FR2758323A1 - METHODS OF MANUFACTURING GEOPOLYMERIC CEMENTS AND CEMENTS OBTAINED BY THESE METHODS - Google Patents

Abstract

The invention concerns a method for making geopolymeric cement consisting in producing a reaction mixture containing (parts in weight of dry matter):<u>reagent (I):</u>100 parts by weight of aluminosilicate oxide [Si2O5,Al2O2]9[Si2O5,Al2(OH)3], or simplified below as (Si2O5Al2O2)(IV-V); <u>reagent (II):</u> 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; <u>reagent (III):</u> 80-110 parts of basic silicate, in glass state, consisting partly of gehlenite, akermanite and wollastonite; <u>reagent (IV):</u> 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 <29>Si with a band ranging between -85 and -89ppm, and a MAS NMR spectrum for <27>Al with a resonance at 54-58ppm; b) a crystalline phase having a MAS NMR spectrum for <29>Si with a band ranging between -90ppm and -115ppm, and a MAS NMR spectrum for <27>Al with a resonance at 57ppm.

Description

Methods of manufacturing geopolymeric cements and cements obtained by these methods.

The present invention describes methods which make it possible to reduce the cost price of geopolymeric cements. These methods describe the use of alkaline aluminosilicates of geological origin.

Prior techniques.

There are two types of cement: hydraulic cements and geopolymeric cements. Geopolymeric cements result from a reaction of mineral polycondensation 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 hardening modes is carried out within the framework of the standardization of the physical tests carried out at 28 days. The means of investigation used is the Nuclear Magnetic Resonance spectrum. In the MASNMR spectrum for 27Al, the products resulting from the geosynthesis or geopolymerization reaction, as recommended in the present invention, have a characteristic peak at 55 + 5 ppm, attributed to the Al (IV) type coordination.
Q4 (4Si). The hydration compounds obtained in traditional hydraulic binders have a peak at 0 + 5 ppm, characteristic of the Al (VI) coordination, ie calcium hydroxyaluminate. The MASNMR spectrum of 29Si also makes it possible to make a very clear differentiation between geopolymeric cements and hydraulic binders. If we represent the degree of polymerization of the SiO4 tetrahedron by Qn (n = 0,1,2,3,4), we can distinguish between monosilicates (po), disilicates (Qi), silicate groups (Q2 ), grafted silicates (Q3) and silicates forming part of a three-dimensional network (Q4). These degrees of polymerization are characterized in MASNMR of 29Si by the following peaks: (OQ) 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 geopolymeric cements are found in the -85 to -100 ppm zone and correspond to the three-dimensional network (Q4) characteristic of poly (sialates) and poly (sialatesiloxo). On the contrary, the results of the hydration of hydraulic binders leading to hydrated calcium silicate CSH (according to the terminology used in cement chemistry) produce peaks located in the -68 to -85 ppm zone, i.e. the monosilicate (QO) or disilicate (Q1) (Q2);
Binders and cements based on geopolymeric reactions involving three of the four reagents employed in the present invention have been proposed in the past.

Thus, for example, the Davidovits / Sawyer patent US 4,509,985 and its European equivalent EP 153,097 describe geopolymeric compositions allowing the production of rapid-hardening mortar. In the Davidovits / Sawyer patent, the so-called "standard" composition comprises a reaction mixture characterized by the molar ratios of the oxides
K2O: SiO2 0.32
sio2: Al2 3 4.12
H2O: Al203 17.0
K2O: Al203 1.33
H2O: K20 12.03 to which has been added crushed 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 the oxides K2O: SiO2 is of the order of 0.5 (ie K2O: 2SiO2). 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 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 together in Table 1 below. Thus, in Heitzman US Pat. No. 4,642,137, the alkali silicate is produced 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 in order to obtain this rapid hardening it is absolutely necessary to add Portland cement. In publication WO 92/04298, a rapidly hardening geopolymeric cement is described in which powdered potassium disilicate K2 (H3SiO4) 2 is used. The amount of alkali silicate can already be reduced in this way. In the international publication WO 92/04300, it is recommended to manufacture the alkali silicate from various geological materials, such as amorphous silicas, by proceeding by melting at high temperature (around 1000-12500C) with alkali carbonate. The amounts of alkali silicate are either equivalent to those of the Davidovits / Sawyer patent or equal to that of international publication WO 92/04298 (see Table 1). Note also the method described in international publication WO 95/13995 which proposes the manufacture of a glass obtained by melting natural alkali aluminosilicate (volcanic rocks) at a temperature between 10000C and 13500C.

