WO1998031644A1

WO1998031644A1 - Methods for making geopolymeric cements and cements resulting from these methods

Info

Publication number: WO1998031644A1
Application number: PCT/FR1998/000059
Authority: WO
Inventors: Joseph Davidovits
Original assignee: Cordi-Geopolymere S.A.
Priority date: 1997-01-15
Filing date: 1998-01-14
Publication date: 1998-07-23
Also published as: EP0891310A1; AU5871298A; FR2758323B1; FR2758323A1

Abstract

The invention concerns a method for making geopolymeric cement consisting in producing a reaction mixture containing (parts in weight of dry matter):reagent (I):100 parts by weight of aluminosilicate oxide [Si2O5,Al2O2]9[Si2O5,Al2(OH)3], or simplified below as (Si2O5Al2O2)(IV-V); reagent (II): 30-55 parts of alkali silicate in which the mol ratio M2O/SiO2 ranges between 0.5 and 0.8, M representing Na and/or K or the mixture Na+K; reagent (III): 80-110 parts of basic silicate, in glass state, consisting partly of gehlenite, akermanite and wollastonite; reagent (IV): 150-250 parts of alkali aluminosilicate containing at least 5 % by weight of (Na2O+K2O), preferably at least 8 % by weight; then in hardening said mixture by adding water: After hardening the geopolymeric cements are made of two distinct phases: a) a glass phase having a MAS NMR spectrum for 29Si with a band ranging between -85 and -89ppm, and a MAS NMR spectrum for 27Al with a resonance at 54-58ppm; b) a crystalline phase having a MAS NMR spectrum for 29Si with a band ranging between -90ppm and -115ppm, and a MAS NMR spectrum for 27Al with a resonance at 57ppm.

Description

Methods of making geopolymer cements and cements obtained by these methods.

The present invention describes methods which make it possible to reduce the cost price of geopolymer cements. These methods describe the use of alkaline alumino-silicates of geological origin.

Prior techniques.

There are two types of cement: hydraulic cements and geopolymenic cements. Geopolymen cements result from a mineral polycondensation reaction by alkaline activation, called geosynthesis, as opposed to traditional hydraulic binders in which hardening is the result of hydration of calcium aluminates and calcium silicates. As is customary in the profession, the comparison between the two modes of hardening is carried out within the framework of the standardization of physical tests carried out at 28 days. The means of investigation used is the Nuclear Magnetic Resonance spectrum. In the MASNMR spectrum for 27A |, the products resulting from geosynthesis or geopolymerization reaction, as recommended in the present invention, have a characteristic peak at 55 ± 5 ppm, attributed to coordination AI (IV) of type Q.4 ( 4Si). The hydration compounds obtained in traditional hydraulic binders have a peak at 0 ± 5 ppm, characteristic of coordination AI (VI), that is to say of calcium hydroxy-aluminate. The MASNMR spectrum of ²⁹ Sι also makes it possible to make a very clear differentiation between geopolymenic cements and hydraulic binders. If we represent the degree of polymerization of the tetrahedron S1O4 by Q _n (n = 0, 1,2,3,4), we can distinguish between monosilicates (Q ₀ ), disilicates (Qi), silicate groups (Q2), the grafted silicates (Q3) and the silicates forming part of a three-dimensional network (Q4). These degrees of polymerization are characterized in MASNMR of ²⁹ Sι by the following peaks: (Q ₀ ) from -68 to -76 ppm; (Qi) from -76 to -80; (Q2) from -80 to -85 ppm; (Q3) from -85 to -90 ppm; (Q4) from -91 to -130 ppm. The peaks characterizing the geopolymen cements are found in the range -85 to -100 ppm and correspond to the three-dimensional network (Q4) characteristic of poly (sialates) and poly (sιalate-siloxo). On the contrary, the results of the hydration of hydraulic binders leading to hydrated calcium silicate CSH (according to the terminology used in the chemistry of cements) produce peaks located in the range -68 to -85 ppm or monosilicate (Q ₀ ) or disilicate (Q1XQ2); Binders and cements have been proposed in the past based on geopolymeric reactions involving three of the four reactants employed in the present invention.

For example, the Davidovits / Sawyer US Pat. No. 4,509,985 and its European equivalent EP 153,097 describe geopolymeric compositions allowing the production of fast-hardening mortar. In the Davidovits / Sawyer patent, the so-called "standard" composition comprises a reaction mixture characterized by the molar ratios of the oxides: K ₂ O: SiO ₂ 0.32

SiO ₂ : AI ₂ O ₃ 4.12

H O: AI θ3 17.0

K ₂ O: AI ₂ O ₃ 1.33

H ₂ 0: K ₂ O 12.03 to which was added milled blast furnace slag.

