EP0507895A1

EP0507895A1 - Method for preparing a spherosilicate-type cement and cement thereby obtained

Info

Publication number: EP0507895A1
Application number: EP91914369A
Authority: EP
Inventors: André LERAT
Original assignee: Holderbank Financiere Glarus AG
Current assignee: Holcim Ltd
Priority date: 1990-09-03
Filing date: 1991-08-24
Publication date: 1992-10-14
Also published as: CS270091A3; WO1992004294A1; MX9100897A; GB9118639D0; AU8422591A; ECSP910776A; WO1992004295A1; ES2033584B1; ES2033584A1; GB2247453A

Abstract

On prépare un ciment du type sphérosilicate en poudre, durcissant à froid et développant au bout de 4 heures à 20 °C une résistance à la compression supérieure ou égale à 15 MPa avec un rapport eau/liant compris entre 0,20 et 0,27, en utilisant les trois éléments réactifs suivants: a) un oxyde alumino-silicate (2SiO2, Al2O3) ayant le cation Al en coordination (IV-V) comme déterminé par le spectre d'analyse en Résonance Magnétique Nucléaire MASS-NMR pour 27Al; b) un disilicate alcalin de sodium et/ou de potassium, (Na2, K2)(H3SiO4); c) un silicate de calcium caractérisé en ce que les rapports molaires entre les trois éléments réactifs sont égaux ou compris entre (Na2, K2)(H3SiO4)2/(2SiO2, Al2O3) 0,40 et 0,60; Ca++/(2SiO2, Al2O3) 0,60 et 0,40; de telle sorte que (Na2, K2)(H3SiO4)2 + Ca++/(2SiO2, Al2O3) = 1,0 avec Ca++ désignant l'ion calcium appartenant à un silicate de calcium faiblement basique dont le rapport atomique Ca/Si est inférieur à 1.A cement of the powdered spherosilicate type is prepared, cold hardening and developing after 4 hours at 20 ° C. a compressive strength greater than or equal to 15 MPa with a water / binder ratio of between 0.20 and 0.27 , using the following three reactive elements: a) an alumino-silicate oxide (2SiO2, Al2O3) having the cation Al in coordination (IV-V) as determined by the spectrum of analysis in Nuclear Magnetic Resonance MASS-NMR for 27Al; b) an alkaline disilicate of sodium and / or potassium, (Na2, K2) (H3SiO4); c) a calcium silicate characterized in that the molar ratios between the three reactive elements are equal or between (Na2, K2) (H3SiO4) 2 / (2SiO2, Al2O3) 0.40 and 0.60; Ca ++ / (2SiO2, Al2O3) 0.60 and 0.40; so that (Na2, K2) (H3SiO4) 2 + Ca ++ / (2SiO2, Al2O3) = 1.0 with Ca ++ denoting the calcium ion belonging to a weakly basic calcium silicate whose atomic ratio Ca / Si is less than 1.

Description

Process for preparing a cement of the spherosilicate type and cement thus obtained

The present invention relates to a process for preparing a cement of the spherosilicate type which hardens quickly at room temperature, as well as the cement obtained by this process. More specifically, the mineral compositions described in the invention make it possible to obtain a cement of the spherosilicate type having a setting time equal to or greater than 30 minutes at the temperature of 20 ° C. and a curing speed making it possible to obtain resistances at compression (Rc) equal to or greater than 15 MPa, after only U hours at 20 C, when tested according to the standard standard applied to hydraulic binder mortars with a binder / sand ratio equal to 0.38 and a ratio water / binder between 0.22 and 0.27.

The mineral compositions of the spherosilicate type according to the present invention, making it possible to obtain a cement of the spherosilicate type with rapid hardening, (Rc)> 15 MPa at 4 h - 20 C, essentially comprise three reactive elements.

The first reagent is an aluminum silicate oxide (2SiO_, ALO_) having the cation Al in coordination (IV-V) as determined by the analysis spectrum of Nuclear Magnetic Resonance MASS-NMR

27 for Al; this alumino-silicate oxide (2Si0 ₂ , ALO-) is obtained by heat treatment, in an oxidizing medium, of natural hydrated alumino-silicates, in which the cation Al is in coordination (VI) as determined by the spectrum Resonance analysis

27 Nuclear Magnetic MASS-MNR for Al. In some previous publications alumino-silicate oxide (2SiO ₂ , A O_) was only defined by the cation Al in coordination (IV), which represented the state of research previous scientist. Today, the use of Nuclear Magnetic Resonance, MASS-NMR, has allowed to detect coordination of type AI (V). Indeed, the MASS-NMR spectrum for AI presents two peaks, one around 50-65 ppm characteristic of AI (IV) coordination and the other around 25-35 ppm that some scientific authors define as indicating AI coordination. (V), while others prefer to consider it as a distorted Ai (IV) coordination (see for this MacKenzie et al. Journal of the American Ceramic Society, Volume 68, pages 293-297, 1985). We will adopt, in what follows, the notion of mixed coordination Al (IV-V) for this oxide (2SiO ₂ , AI ₂ O ₃ ).

The second reagent is a sodium and / or potassium disilicate, soluble in water, (Na ₂ , K_) (H_SiO ^) ₂ ; potassium disilicate K ₂ (H ₃ SiO ₂ ) _{2 will} preferably be used although the sodium disilicate Na- (H, SiO ₂ ) ₂ also makes it possible to produce mineral compositions of the spherosilicate type according to the invention. It is also possible to use a mixture of the two alkaline disilicates.

