MXPA98007287A - Auction suspensions of silice and its applications in the compositions based on argamasa mine - Google Patents

Abstract

The present invention relates to an aqueous suspension comprising a mixture of at least one aqueous suspension of precipitated silica and of at least one latex, in which said aqueous suspension of precipitated silica has a dry matter content comprised between 10 and 40% by weight, it has a viscosity of less than 4.10-ÅPa.s for a shear of 50 s-û and that produces after centrifugation at 7,500 turns per minute for 30 minutes, a supernatant containing more than 50% by weight of silica initially in suspension. This suspension is usable in the compositions based on a mineral mortar, and in the concrete compositions

Description

* • AQUEOUS SUSPENSIONS OF SILICA AND ITS APPLICATIONS IN THE COMPOSITIONS BASED ON ARGAMASS MINERAL Field of the Invention The present invention relates to aqueous suspensions comprising precipitated silica and its use in the preparation of compositions based on cement or analogous mineral mortar or compositions derivatives.

Description of the invention The invention applies to all types of compositions comprising a mineral mortar, such as cement, slag or the like, either as a base ingredient or in combination with other constituents. For the purposes of the present description, "cement composition" means a composition based on cement or any other analogous mineral mortar, and water. These compositions constitute products that are obtained as such, especially as a coating, or that are intended for use as a coating. incorporate especially mineral charges of variable granulometry. Such compositions containing a mineral mortar and a mineral filler in the form of granules are very generally considered as concretes. Thus the specialist has been accustomed to describe more specifically the concrete as a composition in which the mineral charge is based on relatively coarse granules (of the order of 4 to 15 mm), and to the mortar as a composition in which the mineral charge is based on less coarse granules (less than 4 mm), the term "concrete" will be used interchangeably in the present description to designate all types of compositions whatever their granulometry to simplify exposure. It is desirable to be able to control the properties of these various compositions both during their manufacture, as well as in their putting into operation, as well as in the products derived after hardening. Thus, concrete compositions for a set of masterpieces (realization of walls, coatings, posts, cement layers, slabs, industrial floors) must meet the particular requirements in terms of: rapid setting kinetics for early or early stripping; reduced plastic shrinkage and absence of fissures particularly for cement layers; good mechanical properties at 28 days; durability (resistance to abrasion, reduced permeability in gas and in liquids, impermeability for the particular case of underground concretes or marine concretes in contact with water.) Furthermore, concretes can either be manufactured at the site of the work, or be manufactured in a central and dispatched on the place of use (concrete ready for use). In order for the composition to retain acceptable, identical properties during a fourth period, a stability in the hydrated state must be ensured, especially by keeping its fluidity intact or by limiting the segregation of materials in suspension. More specifically, architectural concretes, that is, the concretes seen, must satisfy, in addition to the requirements at the level of aesthetics: a homogeneous aspect of the surface; a reduction of the efflorescence that forms deposits of salts on the surface (in particular for acid concretes). The prefabricated concretes for the realization of elements of facades, of paving stones, paving, laying of pipes, must present more particularly a reduced permeability to gases and liquids for an optimal durability, as well as the same aesthetic qualities as the architectural concretes for the visible elements. The mortar compositions or coatings for the second work (plaster or reconstruction coatings, smoothing coatings, glue mortars, projection coating) must also satisfy a certain number of particular requirements: - good retention of. water to prevent water escaping by penetration into the porous support or by preferential drying on the surface (risk of cracking and formation of powder similar to flour on the surface); good adherence to the support; resistance to abrasion and shocks; good fluidity associated with good water retention (particularly for smoothing coatings, these contradictory properties are difficult to obtain together.) In general, during use, the critical parameters are fluidity to ensure start-up, rates of rezowing or adherence to the support, water retention To satisfy these requirements, appropriate additives are usually incorporated into cement compositions or derived compositions, however, it is not uncommon for an additive to procure, at the cost of a positive effect. For this, a fluidizing agent can improve the fluidity of a composition, but the high contents, sometimes necessary to achieve the desired result, very clearly favor the exudation and decrease the kinetics. of setting and thus the acquisition of mechanical strength with respect to the characteristics as achieved initially (fight against cracking, aptitude or capacity of stripping, early start-up ...).

