GEOPOLYMER BINDERS BASED ON CHARGED DEAD CLAY

Description

Technical Field

[0001] The present invention relates to the field of construction materials. More specifically, the invention concerns a geopolymer binder based on a so-called "TOT" clay. This binder enables the production of grouts, mortars, and concrete with a low environmental footprint. State of the art

[0002] In the construction industry, three types of binders are generally used: hydraulic binders based on Portland cement, alkali-activated binders, and geopolymer binders. Geopolymer binders, or geopolymers, are so named because they are obtained by polymerizing inorganic materials, such as aluminosilicate oxides, in the presence of an alkali activator. Geopolymers possess a very strong three-dimensional structure composed of Si-O-Si and Si-O-Al covalent bonds.

[0003] The production of geopolymers is more environmentally friendly than that of conventional Portland cement. Indeed, producing one tonne of Portland cement involves calcining limestone and clay at 1450°C. This calcination of limestone results in the emission of approximately one tonne of CO2, in addition to the high energy cost of thermal activation.

[0004] In comparison, the energy cost of preparing the precursor materials for a conventional geopolymer, namely metakaolins, is only one-third that of Portland cement. Metakaolin is obtained by grinding kaolin followed by a few seconds of immersion in a chamber at a temperature between 900 and 1000°C. Such metakaolin generally has a particle size of less than 10 µm and therefore high reactivity (due to its large specific surface area). However, preparing a geopolymer binder from metakaolin requires a significant amount of alkaline activator, typically an alkaline silicate solution, for the binder to be workable and thus possess a certain degree of workability. The production cost of a metakaolin-based geopolymer binder can be high (given the quantity required and the price of the alkaline activation solutions).In addition, when corrosive alkaline silicate solutions are used (i.e. when the molar ratio M 2 O:SiO 2 > 0.625 with M = Na or K), the presence of qualified personnel is necessary to avoid any accidents during the handling of these substances.

[0005] The preparation of geopolymers from metakaolin is described in particular in US patent applications 2012 / 0192765, WO 2016 / 156722, WO 2008 / 012438, and FR-A-2966823. Work on geopolymers is also documented in the literature. For example, Buchwald et al. (The suitability of thermally activated illite / smectite clay as raw material for geopolymer binders. Applied Clay Science, 46 (2009) 300-304) investigated the suitability of illite / smectite-based clay as a precursor to a geopolymer. The precursor was thermally activated at 850°C. A silicate solution containing 10% NaOH was mixed with the calcined illite at a liquid-to-solid (L / S) ratio of 0.41. Grase et al. (Chemically treated submicron illite clays for product with improved strength. Advanced Materials Research, 1117 (2015) 152-155) synthesized geopolymers based on illite derived from red and grey clay.This illite was mixed with a 4M NaOH solution and then cured for 3 days at 60°C and then for 3 days at 100°C. Dietel et al. (The importance of specific surface area in the geopolymerization of heated illitic clay. Applied Clay Science, 139 (2017) 99-107) synthesized a geopolymer whose precursor is clay composed of 30% illite. The clay was calcined at 875°C for 3 h and then mixed with a 5M KOH solution with an L / S ratio of 0.5. Hu et al. (The influence of alkali activator type, curing temperature and gibbsite on the geopolymerization of an interstratified illite-smectite rich clay from Friedland. Applied Clay Science, 135 (2017) 386-393) investigated the influence of several alkali activators on the geopolymerization of illite-smectite rich clay. This clay was calcined at 850°C and then ground for 2 hours with a planetary mill using agate balls.Several proportions of gibbsite Al(OH)₃ were mixed with the precursor, and geopolymers were obtained by adding 6M NaOH or 6M KOH with a liquid / solid mass ratio (L / S) of 0.5. The mechanical performance of these illite-based geopolymers is, however, only average, with, for example, a 28-day compressive strength of approximately 30 MPa (Hu et al., op. cit.). MacKenzie et al. (Formation of inorganic polymers (geopolymers) from 2:1 layer lattice aluminosilicates. Journal of the European Ceramic Society, 2007, 28(1), 177-181) describe the formation of geopolymers from pyrophyllite in the presence of a sodium silicate solution. According to the experimental section, pyrophyllite is ground and then mixed with a sodium silicate solution with a Na2O / SiO2 molar ratio of 0.37. The liquid / solid ratio of this mixture is equal to 2. Furthermore, no concrete data illustrates the mechanical properties of the geopolymers obtained.