The third reagent is a basic calcium silicate, that is to say with a Ca / Si atomic ratio equal to or greater than 1. It will be 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 Ca / Si atomic ratio of less than 1, preferably close to 0 , 5. This characterization will be established using X-ray Photoelectron Spectrometry (X.p. s.) And by analysis of the Ca_ / Si- relationships as indicated by M. Regourd, Phil. Trans. Royal Society London, A.310, pages 85-92 (1983).

The mineral compositions of the invention are also called mineral compositions of the spherosilicate type, since the cement of the spherosilicate type obtained results from a mineral polycondensation reaction as opposed to traditional hydraulic binders in which hardening is the result of hydration of calcium aluminates and calcium silicates. Here too, the means of investigation used is the Magnetic Resonance spectrum

27 Nuclear, MASS-NMR for Al. The products resulting from the mineral polycondensation reaction, as recommended in the present invention, have a single peak at 55 ppm, characteristic of coordination AI (IV), while the hydration compounds obtained in traditional hydraulic binders have a peak at 0 ppm, characteristic of Al (IV) coordination, ie of calcium hydroxyaluminate.

29 The MASS-NMR spectrum of Si also makes it possible to make a very clear differentiation between materials of the spherosilicate type and hydraulic binders. If we represent the degree of polymerization of the tetrahedron SiO „by Qn (n = O, 1,2,3,4), we can distinguish between monosilicates (QO), disilicates (Q1), silicate groups ( Q2), the grafted silicates (Q3) and the silicates forming part of a three-dimensional network (Q4). These degrees of polymerization are characterized

29 in MASS-NMR of Si by the following peaks: (QO) from -68 to -76 ppm; (Ql) from -76 to -80 ppm; (Q2) from -80 to -85 ppm; (Q3) from -85 to -90 ppm; (Q4) from -91 to -130 ppm. The peaks characterizing the materials of the spherosilicate type are found in the range -85 to -100 ppm and correspond to the three-dimensional network (Q4) characteristic of poly (sialates) and poly (sialate-siloxo). On the contrary, the results of the hydration of the hydraulic binders leading to the hydrated calcium silicate CSH (according to the terminology used in the chemistry of cements) produce peaks lying in the range -68 to -85 ppm, namely the monosilicate (Q0 ) or disilicate (Q1) (Q2); (see for example J. Hjorth, Cernent and Concrete Research, Vol. 18, No., 1988).

According to the terminology in force for materials of the spherosilicate type, the fast-curing mineral binder, (Rc) 15 MPa at 4h - 20 ° C, corresponds to a material of the spherosilicate type of the type (Ca, K) -poIy (sialate-siIoxo) of formula varying between

(0.6K + 0.2Ca) (-Si-O-AI-O-Si-O-), H ₂ O and

(0, 4K + 0, 3Ca) (-Si-O-AI-O-Si-O-), H ₂ O.

Binders and cements having rapid hardening and based on reactions of the mineral polycondensation type involving the three reagents used in the present invention have been proposed in the past. There are thus known compositions of the spherosilicate type allowing the production of fast-hardening mortar, developing a compressive strength Rc = 6.89 MPa after 1 hour at 65 ° C and Rc = 41.34 MPa after 4 hours at 65 C. A composition of the spherosilicate type is also known which develops a resistance to compression Rc = 24 MPa after 4 hours at 23-25 C. According to the experience acquired by a person skilled in the art, a resistance to compression Rc = 15 MPa after 4 hours at 20 ° C is equivalent to Rc = 22.5 MPa after 4 hours at 25 ° C. This composition comprises 840 g of a so-called "standard" reaction mixture to which has been added, in addition to inert fillers, 220 g of ground blast furnace slag. The reaction components of the spherosilicate type are characterized by the molar ratios of the oxides:

which corresponds, to allow comparison with the mineral compositions of the spherosilicate type according to the invention, to a composition of the spherosilicate type comprising 1 mole of the oxide alumino-silicate (2SiO ₂ , ALO ₃ ), i.e. 222 g, 1.12 moles of potassium disilicate K ₂ (H ₃ SiO _, or 300 g, 0.21 moles K ₂ 0 corresponding to 28 g of anhydrous KOH at 90 I, and 290 g of water and 220 g of slag.

As can easily be seen, with respect to the aluminum silicate oxide (2Si0 ₂ , ALO_) the molar ratio between K ₂ (H ₃ SiO _Z} ) ₂ and (2SiO ₂ , AI ₂ O ₃ ) is equal to 1.12. It was therefore very important to be able to very significantly reduce the quantity of this very expensive product. This is the main objective of the present invention.

In the context of the invention, the mineral compositions of the spherosilicate type are characterized by the molar ratios between the three reactive elements which are equal or between

(Na ₂ , K ₂ ) (H ₂ SiO, ₁ ) _: 0.40 and 0.60 (2Si0 ₂ , AI ₂ 0 ₃ )

Ca ^ττ 0.60 and 0.40 (2Si0 ₂ , AI ₂ 0 ₃ )

so that

= 1.0

with Ca denoting calcium ion belonging to a weakly basic calcium silicate.

As can be seen, the amount of alkaline disilicate is reduced from 200% to 300% compared to the prior state of the art. It was not enough, for this, to simply lower the amount of this alkaline disilicate. Indeed, it was surprising to note that it was essentially necessary to change the physical state of the constituents.

Thus, the aforementioned known compositions are in the liquid phase. The slag is added to an aqueous reaction mixture containing the aluminum silicate oxide (2SiO ₂ , ALO ₂ ), the alkalis, the water and the potassium polysilicate in solution.

On the contrary, in the context of the invention, the mineral compositions of the spherosilicate type are in the solid phase, in particular the second reagent, the sodium and / or potassium disilicate (Na ₂ , K ₂ ) (f-SiO. is a finely divided powder, water being added only in the final phase of mixing the mortar or binder.