In the same way, the setting retarders allow to conserve and transport a composition for a certain time after its preparation, and they also have a very marked effect on the exudate and setting kinetics. Such difficulties appear in particular in the case of compositions of cement pastes and self-leveling fluid concretes which must have, according to the books, classical loads, rheological characteristics of subsidence (measured with respect to the cone of Abrams) or static exposure. or dynamic. The solutions that allow the obtaining of fluid concretes or mortars, known up to now, are consistent either in optimizing the granulometric tank by the introduction of fine or ultra-fine materials as described in patent EP-A-0 184 386, this solution presents, besides the disadvantage of needing the manipulation of important amounts of dust, the inconvenience of being very sensitive to small variations of the content or quality of the products used, which makes them in practice difficult to use on a work, or in adding , in significant quantities, fluidizing agents, retardants and possibly water retaining agents to maintain the handling of the material during an interval of sufficient time, which generally involves a delay setting that penalizes the productivity of the delayed demolition work or the need for plaster in the case of early or early stripping) and a high sensitivity to small variations around the optimized composition. In practice, it is common to face problems of redhibitory diminution of manageability in the case of erring the dosage, of segregation of the mortar or concrete, of significant wear, of prolongation of the setting time and of reduction of the final mechanical properties, in particular in the case of an overdosage of water. In fact, it is found that it is very difficult to produce cement compositions, or derived compositions, which respond to all the desired imperatives in view of one application. It is already known from patents US-5 149 370 and GB-2 212 489 to improve the properties of oozing and segregation of the compositions by adding silica soils. However, the properties of these compositions are still insufficient. The present invention aims to respond to this demand for improved additives that allow to combine various advantageous properties among those mentioned above. The object of the invention is to provide a new additive for the cement compositions or the derivative compositions, which makes it possible to reduce the effects of oozing and segregation of the concrete compositions. Another object of the invention is to provide an additive which allows an improved fluidity to be combined, good water retention, even in the case of strong water contents and / or fluidizing agents or plasticizers, and ensure a good durability, especially a reduction in permeability to water and gases, to the hardened product, which reduces the efflorescence. For this purpose, the invention has for its object an aqueous suspension comprising a mixture of at least one aqueous suspension of precipitated silica and of at least one latex, in which said aqueous suspension of precipitated silica has a content of dry matter comprised between 10 and 40% by weight, has a viscosity lower than 4.10"2 Pa.s for a shear of 50 s_1 and produces after centrifugation at 7500 rounds per minute for 30 minutes a supernatant containing more than 50% by weight of the silica initially in suspension. The first essential component of the mixture forming the aqueous suspension object of the invention is an aqueous suspension of precipitated silica with a high content of dry matter, which has a reduced viscosity and good stability over time. Such suspensions are described, as well as their manufacturing process, in the patent FR-A-2 722 185. Preferably, the dry matter content of said suspension is between 15 and 35% by weight. The viscosity of said suspension is advantageously less than 4.10-2 Pa.s for a shear of 50 s_1. These suspensions are very stable and their stability can be appreciated thanks to a sedimentation test consisting of centrifuging said suspension at 7500 tr / min for 30 minutes. The amount of silica contained in the supernatant obtained at the exit of this centrifugation, measured after drying the supernatant at 160 ° C until obtaining a constant weight of the material, represents more than 50%, preferably more than 60% of the weight of the silica contained in the suspension.

Advantageously, the amount of silica contained in the supernatant obtained after the centrifugation represents more than 70%, in particular more than 90% of the weight of the silica in suspension. Another characteristic of these suspensions refers to the granulometry of the silica particles in suspension. In fact, the concentrated silica suspensions known hitherto, in addition to their high viscosity, have the drawback of carrying large agglomerates in suspension which induce a sedimentation with the passage of time. The granulometric distribution of the suspended materials can be defined by means of the average diameter D50, which is the diameter of the grain such that 50% of the population of suspended grains has a smaller diameter. In the same way, D5 represents the diameter of the grain such that 95% of the population of grains in suspension has a smaller diameter. Another major feature of the suspensions is the FD deagglomeration factor. This factor, higher when the silica suspension is deagglomerated, is indicative of the fine material rates, ie the rates of particulate materials less than 0.1 μm that are not detected by a common granulometry. The granule characteristics of the silica suspensions are determined by means of a granulometric measurement carried out on the suspensions, with the help of a SYMPATEC granulometer. FD is measured by introducing in a granulometer a known volume V of suspension diluted so as to obtain a silica content of 4% by weight and is equal to the ratio (10 x V in ml / optical concentration detected by granulometry). The silica agglomerates present in these suspensions are small in size. Preferably, the particle size distribution of the agglomerates in suspension is such that their average diameter D5o is less than 5 μm and the deagglomeration factor FD is greater than 3 ml. Advantageously, the diameter D50 is less than 2 μm, the factor FD is greater than 13 ml and in addition, the diameter D95 is less than 20 μm. The second essential compound of the mixture forming the aqueous suspension object of the invention is a latex, namely an aqueous suspension of natural or synthetic resin particles.

