EP0946441A1

EP0946441A1 - Textile additive for cement material, materials and product containing same

Info

Publication number: EP0946441A1
Application number: EP97947100A
Authority: EP
Inventors: Jean-Luc Joutang; Alain Debouzie; Michel Conche; Marc Lepont
Original assignee: Saint Gobain Isover SA France
Current assignee: Saint Gobain Isover SA France
Priority date: 1996-11-28
Filing date: 1997-11-20
Publication date: 1999-10-06
Also published as: WO1998023547A1; AU5227298A

Abstract

The invention concerns a textile additive for cement material, particularly for mortar, concrete, or gunite, containing mineral wool, characterised in that the mineral wool is capable of dissolving in a physiological medium. This additive can be incorporated in materials with a cement matrix, dry or hydrated, to form for example products, particularly in slab form, reinforced with fibers or guniting with mineral wool base.

Description

FIBROUS ADDITIVE FOR CEMENT MATERIAL, MATERIALS AND PRODUCT CONTAINING THE SAME

The present invention relates to the field of cementitious products and relates more particularly to a fibrous additive to be incorporated into cementitious materials.

In the present application, the term "cementitious material" means a material containing a hydraulic binder based on cement mixed with water and possibly aggregates of variable particle size (gravel, gravel, sand, fine and / or ultra-fine ), which is implemented in particular by casting, by extrusion or by projection, then matured. Furthermore, the term “additive” is used here to denote an ingredient intended to enter into the composition of a cementitious material as defined above. This term does not have a quantitative nuance here and should not be limited to minority constituents of said materials.

It is now common practice to reinforce cement-based products, such as mortar or concrete, by incorporating reinforcing fibers, in particular mineral fibers, into the matrix. In particular, the presence of fibers in the matured product gives it a better ductility, due to the possibility of relative sliding of the matrix with respect to the fibers, which allows the dissipation of stresses at the interface between the fibers and the matrix. The reinforcing mineral fibers are generally so-called glass fibers

"Textiles", obtained by mechanical drawing and collected in son with a sizing composition, or mineral wool, in particular rock, obtained by centrifugal drawing of a ^"melt fillet falling on a set of rotating rolls, or by stretch blowing the melted material passing through an appropriate die. To be suitable for reinforcing a cementitious product, the fibers must satisfy two major requirements: chemical stability in the hydrated matrix, on the one hand, and the ability to mix homogeneously with the other constituents during the mixing, without too much affecting the rheological properties of the hydrated mixture, on the other hand.

Glass fibers are now available, the composition of which has been studied to resist strongly basic media such as that which results from the hydration of cement. These so-called alkali-resistant fibers, described in particular in FR-A-2 447 801, guarantee that the composite maintains high mechanical characteristics, even after severe aging conditions. To remedy the rheological difficulties linked to the incorporation of fibrous material in the hydrated mixture, a known solution consists in modifying the composition of the mixture by adding either excess water with an increased risk of cracking, or additives such as thinning agents which significantly increase the cost of the product. These modifications of the composition are also not without influence on the setting time of the composition.

Document FR-A-2 728 560 proposes an alternative which consists in using a fibrous additive based on rock wool, such as basalt, provided with a size allowing the dispersion of the fibers during mixing, this additive being susceptible to promote the fluidity of the cement-based material in which it is added, and in some cases, to totally or partially replace a chemical plasticizer. Obtaining a homogeneous distribution of the fibers in the matrix may, however, require very vigorous mixing.

In general, the incorporation of mineral wool, during the mixing of concrete or mortar, continues to pose a certain number of mixing difficulties between the aggregates and the fibers in the cementitious paste.

Other cementitious products to which the invention applies are fire protection, thermal or acoustic insulation coatings, obtained by spraying a mixture of mineral wool flakes and cement onto the surfaces to be protected or insulated. The application of the coating on the surface is usually done by means of a machine which simultaneously projects onto the same area of the surface a jet of dry composition containing the mineral wool and the cement, and a jet of water, which mix to each other by hitting the surface.

The qualities of the final coating depend more particularly on the homogeneity of the wool coating with hydrated cement to obtain a uniform and continuous sprayed layer without cracks, as well as on the stability over time of the mixture. The quality of the sprayed mixture can however be difficult to reproducibly control during a campaign of use.

The present invention proposes to overcome these difficulties and to allow the manufacture, with the usual mixing or spraying techniques, of a cementitious product containing a mineral fibrous additive homogeneously mixed with the cementitious matrix, and in which the fibers are chemically stable throughout the life of the product. These aims, as well as others which will appear subsequently, are achieved according to the invention thanks to a fibrous additive for cement-based material, in particular for mortar or concrete, comprising mineral wool, characterized in that the wool mineral is likely to dissolve in a physiological environment. By mineral wool is meant, within the meaning of the present invention, a material capable of being obtained by fiberizing a silicate mineral composition in the molten state, based on natural rock, possibly modified by the addition of one or more several metallic oxides and / or vitrified materials such as blast furnace slag. Typically, these silicate compositions with a high melting point are characterized by a content by weight of alkaline-earth elements greater than the content of alkaline elements, in the form of oxides.