Also found in the prior art are mineral powder compositions, for example mineral compositions comprising:

100 parts of metakaolin 20 to 70 parts of slag 85 to 130 parts of fine fillers (fly ash, calcined clays) 70 to 215 parts of amorphous silica

55 to 145 parts of a mixture containing potassium silicate and potassium hydroxide, with at least 55 parts of potassium silicate alone.

In this latter composition, the role of amorphous silica is essentially to replace part of the potassium silicate necessary for mineral polycondensation, that is to say that the amorphous silica reacts with potassium hydroxide to produce, in the mortar, the quantity of potassium silicate desired. For those skilled in the art, the term "potassium silicate" means industrial potassium silicate, in powder form, corresponding to the formula K ₂ O, 3SiO ₂ , 3H ₂ O, soluble in water and making it possible to produce binders and adhesives having the same properties as "soluble glasses" or alkali silicate in solution.

However, a composition having a formulation of this type does not harden at room temperature, since to obtain this rapid hardening, it is absolutely necessary to add portiand cement. But, even with the addition of portiand cement, these compositions do not make it possible to obtain (Rc)> 15 MPa at 4 h - 20 C. Thus, for example, the following mixture was recommended:

68 parts of metakaolin

36 parts of slag

60 parts of fly ash 103 parts of silica smoke

44 parts of potassium silicate

22 parts of potassium hydroxide and

423 parts of portian cement.

For the mortar obtained, the compressive strength Rc at 4 h - 23 C is only around 6.9 MPa, which is much lower than (Rc)> 15 MPa at 4 h - 20 ° C, as claimed in the present invention. In another known example, Rc at 4 h - 23 C is only about 4.6 MPa, while in still other examples, only Rc at around 65 C are given, Rc at 4 - 23 C being too weak to be mentioned.

Assuming that metakaolin corresponds to our aluminum silicate oxide (2SiO_, ALO ₃ ) and that potassium hydroxide has made it possible to transform potassium silicate K ₂ O .3Si0 ₂ .3r O into disilicate K_ (H, SiO _y ) ₂ , we obtain the following compositions expressed in moles: (2SiO ₂ , AI ₂ 0 ₃ ) 0.30 moles K ₂ (H ₃ Si0 ₄ ) ₂ 0, 20 moles i.e. a ratio K ^ l- ^ SiO ^ on (2Si0 ₂ , AI ₂ 0 ₃ ) equal to 0, 66. In fact this ratio is higher since, the excess of potassium hydroxide being 0.13 moles of KO, as this potash reacted with the silica smoke to also produce 0.13 moles of K ₂ (H ₃ SiO.) ₂ , we thus arrive at a total of K ₂ (H ₃ SiO ₂ equal to 0.33 leading to the ratio K ₂ (H ₃ SiO ₄ ) ₂ on (2SiO ₂ , AI ₂ O ₃ ) equal to 1 , That is to say exactly that of the known compositions cited first.

These examples clearly show that the simple replacement of the silicate in solution by powdered silicate causes a very marked slowing down of the curing since with these known compositions thermal activation is necessary when it is desired to obtain a rapid curing in a few hours.

Now, precisely, in the context of the present invention, unlike the prior art, the powdered alkaline disilicate makes it possible to obtain a cement of the spherosilicate type having a rapid hardening, at 20 ° C., in a few hours, i.e. (Rc)> 15 MPa at 4h - 20 ° C.

I t is also known to replace all of the potassium silicate in solution with a mixture of amorphous silica (silica fume) and potassium hydroxide. Here too, rapid hardening requires the addition of portiand cement, and in the best of cases the compressive strength Rc at 4 h - 23 C is around 7.5 MPa, which is much lower than (Rc)> 15 MPa at 4h - 20 ° C as claimed in the present invention. Still in this last known example, the mineral composition of the spherosilicate type comprises for 52 parts of metakaolin, 24 to 28 parts of potassium hydroxide, 73 to 120 parts of silica smoke, 18 to 29 parts of slag. Silica smoke reacts with potassium hydroxide to produce potassium silicate in the mixture, which is a way of lowering the cost price of this very expensive reagent. We thus obtain in mole, according to the same reasoning as previously:

(2Si0 ₂ , AI ₂ O-) 0.23 moles

K ₂ (H ₃ SiO) ₂ from 0.215 to 0.25 moles which gives a ratio K _j on (2SiO ₂ , ALO_) between 0.93 and 1.08, again practically the ratios discussed above.

These examples of the prior art clearly show that the simple replacement of the silicate in solution with a mixture of silica smoke and potassium hydroxide causes a very marked slowing down of the hardening since thermal activation is necessary when the we want to get a quick hardening, in a few hours.

The known examples described above demonstrate that rapid hardening requires a temperature of 40 to 60 ° C. In other terms, the claimed mixtures are endothermic; they absorb calories.

The following tests clearly show that in the prior art, the endothermicity of the mixtures was too great to allow rapid hardening to be obtained at room temperature. We know that the mineral polycondensation reaction is exothermic, this exothermicity is very well demonstrated when the curing takes place at 40-60 C. The exothermicity of the mixtures containing or not containing amorphous silica, such as silica smoke. The means of analysis is Differential Thermal Analysis.

Two powder mixes were prepared: mixture A: oxide (2Si0 ₂ , AL0 ₃ ) 400 g micronized mica 100 g

mixture B: oxide (2Si0 ₂ A! ₂ 0 ₃ ) 400 g silica smoke 100 g

and 2 liquid mixtures:

liquid 1: 40% potassium silicate solution 520 g

90% KOH 82 g

liquid 2: 40% sodium silicate solution 1040 g

NaOH powder 120 g

The mixture between the powder and the liquid is carried out according to the pro¬ portions indicated in the table, and the mineral polycondensation is followed by Differential Thermal Analysis. The values of the J / g ratio are compared, that is to say the amount of energy measured in Joules on the weight of the sample in grams. The mineral polycondensation temperature is 60 C.

