FR2813074A1 - CONCRETE BASED ON HYDRAULIC BINDER FOR PREFABRICATING TILES, PLATES AND SIMILAR - Google Patents

Abstract

The invention concerns a concrete obtained by mixing water with a composition comprising: a) a cement, b) ultrafine elements with pozzolanic reaction, c) granular elements, d) cement additives, e) an amount of water E added to the mixture, f) a dispersing agent, whereof the constituents (a), (b), (c), and (d), expressed in volume, satisfy the following relationships: ratio 1: 0.50 </= [(a)+(b)+(d)]/c </= 1.10; ratio 2: 0.40 </= [(b)+(d)]/(a) </= 0.80; ratio 3: 0.10 </= (b)/(a) </= 0.30, and a water/cement weight ratio W/C </= 0.30.

Description

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The present invention relates to a concrete, and more particularly to a high performance concrete for the production of prefabricated, tiles, plates or the like, cast or extruded and continuously molded, the composition of which comprises a hydraulic binder such as cement, preferably Portland cement with high silica content, and whose performance is improved over that of concretes of the prior art, in particular with regard to workability and mechanical strength, bending and compression.

The term "concrete" used above generally includes either concrete, mortar or grout, which will be discussed later in the text.

Generally, the products of the concrete construction comprising a hydraulic binder of the Portland cement type or the like for roofs, facade wall coverings, or floors, require mechanical resistance to bending (Rf) at 28 days of the order of 6 at 8 MPa. In this case, the thicknesses of the tiles or corresponding plates are generally greater than 15 mm, if ordinary concretes are used. This results, for a given surface, tiles or relatively heavy plates.

If, as is the trend today, we want to have both prefabricated thin (less than 15 mm) and large areas (for example 5 tiles per m2), it is necessary to have high performance concrete and it is then necessary to have 28-day flexural strengths Rf of at least 15 MPa.

The prior art already proposes several types of solutions for achieving this objective. These are concretes with a high content of reinforcing fibers, typically greater than 5%, or very high performance concretes with fiber volumetric contents. weaker, but with granular skeletons particularly studied and making it possible to increase the compactness of the concrete in the dry state while aiming at the decrease of the defects of structure,

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 - Concretes reinforced with polymers compatible with the hydraulic binder.

Fiber cement panels with a high fiber content, derived from asbestos cement technologies whose asbestos has been replaced by cellulosic or organic fibers, are well known to professionals. These techniques can lead to prefabricated thin. However, the quality of the surface and the dimensional stability of these products are not very satisfactory for use in the form of tiles, roofing panels or facade panels.

There are also other solutions of very high performance concrete with low fiber content. These are of high compactness (greater than 80%), and relatively high levels of ultrafine grains smaller than 1 μm are used, such as for example silica fumes. In order to obtain the desired flexural strengths Rf, that is to say Rf = 20 MPa, it is generally possible to obtain high silica fume contents, typically greater than 20% by weight of the concrete composition. dry state.

Patents such as EP-10777 or WO99 / 28267 and WO 99/58468 provide high performance concrete solutions also comprising silica fibers and fumes. However these solutions are not suitable for the manufacture of tiles or plates because they lead to prohibitive costs.

The applicant has also in the past developed concrete compositions for tiles that are not very compact, and without ultrafine elements such as very expensive silica fumes, but using a reinforcement using organic fibers, with a moderate volume content in concrete (see patent EP-347092). This solution, because of the presence of reinforcing fibers has proved difficult to industrialize and market. Also, while seeking to formulate concretes with little or no fiber, that is to say a content of less than 1% by volume,

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 preferentially less than 0.5% by volume, the applicant had to resolve, after many tests, to abandon the concepts of formulation of granular skeletons based on the prior art and had to move towards a different composition, adapted to technical and economic constraints of prefabrication of concrete tiles or slabs.

The object of the present invention is therefore to provide a concrete, and in particular a concrete that does not contain, or if necessary, little, reinforcing fibers for the manufacture of prefabricated tiles, tiles, plates or the like, overcoming the disadvantages of prior art.