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

Disclosure 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 patent US 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 K2O reagent produced by the chemical industry, by K2O extracted from volcanic rocks. . The method of the invention shows that certain volcanic rocks of the alkaline aluminosilicate type make it possible to reduce by 70-80% by weight the amount 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 Present
US 4,509,985 US 4,642,137 WO92 / 04300 WO92 / 04298 invention aluminosilicate oxide 100 100 80-140 100 100
Alkali 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
Fly ash alumina silicate 0 85-130 0 0 0
Alkali aluminosilicate, M2O> 5% 0 0 ~ 0 0 150-250
The method of manufacturing a geopolymeric cement which does not contain Portland cement, according to the present invention, consists in producing the reaction mixture, the components of which, expressed as dry matter, are:
- reagent 1: 100 parts by weight of an aluminosilicate oxide [Si2O5, Al2O2] 9 [Si2O5, Al2 (OH) 3],
having the Al cation in mixed coordination (IV-V) as determined
by the analysis spectrum in Nuclear Magnetic Resonance
MASNMR for 27Al, or to simplify in the following, (si2o5tAl2o2) (Iv-v)
- reagent II: 30-55 parts of sodium and / or potassium silicate in
in which the M2O / SiO2 ratio is between 0.5 and 0.8, M denoting
Na and / or K or the mixture of Na + K.

- reagent III: 80-110 parts of basic silicate, in the vitreous state, compound
partly of gehlinite, akermanite and wollastonite.

- reagent IV: 150-250 parts alkali aluminosilicate containing at least
5% by weight of (Na20 + K2O), preferably at least 8% by weight; then hardening said mixture by adding water.

The reagent (I), the aluminosilicate oxide of simplified formula (Si2051A1202) (IV-V) r is obtained by calcining a kaolinitic material at a temperature below 10000C.

Reagent (II) is powdered sodium and / or potassium silicate, for example potassium disilicate K2 (H3SiO4) 2, or a mixture of silicate and solid NaOH / KOH. The alkali silicate can also be used in the form of an aqueous solution. In the examples illustrating the methods of the present invention, use will be made of a solution of potassium silicate containing 20-23% by weight of SiO2, 20-26% by weight of K2O, and 50-55% by weight of 'water.

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 raw 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, i.e. 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 Si: Al atomic ratio is between 2.5 and 5, the M2O: Al203 molar ratio is between 0.7 and 1.1 and the molar ratio (M2O + CaO ): Al203 is between 0.8 and 1.6. This alkali aluminosilicate material is usually calcined at a temperature below 8500C, but some geological varieties can be used without calcination. Calcination has the advantage of reducing the amount of water that must be added to the mixture in order to obtain good fluidity in the mortar. The prior art shows that the mechanical strengths of geopolymeric cements decrease when the quantity of water increases. It will therefore, in general, 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 uncalcined (natural) product and the calcined product. The decision whether or not to calcine these alkaline aluminosilicates depends solely on the rheology of the mortars and concretes which will be obtained with these cements.

