EP1019333A1

EP1019333A1 - Aqueous suspension based on alkaline aluminium polysulphate, preparation method and use in the field of building materials

Info

Publication number: EP1019333A1
Application number: EP98947601A
Authority: EP
Inventors: Sylvie Touzet; Jean-Yves Chane-Ching; Evelyne Prat
Original assignee: Rhodia Chimie SAS
Current assignee: Rhodia Chimie SAS
Priority date: 1997-10-03
Filing date: 1998-10-05
Publication date: 2000-07-19
Also published as: WO1999018045A1; ZA988997B; FR2769308A1; CA2305486A1; FR2769308B1; JP2001519309A; US6423133B1; AU9445998A; CA2305486C

Abstract

The invention concerns an aqueous suspension comprising: A) silica and/or alumina particles; and B) a compound of global formula (I): Al(OH)a(SO4)b(SiOx)c(Y)d with: a ranging between 0.4 and 2; b ranging between 0.3 and 1.35; c ranging between 0 and 0.1; d being more than 0.05; Y selected among the alkaline and alkaline-earth metals; x ranging between 2 and 4, and its derivatives. Said compound (B) being present in the suspension at a concentration of at least 1.65 mol/l expressed in aluminium mol derived from said compound. It also concerns a method useful for preparing said suspension and their uses in the field of cement pastes, mortars and concrete and particularly as setting and hardening accelerator of cements.

Description

Aqueous suspension based on alkali aluminum polysulfate, process for its preparation and its use in the field of building materials "

The present invention relates to aqueous suspensions comprising at least one alkaline compound (B) associated with silica and / or alumina, a process useful for the preparation of these compositions and their uses in the field of cementitious pastes, mortars and concrete and in particular as an accelerator for setting and stiffening cements.

Conventionally, in the concrete industries, layers of concrete or mortar are applied on a support or surface to be concreted using two spraying techniques, one by dry process and the other by wet.

The methods of spraying concrete by dry route, use a dry mixture comprising all the traditional anhydrous components of a concrete or a mortar. This is transported to a spray nozzle where wetting with mixing water is then carried out. A ^{• setting} accelerator is generally added, upstream or at the level of the projection nozzle, and the mixture obtained is sprayed onto the surface to be concreted. Unfortunately, we are witnessing with this type of process a phenomenon of concrete rebound which is detrimental on the economic level and which, moreover, represents a risk for the safety of the technician ensuring the projection.

The wet spraying process, which uses a cement mixture which is usually well wetted, overcomes in part the two problems mentioned above. However, the presence of excess water affects the density of the concrete or mortar and the introduction of a setting accelerator to compensate for this effect, on the other hand harms the mechanical resistance over time of the concrete or mortar, once projected.

Recently, it has been proposed in patent applications EP 736 489 and EP 736 501, the use of mixtures based on silica and aluminum sulphate, in the form of a reversible gel, as products replacement of conventional setting accelerators, in the concrete industries. This type of additive is advantageously less corrosive than conventional setting accelerators and is also economically satisfactory. By being present in shotcrete, it significantly reduces the rebound phenomenon mentioned above.

Unexpectedly, the Applicant has highlighted a new family of aqueous compositions based on aluminum derivatives specific, even more efficient than those described in patent application EP 736 501.

The present invention therefore has for first object an aqueous suspension comprising:

A) particles of silica and / or alumina, and

B) a compound of global formula (I):

AI (OH) a (SO ₄ ) b (SiOx) c (Y) _d (I) with: a between 0.1 and 2, b between 0.3 and 1.5, c between 0 and 0, 1, d greater than 0.05,

Y chosen from alkali and alkaline earth metals x between 2 and 4 and its derivatives, said compound (B) being present in the suspension at a concentration of at least 1.65 mol / l expressed as mole of aluminum originating of said compound.

Preferably, Y represents a sodium atom.

Unexpectedly, the Applicant has shown that the use of an aqueous suspension as defined above significantly increases the hardening kinetics of cementitious pastes, concrete or mortar compared to conventional setting accelerators.

The examples presented below illustrate more precisely this accelerating effect of setting suspensions according to the invention.

Compound (B) of global formula (I) comprises soluble species and solid species.

The soluble species are generally ions, or even polyions, such as hydrolysis complexes, aluminum polysulfates and optionally silicates. The soluble species can be present individually in the solution or adsorbed on the silica or alumina particles.

The solid species are particles of micron or nanometric size of AI (OH) ₃ , AIOOH and / or AI ₃ (OH) ₆ (SO ₄ ) ₂ Na for example. In in general, at least part of these solid species is amorphous, the others being crystallized. These solid species can be dispersed within the dispersion or interact with the silica or alumina particles. According to a preferred embodiment of the invention, the compound (B) has, after being dried, an amorphous structure, said structure representing at least 15% by weight of the compound (B).