In the compositions described by the Davidovits / Sawyer patent, use is made of soluble alkali silicate, in particular potassium silicate in which the molar ratio of oxides l <2θ: Siθ2 is of the order of 0.5 (or! <Θ : 2Siθ2). In the cost price of the geopolymeric mineral compositions described in the previous formulations, the most expensive part is that allocated to this potassium silicate. It was therefore very important to be able to very significantly reduce the cost price of this very expensive product, in order to be able to produce a geopolymeric cement whose price could be comparable to that of Portland cement. This is the main objective of the present invention.

Various methods have already been proposed in the prior art for reducing the amounts of this relatively expensive reagent. These different methods are grouped in Table 1 below. Thus in Heitzman US Pat. No. 4,642,137, the alkali silicate is manufactured in the in-situ mixture, by alkaline reaction with amorphous silica. However, these formulations according to the Heitzman patent do not harden at room temperature, since to obtain this rapid hardening, it is absolutely necessary to add Portland cement. In publication WO 92/04298, a rapidly hardening geopolymer cement is described in which potassium disilicate! <2 (H3Siθ4) 2 is used in powder form. We can already reduce the amount of alkali silicate in half. In the international publication WO 92/04300, it is recommended to manufacture the alkali silicate from various geological materials, such as amorphous silicas, proceeding by fusion at high temperature (around 1000-1250 ° C) with alkaline carbonate. The amounts of alkali silicate are either equivalent to those of the Davidovits / Sawyer patent or equal to that of the international publication WO 92/04298 (see Table 1). Note also the method described in the international publication WO 95/13995 which proposes the manufacture of a glass obtained by the fusion of natural alkaline aluminosilicate (volcanic rocks) at a temperature between 1000 ° C and 1350 ° C.

The present invention also makes it possible to reduce the amount of alkali silicate by 70-80% by a means different from those recommended in the prior art.

Statement of the invention.

The main object of the invention is to radically reduce the amounts of alkali silicate compared to the geopolymeric cements of the prior art. Compared to the Davidovits / Sawyer US Pat. No. 4,509,985, the method recommended in the present invention starts from the idea that it should be possible to replace a certain quantity of the reagent K2O produced by the chemical industry, by K2O extracted from volcanic rocks. . The method of the invention shows that certain volcanic rocks of the alkaline alumino-silicate type make it possible to reduce by 70-80% by weight the quantity of K2O of chemical origin.

Table I: composition of the cements of the prior art and of the present invention (parts by weight of dry matter).

EP 0153097 EP 0500845 Presents US 4,509,985 US 4,642,137 WO92 / 04300 WO92 / 04298 invention aluminosilicate oxide 100 100 80-140 100 100

Alkaline silicate 148 55-145 6-110 48-72 30-55 amorphous silica 0 70-215 40-500 0 0

Basic silicate 100 20-70 20-120 50-70 80-110

Alumina silicate fly ash 0 85-130 0 0 0

Alkaline aluminosilicate, M2θ> 5% 0 0 0 0 150-250

The process for manufacturing a geopolymeric cement which does not contain Portland cement, according to the present invention, consists in producing the reaction mixture whose components expressed as dry matter are: - reagent I: 100 parts by weight of an aluminosilicate oxide

[Si ₂ θ5, Al2θ2] 9 [Si2θ5, Al ₂ (OH) 3], having the cation Al in mixed coordination (IV-V) as determined by the analysis spectrum in Nuclear Magnetic Resonance MASNMR for ²⁷ AI, or for simplify in what follows,

(If ₂ θ5, AI ₂ θ2) (iv-V) ^•

- reagent II: 30-55 parts of sodium and / or potassium silicate in which the molar ratio M2θ / Siθ2 is between 0.5 and 0.8, M denoting Na and / or K or the Na + K mixture. - reagent III: 80-110 parts of basic silicate, in the vitreous state, composed in part of gehlinite, akermanite and wollastonite.

- reagent IV: 150-250 alkaline aluminosilicate parts containing at least

5% by weight of (Na2θ + I <2θ), preferably at least 8% by weight; then hardening said mixture by adding water.

The reagent (I), the aluminosilicate oxide of simplified formula (S ^' i2θ5, Al2θ2) (iv-V) / is obtained by calcination of a kaolinitic material at a temperature below 1000 ° C.