Although it has not been shown that the inhalation of microfibers from mineral wool can cause any pathological action, mineral wool degradable in physiological medium has been developed for the manufacture of thermal and acoustic insulation products in order to '' eliminate any potential problem for the manipulators who equip the buildings.

The ability to dissolve after inhalation of mineral wool fibers in a human body is generally appreciated by measuring in vitro the rate of dissolution of wool in a solution which simulates an extracellular fluid. According to one aspect of the invention, the biodegradable nature of mineral wool can also be assessed by "in vivo" tests reflecting the ability of the inhaled material to remain in the lungs despite physiological evacuation mechanisms and environmental conditions. This capacity, which will later be called "biopersistence", can be influenced in particular by the possible action of macrophages or by the possible "mechanical" actions undergone by the fibers in the pulmonary medium which can lead to the breaking of the fibers. constituting the wool in fibers of smaller size, which can be a factor influencing their speed of dissolution and / or their capacity to be evacuated by the organism.

Surprisingly, it has been found by the present inventors, on the one hand, that these biodegradable wools can be introduced into a hydrated cement mixture without posing any problem of handling the mixture or can be coated with a hydrated cement mixture on a regular basis. , and on the other hand that they are not degraded in the strongly alkaline medium resulting from the hydration of the cement. More particularly in the case of fiber-reinforced products, another advantage, which will be detailed later, lies in the fact that these wools easily disperse homogeneously in the hydrated matrix, to give the matured product improved resistance. In addition, the biodegradability of wool makes the manufacture of the product free of any potential risk, from the handling of the free additive to the maturing stage of the material. The same applies to the use of the finished product.

Mineral wools which can be used according to the invention advantageously have a composition rich in alkaline-earth, in particular lime and magnesia, and relatively poor in alumina. Preferably, the wools usable according to the invention have an index K1 of at least 40, this index being defined by the following relationship:

Kl = Σ (% by mass of Na ₂ O, K ₂ O, CaO, MgO, BaO, B ₂ O ₃ ) - 2 x (% by mass of Al ₂ O ₃ )

This index recently proposed by the German government is quite significant of degradability in a physiological environment. Values of 40 and above are currently considered to be far beyond any potential risk.

In the context of the present invention, wools having a K1 index of the order of 30 and more are compatible with the requirements on the quality of the cementitious material.

Advantageously, the wools degradable in a physiological medium have an alumina content of less than 12%, more particularly to 8%, in particular to 4%, and a CaO content of the order of 7 to 45%. The MgO content is preferably from 0 to 16%, in particular from 1 to 16%.

Advantageous mineral wools are those of the type described in WO-A-93 22 251, the composition of which comprises the following constituents according to the following weight proportions:

• SiO ₂ 48 to 67%

. Al ₂ O ₃ O at 8%

• Fe ₂ O ₃ 0 to 12%

(total iron)

. CaO 16 to 35%

. MgO l at 16%

. Na ₂ O + K ₂ OO at 6.5%

P ₂ O ₅ O at 5% respecting the following relationships . Na ₂ O + P ₂ O ₅ > 2%

. Fe ₂ O ₃ + Al ₂ O ₃ <12%

. CaO + MgO + Fe ₂ O ₃ > 23%

In addition to their high solubility in a physiological medium, these wools are advantageously characterized by good mechanical strength, in particular when they are subjected to heat.

Very advantageously, the wool composition comprises the following constituents according to the following weight proportions:

. SiO ₂ 50 to 67%, especially 50 to 66%

• Al ₂ O ₃ O at 7%, especially less than 4%

. 11% Fe ₂ O ₃ O, especially 0 to 7%

(total iron)

. CaO 16 to 35%

. MgO l at 16%, especially from 3 to 16%

. Na ₂ O + K ₂ O l at 6.5%, especially from 1 to 6%

• P ₂ 0 ₅ O at 5% with. Fe ₂ O ₃ + Al ₂ O ₃ <8%

. CaO + MgO + Fe ₂ O ₃ > 25%

Preferred wools are those which, corresponding to any of the preceding definitions, comprise less than 4% of Al ₂ O ₃ .

When the Fe ₂ O _{3 content} of the wools is equal to or greater than 7%, their Al ₂ O _{3 content} is preferably equal to or less than 1%. When the Fe ₂ O _{3 content} of the wools is equal to or greater than 7%, their P ₂ O _{5 content} is preferably greater than 1%.