More preferably, the compound (B) present in the aqueous suspensions claimed is at least partially in the form of an amorphous dispersed solid. Within the meaning of the invention, the amorphous nature of the dispersed solid is that determined by X-rays. More specifically, the control method is carried out by X-ray diffraction. On the RX spectrum, the amorphous character results in the presence of halos in place of the main lines. The control can be carried out either on the dried suspension or on the suspension as it is.

In the first case, the suspension is dried at room temperature so as to remove the free water, but to conserve the water of constitution of the components of the suspension. The RX spectrum obtained on the dry solid gives access to the quantity of crystallized solid, and therefore by difference to the quantity of amorphous solid. At this quantity of amorphous solid, it is necessary to remove the quantity of silica (it is amorphous) from the suspension to obtain the quantity of amorphous compound (B).

In the second case, the RX analysis is carried out directly on the aqueous suspension. More preferably, the indices a and b present in the overall formula of the compound (B) are respectively between approximately 0.75 and 2 and 0.3 and 1, 2.

According to a preferred embodiment of the invention, said suspension comprises approximately 2.1 to 3.5 mol / l of aluminum, approximately 2.25 to 4 mol / l of sulfate and approximately 0.2 to 3.5 mol / l of silica.

The suspension according to the invention has a pH (measured according to ISO standard 787/9) of between 2.5 and 4. According to a preferred embodiment of the invention, it has a value of between 3 and 4 and more preferably is around 3.7. Advantageously, the aqueous suspensions claimed constitute an optimum with respect to the compromise of the properties sought in the field of cements, mortars and concretes. These properties are accelerated stiffening and setting kinetics and increased mechanical resistance of the grout, mortar or hardened concrete incorporating them.

Generally, an optimization of one of these kinetics is acquired at the expense of mechanical strength and vice versa. Surprisingly, the aqueous suspensions claimed significantly accelerate the stiffening kinetics compared to a conventional suspension, based on a silica / aluminum sulfate mixture, without affecting the long-term mechanical properties of the mortars incorporating them. These remain completely satisfactory. These results are presented in more detail in the examples below.

According to a preferred embodiment of the invention, the aqueous suspension comprises a compound (B) of global formula I in which a has a value of the order of 1.26 ± 0.1, 0.5 ± 0.1 and of 0.88 ± 0.1.

More particularly preferred, the aqueous suspensions comprising a compound (B) of global formula I in which a is between 0.1 and 1.5, with said suspension comprising approximately from 2.2 to 3.1 mol / l of aluminum and about 2.3 to 3.9 mol / l of sulfate.

By way of representative of the aqueous suspensions claimed, particular mention will be made of the suspensions described in the examples below.

According to a preferred variant of the invention, the aqueous suspensions claimed have a silica concentration of between approximately 0.7 and 2.4 mol / L.

In the aqueous suspensions proposed according to the invention, is associated with compound (B) at least one compound selected from:

a silica chosen in particular from silica fumes, precipitated silicas, silica soils, silica gels, fumed silicas, silica compounds of natural or synthetic origin, silico-aluminates, smectites, magnesium silicates, clays, wollastonite, talc, mica, attapulgite, sepiolite, montmorrillite, bentonites,

- an alumina.

In addition, the aqueous suspensions according to the invention can comprise an alkaline or metallic sulfate of the sodium sulfate, iron sulfate, aluminum sulfate ... type. It is preferably sodium sulfate.

The claimed suspensions may also incorporate calcium silicates and aluminates.

Thus, in the particular case where the aqueous suspension combines with compound (B) a silica, there is a beneficial effect on the activity as an accelerator for setting said suspension, resulting in particular in a significant reduction in the rebound phenomenon observed during. concrete splashes.

With regard more particularly to the silica contained in the suspension according to the invention, very particularly suitable is a silica chosen from silica fumes, precipitated silicas, silica compounds of natural or synthetic origin comprising in particular selected silica among the silico-aluminates, for example the ®Tixosil 28 marketed by Rhône-Poulenc, smectites, magnesium silicates in general, and their mixtures. At least one precipitated silica is preferably used, as silica. The term “precipitated silica” is understood here to mean a silica obtained by precipitation from the reaction of an alkali metal silicate with an acid, generally inorganic, at an adequate pH of the precipitation medium, in particular a basic pH, neutral or little acid.

The mode of preparation of the silica can be arbitrary (addition of acid on a silicate base stock, simultaneous total or partial addition of acid or silicate on a base stock of water or silicate solution, etc. .) and is chosen according to the type of silica that one wishes to obtain. At the end of the precipitation step, there is generally a step of separation of the silica from the reaction medium according to any known means, press filter or vacuum filter for example; a filter cake is thus collected, which is washed if necessary; this cake can be, possibly after disintegration, dried by any known means, in particular by atomization, then optionally ground and / or agglomerated. All of these protocols make the subject of a detailed description in application EP 736 501 to which reference will be made.

The precipitated silica preferably contained in the suspension according to the invention generally has a CTAB specific surface of between 50 and 250 m / g, in particular between 100 and 240 m ² / g.

The suspension according to the invention advantageously contains a precipitated silica having a very good capacity for dispersion and disagglomeration.

