METHOD FOR MANUFACTURING AN ULTRA-LIGHT MINERAL FOAM

Abstract

The invention relates to a process for manufacturing a mineral foam comprising the following steps: (i) independently preparing a cement grout and an aqueous foam, the cement grout being prepared by mixing water e and cement c, the cement c comprising an amount x of soluble Na2O equivalent, x expressed by mass per 0 parts of cement, said grout having a ratio x / (e / c) less than or equal to 0.75, with e / c expressed by mass, and the particles of cement c having a particle size distribution such that the ratio d max(h / 2) / d min(h / 2) of the particle size distribution is between 5 and 25; (ii) contact the cement grout with the aqueous foam to obtain a foamed cement grout; and (iii) shape the foamed cement grout obtained in step (ii) and allow it to set.<!--endfragment-->

Description

[0001] The present invention relates to a method for producing an ultralight mineral foam. In general, mineral foam, particularly cement foam, is highly advantageous for numerous applications due to its properties such as thermal insulation, acoustic insulation, durability, fire resistance, and ease of application.

[0002] Mineral foam refers to a foam-like material. This material is lighter than traditional concrete due to its pores, or voids. These pores are caused by the presence of air within the mineral foam and can appear as bubbles. Ultralight foam is defined as foam with a dry density typically ranging from 30 to 300 kg / m³.

[0003] When a mineral foam element is cast, it can sag due to a lack of stability in the mineral foam itself, for example, during placement or before it has fully hardened. These foam sagging problems can be caused by coalescence, Ostwald ripening, hydrostatic pressure, or drainage, the latter being particularly pronounced for tall elements.

[0004] The difficulty in producing mineral foams lies in manufacturing a stable foam that overcomes these sagging problems. However, the known techniques for obtaining a sufficiently stable foam rely on mixtures of cementitious compounds containing numerous additives, the production of which is difficult and expensive.

[0005] Thus, the simultaneous use of cationic (I) and anionic (II) compounds for the production of foams has already been proposed in US patent 5,696,174. Such cementitious foams include ammonium stearate as the anionic compound and a cationic compound called Arquad T.

[0006] Application WO 2013 / 150148 describes cement-based foams comprising various additives. These foams may include calcium aluminate to enable rapid setting or fine mineral particles.

[0007] Application WO 2012 / 069024 describes a process for manufacturing a mineral foam by mixing a cement grout comprising a quantity of Na2O with an aqueous foam.

[0008] In order to meet user requirements, it became necessary to find a way to produce an ultralight, highly stable mineral foam that is simple and inexpensive to manufacture.

[0009] The problem that the invention aims to solve is to find a stable ultra-light mineral foam formulation that does not collapse when the foam is poured vertically and whose production is relatively easy and inexpensive.

[0010] The invention relates to a method for manufacturing a mineral foam comprising the following steps: (i) independently prepare a cement grout and an aqueous foam, the cement grout being prepared by mixing water E and cement C, the cement C comprising an amount x of soluble Na2O equivalent, x expressed by mass per 100 parts of cement, said grout having a ratio x / (W / C) less than or equal to 1.75, with W / C expressed by mass, and the particles of cement C have a particle size distribution such that the ratio dmax(h / 2) / dmm(h / 2) of the particle size distribution is from 5 to 25; (ii) bring the cement grout into contact with the aqueous foam to obtain a foamed cement grout; and (iii) shape the foamed cement grout obtained in step (ii) and allow it to set.

[0011] The amount of soluble Na₂O equivalent, or alkali content, of the cement grout is therefore surprisingly an important characteristic in the manufacture of a stable mineral foam. Here, the expression "alkali content" is used to designate the mass proportion of soluble Na₂O equivalent, that is, of soluble sodium and potassium ions ((M Na₂O / M K₂O) * K₂O + Na₂O) = Na₂O eq in the cement used in the implementation of the process according to the invention, with M being the molar mass of the compounds indicated as subscripts. The K₂O and Na₂O content is measured by atomic emission spectrometry, a method called ICP-AES after dissolution, described below.

[0012] This cement C is placed in the presence of a given quantity of water E in the grout, characterized by the mass ratio W / C. The limit value in terms of alkalis to allow the stability of the final mineral foam is characterized by the ratio x / (W / C) which must not exceed 1.75, x being the quantity of soluble Na 2 O equivalent (Na 2 Oeq) by mass for 100 parts of cement.

[0013] Advantageously the mass ratio x / (E / C) is less than or equal to 1.60, preferably less than or equal to 1.50.

[0014] Preferably the mass ratio x / (W / C) is between 0.1 and 1.75.

