Process for preparing a hydraulic binder comprising magnesium and its use

Abstract

The present invention relates to a process for preparing a hydraulic binder comprising the following steps: a) Supplying at least one first mineral compound comprising: at least 10% by weight of magnesium oxide (MgO), and a proportion of hydrated phase(s) greater than or equal to 1% by weight, the percentages being expressed relative to the total weight of said first mineral compound; b) mechanical and / or thermal activation of said first mineral compound. Figure for the abstract: no figure

Description

Title of the invention: Process for preparing a hydraulic binder comprising magnesium and its use. TECHNICAL FIELD OF THE INVENTION

[0001] The present invention relates to a process for preparing a hydraulic binder, the hydraulic binder thus obtained and its various uses. Description of the invention

[0002] Portland cement, the main component used as a binder in the production of concrete, is the most widely used manufactured product in the world (4.3 billion tonnes / year). Its production accounts for approximately 8% of global CO2 emissions. As its production continues to grow, it is likely that its CO2 impact will represent at least 15% of CO2 emissions by 2050.

[0003] Decarbonizing the cement industry is one of the most difficult to achieve. This is primarily due to the fact that CO2 emissions in this case are largely linked to the intrinsic chemical process of manufacturing the product. Indeed, clinker, the main constituent of Portland cement, is manufactured by calcining at 1450 °C a mixture composed of approximately 80% limestone (essentially calcium carbonate: CaCO3) and 20% clay. Thus, a large part of the CO2 emissions is linked to the decomposition of limestone at around 900 °C (CaCO3 → CaO (lime) + CO2).

[0004] There are currently several research / development avenues aimed at reducing the CO2 impact of cement and moving towards carbon neutrality in this industry.

[0005] The main approach favored to date by the cement industry to achieve carbon neutrality in this sector remains the capture of CO2 emitted during clinker production, its transport, and its storage in geological formations. However, this approach involves considerable investment costs and technological uncertainties and will likely not be implemented on a large scale for several decades.

[0006] Other alternatives are proposed, which essentially consist of replacing a portion of the Portland clinker with substitute materials and / or minimizing the use of Portland clinker in the formulation of construction materials. However, in both cases, Portland clinker remains an essential component in the composition of these so-called low-carbon cements.

[0007] Thus, there is an urgent need to provide an economically viable and short-term alternative to Portland clinker that would enable carbon neutrality to be achieved in this industry.

[0008] In this context, the inventors worked on an alternative production of a hydraulic binder that avoids the use of limestone and thus provides a process that reduces CO2 emissions, while obtaining a hydraulic binder with mechanical properties equivalent to those obtained with conventional processes.

[0009] The present invention relates first to a process for preparing a hydraulic binder comprising the following steps:

[0010] a) Supply of at least a first mineral compound comprising: - at least 10% by weight of magnesium oxide (MgO), and - a proportion of hydrated phase(s) greater than or equal to 1% by weight,

[0011] the percentages being expressed in relation to the total weight of said first mineral compound,

[0012] b) mechanical and / or thermal activation of said first mineral compound.

[0013] By "mineral compound" is meant a solid inorganic substance that is in crystalline or amorphous form

[0014] Advantageously, said first mineral compound comprises between 10 and 99% by weight of MgO, preferably between 20 and 60% by weight, more preferably between 30 and 50% by weight of MgO relative to the total weight of said mineral compound.

[0015] It should be noted that in the context of this application, and unless otherwise stipulated, the ranges of values ​​indicated are understood to include the limits.

[0016] By "proportion of hydrated phase" is meant the percentage by weight of mineral phases comprising hydroxyl groups (-OH), on the total weight of the mineral compound.

[0017] Advantageously, said first mineral compound comprises between 1 and 100% by weight of hydrated phases, preferably between 5 and 80% by weight of hydrated phases, more preferably between 10 and 40% by weight of hydrated phases, relative to the total weight of said mineral compound.

[0018] Advantageously, said first mineral compound comprises at least 10% by weight of silicon dioxide (SiO2), preferably between 10 and 70% by weight, more preferably between 20 and 60% by weight, even more preferably between 30 and 50% by weight, relative to the total weight of said mineral compound.

[0019] Advantageously, said first mineral compound comprises or is made up of at least one igneous rock.