[0006] With the aim of having geopolymers whose cost price is controlled and whose mechanical performance allows their application in various fields such as prefabricated elements and protective coatings, the present invention has been realized. Summary of the invention

[0007] The invention relates to a geopolymer binder in which all or part of the metakaolin traditionally used for the preparation of geopolymers is replaced by an activated charged TOT clay. More particularly, the invention relates to a geopolymer binder comprising: an aluminosilicate material containing at least 20% by mass of charged TOT clay, and an alkaline silicate solution having a molar ratio M2O / SiO2 (M = Na or K) in the range of about 0.45 to about 0.8, said geopolymer binder having a liquid / solid mass ratio (L / S) in the range of about 0.4 to about 1.0 (0.4 ≤ L / S ≤ 1.0).

[0008] The invention also relates to a mortar or concrete obtained from the above geopolymer binder.

[0009] The invention further relates to a process for preparing a geopolymer binder precursor which includes a mechanical activation step of charged TOT clay, this step being optionally preceded by a thermal activation step of said clay. Brief description of the figure

[0010] There figure 1 represents the structure of a TOT-charged clay. Description of the invention

[0011] According to one aspect, the invention relates to a geopolymer binder comprising: an aluminosilicate material containing at least 20% by mass of activated charged TOT clay, and an alkaline silicate solution having a molar ratio M 2 O / SiO 2 (M = Na or K) in the range of about 0.45 to about 0.8, said geopolymer binder having a liquid / solid mass ratio in the range of about 0.40 to about 1.0.

[0012] The term "activated charged TOT clay" means a charged TOT clay whose amorphous phase content is at least 20% by mass, advantageously at least 30% by mass, for example at least 40% by mass or at least 50% by mass, and very advantageously at least 70% by mass, for example at least 80% by mass or at least 90% by mass.

[0013] TOT-loaded clays are clays with a structure composed of an aluminous octahedral sheet denoted O between two tetrahedral siliceous sheets denoted T (cf. figure 1 They are also called 2:1 clays. Among these clays, charged TOT clays are clays whose charge is compensated by cations (Cn+) and whose quantity is high, between 0.6 and 2 moles per half-unit cell. They form the class of micas.

[0014] Filled TOT clays can originate from a natural geological formation, such as the green clay of Romainville or the blue marl of Argenteuil, both from geological formations in the Paris Basin. It is also possible to use commercially available filled TOT clays, such as green clays. Advantageously, the filled TOT clay is selected from clay minerals of the illite, muscovite, smectite (including montmorillonite), vermiculite, or mixtures of these clay minerals. Ideally, the filled TOT clay comprises at least 10% by mass of one of the aforementioned clay minerals; for example, at least 20% by mass, at least 30% by mass, at least 40% by mass, at least 50% by mass, at least 60% by mass, or at least 70% by mass.

[0015] The aluminosilicate material comprises at least 20% by mass, advantageously at least 30% by mass, at least 40% by mass, or at least 50% by mass, and even more advantageously at least 70% by mass of activated TOT charged clay. Most advantageously, the aluminosilicate material consists solely of activated TOT charged clay.

[0016] It is understood from the above that the aluminosilicate material may not consist exclusively of activated charged TOT clay. In this case, the aluminosilicate material may also comprise at least one compound selected from quartz, a carbonate, a feldspar, a metakaolin, and a thermally unactivated aluminosilicate. For the purposes of the present invention, the expression "at least one compound selected from" encompasses not only a single compound (for example, quartz) but also a mixture of several compounds of the same type (for example, several carbonates or several metakaolins), as well as a mixture of one or more compounds of a first type with one or more compounds of one or more other types (for example, a mixture of metakaolin(s) and thermally unactivated aluminosilicate(s)).In one embodiment, the thermally unactivated aluminosilicate is selected from kaolin, bentonite, fly ash, blast furnace slag, or a mixture of these compounds. In another embodiment, the carbonate is selected from calcite and / or dolomite. It is desirable that, when the aluminosilicate material comprises metakaolin and / or a thermally unactivated aluminosilicate, these materials should not constitute more than 50% by mass of the mass of the aluminosilicate material.