It is thus possible to use a precipitated silica as described in European patent application EP 520 862.

As a representative of the precipitated silicas capable of being used in the suspensions claimed, it is also possible to propose the precipitated silicas described in application EP 736 489.

The silica, in particular precipitated silica, contained in the suspension according to the invention can be finely divided, in particular following grinding (for example wet grinding) or deagglomeration with ultrasound.

A second aspect of the present invention relates to a process useful for preparing aqueous suspensions based on at least one compound (B) of global formula I as described above.

More specifically, the subject of the present invention is also a process useful for preparing an aqueous suspension, as described above, characterized in that it comprises the steps consisting in:

A - mix aluminum sulphate, silica and / or alumina particles and optionally water;

B - optionally add to the mixture obtained according to step A an alkaline silicate in the form of an aqueous solution and homogenize said mixture at room temperature;

C - adding to the mixture obtained according to step B, an alkaline aluminate in the form of an aqueous solution, with vigorous stirring and at room temperature; D - bring the entire mixture to a temperature between 40 and 90 ° C and recover the expected suspension. According to a preferred variant of the invention, the process of preparation is carried out during the incorporation of an aluminum sulphate. This can be added either all at once during one of the steps of said process or in several times at steps A, B, C and D of the process. It can be added as a powder or solution.

Thus, it can be mixed either in the solid state, that is to say in the form of a powder, or in the molten state, that is to say in the form of a solution brought to a temperature between 95 ° C and 130 ° C.

More preferably, the addition of aluminum sulfate is carried out in the form of a powder or a suspension during step A.

As regards silica and / or alumina, used in step A, they are introduced in the form of suspension (s) or powder (s).

It is preferably an aqueous suspension of silica and more. preferably from a precipitated silica, such as those described in patent application EP 736 501. This aqueous suspension of precipitated silica may have been obtained beforehand by mechanical disintegration of a filtration cake resulting from a silica precipitation reaction. With regard to the protocols for preparing such a filtration and disintegration cake, reference will be made to the description of application EP 736 489. The examples given below present a particular embodiment of this process.

As regards stage B, it is possible to use as silicate all common forms of silicates, such as metasilicates, dissilicate and advantageously an alkali metal silicate M, in which M is sodium or potassiurπ.

Preferably, the silicate has a molar ratio Rm =

SiO ₂ / Na ₂ O between 3 and 3.8. Step B is preferably carried out at a temperature between 10 and 40 ° C and more preferably at room temperature. The silicate is incorporated into the mixture of step A, in the form of a concentrated solution and with strong mechanical stirring.

The third step C relates to the incorporation of the aluminate.

This is also added in the form of a concentrated solution and with vigorous stirring. With regard to the mode of agitation, it may be a shear applied by a homogenizer of the UltraTurrax® type. The mixture thus obtained undergoes in step D, a temperature treatment so as to perfect the homogenization of the reaction assembly. This heat treatment can, for example, consist of a temperature rise for one hour to a temperature between 50 and 90 ° C and preferably of the order of 65 ° C and maintaining the mixture at this temperature for approximately one hour at the end of which the mixture is allowed to cool naturally.

It is clear that the concentrations of silica, aluminum sulphate, silicate and aluminate are adjusted so as to obtain an aqueous suspension as characterized according to the present invention.

As stated above, the aqueous suspensions claimed are particularly advantageous for the preparation of cementitious pastes, concretes and mortars. The advantages obtained are due in part to the use of compound (B) and are particularly optimized when the compound (B) is associated with silica and is in the form of a suspension as described above.

Consequently, another aspect of the present invention relates to the use of compound (B) in the field of building materials.

Thus, it can be used for the preparation of cementitious pastes (grout or tempered compositions formed from cement and water and, optionally, usual additives), mortars and concretes and more particularly as an accelerator of setting and / or stiffening of cementitious pastes, mortars or concretes.

In these applications, the compound (B), preferably in the form of a suspension according to the invention, provides remarkable and unexpected advantages which are particularly advantageous in the field of grouts, mortars and sprayed concretes.

As explained above, the compound (B), preferably in the form of a suspension as claimed, constitutes an optimum with respect to the compromise of properties: stiffening kinetics / setting kinetics / mechanical resistance of the grouts, mortar or hardened concrete.

Thus, in the particular case where the amount of compound (B) used to prepare cement paste, mortar or concrete, is expressed in moles is greater than approximately 0.003 moles per 100 g of cement, a particularly rapid hardening of the sprayed layer is observed, making it possible to work with maximum security, for example under the vault, from a few hours after the spraying (application to the production of structural mortars in particular).

The use of the aqueous suspensions described above is preferred. They do not degrade the mechanical properties of the cement compositions over time. On the contrary, it is found that they lead to high compressive strength values at 28 days, in particular when an amount is used such that the amount by mass of silica used (expressed as anhydrous silica) is between 0.2 and 5%, in particular between 0.4 and 2.5% relative to the mass of cement used to prepare the cementitious, mortar or concrete paste.