[0015] To implement the invention and achieve the mass ratio x / (W / C), one of the elements to consider is the alkali content in the cement. Selecting a cement with a low alkali content from the manufacturing stage (for example, a low-alkali CEM I type cement or the use of a blended cement) is a simple way to achieve this ratio and obtain an ultralight foam. However, there are other ways to obtain the target ratio, for example, by diluting the cement with water.

[0016] The cement used in the process according to the invention comprises particles having a particle size distribution such that the ratio d max(h / 2) / d mm(h / 2) of the particle size distribution (according to a volume distribution) is between 5 and 25, preferably, this ratio d max(h / 2) / d mm(h / 2) is between 6 and 14.

[0017] The particle size distribution in a sample is measured by laser diffraction. Such a particle size distribution can be that of a monodisperse population of solid particles. Monodisperse means that the graphical representation of the particle size distribution (volume abundance as a function of size, graded according to a Renard series scale) shows only a single peak (a single population). This definition of "monodisperse charge" preferably excludes a granular stacking of several particle populations of different sizes.

[0018] A set of particles of different sizes can be characterized, in particular, by the ratio between (i) the size of the largest particles at half their height (d max(h / 2) ) and (ii) the size of the smallest particles at half their height (d mm(h / 2) ). For the implementation of the invention, this ratio is on the order of 5 to 25 in the cement used, preferably between 6 and 14.

[0019] The values ​​d max(h / 2) and d min(h / 2) are obtained as follows: The height h is the height of the highest peak measured by laser granulometry according to a volume representation (see for example the Figure 1 Taking a height h / 2 as a reference, d max(h / 2) and d min(h / 2) are defined as respectively the largest particle size and the smallest particle size having a proportion equal to h / 2.

[0020] Preferably, the cement used in the process according to the invention comprises particles having a monodisperse particle size distribution.

[0021] Cement is a hydraulic binder comprising at least 50% by mass of calcium oxide (CaO) and silicon dioxide (SiO2). Cement may therefore include other compounds in addition to CaO and SiO2, and in particular include Portland clinker, slag, silica fume, pozzolans (natural and calcined natural), fly ash (siliceous and calcareous), shale, and / or limestone. Cements that can be used in the process described for producing mineral foams may be selected from those described in standard NF-EN197-1 of April 2012, specifically CEM I, CEM II, CEM III, CEM IV, or CEM V cements.

[0022] The cement used to carry out the invention is preferably chosen from commercially available cements with a sufficiently low alkali content, referred to as "low-alkali cements." Low-alkali Portland cements are preferred. However, if Portland cements, and more specifically the clinker they contain, have too high a proportion of alkalis, such cements can be diluted by adding compounds such as limestone (CaCO3), slag, fly ash, pozzolans, or mixtures thereof. In this case, composite cements of types CEM II to V, containing a significant proportion of components other than clinker, allow the alkalis to be diluted and the desired concentration to be achieved.

[0023] According to a particular embodiment, the cement suitable for use according to the present invention has a Blaine specific surface area of ​​3,500 to 10,000 cm² / g, preferably of 6,000 to 9,000 cm² / g.

[0024] The Portland cement that can be used according to the present invention can be ground and / or separated (by a dynamic separator) to obtain a cement having a Blaine specific surface area greater than or equal to 5,500 cm² / g. This cement can be described as ultrafine. The cement can, for example, be ground using two methods.

[0025] According to one method, cement or clinker can be ground to a Blaine specific surface area of ​​5,500 to 10,000 cm² / g. A high-efficiency, second-generation, or third-generation separator, or a very high-efficiency separator, can be used in this first stage to separate the cement to the desired fineness. The material not having the desired fineness is returned to the mill.

[0026] Examples of mills that can be used in this method include a ball mill, a vertical mill, a roller press, a horizontal mill (e.g., Horomill© type), a vertical agitated mill (e.g., Tower Mill type), an agitated ball mill, or any other type of mill suitable for the fine grinding of mineral particles.

[0027] According to a second method, Portland cement can be passed through a dynamic separator to extract the finest particles, thereby achieving the target fineness (greater than 5,500 cm² / g). The fine material can be used as is. The coarse material is removed, used for other applications, or returned to a different grinding circuit.

[0028] The cement grout used in the process according to the invention may advantageously include a water-reducing agent of the plasticizer or superplasticizer type. A water-reducing agent reduces the amount of mixing water by approximately 10 to 15% by mass for a given working time. Examples of water-reducing agents include lignosulfonates, hydroxycarboxylic acids, carbohydrates, and other specific organic compounds, such as glycerol, polyvinyl alcohol, sodium aluminomethyl siliconate, sulfanilic acid, and casein (see Concrete Admixtures Handbook, Properties Science and Technology, VS Ramachandran, Noyes Publications, 1984). Superplasticizers belong to the new generation of water-reducing agents and reduce the amount of mixing water by approximately 30% by mass for a given working time.Examples of superplasticizers include PCP superplasticizers without antifoaming agents, POE diphosphonates, and POE polyphosphates. The term "PCP," or "polycarboxylate polyoxide," according to the present invention, refers, among other things, to a copolymer of acrylic acids or methacrylic acids and their poly(ethylene oxide) (POE) esters.