[0017] The geopolymer binder also comprises an alkaline silicate solution having a molar ratio M2O / SiO2 (M = Na or K) in the range of about 0.45 to about 0.80. Advantageously, the molar ratio M2O:SiO2 is in the range of about 0.5 to about 0.67, preferably in the range of about 0.50 to < 0.625, and preferably still in the range of about 0.53 to about 0.59. Such a silicate solution is either directly available commercially (for example from VWR or Woellner GmbH), or obtained from a precursor solution (commercial or not) having a molar ratio M 2 O / SiO 2 outside the range of values ​​mentioned above, molar ratio which is subsequently adjusted to the desired value with an appropriate amount of alkali hydroxide MOH (for example in the form of pellets or powder).In this latter case (adjustment of the molar ratio M 2 O / SiO 2 ), the addition of the alkali hydroxide can take place before or after the mixing of the alkaline silicate solution and the aluminosilicate material.

[0018] The respective proportions of aluminosilicate material and alkaline silicate solution are such that the binder has a liquid / solid mass ratio (L / S) in the range of approximately 0.4 to approximately 1.0 (0.4 ≤ L / S ≤ 1.0), advantageously in the range of approximately 0.5 to approximately 0.8 (0.5 ≤ L / S ≤ 0.8), and most advantageously in the range of approximately 0.5 to approximately 0.75 (0.5 ≤ L / S ≤ 0.75). This liquid / solid mass ratio allows control of the amount of alkaline solution in the geopolymer binder, thereby promoting optimal geopolymerization and controlled porosity during the hardening of the mortar or concrete that may be produced from said geopolymer binder.

[0019] In one embodiment the geopolymer binder is free of additives, and in particular of crosslinked carboxylic acid type superplasticizer (such as a crosslinked acrylic acid homopolymer, in particular a crosslinked acrylic acid homopolymer with polyalkenyl ethers or divinyl glycol), or is free of copper ion sources.

[0020] In another aspect, the invention relates to a mortar or concrete comprising the geopolymer binder defined above. Conventionally, mortar is obtained by mixing sand with the geopolymer binder, and concrete is obtained by mixing sand and aggregates with the geopolymer binder. The mortar or concrete may optionally include reinforcing fibers of metallic, organic, or mineral origin; the organic fibers are of natural origin (hemp, flax, or bamboo, for example) or synthetic origin. In another aspect, the invention relates to a process for preparing an activated, filled TOT clay, useful as a precursor to a geopolymer binder.

[0021] Typically, kaolinite-type clays, whose layers exhibit a TO structure (i.e., a tetrahedral siliceous layer bonded to an octahedral aluminous layer), are activated by heat treatment. This treatment leads to the dehydration of these clays at the crystalline level: the OH groups bonded to the octahedral layer leave the layers after heating for a few hours at temperatures ranging from 500°C to 850°C. However, as shown by the figure 1The configuration of the TOT clay sheets is more complex. This configuration does not allow for easy dehydroxylation of the sheets, which requires thermal activation for at least several hours at 850°C. Thermally activated clay does not necessarily exhibit a sufficient level of amorphization to allow optimal geopolymerization when mixed with an alkaline silicate solution. The present invention aims to overcome this problem by providing a geopolymer binder precursor (the aluminosilicate material) comprising a filled TOT clay that has a minimum amorphization level of 20% by mass.

[0022] According to one aspect of the invention, the filled TOT clay contained in the aluminosilicate material is subjected to a mechanical activation step. This step is typically carried out by grinding the starting aluminosilicate material. Those skilled in the art will bear in mind that the starting material (before grinding) must have a particle size of less than 1 mm; if this is not the case, a pre-grinding step is necessary. Any type of mill can be used to perform this mechanical activation step. Suitable mills for the purposes of the invention include a gyratory mill or a planetary mill. This type of mill allows for the impact fragmentation of the aluminosilicate material using grinding media.These mills are generally used with a rotational speed ranging from approximately 30 rpm to approximately 600 rpm, for a sufficient duration to ensure that the loaded TOT clay has an amorphous phase content of at least 20% by mass; a grinding time ranging from approximately 15 minutes to approximately 6 hours generally achieves the desired amorphous phase content. Furthermore, it is desirable that the mass ratio between the grinding media and the starting aluminosilicate material (with a particle size of less than 1 mm) be in the range of approximately 3.0 to approximately 20.0, advantageously in the range of approximately 7.0 to approximately 15.0.