[0020] By "magmatic rock", also called igneous rock, we mean a rock formed by the solidification and cooling of magma or lava. It can form either within the Earth's crust where magma cools slowly (plutonic or intrusive rocks), or at the surface, following volcanic eruptions (volcanic or extrusive rocks).

[0021] Among igneous rocks, mafic and ultramafic rocks are found. These rocks are rich in ferromagnesian minerals.

[0022] By "ultramafic rock" also called ultrabasic, we mean a magmatic rock comprising at least 90% by weight of mafic minerals relative to the weight of the rock.

[0023] By "mafic rock" is meant an igneous rock comprising less than 90% by weight of mafic minerals, preferably between 60 and 90% by weight of mafic minerals, relative to the weight of the rock.

[0024] The term "mafic" is used to describe a mineral or silicate rock rich in magnesium, preferably comprising at least 10% by weight of magnesium oxide, preferably between 10 and 60%, preferably between 30 and 50% by weight of magnesium oxide, relative to the weight of the mineral. In addition to magnesium, ultramafic or mafic rocks may also contain metals such as iron, nickel, chromium, manganese, and / or calcium.

[0025] Advantageously, said first mineral compound comprises or is made up of at least one mafic rock or ultramafic rock.

[0026] Mafic and ultramafic rocks constitute more than 50% of the Earth's mantle. Under the influence of subduction / obduction movements of tectonic plates, these rocks rise to the surface and may become partially hydrated under high pressure / temperature in contact with seawater. These hydrated rocks are well distributed across the globe, particularly along ocean coastlines. Consequently, these rocks have the advantage of being an easily accessible raw material. This wide availability and accessibility facilitate the large-scale and economically viable industrialization of the hydraulic binder according to the invention.

[0027] Advantageously, said first mineral compound comprises or is made up of magnesium silicate.

[0028] Advantageously, the first mineral compound does not comprise sedimentary rock. "Sedimentary rock" is understood to mean a rock formed by the accumulation of sediments derived from the weathering of other rocks, organic matter, or chemical precipitation. Limestone is an example of sedimentary rock.

[0029] Advantageously, sedimentary rocks such as limestone are excluded from the process according to the invention.

[0030] Advantageously, said first mineral compound is not obtained by an electrolytic process or by a solution chemistry process.

[0031] Advantageously, said first mineral compound has an MgO / SiO2 ratio between 0.1 and 2, preferably between 0.5 and 1.5, even more preferably between 0.8 and 1.3.

[0032] Advantageously, said first mineral compound comprises at least 25% by weight of MgO and at least 30% by weight of SiO2, preferably at least 35% by weight of MgO and at least 35% by weight of SiO2, more preferably at least 40% by weight of MgO and at least 40% by weight of SiO2, relative to the total weight of said mineral compound.

[0033] Advantageously, said first mineral compound comprises one or more minerals selected from the group consisting of: olivine ((Mg,Fe)2SiO4), amphibole ((Ca,Na)2-3(Mg, Fe,Al)5(Si,Al)8O22(OH)2), serpentine ((Mg,Fe)3Si2O5(OH)4), talc (Mg3Si4Oio(OH)2), chlorite ((Mg,Fe,Al)6(Si,Al)4Oio(OH)s), brucite (Mg(OH)2), dunite (Mg2SiO4), biotite (K(Mg,Fe)sAlSi3Oio(F,OH)2), antigorite (Mg3Si2Os(OH)4), lizardite (Mg3Si2Os(OH)4), clinochlore ((Mg,Fe)5Al(Si3Al)Oio(OH)s), phlogopite (KMg3(AISi3Ow)(OH)2), vermiculite (Mg,Fe,AI)3(AI,Si)4Oio(OH)2'4H2O), saponite (Cao.3(Mg,Fe)3(Si,AI)4Oio(OH)2-4H2O), peridotite, ophiolite and pyrophyllite (AI2Si4Oio(OH)2 substituted by Mg).

[0034] Preferably, said first mineral compound is chosen from the group consisting of olivine, serpentine and talc.

[0035] Advantageously, said first mineral compound is characterized by an X-ray diffraction (XRD) diagram comprising at least one peak position less than 15°, preferably between 4° and 15°, more preferably between 6° and 13°, measured using CuKa radiation at a Bragg angle of 20.

[0036] Advantageously, said first mineral compound is characterized by the presence of at least one endothermic peak at a temperature between 250°C and 1400°C, preferably between 400°C and 1100°C, preferably between 500°C and 950°C measured by DSC-ATG.