Advantageously, said particles are the polymerization products of at least one monomer with an ethylenic unsaturation. Preferably, the latex itself is the result of the emulsion polymerization of at least one monomer with an ethylenic unsaturation. In particular, the monomer with an ethylenic unsaturation can be advantageously chosen from styrene, butadiene, acrylic acid, methacrylic acid, esters of acrylic or methacrylic acid, preferably with C 1 -C 2, vinyl esters, and its mixtures. The latex which can be used according to the invention can thus comprise homopolymer or copolymer resin particles, an example being a styrene-butadiene rubber latex. The size of the particles of the latex is variable following the contemplated application. In a first advantageous embodiment, this size is from 0.1 to 5 μm. Mention may be made especially of latices with a particle size of 0.1 to 0.3 μm, preferably of styrene-butadiene latices, or latices with a particle size of 1 to 5 μm, preferably of acetate latices. / versatato. In a second advantageous embodiment, this size it's at a lot of 100 nm; These nanolatices can be very varied in nature. The two compounds mentioned are associated in the appropriate proportions for the desired application. Generally, it is preferable that the aqueous suspension according to the invention comprises from 3 to 25 parts by weight of the silica, expressed as dry weight, for 100 parts by weight of the suspension, more preferably from 5 to 20 parts by weight of silica for 100 parts of suspension. On the other hand, it is preferable that the dry weight of the latex represents the value of 5 to 50 parts per 100 parts by weight of the aqueous suspension according to the invention, advantageously from 10 to 40 parts by weight 100 parts of the suspension. The aqueous suspensions according to the invention can be incorporated into the cement pastes or more generally of the cement compositions, based on mineral mortar and water, to which they especially endeavor a resistance to water segregation and retention associated with an increase in fluidity due to a synergy effect between the silica suspension and the latex.