As such, they are therefore particularly advantageous for the application of layers of cementitious pastes, concretes or mortars by spraying techniques.

They are first of all perfectly pumpable by the projection machines conventionally used.

The health and safety conditions, in particular for the technician, implementing the spraying process, are improved due to the very slightly irritating nature of the suspension according to the invention, in particular thanks to its pH of between 2.5 and 4.

The use of suspensions according to the invention also makes it possible to limit losses from rebound projection and to obtain very thick projected layers, thereby increasing productivity. This is possible in particular thanks to the homogeneity, cohesion and / or adhesion (tacky appearance) of these cement compositions.

They also favor concreting in cold weather. Finally, the suspensions according to the invention can be used for the preparation of cementitious pastes (grout or tempered compositions formed from cement and water and possibly common additives), mortars and concretes for the consolidation of wells. oil.

Indeed, following a drilling, cement must be placed between the tubes which must casing the well and the wall of the hole to seal this annular space. Depending on the depth of placement of the cement, specific additives can be added to the cement to adjust its hydraulic and mechanical characteristics, which are affected by the temperature and pressure varying with the depth. In some cases, in especially in areas near the sea floor, where temperatures are around 4 ° C, the setting times of mixtures are excessively long. It is then necessary to improve their homogeneity while waiting for hardening.

Preferably, the suspensions according to the invention are used at an estimated concentration in mole of compound (B) of global formula I greater than about 0.003 mole per 100 g of cement used to prepare the cement paste, mortar or concrete. A particularly rapid hardening of the mixture is thus obtained.

The present invention also relates to a method of spraying concrete or mortar for applying a layer of concrete or mortar to a surface, characterized in that a compound (B) is added just before or at the level of the spraying means. as described above. This. process can be carried out, dry or, preferably, wet.

According to a particular embodiment of the invention, an amount is used such that the concentration in moles of said compound (B) is greater than approximately 0.003 moles per 100 g of cement used to prepare the concrete or mortar.

Preferably, the compound (B) is introduced in the form of an aqueous suspension as defined above.

According to one embodiment of the invention, the process is carried out dry.

Generally, a dry mixture of concrete or mortar is then formed, the said mixture is moved to introduce it into a projection means, the compound (B) is added to the mixture, preferably in the form of a suspension. aqueous according to the invention, just before or at the level of the spraying means and the resulting mixture is sprayed from the spraying means onto the surface or the support to be coated.

Compound (B), preferably in the form of a claimed aqueous suspension in accordance with the invention, and the mixing water can be introduced into the dry mixture separately, that is to say by two different means (for example using two different pumps). They can also be introduced into the mixture jointly, that is to say by the same means; they are then in particular mixed with each other prior to their introduction into said mixture. The use of suspension according to the invention makes it possible to reduce the rebound and to reduce the formation of dust.

It should be noted that the claimed aqueous suspension can be used, in particular, as mixing water. Although the spraying process can be carried out dry as described above, its implementation by wet gives particularly excellent results.

Thus, according to a preferred embodiment of the invention, the process is carried out by the wet process.

In general, a mixture of tempered concrete or mortar is then formed, the said mixture is moved to introduce it into a spraying means, the compound (B) is added to said tempered mixture, preferably in the form of an aqueous suspension. as claimed, just before, or at the level of the projection means and the resulting mixture is projected from the projection means onto the surface (or the support).

In the two embodiments of the invention, the means used to form the dry mixture or the tempered mixture, to move and then introduce this mixture into the spraying means and to spray the mixture onto the surface to be concreted from said means correspond to those usually used in the field of concrete or mortar spraying and are therefore well known to those skilled in the art.

Thus, the dry mixture and the mixed mixture are generally each formed by kneading the products entering into their composition; the order of introduction of said products into the mixer can be arbitrary; for example, in the case of the wet spraying process, aggregates or aggregates (sand in the case of a mortar; aggregates or larger aggregates such as gravel and / or pebbles, and generally sand, in the case of a concrete) and the cement are first kneaded together, the water then being introduced, the wet mixture thus formed being finally kneaded.

Additives, such as a plasticizer for example, can optionally be incorporated at any suitable time during the preparation of the dry mixture (dry process) or the mixed mixture (wet process). Mention may be made, as fluidizers, in particular melamine, sodium polynaphthalene sulfonate, sodium polyacrylate, sodium polycarboxylate. It is also possible to incorporate reinforcing fibers such as polyvinyl alcohol, polypropylene, steel, polyacrylonite, cellulose, carbon, kevlar®, polyamide, polyethylene, etc. fibers. In addition, in the case of the dry spraying method, the dry formed mixture is introduced into the spraying means generally after having been transported using a stream of compressed air in a pipe (or pipe). ; in the case of the wet process, the tempered mixture is introduced into the spraying means generally after having been conveyed using a suitable pump, for example a piston pump or a screw pump, in a pipe ( or driving).