[0023] When a planetary mill is used, it is advantageously operated at a rotational speed in the range of approximately 30 rpm to approximately 600 rpm, particularly in the range of approximately 400 rpm to approximately 600 rpm, for a duration in the range of approximately 15 minutes to approximately 6 hours, particularly in the range of approximately 2 hours to approximately 4 hours. When a gyratory mill is used, it is advantageously operated at a rotational speed in the range of approximately 30 rpm to approximately 100 rpm, for a duration in the range of approximately 15 minutes to approximately 6 hours, particularly in the range of approximately 2 hours to approximately 4 hours.According to another aspect of the invention, the mechanical activation step of the charged TOT clay contained in the starting aluminosilicate material can be preceded by a "conventional" thermal activation step, namely calcination of the starting aluminosilicate material (with a particle size of less than 1 mm) in a temperature range from approximately 200°C to approximately 1000°C, preferably in a temperature range from approximately 800°C to approximately 900°C for approximately 2 to 6 hours. The thermal activation is carried out, for example, in a programmable furnace, such as a muffle furnace, a rotary kiln, or a flash calcination furnace, using a crucible made of refractory material to contain the material.

[0024] At the end of the mechanical activation step (whether or not it has been preceded by a thermal activation step) the charged TOT clay contained in the aluminosilicate material comprises at least 20% by mass, advantageously at least 30% by mass and very advantageously at least 70% by mass, of amorphous phase.

[0025] The present invention enables the partial or total substitution of metakaolin, conventionally used in the manufacture of geopolymer binders, with an aluminosilicate material based on activated TOT clay. Metakaolin is obtained by calcining natural kaolin extracted from quarries. However, areas where natural kaolin is extracted are much less common than areas rich in TOT clay (particularly in France). The invention therefore contributes to conserving scarce natural resources in favor of more readily available resources, even those found in the form of waste (quarry or excavation waste).

[0026] It is possible, by implementing the present invention, to obtain geopolymer binders that can achieve very high mechanical performance (Rc > 120 MPa at 28 days), which, to the Applicant's knowledge, is very rare or even impossible for geopolymer binders whose aluminosilicate precursor is composed exclusively of metakaolin.

[0027] Another advantage lies in the fact that the water requirement of the aluminosilicate precursor according to the invention is significantly lower than that of flash-cured metakaolin. Activated TOT clay reacts much less rapidly with the alkaline solution (slower hardening), which allows for a drastic reduction in the amount of water in the mixture without the need for a superplasticizer. The present invention therefore makes it possible to increase the mechanical properties of the geopolymer after curing while maintaining acceptable workability during the application of the binder, mortar, or concrete before the curing period, whether this is carried out in an oven or at ambient temperature. Reducing the amount of alkaline silicate solution also lowers the environmental and financial costs of this type of geopolymer, as this solution is industrially produced and accounts for the majority of the geopolymer's cost.

[0028] Due to its rheological and mechanical properties, the geopolymer binder according to the invention is suitable for use: for the production of prefabricated building elements (concrete blocks, breeze blocks, bricks, tiles, slabs, or insulation material, etc.); as a material directly poured on site in the form of grout, mortar or concrete; as an adhesive; as a coating for building or surface elements, plasters; for the manufacture of ceramics (pipes, refractory molds, etc.).

[0029] The invention will be better understood with the aid of the following examples, given purely for illustrative purposes. In these examples, the compressive strength (Rc) measurements at 48 hours and 28 days were carried out according to the principle of standard EN 12390-3. Unless otherwise specified, the alkaline silicate solutions used are commercial solutions. Example 1

[0030] A geopolymer binder was prepared from Romainville Green Clay, sourced from the surface layer of a gypsum quarry in eastern Île-de-France. This clay material contains TOT-filled clays, including an average of 48% illite / muscovite by mass.

[0031] 500 g of green clay with a particle size of less than 1 mm was placed in an alumina crucible, which was then placed in a Nabertherm® LE 14 / 11 / B150 muffle furnace. The furnace was programmed to heat for 30 minutes, followed by a holding time at 850°C for 2 hours. Cooling to ambient temperature occurred naturally within the closed furnace. Once the heat treatment was complete, the material was transferred to a tungsten carbide crucible connected to a Retsch® PM100 planetary mill. 30 mm diameter tungsten carbide balls were added to achieve a ball-to-powder mass ratio of 7.7. The crucible was then sealed and mounted on the rotation axis of the planetary mill. The grinding was carried out for 4 hours at 400 revolutions per minute.At the end of grinding, the powder obtained comprises at least 40% by mass of amorphous phase, and has a D 100 <100µm and a specific surface area BET = 5 m 2< / g.

