WO2007000501A1

WO2007000501A1 - Method for making a calcium sulpho-aluminate based composition

Info

Publication number: WO2007000501A1
Application number: PCT/FR2005/001617
Authority: WO
Inventors: Edouard Dumoulin
Original assignee: Gypsmix Sarl
Priority date: 2005-06-27
Filing date: 2005-06-27
Publication date: 2007-01-04

Abstract

The invention concerns a method for making a calcium sulpho-aluminate based composition and the resulting composition. The invention is characterized in that it consists in temperature reacting a mixture comprising anhydrite III and alumina to form calcium sulpho-aluminate. The resulting composition is in particular used as ingredient for preparing a mortar- or concrete-type material, for example a hydraulic binder or an active filler. The invention is preferably used for preparing a refractory material, as refractory hydraulic binder or as refractory active filler. The invention aims at providing a method for making a sulpho-aluminous composition easy to implement and consuming a small amount of thermal energy.

Description

PROCESS FOR PRODUCING A SULFICALLY BASED COMPOSITION

CALCIUM ALUMINATE

Description

The invention relates to the general technical field of cement compositions.

It relates to a process for producing a composition based on calcium sulfoaluminate and the composition thus obtained.

It also relates to the use of this composition based on calcium sulfoaluminate as an active ingredient for the manufacture of a material of the mortar or concrete type and more particularly for the manufacture of a refractory material.

In cement notation, calcium sulphoaluminate (CaO) 4 (Al ₂ O ₃ ) ₃ Sθ ₃ is represented by C 4 A ₃ S (C represents CaO, A represents Al ₂ O ₃ , S represents SO 3).

Sulfoamumin cements appeared in the 1970s. Those skilled in the art know various processes for obtaining C4A ₃ S and in particular those described in the following documents:

US Pat. No. 3,155,526 (KLEIN) describes a process for producing a sulfo-aluminous cement obtained by calcining a mixture of CaO, SO ₃ and Al ₂ O ₃ . This process makes it possible to obtain approximately 70% of C ₄ AsS, approximately 2% of free hydraulic lime and approximately 2% of CaSO ₄ anhydrite. The yield is not optimal and the presence of CaSO ₄ makes it impossible to use the cement obtained for long-time applications.

Patent FR2186442 (US GYPSUM COMPANY) teaches to calcine a mixture of CaO, SiO 2, Al 2 O 3 and SO 3 at a temperature of between approximately 1200 ^° C. and approximately 1600 ^° C. for a duration of between approximately 1 hour and approximately 5 hours in order to obtain a cement comprising only 20% to 40% by weight of C ₄ AsS, which is a very low yield.

Patent EP0476031 (KUNBARGI) discloses a process for producing a sulfo-aluminous cement consisting of mixing CaO, SiO 2, Al 2 O 3 and SO 3 and Fβ 2 O 3, to subject these constituents to a heat treatment at temperatures between 1000 ^° C. and 1200 ⁰ C for a period of time sufficient to obtain a clinker containing 15 to 75% by weight of C ₄ AsS. Such a process, however, causes the formation of about 10% CaSO ₄ which makes it impossible to use the cement obtained for long-time applications.

Patent FR2831161 (FRENCH CIMENTS) discloses a sulfoaluminous clinker prepared by a process comprising the mixture of limestone, bauxite, sand and gypsum, and then firing this mixture between 1250 ^° C. and 135 ^° C. for a period of time. long enough to combine all the hydraulic lime, followed by rapid cooling of the mixture in a non-oxidizing atmosphere. The clinker obtained contains 55% to 72% by weight of C4A3S and 2% to 9% by weight of CaSO ₄ . The efficiency is still not optimal and the presence of CaSO ₄ prevents the use of the clinker for long-time applications.

In addition to their very good refractory properties, C ₄ A ₃ S-based cements can be used in many applications. Indeed, the C ₄ A3S provides materials with desired properties in terms of shrinkage or expansion, setting time and hardening, strength, corrosion resistance, water resistance etc.