Compound (B), preferably in the form of an aqueous suspension in accordance with the invention, can be brought just before or at the level of the spraying means, for example by a metering pump. The projection means is usually constituted by a projection nozzle; the assembly formed from the dry mixture, the mixing water and the compound (B), preferably in the form of a claimed aqueous suspension, is then sprayed, from this spray nozzle, generally at the using propellant air which feeds said nozzle, the propellant air usually being compressed air.

The use of compound (B), preferably in the form of an aqueous suspension as defined according to the invention, and its place of introduction into the mixture are essential characteristics of the invention.

The examples and figures presented below illustrate the invention without however limiting its scope ^w.

- Figure 1 is a representation of the stiffening kinetics obtained with two control mortars and 8% additive mortars in aqueous suspensions according to the invention.

- Figure 2 is a representation of the stiffening kinetics obtained with a control mortar and 10% additive mortars in aqueous suspensions according to the invention.

- Figure 3 is a representation of the tensile strength by bending obtained with a control mortar and additive mortars at 6% in suspension S1 and S2. - Figure 4 is a representation of the resistance in simple compression obtained with a control mortar and additive mortars at 6% in suspension S1 and S2.

- Figure 5 is a RX diffraction representation of the suspension S1 dried at room temperature.

EXAMPLE 1

Preparation of an aqueous composition at 2.37 M in compound (B) free of SiO ₂ .

In a reactor equipped with a stirrer Ultraturrax type, 600 ml was poured in a solution of 2M aluminum Al sulfate. The geometry of the reactor is set so as to obtain a maximum shear ^'choosing for example a reactor small area and high height. After switching on the stirrer, continuously are added at room temperature 37.6 ml of a solution of sodium silicate of R _m = (SiO ₂ / Na ₂ O) molar = 3.45 and 5, 72 M in SiO ₂ . The addition is carried out over a period of approximately 3 min. 94 ml of a 5.7 M sodium aluminate solution in Al are then added continuously at room temperature and still under high shear. The addition is carried out over a period of approximately 8 min.

The dispersion obtained is then transferred to a double jacket reactor provided with a thermostated enclosure. The whole is stirred and a heat treatment is carried out according to the following profile:

- temperature rise for 60 min to 65 ° C

- temperature plateau of 65 ° C for 60 min

- natural cooling. The dispersion obtained has the following characteristics:

OH / AI = 1, 23

Al = 2.37 M

S0 ₄ = 2.46 M.

It is called PASS 2.4 M. It has a milky appearance and requires stirring to avoid decantation. It is a suspension of dispersed solids. EXAMPLE 2

Preparation of aqueous compositions with a lower concentration of compound (B) of global formula I and free of SiO ₂ .

10 ml of the composition prepared in Example 1 are taken up and 2.33 ml of demineralized water are added with stirring at room temperature. The dispersion thus obtained has an aluminum concentration of 1.92 M. It is called PASS 1.9 M. 10 ml of the composition of Example 1 are taken up and 4.06 ml of is added with stirring. Demineralized Water. The dispersion thus obtained has an aluminum concentration of 1.69 M.

It is called PASS 1, 7 M. It has a milky appearance and requires stirring to avoid decantation. It is a suspension of dispersed solids.

EXAMPLE 3

Determination of the stiffening kinetics obtained with the aqueous compositions of Examples 1 and 2.

Cement slurries are prepared in the following manner: 40 g of water, 8 g of an aqueous composition prepared according to examples 1 and 2 and 100 g of cement are introduced into a cylindrical mold of ^w 250 ml (triggering of the stopwatch), mixed using an RW 20® type agitator fitted with a three-bladed marine propeller for one minute. The grout is then tamped down with light tapping. The stiffness monitoring measurements are carried out using a Stevens® texturometer.

The Stevens® texturometer is a device for measuring the force necessary to make a probe penetrate the grout. Its technical characteristics are as follows:

- force sensor TA 1000 (from 5 to 1000 g, ie from 0.049 to 9.81 N);

- penetration speed 0.2 mm / s;

- penetration depth 4 mm;

- probe: needle V_ ', diameter for TA 1000, cross section. A measurement is carried out approximately every 2 to 15 minutes (stop before 15 minutes if the force scale stop is reached).

The results obtained are represented in FIG. 1 which also accounts for the kinetics obtained with a first control composition comprising a concentration of 1.64 mol / L of the same compound (B) with aluminum concentration 1.6, and a second control composition called S1 to base of an aluminum sulphate obtained according to Example 6 below.

It is noted that the best stiffening kinetics are obtained with compositions having a concentration of the order of or greater than 1.65 moles per liter of compound B.

EXAMPLE 4

Preparation of a precipitated silica cake G1

In a stainless steel reactor equipped with a propeller stirring system and a jacket heating:

• 346 liters of water • 7.5 kg of Na2Sθ4 (electrolyte)

• 587 liters of aqueous sodium silicates with a Siθ2 Na2θ weight ratio equal to 3.50 and a density at 20 ° C equal to 1.133.