Reagent (II) is powdered sodium and / or potassium silicate, for example potassium disilicate K2 (H3Siθ4) 2, or sodium disilicate Na2 (H3Siθ4) 2, or potassium and potassium double disilicate sodium (K, Na) (H3Siθ) 2, or a mixture of alkaline silicate and solid NaOH / KOH. The alkali silicate can also be used in the form of an aqueous solution. The M2θ / Siθ2 molar ratio is generally between 0.5 and 0.8, M denoting Na and / or K or the Na + K mixture.

The reagent (III) is a weakly basic calcium silicate, that is to say having a Ca / Si atomic ratio of less than 1. It is obtained by using as basic material a basic calcium silicate, that is to say having a Ca / Si atomic ratio equal to or greater than 1 essentially characterized by its ability to generate, under the action of an alkaline attack, the formation of weakly basic calcium silicate, that is to say having a lower Ca / Si atomic ratio to 1, preferably close to 0.5.

The reagent (IV) is a geological material, alkaline aluminosilicate, in which the atomic ratio Si: Al is between 2.5 and 5, the molar ratio M2θ: Al2θ3 is between 0.7 and 1.1 and the molar ratio (M2θ + CaO ): AI2O3 is between 0.8 and 1.6. This alkaline aluminosilicate material is generally calcined at a temperature below 850 ° C, but some geological varieties can be used without calcination. The calcination has the advantage of reducing the amount of water that must be added to the mixture in order to obtain good fluidity with the mortar The prior art shows that the mechanical strengths of geopolymeric cements decrease when the amount of water increases. It will therefore generally be advantageous to carry out this calcination. Certain geological varieties, such as those described in Examples 2, 3, 6, have mechanical strengths which are substantially equivalent for the non-calcined (natural) product and the calcined product. The decision to calcine or not these alkaline aluminosilicates depends solely on the rheology of the mortars and concretes which will be obtained with these cements. The mixture of reagents which constitutes the assembly comprising the reagents (I) + (II) + (III), see Table 2, has a molar ratio

Ca ^{+ +} / (Si2θ5, Al2θ2) (i -V) Q ^{ui is} greater than 1 and a ratio (Na +, ⁺ , Ca ^{+ +} ) / (Si2θ5, Al2θ2) (iv-V) ^{u1 'is} greater than 1, 5. After hardening, the geopolymeric cement consists of two distinct phases: a) a so-called vitreous phase which has a MAS NMR spectrum for ²⁹ Si having a band between -85 and -89ppm, and a MASNMR spectrum for ²⁷ AI having a resonance at 54-58ppm. This so-called glassy phase is a geopolymeric compound consisting of groups (AIO4) of type 0_4 (4Si) polymerized with groups (Siθ4) of type Q_4 (3AI, lSi), associated with a hydroxylated aluminosilicate consisting of (Si0 ₄ ) ₃ (2Si, IAI, 10H); b) a crystalline phase which has a MAS NMR spectrum for ⁹ Si having a band between -90ppm and -115ppm, and a MAS-NMR spectrum ²⁷ AI having a resonance at 57ppm. This so-called crystalline phase corresponds to an alkaline aluminosilicate.

The geopolymeric cement obtained according to the methods described in the present invention is resistant to corrosion of sulfuric acid and it is not subject to the ASR reaction. The mechanical characteristics are good. Thus, the compressive strength at 28 days is between 25 Mpa and 60 Mpa, without adding special loads. It varies according to the particle size of the powdered elements. In general, the average particle size is between 7 microns and 10 microns.

Best Ways to Carry Out the Invention

In the methods of the invention, the reagent (I), the aluminosilicate oxide of simplified formula (Si2θ5, Al2θ2) (iv-v) / is obtained, as in the prior art, by calcination of a kaolinitic material at a temperature below 1000 ° C. Said calcination is carried out so that said aluminosilicate oxide has an analysis spectrum in Nuclear Magnetic Resonance MASNMR for ²⁷ AI having in addition the two main resonances at 20 ± 5 ppm [coordination AI (V)] and 50 ± 5 ppm [ AI (IV) coordination], a secondary resonance at 0 ± 5ppm of much lower intensity [AI (VI) coordination]. The kaolinitic material is generally a clay containing at least 30% by weight of the mineral kaolinite. The calcination is carried out at a temperature below 1000 ° C., this temperature varying with the method used. Calcination in a vertical or rotating oven takes place at a temperature between 650 ° C and 800 ° C. In the fluidized bed process, the temperature is between 700 ° C and 850 ° C. In the flash process, with a hot air current, the temperature is between 900 ° C and 1000 ° C. Certain industrial residues already contain the said aluminosilicate oxide (S ^' i2θ5, Al2θ2) (iv-V) like the ashes resulting from the combustion of coal in thermal power plants called low temperature or in a fluidized bed; calcined bauxite also contains a certain amount of (Si2θ5, Al2θ2) (iv-) - ⁰ⁿ P ^had also include calcination products of paper waste, loaded kaolin.