For example, when the C ₄ AsS is hydrated alone, the pasty mixture obtained remains malleable for a long time. In the presence of calcium sulphate, setting time is much faster with a period of malleability greater than 30 minutes. In addition, with an excess of calcium sulfate, C4A3S cements are expansive. In addition, by adding Portland cement, a mortar or concrete with high mechanical strength is obtained (see FR2831161).

It appears that the various manufacturing processes mentioned above are not completely satisfactory because their implementation is complex and require a significant thermal energy consumption because the temperature and the cooking time are relatively high.

In addition, the processes using bauxite are unprofitable at the industrial level, this mineral being rare and expensive. Another disadvantage lies in the fact that these traditional manufacturing processes have a non-optimal yield, of the order of 70% to 75% of C ₄ A ₃ S.

Also, a significant proportion of products of the CaO or CaSO 4 type result from these processes, the sulfo-aluminous cements obtained can therefore only be adapted for limited applications.

The purpose of the present invention is to overcome this state of affairs, in particular since it proposes a process for manufacturing a sulfoaluminous composition which is easy to implement and consumes a smaller quantity of thermal energy than those of the processes. of the prior art.

Another object of the invention is to provide a method for obtaining a higher yield of C4A3S than those of the processes of the prior art. The object of the invention is also to provide a composition based on

C4A3S can be used in many applications.

The invention also aims to use this sulfoaluminous composition as an active ingredient for improving the mechanical and / or refractory properties of a mortar or concrete type material. - AT -

The Applicant has now surprisingly demonstrated that the calcium sulfoaluminate can be very easily formed by heating a mixture of anhydrite III and alumina according to the following reaction:

4 (CaSO ₄ , εH ₂ O; ε = 0.1 to 0.2) + 3 Al ₂ O ₃ - »(CaO) ₄ (Al ₂ Oa) ₃ SO ₄ + calcium aluminates

It has been proposed in patent FR2839969 (COUTURIER) to mix a first pozzolanic hydraulic binder (comprising alumina) and a second hydraulic binder based on anhydrite III, to produce a hydraulic binder of cement type allowing to obtain high mechanical strength properties with the possibility of modulating the setting time. This document, however, does not teach heating the mixture of anhydrite III and alumina to form calcium sulfoaluminate.

Accordingly, the aforementioned objects are particularly achieved by a process for producing a calcium sulfoaluminate-based composition comprising reacting a mixture comprising anhydrite III and alumina in temperature to form sulfo -aluminate of calcium. Since anhydrite III is formed from natural or synthetic gypsum, the cost of the raw material needed to produce the calcium sulfoaluminate is relatively low compared to processes using bauxite.

The composition obtained by this new process is used in particular as an active ingredient for the preparation of a material of the mortar or concrete type, for example as a hydraulic binder or active filler. It will preferably be used for the preparation of a refractory material, as a refractory hydraulic binder or as a refractory active filler.

According to an advantageous characteristic of the invention making it possible to facilitate the implementation of the manufacturing process, stabilized anhydrite III is used.

According to another characteristic making it possible to optimize the yield of G4A3S, it is advantageous to react from 3 to 5 moles of anhydrite III with 2 to 4 moles of alumina and preferentially, 4 moles of anhydrite III are reacted with 3 moles of alumina.

According to another advantageous characteristic of the invention making it possible to promote the solid / solid reaction of the compounds, the anhydrite III and the alumina have a particle size of less than 400 μm and preferably the anhydrite III and the alumina have a particle size of between 50 and 150 μm.

According to another characteristic of the invention for effectively rehydrating the sulfo-aluminous composition according to the invention when it is used in the manufacture of a concrete or a mortar, after reacting the anhydrite III with the alumina, the resulting calcium sulfaluminate composition is milled to obtain a granular composition having a particle size of less than 400 μm.