Test No. Mixture J / g

247

53

116

It is clear that the addition of silica smoke, that is to say the formation of potassium silicate in the mixture, absorbs calories. The exothermicity of test No. 2 (with silica smoke) is divided by 5 compared to that of test No. 1 (without silica smoke), and that of test No. 3 is divided by 2.

This explains why the mixtures known in the prior art have no rapid hardening at room temperature.

On the contrary, in the case of the invention, amorphous silica such as silica fume or other silicas which it is known that they can easily transform into potassium or sodium silicate, at moderate or even ambient temperature, will be added in such a quantity that it will not disturb the natural exothermicity of the mixture of the spherosilicate type. Amorphous silica, such as, for example, silica smoke, rice ash, diatomaceous earth, silicic smectites, certain strongly silicic pozzolans (with a high percentage of allophane and glass of volcanic origin) are considered as finely divided, reactive loads. The reactivity of these charges causes them to react on the surface with the reaction medium of the spherosilicate type, thus increasing the mechanical resistance of the mineral binder poly (sialate-siloxo). These silicic materials are not dissolved, at first, at ordinary temperature, that is to say within the framework of the invention. However, as in the case of the hydraulic binders containing them, it will be possible, after 28 days or later, to note their digestion by the matrix of the spherosilicate type or by the basic silicates still present in the matrix.

The third reagent of the invention is weakly basic calcium silicate with the Ca / Si atomic ratio of less than 1.

This will be for example calcium disilicate Ca f H-SiO ^ or tobermorite Ca ^ SL -O, ..) (OH) _β , 8H ₂ O. This third reagent is linked to the preceding ones by the molar ratios between the three reactive elements equal to or comprised between

(Na _2, _K:) (H, SiO, ₁₎ 0.40 and 0.60

(2Si0 ₂ , AI ₂ 0 ₃ )

Ca ^"1" * ^" 0.60 and 0.40

(2Si0 ₂ , AI ₂ 0 ₃ )

In the case of calcium disilicate Ca (H, SiO _j _ and potassium disilicate K ₂ (H, SiO „) ₂ we have the following reports:

K ₂ (H ₃ SiO _} ) ₂ / (2Si0 ₂ , AI ₂ 0 ₃ ) between 0.40 and 0.60

Ca (H ₃ SiO _{/ J} ) ₂ / (2Si0 ₂ , Ai ₂ 0 ₃ ) between 0.60 and 0.40.

In other words, the sum of the number of moles of calcium disilicate, Ca (H, SiO _y ) _, and the number of moles of potassium disilicate, K_ (H, SiO _y ) _, is equal to the number of moles of the aluminum silicate oxide (2SiO_, ALO_). This alumino-silicate oxide (2Si0 ₂ , AL0 ₃ ) determines all the reaction conditions of the mineral compositions of the spherosilicate type. It will react with an alkaline or alkaline earth disilicate to form, after mineral polycondensation, a compound (Si ₂ O_, ALO ₂ , Si ₂ O ₅ , (K ₂ O, CaO)), i.e. (K, Ca) -poly (sialate-siloxo) of formula between

(0.6K + 0.2Ca) (- Si-O-AI-O-Si-O-) and

(0.4K + 0.3Ca) (- Si-O-AI-O-Si-O-).

The oxide (2Si0 ₂ , AL0 ₃ ) reacts first with the most soluble disilicate which is always the alkaline disilicate (Na ₂ , K ₂ ) (H ₃ SiO.) ₂ . The amount of calcium dislicate involved in the mineral polycondensation reaction is essentially determined by the amount of alkaline disilicate. If the sum of the moles of these disilicates is greater than 1, the non-reacting part will be that which is the least soluble, that is to say the calcium disilicate.

However, it is the calcium ions Ca which determine the rate of hardening by making alkaline inorganic polycondensation gels less soluble, the optimal speed of hardening being reached when these Ca ions are integrated into the structure of the spherosilicate type. If the amount of alkaline Na

-j. and / or K is important it will require a larger amount of ion

This leads to the same curing speed. On the other hand, if the amount of alkaline disilicate (Na ₂ , K ₂ ) (H_SiO.) ₂ is too low, the dissolution of the calcium disilicate

Ca (H ₃ SiO ₂ will be reduced, and the rapid hardening at 20 ° C will not take place either, and the mechanical strengths will be weaker.

This explains why in certain compositions according to the prior art, for which the ratio K ₂ (H ₃ Si0 ₄ ) ₂ / (2Si0 ₂ , AI ₂ O ₃ ) was close to or greater than 1, the solubility too strong of the reaction medium slowed down the precipitating action of Ca ions originating for example from slag or portian cement.

Calcium disilicate Ca (H_SiO _i .) ₂ can be produced separately, for example by hydrothermal reaction between lime and silica.

However, according to a preferred method of the invention, it will be produced, in the nascent state, in the binder, after the addition of the water necessary for the solubilization of the various powdered reagents. The starting material is a basic calcium silicate, that is to say with the Ca / Si atomic ratio greater than or equal to 1. This will be for example wollastonite Ca (Si0 ₃ ), gehlenite (2CaO .AI ₂ 0 _3. Si0 ₂ ), bicalcium silicate C ₂ S (2CaO.Si0 ₂ ), tricalcium silicate CS (3CaO .Si0 ₂ ), Akermanite (2CaO.SiO ₂ ). When the grains of these materials are brought into contact with an alkaline solution (NaOH or KOH) a desorption of CaO takes place very quickly so that the Ca / Si atomic ratio becomes less than 1 and tends towards 0, 5 for basic silicates initially with a Ca / Si ratio equal to or less than 2, such as wollastonite, C ₂ S, gehlenite, akermanite.