The silicate concentration (expressed as Siθ2) in the base is then 85 g / l. The mixture is brought to 79 ° C. while keeping it under stirring. Then introduced into the mixture 386 liters of dilute sulfuric acid with a density at 20 ° C equal to 1.050, until a pH value equal to 8 is obtained (measured at the temperature of the medium). The temperature of the reaction medium is 79 ° C. for the first 25 minutes, then it is brought from 79 ° C. to 86 ° C. in 15 min, and then maintained at 86 ° C. until the end of the reaction.

Once the pH value equal to 8 is reached, 82 liters of aqueous sodium silicate with a Siθ2 / Na2θ weight ratio equal to 3.50 and a density at 20 ° C equal to 1.133 and 131 liters of acid of the type described above, this simultaneous introduction of acid and silicate being carried out in such a way that the pH of the reaction medium is constantly equal to 8 ± 0.1. After introducing all of the silicate, the diluted acid is continued to be introduced for 9 min so as to bring the pH of the reaction medium to a value equal to 5.2. We stop then the introduction of acid and the reaction mixture is maintained for another 5 min with stirring.

The total duration of the reaction is 1 18 min.

A precipitated silica slurry is obtained which is filtered and washed using a filter press so that a G1 silica cake is finally recovered, the loss on ignition of which is 78% (therefore a dry matter content 22% by weight) and whose Na2Sθ4 content is 1% by weight.

EXAMPLE 5

Preparation of a suspension of silica G2.

We introduce into a CELLIER mixer, 4 kg of the cake

G1 prepared in Example 4 (obtained by press filtration and having a dry matter content of 22% by weight and an Na2SO4 content of 1% by weight), previously brought to 60 ° C.

Then, during deflocculation, cake 13 is introduced simultaneously, 1 ml of a sodium aluminate solution (having a content of

AI2O3 of 22% by weight and an Na2θ content of 18% by weight (density:

1, 505)) and 7.47 ml of a sulfuric acid solution at 80 g / l (density: 1.505), so as to maintain the pH at a value of 6.5.

The AI / Siθ2 weight ratio is approximately 2600 ppm. It is left to mature for 20 minutes while continuing the mechanical deflocculation.

The ^* G2 suspension of silica obtained is characterized by:

• a viscosity of 0.06 Pa.s (measured under a shear of 50 s ~ 1 for 1 minute); • a particle size such as d-i o = 5 μm, dso = 19 μm, dgo

= 60 μm.

After a week of storage, gold observes:

• the formation, at the bottom of the storage container, of a deposit that is excessively difficult, if not impossible, to redisperse; • an increase in the viscosity of the suspension: its viscosity is then 0.45 Pa.s (measured under a shear of 50 s ^"1 for 1 minute). EXAMPLE 6

Preparation of an aqueous suspension of control silica S1.

1,020 kg of suspension G2 prepared in Example 5 (taken after disintegration), having a dry matter content of 22% by weight, and 85 grams of water are added to 1,150 grams of hydrated aluminum sulphate Al2 (Sθ4) 3, 17H2O melted at 110 ° C in its water of crystallization.

The addition is carried out in about fifteen minutes.

A homogeneous G3 suspension is obtained having the following characteristics:

• pH 2.3

• dry matter content (% by weight) 37.0

• silica content (% by weight) 10.0 (calculated as anhydrous silica)

• aluminum sulphate content (% by weight) 27.0 (calculated as anhydrous aluminum sulphate)

It is noted that after 24 hours of rest, said suspension solidifies and therefore takes the form of a gel. It is referred to below as "S1".

EXAMPLE 7

Preparation of an aqueous suspension of silica S2 according to the invention.

268 ml of an aqueous dispersion aluminum sulphate-particles of Siθ ₂ are poured into a reactor equipped with an Ultra-Turrax®; This dispersion has an Al concentration of 2.2 M, SO ^" of 3.3 M and in silica particles expressed as Siθ ₂ of 2.3 M. This dispersion is prepared according to the procedure described in Example 6 and diluted with demineralized water so as to present the abovementioned concentrations. reactor geometry is defined so as to obtain maximum shear by choosing, for example, a reactor with a small surface area and a high height.

After the Ultra-Turrax® is started up, 17 ml of sodium silicate solution of Rm = SiO ₂ / Na ₂ O = 3.35 and Si concentration = 3.9 are added continuously at room temperature Mr.

The addition is carried out over a period of approximately one minute. 48 ml of a sodium aluminate solution with a concentration of 5.7 M Al concentration are then added continuously and at room temperature, still under high shear. The addition is carried out over a period of approximately four minutes.

The dispersion obtained is then transferred to a double jacket reactor, provided with a thermostated enclosure. The whole is stirred and a heat treatment is carried out according to the following profile:

- temperature rise for 60 minutes to 65 ° C; - temperature plateau of 65 ° C for 60 minutes;

- natural cooling.

The dispersion obtained has the following characteristics: Al = 2.6 M SO ₄ = 2.7 M SiO ₂ = 2.05 M

OH / AI = 1, 4

The dispersion, designated "S2", is stable with respect to decantation over time.