The invention thus also relates to compositions based on a mineral mortar and water, characterized in that they comprise an aqueous suspension as defined above. The mineral mortar may be of any known type, especially cement of the type PORTLAND CPA HP, CPA 55, CPJ 45, CPA CEM I, CPA CEM I PM, CPA CEM I PMES, CPJ CEM II, CPJ CEM II PM, CPJ CEM II PMES, CHF CEM II, CLK CEM II, slag from blast furnaces, or pozzolanic mortars. The ratio of water to the mortar is variable and depends above all on the desired fluidity for the composition. This ratio can be in particular from 0.3 to 2, preferably from 0.3 to 1.5. In these compositions, it is preferable that the silica represents from 0.3 to 5% by weight with respect to the mortar, expressed in relation to dry weight, preferably from 0.8 to 1.5%. It is also advantageous that the dry weight of the latex represents the value of 0.2 to 50% by weight with respect to the mortar, expressed in relation to the dry weight, preferably from 3 to 30%. To complete the effect procured by the aqueous suspension according to the invention, the compositions may further comprise at least one fluidizing agent. This agent can be chosen among the substances commonly used for this purpose in cement compositions. It will be advantageously chosen from lignosulfonates, casein, polynaphthalenates, in particular alkali metal polynaphthalene sulfonates, melamines, polymelamines, formaldehyde derivatives, polyacrylates of alkali metals, polycarboxylates of alkali metals and grafted ethylene polyoxides. Such an agent can be advantageously used at a ratio of 0.1 to 10% by weight with respect to the mortar. This agent can be introduced separately from the aqueous suspension according to the invention, or simultaneously by means of a suspension comprising at the same time the suspension of the silica, the latex and the agent. Similarly, the compositions may further comprise at least one water retention agent, which may be chosen from substances commonly used for this purpose in cement-based compositions. It will be advantageously chosen from polyvinyl alcohols optionally modified, polyethylene glycols, polyoxyethylenes, acrylic polymers, especially polyacrylamides, polysaccharides of origin bacterial, such as xanthan gum, guar gums, cationized guar gums, carob bean extracts, alginates, pectins, celluloses, cellulose ethers, especially carboxyalkylcelluloses, alkylcelluloses, hydroxyalkylcelluloses, such as methylhydroxypropylcelluloses, polyvinylpyrrolidone, sugars, especially dextrose, ribose, corn starches, cationized wheat or not, lignite, leonardite and derivative products, alkali metal polyacrylates and polystyrene sulphonates. One such agent can be advantageously used at a ratio of 0.01 to 10% by weight in relation to the mortar. On the other hand, the compositions may also advantageously comprise a setting accelerator, such as aluminum sulphate, with a content of 0.01 to 3% by weight in relation to the mortar (expressed in relation to the dry weight). In the case of aluminum sulphate, this content is expressed by weight of the anhydrous aluminum sulfate. This agent can be introduced separately from the aqueous suspension according to the invention, or simultaneously by means of a suspension comprising both the suspension of silica, the latex and the agent. It will also be advantageously used in the compositions, the reinforcing fibers that allow to improve the resistance to cracking. These fibers are preferably chosen from polyvinyl alcohol, polypropylene, polyethylene, steel, polyacrylonitrile, cellulose, carbon, kevlar, polyamide and polyester fibers. The cement compositions based on a mineral mortar and water to be described, can be used either as such or combined with other materials, especially to form concrete (or mortar) compositions. As previously stated, concrete is understood as the mixture of a mortar - mineral, water and granulates of variable granulometry, especially of rock, sand and possibly fine materials, even of ultra - fine materials. In this regard, the invention also relates to concrete compositions comprising an aqueous suspension described above. These compositions can be obtained by mixing the suspensions according to the invention with a mineral mortar, granulated materials and optionally water complementary, or by mixing a cement composition described above with the granulates and optionally complementary water. Another object of the invention is therefore the use of the aqueous suspensions or of the cement compositions described above in concrete compositions, in particular of the specialty concretes of the aforementioned types and of the coatings of the second work. Aqueous suspensions or cement compositions which respond to at least one of the preferred characteristics indicated above will be advantageously used as regards the relative contents of silica and latex, and optionally of fluidizing or water retention agents, and once the cement case. The proportion of the granulates in these concrete compositions can be chosen in the manner known per se in the usual ranges corresponding to the type of concrete desired. The expression finds a particular application in the so-called specialty concretes that must manifest particular properties of the appearance of the surface, of mechanical resistance, of durability of the finished product, of the fluidity at the moment of the putting into operation a reduced tendency to segregation. Mention may be made, for example, of fluid concretes, concrete for the manufacture of paving stones (layers of cement and fluid mortars for the layers), underwater concretes that must be easily pumpable and injectable, facing concretes, prefabricated concretes by centrifugation or Hot pressing, surface smoothing and reconstruction coatings, especially of floors, colored concretes, which must have a homogeneous surface without efflorescence and a relatively clear base ink, as well as light concretes, concrete for industrial floors, waterproof concrete and concrete foundation of oil wells, which must have a reduced porosity, all these concretes are improved their properties thanks to the invention. More particularly, in the case of concrete and fluid cements, the high fluidity which is frequently desirable is achieved thanks to the invention, improving the water retention capacity of the compositions, which makes it easier to put in place and reduce the cracking problems due to a water outlet that causes a plastic shrinkage shortly after putting it in place. The subject of the invention is therefore the use of the aqueous suspensions described above either as the water retention agent in the cement or concrete compositions. This use, which allows to reduce the plastic shrinkage and consequently the cracking, is particularly interesting for the cement layers and the smoothing coatings. Among the advantageous properties conferred to the cement-based compositions or to the concrete compositions by the aqueous suspensions according to the invention, the reduced tendency to segregation of the hydrated compositions, especially of the high-content compositions, is more particularly taken into account. Water. In this regard, the invention also relates to the use of aqueous suspensions such as those defined above, either as the antisegregation agent in cement compositions based on mineral mortar and water and in concrete compositions, especially in compositions where the weight ratio of water / cement or more generally water / mortar is from 0.3 to 2, preferably from 0.3 to 1.5. The invention is also very advantageous for the realization of prefabricated facing concretes or waterproof concrete, because it allows to obtain a better dispersion of the cement, and therefore a better homogeneity. This improves the appearance of the surface in terms of the regularity and durability of the hardened product due to the limited penetration of water and gases. In the case of facing products, smoothing and reconstruction coatings, they are accompanied by a color clarification and an improvement in the appearance of the surface, a better resistance to carbonation and a limitation of the appearance of efflorescence, as well as a reduction of the corrosion of the reinforcements. Another subject of the invention is the use of aqueous suspensions described above as a permeability reducing agent for gases and for liquids in compositions based on a mineral and water mortar, or in concrete compositions. The resistance to the penetration of water is a decisive advantage for the impermeability of works located in a flood or humid area or works destined to receive water (deposits, dams, aqueducts, swimming pools, water pipes). Other advantages of the invention will appear more clearly in the light of the following examples.