Other rock wools which can be used according to the invention are those of the type described in EP-A-0 459 897 and advantageously correspond to the following formula:

. SiO ₂ 40 to 58%

• Al ₂ O ₃ 3 at 11.5%

. Fe ₂ O ₃ 0.1 to 15% (total iron)

. CaO 7 at 40%

. MgO 4 at 16%

• P ₂ 0 ₅ l at 7%

. Impurities <3% . Na ₂ O + K ₂ O <7% with. CaO + MgO + Fe ₂ O ₃ > 25%

As other examples of biodegradable wools suitable for the invention, mention may be made of those of the type described in WO-A-96 04 213, the composition of which comprises the constituents below according to the following weight proportions:

. SiO ₂ 40 less than 52%

. Al ₂ O ₃ less than 4%

. CaO more than 25 and up to 45%

. MgO 5 to 15%. BaO 0 to 7%

. Na ₂ O 2 at 12%

. K ₂ OO at 10%

. Na ₂ O + K ₂ O 2 at 15%

. TiO ₂ , Fe ₂ O ₃ , MnO 0 to 5% Yet another example of biodegradable wool suitable for the invention is given in WO-A-95 31 410, which relates to wool whose composition comprises the following constituents according to the following weight proportions:

. SiO ₂ 40 to 67%

. CaO 20 to 45%. MgO 0 to 12%

. Na ₂ OO at 10%

. B ₂ O ₃ 0 to 15%

. Na ₂ O + B ₂ O ₃ 0 to 25%

. P ₂ O ₅ 0 to 5% - Al ₂ O ₃ 0 to 3%

. TiO ₂ , Fe ₂ O ₃ , BaO, MnO, K ₂ O 0 to 5%

Among mineral wools which can advantageously be used according to the invention, there are wools having a low or non-biopersistent character, in particular those characterized by a half-life time by in vivo test of pulmonary biopersistence by inhalation on animals, for fibers say WHO (defined by the World Health Organization as those having both a length greater than 5 μm and a diameter of less than 3 μm), less than or equal to 25 days, preferably less than 20 days. The conditions of this test are described in the publication entitled “772nd evaluation of soluble fibers using the inhalation biopersistence model, a nine fiber comparison ”published in the journal Inhalation

Toxicology, Volume 8, pages 345-385, 1996.

Another advantageous characteristic is a half-life time by in vivo pulmonary biopersistence test by inhalation for fibers of length greater than 20 μm less than or equal to 15 days, preferably less than or equal to 10 days, always under the conditions below. -above.

Another useful test is an in vivo measurement test of pulmonary biopersistence by intratracheal instillation on animals, the protocol of which is described in the publication.

"Biopersistence of different types of ore fibers in rat lungs after intratracheal application" (BAU, Fb711, 1995). According to the invention, wools characterized by a half-life can be used in this test, for so-called WHO fibers, less than or equal to 40 days, preferably less than or equal to 35 days. It is also possible to use wools characterized by a half-life time in this test, for fibers of length greater than 20 μm, less than 35 days, preferably less than or equal to 30 days. The composition of non-biopersistent wool advantageously meets the following conditions, expressed on the weight proportions of the constituents indicated:

. SiO ₂ > 35%

. Al ₂ O ₃ <15%

. 1 Na ₂ O + 1 K ₂ O + 1 CaO + 1 MgO + 3 P ₂ O ₅ + 1 B ₂ O ₃ - 0.5 Fe ₂ O ₃ - 2 Al ₂ O ₃ - 4 ZnO - 1 TiO ₂ > 26 % in particular> 28% in particular> 35%.

By way of example of mineral wool usable according to the invention, mention may also be made of materials the composition of which comprises the following constituents, the contents of which are indicated by weight of oxide:

. SiO ₂ 30 to 51%

. Al ₂ O ₃ 10 to 30%

. CaO 2 at 30%

. MgO 0 to 20%. Na ₂ O + K ₂ O 0 to 19%

. TiO ₂ 0 to 6% or TiO ₂ + Fe ₂ O ₃ 6 to 18%

. others up to 15% Despite their relatively high alumina content, these wools have a very low biopersistent character, thanks to an appropriate selection of the proportions of the other constituents.