[0037] According to one embodiment of the invention, the process comprises supplying a second mineral compound distinct from the first mineral compound, said second mineral compound comprising at least 10% by weight of SiO2, preferably between 10 and 70% by weight, more preferably between 20 and 60% by weight, even more preferably between 30 and 50% by weight, relative to the total weight of said second mineral compound.

[0038] According to this embodiment, said second mineral is chosen from the group consisting of silica salt, natural pozzolans, pumice stone, silica fume, precipitated silica, fly ash, activated shale, clay such as activated kaolinite, activated illite or activated bentonite; activated montmorillonite, activated silica, biomass ash, rice hull ash, diatomaceous earth, crushed opal, blast furnace carbonated steel slag, electric arc furnace carbonated steel slag, carbonated olivine, carbonated wollastonite, carbonated recycled concrete, carbonated silicate minerals, crushed waste glass and mixtures thereof.

[0039] Preferably, the second mineral compound is chosen from the group consisting of natural pozzolana silica salts, silica fume, precipitated silica, fly ash, activated clay, activated montmorillonite, carbonated olivine, carbonated recycled concrete, carbonated silicate minerals, crushed waste glass and mixtures thereof.

[0040] More preferably, the second mineral compound is a silica salt such as sodium silicates.

[0041] Advantageously, the process according to the invention includes prior to step b) of activation, a step of crushing the mineral compound into particles, said particles having a Mohs hardness of dl.

[0042] Preferably, the particles have a D50 less than or equal to 10 mm, preferably less than 5 mm, more preferably less than 2 mm, the particles obtained having a Mohs hardness of dl.

[0043] The expression "D50 less than or equal to 10 mm" means that 50% of the particles have a size less than or equal to 10 mm.

[0044] In the field of hydraulic binder production, activation refers to a method aimed at improving the reactive properties of the materials used.

[0045] According to a first embodiment, the activation step b) is a mechanical activation.

[0046] Advantageously, mechanical activation is achieved by grinding. The grinding can be dry or wet grinding.

[0047] The term "dry grinding" in the present context refers to a grinding operation where there is a very low water content, or even essentially no water. A very low water content means that the water content at the time of grinding said mineral compound is less than 1% by weight (w%), preferably less than 0.1%, and more preferably equal to or less than 0.06%, in each case relative to the total weight of the mineral compound.

[0048] In the case of wet grinding, this can be carried out in the presence of an alkali salt. Preferably, the alkali salt is chosen from sodium chloride (NaCl), sodium carbonate (Na2CO3), sodium silicate (Na2SiO3), and sodium aluminate.

[0049] Preferably, the mechanical activation step is carried out by grinding.

[0050] Step b) of grinding can be carried out in a continuous or discontinuous process.

[0051] The grinding can be carried out by any type of grinder known to those skilled in the art such as an attrition mill, a compression mill, in particular a ball mill or a vertical roller mill, a hammer mill, a roller mill, a cone mill, a ball mill, a jaw crusher or jaw crusher.

[0052] Preferably, the grinding is carried out by a ball mill.

[0053] Advantageously, a co-milling mineral compound is added in step b) of mechanical activation by milling, this co-milling mineral compound having a Mohs hardness d2 greater than the Mohs hardness dl of said particles.

[0054] Advantageously, the content of said co-milling mineral compound is at least 5% by weight, preferably between 5 and 20% by weight, more preferably between 5 and 10% by weight relative to the weight of said first mineral compound.

[0055] Advantageously, the co-milling mineral compound is chosen from the group consisting of olivine, forsterite, fayalite, quartz and basalt.

[0056] Preferably, the mineral co-grinding compound is quartz.

[0057] According to a second embodiment, the activation step b) is a thermal activation.

[0058] Advantageously, thermal activation is carried out at a temperature determined according to the following calculation: T°C endo+(T°Cexo-T°Cendo) / 2

[0059] in which: - T°C endo refers to the minimum heat flux temperature of the endothermic peak, - T°C exo denotes the maximum heat flux temperature of the exothermic peak,

[0060] said temperatures being determined from the thermogram obtained by differential scanning calorimetry coupled to thermogravimetric analysis (DSC-TGA) of said first mineral compound.

[0061] According to a third embodiment, the activation step b) comprises a mechanical activation step followed by a thermal activation step.