Preparation Example: Preparation of a precipitated silica suspension 1. A pellet of precipitated silica Gl is prepared in the following manner. In a stainless steel reactor equipped with a system of agitation by propellers and a heating by a double envelope, enter: 346 liters of water, - 7.5 kg of Na2SO4 (electrolyte), 587 liters of aqueous sodium silicate presenting a weight ratio of Si02 / Na20 equal to 3.50 and a density at 20 ° C equal to 1.133. The silicate concentration (expressed in Si02) at the foot 'of the tank is then 85 g / 1. The mixture is brought to 79 ° C keeping under stirring. 386 liters of dilute sulfuric acid of density at 20 ° C equal to 1.050 are immediately introduced into the mixture until obtaining a pH value equal to 8 (measured at medium temperature). The temperature of the reaction medium is 79 ° C during the first 25 minutes, then it is brought from 79 ° C to 86 ° C in 15 minutes, and it is maintained immediately at 86 ° C until the end of the reaction. Once the pH value equal to 8 is achieved, 82 liters of aqueous sodium silicate with a weight ratio of Si02 / Na20 equal to 3.50 and a density at 20 ° C equal to 1133 are introduced together into the reaction medium. 131 liters of acid of the type described above, this simultaneous introduction of the acid and the silicate is carried out in such a way that the pH of the reaction medium is constantly equal to 8 + 0.1. After the introduction of the entire silicate, the introduction of the diluted acid is continued for 9 minutes so as to bring the pH of the reaction medium to a value equal to 5.2. The introduction of the acid is then stopped and the reaction pulp is maintained for an additional 5 minutes under stirring. The total duration of the reaction is 118 minutes. A precipitated silica paste is obtained which is filtered and washed by means of a filter press in such a way that finally a Gl cake of silica is recovered, the fire loss of which is 78% (the content of which dry material is 22% by weight) and thus the Na2SO content is 1% by weight. 2. CELLIER, 4 kg of Gl concrete (obtained by filtration in a filter press and having a dry matter content of 22% by weight and a Na2SO4 content of 1% by weight), previously brought to 60, is introduced into a CELLIER slurry mixer. ° C. Then, during the deflocculation of the concrete, 13.1 ml of a sodium aluminate solution (having an A1203 content of 22% by weight and an Na20 content of 18% in weigh-density: 1.505) and 7.47 are simultaneously introduced. ml of a sulfuric acid solution at 80 g / 1 (density: 1,505), so that the pH is maintained at a value of 6.5. The weight ratio of Al / SiO2 is approximately 2600 ppm. It is left to mature for 20 minutes continuing the mechanical deflocculation. The silica suspension G2 obtained is characterized by: a viscosity of 0.06 Pa.s (measured under a shear of 50 s_1 for 1 minute); a granulometry such that Dio = 5 μm, D50 = 19 μm, D9o = 60 μm. After one week of storage, the following can be observed: - the formation, at the bottom of the storage container, of an excessively difficult, if not impossible, sediment to disperse; 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). 3. The chamber of a NETZCH LMEl shredder is fed with 2 liters of G2 suspension (pre-washed after desilling), which have a dry material content of 22% by weight, at a flow rate of 5 liters / h; The filling rate of the chamber with aluminum balls (diameter: 0.6-1 mm) is 75% and the rotation speed of the shaft or shaft is 2000 tr / minute. At the outlet of this wet trituration step, a suspension is obtained characterized by: a viscosity of 29 mPa.s (measured under a shear of 50 s "1 for 1 minute); a granulometry such as D10 = 1.13 μm, D50 = 4.1 μm, D90 = 9.33 μm; a content of dry material. 22% by weight; - an amount of silica recovered in the 63% supernatant (following the sedimentation test under centrifugation defined above). In a stirred reactor, 4 540 of the silica suspension thus prepared are introduced, and the pH is adjusted to 9.5, with stirring with the aid of concentrated soda, in order to stabilize the medium. 100 000 g of a 50% styrene-butadiene rubber latex of the dry extract, having a particle size of 0.1-0.2 μm, marketed under the name, are immediately introduced under stirring at a flow rate of 100 g / minute. SB 112 by the company Rhone-Poulenc. After a half hour of stirring, the pH is readjusted to 9.5 and a suspension having a viscosity of 30 mPa.s is obtained under a shear of 50 s ~ x. This suspension is perfectly stable against sedimentation for more than three months.