According to another characteristic making it possible to improve the mechanical and / or refractory properties of a concrete or a mortar, a hydraulic binder based on anhydrite III and / or anhydrite II is used as the source of anhydrite III. to manufacture the composition according to the invention.

According to another characteristic making it possible to improve the mechanical and / or refractory properties of a concrete or a mortar, the following minerals are used as the source of alumina, taken alone or in combination: calcined bauxite, tabular alumina, calcined alumina , calcined refractory clay, refractory fireclay, perlite, vermiculite, bentonite, magnesite, dolomite, slag, white or brown corundum, kerphalite, alumina hydrate, recycled asbestos, aluminous melted cement, magnesia alumina spinel, andalusite.

According to another characteristic making it possible to optimize the formation reaction of the calcium sulphoaluminate, anhydrite III and alumina are reacted at a temperature of between approximately 1000 ^° C. and approximately 1300 ^° C., advantageously around 1100 ^° C. ⁰ C.

According to a particular embodiment, the anhydrite III and the alumina are reacted by ramp-up heating and, advantageously, the temperature rise is from 20 ^° C. to a temperature of between 1000 ^° C. and 1300 ⁰ C, for a period of time between 30 and 45 minutes depending on the characteristics of the oven. This heating mode makes it possible to completely react the anhydrite III with the alumina, even at the heart of the mixture.

In an alternative embodiment, anhydrite III and alumina are reacted by direct calcination by means of a flame.

In another variant embodiment, anhydrite III and alumina are reacted by direct aeraulic calcination.

In another alternative embodiment, anhydrite III and alumina are reacted by direct heating using electrical resistors. In another alternative embodiment, anhydrite III and alumina are reacted by microwaves cooking.

In another variant embodiment, the anhydrite III and the alumina are reacted by hybrid firing consisting of preheating the mixture with the aid of electrical resistances and then completing the reaction using the microwaves.

According to a preferred embodiment which is simple to implement, an anhydride III-based powder, an alumina-based powder and / or anhydrite-II powder and / or lime are dry-blended. hydraulic, and then reacted in temperature (heating) said mixture to obtain a granular composition based on calcium sulfoaluminate.

Anhydrite II is used to modify the rheological properties of a mortar or a concrete prepared from the composition in accordance with the invention.

Hydraulic lime is used to optimize the binder properties of the composition according to the invention. Hydraulic lime can also be replaced in an equivalent way by a limestone powder.

According to an embodiment characteristic, if the anhydrite powder II or the hydraulic lime are not mixed with the anhydrite III and the alumina before the heating step, they can be mixed with the granular composition based on calcium sulfoaluminate obtained after said heating step. According to another embodiment characteristic, if the hydraulic lime is mixed with the anhydrite III and the alumina before the heating step, this mixture is reacted between 1200 ^° C. and 1300 ^° C.

According to an advantageous characteristic of the invention, between about 5% and about 40% by weight of hydraulic lime is mixed, preferably about 10%.

In an alternative embodiment, water is mixed with an anhydrite powder III, an alumina powder and / or an anhydrite powder II to form a pasty mixture that is made dry until it hardens. Then, this cured mixture is milled to obtain a granular mixture. This granular mixture is then reacted at temperature (heating) until a granular composition based on calcium sulfoaluminate is obtained.

According to an embodiment characteristic, if the anhydrite powder II is not mixed with the anhydrite III and the alumina at the time of formation of the pasty mixture, it can be mixed with the granular mixture obtained after the step of forming. grinding or the granulose composition based on calcium sulfoaluminate obtained after the heating step.

According to another embodiment, hydraulic lime is added to the granular mixture obtained after the milling step, or to the granular composition obtained after the heating step.

According to a preferred feature of the invention, the proportion of anhydrite III is greater than the proportion of anhydrite II to improve the rheological properties of a mortar or a concrete prepared from the composition according to the invention.