A particular example of a composition which can be used according to the invention meeting the above conditions is as follows:

. SiO ₂ 30 to less than 51%, especially less than 47%

. Al ₂ O ₃ more than 11.5%, in particular more than 13%, up to 25%

. CaO 2 at less than 23%, especially 4 to 20%

. MgO 0 to 15%. Na ₂ O + K ₂ O more than 10 to 19%, especially more than 10 to 18%

. TiO ₂ + Fe ₂ O ₃ 6 to 18%, especially 7 to 16%

. other 0 to 3%, especially 0 to 2%

Another particular example of a composition which can be used according to the invention meeting the above conditions is as follows:. SiO ₂ 32 to 48%, especially 35 to 45%

. Al ₂ O ₃ 10% to 30%, especially 13 to 26%

. CaO 10 to 30%, especially 14 to 25%

. MgO 2 to 20%, especially 5 to 15%

. Na ₂ O + K ₂ O 0 to 12%, in particular 2 to 10%, in particular 6 to 10%. TiO ₂ 0 to 6%, especially 0.5 to 3%

. others 0 to 15%

In the fibrous additive according to the invention, the shape of the wool is not decisive and can be chosen in a manner known per se by the specialist. The wools which can be used according to the invention in particular have an average diameter of the order of 3 to 25 μm. Among this range, we prefer wools whose average diameter is of the order of 5 to 10 μm, which disperse perfectly in the matrix without increasing the viscosity of the mixture.

The fibrous additive according to the invention shows an excellent ability to disperse in the hydrated mixture, whether the wool is introduced in free form or conditioned in the form of more or less entangled nodules. In a particular embodiment, the additive comprises fibrous nodules of approximately 4 to 16 mm in diameter containing fibers of average length from 0.2 to 0.5 mm. Such nodules can be manufactured in particular as described in FR-A-2 677 987. During the manufacture of cementitious products of the concrete or mortar type reinforced, it was surprising to find that under usual mixing conditions, the fibrous additive in this relatively compact form very easily releases the wool which disperses very homogeneously within the hydrated mixture. It has also been found, when these nodules were used to produce sprayed coatings, that they mixed very intimately with the cementitious binder to give a very homogeneous sprayed layer.

The mineral wool is advantageously sized, in particular with a mineral oil or a surface-active substance optionally combined with an anti-foaming substance, as described in particular in FR-A-2 728 560. The invention further relates to compositions for cementitious material, comprising a cement-based binder, which can be dry or hydrated, characterized in that they contain a fibrous additive as described above.

A first embodiment relates to compositions for products of the concrete or mortar type in which the cementitious binder is a major constituent and the fibrous additive is dispersed in this cementitious matrix. In this first embodiment, the invention relates more particularly to a composition comprising a hydrated matrix, since the fibrous additive is preferably mixed with the other constituents after the water has been introduced.

It may especially be mortar compositions, a material based on cement, sand and water, and possibly fines, or a concrete composition which also comprises gravel and / or gravel.

Such compositions can in particular comprise up to approximately 20% by weight of fibrous additive relative to the weight of dry matter, without any problem of kneading of the hydrated mixture being encountered. A wool content of up to 15%, especially from 5 to 15%, is advantageous for obtaining good reinforcement characteristics with optimum ease of use. Lower contents, in the range of up to 5% by weight, in particular of the order of 0.5 to 5%, in particular of 0.5 to 3%, very advantageously make it possible to combine good mechanical performance and ease of implementation at a competitive cost.

These compositions are obtained by mixing the constituents in conventional devices, the fibrous additive being preferably introduced last after the water has been mixed with the other dry materials. They can be shaped as required by all the techniques known per se, in particular by casting, by extrusion or by calendering. Depending on the applications, the composition may also include various suitable additives, such as plasticizer, extrusion agent, dye ...

The invention also relates to a shaped article consisting of a plate, preferably thin, made from a hydrated composition described above. Such a thin plate product, of variable thickness up to approximately 1.5 cm, in particular from 0.4 to 1 cm, can advantageously be produced according to the invention by extrusion or calendering from a mortar composition added with wool.

A plate product according to the invention may also contain other reinforcing agents, such as reinforcing fibers (or textile fibers), in the form in particular of continuous threads and / or cut threads. This variant has proven to be very advantageous because the fibrous additive and the textile fibers have two complementary reinforcing actions in the product. This combination makes it possible to advantageously reduce the proportion of reinforcing fibers to obtain an equivalent result, and consequently to reduce the cost of the product, the wool constituting the fibrous additive according to the invention being substantially less expensive than the textile fibers. Another particular embodiment of the invention relates to compositions for products of the sprayed protective or insulating type, in which the mineral wool is in much higher proportion. In this second embodiment, the invention relates in particular to a dry composition to be sprayed comprising the fibrous additive and a cement-based binder which may optionally also comprise at least one other inorganic binder, such as clays or inorganic salts, and / or organic such as a polyvinyl alcohol.

Such a composition to be sprayed can advantageously comprise of the order of 15 to 35%, in particular 18 to 25% by weight of dry binder, relative to the mineral wool.