The mixture of reactants which constitutes the set comprising the reactants (I) + (II) + (III), see Table 2, has a molar ratio
Ca ++ / (Si2O5, Al2O2) (IV-V) which is greater than 1 and a (Na +, K +, Ca ++) / (5i2Os, Al2O2) (Iv v) ratio which 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 29Si
having a band between -85 and -89ppm, and a MAS spectrum
NMR for 27Al having a resonance at 54-58ppm. This so-called phase
vitreous is a geopolymeric compound made up of groups
(ale4) type Q4 (4Si) polymerized with (SiO4) groups of
type Q4 (3Al, lSi), associated with a hydroxylated aluminosilicate consisting of
of (SiO4) of type Q3 (2Si, îAl, îOH)
b) a crystalline phase which has a MAS NMR spectrum for 29Si
having a band between -90ppm and -115ppm, and a spectrum
MAS-NMR 27Al having a resonance at 57ppm. This so-called phase
crystalline corresponds to an alkaline aluminosilicate.

The geopolymeric cement obtained according to the methods described in the present invention is resistant to corrosion by 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 any particular loads. It varies depending on 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 (Si205, Al202) (IV V), is obtained, as in the prior art, by calcining a kaolinitic material at a temperature below 10000C. Said calcination is carried out so that said aluminosilicate oxide has a Resonance analysis spectrum
Nuclear Magnetic MASNMR for 27Al having in addition to the two main resonances at 20 + 5ppm [coordination Al (V) J and 50 + 5ppm [coordination Al (IV) j, a secondary resonance at 0 + 5ppm of much lower intensity [coordination Al (VI)]. The kaolinitic material is generally a clay containing at least 30% by weight of the kaolinite mineral.

Calcination is carried out at a temperature below 10000C, this temperature varying with the method used. Calcination in a vertical or rotary kiln is carried out at a temperature between 6500C and 8000C. In the fluidized bed process, the temperature is between 7000C and 8500C. In the flash process, hot air current, the temperature is between 9000C and 10000C. Certain industrial residues already contain the so-called aluminosilicate oxide (Si205, Al202) (IV v) such as the ash resulting from the combustion of coal in thermal power stations called at low temperature, in a fluidized bed, at 8000C; calcined bauxite also contains a certain amount of (Si205, Al202) (IV V). Mention may also be made of the products of calcination of stationery waste, loaded with kaolin.

Reagent (II) is a water soluble alkali silicate. From the description of the Davidovits / Sawyer patent, those skilled in the art know that, in this alkali silicate, the M2O: SiO2 ratio (M denoting either Na, or K, or the mixture of Na + K) must be close to 0 , 5, that is to say correspond substantially to a silicate M2O: 2SiO2, nH2O, n being between 2 and 6. Preferably, in the method of the invention, M is K. Although the potassium silicate is more expensive than sodium silicate, the properties of cements obtained with potassium silicate are much superior to those obtained with sodium silicate. Indeed, experience shows that with a double silicate of sodium and potassium, the cement thus obtained develops a lower compressive strength than that with potassium silicate. In the present invention, the M2O: SiO2 ratio 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 SiO2, 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, like wollastonite
Ca (SiO3), gehlenite (2CaO.Al203.SiO2), akermanite (2CaO. MgO.2SiO2).

When the grains of these materials are brought into contact with the alkali silicate of the reagent (II), a desorption of CaO very quickly occurs 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 (H3SiO4) 2 which takes part in the geopolymeric reaction.

Certain industrial treatment or high temperature combustion by-products 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 glassy state. When we look under a microscope at the cements hardened 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 form, in the form of an envelope presumably made of akermanite which has not reacted. This process is very smooth 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 interconnecting the reactants (I), (II) and (III).

Table 2: Molar ratio of the different oxides linking the reactants together
(I), (II), (III) of the present invention and of the prior art.