Blast furnace slag essentially contains the basic silicates gehlenite, akermanite, wollastonite and is therefore very suitable. In addition, as can be seen by X-ray photoelectron spectrometry (X. Ps) as indicated above, this alkaline attack on the basic silicate produces a weakly basic silicate with an atomic ratio Ca / Si = 0.5, which is precisely the calcium disilicate Cal H-.SiO _^ . This process is very regular and can be completed in 30 minutes, at room temperature. On the contrary, in the case of C ₂ S, there occurs in a few seconds a high concentration of weakly basic silicate Ca / Si less than 1; then the attack is stopped, and then continues more regularly. This is called the "flash-set" or formation of a gel creating a false catch. To avoid the sudden formation of calcium disilicate, in the case of C ₂ S, it is necessary to use setting retarders like those commonly used in cement mixtures portiand.

The mineral polycondensation reaction used in the present invention should not be confused with the simple alkaline activation of hydraulic binders, or with the action of alkali setting accelerator on portland cements and other hydraulic binders. Indeed, the simple action of alkalis, NaOH or KOH, on portland cements or blast furnace slag, results in the production of hydrated calcium silicates, as mentioned above. In contrast to what happens in the present invention, these hydrated silicates crystallize to form CSH, the main constituent of hydraulic calcium cements. The CSH is a monosilicate and / or a bisilicate, that is to say that the SiO 2 tetrahedra which constitute it belong to the category (QO), (Ql) and possibly (Q2). On the contrary, the mineral polycondensation leads to the formation of SiO tetraera of type (Q4, as determined by the analysis spectrum in Nuclear Magnetic Resonance MASS-NMR for ²⁹ Si.

Although the alkalis, NaOH and KOH, are setting accelerators, they do not constitute hardening accelerators capable of achieving the object of the invention, that is to say (Rc) 15 MPa at 4 h - 20 ° C .

In the case of blast furnace slag, the alkalis are not setting accelerators, but develop the latent hydraulicity of slag. The hardening accelerator is usually temperature or the addition of portiand cement. It is for example known to use a cement based on slag, portian cement or lime, and an alkaline accelerator such as NaOH and sodium and or potassium carbonates. The compressive strengths are all obtained after heating to 50 ° C. or 70 ° C. With this known technique, an average Rc of 10 to 30 MPa is obtained after 6 hours at 70 ° C. The experience of a person skilled in the art indicates that these resistances of 30 MPa obtained after 6 hours at 70 C correspond to Rc = 1 to 3 MPa maximum after 4 hours at 20 ° C.

Scientific analysis using Nuclear Magnetic Resonance

27 MASS-NMR for Al shows that hydraulic slag cements result from the hydration of aluminates, silicates and calcium silico-aluminates, with the formation of either hydrated gehlenite, 2CaO, ALO ₃ , SiO ₂ , 8H ₂ 0 or hydrated calcium aluminate 4CaO.ALO ,, 10H, O in which the cation Al is in

29 Al coordination (VI). The MASS-NMR spectra for Si show that the SiO 2 tetrahedra are mostly of the type (QO), (Q1),

(Q2), characterizing C-S-H.

Likewise, a mixture comprising alumino-silicate oxide (2Si0 ₂ , AL0 ₃ ), slag (or cement) and alkalies KOH, NaOH, does not constitute a mineral binder of mineral polycondensation according to the present invention. It is known that a mortar made with this mixture and water does not harden at 20 C for 24 hours. Thus it is known that if the oxide (2Si0 ₂ , ALO_) is not masked by a polysilicate solution against the attack of strong bases KOH, NaOH, a simple poly (sialate) of the type is formed. hydroxysodalite and which precipitates without binding function. It is known that hydroxysodalite constitutes a binder only in ceramic pastes, with very little water and when the material is compressed.

In the context of the invention, the third reagent of the mineral polycondensation composition is calcium silicate. It can be accompanied by complex calcium aluminates and silicates.

Thus the blast furnace slag is partly formed of a glass composed inter alia of gehlenite 2CaO.AL0 ₃ .Si0 ₂ , of akermanite 2Ca0.Mg0.2Si0 ₂ , of wollastonite.

In the context of the invention, the part of these silicates not transformed into weakly basic calcium silicate during the alkaline attack, or that which could not participate in the mineral polycondensation reaction once the ratio K ₂ (H ₃ Si0 ₄ ) ₂ + Ca (H ₃ SiO _{Z {} ) ₂ of 2 (Si0 ₂ , AI ₂ 0 ₃ ) has reached the value of 1, these silicates and alumino-silicates will hydrate according to the known mechanism in force for silicates of calcium constituting hydraulic cements. Then, in addition to the material of the spherosilicate type (K, Ca) (-Si-O-AI-Si-O-), the formation of hydrated gehlenite, CSH, hydrated calcium aluminate, and other silicates is obtained. magnesium.

Nuclear Magnetic Resonance spectrometry analysis

27 indicates for MASS-NMR of Al the presence of both peaks corresponding to the coordination Al (IV) and λl (VI). In general, in the context of the present invention the concentration of Al (IV) is 4 to

6 times that of Al (VI). It may decrease if other silico-aluminous or aluminous fillers are added to the mixture, but even in this case the ratio between the concentration of AI (IV) on the concentration of AI (VI) will be

AI (V1) equal to or greater than 1.