By simple dry mixing of the additive according to the invention with the constituents of the cementitious binder, a perfectly homogeneous spray mixture is obtained in which the binder is distributed uniformly over the mineral wool. The hydration of this mixture is therefore facilitated and a very homogeneous hydrated material is directly obtained without resorting to specific mixing operations. The composition to be sprayed according to the invention therefore advantageously lends itself to the usual spraying technique used to produce protective or insulating coatings by giving coatings of very good quality. The invention therefore also relates to a building surface coating, in particular a fire protection coating or thermal or acoustic insulation, produced from a hydrated composition described above. These density coatings π between 120 and 300 kg / m depending on the applications can be obtained by the usual projection technique.

Other features and advantages of the invention will emerge from the detailed description of the following examples. Examples of additives A to L according to the invention, as well as comparative X. Y and Z

Table 1 below presents the composition (in weight percentages) of mineral wools which can be used to constitute a fibrous additive for cementitious material:

- the rock wools A to L are wools soluble in physiological medium, with an average diameter of approximately 5 μm and a length of the order of a few centimeters, obtained by dropping a stream of molten rock on the peripheral surface of successive rotary rollers with horizontal axis, water cooled;

wool X is a rock wool indicated for comparison, of the type used to constitute the fibrous additive of FR-A-2 728 560, obtained like the preceding wools, in which the fibers have an average diameter of the order from 10 to 15 μm, and whose composition is such that it cannot be degraded in a physiological medium within a sufficiently short time;

- wool Y is another rock wool indicated for comparison: it was obtained by passing the molten material through a die followed by a drawing blower; it also cannot be degraded in a physiological environment within a sufficiently short time.

- wool Z is a wool obtained from standard blast furnace slag by the same technique as wool A to L. Slag is commonly used as a powder additive in cement-based products. The properties of this material, especially in the form of wool, are interesting for a comparative analysis of the reactivity of the mineral wools used.

If the sum of the weight percentages indicated for all the constituents of an example in Table 1 is less than 100%, it should be understood that the residual level corresponds to the non-analyzed impurities and / or minority components, in particular of the SO ₃ , MnO type. . If it turns out to be slightly higher than 100%, the reason comes from the tolerances allowed on analyzes in this area. Table 1 presents for each composition the value calculated from the percentages by weight of the following expression (I): (I) IN + 1 K ₂ O + 1 CaO + 1 MgO + 3P ₂ O ₅ + 1 BA - 0 , 5 Fe - 2Al ₂ O ₃ - 4ZnO - 1 TiO ₂ The materials are characterized in table 1 by: - the in vitro biosolubility expressed by the dissolution rate K _dis in ng / cm ² .h (expressed from all the elements passing through solution, in particular SiO ₂ and CaO) of a sample of 200 mg of fibers placed in a cell consisting of two discs and a circular ring, through which circulates a liquid simulating a physiological fluid at a flow rate of 300 ml / day, the liquid being of pH 7.4 to simulate an extracellular fluid or of pH 4.5 to simulate the action of pulmonary macrophages. This in vitro test was developed by SCHOLZE et al. and its protocol is described in Annals of Occupational Hygiene 31 (4B) 1987. The quantities K _dis are indicative of degradability in physiological medium; - the NBO / T value which indicates the proportion of oxygen atoms of the material not engaged in a bond with silica and therefore free to create new bonds implying a possibility of attack on these sites; this quantity is indicative of the degrading reactivity of the material. A high NBO / T indicates a great ability to migrate modifier ions such as Ca out of the material; - the half-life times measured in days by in vivo pulmonary biopersistence tests by inhalation (INH) and by intratracheal instillation (IT), the protocols of which were referenced above, on the one hand on fibers called WHO [measurements of t _{1 2} .INH (WHO) and t _{1 2} .IT (WHO)] and on the other hand on fibers of length greater than 20 microns [measurements of t _1/2 .INH (20 μm) and t _{1 / 2} .IT (20 μm)]. Schematically, the inhalation test consists in exposing laboratory rats by inhalation for 6 hours per day for 5 consecutive days, in an atmosphere containing mineral wool of which at least a part is breathable by these animals. After this exposure period, subgroups of animals are sacrificed at specified intervals and their lungs analyzed. The analyzes include the characterization of the number, the size distribution and the chemical composition of the fibers, as well as the abovementioned half-life times corresponding to the time necessary for 50% of the fibers to have disappeared, for those longer than 20 μm and for those called WHO.

The test by intratracheal instillation also consists, schematically, of instilling intratracheal route to laboratory rats of the fiber suspensions which have been optimized to be breathable by these animals, and this once a day for 4 consecutive days, then to sacrifice the animals at specified intervals and analyze their lungs. The analyzes include the same types of results as in the inhalation test, including the half-life times.