[0062] Advantageously, step b) of mechanical and / or thermal activation is carried out: - until reaching an activation rate of at least 10%, preferably at least 20%, more preferably between 20 and 100%, and / or - until partial or total reduction of the hydrated phase of said first mineral compound.

[0063] The activation rate can be determined by different methods such as by DRX or by DSC-ATG.

[0064] In particular, the activation rate (in %) is determined according to the following formula:

[0065] (1 - FWHMbnite )*100, FWHM^

[0066] in which: - Crude FWHM corresponds to the full width at half maximum (in °) of the most intense peak in the portion between 5° and 15° determined from the X-ray diffraction pattern of said mineral compound before activation, - Activated FWHM corresponds to the full width at half maximum (in °) of the most intense peak in the portion between 5° and 15° determined from the X-ray diffraction diagram of said mineral compound after activation.

[0067] The partial or total reduction of the hydrated phase of said first compound can be determined by different methods such as by XRD, by DSC-TGA or by infrared.

[0068] In particular, the partial or total reduction of the hydrated phase of said first compound is determined by XRD.

[0069] A partial reduction of the hydrated phase is obtained when at least one peak position less than 15° preferably between 4° and 15°, more preferably between 6° and 13°, present on the X-ray diffraction diagram (CuKa radiation at a Bragg angle of 20) of the mineral compound before activation, is no longer present on the X-ray diffraction diagram (CuKa radiation at a Bragg angle of 20) of the same mineral compound after activation.

[0070] A total reduction of the hydrated phase is obtained when the X-ray diffraction pattern of the mineral compound after activation includes a scattering halo at positions less than 15° preferably between 4° and 15°, more preferably between 6° and 13°, measured using CuKa radiation at a Bragg angle of 20.

[0071] Advantageously, at least one adjuvant is introduced during step b) of activation, said adjuvant being chosen from the group consisting of a plasticizer and / or superplasticizer, a complexing agent, and a mixture thereof.

[0072] Advantageously, the adjuvant is introduced during step b) of activation or at the end of said step.

[0073] Advantageously, the plasticizer and / or superplasticizer is chosen from among NBSPs (naphthalene-based superplasticizers), PNSs (polynaphthalene sulfonates), MBSPs (melamine-based superplasticizers), PMSs (polymelamine sulfonates), HCAs (hydroxycarboxylic acids), (P)AAs (poly(acrylic acid)), LSs (lignosulfonates), in particular ammonium, calcium or sodium lignosulfonates, PCEs (polycarboxylic ethers), PCAs (polycarboxylic acids), modified phosphonates, their salts and / or derivatives and mixtures thereof.

[0074] Preferably the plasticizer and / or superplasticizer is chosen from PCEs, modified phosphonates and a mixture thereof.

[0075] By “Complexant” is meant any product capable of complexing an ion; preferably a cation; more preferably a metallic cation.

[0076] Advantageously, the complexing agent is a magnesium, aluminum or iron complexing agent.

[0077] The complexing agent may be a compound selected from carboxylic acids, amino acids, amino alcohols, phosphates, phosphonates, amino-phosphonates (-NH-C-PO(OH)2) and amino-phosphates.

[0078] Carboxylic acids can be selected from: formic acid, acrylic acid, citric acid, tartaric acid, maleic acid, malic acid, gluconic acid, fumaric acid, mandelic acid; their derivatives, their salts; and their mixtures.

[0079] Amino acids can be selected from: glycine, glutamic, aspartate, orotic, anthranilic, DTPA (diethylenetriaminopentaacetic acid), DCTA (diaminocyclohexanetetraacetic acid), EDTA, GLDA (glutamate diacetate).

[0080] Phosphates can be chosen from orthophosphates, pyrophosphates, polyphosphates and metaphosphates (tri and hexa).

[0081] The phosphonates can be chosen from monophosphonates and / or diphosphonates: HEDP (1-hydroxyethylidene-1,1-diphosphonic acid).

[0082] Aminophosphonates can be selected from ATMP (Amino-TriMethylene Phosphonic acid), NTMP (NitriloTris-Methylenephosphonic acid), EDTMP (EthyleneDiamine Tetra(Methylene Phosphonic acid), DTPMP (DiethyleneTriamine-Penta[Methylene Phosphonic acid]), EDTMPA (EthyleneDiamine-Tris[Methylene Phosphonic acid]), and their derivatives, salts and mixtures.

