and Ref 2 correspond to control formulas without plant aggregates.

Ex. 1 Ex. 2 Ex. 3 Ex. 4 Ex. 5 Ref. 1 Ref. 2 coefficient k 1.75 1.75 2.25 2.25 2

 E / C ratio 0.5 0.64 0.5 0.5 0.5

average _gm [kg / m ³ ] 1200 1538 2670 2670 2670

average m _gv [kg / m ³ ] 200 200 200 200 200 Ex. 1 Ex. 2 Ex. 3 Ex. 4 Ex. 5 Ref. 1 Ref. 2

 Density 950 1050 1200 1200 1500

 dry target d [kg / m3]

 CEM cement I 52.5 200 220 180 200 120 170

[kg / m ³ ]

 CEM III cement 52.5 L 180

[kg / m ³ ]

 Vegetable aggregate 27 46 47 47 39

[kg / m ³ ]

Cassis 0-1,6 [kg / m ³ ] 205,636 870 700 715

Cassis 1.6-3 [kg / m ³ ] 20.5 64 87 70 71

Cassis 3-6 [kg / m ³ ] 256 445 1000

 Pierre Ponce 0-6 685 522 906

[kg / m ³ ]

Total water [kg / m ³ ] 231 387 145 145 150 63 225

Accelerator of 2 2,2 1,8 1,8 2

hardening [kg / m ³ ]

Inerting [kg / m ³ ] 3 5 5 5 4.2

Density 966 1100 1220 1240 1490 1940 1103 actual dry [kg / m ³ ]

 Resistance to 5.54 5.93 2.9 2.51 7.2 8.84 7.25 compression [MPa]

 Conductivity 0.271 0.336 0.41 0.45 0.65 1.38 0.33 Thermal [W / (m.K)]

The examples, Ex.1 to Ex.5, show that it is possible to obtain a good compromise between mechanical strength and thermal conductivity.

In particular, the concrete according to the formula Ex.2 in comparison with the control Ref. 2 shows that it is possible to substitute 40% of mineral granules of pumice with vegetable aggregates and standard mineral aggregates, while maintaining comparable mechanical and thermal performance.

 In particular, the concrete according to the formula Ex.1 in comparison with the control Ref. 2 shows that it is possible to substitute 25% of mineral aggregate of pumice stone with plant aggregates, while maintaining comparable mechanical performance and reducing the thermal conductivity of 33%.

 In particular, the concrete according to the formula Ex.5 in comparison with the control Ref. 1 shows that it is possible to reduce the density of concrete by 25% while maintaining comparable mechanical performance and reducing the thermal conductivity by 50%.

Claims

A method of manufacturing a concrete whose density (d) in the dry state is from 800 to 1500 kg / m ^3, comprising the following steps:  (i) mix  100 to 300 kg of cement; water with a Water / Cement (E / C) mass ratio of 0.3 to 0.9; 10 to 80 kg of identical or different plant aggregates (M _gv ), this mass being calculated from the following formula: M _gv = [d - (0.75 X m _gm ) - ( _1.17 XC)] / [ 1 - (0.75 X k X (m _gm / m _gv ))] where: _Mgv , d, C and E are respectively the mass in kg of plant aggregates, the target density in kg / m ³ of dry concrete, the mass in kg of cement and the mass in kg of water, m _gv is the arithmetic mean of the real densities in kg / m ³ of the plant aggregates, weighted by the volume proportions of the plant aggregates, m _gm is the arithmetic mean of the real densities in kg / m ³ of the mineral aggregates, weighted by the volume proportions of the mineral aggregates,  k is an adjustment coefficient of 0.8 to 4; 150 to 1300 kg of identical or different mineral aggregates (M _gm ), this mass being calculated from the following formula: M _gm = 0.75 X m _gm X [1 - (k X (M _g Jm _gv ))], where: M _gm is the mass in kg of mineral aggregates;  0 to 3% by weight relative to the mass of cement of a hardening accelerator;  0.1 to 30% by weight relative to the mass of plant aggregates of an inert which is a source of trivalent cations soluble in aqueous medium;  (ii) vibrate the mixture obtained in step (i), and optionally squeeze this mixture. The process of claim 1 comprising:  a step of pre-wetting the plant aggregates with the water containing the source of soluble trivalent cations in an aqueous medium; and a mixing step between the pre-wetted plant aggregates and the mineral aggregates, the cement, the water and possibly the hardening accelerator. 3. The method of claim 1 or 2 wherein in step (ii) the mixture is vibrated and pressed simultaneously. 4. Method according to any one of the preceding claims wherein in step (i) the coefficient k is from 1 to 3. 5. Concrete obtainable according to the method of claims 1 to 4. 6. Concrete according to claim 5, wherein the cement is CEM I or CEM III type cement and mixtures thereof. 7. Concrete according to any one of claims 5 or 6 wherein the plant aggregates are selected from the aggregates of hemp (hemp), corn cob, sorghum, shives, miscanthus (elephant grass) , rice balls (rice husk), cane bagasse, cereal straw, rape straw, sunflower straw, corn straw, kenaf, coconut, olive kernels, bamboo, wood pellets, wood chips and mixtures thereof. 8. Concrete according to any one of claims 5 to 7 wherein a curing accelerator is selected from anhydrous calcium sulfate, calcium sulfate hemihydrate, calcium hydroxide, calcium chloride, nitrite de calcium, calcium nitrate and their mixtures. 9. Concrete according to any one of claims 5 to 8 wherein the source of soluble trivalent cations in an aqueous medium is selected from iron salts, aluminum salts and mixtures thereof. 10. Use of a concrete according to any one of claims 5 to 9 as a construction material. 1 1. Use of a concrete as claimed in any of claims 5 to 9 for making blocks or panels. Block comprising the concrete according to any one of claims 5 to 9.