[0029] Preferably, the cement grout used to produce the mineral foam according to the invention comprises from 0.05 to 1%, more preferably from 0.05 to 0.5% of a water reducing agent, a plasticizer or a superplasticizer, the percentage expressed as a dry mass relative to the mass of cement grout.

[0030] Preferably, the water-reducing agent of the plasticizer or superplasticizer type does not include an anti-foaming agent.

[0031] Cement grout or aqueous foam may also contain 0.05 to 2.5% of an accelerator, expressed as a dry mass relative to the cement. This accelerator may be derived from one or more salts selected from: calcium salts, potassium salts and sodium salts, in which the anion may be a nitrate, nitrite, chloride, formate, thiocyanate, sulfate, bromide, carbonate or mixtures thereof; and alkali silicates and aluminates, for example sodium silicate, potassium silicate, sodium aluminate, potassium aluminate or mixtures thereof; aluminium salts, for example aluminium sulfate, aluminium nitrate, aluminium chloride, aluminium hydroxide or mixtures thereof.

[0032] According to a particular embodiment, the aqueous foam does not include an accelerator, in particular calcium salts.

[0033] Other additives can be added either to the cement grout or to the aqueous foam. Such additives may, for example, be a thickening agent, a viscosifying agent, an air-entraining agent, a retarder, a clay inert, pigments, colorants, hollow glass beads, film-forming agents, hydrophobic or depolluting agents (such as zeolites or titanium dioxide), latex, organic or mineral fibers, mineral additions or mixtures thereof.

[0034] Preferably, the additives used do not include anti-foaming agents.

[0035] Preferably, the mineral foam as described includes a mineral additive. This mineral additive can be added to the cement grout during the process according to the invention.

[0036] Mineral additions include, for example, slags (e.g., as defined in standard NF EN 197-1 of April 2012, paragraph 5.2.2), pozzolans (e.g., as defined in standard NF EN 197-1 of April 2012, paragraph 5.2.3), fly ash (e.g., as defined in standard NF EN 197-1 of April 2012, paragraph 5.2.4), calcined shale (e.g., as defined in standard NF EN 197-1 of April 2012, paragraph 5.2.5), calcium carbonate-based materials, such as limestone (e.g., as defined in standard NF EN 197-1 of April 2012, paragraph 5.2.6), and silica fume (e.g., as defined in standard NF EN 197-1 of April 2012). 2012, paragraph 5.2.7), metakaolins or their mixtures.

[0037] However, according to a particularly preferred aspect of the invention, only a limited number of components are used. Thus, the mineral foam may consist of either only cement, water and a foaming agent, or only cement, water, a foaming agent and a water-reducing agent of the plasticizer or superplasticizer type, such as a PCP.

[0038] Such a formulation allows for considerable time and cost savings and goes against the technical prejudices that the use of various additives is necessary to ensure the stability of a cement foam.

[0039] Preferably, the mineral foam obtained by the process according to the invention contains substantially no fine particles. The term "fine particle" refers to a population of particles whose median diameter D50 is strictly less than 2 µm. D50, also denoted DV 50, corresponds to the 50th percentile of the volume distribution of particle size, i.e., 50% of the volume consists of particles smaller than D50 and 50% larger than D50.

[0040] By the term "substantially" we mean less than 1%, advantageously less than 5%, expressed by mass relative to the mass of cement.

[0041] According to another aspect of the invention, the mineral foam obtained by the process according to the invention does not contain a mixture of two organic compounds forming respectively an anionic compound and a long-chain cationic compound as described in US patent 5,696,174.

[0042] Cements that are unsuitable or poorly suited for the implementation of the invention are calcium aluminate cements or mixtures thereof. Calcium aluminate cements are cements generally comprising a C4Al3, CA, C12A7, C3A, or C11A7CaF2 mineralogical phase, or mixtures thereof, such as, for example, Ciments Fondu®, sulfoaluminate cements, and calcium aluminate cements conforming to the European standard NF EN 14647 of December 2006. Such cements are characterized by an alumina (Al2O3) content greater than or equal to 35% by mass. Thus, for the implementation of the process according to the invention, the alumina content of the dry mineral compound used to produce the foam is less than 35% by mass of the dry mineral compound. Preferably this content is less than or equal to 30%, advantageously less than or equal to 20%, more advantageously less than or equal to 15%, and even more advantageously less than or equal to 10%, by mass of the dry compound.