[0083] The phosphonocarboxylates can be selected from PPCA (phosphino-polyacrylates), PBTC (phosphonobutane-1,2,4-tricarboxylic acid), and PPCA (polyphosphonocarboxylic acid), and mixtures thereof.

[0084] Preferably, the complexing agent is chosen from carboxylates, phosphates and phosphonates, more preferably from amino-phosphonates, amino-carboxylates and polyphosphates.

[0085] The invention also relates to a hydraulic binder obtained or capable of being obtained by the process as described above.

[0086] The invention also relates to an article comprising the hydraulic binder according to the invention.

[0087] Advantageously, said article being chosen from the group consisting of concrete, mortar, grout, brick, tile, and monolithic element. Preferably, said article is mortar.

[0088] Advantageously, said article further comprises an adjuvant selected from the group consisting of a plasticizer and / or superplasticizer, a complexing agent, and a mixture thereof.

[0089] Said adjuvant being as defined above, including preferred embodiments.

[0090] Advantageously, the mortar comprises: - at least 20%, preferably between 30 and 50% by weight of hydraulic binder according to the invention, - at least 40%, preferably between 50 and 80% by weight of sand, - at least 2%, preferably between 6 and 25% by weight of water, - optionally, at least 0.1% by weight of adjuvant, preferably between 0.3% and 10% by weight of adjuvant,

[0091] the percentages by weight being expressed in relation to the total weight of the dry mortar.

[0092] Advantageously, the sand has a grain size between 0 and 5 mm, preferably between 0.06 and 2 mm, more preferably between 0.2 and 1 mm.

[0093] Advantageously, the adjuvant is a plasticizer and / or superplasticizer in combination with a complexing agent.

[0094] Preferably the plasticizer and / or superplasticizer is chosen from among the polycarboxylate ethers.

[0095] Preferably the complexing agent is chosen from amino-phosphonates, polyphosphonates and amino-carboxylates.

[0096] Advantageously, the mortar comprises a water / hydraulic binder ratio of between 0.1 and 0.5, preferably between 0.2 and 0.4.

[0097] Advantageously, the mortar has a mechanical resistance of at least 2 MPa, preferably of at least 5 MPa, more preferably of at least 7 MPa.

[0098] The invention also relates to the use of the hydraulic binder according to the invention for the manufacture of mortar, cement, concrete, brick, or grout. BRIEF DESCRIPTION OF THE FIGURES

[0099] Other features and advantages of the invention will become apparent in the following illustrative examples, with reference to: - Figures a) to Id) ([Fig.la], [Fig.lb], [Fig.le], [Fig.ld]) respectively represent the X-ray diffraction (XRD) diagrams corresponding respectively to compounds no. 1 to 4 of example 1 (source: Ka of Copper). - Fig. 2 represents the thermograms obtained by differential scanning calorimetry coupled with thermogravimetric analysis (DSC-TGA) of mineral compounds no. 1 and no. 4 shown respectively in figures 2a), 2b). - Figure 3 represents the X-ray diffraction (XRD) diagrams of mineral compounds No. 1 ([Fig.3a]), No. 2 ([Fig.3b]), No. 3 ([Fig.3c]) and No. 4 ([Fig.3d]) before mechanical activation and after mechanical activation (bold curve) (source: Ka of Copper).

[0100] Example 1: Characterization of mineral compounds Mineral compounds considered in the examples#:

[0101] Mineral compound no. 1: Olivine

[0102] Mineral compound no. 2: Olivine

[0103] Mineral compound no. 3: ophiolite

[0104] Mineral compound no. 4: Talc with 98% purity

[0105] Table 1 below shows the mass proportions in terms of oxides of mineral compounds No. 1 to 4. These mass proportions were measured by energy-dispersive X-ray spectroscopy (EDX). These mineral compounds contain at least 10% by weight of MgO.