Still another object of the present invention is to provide a concrete, particularly for the manufacture of tiles, plates and the like which has, after curing, improved mechanical properties, such as flexural strength greater than 15 MPa at 28 days.

In the remainder of the text, grain size D75 and D50 are understood to mean respectively the sizes of the sieves of which the passer constitutes respectively 75% and 50% of the total volume of the corresponding grains.

The objects of the present invention are achieved by making a concrete for the manufacture of tiles, plates and the like obtained by mixing with water a composition of solid constituents comprising: a) a cement whose particles have a grain size D50 from 10 pm to 20 pm, (b) ultra-fine pozzolanic reaction elements having an elemental particle size of not more than 1 pm, (c) granular elements having a grain size of D75 of not more than 2 mm, preferably of not more than 1 mm, d) cementitious additions having a D50 grain size of less than or equal to 10 μm, e) an amount of water E added to the mixture,

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 f) a dispersing agent, preferably a superplasticizer, for example selected from polyoxyethylene phosphonates, polyox polycarboxylates, and mixtures thereof, g) optionally a setting accelerator and / or hardening characterized in that the contents of the constituents (a) , (b), (c), (d) expressed in volume, satisfy the following relationships ratio 1: 0.50 <[(a) + (b) + (d)] / (c) <_ 1,10ratio 2 : 0.40s [(b) + (d)] / (a) <0.80 ratio 3: 0.10 <_ (b) / (a) <0.30 and that we have a ratio weight of water / cement E / C <0.30. Preferably, the contents of constituents (a), (b), (c), (d) expressed in volume, satisfy the following relations ratio 1: 0.60 <_ [(a) + (b) + (d) ] / (c) <_ 1, OOratio 2: 0.42 <_ [(b) + (d)] / (a) <_ 0.76 ratio 3: 0.10 <_ (b) / (a) <0.28 The cement (a) of the composition according to the invention is advantageously a Portland cement such as CPA Portland cements PMES, HP, HPR, CEM 1 PMES, 52.5 or 52.5R or HTS (high silica content). Preferably, the cement of the composition according to the invention is a Portland cement HTS, said cement comprising at least 20% of combined silica. The cement may also be a cement based on calcium aluminates, or any hydraulic binder based on blast furnace slags, or any hydraulic binder based on mixtures of these cements and / or slags.

The ultra-fine pozzolanic reaction elements (b) are known in the art. They are generally chosen from silica fumes.

The granular elements (c) can be any granular elements conventionally used for the manufacture of concretes. They include sands or mixtures of sands, sieved or crushed.

Cement additions (d) include fly ash and / or calcareous fillers, and / or slags and / or

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 siliceous sands, in particular quartz flour or crushed fine limestone.

In a preferred embodiment, the cement particles (a) have a grain size D50 of the order of 15 μm, the ultrafine elements pozzolanic reaction (b) have a particle size D75 of at most 0.5 Nm, the granular elements (c) have a grain size D75 of at most 400 Nm, the cementitious additions (d) have a grain size D50 less than or equal to 10 μm.

The composition according to the invention may also comprise a dispersing agent, preferably a superplasticizer, present in a proportion of 2 to 10%, and preferably of the order of 2 to 5%, relative to the weight of dry cement.

Superplasticizers are conventional constituents of concretes which aim to improve the initial rheology of concrete. Among these superplasticizers, POE polyoxyethylenated phosphonates, PCP polyox polycarboxylates, and mixtures thereof are particularly recommended. These superplasticizers are commercially available products; by way of example, mention may be made of the OPTIMA 100O and OPTIMA 175 products marketed by CHRYSO.

The concretes according to the invention may also comprise various additives, such as in particular coloring pigments, dispersing agents, defoamers, antirreasing agents, anti-sedimentation agents, accelerating agents or aqueous emulsions of organic products, which are well known in the art. the skilled person. In particular, for the usual industrial manufacturing processes of concrete tiles or slabs, it is necessary to have minimum bending strengths at 6 hours, greater than 5 MPa. In this case, it is advisable to accelerate the setting and hardening of the concrete by means of accelerators without this addition causing disturbances in the rheology, and therefore the workability.