[0043] According to a first embodiment, the cement grout can be prepared by introducing the cement, and possibly all other materials in powder form, into a mixer. The cement is mixed to obtain a homogeneous mixture. Then, water is added to the mixer. The additive(s), such as a water-reducing agent, are added with the water if they are present in the mineral foam formulation. The resulting paste is mixed to obtain a cement grout.

[0044] Preferably, the cement grout is kept under agitation, for example with a deflocculating blade, the speed of the blade being able to vary from 1000 revolutions per minute to 400 revolutions per minute depending on the volume of grout during the entire duration of the mineral foam manufacturing process according to the invention.

[0045] According to a second embodiment, the cement grout can be prepared by introducing part of the water into a mixer, then the cement, and then the other compounds.

[0046] According to a third embodiment, the cement grout can be generated continuously.

[0047] To make the cement grout, the W / C ratio of this grout can advantageously be between 0.23 and 2.0, preferably between 0.25 and 0.60, for example equal to 0.29, the ratio being expressed by mass.

[0048] Aqueous foam can be produced by mixing water and a foaming agent, then introducing a gas. Thus, aqueous foam comprises water and a foaming agent. This gas is preferably air. The amount of foaming agent is generally between 0.25% and 5% by mass of dry foaming agent relative to the mass of water, preferably from 0.75% to 2.5%. Air can be introduced by agitation, bubbling, or pressure injection. Preferably, aqueous foam can be produced using a turbulent foamer (such as a glass bead bed). This type of foamer allows pressurized air to be introduced into an aqueous solution containing a foaming agent.

[0049] Preferably, aqueous foam can be generated continuously.

[0050] The aqueous foam generated has an air bubble size with a D50 that is less than or equal to 400 µm, preferably between 100 and 400 µm, more preferably between 150 and 300 µm. The D50, also denoted DV 50, corresponds to the 50th percentile of the volume distribution of particle size, i.e., 50% of the volume consists of particles whose size is less than D50 and 50% of a size greater than D50.

[0051] Preferably the aqueous foam generated has an air bubble size exhibiting a D50 equal to 250 µm.

[0052] The D50 of the bubbles is measured by backscattering. The instrument used is the Turbiscan® Online supplied by Formulation. Backscattering measurements make it possible to estimate the D50 for the bubbles in an aqueous foam, knowing the bubble volume fraction and the refractive index of the foaming agent solution.

[0053] Preferably, the foaming agent is an organic derivative of animal-based proteins (for example, the foaming agent Propump26, hydrolyzed keratin powder, sold by Propump) or plant-based proteins. Foaming agents can also be cationic surfactants (for example, cetyltrimethylammonium CTAB), anionic surfactants, amphoteric surfactants (for example, cocoamidopropyl betaine CAPB), or nonionic surfactants, or mixtures thereof.

[0054] The contacting of the cement grout with the aqueous foam to obtain a foamed cement grout can be done by any means and for example with the help of a static mixer.

[0055] According to a more particular embodiment, the cement grout is pumped at a constant volumetric flow rate depending on the target foamed cement grout composition.

[0056] The cement grout is then brought into contact with the aqueous foam already circulating in the process circuit. The foamed cement grout according to the invention is then generated. This foamed cement grout is shaped and left until it sets.

[0057] Advantageously, the process according to the invention does not require an autoclave step, a curing step, or a heat treatment step, for example at 60-80°C, in order to obtain a cement foam according to the invention.

[0058] Mineral foam can be prefabricated or directly prepared on a construction site by installing a foaming system on site.

[0059] Preferably, the mineral foam obtained by the process according to the invention has a dry density of 35 to 300 kg / m³, more preferably 50 to 150 kg / m³, and even more preferably 50 to 80 kg / m³. It should be noted that the density of the foamed cement grout (wet density) differs from the density of the mineral foam (hardened material density).

[0060] Preferably, the mineral foam obtained by the process according to the invention has a thermal conductivity of 0.030 to 0.150 W / (mK), preferably 0.030 to 0.060 W / (mK), and more preferably 0.030 to 0.040 W / (mK), with a margin of error of ± 0.4 mW / (mK). The mineral foam obtained by the process according to the invention can be used for pouring walls, floors, and roofs during construction. It is also envisaged that prefabricated elements, such as blocks and panels, can be produced in a prefabrication plant using the foam according to the invention.

[0061] Advantageously, the mineral foam obtained by the process according to the invention makes it possible in certain cases to replace glass wool, mineral wool or polystyrene and polyurethane insulation.