Reagent (II) is a water soluble alkali silicate. From the description of the Davidovits / Sawyer patent, a person skilled in the art knows that, in this alkaline silicate, the molar ratio M2θ: SiO2 (M denoting either Na, or K, or the mixture Na + K) must be close to 0.5, that is to say substantially correspond to a silicate M2θ: 2Siθ2, nH2θ, n being between 2 and 6. Preferably, in the method of the invention, M is K. Although the silicate of potassium is more expensive than sodium silicate, the properties of cements obtained with potassium silicate are much better than those obtained with sodium silicate. Indeed, experience shows that with a double sodium and potassium silicate, the cement thus obtained develops a lower compressive strength than that with potassium silicate. In the present invention, the molar ratio M2θ: Siθ2 is between 0.5 and 0.8. The alkali silicate can either be in the form of a water-soluble alkali silicate powder, or a mixture of powdered alkali silicate and solid NaOH / KOH, or in the form of a solution. In the case of the examples below, the solution contains 20-23% by weight of SiO 2, 20-26% by weight of K2O, and 50-55% by weight of water.

Reagent (III) is a basic calcium silicate, i.e. with the Ca / Si atomic ratio greater than or equal to 1, such as wollastonite Ca (Si0 ₃ ), gehlenite (2CaO.AI ₂ θ3.Si0 ₂ ), akermanite (2CaO. Mg0.2Si0). When the grains of these materials are brought into contact with the alkali silicate of the reagent (II), a desorption of CaO takes place very quickly so that the Ca / Si atomic ratio becomes less than 1 and tends towards 0.5. There is in situ production of calcium disilicate Ca (H3Siθ4) 2 which participates in the geopolymeric reaction.

Certain by-products of industrial treatments or of combustion at high temperature essentially contain the basic silicates gehlenite, akermanite, wollastonite and are therefore very suitable. We will cite, by way of nonlimiting example, blast furnace slag, certain slag and certain ash from high temperature thermal power stations, these products preferably being in the vitreous state. When we look under a microscope at hardened cements from the mixtures described in examples 1 to 10, we see that, in the case of blast furnace slag, the majority of the slag grains have disappeared. We only see an imprint of their initial shape, in the form of an envelope probably made of unreacted Akermanite. This process is very regular and can be completed in 30 minutes, at room temperature. However, as can be seen in Table 2, the amount of basic calcium silicate participating in the geopolymeric reaction is greater than that of the prior art. This is expressed by the molar ratios of the oxides connecting the reactants (I), (II) and (III) to each other.

Table 2: Molar ratio of the various oxides connecting the reagents (I), (II), (III) of the present invention and of the prior art. relationship between US ratios 4,509,985 WO 92/04298 Present invention molar reagents Examples 2 to 9 Examples 1 to 10

(II) / (I) Na ₂ 0, K2θ / (Si2θ5, Al ₂ θ2) 1.33 0.40-0.60 0.441

(III) / (I) Ca ++ / (Si2θ5, AI ₂ θ2) 0.9-1.6 0.60-0.40 1.29

(II) + (IH) / (I) Na ₂ 0, K2θ, CaO / (Si2θ5, Al2θ2) 2.2-2.9 1.0 1.731

The reagent (IV) is a geological material, alkaline aluminosilicate, which contains at least 5% by weight of Na2θ + K2θ. It belongs to the class of volcanic rocks. Tables 3 and 4 give the chemical characteristics of the alkaline aluminosilicates used in the examples below. They are very different from the alumina silicates described in US Pat. No. 4,642,137 which are either fly ash from power plants thermal coal, very poor in alkali, or calcined clays. It is also very different from the amorphous silica used in US patent 4,642,137 or from the geological material of international publication WO92 / 04300. In international application WO 92/04298, the use of amorphous silica is recommended, such as, for example, silica smoke, rice ash, but also silicas of geological origin such as diatomaceous earth, silicic smectites, some highly silicic pozzolans (with a high percentage of allophane and glass of volcanic origin). It is explained there, page 9, lines 17-21, that these materials of geological origin are considered as finely divided, reactive charges. The reactivity of these charges makes them react on the surface with the geopolymeric reaction medium, thus increasing the mechanical resistance of the mineral binder poly (sialate-siloxo).