The concretes according to the invention may optionally comprise reinforcing elements of anisotropic shape intended to

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 to improve the toughness of concrete, with a dimension of at most 2 mm. In general, the reinforcements of the composition according to the invention are in acicular form or in the form of platelets.

Advantageously, the acicular reinforcement elements are chosen from among the wollastonite fibers, the bauxite fibers, the mullite fibers, the potassium titanate fibers, the silicon carbide fibers, the cellulose fibers or derivatives, carbon fibers, calcium phosphate fibers, (alkali-resistant) glass fibers or derived products obtained by grinding glass fibers and mixtures of these fibers, of short fibers (length of not more than 2 mm, preferably at most 1 mm) of polyvinyl alcohol, polyacrylonitrile, high-density polyethylene, polyamide, aramid or polypropylene may also be present as well as materials such as steel wool.

The platelet reinforcements may be selected from mica platelets, talc platelets, mixed silicate platelets (clays), vermiculite platelets, alumina platelets.

The needle-shaped reinforcing elements are particularly suitable. They have an average size of at most 1 mm. In the concrete composition according to the invention, they are present in a mass proportion of between 0 and 30% relative to the weight of the cement. Preferably, the acicular reinforcing elements are wollastonite fibers, for example NYAD G. from the company NYCO.

The concretes obtained according to the present invention have a flexural strength on 4cm x 4cm x 16cm prisms from 15 to 25 MPa, preferably from 20 to 25 MPa at 28 days.

To obtain such mechanical properties, the water / cement mass ratio (W / C) must be less than or equal to 0.30, and preferably, for a casting process, maintained in a given range:

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 0.25 <E / C <0.30 This ratio will vary in this range depending on the nature and proportions of the ultrafine elements with pozzolanic reaction and the presence or absence of acicular reinforcing elements: the mass ratio E / C decreases as the content of fine pozzolanic reaction increases. Thus, this ratio is preferably between 0.25 and 0.27 when the concrete according to the invention does not comprise acicular reinforcing elements, and it is between 0.27 and 0.30 when the concrete according to the invention. The invention comprises acicular reinforcing elements. In the case of a method of implementation by calendering, extrusion or pressing, this ratio E / C can decrease below 0.2.

The concretes according to the invention can be subjected, after ripening, to a maturation phase at a temperature which can vary from 20 to 90 ° C., in an atmosphere with relative humidity> 90%.

The following examples illustrate the invention without, however, limiting its scope.

Preparation of samples 1) Raw materials In order that the comparisons made have their full significance, the same constituents indicated below have been used for all the examples.

 # cement: high-silica Portland cement, type HTS (LAFARGE CIMENTS FRANCE) # granular elements - sand: quartz sand BE 31 from SIFRACO France # cementitious additions - filler: quartz flour, quality C400 from SIFRACO France - limestone DURCAL 2 from OMYA Company # ultra-fine elements with pozzolanic reaction: - silica fumes: vitreous microsilica ELKEM 940U # superplasticizing additives:

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 - Mixture of polyoxyethylenated phosphonate (POE) and polycarboxylic polyox (PCP), OPTIMA 1750 Company CHRYSO, FRANCE, # adjuvant accelerator - based on calcium chloride, such as CHRYSOXEL C4 CHRYSO, France.

2) Method of preparation In the examples, the procedure for the manufacture of the test specimens consisted of using an EIRICH kneader, type R02F. The samples are conventionally prepared according to any method known to those skilled in the art, in particular by mixing the solid constituents, placed in the mold, then curing under determined ripening conditions.

During the preparation step of the mortar, the constituents are kneaded in the following order: - kneading of the pulverulent constituents of the matrix for 4 minutes, - introduction of water and a part of the adjuvants (such as pigments, superplasticizers or dispersing agents, anti-foaming agents) for about 30 seconds, - mixing of the concrete for one minute, - introduction of the remaining fraction of the admixtures, - mixing of the concrete for 3 minutes, - introduction of the reinforcing fibers (if applicable), - mixing.