[0062] Preferably, the mineral foam obtained by the process according to the invention therefore exhibits very low thermal conductivity. Reducing the thermal conductivity of building materials is highly desirable since it allows for energy savings in heating in residential or commercial buildings. Furthermore, the mineral foam according to the invention provides good insulation performance at thin thicknesses, thus preserving living space and volume. Thermal conductivity (also called lambda (λ)) is a physical quantity characterizing the behavior of materials during heat transfer by conduction. Thermal conductivity represents the amount of heat transferred per unit area per unit time under a temperature gradient. In the International System of Units (SI), thermal conductivity is expressed in watts per meter kelvin (W·m⁻¹·K⁻¹).Conventional or traditional concretes have a thermal conductivity between 1.3 and 2.1 measured at 23°C and 50% relative humidity. The mineral foam according to the invention can be chosen from foams having a thermal conductivity ranging from 0.030 to 0.150 W / (mK), preferably from 0.030 to 0.060 W / (mK) and more preferably from 0.030 to 0.040 W / (mK), the margin of error being ± 0.4 mW / (mK).

[0063] Advantageously, the mineral foam obtained by the process according to the invention can be used to fill or seal a void or hollow space in a building, wall, partition, masonry block (e.g., a concrete block), brick, floor, or ceiling. Such composite materials or building elements comprising the mineral foam according to the invention are also objects of the invention. per se.

[0064] Advantageously, the mineral foam obtained by the process according to the invention can be used as a facade cladding, for example, to insulate a building from the outside. In this case, the mineral foam according to the invention can be coated with a finishing coat.

[0065] The mineral foam obtained by the process according to the invention can be poured vertically between two walls, chosen for example from concrete walls, brick walls, plasterboard, wood panel, for example oriented thin-laminated wood panels, or fiber cement panels, all forming a device.

[0066] The invention will be better understood upon reading the following examples and figures, which are not intended to be limiting, and in which: There Figure 1 is a graphical representation of the particle size distribution present in a typical cement used to carry out the invention.

[0067] The following measurement methods were used: Laser particle size analysis method

[0068] The particle size distribution curves of the different powders are obtained from a Mastersizer 2000 type laser particle size analyzer (year 2008, series MAL 1020429) sold by the company Malvern.

[0069] The measurement is performed in a suitable medium (e.g., aqueous) to disperse the particles; the particle size must be between 1 µm and 2 mm. The light source consists of a red He-Ne laser (632 nm) and a blue diode (466 nm). The optical model is that of Fraunhofer, and the calculation matrix is ​​of the polydisperse type.

[0070] A background noise measurement is first performed with a pump speed of 2000 rpm, an agitator speed of 800 rpm, and a noise measurement taken over 10 seconds, in the absence of ultrasound. It is then verified that the laser light intensity is at least 80%, and that a decreasing exponential curve is obtained for the background noise. If this is not the case, the cell lenses must be cleaned.

[0071] A first measurement is then performed on the sample with the following parameters: pump speed of 2000 rpm, agitator speed of 800 rpm, no ultrasound, and an obscuration limit between 10 and 20%. The sample is introduced to achieve an obscuration slightly greater than 10%. After the obscuration has stabilized, the measurement is taken with a time interval of 10 seconds between immersion and measurement. The measurement time is 30 seconds (30,000 diffraction images analyzed). The resulting particle size distribution must be considered in light of the possibility of agglomeration of some of the powder particles.

[0072] A second measurement is then performed (without draining the tank) using ultrasound. The pump speed is increased to 2500 rpm, the agitator speed to 1000 rpm, and the ultrasound is emitted at 100% (30 watts). This regime is maintained for 3 minutes, then the initial parameters are returned: pump speed of 2000 rpm, agitator speed of 800 rpm, and no ultrasound. After 10 seconds (to allow any air bubbles to escape), a 30-second measurement is taken (30,000 images analyzed). This second measurement corresponds to a powder deagglomerated by ultrasonic dispersion.

[0073] Each measurement is repeated at least twice to verify the stability of the result. The device is calibrated before each working session using a standard sample (Sifraco C10 silica) with a known particle size distribution curve. All measurements presented in the description and the advertised ranges correspond to the values ​​obtained with ultrasound. BLAINE Specific Surface Area Measurement Method

[0074] The specific surface area of ​​the different materials is measured as follows.