[0032] The resulting powder was placed in a turbotest-type mixer with a deflocculating turbine, marketed by VMI-RAYNERI. An alkaline sodium silicate solution with a Na₂O / SiO₂ molar ratio of 0.54 was then added. This solution was prepared by mixing an industrial solution with a Na₂O / SiO₂ molar ratio of 0.21 with anhydrous sodium hydroxide pellets. The liquid / solid mass ratio (L / S) of the mixture was 0.5. The mixture was then mixed in automatic mode at medium speed (1000 rpm) for 1 to 3 minutes, then in manual mode for 30 seconds, and finally in automatic mode at high speed (1500 rpm) for 1 to 3 minutes.

[0033] The resulting mixture was poured into a cylindrical plastic mold (33 mm diameter, 70 mm height). The filled mold was placed on a vibrating table and vibrated for 3 minutes at a high frequency (2100 vibrations / min). The mold was then cured in an oven under the following conditions: 24 hours at 40°C followed by 24 hours at 70°C. After 48 hours, the prefabricated part was ready for use after demolding.

[0034] The measurement of compressive strength (Rc) at 48h and at 28 days is reported in Table 1. Examples 2 and 3

[0035] The procedure from example 1 was repeated, but using a mass L / S ratio of 0.75 and 1.0 respectively. The Rc measurement at 48h and 28 days is reported in Table 1. Example 4

[0036] The procedure from Example 1 was repeated, but using (i) Argenteuil blue marl as the starting material (which comprises 20% by mass of charged TOT clay and approximately 35% by mass of carbonates - calcite and dolomite), (ii) an alkaline sodium silicate solution with a molar ratio Na₂O / SiO₂ = 0.59, and (iii) a mass ratio L / S of 1.0. The Rc measurements at 48 hours and 28 days are reported in Table 1. Example 5

[0037] The procedure from example 1 was repeated, but for the grinding step, a gyratory mill was used (grinding for 4 hours at 40 rpm), along with an alkaline sodium silicate solution with a molar ratio Na₂O / SiO₂ = 0.59 and a mass ratio L / S of 0.75. The Rc measurement at 28 days is reported in Table 1. Example 6

[0038] The procedure from example 1 was repeated, but for the grinding step, a gyratory mill was used (grinding for 4 hours at 40 rpm), along with an alkaline potassium silicate solution with a molar ratio K₂O / SiO₂ = 0.66 and a mass ratio L / S of 0.75. The Rc measurement at 28 days is reported in Table 1. Example 7

[0039] Eighty grams of Argenteuil blue marl were placed in a tungsten carbide crucible connected to a Retsch®< PM100 type planetary mill, and 30 mm diameter tungsten carbide balls were added to achieve a ball-to-powder mass ratio of 7.7. The crucible was sealed and placed on the planetary mill's solar wheel. Grinding was carried out for 4 hours at 400 rpm. Separately, 500 grams of Romainville green clay (D 100 <1 mm) were placed in an alumina crucible, which was then placed in a Nabertherm®< LE 14 / 11 / B150 type muffle furnace. A 30-minute heating period followed by a 2-hour holding time at 850°C was programmed. Cooling to room temperature occurred naturally within the closed oven. Once the heat treatment was complete, the material was ground using a gyratory mill for 4 hours at 40 rpm.

[0040] A mixture of 80 / 20 (by mass) green clay (thermally and mechanically activated) and blue marl (mechanically activated) was then prepared. This mixture was subsequently added to an alkaline sodium silicate solution with a molar ratio of Na₂O / SiO₂ = 0.59, following the procedure described in Example 1, to obtain a mass ratio L / S of 0.69. The Rc measurements at 48 hours and 28 days are reported in Table 1. Examples 8 and 9

[0041] We repeated the procedure of example 1 but using a mass ratio of beads / powder of material of 11 and 15 respectively. The measurement of the Rc at 28 days is reported in table 1. Example 10

[0042] The procedure from example 1 was repeated but using an alkaline sodium silicate solution with a molar ratio Na2O / SiO2 = 0.59 and a mass ratio L / S of 0.75. The measurement of Rc at 28 days is reported in Table 1. Example 11