AI (VI)

29 In the MASS-NMR spectrum of Si, these same basic calcium silicates will lead to the presence of both SiO ^ tetrahedra

(Q), (QO), (Q1), (Q2). In general, the concentration of tetrahedra

SiO _j , (Q) is 4 to 6 times greater than the sum of the concentrations of SiO tetrahedrons „(QO) + (Q1) + (Q2), and depending on the nature of the charges we will have

(Q4) equal to or greater than 1

(QO) + (Q1) + (Q2)

Blast furnace slag is a cheap source of wollastonite, gehlenite and ackermanite. The mineral polycondensation compositions of the invention containing blast furnace slag make it possible to produce a mineral polycondensation binder, in powder form, containing: a) 100 parts by weight of aluminum silicate oxide (2SiO-, ALO,) having the cation Al in coordination

(IV-V) as determined by the analysis spectrum in

27 Nuclear Magnetic Resonance MASS-NMR for Al, and b) -48-72 parts of potassium disilicate K ₂ (H ₃ SiO.) ₂ and c) 50-70 parts of blast furnace slag of average particle size 10 microns, compound partly gehlenite, akermanite, wollastonite.

The mortar obtained by adding a quantity of water such that the water / binder ratio is between 0.20 and 0.27 and a quantity of standardized sand such that the binder / sand ratio = 0.38 hardens cold and develops after 4 hours at 20 ° C a compressive strength greater than or equal to 15 MPa.

When the manufacturing conditions do not allow the alkaline disilicate K _j th SiO ^) to be obtained directly, the 48 to 72 parts of potassium disilicate K ₂ (H ₃ SiO _y ) ₂ are replaced by a powder mixture containing

35-40 parts of potassium silicate K ₂ O, 3SiO ₂ , 3H ₂ O

7-15 parts of 90% anhydrous KOH potassium hydroxide

0-65 parts of amorphous silica.

The comparison between the milk / water weight ratio makes it possible to clearly highlight the essential differences between the mineral polycondensation compositions according to the present invention and the prior art. The limit values of this ratio are known, beyond which it is no longer possible to use the binders thus produced, because the mixture immediately sets in the mixer, setting being practically instantaneous. It should also be noted that certain known formulations which use the maximum amount of slag also contain calcium fluoride, F_Ca. We know that fluorides have a delaying action on the formation of weakly basic calcium silicate and therefore on the precipitating action of io ^ s Ca, thus promoting a longer setting time, avoiding the effect of false setting.

On the contrary, in the context of the present invention, setting is considered to be slow, since it takes place after a time of more than 30 minutes without the addition of retarder, which allows use in industry, with traditional mixers . Anyone skilled in the art will understand the advantage of this setting characteristic at t> 30 minutes at 20 ° C.

The table groups the setting times for different milk / water weight ratios, compositions involving alkali silicate solutions and inorganic polycondensation compositions containing powdered alkaline disilicates, according to the present invention.

milk / water ratio 1, 0 0, 85 0, 70 0, 55 0, 42

start of setting (at around 23 C) for a known composition 0 0 12 min 30 min 60 min

start of setting (at 20 ° C.) for the present invention 30 min 60 min 90 min 3 hours

Those skilled in the art know that the lower the amount of water contained in the cement, the higher the mechanical strengths. In the prior art, the maximum lateral / water ratio is 0.70. The workability of mortars and concretes generally requires setting times of at least 30 minutes, which requires for example in a known composition to choose a milk / water ratio of 0.55. However, this high amount of water lowers the compressive strength Rc by about 30%. On the contrary, in the present invention, the workability of the mortar is good even with a milk / water ratio of 1.0. Strong mechanical resistance is therefore obtained, with in addition all the other physical characteristics accompanying the small amount of water, as in. example a high densification and a low porosity, while having decreased from more than 200% to 300% the amount of disilicate (Na ₂ , K ₂ ) (H ₃ SiO ₂ , the most expensive of all the reagents.

Instead of potassium disilicate K ₂ (H., SiO _2, it is also possible to use 42 to 64 parts of sodium disilicate Na ₂ (H, SiO _tt ) _, or the mixture of two silicates. This makes it possible to use sources of impure alkalis containing both potassium and sodium. This is often the case for industrial waste very rich in alkalis such as filter dust from portain cement calcining furnaces or alkaline detergents from the mining industry or chemical.

The advantage of the present invention also lies in the fact that the use of alkaline disilicate (Na ₂ , K ₂ ) (H ₃ SiO ₂ ) ₂ in powder makes it possible to use inexpensive raw materials coming from industrial waste. An interesting source of amorphous silica is the silica smoke recovered in the filters above the melting furnaces of ferro-silicone steels. These silica fumes contain 90-95% Si0 ₂ , carbon, and 0.5-1% finely dispersed metallic silicon. These silica fumes make it possible to manufacture the alkaline disilicate at very low temperatures, even at ordinary temperature. On the contrary with silica sands, it is generally necessary to work in an autoclave when reacting alkali hydroxides, or in fusion when using alkali carbonates. It is also possible to use amorphous silica of natural origin such as diatomaceous earth, very siliceous smectics and gaizes, very siliceous volcanic glasses and pozzolans. Ash rich in silica, obtained by calcining plants (rice for example), can also be used for this purpose.

The manufacture of aluminum silicate oxide (2SiO ₂ , ALO,) is carried out by treating between 650 ° C and 800 ° C kaolinitic clays. Kaolinitic sands can be used as raw material, as well as certain clays containing at the same time kaolinite, montmorillonite and illite; likewise lateritic soils and laterites containing both kaolinite. Tests carried out on pyrophillites show that these materials are suitable for mineral polycondensation.