Compared with the wools X and Y constituting the additive of the prior art, the wools A to L are characterized by their degradability in physiological medium largely superior to that of these conventional wools. In terms of compositions, the wools A to I are remarkable in particular for their high content of alkali metal oxides and their low content of alumina; while wools J to L have a relatively higher content of alumina.

As an indication, the chemical behavior of wool A is extremely close to that of slag Z. In particular its NBO / T value is equivalent to that of pure blast furnace slag, and suggests an identical reactivity for these two materials. However, it is known that the slag is attacked in a solution of basic pH such as that reached during hydration and setting of the cement. Therefore, one would have expected that this biodegradable wool, as well as others of similar compositions, would be degraded in the presence of a cement matrix. The following application examples show, on the contrary, the astonishing stability of biodegradable wool in cementitious materials according to the invention.

Application example 1: Incorporation of a fibrous additive into a mortar composition

The performance of wool A was tested as a fibrous additive for reinforcing a cementitious product of the mortar type according to the invention, and it was compared with that of an additive of the prior art based on the wool X. To constitute the fibrous additive, the two wools A and X were sized with a mineral oil such as the oil marketed under the brand MULREX or PROREX and packaged in the form of nodules, most of which had a size of 4 at 16 mm.

Each additive was incorporated into an extruding mortar composition corresponding to the following formula: CPA cement 52.5 100 kg

Silica sand 100 kg

Silica smoke 10 kg

Extrusion agent 1.5 kg

Fluidifier 1.5 kg Black dye 5 kg

Water 47 kg the percentage by weight of additives added relative to the dry matter being 15%. The sizing oil has the effect of facilitating the dispersion of the additive in the mixture hydrate.

Dry mixing of the cement, sand and silica smoke is carried out for 5 minutes, then water, the fluidizer, the dye and the extrusion agent are added. After a first wet kneading, the fibrous nodules are added and the kneading is continued to obtain a homogeneous cement paste.

This paste is ready to be extradited to form articles of variable dimensions, in particular in thin plates up to a centimeter thick, which are left to mature to ensure the setting of the cement.

To characterize the mechanical properties of the ripened products, samples are prepared which will be subjected to flexural strength tests according to the European standard on glass-cement composites EN 1170-5 (final project of March 1995). From the fresh mortar, 4 standard test pieces are formed which are stored in plastic for 24 h at 20 ° C, then 27 days in a room regulated at 20 ° C and 98% relative humidity. After ripening, three samples are immersed in a water tank regulated at 50 ° C to simulate accelerated aging, for respectively 28, 56 and

84 days (this last period corresponding to a cement reinforced with glass fibers to an aging in a temperate climate of 15 years).

At the various deadlines, the samples were broken in 4-point bending according to the pr 1170-5 standard, and the rupture modulus (MOR) was measured in MPa, the proportionality limit (LOP) in MPa, and the deformation at break (in% elongation).

By microscopic observations, in scanning electron microscopy, the state of the wools within the matrix was characterized at each stage and the chemical stability of the product was estimated.

Comparative results When preparing the mortar compositions as described above, the wool-containing additive A mixes very easily with the other constituents, the viscosity of the mixture remains in the usual range and does not require any strength. excessive mixing. The wool disperses very homogeneously in the mass of the hydrated mixture. With wool X, the dispersion is less good and we observe the formation of numerous clumps of fibers (nests) in the hydrated mixture.

A first observation of the samples after 28-day ripening provides information on the distribution of wool in the matrix of the reinforced composite and confirms that the wool

A is more evenly distributed in the matrix than wool X. This first observation also shows that wool A remains intact in the alkaline matrix of the sample. This result is very surprising taking into account the reactivity of wool A expected from the NBO / T value identical to that of slag and which suggested a reactivity in the direction of corrosion in an environment as aggressive as the alkaline medium. the hydrated matrix.

The microscopic observations of the samples containing wools A and X at the different stages of aging are quite similar. After 28 days of ripening, the matrix is compact and has closed pores with regular edges and not cracked; the wools show no sign of corrosion by the alkaline matrix. After aging, at each stage, the matrix becomes very dense and very compact by progressive hydration of the binder, but the wools are still not corroded.

These properties are collated in Table 2 below, with the mechanical performance of samples A and X measured as indicated above.

Table 2

The samples reinforced with wool A show very good mechanical resistance and moreover exhibit almost constant characteristics whatever the stage of aging. They are therefore very stable products which can be used with great reliability. Once again, the effectiveness, as an agent for reinforcing an alkaline matrix, of this mineral wool is surprising with regard to its degradability in physiological fluids.