[0075] The Blaine method at 20°C with a relative humidity not exceeding 65% using a Blaine Euromatest Sintco apparatus conforming to the European standard EN 196-6; Before measuring the specific surface area, the wet samples are dried in an oven until a constant mass is obtained at a temperature of 50 to 150°C (the dried product is then ground to obtain a powder with a maximum particle size of less than or equal to 80 µm). Method for measuring alkali content:

[0076] The alkali content (%K₂O and %Na₂O) of these cements was measured by atomic emission spectrometry, a method known as ICP-AES (ICP for Inductively Coupled Plasma, AES for Atomic Emission Spectrometry). The measuring instrument was the Varian 720-ES model, serial number EL06093608, from 2006. To perform this measurement, a 2 g sample of cement was dissolved in 100 mL of demineralized water for 15 minutes and then filtered using two superimposed paper filters, for example, one of type MN640W and the other of type MN640DD, into a 200 mL volumetric flask, and then rinsed with demineralized water. 20 mL of hydrochloric acid at a concentration of 1 / 20 (volume / volume) was added. The flask was filled to the mark. 200 mL by adding demineralized water. This solution is then analyzed using the ICP-AES instrument. The soluble Na₂O equivalent content is then calculated based on the following formula: ((M Na2O / M K2O)* K 2 O+Na 2 O) = Na 2 O eq , M being the molar mass of the compounds shown as subscripts. EXAMPLES OF ACHIEVEMENTS

[0077] The process according to the invention has been put into practice to produce cement foams of formulas I, II, V, VII, VIII, IX, X and XI. Comparative examples III, IV and VI have also been carried out in order to highlight the advantageous aspects of the process according to the invention. Materials:

[0078] The cements used are Portland cements from various Lafarge cement plants, identified by their location as specified in Table (I). These cements are standard type cements. The letters "R" and "N" correspond to the definition in standard NF EN 197-1, April 2012 version.

[0079] Micro A anhydrite is anhydrous calcium sulfate from the company Anhydrite Minérale France.

[0080] The superplasticizers used are blends containing a polycarboxylate polyoxide (PCP) from the Chryso company under the names Chrysolab EPB530-017 (Formulas III to X) and Chrysolab EPB530-026 (Formulas I and II). They are based on the products Premia180 (for Chrysolab EPB530-017) and Optima203 (for Chrysolab EPB530-026) and do not contain an antifoaming agent. The dry extract of Chrysolab EPB530-017 is 48% by mass. The dry extract of Chrysolab EPB530-026 is 58% by mass.

[0081] The foaming agents used are derived from animal proteins and are as follows: Propump26 and Propump 40 from the company Propump, whose dry extracts are respectively 26 and 34%, percentage by mass; MAPEAIR L / LA from the company MAPEÏ, whose dry extract is 26%, percentage by mass; Foamcem from the company LASTON, whose dry extract is 28%, percentage by mass; EFA 1500 from the company Edama, whose dry extract is 36%, percentage by mass.

[0082] The water is tap water. Materials used : R Mixers has yneri:

[0083] A Rayneri R 602 EV mixer (2003). The mixer consists of a frame onto which tanks ranging from 10 to 60 liters are mounted. The 10L tank was used with a paddle-type blade adapted to the tank's volume. This blade rotates on its own axis while simultaneously rotating planetarily around the tank's axis. A Rayneri Turbotest mixer (MEXP-101, model Turbotest 33 / 300, serial number: 123861). This is a vertical shaft mixer. Pumps:

[0084] A Seepex™ eccentric screw pump type MD 006-24 commission no. 244920. A Seepex™ eccentric screw pump type MD 006-24 commission no. 278702. Foamer:

[0085] A foamer consisting of a bed of SB30 type glass beads with a diameter between 0.8 and 1.4mm packed together in a tube 100mm long and 12mm in diameter. Static mixer:

[0086] A static mixer composed of 32 Kenics-type helical elements, 19mm in diameter, reference 16La632 from ISOJET

[0087] In the following examples, mineral foams were produced. Each cement grout is referenced by a number from I to XI and each aqueous foam is numbered from 1 to 6. The cement foam (or mineral foam according to the invention) obtained is a combination of one of these cement grouts with one of these aqueous foams. I. Production of mineral foams I.1 Preparation of a cement grout