The molds are then filled, then vibrated according to the usual procedures.

Maturation For the tests, the test pieces were subjected to a maturation treatment at 20 ° C., as follows: the specimens, after maturing at 20 ° C., were demolded and stored in an atmosphere at 20 ° C. with 100% relative humidity RH for at least two days, # while keeping them in this environment, the evaluation of the mechanical performances is carried out in 28 days.

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 In the case of the mixture 6 which comprises the CHRYSOXEL C4 accelerator, the bending strength is also measured at 6 hours.

The ripening consists in storing the sample in its mold, under water at 20 ° C, for 2 days.

Methods of measurement 1) Measurement of spreading on a vibrating table The principle of measurement consists of measuring the diameter of the concrete slab formed after the concrete, subjected to vibration, has spread under its own mass. The measurement method used is a variant of ASTM C 230-97, in which the steel table is vibrated at a frequency of 50 Hz and amplitude 0.75 mm for 1 minute.

2) Measurement of the mechanical strengths in bending and compression The principle of the measurement consists of determining the flexural strength and compressive strength values of prismatic test pieces with dimensions 40 mm x 40 mm x 160 mm.

These test pieces are made from a plastic mortar mix, the composition of which is one of the compositions defined for mixtures 1, 2, 3, 4, 5, 6, 7.

It is an application of standardized measurement methods: - compressive strength according to the French standard NF P18-400, and the European standard EN 196-1.

- resistance to bending according to EN 196-1, the only differences between the measuring methods used and these standardized methods (NF P18-400 and EN 196-1) residing in the preparation of the mortar, in terms of composition , dosing and mixing.

COMPARATIVE EXAMPLES Various siliceous sand mortars have been prepared hereinafter referred to as mixtures 1 to 7.

In Table 1, the compositions are shown. Table 2 shows the results of the measurements.

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 *: The ratios 1, 2, 3 are obtained from the proportions of constituents expressed in volume, as previously defined.

 **: The cost indices were determined by assigning the index 100 to blend 7 which has the highest raw material cost in absolute terms and determining the other costs against this index.

The invention relates to concretes making it possible to produce thin pieces (<_ at 15 mm) having a flexural strength value Rf at 28 days, such that: Rf> _ 15 MPa Obtaining an Rf value > 20 MPa at the industrial level guarantees a minimum of 15 MPa.

Comparative blend 1 is a low silica fume composition in which component proportions do not meet ratios 1, 2 and 3. Minimum bending strength is not obtained.

Comparative mixture 7 is a composition with a high silica fume content in which the proportions of constituents do not satisfy ratios 1, 2 and 3. The flexural strength is good, but the very high content of ultra-fine pozzolanic reaction elements that this composition is not adapted to the economic constraints of prefabrication of concrete tiles or slabs.

Mixtures 2, 3, 4, 5, 6 are compositions according to the invention free of reinforcing fibers. They all correspond to the criteria of resistance to flexion.

Mixes 2 and 3: spreads are weak; these mixtures would be more suitable for extrusion, calendering or pressing processes. Blends 4, 5 and 6: they satisfy all the techno-economic criteria required, in particular blend 6 which corresponds to the best performing blend. These mixtures can be used depending on the water content, for several types of implementation, pouring, extrusion, etc.

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 In example 6, it is noted that the addition of the accelerator CHRYSOXEL C4 makes it possible to obtain a concrete having both a very high spreading and a mechanical performance in bending of 9.7 MPa, at 20 C, at the end 6 hours, compatible with the requirements of some prefabrication processes.