The heat treatment temperatures of the raw materials must be adjusted so that they allow optimum production of aluminum silicate oxide (2SiO ₂ , AO ₃ ) having the highest concentration of Al coordinating Al (IV-V) as

27 determined by the MASS-NMR spectrum for Al. Siliceous materials which, for technological reasons, must also be roasted, will be treated at temperatures below the point of transformation of silica arrc-phes into cristobalite when it is desired to use them as a raw material ≤ in the manufacture of alkaline disilicate powder ( Na ₂ , K ₂ ) (H-SiO _^ . In general this temperature is close to 700 ° C.

The alkalis are generally the sodium and / or potassium hydroxides produced industrially by electrolysis. They are also the result of the chemical reaction between an alkaline salt and calcium hydroxide or a material producing it in situ. The alkaline salts are selected from sodium and potassium carbonates, potassium sulfates, potassium sulfites. It is thus possible to use the dust collected on the filters of portiand cement kilns which are very rich in sulfites and sulfates. potassium, convert them to carbonates using the Leblanc process, or react them with clinker to produce potassium hydroxide in situ. The powdered alkaline disilicates obtained in this case during the reaction between the amorphous silicas and the alkalis as in Example 1 below are rather double potassium and calcium disilicates. They also allow the present invention to be carried out.

The following examples illustrate the present invention. They are not limiting on the overall scope of the invention as presented in the claims. All parts shown are by weight.

Example 1

Manufacture of alkaline disilicate K ₂ (H_SiO ₂ powder.

130 parts by weight of silica smoke are mixed with 125 parts of 90% KOH and then 30 parts of water are added. The mixture becomes exothermic after a certain time and begins to foam due to the action of KOH on metallic silicon. The mixture acquires the consistency of a paste which cools and hardens into a very brittle foamed material. A product is obtained which is very soluble in cold water, containing 86% of dry extract and 14% of water corresponding to potassium disilicate K ₂ (H ₃ SiO „) ₂ technical with 3 to 5% of impurities in the form of insoluble potassium carbon and silicon aiuminate. Example 2

222 g of oxide (2SiO ₂ , AI ₂ O ₃ ) and 28 g of 90% KOH are mixed and a previously prepared liquid mixture containing 310 g of powdered disilicate from Example 1 and 290 g is added to this mixture of water, then 220 g of blast furnace slag.

The binder thus obtained is used to make a standardized mortar having a binder / sand ratio = 0.38 and in which the water / binder ratio is 0.27.

The mortar sets after 15 minutes and has a compressive strength Rc = 16 MPa at 20 ° C after 4 hours.

The molar ratio K ^ H ^ iO ^ / SiO ^ A! ^) Is equal to 1.12 and the ^" " milk weight contribution / alkaline disilicate is equal to

0.73 for L milk / water weight ratio = 0.75.

Example 3

22 parts of oxide (2Si0 ₂ , ALO ₃ ), 13 parts of slag, 18 parts of silica smoke, and 36 parts of a previously prepared liquid mixture containing 12 parts of the disilicate prepared according to Example 1, 4 are mixed parts of KOH and 20 parts of water.

A mortar is produced as in Example 2. The setting takes place after 3 hours and Rc = 2 MPa at 20 ° C after 4 hours.

The molar ratio K ₂ (H ₃ SiO.) ₂ / (2Si0 ₂ , AL0 ₃ ) is equal to 0.43. The dairy / alkaline disilicate weight ratio is equal to

1.08 and the milk / water weight ratio = 0.65. Example 4

22 parts of oxide (2SiO _{2 #} AI ₂ 0 ₃ ), 15 parts of slag, 18 parts of silica smoke and 40 parts of a previously prepared liquid mixture containing 15 parts of the disilicate prepared according to Example 1 are mixed , 4 parts of KOH and 22 parts of water.

A mortar is made as in example 2. The setting takes place at the bobo ddee 22 hheeuurreess 3300 mmiinnuutteess eett F Rc = 4 MPa at 20 ° C after 4 hours, with a water / binder ratio = 0.29.

The molar ratio K ₂ (H ₃ SiO ₂ / (2Si0 ₂ , ALO,) is equal to 0.56. The milk / alkaline disilicate weight ratio is equal to

1.0 and the milk / water weight ratio = 0.68.

Example 5

22 parts of (2Si0 ₂ , AL0 ₃ ), 15 parts of slag, 20 parts of silica smoke and 11 parts of KOH are mixed dry, then the sand is added and then 25 parts of water. A mortar is thus obtained as in Example 2. There is no setting, even at 24 hours at 20 ° C.

Example 6

A mixture containing 27 parts of (2SiO ₂ , ALO_), 21 parts of slag, 15 parts of fumed silica and 19 parts of potassium disilicate K ₂ (H ₃ SiO ₂ prepared according to Example 1) is prepared dry. 215 parts of standardized sand and then 21.5 parts of water.

The starts after 35 minutes, and the resistance Rc after 4 hours at 20 ° C is 16 MPa, with a water / binder ratio = 0.26. The molar ratio K ₂ (H ₃ SiO ₂ is equal to 0.58. The milk / alkaline disilicate weight ratio is equal to 1.10 and the milk / water weight ratio = 1.023.

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

Claims

1) Process for preparing a cement of the spherosilicate powder type, cold hardening and developing after 4 hours at 20°C a compressive strength greater than or equal to 15 MPa with a water/binder ratio of between 0, 20 and 0.27, said cement containing the following three reactive elements:

a) an alumino-silicate oxide (2SiO ₂ , ALO_) having the Al cation in coordination (IV-V) as determined by the MASS-NMR Nuclear Magnetic Resonance analysis spectrum for

“Al;

b) an alkaline disilicate of sodium and/or potassium, (Na ₂ ,K ₂ )(H ₃ SiO _i} );

c) a calcium silicate characterized in that the molar ratios between the three reactive elements are equal to or between

(Na ₂ ,K )(H ₃ SiO, ₁ ) _: 0.40 and 0.60

(2Si0 ₂ ,Ai ₂ 0 ₃ )

Ca ⁺⁺ 0.60 and 0.40

(2Si0 ₂ ,Al ₂ 0 ₃ )

in such a way that

++

(Na„ CT K ₂ )(H,SiO, ₁ ). + Ca = 1.0

(2SiO ₂ ,AI ₂ 0 ₃ )

++ with Ca designating the calcium ion belonging to a weakly basic calcium silicate whose Ca/Si atomic ratio is less than 1.