EXAMPLE 8

Preparation of an aqueous suspension of silica according to the invention S3.

By reproducing the protocol described in Example 7, but adding at the end of the temperature plateau 53.3 g of AI ₂ (SO ₄ ) ₃ , 15.66 H ₂ 0 gradually over approximately 5 minutes. The mixture is left stirring at temperature for 5 minutes. The dispersion is naturally cooled. An aqueous suspension is obtained having the following characteristics:

Al = 3M

SO ₄ = 3.2 M

OH / AI = 1.18 the suspension is designated "S3" below.

EXAMPLE 9

Determination of the stiffening kinetics obtained with aqueous suspensions in accordance with the present invention.

Cement slurries are prepared as follows: 40 g of water, 10 g of suspensions S1, S2 and S3 prepared according to the previous examples and 100 g of cement are introduced into a 250 ml cylindrical mold (start of the stopwatch) , mixed using an RW 20® type agitator fitted with a three-bladed marine propeller for one minute. The grout is then tamped down with light tapping. The measures of. follow-up of stiffening are carried out using a Stevens® texturometer described above.

A measurement is carried out approximately every 2 to 15 minutes (stop before 15 minutes if the force scale stop is reached).

The results obtained with a CPA CEM I 52.5 cement and 10 g of S1, S2 or S3 are shown in FIG. 2.

It is noted that the suspensions S2 and S3 (containing compounds (B)) activate the stiffening kinetics much more strongly than the suspension S1 (based on aluminum sulphate).

EXAMPLE 10

Mortars are prepared from 450 g of high resistance Portland cement (corresponding to the European standard) CEM I 52.5). 1350 g of standardized sand, 225 g of water (water / cement = 0.5), 4.5 g of GT resin (1% superplasticizer) and x% suspension S1 or S2 relative to the mass of cement.

The procedure is as follows:

In a Perrier® type mixer, the water, GT resin and cement mixture is introduced. We mix at moderate speed, while adding the sand, we mix for two minutes at high speed (≈ 120 rpm), we introduce the accelerator and we mix for two minutes at high speed ((≈ 120 rpm). VICAT needle take-up kinetics are then monitored in accordance with standard NF P 15-414. The start times for setting are shown in the following table I:

TABLE I

The suspensions S1 and S2 lead to comparable grip kinetics. The mechanical strengths were measured at 7 and 28 days on broken 4x4x16 test pieces with a Toni Technick type 202 press.

Figures 3 and 4 show the tensile strengths by bending and simple compression obtained with the reference mortar (x = 0) and with the additive mortars to 6% of suspensions S1 or S2. The mechanical strengths obtained with the suspensions S1 and S2 are substantially equivalent and equal to approximately 80 to 90% of the strengths of the reference mortar.

These results clearly demonstrate that the strong activation of the stiffening given by the use of silica suspension and compound (B) is not carried out to the detriment of the long-term mechanical properties of the mortars.

EXAMPLE 11

Characterization of dried products by X-ray diffraction.

An X-ray analysis (X-ray diffraction - Philips PW 1800 device) is first performed on the S1 and S2 products after drying at room temperature. The spectrum obtained on the product S1 after drying shows a high proportion of crystallized aluminum sulphate: 90% of the AI takes part in a crystallized phase.

On the contrary, the spectrum obtained on product S2 after drying (FIG. 5) essentially shows amorphous compounds: less than 10% of the crystallized phase is observed (alunite-type phase).

These analyzes associated with the evaluations presented in Examples 9 and 10 demonstrate the advantage obtained with the products according to the invention, that is to say in which, after drying, the aluminum is present at least partially in one or more amorphous mineral phases.

EXAMPLE 12

Demonstration of an amorphous dispersed solid.

After centrifugation of the suspension S2 for 6 h at 30,000 rpm, 1 ml of the supernatant is removed, acidified with 1 ml of 1% nitric acid, then the aluminum is assayed by plasma emission spectrometry. The results are given with 10% relative uncertainty. This assay associated with the quantification of the supernatant, and the decantal makes it possible to go back to the percentage of total aluminum in solution and, by difference to the percentage of aluminum present in dispersed solid phases.

In the suspension S2, the compounds containing Al are distributed as follows:

- 75% of the aluminum is in solution,

- 25% is present in dispersed solid phases.

It is therefore shown that, on the product as it is, aluminum is present at least partially in a dispersed solid compound (capable of decanting during an ultracentrifugation).

In addition, an X-ray analysis (X-ray diffraction - Siemens D 500 device (theta-theta)) is carried out on a sample of product S2 as protected from drying by a film of milar. The product is almost completely amorphous (less than 1% of crystallized aluminum sulphate). It is demonstrated, by bringing these two observations together, that in product S2, aluminum is present at least partially in mineral phases in the form of an amorphous dispersed solid.