Other features and advantages of the present invention will emerge more clearly on reading the embodiments which follow, given as indicative and non-limiting examples. In the present invention all temperatures are determined at atmospheric pressure.

The term "and / or" in the expressions of the type "A and / or B" must be understood according to the invention as meaning "A alone" or "A and B combined".

According to a preferred method of manufacture, before being heated, the anhydrite III and the alumina are mixed dry, that is to say without the presence of water and preferably in a dry atmosphere having a weight content. in humidity less than 5%, preferably less than 1%.

Methods of making anhydrite III are well known to those skilled in the art. Extensive dehydration (from 22O ⁰ C to 36O ⁰ C) of natural calcium sulphate (gypsum) or of synthesis (sulphogypsum, phosphogypsum, borogypsum, titanogyps, etc.), of formula (CaSO ₄ , 2H 2 O) leads to the formation of the anhydrite III of formula (CaSO ₄ , εH ₂ O) with ε of 0.1 to 0.2.

Since anhydrite III is highly hygroscopic, it rapidly rehydrates in traditional hemihydrate or β-plaster of the formula (CaSO ₄ , ¹ ^ H ₂ O) and then returns to the gypsum state as a function of the hygrometry of the area.

The person skilled in the art knows, in particular by the patents FR2733496 (DUSSEL), FR2767815 (COUTURIER) and FR2767816 (COUTURIER), processes for the preparation of stabilized anhydrite III which comprise the following two stages: baking the gypsum to form the anhydrite III, then thermal quenching to stabilize the metastable phase of anhydrite III.

The use of stabilized anhydrite III makes it possible to obtain materials of the mortar or concrete type having a high mechanical strength and thermal and acoustic insulation properties superior to those of traditional plasters or cements.

100% stabilized anhydrite III (always in combination with hemihydrate (CaSO ₄ , 14H ₂ O) and impurities from the purity of the starting calcium sulfate) is never obtained. stabilized anhydrite III is a function of the process used (temperatures, baking and quenching, particle size of the calcium sulphate used are decisive).

According to a preferred method of manufacture: a) natural or synthetic calcium sulphate is heated to a dewatering temperature of between 220 ^° C. and 36 ^° C. according to the nature of the calcium sulphate treated to form anhydrite III; b) the material thus transformed is subjected to thermal quenching so as to lower its temperature by at least 150 ^° C. so as to reach a temperature of at least less than 110 ^° C., preferably less than 80 ^° C., more preferably less than 80 ^° C. less than 2 minutes.

This process, as well as the industrial installation allowing the implementation of said process, are described in more detail in the application FR 2 804423 (EII) and make it possible to obtain, industrially, stabilized anhydrite III with a degree of purity of at least 85%, up to 95% or more based on the total weight of the compounds derived from the transformation of the calcium sulfate hydrate in the starting material.

According to the method described in FR2856679 (COUTURIER), it is possible to obtain stabilized anhydrite III in an industrial manner with a degree of purity at least equal to that obtained by the method of FR2804423 and of better quality, using as a material starting powder, ground β hemihydrate or traditional β plaster, particle size less than 200 microns, preferably less than 150 microns, more preferably less than 100 microns and performing the same successive steps of baking and quenching described in FR2804423, without however requiring a pre-drying step insofar as the commercially available plaster β is already dry.

Other compounds, especially powders based on anhydrite III may be employed, but in order to simplify the manufacturing process, use is preferably made of hydraulic binders based on stabilized anhydrite III, manufactured according to the specific processes described above. and more especially those manufactured according to the process described in the patent application FR2804423.

Alumina Al 2 O 3 (aluminum oxide) used is preferably without trace water. The alumina-based compounds employed never contain 100% Al ₂ O ₃ and generally contain impurities.

Table 1 which follows includes various alumina-based minerals that can be used alone or in combination to make the composition object of the invention. These minerals are advantageously ground and / or sieved before using them.