It is believed that reagent IV of the present invention also reacts on the surface but with a different chemical mechanism. In fact, in all the patents of the prior art, the objective is to dissolve silica in order to transform it into soluble alkaline silicate. Therefore, in addition to the alkali silicate, sodium hydroxide NaOH and / or potassium KOH which must form alkali silicate with the amorphous silica. After hardening and geopolymerization, the cement of the prior art is of the tecto-alumino-silicate type, that is to say a three-dimensional structure in which the groups (SiO 4) are of type Q 4 exclusively. In the prior art, the MASNMR spectrum of ²⁹ Si is very characteristic since it has a resonance towards -92, -94 ppm, Q4 (2Si, 2AI) and a resonance around -110 ppm, Q4 (4Si). Examples of these spectra can be found in publication WO92 / 04300, Figure 7, and in the publication "Geopolymers: man-made rock geosynthesis and the resulting development of very early high strength cernent" by J. Davidovits, Journal of Materials Education , Flight. 16, numbers 2 & 3, pages 91-137, 1994, figure 13. The first resonance at -92. -94 ppm characterizes the matrix of the geopolymeric cement, the resonance at - 115 ppm being attributed to the siliceous filler.

Examples of the MASNMR spectrum of ²⁹ Si cements obtained by the method of the present invention are in Figure 1. These spectra are different from those of the prior art. They consist of two main resonances: the first is that of the so-called vitreous phase or geopolymeric matrix which results from the reaction between the reactants (I) - (II) - (III); the second is that of the so-called crystalline phase specific to reagent IV.

The so-called glassy phase has a MAS NMR spectrum for ²⁹ Si which has a band between -85 and -89ppm. The MAS-NMR spectrum for ²⁷ AI of this so-called glassy phase is 54-58ppm. The spectrum of all the hardened reagents (I) + (II) + (III) is identical to that of the glassy phase. Said vitreous phase is a geopolymeric compound consisting of an alkaline silico-aluminate structure which contains a group (AIO4) of the type

Q4 (4Si), polymerized with groups (Si0 ₄ ) of type Q4 (3AI, lSi), associated with a hydroxylated aluminosilicate consisting of (Siθ4) of type Q3 (2Si, lAI, 10H).

Said crystalline phase has a MAS NMR spectrum for ²⁹ Si which has a band between -90 and -115 ppm. The MAS-NMR spectrum for ²⁷ AI has a resonance at 57-58 ppm corresponding to (AIO4) of type Q4 (4Si).

Each reactive natural alkaline aluminosilicate IV has its very specific spectrum which is practically identical to that of the crystalline phase. It is believed that the alkaline action of the reaction mixture produces a hydrolysis of the surface of the crystalline phase, with the formation of the silanol -Si-OH ^" M ^{+ function} , M being either K or Na. It is believed that this surface hydrolysis is favored by the fact that this crystalline phase already contains in situ alkalis Na2θ, K2θ. It is also thought that the reaction between the matrix, glassy phase, and the reagent IV, crystalline phase, takes place by polycondensation between the hydroxyls -OH of the groups (Si0 ₄ ) type Q3 (2Si, IA, 10H) of the glassy phase and the silanol -Si-OH "M ⁺ at the surface of the crystalline phase.

The method of the invention is illustrated by the following Examples. They are not limiting on the overall scope of the invention as presented in the claims. All parts shown are by weight.

Examples 1 to 10:

In this group of examples the reaction mixture of the reactants (I) + (II) + (III) is unchanged. It is called "base". This base consists of the following mixture, parts by weight:

composition parts by weight

- reagent (I) calcined kaolin clay 30

- reagent (II) silicate solution of K,

(in po ids) K? 0: 26%, SiO? : 21%, H? 0: 53% 25

- reagent (III) blast furnace slag, average particle size 8 microns 27

- water 31 total base 113 By adding to 113 parts by weight of "base", 50 parts by weight of geological alkaline aluminosilicates described in Tables 3 and 4 (reagent IV), Examples 1 to 10 are carried out. The geological materials were selected in the context of the European research program Brite- Euram / Geocistem, referenced SAOl / SA07 / CAOl / CA02 / LAOl / LA02 / TO03 / ES03 / GC05 / TE03 (Dpt Scienze délia Terra, University of Cagliari, Italy, BRGM, Orléans, France, Facultat de Geologia, University of Barcelona, Spain).