Claims

1. Aqueous suspension comprising:

A) particles of silica and / or alumina, and B) a compound of global formula (I):

AI (OH) a (S0 ₄ ) b (SiOx) c (Y) _d (I) with: a between 0.1 and 2, b between 0.3 and 1.5, c between 0 and 0, 1, d greater than 0.05.

Y chosen from alkali and alkaline earth metals x between 2 and 4 and its derivatives, said compound (B) being present in the suspension at a concentration of at. minus 1.65 mol / l expressed as mole of aluminum originating from said compound.

2. Aqueous suspension according to claim 1, characterized in that the compound (B) of global formula (I) has, after being dried, an amorphous structure, said structure representing at least 15% by weight of the compound (B).

3. Aqueous suspension according to claim 1 or 2, characterized in that the compound (B) is at least partially in the form of an amorphous dispersed solid.

4. Aqueous suspension according to one of claims 1 to 3, characterized in that in the overall formula of the compound (B): a is between approximately 0.75 and 2 and b is between approximately 0.3 and 1, 2.

5. Aqueous suspension according to one of claims 1 to 4, characterized in that said suspension comprises approximately 2.1 to 3.5 mol / l of aluminum, approximately 2.25 to 4 mol / l of sulfate and approximately from 0.2 to 3.5 mol / l of silica.

6. Aqueous suspension according to one of claims 1 to 5, characterized in that it has a pH of between 2.5 and 4.

7. Aqueous suspension according to one of claims 1 to 6, characterized in that it uses a compound (B) of global formula I in which a has a value of about 1.26 ± 0.1 , 0.5 ± 0.1 or 0.88 ± 0.1.

8. Aqueous suspension according to one of claims 1 to 6, characterized in that it uses a compound of global formula I in which a is between 0.1 and 1.5, and in that it comprises approximately 2.2 to 3.1 mol / l of aluminum and approximately 2.3 to 3.9 mol / l of sulfate.

9. Aqueous suspension according to one of claims 1 to 8, characterized in that it comprises approximately 0.7 to 2.4 mol / L of silica.

10. Aqueous suspension according to one of claims 1 to 9, characterized in that the silica is chosen from silica fumes, precipitated silicas, silica soils, silica gels, fumed silicas, compounds of silica of natural or synthetic origin, silico-aluminates, smectites, magnesium silicates, clays, wollastonite, talc, mica, attapulgite, sepiolite, montmorrillite and bentonites.

11. Aqueous suspension according to one of claims 1 to 10, characterized in that it also comprises calcium silicates and aluminates.

1_>, A method useful for preparing an aqueous suspension as defined in claims 1 to 11, characterized in that it comprises the steps consisting in:

C - adding to the mixture obtained according to step B, an alkaline aluminate in the form of an aqueous solution, with vigorous stirring and at room temperature;

D - bring the entire mixture to a temperature between 40 and 90 ° C and recover the expected suspension.

13. The method of claim 12, characterized in that it further comprises the addition of an aluminum sulfate during one or more of steps A, B, C or D.

14. The method of claim 12 or 13, characterized in that the aluminum sulfate, mixed in step A with the silica and / or alumina suspension, is in the form of either a powder or a solution brought to a temperature between 95 and 130 ° C.

15. Method according to one of claims 12 to 14, characterized in that the aluminum sulfate is introduced in the form of a solution or a powder during step A.

16. Method according to one of claims 12 to 15, characterized in that during step A, the silica and / or alumina are introduced in the form of suspension (s) or powder (s).

17. Method according to one of claims 12 to 16, characterized in that the silica is introduced in the form of an aqueous suspension, said aqueous silica suspension being an aqueous suspension of precipitated silica obtained by mechanical disintegration of a cake of filtration resulting from a precipitation reaction of silica.

18. Use of a compound (B) of global formula (I) as accelerator for setting and or stiffening a cement paste, a mortar or a reton.

19. Use according to claim 18, characterized in that the compound (B) of global formula I is used at a concentration greater than about 0.003 mole per 100 g of cement used to prepare a cement paste, a mortar or a concrete .

20. Use according to claim 18 or 19, characterized in that the compound (B) is used in the form of a suspension according to one of claims 1 to 11.

21. A method of spraying concrete or mortar to apply a layer of concrete or mortar to a surface, characterized in that a compound (B) of global formula (I) is added just before or at the level of the spraying means as defined in claims 1 to 11.

22. Method according to claim 21, characterized in that a compound of global formula (B) as defined in one of claims 1 to 11 is used, at a concentration greater than approximately 0.003 mole per 100 g of set cement. used to prepare concrete or mortar.

23. The method of claim 21 or 22, characterized in that either a dry mixture of concrete or mortar, or a mixture of concrete or tempered mortar, said mixture is moved to introduce it into a means of projection, a compound (B) of global formula (I) as defined in claims 1 to 11 is added to the mixture, whether or not spoiled, just before or at the level of the projection means, and the resulting mixture is projected from the means projection on the surface to be treated.

24. Method according to one of claims 21 to 23, characterized in that the compound (B) is introduced in the form of an aqueous suspension according to one of claims 1 to 11.