2) Method according to claim 1, characterized in that said weakly basic calcium silicate whose Ca/Si atomic ratio is less than 1 is obtained in the nascent state by the alkaline attack of an anhydrous basic calcium silicate of which the Ca/Si atomic ratio is equal to or greater than 1 and results in the in-situ formation of hydrated calcium silicate whose Ca/Si atomic ratio is equal to 0.5 such as the disilicate Ca(H,SiO.) ₂ or between 0.5 and 1 like tobermorite Ca _1Q (Si ₁₂ O ₃ .) (OH) _β .8H ₂ O, as determined by the Ca ₂ /SL ratio in Xps (X-ray photoelectron spectrometry).

3) Soherosilicate type cement prepared following the process according to one of the claims. s i or 2, characterized in that said alkaline disilicate is potassium disilicate

K ₂ (H _g SiO _y ) ₂ ; spherosilicate type cement corresponds to the formation of a mineral polycondensation material of the type

(Ca,K)-poly(sialate-siloxo) of formula varying between

(0.6K + 0.2Ca)(-Si-0-AL-0-Si-0-),H ₂ O and

(0.4K + 0.3Ca)(-Si-0-AL-0-Si-0-),H ₂ O.

4) Spherosilicate type cement prepared according to the process according to one of claims 1 or 2, characterized in that, after hardening, the Al cation is entirely in coordination (IV) as determined by the Magnetic Resonance analysis spectrum

27 Nuclear MASS-NMR for Al, and the degree of polymerization of the SiO tetrahedron. is (Q4) as determined by the MASS-NMR spectrum

29 for Si. 5) Cement of the spherosilicate type prepared according to the process according to one of claims 1 or 2, in which said anhydrous basic calcium silicate is in solid solution with a calcium aluminate or a calcium alumino-silicate whose cation Al is in coordination (IV), and said alumino-silicate oxide (2SiO_, ALO_) having AI in coordination (IV-V) is mixed with aluminous (ALO_) or silico-aluminous powders (nSiO ₂ , AIO, ) natural or artificial whose Al cation is in coordination (VI), characterized in that, after hardening, the ratio between the concentration of coordination Al cation (IV) and the concentration of coordination Al cation (VI) is :

Al (lV) equal to or greater than 1

AI (VI)

as determined by the Magnetic Resonance analysis spectrum

27 Nuclear MASS-NMR for Al, and the ratio between the concentration in SiO„ tetrahedron (Q4) and the concentration in SiO^ ^' tetrahedron (Qo) + (Q1) + (Q2) is:

(Q4) equal to or greater than 1:

(QO) + (Q1) +(Q2)

as determined by the MASS-NMR Nuclear Magnetic Resonance analysis spectrum for ²⁹ Si.

6) Method according to claim 2, characterized in that said basic calcium silicate whose Ca/Si atomic ratio is equal to or greater than 1 is selected from wollastonite Ca(SiO^), gehlenite (2CaO, MgO, 2Si0 ₂ ), dicalcium silicate C ₂ S (2CaO,SiO), tricalcium silicate C ₃ S (3CaO, Si0 ₂ ), akermanite (2CaO,MgO,2SiO ₂ ).

7) Spherosilicate type cement, powder, containing: a) 100 parts by weight of alumino-silicate oxide (2Si0 ₂ , AL0 ₃ ) having the AI cation in coordination (IV-V) as determined by the MASS-NMR Nuclear Magnetic Resonance analysis spectrum for ²⁷ AI,

b) 48-72 parts of potassium disilicate K ₂ (H ₃ SiO. ) ₂ , and

c) 50-70 parts of blast furnace slag with an average particle size of 10 microns, composed in part of gehlenite, akermanite and wollastonite,

the mortar obtained by adding a quantity of water such that the water/binder ratio is between 0.20 and 0.27 and a quantity of standardized sand such that the binder/sand ratio = 0.38 hardens when cold and developing after 4 hours at 20 C a compressive strength greater than or equal to 15 MPa.

8) Spherosilicate type cement according to claim 7, characterized in that the 48 to 72 parts of potassium disilicate K ₂ (H,Si0 ₂ ) are replaced by a mixture containing

35-40 parts of potassium silicate K ₂ _0.3Si0H 2.3H ₂ 0

7-15 parts of 90% anhydrous KOH potassium hydroxide, and

0-65 parts of amorphous silica.

9) Spherosilicate type cement, powder, containing:

a) 100 parts by weight of aluminosilicate oxide (2Si0 ₂ , ALO, ) having the Al cation in coordination (IV-V) as determined by the Magnetic Resonance analysis spectrum

97A I

Nuclear MASS-NMR for ^,

b) 42-64 parts of sodium disilicate N^ Mç-n _ù )? ' ^And c) 50-70 parts of blast furnace slag with an average particle size of 10 microns, composed partly of gehlenite and akermanite,

10) Cement of the spherosilicate type, cold hardening and developing after 4 hours at 20 C a compressive strength greater than or equal to 15 MPa, obtained by adding to 100 parts by weight of the mineral binder of the spherosilicate type according to one of claims 7 to 9, 10 to 30 parts by weight of fine filler or filler selected from calcium carbonate, fly ash, calcined clays, calcined shales, calcined smectites.