The cement thus obtained, called paste, is poured without addition of filler, into a mold and allowed to harden at room temperature. The compressive strength Rc is measured at 28 days. For each of Examples 1 to 10, two cements were obtained, one containing the natural reagent (IV), the other containing the reagent (IV) which had previously been calcined at a temperature equal to or greater than 600 ° C. . In the context of Examples 1 to 10, the calcination took place at 800 ° C for 3 hours. The reagent (IV) was also ground to an average particle size of 8 microns.

Table 3: Chemical composition, by weight, of the geological alkaline aluminosilicates (reagent IV), used in Examples 1 to 10

Examples 1 2 3 4 5 6 7 8 9 10

Si0 ₂ 71.48 74.16 5aœ 5252 5535 8a42 57.94 57.61 56.50 56.76

Al ₂ 0 ₃ 14.55 ι 80 19.26 1641 19.20 10.80 17.66 ι s9 1586 1R45

Fe ₂ 0 ₃ 160 1.13 4.17 3.67 400 530 3.72 4.74 3.74 339

MgO 004 0.17 120 1.73 1.15 868 0.70 1.16 063 0.47

CaO 0.07 0.43 3.14 754 235 256 261 352 0.44 039

Na ₂ 0 069 433 222 058 235 150 350 325 621 728

K ₂ 0 10.41 469 8S0 634 825 835 799 760 563 5.77

Tι0 ₂ 0.16 0.13 0JB1 051 054 1.40 0.41 0.47 0.74 0.45

P ₂ 0 ₅ 004 002 0.15 0.17 0.17 0.76 0.13 0.19 <0.05 <0.05

MnO 001 002 0.16 0.10 0.13 009 0.12 0.16 027 025

Law. 036 052 223 10.43 600 1.15 5.76 256 934 667

The results are grouped in Table 5. They are averages of 4 samples for each mixture with natural or calcined geological material. The Maximum Rc is the value of the best resistance obtained for each geological deposit. It is not an average. Table 4: Petrographic type, chemical composition (expressed in moles) and atomic ratio for various geological alkaline aluminosilicates (reagent IV).

Example 1 Example 2 Example 3 Example 5 Example 6 Example 9 type Ignimbrite Tuff Lava Pumice Ignimbrite petrographic volcanic andesitic volcanic type A potassium lamproitic phonolitic

Si0 ₂ 1.191 1.236 0.967 0.922 0.973 0.936

Al ₂ 0 ₃ 0.142 0.135 0.188 0.188 0.105 0.155

Na ₂ 0 0.011 0.069 0.035 0.037 0.024 0.100

K ₂ 0 0.108 0.051 0.091 0.086 0.086 0.058

CaO 0.001 0.007 0.056 0.052 0.045 0.007

If: Al 4.25 4.55 2.59 2.44 4.6 3.03

(Na + K): AI 0.767 0.888 0.670 0.654 1.047 1.019

(Na + K + Ca) - Al 0.845 0.940 0.968 0.930 1.476 1.067

Table 5: Resistance to compression Rc at 28 days, Mpa on the dough, without load

Examples 1 2 3 4 5 6 7 8 9 10

Rc Mpa, natural 48 50 46 31 33 50 30 36 34 33

Rc Mpa, calcined 44 45 54 43 51 51 39 47 51 45

Rc Mpa, maximum 67 63 59 55 67 56 40 61 60 47

In general, calcination very significantly increases the mechanical resistance. It is however obvious that, when the geological deposit allows it, this calcination can be avoided and consequently the cost of manufacturing the geopolymeric cement of the invention can be reduced.

FIG. 1 shows the MASNMR spectra for ²⁹ Si of each geopolymeric cement obtained in examples 1 to 10. All the spectra consist of the addition of two spectra, one belonging to the glassy phase (identical to that of all reagents I + II + III), the other in the crystalline phase (identical to that of reagent IV geological). Example 2 in Figure 1 shows these two spectra as well as the full spectrum. In the other Examples of Figure 1, we find both the full spectrum and the spectrum of the glassy phase. Example 11:

With the ingredients and the geological material of Example 2, the physico-chemical properties of the mortars are studied by comparing them with a hydraulic binder based on Portland cement, for example the CEM I 42.5 R from Cementi Buzzi (Italy). The sand + cement mixture is carried out according to the European standard and procedure, namely: the powdered reagents (I), (III) and (IV) are homogenized for 30 sec with the standardized sand (ISO sand), then the liquid and water reagent (II), mixing for 270 sec, and finishing at high speed for 60 sec. The prisms are shaped in standard molds (DIN 1164). The mortar contains 450 parts of sand for 190 parts of cement + water.