It contains approximately 10% by dry weight of silica and 26% by dry weight of latex.

Application example 1; Realization of a concrete of facing Test 1 A concrete composition is prepared according to the following formula: Granules (5-15): 1 000 kg Granules 0-4 (sand): 800 kg HPR cement: 425 kg • Fluidizer (Rhéobuild 2000 PF Marketed by MBT): 1.7 kg ( 0.1% with respect to the weight of cement) Water: 147 1 In a planetary mixer of the HOBART type, the granulates that are introduced are introduced. knead for one minute, then introduce the cement and mix for 30 seconds. They are introduced immediately after mixing, water and fluidizer and 42.5 kg (10%) with respect to the cement) of the aqueous suspension of the reference example. The amount of silica added corresponds to 1% of the weight of the cement introduced. The water / cement weight ratio of this concrete composition is thus 0.41.

Test 2 A concrete composition is similarly prepared by increasing the initial water content so that a weight ratio of water / cement is obtained. of 0.49, the amount of all the other constituents is kept identical.

Comparative tests 1 and 2 The analogous compositions are prepared to those of tests 1 and 2 in which the aqueous suspension of Example A is omitted but the water / cement ratio is retained. The characteristics of these four compositions are evaluated by emptying a concrete in identical hermetic molds and demolding after three days.

It is remarked first that in tests 1 and 2, the fluidity of the concrete is better and putting it in place in the formwork is better. On the other hand, in tests 1 and 2, the segregation of the granulates and the exudate is not observed, which is incompatible up to the present with a good fluidity. The characteristics of hardened concretes are also evaluated. The bleach of the product is measured by means of a XENOTEST colorimeter and quantified by means of chromatic coordinates L *, a * and b * in the CIÉ system 1976 (L *, a *, b *) as defined by the International Search Commission and located as a repertoire of the French Standards (AFNOR) colorimetric color No. X08-12 ( 1983). A better homogeneity of the surface and a lightening of the sensitive color are noted in the tests 1 and 2. The eventual formation of efflorescence is verified after 28 days. On this date, no efflorescence is evident in tests 1 and 2 when the products of the comparative tests show numerous whitish efflorescence on the surface. The results are recorded in the following table 1.

Table 1 It would seem that the combined action of silica and latex provides a filling of the porosity of the concrete that reduces efflorescence at the end. It is also observed that the permeability in water and gases of the concretes of tests 1 and 2 is reduced with respect to that of comparative tests 1 and 2, which leads to a greater durability to provide resistance to carbonation, to the attacks by the aggressive waters, ... In addition, the adhesion of the concrete on a support is improved due to the presence of the suspension of silica and latex, as well as to the resistance to abrasion (reduction of the formation of dust ).

A decrease in the number of cracks is also observed due to an improvement in water retention.

Application example 2: Realization of a cement composition with a high content of water (or mortar) This example contemplates to demonstrate the effect of synergy produced by the suspension of silica and latex on the rheological and stability properties of cement pastes with a high water content. A first series of tests not in accordance with the invention is carried out, which show that silica or latex alone does not solve the problems presented by these mortars, when compared with two tests according to the invention.

Comparative test 1 A mortar is prepared comprising a suspension of silica prepared in the same manner as in preparation example A, but without adding latex. It responds to the following formula: HTS cement 100 g fluidizer (Melmentplast N40) 2.5 g * setting retarder 0.8 g * (Melretard) - aqueous suspension of silica to 23% of the dry extract 5 g water 24 g * marketed by CIA The water / cement ratio is thus 0.28. In a ladle apparatus agitated by a shovel, water, the fluidizer and the retarder are introduced, then the cement is added under agitation for 3 minutes. The silica suspension is then introduced under stirring which is continued for 10 minutes.

Comparative test 2 A similar mortar is prepared in the same way where the water / cement ratio is 0.35.