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Claims (18)

1. Concrete obtained by mixing with water a composition comprising: a) a cement whose particles have a D50 grain size of 10 pm to 20 Nm, b) ultrafine elements pozzolanic reaction having a size of elementary particle of not more than 1 Nm, c) granular elements having a grain size D75 of not more than 2 mm, preferably not more than 1 mm, d) cementitious additions having a grain size D50 equal to or less than at 10 μm, e) an amount of water E added to the mixture, f) a dispersing agent, characterized in that the contents of constituents (a), (b) (c) and (d), expressed by volume, satisfy the following relationships ratio 1: 0.50 <_ [(a) + (b) + (d)] / (c) s 1.10 ratio 2: 0.40 <[(b) + (d)] / (a) <0.80 ratio 3: 0.10 <(b) / (a) <0.30 and that a water / cement weight ratio E / C <0.30, 2. Concrete according to claim 1, characterized in that the contents of the constituents (a), (b) (c) and (d), expressed in volume, satisfy the following relations ratio 1: 0.60 <_ [(a ) + (b) + (d)] / (c) <1.00 ratio 2: 0.42 <_ [(b) + (d)] / (a) <0.76 ratio 3: 0.10 < (b) / (a) <0.28 3. Concrete according to claim 1 or 2, characterized in that: a) the cement particles (a) have a grain size D50 of the order of 15 g, b) the ultrafine elements pozzolanic reaction (b) have particle size D75 not more than 0.5 ntm, c) granular elements (c) have a grain size D75 of not more than 400 @tm, d) cementitious additions (d) have a grain size D50 less than or equal to 10 μm. <Desc / Clms Page number 15>  4. Concrete according to one of the preceding claims, characterized in that the cement is a cement with high silica content, said cement comprising at least 20% by weight of silica combined with the weight of the cement. 5. Concrete according to any one of the preceding claims, characterized in that it comprises a superplasticizer, present in a proportion of 2 to 10%, and preferably 2 to 5% by weight, relative to the weight of cement. 6. Concrete according to claim 5, characterized in that the superplasticizer is selected from polyoxyethylenated phosphonates, polyox polycarboxylates and mixtures thereof. 7. Concrete according to one of the preceding claims characterized in that it has a flexural strength of between 15 and 25 MPa, and preferably between 20 and 25 MPa, 28 days. 8. Concrete according to any one of the preceding claims, characterized in that it comprises an anisotropic reinforcing element. 9. Concrete according to claim 8, characterized in that the reinforcing element is an acicular reinforcement element chosen from: - wollastonite fibers, bauxite fibers, mullite fibers, potassium titanate fibers, silicon carbide fibers, cellulose fibers or derivatives thereof, carbon fibers, calcium phosphate fibers, (alkali-resistant) glass fibers or derived products obtained by grinding said fibers and mixtures of said fibers, short fibers (length of at most 2 mm, preferably at most 1 mm) of polyvinyl alcohol, polyacrylonitrile, high density polyethylene, aramid or polypropylene polyamide which may also be present as well as materials such as steel wool. 10. Concrete according to claim 8, characterized in that the reinforcing element is a reinforcing element in the form of a wafer, selected from mica wafers, wafers of <Desc / Clms Page number 16>  talc, mixed silicate platelets (clay), vermiculite platelets and alumina platelets. 11. Concrete according to claim 9, characterized in that the acicular reinforcing elements are wollastonite fibers. 12. Concrete according to any one of the preceding claims, characterized in that the ultrafine elements pozzolanic reaction (b) consist of silica fumes. 13. Concrete according to one of the preceding claims, characterized in that the granular elements (c) are sands or sand mixtures, sieved or crushed. 14. Concrete according to one of the preceding claims characterized in that the cementitious additions (d) are fly ash and / or calcareous fillers, and / or slags, and / or siliceous sands, in particular flour of quartz, or hard limestone. 15. Concrete according to one of the preceding claims, characterized in that it undergoes, after roaring, a maturation phase at a temperature of 20 C to 90 C, in a relative humidity> 90% atmosphere. 16. Concrete according to one of the preceding claims comprising a setting accelerator and hardening. 17. Concrete according to claim 16, characterized in that the setting and hardening accelerator is based on calcium chloride. 18. Prefabricated elements such as tiles, plates or the like made using a concrete as defined in one of claims 1 to 17.