Table 1: different alumina-based minerals

% AI2O3

Minerals Application

(W / Pgranulat)

Calcined bauxite 90 any temperature

Burned refractory clay 40 Low temperature

Calcined alumina 99.5 High temperature

Tabular alumina 99.5 High temperature

Refractory chamotte 42 Low temperature

Perlite 13 Low temperature

Vermiculite <50 Low temperature bentonite <50 Low temperature

Magnesite> 50 High temperature

Dolomite 63 High temperature

Dairy 14 Low temperature

White or brown corundum High content High temperature

Kerphalite 60 High temperature

Alumina Spinel Magnesia 66 Very High Temperature Alumina Hydrate 65 High Temperature

Asbestos recycled 4 Low temperature aluminous melted cement> 50 High temperature andalusite> 50 High temperature

The Applicant has found that the higher the proportion of alumina, the more the material of the type mortar or concrete manufactured has high refractory properties. Alumina-based minerals can therefore be chosen according to the application that will be made of the material made from the composition object of the invention: resistance to low temperatures (> 1000 ⁰ C) or high temperatures (> 1600 ⁰ C).

Extensive dehydration (> 360 ° C) of the gypsum leads to the formation of anhydrite II (CaSO ₄ , OH ₂ O).

The source of anhydrite II used for carrying out the invention can come from a pure anhydrite II powder obtained by extensive dehydration of the gypsum. It may also come from a powder comprising a mixture of anhydrite III and anhydrite II obtained by dehydrating the gypsum at a temperature greater than 360 ^° C., but sufficiently low so that the whole of the anhydrite III is not overcured. .

When the composition is used for the manufacture of a material of the mortar or concrete type, it is mixed with water to form a pasty mixture. The Applicant has demonstrated that the presence of anhydrite II modifies the rheological properties of this pasty mixture, these properties being improved when the proportion of anhydrite III is greater than the proportion of anhydrite II.

The hydraulic lime used is obtained in a conventional manner by the calcination of siliceous and aluminous limestones.

The Applicant has found that the use of hydraulic lime improves the binding properties of the calcium sulfoaluminate-based composition obtained according to the invention. The use of lime is therefore quite advantageous when the composition object of the invention is used as a hydraulic binder for the manufacture of a building material of the mortar or concrete type.

The Applicant has also found that the use of a limestone-based powder can be used in a manner equivalent to hydraulic lime. Other minerals, compounds or adjuvants making it possible to improve one or more characteristics of either the sulfo-aluminous composition object of the invention or the material made from the latter, can also be used.

By heating a dry mixture comprising anhydrite III and alumina, calcium sulphoaluminate is obtained according to the reaction:

4 (CaSO _4, εH ₂ O; ε = 0.1 to 0.2) + Al ₂ O 3 ₃ - '(CaO) ₄ (Al ₂ θ3) 3SO ₄ + calcium aluminates

The residues are essentially calcium aluminates.

Anhydrite III in excess of alumina can be converted into anhydrite II according to the cooking temperature.

When 3 to 5 moles of anhydrite III are mixed with 2 to 4 moles of alumina, this reaction makes it possible to obtain more than 80% of C4A3S by weight of the composition, this percentage being maximal when mixing approximately 4 moles of anhydrite III with about 3 moles of alumina.

According to a preferred embodiment, 50 to 80% by weight of hydraulic binder comprising at least 70% by weight of anhydrite III is mixed with between 20 to 50% by weight of calcined alumina or of tabular alumina.

For example, mixing 64% by weight of hydraulic binder of stabilized anhydrite III manufactured by the method described in the patent application FR2804423 and 36% by weight of powder of calcined alumina is obtained at 1100 ⁰ C, 81.25% by weight of C ₄ A ₃ S.