relationship between ratios US 4,509,985 WO 92/04298 Present inventio molar reagents Examples 2 to 9 Examples 1 to 10 (II) / (I) Na2O, K2O / (Si2O5, Al2O2) 1.33 0.40-0.60 0.441 (III) / (I) Ca ++ / (Si2O5, Al2O2) 0.9-1.6 0.60-0.40 1.29 (II) + (III) / (I) Na2O, K2O, CaO / (Si205, Al2O2) 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 Na2O + K2O. It belongs to the class of volcanic rocks. Tables 3 and 4 give the chemical characteristics of the alkali aluminosilicates used in the examples below. They are very different from the aluminas silicates described in US Pat. No. 4,642,137 which are either fly ash from coal-fired power stations, very low in alkali, or calcined clays. It is also very different from the amorphous silica used in the patent.
US 4,642,137 or the geological material of the international publication WO92 / 04300. In international application WO 92/04298, the use of amorphous silica, such as silica fume, rice ash, but also silicas of geological origin such as diatomaceous earth, silica smectites, is recommended, some strongly silicic pozzolans (with a high percentage of allophane and glass of volcanic origin). It is explained, page 9, lines 17-21, that these materials of geological origin are considered as finely divided, reactive charges. The reactivity of these fillers causes them to react at the surface with the geopolymeric reaction medium, thus increasing the mechanical resistance of the inorganic poly (sialate-siloxo) binder.

It is believed that Reagent IV of the present invention also reacts on the surface but with a different chemical mechanism. Indeed, in all the patents of the prior art, the objective is to dissolve silica in order to transform it into soluble alkali silicate. Therefore, in addition to the alkali silicate, sodium hydroxide NaOH and / or potassium KOH is added, which will have to form alkali silicate with the amorphous silica. After hardening and geopolymerization, the cement of the prior art is of the tecto-aluminosilicate type, ie a three-dimensional structure in which the groups (SiO4) are of the Q4 type exclusively. In the prior art, the MASNMR spectrum of 29si is very characteristic since it exhibits a resonance towards -92, -94 ppm, Q4 (2Si, 2Al) and a resonance towards -110 ppm,
Q4 (4Si). Examples of these spectra can be found in the publication W092 / 04300, figure 7, and in the publication Geopolymers: man-made rock geosynthesis and the resulting development of very early high strength cernent par 3. Davidovits, Journal of Materials Education, Vol . 16, numbers 2 & 3, pages 91-137, 1994, figure 13. The first resonance at -92, -94 ppm characterizes the very matrix of the geopolymeric cement, the resonance at
115 ppm being attributed to the siliceous filler.

Examples of the MASNMR spectrum of 29Si of the cements obtained by the method of the present invention are in FIG. 1. These spectra are different from those of the prior art. They consist of two resonances
main: 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 29Si which has a band between -85 and -89ppm. The MAS-NMR spectrum for 27Al of this so-called glass phase is 54-58ppm. The spectrum of all the hardened reactants (I) + (II) + (III) is identical to that of the vitreous phase. Said vitreous phase is a geopolymeric compound consisting of an alkaline silico-aluminate structure which contains an (ale4) group of type
Q4 (4Si), polymerized with (SiO4) groups of Q4 type (3Al, lSi), associated with a hydroxylated aluminosilicate consisting of (SiO4) of Q3 type (2Si, lAl, lOH).

The so-called crystalline phase has a MAS NMR spectrum for 29Si which has a band between -90 and -115ppm. The MAS-NMR spectrum for 27Al has a resonance at 57-58 ppm corresponding to (ale4) of type Q4 (4Si).

Each natural alkaline aluminosilicate, reagent 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 hydrolysis of the surface of the crystalline phase, with the formation of the silanol -Si function.
OH- M +, 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 Na2O, K2O. It is also believed that the reaction between the matrix, glassy phase, and the reagent IV, crystalline phase, takes place by polycondensation between the -OH hydroxyls of the (SiO4) groups of the Q3 type (2Si, lAl, lOH) of the glassy phase and silanol -Si-OH- M +. at the surface of the crystalline phase.

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

Examples i 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) K silicate solution,
K2O: 26%, SiO2: 21%, H2O: 53% 25 - blast furnace slag reagent (III)
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 alkali aluminosilicates described in Tables 3 and 4 (reagent IV), Examples 1 to 10 are produced. The cement thus obtained, called paste, is poured without addition of filler, in 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 been previously calcined at a temperature equal to or greater than 6000C.

In the context of Examples 1 to 10, the calcination took place at 8000C for 3 hours. Reagent (IV) was also ground to an average particle size of 8 microns.