It has been able to demonstrate in particular that the additive according to the invention makes it possible to combat the phenomenon of micro-cracking which plays an essential role in the resistance to aging in a humid atmosphere. The presence of mineral wool in the entire volume of the composite, obtained according to the invention thanks to the excellent dispersibility of the fibrous additive in the mortar mix, provides reinforcement throughout the material which is particularly effective against micro-cracking. By avoiding the appearance of micro-cracks, a more satisfactory product is obtained from an aesthetic and mechanical resistance point of view, since the fixation of water which limits the appearance and brittleness of the material is limited. . The use according to the invention of degradable wool in a physiological medium also proves to be very advantageous since the manufacture and use of this very high-performance product are not potentially liable to be questioned with regard to the health of manipulators and users.

Application example 1 illustrates the invention more particularly in the context of the preparation of extrudable mortars in which the mineral wool content can be freely chosen, in particular at values of less than 15%, for example of the order of

5% or less. The specialist is also able to modify the composition of the mortar according to the shaping technique which he wishes to apply in order to obtain different degrees of fluidity, and may in particular vary the water / binder ratio in a manner known in oneself. It should be noted that the additive according to the invention lends itself to other shaping techniques, such as in particular the calendering described in EP-A-0 173 873, which also makes it possible to incorporate textile fibers reinforcement. In this variant, it is noted that the addition of the fibrous additive in the mixing of the mortar makes it possible, with equal final mechanical properties, to reduce the proportion of reinforcing fibers to a content of less than 5%, in particular of the order of 2%.

Application example 2: Incorporation of a fibrous additive into a sprayed protective coating

In this example, a spraying composition is prepared containing the fibrous nodules obtained from rock wool A used in application example 1, and a cement-based binder in the following proportions (in parts by weight) :

Additive A 100

Cement 17

Bentonite 4 Calcium sulfate 2

The total binder content (hydraulic binder + inorganic binder) is therefore 23% relative to the weight of mineral wool.

This composition is prepared by simple dry mixing of the constituents in a conventional mixer, in particular of the router type. Under the usual mixing conditions, the additive mixes perfectly with the mineral binder, resulting in light flakes of light color in which the binder is intimately combined with the mineral wool in a very homogeneous manner.

This composition is used to make a fire-resistant protective coating on the walls and ceiling of a living room. It is implemented by projection using a conventional machine which simultaneously projects a jet of dry matter flakes and a jet of water onto the surface to be protected. The composition to be sprayed according to the invention hydrates spontaneously very regularly to form a sprayed layer of homogeneous hydrated material. The machine being adjusted so that the hydrated sprayed material has a density of between approximately 180 and 260 kg / m, a dense protective layer, approximately 30 mm thick, is easily produced on the walls and on the ceiling. Under these spraying conditions, the amount of water combined with the dry composition is such that the pH of the hydrated material is approximately 10. The surface of the coating is then smoothed with a roller for a beautiful finish.

The mechanical strength of the sprayed coating was evaluated after 30 days and after 300 days of curing. The test consisted in sticking with a suitable adhesive a wooden plate of given dimensions on the mineral wool covering, then in measuring the tearing stress for a traction perpendicular to the surface of the plate.

After 30 days as after 300 days, the sprayed layer retains its initial appearance and no degradation is observed. In particular, the layer does not show any sign of crumbling liable to release particles of mineral wool.

The stress measured after 300 days of curing, equivalent to that measured at 30 days, proves the excellent stability over time of the sprayed layer, that is to say the excellent resistance of the rock wool A coated by the alkaline binder.

As a variant, it is possible to produce from this composition to be sprayed a coating of thermal or acoustic insulation by adapting the setting of the spraying machine of so as to produce a layer with a density of 120 to 180 kg / m ³ . This also alkaline material (pH of the order of 9 to 10) has the same stability characteristics as the fire-fighting layer described above. Thanks to the solubility of rock wool A in a physiological medium, the composition to be sprayed according to the invention is completely harmless and guarantees safe handling from the manufacture of the dry mixture, during loading of the spraying machine and up to the finish of the sprayed material.

Claims

1. Fibrous additive for cementitious material, in particular for mortar / concrete or spraying material, comprising mineral wool, characterized in that the mineral wool is capable of dissolving in a physiological medium.

2. fibrous additive according to claim 1, characterized in that the wool has an index Kl equal to or greater than 40, this index being defined by the following relationship: Kl = Σ (% by mass of Na ₂ O, K ₂ O, CaO, MgO, BaO, B ₂ O ₃ ) - 2 x (% by mass of Al ₂ O ₃ )

3. fibrous additive according to claim 1, characterized in that the wool has an index Kl equal to or greater than 30, this index being defined by the following relationship: Kl = Σ (% by mass of Na ₂ O, K ₂ O, CaO, MgO, BaO, B ₂ O ₃ ) - 2 x (% by mass of Al ₂ O ₃ )

4. Fibrous additive according to any one of claims 1 to 3, characterized in that the wool has little or no biopersistent character.