[0043] The procedure from example 1 was repeated but using an alkaline potassium silicate solution with a molar ratio K2O / SiO2 = 0.66 and a mass ratio L / S of 0.5. The measurement of Rc at 28 days is reported in Table 1. Example 12

[0044] The procedure from example 1 was repeated, but using an aluminosilicate material from eastern France (argillite is an aluminosilicate material containing approximately 33% of filled TOT clays (mainly illite / muscovite) and 21% carbonates) and a mass ratio L / S of 1.0. The Rc measurement at 28 days is reported in Table 1. Examples 13 to 16

[0045] The procedure from Example 3 was repeated, but using grinding times of 30 min, 1 h, 2 h, and 3 h respectively. The Rc measurement at 48 h is shown in Table 1. Example 17

[0046] The procedure from Example 3 was repeated, but using illite from the Arvel quarries as the starting material (which comprises 80% TOT clay by mass). The Rc measurement at 48h is reported in Table 1. Example 18

[0047] The procedure from example 5 was repeated, but using a mass ratio L / S of 0.7 and a mass ratio of beads / material powder of 3.7. The Rc measurement at 48h and 28 days is reported in Table 1. Example 19

[0048] The procedure from example 5 was repeated but using a mass ratio L / S of 0.65 and a mass ratio of beads / material powder of 3.7. The measurement of Rc at 48h and 28 days is reported in Table 1. Example 20

[0049] The procedure from example 5 was repeated but using a mass ratio L / S of 0.6 and a mass ratio of beads / powder of material of 3.7. The measurement of Rc at 48h and at 28 days is reported in table 1. Example 21

[0050] The procedure from example 5 was repeated but using a mass ratio L / S of 0.55 and a mass ratio of beads / powder of material of 3.7. The measurement of Rc at 48h and at 28 days is reported in table 1. Example 22

[0051] The procedure from example 6 was repeated but using a mass ratio L / S of 0.7 and a mass ratio of beads / powder of material of 3.7. The measurement of Rc at 28 days is reported in Table 1. Example 23

[0052] The procedure from example 6 was repeated but using a mass ratio L / S of 0.6 and a mass ratio of beads / powder of material of 3.7. The measurement of Rc at 28 days is reported in Table 1. Example 24

[0053] The procedure from example 6 was repeated but using a mass ratio L / S of 0.55 and a mass ratio of beads / powder of material of 3.7. The measurement of Rc at 28 days is reported in table 1. Example 25

[0054] The procedure from example 6 was repeated, but using a mass ratio L / S of 0.50 and a mass ratio of beads / powder of material of 3.7. The measurement of Rc at 28 days is reported in Table 1. Example 26

[0055] The procedure from example 6 was repeated but using a mass ratio L / S of 0.45 and a mass ratio of beads / material powder of 3.7. The measurement of Rc at 48h and at 28 days is reported in table 1. Example 27

[0056] The procedure from example 6 was repeated but using a mass ratio L / S of 0.4 and a mass ratio of beads / powder of material of 3.7. The measurement of Rc at 48h and at 28 days is reported in table 1. Example 28

[0057] The procedure from example 5 was repeated but using a sodium silicate solution with a molar ratio Na2O / SiO2 = 0.54, a mass ratio L / S of 0.75 and a mass ratio of beads / powder of material of 3.7. The measurement of Rc at 28 days is reported in Table 1. Example 29

[0058] The procedure from example 28 was repeated, but using a mass ratio L / S of 0.7. The measurement of the Rc at 28 days is reported in Table 1. Example 30

[0059] The procedure from example 28 was repeated but using a mass ratio L / S of 0.6. The measurement of the Rc at 28 days is reported in Table 1. Example 31

[0060] The procedure from example 28 was repeated but using a mass ratio L / S of 0.55. The measurement of the Rc at 28 days is reported in Table 1. Example 32

[0061] The procedure from example 28 was repeated but using a mass ratio L / S of 0.5. The measurement of the Rc at 28 days is reported in Table 1. Example 33

[0062] The procedure from example 28 was repeated, but using a mass ratio L / S of 0.45. The measurement of the Rc at 28 days is reported in Table 1. Example 34