[0088] The chemical compositions of the various cement grouts used to carry out the invention are presented in Table I. The grouts were prepared using the Rayneri R 602 EV mixer by first introducing the solid components (cement) and then progressively adding water and the admixture. The grout was then mixed for a further two minutes. Table (I): Formulation of cement grouts Formulas I II III IV V VI VII VIII IX type of cement CEM I 52.5 N CEM I 52.5 R CEM I 52.5 R CEM I 52.5 R CEM III / B 42.5 N CEM I 52.5 R CEM I 52.5 R CEM I 52.5 R CEM I 52.5 R Lafarge factory Le Havre Le Teil The Trunk Port La Nouvelle The Trunk Saint Pierre La Cour Saint Pierre La Cour Saint Pierre La Cour Val d'Azergue x (%Na2O eq soluble) 0,22 0,14 0,78 0,54 0,43 0,66 0,66 0,66 0,4 cement (% by mass) 78,80 77,54 77,30 77,44 77,99 76,87 68,87 66,56 66,18 water (% by mass) 21,20 22,46 22,70 22,56 22,01 23,13 31,13 33,44 33,82 Superplasticizer (% by mass) 0,06 0,08 0,18 0,10 0,13 0,13 0,01 0,00 0,00 E / C ratio (by mass) 0,27 0,29 0,29 0,29 0,29 0,28 0,45 0,5 0,51 x / (E / c) 0,759 0,483 2,69 1,862 1,483 2,276 1,467 1,320 0,784 d max(h / 2) / d min(h / 2) 8,4 10,5 13,4 6,5 7,2 6,8 6,8 6,8 10,2 X XI type of cement CEM I 52.5 R (Blaine = 6340 cm2 / g) CEM I 52.5 R (Blaine = 9000 cm2 / g) Lafarge factory Saint Pierre La Cour Saint Pierre La Cour Cement (% by mass) 16,33 16,15 Addition (% by mass) 60,33 59,79 Micro A Anhydrite (mass %) 0,37 0,74 Water (% by mass) 22,85 23,15 SP superplasticizer (% by mass) 0,12 0,18 E / C ratio (by mass) 1,40 1,43 E / L ratio (mass) 0,30 0,30 x (%Na2O eq soluble) 0,61 0,69 x / (E / C) 0,436 0,480 d max(h / 2) / d min(h / 2) 18,2 24,5

[0089] The values ​​of d max(h / 2) and d min(h / 2) are measured as described above, with reference to the Figure 1 .

[0090] The results are usually visualized as a graph, such as the one shown in the... Figure 1 which represents a typical volume granular distribution. The height h is the height of the highest peak measured by laser granulometry ( Figure 1 Taking a height h / 2 as a reference, d max(h / 2) and d min(h / 2) are defined as respectively the largest particle size and the smallest particle size having a passer equal to the quantity h / 2. 1.2 Preparation of the aqueous foam

[0091] An aqueous solution containing the foaming agent was introduced into a buffer tank. The composition of this aqueous foaming agent solution (including the concentration and nature of the foaming agent) is reported in Table II. The foaming agent solution was pumped using the Seepex™ MD 006-24 eccentric screw volumetric pump (commission no. 278702).

[0092] This foaming agent solution was co-introduced through the foamer bead bed with pressurized air (range from 1 to 6 bar) using a T-junction. Aqueous foam was generated continuously at the flow rate indicated in Table II. Table II: Formulation of aqueous foams and flow rate Aqueous foam number 1 2 3 4 5 6 Foaming Agent Propump 26 Propump 40 MapeAIR L / LA Foamcem EFA1500 Propump26 Concentration (% liquid / water) 4,5 3 2,5 3 1,5 3,5 Concentration (% dry / water) 1,17 1,02 0,65 0,84 0,54 0,91 Airflow (L / min) 8 8 8 8 8 8 Solution flow rate (L / min) 0,41 0,418 0,41 0,41 0,418 0,418 1.3 Preparation of a foamed cement grout:

[0093] The previously prepared cement grout was poured into a buffer tank kept under agitation using a Rayneri Turbotest mixer (MEXP-101) equipped with a deflocculating blade (blade speed adjustable from 1000 rpm to 400 rpm depending on the grout volume). The grout was pumped using a Seepex™ MD 006-24 eccentric screw positive displacement pump (commission no.: 244920).

[0094] The pumped grout and the previously generated aqueous foam were brought into contact in the static mixer, respecting the flow rates specified in Table II. The volume of cement grout used was approximately 33 L / m³ and the volume of aqueous foam was approximately 967 L / m³. The foamed cement grout was then generated. 1.4 Obtaining a mineral foam

[0095] The foamed cement grout was poured into 10x10x10 cm polystyrene cubes and into cylindrical columns 2.50 m high and 20 cm in diameter. Three cubes were made for each foamed grout. The cubes were demolded after one day and then stored for seven days at 100% relative humidity and 20°C. The cubes were then dried at 45°C until a constant mass was achieved. One column was made for some of the foamed grouts. The columns were demolded between three and seven days and then cut into 25 cm long sections. The sections were dried at 45°C until a constant mass was achieved. II. Analysis of mineral foam II.1 Stability of mineral foam

[0096] The stability of the foams was measured simply by visual inspection of the cubes produced before demolding. A foam was described as "stable" if the cube maintained a height of 10 cm after setting. A foam was characterized as "unstable" if the cube collapsed during setting. Each test was performed on three 10 x 10 x 10 cm cubes. The results show similar behavior among the three cubes. Where applicable, the results expressed are the average of these three cubes.