Comparative test * 3 A mortar is prepared that responds to the following formula: HTS cement 100 g fluidizer (Melmentplast) 2.5 g retarder (Melretard) 0.8 g styrene-butadiene latex in 50% aqueous suspension (SB 112) 5 g water 25 g The water / cement ratio is thus 0.28. The preparation is analogous to the comparative test 1, the latex is introduced instead of the suspension of the silica.

Test 1 According to the invention, a mortar is prepared according to the formula: - cement HTS 100 g fluidizing (Melmentplast) 2.5 g retarder (Melretard) 0.8 g aqueous suspension of example A 9.6 g or: silica (dry weight): 1 g latex (weight dry): 2.5 g water 22 g The water / cement ratio is 0.28. The preparation is analogous to that of the comparative tests.

Test 2 A mortar similar to that of test 1 is prepared in which the water content is adjusted to obtain a water / cement ratio of 0.35. These five compositions are subjected to the following rheological measurements carried out on a RHEOMAT 115 apparatus equipped with a MS cell or cell DIN 145. The mortar is subjected to a transverse shear of 0 to 1000 s-1 for 1 minute, then a constant shear of 1000 s "1 for 1 minute, and lower the shear to 0 s" 1 in 1 minute, measuring the viscosity. The final viscosity is determined. The aptitude with respect to segregation and exudation is evaluated: in a static way: the appearance of a test tube filled with 200 ml of mortar is observed, during a time interval of 24 hours; - in a dynamic way under pressure: a given amount of mortar is placed in an API filter above which an air pressure of 7.105 Pa is imposed; the amount of water expelled from the pulp is measured and after drying at 160 ° C the dry extract from the upper part (side air) and from the lower part (side filter) of the obtained filtration concrete. The dry extract of the lower or higher extraction of the concrete is defined by the formula: Total extraction mass - mass of water from extraction Dry extract = x 100 Total extraction mass A difference between the two values is indicative of a heterogeneous concrete, a lower dry extract higher than the upper dry extract, which means a segregation. The results are expressed by the following values: the percentage of water recovered by filtration amount of water received Er = x 100 amount of initial mortar the water content of the concrete after filtration initial water - water recovered by filtration Tf = x 100 mass of the filtered concrete with respect to the initial water content of the Ti mortar with initial water i = x 100 initial concrete mass It is noted that with respect to the comparative test 2, the combined addition of a suspension of silica such as defined in the invention and of a latex in the test 2 leads to the release properties superior to those obtained with the suspension of the silica alone. . Furthermore, it is observed that the addition of latex alone in the comparative test 3 leads to a cement composition having poor seepage and segregation properties. Consequently, the excellent anti-oozing and segregation properties of the additives according to the The invention is completely unexpected insofar as the person skilled in the art would be aware of a decrease in the properties of oozing and segregation by combining an aqueous suspension of silica with a latex, and not an improvement. The results are gathered in Table 2, which is given below. ts) O TABLE 2 (*) important decanting that leads to filter clogging It appears from the foregoing results that the silica used alone in comparative test 1 leads to a stable homogeneous mortar but has the tendency to form a gel at rest (which will however be destroyed under reduced shear). However, when the E / C ratio increases, a tendency to rejuvenation and settlement (segregation) appears. In the dynamic reheating test, the concrete obtained is more heterogeneous, which explains the settlement observed in the statistics. Silica is of limited effectiveness. In comparative test 3, the tendency to exudate and to segregate is very important in static and under pressure. Latex does not have an advantageous effect against these phenomena. In the test 1, it is noted with respect to the comparative test 1 a lower tendency to gel, the behavior of the mortar is almost Newtonian. The concrete does not present any problems of oozing or segregation: it remains perfectly homogeneous both in the static mode and. in the dynamic mode, although it is much more fluid than the mortar of the comparative test 1. In the test 2, at the moment in which the ratio E / C is 0.35, the mortar remains perfectly stable and homogeneous in the mode static and dynamic, contrary to the mortar of comparative test 2. In addition, although the mortar is more fluid (50 mPa.s against 65), a very improved retention of water in the test 2 is observed.

It is noted that in relation to this date, the best method known by the applicant to carry out the aforementioned invention, is the conventional one for the manufacture of the objects to which it relates.