It is also possible to use an anhydrite powder II which is mixed with the anhydrite powder III and the alumina powder, advantageously respecting the molar ratio between the anhydrite III and the alumina and preferably using a proportion of anhydrite III greater than the proportion of anhydrite II.

It is also possible to use hydraulic lime which is mixed with the anhydrite powder III, the alumina powder and / or the aluminum powder. anhydrite base II. Advantageously, from 5 to 40% by weight of the hydraulic lime mixture is used, preferably around 10%. For example, it is possible to mix 58% by weight of a hydraulic binder manufactured according to the process described in the patent application FR 2 804423, 32% by weight of tabular alumina and 10% by weight of natural hydraulic lime.

The firing temperature depends on the pressure at which the mixture of anhydrite III and alumina is subjected, the Applicant having found that the C ₄ A ₃ S is formed at about 1100 ⁰ C ₁ between 1000 ⁰ C and 1300 ⁰ C on average, at atmospheric pressure.

For temperatures below about 1100 ^° C., only a solid / solid diffusion of the atoms appears. To promote this diffusion and to optimize the formation reaction of C ₄ A ₃ S, the anhydrite III and / or the anhydrite II and the alumina have a particle size of less than 400 μm and preferably between 50 and 150 μm. If the hydraulic compounds, powders or binders based on anhydrite III and / or anhydrite II used have too large a particle size, is carried out a prior grinding or sieving. It is the same for compounds or powders based on alumina.

Cooking must be long enough to combine all the anhydrite

III with alumina. This time depends on the characteristics of the anhydrite III and alumina used and in particular the particle size, the cooking conditions and the heating methods used, however, a duration of 30 minutes to 2 hours is generally sufficient. According to a preferred embodiment, the mixture comprising anhydrite

III and alumina passes through a cooking tunnel of the type known to those skilled in the art, other facilities that can be used.

A first method of cooking consists in reacting the anhydrite III with the alumina by heating with a ramp for raising the temperature, preferably 20 ^° C. up to a temperature of between approximately 1000 ° C. and approximately 1300 ^° C. uses for example electrical resistors to variable power. The solid / solid diffusion and formation of C4A3S is thus optimal.

In an alternative embodiment, the anhydrite III is reacted with the alumina by direct calcination by means of a flame. The latter licks the mixture until it reaches the desired reaction temperature.

In another alternative embodiment, the anhydrite III is reacted with the alumina by a direct aeraulic calcination, usually called a "flash" type process. This process consists in injecting on the mixture of anhydrite III and alumina, a hot air fluid having a temperature of the order of 1400 ^° C., for a relatively short period of time, of the order of a few seconds to a few minutes.

In another variant embodiment, the anhydrite III is reacted with alumina by direct heating using electrical resistances so that the temperature in the cooking tunnel is of the order of 1400 ^° C. then the formation reaction of C ₄ AsS by quickly passing through the cooking tunnel, the mixture arranged in a low layer, for example on a conveyor belt.

In another alternative embodiment, the anhydrite III is reacted with the alumina by cooking using the microwaves. The formation reaction of C4A3S is thus very rapidly and optimally.

In another variant embodiment, the anhydrite III is reacted with the alumina by hybrid firing consisting of preheating said mixture with the aid of electrical resistances in order to accelerate the solid / solid diffusion and then to complete the reaction of formation of C ₄ AaS using microwaves.

Advantageously, when the mixture to be heated comprises lime, baking is carried out between 1200 ^° C. and 1300 ° C., preferably at 125 ^° C. for a period of 1 to 4 hours depending on the characteristics of the cooking tunnel. When the mixture comprising anhydrite III and alumina does not comprise anhydrite II before the heating step, it is possible to directly mix an anhydrite II-based powder with the resulting calcium sulfoaluminate-based composition. according to the invention, advantageously using a proportion of anhydrite II less than the proportion of anhydrite III used.

Also, when the mixture comprising anhydrite III and alumina does not comprise lime before the heating step, the lime can be mixed directly with the calcium sulphoaluminate-based composition obtained according to the invention. , advantageously using from 5 to 40% by weight of lime, preferably approximately 10%.