[0063] The procedure from example 28 was repeated but using a mass ratio L / S of 0.4. The measurement of the Rc at 28 days is reported in Table 1. Table 1 Example L / S beads / powder Rc 48h (MPa) Rc 28 j (MPa) 1 0,5 7,7 79,4 101,6 2 0,75 7,7 65,5 70,8 3 1,0 7,7 51,0 55,7 4 1,0 7,7 24,0 26,9 5 0,75 7,7 - 43,3 6 0,75 7,7 - 45,9 7 0,69 7,7 56,6 58,1 8 0,5 11 - 116,8 9 0,5 15 - 126,1 10 0,75 7,7 - 73,6 11 0,5 7,7 - 86,7 12 1,0 7,7 - 29,1 13 1,0 7,7 17,0 - 14 1,0 7,7 36,1 - 15 1,0 7,7 41,7 - 16 1,0 7,7 52,4 - 17 1,0 7,7 62,1 - 18 0,7 3,7 36,9 53,4 19 0,65 3,7 45,4 56,8 20 0,6 3,7 43,0 67,8 21 0,55 3,7 58,1 85,2 22 0.7 3.7 - 48,9 23 0.6 3.7 - 67,8 24 0.55 3.7 - 80,4 25 0.5 3.7 - 94,9 26 0,45 3,7 73,2 101,2 27 0,4 3,7 76,5 110,9 28 0.75 3,7 - 12,0 29 0.7 3,7 - 15,6 30 0.6 3,7 - 22,7 31 0.55 3,7 - 31,9 32 0.5 3,7 - 36,3 33 0.45 3,7 - 50,3 34 0.45 3,7 - 60,0

[0064] It can be noted from the table above that a decrease in the L / S mass ratio increases the Rc at 48h and 28 days: in the case of examples 1 to 3, the Rc at 28 days is increased by 82% when the L / S ratio goes from 1.0 to 0.5. Thus it is possible to reduce the cost of obtaining the geopolymer binder (a lower L / S ratio indicates a smaller quantity of alkaline silicate solution) while improving its mechanical properties. Example 35

[0065] The procedure from Example 1 was repeated, but a gyratory crusher was used for the grinding step (grinding for 4 hours at 40 rpm), along with a L / S mass ratio of 0.75. The resulting geopolymer binder was then mixed with 0 / 2 mm Seine sand (sand / binder mass ratio = 3 / 1) to obtain a mortar. Test specimens (4x4x16 cm) were prepared from this mortar; the compressive strength of these specimens at 28 days, measured according to the EN 196-1 standard, was 36.3 MPa.

Claims

1. A geopolymer binder comprising: - an aluminosilicate material containing at least 20% by mass of charged TOT clay with an amorphous phase content of at least 20% by mass; - an alkaline silicate solution having a molar ratio M2O / SiO2 (M = Na or K) in the range from 0.45 to 0.8; said binder having a liquid / solid mass ratio in the range from 0.4 to 1.0.

2. The geopolymer binder of claim 1, wherein the charged TOT clay is selected from clay minerals of the muscovite type, smectite type, vermiculite type ans mixtures od fais clay minerals.

3. The geopolymer binder of claim 1 or claim 2, wherein the aluminosilicate material contains at least 50% by mass, preferably at least 70% by mass, of charged TOT clay.

4. The geopolymer binder of any one of the preceding claims, wherein the charged TOT clay has an amorphous phase content of at least 50% by mass.

5. The geopolymer binder of any one of the preceding claims, wherein the aluminosilicate material further comprises at least one compound selected from quartz, a carbonate, a feldspath, a metakaolin, and a non-thermally activated aluminosilicate.

6. The geopolymer binder of claim 5, comprising up to 50% by mass of a compound selected from a metakaolin, a non-thermally activated aluminosilicate, and a mixture of metakaolin and non-thermally activated aluminosilicate.

7. The geopolymer binder of any one of the preceding claims, wherein the alkaline silicate solution has a molar ratio M2O / SiO2 in the range from 0.5 to 0.67.

8. The geopolymer binder of any one of the preceding claims, which has a liquid / solid mass ratio in the range from 0.5 to 0.8.

9. A mortar or concrete comprising the geopolymer binder of any one of the preceding claims.

10. A process for preparing a precursor of a geopolymer binder, which comprises grinding an aluminosilicate material containing at least 20% by mass of charged TOT clay and having a particle size less than 1 mm, such that said charged TOT clay has an amorphous phase content of at least 20% by mass.