[0106] [Tables 1] Mineral compound no. MgO % wt SiO2 % wt Fe3 o4 % wt Al2 o3 % wt CaO % wt Na2S o4 % wt Na2 O % wt Cr 2 o3 % wt MgO+Si o2 MgO / Si o2 1 46.44 41.12 11.44 0.37 0.35 - 0.28 - 87.56 1.13 2 48.43 41.03 8.7 0.7 - 0.81 0.33 - 89.46 1.18 3 43.72 42.55 11.42 0.95 0.83 - 0.4 0.13 86.27 1.03 4 44.23 52.22 0.56 0.4 2.17 - 0.42 - 96.45 0.85

[0107] Table 1: Weight percentage of the different phases observed in compounds 1 to 4 relative to the total weight of the mineral compound, as well as the sums and ratios of the resulting MgO and SiO2 contents

[0108] A measurement of the hydrated phases of compounds No. 1 to 4 is carried out by XRD. The results of these analyses are presented in Figure 1 and show, for each of the mineral compounds No. 1 to 4, the presence of at least one peak position less than 15° measured using CuKα radiation at a Bragg angle of 20°. These peaks reveal the presence of hydrated phase(s).

[0109] DSC-ATG measurements complement the determination of hydrated phase percentages by XRD in the case of amorphous phases. In the case of mineral compounds No. 1 (Fig. 2a) and No. 4 (Fig. 2b), the exothermic dehydroxylation peaks are located in the range (550°C–750°C) and reveal the presence of hydrated mineral phases, whether amorphous or crystalline. These exothermic peaks are followed by an endothermic recrystallization peak. Example 2: Activation stage a) Mechanical activation

[0110] Prior to the mechanical activation step, mineral compounds No. 1, No. 2, and No. 3 undergo a crushing step to obtain particles exhibiting a Size less than 10 mm. Compound No. 4 is already supplied in powder form and does not need to be crushed.

[0111] The sands are then introduced into a ball mill (model BB 250 from Retsch, consisting of a 250 mL jar covered with zirconium oxide ZrO2, and having batches of 49 balls of 6 mm and 596 balls of 3 mm also in zirconium oxide).

[0112] The rotation speed of the jar is fixed at 600 rpm (revolutions per minute). The jar is closed and mechanical activation takes place in ambient air.

[0113] The grinding time is the parameter likely to vary depending on the desired level of activation and the characteristics of the starting compounds.

[0114] Table 3 below shows the activation rate of each of compounds No. 1 to 4 for different mechanical and / or thermal activation methods and different durations. This rate is calculated according to the following formula: (1 - FWHMbruie) * 100, with FWHM the full width at half maximum (in °) of the most intense peak in the portion between 5° and 15°, determined from the X-ray diffraction patterns in Figure 3.

[0115] [Tables2] Mineral compound no. 1 2 3 4 15 min mechanical activation 100% - - - 30 min mechanical activation 100% 100% 21.75% 92.81% 60 min mechanical activation 100% - 78.05% 94.32% 90 min mechanical activation - 100% 82.18% - 30 min mechanical activation with a co-milled compound (quartz) 100% 100% 51.36% -

[0116] Table 2: Activation rate for the different mineral compounds No. 1 to 4 according to different grinding times.

[0117] Thus, depending on the nature of the mineral compound, the grinding time allowing mechanical activation is at least 15 min, preferably this time is between 30 and 90 min.

[0118] In some cases the addition of a co-milling mineral compound (quartz) makes it possible to reduce the duration of mechanical activation; this is the case for mineral compound No. 4 where a rate of mechanical activation with a co-milling mineral compound is more than double the rate of activation without a co-milling mineral compound but for the same duration. b) Thermal activation

[0119] According to one embodiment of the invention, the activation step is a thermal activation step. The mineral compound is pre-ground to reduce the size of the aggregates using the same grinder as in step a), however the rotation speed of the jar is lower (400 rotations per minute) and the grinding time is limited to 5 minutes in order to minimize any potential mechanical contribution to the activation.

[0120] The aggregates obtained are then deposited in a ceramic crucible, then placed in a quenching oven for 30 min, at a temperature varying according to the mineral compound.

[0121] This temperature can be determined from DSC-ATG measurements. It is defined as the temperature between the end of the last endothermic peak and the beginning of the exothermic peak, and varies between 300 °C and 950 °C depending on the mineral compounds considered here.

[0122] Mineral compound No. 3 is used to illustrate the step-by-step thermal activation embodiment. The thermal activation temperature has been set in this case at 725°C.

[0123] The activation rate obtained from the X-ray diffraction diagrams according to the calculation mentioned above is 50%.