The Applicant has also demonstrated that calcium sulphoaluminate can be formed by reacting at a temperature rehydrated anhydrite III with alumina.

To do this, a mixture of anhydrite III and alumina is mixed with water to form a pasty mixture according to the following reaction:

(CaSO _4, EH ₂ O) + Al ₂ O ₃ + (H ₂ O) _n -_> (CaSO ₄ .2H ₂ O) ⁺ Al ₂ O ₃ + (H ₂ O) _n - ₂ (n> 2 )

Rehydrated Anhydrite III (CaSO ₄ , 2H ₂ O) * has the same chemical formula as gypsum, but has a crystalline structure different from that of natural gypsum.

To form the pasty mixture, it is also possible to use an anhydrite powder II which is mixed with the anhydrite powder III and the alumina powder, advantageously respecting the molar ratio between the anhydrite III and alumina and preferably using a proportion of anhydrite III greater than the proportion of anhydrite II.

This pasty mixture is then allowed to dry until it hardens, and then ground to obtain a granular mixture of desired particle size. It is also possible to use an anhydrite powder II which is mixed with the granular mixture obtained after the grinding step mentioned above, advantageously using a proportion of anhydrite III greater than the proportion of anhydrite II. It is also possible to use hydraulic lime which is mixed with the granular mixture obtained after the grinding step mentioned above, advantageously using from 5 to 40% by weight of the hydraulic lime mixture, preferably about 10%.

The granular mixture is then brought to temperature in the same manner as described above to form a granular composition based on calcium sulfoaluminate according to the following reaction:

4 (CaSO ₄ , 2H ₂ O) * + 3 AI ₂ O ₃ -> (CaO) ₄ (Al ₂ O ₃ ) 3SO ₄ + calcium aluminates

In an alternative embodiment, when the mixture comprising anhydrite III and alumina does not comprise anhydrite II or before the mixing step with water, or before the heating step, it is still possible to mix directly an anhydrite-based powder with the granulose composition based on calcium sulfoaluminate obtained according to the process mentioned above, advantageously using a proportion of anhydrite II less than the proportion of anhydrite III used.

If the granular mixture obtained after the milling stage does not comprise hydraulic lime, said hydraulic lime can be mixed with the granulose composition based on calcium sulphoaluminate obtained according to the process mentioned above, advantageously using from 5 to 40 % by weight of the hydraulic lime mixture, preferably about 10%.

The calcium sulphoaluminate-based composition produced according to the methods just described can optionally be ground before being conditioned, advantageously to obtain a granular composition having a particle size less than 400 microns.

It can be stored long term, in a rather dry place, without any other particular constraint because weakly hygroscopic.

The sulfo-aluminous composition produced according to the invention is advantageously used for the preparation of a material of the mortar or concrete type.

It is used directly as a hydraulic binder or in addition as an active filler for combination with industrial cements such as CPA, CEM, CSA, CFA, plaster, hydraulic lime, etc. It can also be used as a simple adjuvant to improve certain characteristics, including mechanical, chemical and refractory, material obtained.

The sulfo-aluminous composition of the invention is conventionally used by mixing it either directly with a granulate when it is used as a hydraulic binder or with cement and aggregates when it is used as an active filler or as an adjuvant. Delayers or setting activators as well as other compounds commonly used by those skilled in the art may be employed.

The resulting mixture is kneaded with water to form a pasty mixture which is then allowed to dry until it hardens and forms the mortar or concrete material according to the granulate employed. Before curing, the pasty mixture can be used by spraying (the pasty mixture having excellent adhesion to the support on which it is used) by casting or molding, by vibrated casting, by injection, by stratification, by extension, by hydraulic pressing, etc. according to the application of the material. So we have a very high ease of implementation. As described above, depending on the amount of anhydrite II contained in the sulfo-aluminous composition object of the invention, the pasty mixture will be more or less fluid.