[0097] A column was considered stable when the density difference between the bottom section and the top section of the column did not exceed 5 kg / m³. II.2 Thermal conductivity of mineral foams

[0098] Thermal conductivity was measured using a thermal conductivity meter: a CT-meter supplied by Alphis-ERE (5Ω resistance, 50 mm probe wire). The measurement was performed on samples dried at 45°C to a constant mass. The sample was then cut into two equal pieces using a saw. The measuring probe was placed between the two flat faces of these two sample halves (sawn edges). Heat was transferred from the source to the thermocouple through the material surrounding the probe. The temperature rise of the thermocouple was measured over time and used to calculate the thermal conductivity of the sample. II.3 Density of mineral foams

[0099] The wet density of the foamed cement grouts was measured by weighing the cubes at the time of pouring.

[0100] The dry density of the samples was measured on samples dried at 45°C until constant mass, always by weighing the cubes. II.4 Results

[0101] The results are presented in Tables III and IV below. Table (III): Analyses of mineral foams with the foaming agent Propump26 Aqueous foam formula 1 1 1 1 1 1 1 1 1 1 1 Coulis Formula I II III IV V VI VII VIII IX X XI wet density of the foamed grout (g / l) 108 113 112 117 114 112 110 113 112 100 102 dry density (g / l) 72 71 - - 76 - 82 71 69 57 59 stability (cube) Stable Stable Not stable Not stable Stable Not stable Stable Stable Stable Stable Stable Stability (column) Stable Stable Not stable Not stable Not Measured Not stable Stable Not Measured Stable Stable Stable Lambda (w / km - CT-meter measurement) 0,043 0,044 - - Not Measured - Not Measured Not Measured Not Measured 0,041 Not Measured Not stable means that the foam has collapsed. Painting ( IV ) Analysis of mineral foams with different foaming agents Aqueous foam formula 2 2 3 3 4 4 5 5 6 6 Coulis Formula II VI II VI II VI II VI II VI wet density of the foamed grout (g / l) 112 118 105 109 104 112 117 111 106 109 dry density (g / l) 73 69 68 76 69 stability (cube) Stable Not Stable Stable Not stable Stable Not stable Stable Not stable Stable Not stable Stability (column) Stable Not Stable Stable Not stable Stable Not stable Stable Not stable Stable Not stable Lambda (w / km - CT-meter measurement) 0,043 0,042 0,043 Not Measured 0,043 Not stable means that the foam has collapsed. II.5 Conclusions

[0102] These examples illustrate the role of the soluble equivalent alkali content in the stability of cement foam. Thus, when the alkali content is kept low, by using a low-alkali cement, or when the w / (w / c) ratio is less than 1.75, the foam is stable. When the alkali content increases, the foam becomes unstable and collapses. It should be noted that the type of clinker used does not affect foam stability. For example, the clinker in the cement of grout formulas III (comparative) and V (according to the invention) is of the same origin. However, the soluble equivalent alkali content of the cement used in formula V is significantly reduced by the addition of slag. This dilution achieves the desired stability.

Claims

1. A Method for producing a mineral foam comprising the following steps: (i) independently preparing a cement slurry and an aqueous foam, the cement slurry being prepared by mixing water W and cement C, the cement C comprising an amount x of soluble Na2O equivalent, x being expressed in weight per 100 parts of cement, said slurry having a ratio x / (W / C) less than or equal to 1.75, with W / C expressed by weight, and the particles of cement C having a particle size distribution such that the ratio dmax(h / 2) / dmin(h / 2) of the particle size distribution is between 5 and 25; (ii) contacting the cement slurry with the aqueous foam to obtain a slurry of foamed cement; and (iii) forming the slurry of foamed cement obtained at step (ii) and leaving to set.

2. The method according to claim 1, wherein the ratio x / (W / C) is less than or equal to 1.60, preferably less than or equal to 1.50.

3. The method according to claim 1 or 2, wherein the ratio dmax(h / 2) / dmin(h / 2) is from 6 to 14.

4. The method according to any one of the preceding claims, wherein the cement is a cement of type CEM I, CEM II, CEM III, CEM IV or CEM V.

5. The method according to any one of the preceding claims, wherein the cement has a Blaine specific surface area of 3,500 to 10,000 cm2 / g.

6. The method according to any one of the preceding claims, wherein the cement slurry comprises a water reducing agent of plasticizer or superplasticizer type.

7. The method according to any one of the preceding claims, wherein the mineral foam comprises a mineral addition.

8. The method according to any one of the preceding claims, wherein the mineral foam contains substantially no fine particles.

9. The method according to any one of the preceding claims, wherein the W / C weight ratio of the cement slurry ranges from 0.23 to 2.0.

10. The method according to any one of the preceding claims, wherein the aqueous foam comprises water and a foaming agent.