5. Fibrous additive according to claim 4, characterized in that the wool has a half-life time by in vivo test of pulmonary biopersistence by inhalation for WHO fibers less than or equal to 25 days.

6. fibrous additive according to claim 4, characterized in that the wool has a half-life time by in vivo test of pulmonary biopersistence by inhalation for fibers of length greater than 20 μm less than or equal to 15 days, preferably less or equal to 10 days.

7. fibrous additive according to claim 4, characterized in that the wool has a half-life time by in vivo test of pulmonary biopersistence by intratracheal instillation for WHO fibers less than or equal to 40 days.

8. Fibrous additive according to claim 4, characterized in that the wool has a half-life time by in vivo test of pulmonary biopersistence by intratracheal instillation for fibers of length greater than 20 μm less than or equal to 35 days.

9. fibrous additive according to any one of claims 4 to 8, characterized in that the wool comprises the following constituents in the following proportions:

SiO ₂ > 35%

Al ₂ O ₃ <15% and in that the composition also verifies the following relationship, expressed in weight percentages:

1 Na ₂ O + 1 K ₂ O + 1 CaO + 1 MgO + 3 P ₂ O ₅ + 1 B ₂ O ₃ - 0.5 Fe ₂ O ₃ -

2 Al ₂ O ₃ - 4 ZnO - 1 TiO ₂ > 26%

10. Fibrous additive according to any one of the preceding claims, characterized in that the composition of the wool comprises the following constituents according to the following weight proportions:. SiO ₂ 48 to 67%. Al ₂ O ₃ O at 8%

• Fe ₂ O ₃ 0 to 12%

(total iron) .CaO 16 to 35% .MgO there 16% .Na ₂ O + K ₂ O O to 6.5%

P ₂ O ₅ O at 5% respecting the following relationships. Na ₂ O + P ₂ O ₅ > 2%. Fe ₂ O ₃ + Al ₂ O ₃ <12%. CaO + MgO + Fe ₂ O ₃ > 23%

11. Fibrous additive according to any one of claims 1 to 9, characterized in that the composition of the wool comprises the following constituents according to the following weight proportions:

. SiO ₂ 40 to 58%

. Al ₂ O ₃ 3 at 11.5%

• Fe ₂ O ₃ 0.1 to 15%

(total iron)

.CaO 7 to 40%

.MgO 4 to 16%

• P ₂ 0 _{5 there} 7%

. Impurities <3%

. Na ₂ O + K ₂ O <7%

. CaO + MgO + Fe ₂ O ₃ > 25%

12. Fibrous additive according to any one of claims 1 to 9, characterized in that the composition of the wool comprises the following constituents according to the following weight proportions:

. SiO ₂ 40 less than 52%

. Al ₂ O ₃ less than 4%

. CaO more than 25 and up to 45%

. MgO 5 to 15%

. BaO 0 to 7%

. Na ₂ O 2 at 12%. K ₂ OO at 10%

. Na ₂ O + K ₂ O 2 at 15%

. TiO ₂ , Fe ₂ O ₃ , MnO 0 to 5%

13. Fibrous additive according to any one of claims 4 to 8, characterized in that the wool comprises the following constituents in the following proportions:. SiO ₂ 30 to 51%

. Al ₂ O ₃ 10 to 30%

. CaO 2 at 30%

. MgO 0 to 20%

. Na ₂ O + K ₂ O 0 to 19%. TiO ₂ 0 to 6% or TiO ₂ + Fe ₂ O ₃ 6 to 18%

. others up to 15%

14. Fibrous additive according to any one of the preceding claims, characterized in that the wool is sized with a mineral oil or a surface-active substance optionally combined with an anti-foaming substance.

15. Fibrous additive according to any one of the preceding claims, characterized in that the wool consists of fibers having an average diameter of 3 to 25 μm, preferably of the order of 5 to 10 μm.

16. Composition of cementitious material, dry or hydrated, comprising a cement-based binder, characterized in that it contains a fibrous additive according to any one of the preceding claims.

17. Composition according to claim 16, characterized in that it comprises up to 15% by weight of additive relative to the weight of dry matter.

18. A plate product, in particular a thin one, produced from a composition of hydrated cementitious material according to any one of claims 16 and 17.

19. Product according to claim 18, characterized in that it also contains textile-type reinforcing fibers.

20. Composition according to claim 16, characterized in that it comprises 15 to 35% by weight of dry binder relative to mineral wool.

21. Composition according to claim 20, characterized in that it comprises, in addition to the cement, at least one other mineral or organic binder.

22. Building surface coating, in particular fire protection or thermal or acoustic insulation produced from a hydrated cementitious composition according to one of claims 16, 20 and 21.

23. Coating according to claim 22, characterized in that it is produced by simultaneous spraying of a dry cement composition and water on said surface.