In order to obtain good workability of the mortar, the geopolymeric cement was produced with the following mixture:

- reagent (I) 23 parts - reagent (III) 20.3 parts

- reagent (IV) 56.7 parts

- reagent (II) 23.4 parts

- water 29 parts

- superplasticizer (naphthalene sulfonate): 1% by weight of the cement

The mortar hardens after 30 minutes. It remains in the mold for 24 hours, then it is removed from the mold and immersed in water. Its resistance to compression and bending is measured at 24 h (demolding), 7 days (in water) and 28 days (in water). The values are as follows: 24_h 7d 28d

Compression resistance (N / mm2) 10.5 34 42.5

Flexural strength (N / mm2) 2.8 5.8 7.4

Example 12:

Prisms are made with the mortar of Example 11 in order to be able to follow the resistance to chemical corrosion, in comparison with prisms made with a hydraulic cement CEM I 42.5 R from Cementi Buzzi (Italy). Corrosion is measured at:

- sulfuric acid: after 24 hours in the mold, the prism is immersed in an aqueous solution containing 5% by weight of sulfuric acid. We measure the weight loss and the resistance to compression and bending at 1d, 7d, 28d. After 28 days, the acid solution has a pH = 0.6. The results are given in FIG. 2.

- the alkali-ASR aggregate reaction: accelerated test according to the Danish standard method. The dimensional variation is measured at 1d, 5d, 14d. The results are given in FIG. 3.

- the sulfate reaction: according to standard ASTM C 1012. The dimensional variations are measured over a long period (6 months). The results are given in FIG. 4.

In all of these chemical corrosion tests, the cements according to the invention have a higher resistance than that of Portland cement.

The reagent (II), an alkaline silicate, is introduced into the reaction mixture, either in the form of a powder, or of a mixture of powdered silicate and solid NaOH / KOH, or in the form of an aqueous solution. The prior art indicates to us that the powdered form makes it possible to obtain mortars which have a relatively long setting time, while developing a mechanical resistance greater than that provided by a reagent in aqueous solution. Only the applications will decide on the choice of one or the other physical form of the alkali silicate. The choice between potassium silicate or sodium silicate is above all dictated by economic considerations, sodium silicate being cheaper. However, experience shows that cements containing only sodium silicate have a low freeze / thaw resistance, compared to cements with potassium silicate. The mixture (2O, Na2θ) in the alkaline silicate must therefore be established according to this freeze / thaw test. It seems obvious that, in regions where the risk of freezing is zero, the choice will be made on a formulation richer in Na2θ than in K2O. Those skilled in the art will be able to determine the best quality for its cement and the most economical alkali silicate composition, without departing from the scope of the invention.

When making mortars and concretes, and during encapsulation and solidification of materials, we can add to these cements the various additives and auxiliary products used by those skilled in the art to improve rheology and behavior hydraulic cements. A particularly interesting additive is silica smoke. As is the case with traditional hydraulic cements, silica smoke here also improves the long-term properties of cements geopolymers. This addition of silica is accompanied, in the MAS NMR spectrum for ²⁹ Si of hardened cement, by the appearance of a resonance at - 110 ± 5 ppm, identical to that already present in the geological reagent IV of Example 1 in Figure 1. This is proof that this silica smoke, unlike the prior art already discussed above, is not transformed into alkaline silicate, but acts as a reactive fine filler.

The applications of geopolymer cements obtained according to the methods of the invention are multiple. First of all, the amount of alkali silicate has been reduced from 70% to 80% compared to the prior art, making it possible to very significantly lower the price of these cements. Then, their manufacture requires very little energy and generates very little release of greenhouse gases such as carbon dioxide Cθ2-Us can therefore advantageously replace traditional hydraulic cements in building and public works applications. They have the physicochemical properties of the geopolymeric binders and cements described in the prior art. They can therefore be used in encapsulation and solidification applications of toxic or radioactive substances, mineral or organic, and also in the stabilization of mining waste. These cements are also temperature stable. Unlike Portland cement, which explodes as a result of the release of its hydration water, geopolymeric cement can be quickly dried from its constituent water, then mounted at temperatures between 400 ° C and 1000 ° C, without damage. It is therefore possible to agglomerate substances which must undergo these temperature variations.

Of course, various modifications can be made by those skilled in the art to the methods and cements Geopolymers which have just been described by way of example, without departing from the scope of the invention.