[0124] Example 3: Preparation of mortars based on the hydraulic binder of this invention and their mechanical performance. Materials used:

[0125] Sand: silica sand with a grain size of 0-1mm

[0126] Hydraulic binder: hydraulic binder of the present invention

[0127] Water: tap water

[0128] D2 (magnesium complexing agent): Ethylene Diamine Tetra (Methylene Phosphonic Acid), marketed by Italmatch under the trade name Dequest 2046,

[0129] HPEG (superplasticizer): high water reducer supplied by Maria®, with the trade name RB 1050®

[0130] SHMP (magnesium complexing agent): Sigma Aldrich sodium hexametaphosphate

[0131] F0100 (superplasticizer): high water reducer supplied by Maria®, with the name commercial PC1901®,

[0132] a) Mechanical performance of mortars prepared from different mechanically activated mineral compounds

[0133] [Tables3] Mineral compound base mortar no. 1 Mineral compound base mortar no. 2 Mineral compound base mortar no. 3 Hydraulic binder (mass in g) 27.01 27.00 27.01 Sand (mass in g) 27.05 27.11 27.00 Water (mass in g) 8.10 8.11- 13.51 HPEG (mass in g) 0.27 0.26 0.27- Short-term mechanical strength (in MPa) 8.71 11.17 7.68 Medium-term mechanical strength (in MPa) Not measured 12.41 Not measured Long-term mechanical strength (in MPa) Not measured 16.00 Not measured

[0134] Table 3: Composition of the 3 mortar formulations made from mineral compounds of different chemical and mineralogical compositions, mechanically activated for 30 min, and their mechanical resistances (in MPa) measured at different time intervals (short term: 2-6 days, medium term: 12-16 days, long term: 24 days and beyond)

[0135] The results presented in Table 3 show that from the hydraulic binder of the invention, mortars with good short, medium and long-term mechanical resistance can be obtained.

[0136] b) Impact of magnesium complexing agent on the mechanical performance of mortars prepared using the hydraulic binder of the invention

[0137] [Tables4] Mortar A with mineral compound no. 3 Mortar B with mineral compound no. 3 Mortar C with mineral compound no. 3 Mortar D with mineral compound no. 4 Mortar E with mineral compound no. 4 Binder (mass in g) 27.01 27.00 27.01 27.01 26.99 Sand (mass in g) 27.01 27.00 27.02 27.11 27.02 Water (mass in g) 13.51 8.10 8.11 13.50 9.44 D2 (mass in g) -0.13 0.81 -0.27 SHMP (mass in g) - - 1.35 - - HPEG (mass in g) 0.27 0.27 - 0.27 0.27 FO100 (mass in g) - - 0.81 - - Short-term mechanical resistance (in MPa) 7.68 33.32 22.86 1.66 49.63 Medium-term mechanical resistance (in MPa) 5.86 36.54 Not measured Not measured Not measured Long-term mechanical resistance (in MPa) 6.72 44.66 Not measured Not measured Not measured

[0138] Table 4: Evaluation of the influence of admixtures on mechanical resistance measured from different mortar formulations with mortar A, B, D, E obtained by mechanical activation, and mortar C obtained by thermal activation.

[0139] Comparison of the mechanical resistance results measured on the one hand between mortar A and mortar B, and on the other hand between mortar C and mortar D, reveals that the presence of a magnesium complexant (D2) in the mortar makes it possible to increase mechanical resistances significantly and considerably.

[0140] The results obtained with mortar C also comprising a magnesium complexant but whose mineral compound has been thermally activated also reveal better mechanical resistance compared with the results obtained with mortar A not comprising a magnesium complexant.

[0141] c) Mechanical performance of mortars based on binders prepared according to the thermal activation method

[0142] [Tables5] Thermally activated mineral compound base mortar No. 3 Mechanically activated mineral compound base mortar Binder (mass in g) 27.01 27.01 Sand (mass in g) 27.04 27.02 Water (mass in g) 8.10 8.11 Hexamethaphosphate (mass in g) 1.35 1.35 FO100 (mass in g) 0.80 0.81 Short-term mechanical strength (in MPa) 16.46 22.86

[0143] Table 5: Mechanical performance of mortars made with a hydraulic binder prepared by thermal activation (in the presence of 5% by weight of SHMP) of mineral compound no. 4, and comparison with mechanical activation in terms of short-term mechanical resistance (2-6 days).

[0144] Thermal and mechanical activation of the same starting mineral compound allows for satisfactory short-term mechanical strengths to be obtained. It should be noted that better mechanical strength is obtained when mechanical activation has been performed.