Table 3: Chemical composition, by weight, of alkali aluminosilicates
geological (reagent IV), used in Examples 1 to 10
Examples 1 2 3 4 5 6 7 8 9 10
SiO2 71.48 74.16 58.06 5252 55.35 88.42 57.94 57.61 56.50 56.76
Al203 14.55 1380 19.26 16.41 19.20 10.80 17.66 18.59 15.86 18.45 Fe203 160 1.13 4.17 3.67 400 580 3.72 4.74 374 339
MgO OD4 0.17 120 173 1.15 868 0.70 1.16 063 0.47
CaO OD7 0.43 3.14 754 295 256 261 352 0.44 099
Na2O 069 433 222 058 235 150 350 325 621 728
K20 10.41 489 880 634 825 835 799 7.60 563 5.77
TiO2 0.16 0.13 0.61 051 054 1.40 0.41 0.47 0.74 0.45
P205 004 OD2 0.15 0.17 0.17 0.76 0.13 0.19 <0.05 <005
MnO OD1 002 0.16 0.10 0.13 OD9 0.12 0.16 027 025
Law. 096 092 223 1Q43 600 1.15 576 256 934 667
The results are grouped in Table 5. They are averages of 4 samples for each mixture with natural or calcined geological material. The Rc Maximum is the value of the best resistance obtained for each geological deposit. She is not an average.

Table 4: Petrographic type, chemical composition (expressed in moles) and ratio
atomic for various geological alkali aluminosilicates (Reacttf IV).

Example 1 Example 2 Example 3 Example 5 Example 6 Example 9 Lava Tuff Ignimbrite Pumice Lava Petrographic andesitic volcanic ignimbrite type A potassium lamproitic phonolibque
SiO2 1.191 1.236 0.967 0.922 0.973 0.936
Al203 0.142 0.135 0.188 0.188 0.105 0.155
Na20 0.011 0.069 0.035 0.037 0.024 0.100 K2O 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 Si: AI 4.25 4.55 2.59 2.44 4.6 3.03 (Na + K): Al 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: Compressive strength Rc at 28 days,
Mpa on dough, no 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 increases the mechanical strength very appreciably. However, it is 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.

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

In the other Examples of Figure 1, both the full spectrum and the glass phase spectrum are found.

Example 11:
With the ingredients and the geological material of Example 2, the physicochemical properties of the mortars are studied by comparing them to a hydraulic binder based on Portland cement, for example CEM I 42.5 R from
Cementi Buzzi (Italy). The sand + cement mixture is carried out according to the European procedure and standard, namely: the powdered reagents (I), (III) and (IV) are homogenized for 30 sec with the standardized sand (sand
ISO), then add the liquid reagent (II) and water with mixing for 270 sec, and finish 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 made 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
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 compressive and flexural strength is measured at 24 h (at demolding), 7 days (in water) and 28 days (in water). The values are as follows:
24 h 7 d 28 d
Compressive strength (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 monitor 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
measures weight loss and resistance to compression and
bending at ld, 7d, 28d. After 28 days, the acidic solution has a pH = 0.6.

The results are given in figure 2.

- the ASR alkali-aggregate reaction: accelerated test according to the standard method
from Denmark. The dimensional variation is measured at lj, 5j, 14j.

The results are given in figure 3.

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

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

The reagent (II), an alkali silicate, is introduced into the reaction mixture, either in the form of a powder, or of a mixture of powdered silicate and of solid NaOH / KOH, or in the form of an aqueous solution. The prior art tells us that the powder form makes it possible to obtain mortars which have a relatively long setting time, while developing a mechanical strength greater than that provided by a reagent in aqueous solution. Only applications will decide whether to choose one or the other physical form of the alkali silicate.

During the preparation of mortars and concretes, and during the encapsulation and solidification operations of the materials, it is possible to add to these cements the various additives and auxiliary products used by those skilled in the art to improve the rheology and the behavior. hydraulic cements. A particularly interesting additive is silica fume.