Claims

1) Method for manufacturing a geopolymeric cement resulting from the mixture of: - reagent (I): aluminosilicate oxide

[Si2θ5, AI ₂ θ2] 9 [Si2θ5, Al2 (OH) 3], having the cation Al in mixed coordination (IV-V) as determined by the analysis spectrum in Nuclear Magnetic Resonance MASNMR for ²⁷ AI, or to simplify in the following,

- reagent (II): soluble alkaline silicate (M2θ, Siθ2), M denoting Na and / or K or the Na + K mixture;

- reagent (III): basic silicate, in a vitreous state, partly composed of gehlinite, akermanite and wollastonite; characterized in that in order to reduce the amount of alkali silicate in the reagent (II), compared with the prior art, a natural alkaline aluminosilicate geological material containing at least 5% by weight of (Na2θ + K2θ) is added to the mixture , called reagent (IV), the said reagent (IV) alkaline aluminosilicate geological material, having an atomic ratio Si: Al between 2.5 and 5, a molar ratio M2Û: Al2θ3 between 0.7 and 1.1 and a molar ratio (M2θ + CaO): AI2O3 between 0.8 and 1.6; then reacting, at room temperature, all of the reactants (I), (II), (III) and (IV).

2) Method according to claim 1, characterized in that said reagent (IV), an alkaline aluminosilicate geological material, is used either in the natural state or after having undergone calcination, without vitrification, at a temperature below 850 ° vs.

3) Method according to claim 1, in which the reagent (II) alkali silicate has an M2θ / Siθ2 molar ratio greater than 0.5, preferably between 0.5 and 0.8, characterized in that in the assembly consisting of the reagents (I) + (II) + (III), the molar ratio

Ca ^{+ +} / (Si2θ5, Al2θ2) (i -V) ^is greater than 1 and the molar ratio (Na ⁺ , K +, Ca ^{+ +} ) / (Si2θ5, Al2θ2) (iv-V) ^is greater than 1.5.

4) Method for manufacturing a geopolymeric cement according to any one of claims 1) to 3), characterized in that it consists in carrying out the following reaction mixture (parts by weight of dry matter):

- reagent (I): 100 parts by weight of an aluminosilicate oxide

[Si ₂ θ5, Al2θ2] 9 [Si2θ5, AI ₂ (OH) 3], having the cation Al in mixed coordination (IV-V) as determined by the analysis spectrum in Nuclear Magnetic Resonance MASNMR for ²⁷ AI, or for simplify in what follows,

(Si2θ ₅ , Al2θ ₂ ) (iv-V) •

- reagent (II): 30-55 parts of soluble alkaline silicate in which the molar ratio M2θ / Siθ2 is between 0.5 and 0.8, M denoting Na and / or K or the Na + K mixture. - reagent (III): 80-110 parts of basic silicate, in the vitreous state, partly composed of gehlinite, akermanite and wollastonite.

- reagent (IV): 150-250 alkaline aluminosilicate parts containing at least

5% by weight of (Na ₂ 0 + K 0); then hardening said mixture by adding water.

5) Method according to any one of claims 1) to 4), characterized in that the said alkaline silicate solube is added in the form of an aqueous solution in which the molar ratio M2O / S1O2 is between 0.5 and 0.8, M denoting either Na or K, or the Na + K mixture.

6) Method according to any one of claims 1) to 4), characterized in that said soluble alkaline silicate is added in the form of powder or powder mixture containing the alkali silicate and solid NaOH / KOH, in which the M2Û / Siθ2 molar ratio is between 0.5 and 0.8, M denoting either Na or K, or the Na + K mixture.

7) Geopolymer cement obtained according to any one of Claims 1) to 6), characterized in that, after hardening, the said cement consists of two distinct phases: a) a so-called vitreous phase which has a MAS NMR spectrum for ²⁹ If having a band between -85 and -89ppm showing a degree of polymerization of the tetrahedron (Si04) of type Q3 (2Si, IA, 10H), and a MAS-NMR spectrum for ²⁷ AI having a resonance at 54-58ppm corresponding to (AI04) of type Q4 (4Si). b) a crystalline phase which has a MAS NMR spectrum for ²⁹ Si having a band between -90ppm and -115ppm, and a MASNMR ²⁷ AI spectrum having a resonance at 57ppm.

8) Geopolymer cement used to stabilize chemical waste or mining waste, resistant to corrosion of sulfuric acid and not subject to the aicali-aggregate reaction ASR, obtained according to any one of claims 1 to 6.

9) Geopolymeric cement which can be dried and mounted up to temperatures between 400 ° C and 1000 ° C, obtained according to any one of claims 1 to 6.

10) Geopolymeric cement, the production of which produces very little carbon dioxide CO2 with greenhouse effect, obtained according to any one of claims 1 to 6.