Having described the invention as above, the content of the following is claimed as property

Claims (22)

1. An aqueous suspension, characterized in that it comprises a mixture of at least one aqueous suspension of precipitated silica and at least one latex, in which said aqueous suspension of precipitated silica has a content of dry material comprised between 10 and 40% by weight, at a viscosity lower than 4.10"2 Pa.s for a shear of 50 s" 1 and produces after centrifugation at 7 500 revolutions per minute for 30 minutes a supernatant containing more than 50% of the weight of the silica initially in suspension.

2. The suspension according to claim 1, characterized in that the latex comprises a product of the polymerization of at least one monomer with ethylenic unsaturation, chosen in particular from styrene, butadiene, acrylic acid, methacrylic acid, esters of acrylic acid or methacrylic, the vinyl esters and their mixtures ..

3. The suspension according to any of the preceding claims, characterized in that the latex has a particle size of 0.1 to 5 μm.

4. The suspension according to any of claims 1 or 2, characterized in that the latex has a particle size of at most 100 nm.

5. The suspension according to any of claims 1 to 4, characterized in that it comprises from 3 to 25 parts by weight of silica, expressed in dry weight, per 100 parts of suspension.

6. The suspension according to any of claims 1 to 5, characterized in that it comprises from 5 to 50 parts by weight of latex, expressed as dry weight, for 100 parts in suspension.

7. A composition based on a mineral mortar, especially cement and water, characterized in that it comprises a suspension according to one of claims 1 to 6.

8 *. The composition according to claim 7, characterized in that it comprises from 0.3 to 5% by weight of silica, expressed in dry weight, with respect to the mortar, preferably from 0.8 to 1.5

9. The composition according to any of claims 7 or 8, characterized in that it comprises from 0.2 to 50% by weight of latex, expressed as dry weight, with respect to the mortar, preferably between 3 and 30%.

10. The composition according to any of claims 7 to 9, characterized in that it comprises at least one fluidizing agent with a content of 0.1 to 10% by weight with respect to the mortar.

11. The composition according to claim 10, characterized in that the fluidizing agent is chosen from lignosulfonates, casein, polynaphthalenes, in particular alkali metal polynaphthalene sulphonates, melamines, polymelamines, formaldehyde derivatives, polyacrylates. of alkali metals, polycarboxylates of alkali metals and polyoxides. of ethylene grafted.

12. The composition according to any of claims 7 to 9, characterized in that it comprises at least one water retention agent in a content of 0.01 to 10% by weight with respect to the mortar.

13. The composition according to claim 12, characterized in that the water retention agent is selected from among the optionally modified polyvinyl alcohols, the acrylic polymers, especially the polyacrylamides, the polysaccharides of bacterial origin, the guar gums, the cationized guar gums , carob seed extracts, alginates, pectins, celluloses, cellulose ethers, especially carboxyalkylcelluloses, alkylcelluloses, hydroxyalkylcelluloses, methylhydroxypropylcelluloses, polyvinylpyrrolidone, sugars, corn starch, cationized wheat or not, lignites, leonardites and derived products, alkali polyacrylates, and polystyrene sulfonates.

14. The composition according to any of claims 7 to 13, characterized in that it comprises a setting accelerator agent in a content of 0.01 to 3% by weight with respect to the mortar.

15. The composition according to any of claims 7 to 14, characterized in that it comprises reinforcing fibers.

16. The composition according to any of claims 7 to 15, characterized in that the weight ratio of the water with respect to the mortar is from 0.3 to 2.

17. A concrete composition, characterized in that it comprises a mineral mortar, granules and an aqueous suspension according to one of claims 1 to 7.

18. The composition according to claim 15, characterized in that the weight ratio of the water with respect to the mortar is from 0.3 to 2.

19. The use of a composition according to any of claims 7 to 16, for the preparation of specialty concretes, especially fluid concretes, concretes for the manufacture of paving stones, underwater concretes, facing concretes, smoothing and plaster coatings or reconstruction of floors, waterproof concrete, lightweight concrete or colored concrete, concrete for concrete industrial floors, prefabricated concretes for centrifugation or hot pressing, foundation concretes from oil wells.

20. The use of a suspension according to any of claims 1 to 6 as an antisegregation agent in cement compositions or in concrete compositions.

21. The use of a suspension according to any of claims 1 to 6, as an agent that reduces the permeability to gases and liquids in cement compositions or in concrete compositions.

22. The use of a suspension according to any of claims 1 to 6, as an agent that allows water retention in cement compositions or in concrete compositions.