As is the case with traditional hydraulic cements, silica fume here also improves the long-term properties of geopolymeric cements. This addition of silica is accompanied, in the spectrum
MAS NMR for 29Si of the hardened cement, by the appearance of a resonance at 1101 5 ppm, identical to that already present in the geological reagent IV of Example 1 of Figure 1. It is the proof that this smoke of silica, unlike the prior art already discussed above, is not transformed into alkali silicate, but acts as a reactive fine filler.

The applications of geopolymeric cements obtained according to the methods of the invention are numerous. First of all, the amount of alkali silicate has been reduced from 70% to 80% compared to the prior art, making it possible to lower the price of these cements very appreciably. Then, their manufacture requires very little energy and generates very little release of greenhouse gases such as carbon dioxide CO2. They can therefore advantageously replace traditional hydraulic cements in building and public works applications.

They have the physicochemical properties of binders and geopolymeric cements described in the prior art. They can therefore be used in applications for the encapsulation and solidification 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 water of formation, then raised to temperatures between 4000C and 10000C, 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 geopolymer methods and cements which have just been described solely by way of example, without departing from the scope of the invention.

Claims (10)

Claims 1) Method of manufacturing a geopolymeric cement which does not contain Portland cement, 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 [Si2O5, Al2O2] 9 [Si2O5, Al2 (OH) 3], having the Al cation in mixed coordination (IV-V) as determined by the analysis spectrum in Nuclear Magnetic Resonance MASNMR for 27Al, or to simplify in the following, (Si205rA1202) (IV-V) - reagent (II): 30-55 parts of alkali silicate in which the ratio M2O / SiO2 is between 0.5 and 0.8, M denoting Na and / or K or the mixture of Na + K. partly composed of gehlinite, akermanite and wollastonite. - reagent (III): 80-110 parts of basic silicate, in the vitreous state, 5% by weight of (Na2O + K2O); then hardening said mixture by adding water. - reagent (IV): 150-250 parts alkali aluminosilicate containing at least 2) Method according to claim 1, characterized in that in said reagent (IV) alkali aluminosilicate, the atomic ratio Si: Al is between 2.5 and 5, the molar ratio M2O: Al203 is between 0.7 and 1.1 and the molar ratio (M2O + CaO): Al2O3 is between 0.8 and 1.6. 3) Method according to claim 1, characterized in that in the assembly consisting of the reactants (I) + (II) + (III), the molar ratio Ca ++ / (Si2O5, Al2O2) (îVV) is greater than 1 and the ratio (Na +, K +, Ca ++) / (Si205, A1202) (I.V-V) is greater than 1.5. 4) Method according to claim 1, characterized in that said sodium and / or potassium silicate is added in the form of an aqueous solution containing 20-23% by weight of SiO2, 20-26% by weight of K2O , and 50-55% by weight of water. 5) Method according to claim i, characterized in that said sodium silicate and / or potassium is added in the form of powder or powder mixture containing the alkali silicate and solid NaOH / KOH. 6) Geopolymeric cement obtained according to any one of claims 1) to 5), characterized in that, after hardening, said cement consists of two distinct phases: a) a so-called vitreous phase which has a MAS NMR spectrum for 29Si having a band between -85 and -89ppm, and a MAS spectrum NMR for 27Al having a resonance at 54-58ppm. NMR 27Al having a resonance at 57ppm. a band between -90ppm and -115ppm, and a MAS spectrum b) a crystalline phase which has a MAS NMR spectrum for 29Si having 7) Geopolymeric cement resistant to corrosion of sulfuric acid and not subject to the alkali-aggregate reaction ASR, obtained according to any one of claims 1 to 5. 8) Geopolymeric cement which can be dried and mounted up to temperatures between 4000C and 10000C, obtained according to any one of claims 1 to 5. 9) Geopolymeric cement used to stabilize chemical waste or mining waste, obtained according to any one of claims 1 to 5. 10). Geopolymeric cement, the manufacture of which produces only very little greenhouse gas CO2, obtained according to any one of claims 1 to 5.