Claims

Demands

1. A process for preparing a hydraulic binder comprising the following steps: a) Supplying at least one first mineral compound comprising: - at least 10% by weight of magnesium oxide (MgO), and - a proportion of hydrated phase(s) greater than or equal to 1% by weight, the percentages being expressed in relation to the total weight of said first mineral compound, b) mechanical and / or thermal activation of said first mineral compound.

2. A process according to claim 1, wherein said first mineral compound comprises at least 10% by weight of silicon dioxide (SiO2), on the total weight of said mineral compound.

3. A process according to claim 1 or 2, wherein said first mineral compound comprises magnesium silicate.

4. A method according to any one of claims 1 to 3, wherein said first mineral compound comprises at least 25% by weight of MgO and at least 30% by weight of SiO2 by weight of the total weight of said mineral compound.

5. A method according to any one of claims 1 to 4, wherein said first mineral compound is characterized by an X-ray diffraction (XRD) pattern comprising at least one peak position less than 15" measured using CuKa radiation at a Bragg angle of 20.

6. A method according to any one of claims 1 to 5, wherein said first mineral compound is characterized by the presence of at least one endothermic peak at a temperature between 250°C and 1400°C, measured by DSC-ATG.

7. A process according to any one of claims 1 to 6, wherein said first mineral compound comprises one or more minerals selected from the group consisting of: olivine ((Mg,Fe)2SiO4), amphibole ((Ca,Na)2-3(Mg,Fe,Al)5(Si,Al)sO22(OH)2), serpentine ((Mg,Fe)3Si2O5(OH)4), talc (MgsSi4O10(OH)2), chlorite ((Mg,Fe,Al)6(Si,Al)4O10(OH)8), brucite (Mg(OH)2), dunite (Mg2SiO4), biotite (K(Mg,Fe)3AlSi3O10(F,OH)2), antigorite (Mg3Si2O5(OH)4), lizardite (Mg3Si2Os(OH)4), clinochlore ((Mg,Fe)5AI(Si3AI)Oio(OH)8), phlogopite (KMg3(AISisOio)(OH)2), vermiculite (Mg,Fe,AI)3(AI,Si)4Oio(OH)2-4H2O), saponite (Cao.3(Mg,Fe)3(Si,AI)4Oio(OH)2-4H2O), peridotite, ophiolite, and pyrophyllite (AkSi4Oio(OH)2 substituted with Mg).

8. A method according to claim 1, comprising supplying a second mineral compound distinct from the first mineral compound, said second mineral compound comprising at least 10% by weight of SiO2, on the total weight of said second mineral compound.

9. A method according to any one of claims 1 to 8, comprising prior to step b) of activation, a step of crushing into particles, said particles having a Mohs hardness of dl.

10. A process according to any one of claims 1 to 9, wherein step b) of mechanical and / or thermal activation is carried out: - until an activation rate of at least 10% is reached, and / or - until partial or total reduction of the hydrated phase of said first mineral compound.

11. A method according to any one of claims 1 to 10, wherein step b) is a mechanical activation step by grinding.

12. A process according to claim 11, wherein a co-milling mineral compound is added at step b) of mechanical activation, said co-milling mineral compound having a Mohs hardness d2 greater than the Mohs hardness dl of said particles.

13. A method according to any one of claims 1 to 10, wherein step b) is a thermal activation step carried out at a temperature determined according to the following calculation: T°C -UTOC -T°CV? A endo~\ A ^exo A '-'endo / ' wherein: - T°C endo denotes the minimum heat flux temperature of the endothermic peak, - T°C exo denotes the maximum heat flux temperature of the exothermic peak, said temperatures being determined from the thermogram obtained by differential scanning calorimetry coupled to a

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18. thermogravimetric analysis (DSC-ATG) of said first mineral compound. A process according to any one of claims 1 to 13, wherein at least one adjuvant is introduced during step b) of activation, said adjuvant being selected from the group consisting of a plasticizer and / or superplasticizer, a complexing agent, and a mixture thereof. Hydraulic binder that can be obtained by the process according to any one of claims 1 to 14. Article comprising the hydraulic binder according to claim 15. Article according to claim 16 said article being chosen from the group consisting of a cement, a mortar, a concrete, a grout, a brick, a tile, a monolithic element. Article according to claim 16 or 17, further comprising at least one adjuvant selected from the group consisting of a plasticizer and / or a superplasticizer, a complexing agent, and a mixture thereof.

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