According to the aggregates used for the preparation of the pasty mixture, the compressive strength varies from 5 to 75 MPa at 28 days (according to standard NF EN 196.1) and the mechanical resistance to flexion varies from 1 to 20 MPa at 28 days (according to standard NF EN 196.1).

To improve the rheological properties of a mortar or a concrete prepared from the composition in accordance with the invention, it is possible to use an anhydrite-based powder II which is mixed with the composition according to the invention .

The mixture thus obtained is conventionally kneaded with water to form a pasty mixture which is then allowed to dry until it hardens and forms the mortar or concrete material according to the granulate employed.

The Applicant has also found that the material manufactured according to the invention had very good properties refractory to high (> 1000 ° C) and very high (> 1600 ° C) temperatures, the sulfo-aluminous composition according to the invention it can thus advantageously be used as a refractory hydraulic binder or as a refractory active filler. The refractory calcium sulpho aluminate material obtained according to the invention is simpler to implement and less expensive than conventional sulfo-aluminous refractory materials.

The applicant has surprisingly demonstrated that the calcium sulphoaluminate formed in accordance with the invention acts as a powerful heat shield, the refractory material according to the invention absorbing only very slightly the thermal energy emitted by a heat source.

The Applicant has calculated the heat exchange on a refractory brick made from a conventional sulfo-aluminous cement and on a refractory brick made according to the invention.

The latter is prepared using a sulpho-aluminous granular composition manufactured by heating at 1100 ^° C. of a mixture comprising 64% by weight of hydraulic binder manufactured according to the process described in the patent application FR 2 80 44 23 and 36% by weight of tabular alumina, said composition being kneaded with 47% w / pπant of water. The two bricks have substantially the same dimensions.

One of the faces of each brick tested is subjected to a flame (torch) of about 1600 ⁰ C (thermal energy emitted). With the aid of sensors arranged at the level of the bricks, the thermal energy reflected by the heated face of said bricks is determined, the thermal energy absorbed (stored) by said bricks and the thermal energy transmitted. The results are summarized in Table 2 below.

Table 2: Results

These results clearly show the refractory brick according to the invention plays the role of a powerful reflective heat shield since

O% of the thermal energy emitted is reflected.

The average thermal conductivity of the refractory brick according to the invention is 0.6 VWm. ⁰ K to 1054 ⁰ C according to ASTM C-417.

According to the same standard, the thermal conductivity is 0.7 W / m 2 K at 152 ° C for a refractory material manufactured in accordance with the invention with 40% w / w water and 0.45 Wm 3. ⁰ K to 182 ⁰ C for a refractory material manufactured according to the invention with 80% w / pπant of water.

The Applicant has also demonstrated that the reflectivity was improved when the sulfo-aluminous composition according to the invention was manufactured using anhydrite II, the reflective properties being optimal when the proportion of anhydrite III is greater than that of Anhydrite II.

The Applicant has further found that the refractory material manufactured in accordance with the invention has a low coefficient of thermal expansion α = 10 " ⁶ K" ¹ which allows it to effectively withstand repeated thermal shocks.

Therefore, many industrial applications are possible. In particular, the material manufactured according to the invention can be used for the passive protection of wood structures, concretes, steels (firebreak for 2 to 6 hours), for the manufacture of fireproof panels, as active fillers for mortar and refractory concretes. , for the storage of nuclear waste, for the recycling of refractory waste, for the lining of metallurgical type industrial furnaces, for the manufacture of fireproof composite panels, for fire protection coatings, for heat shield coatings, etc. .

Claims

claims

A process for producing a calcium sulfoaluminate-based composition, characterized in that a mixture comprising anhydrite III and alumina is reacted at temperature to form sulfoaluminate of calcium.

2. Process according to claim 1, characterized in that stabilized anhydrite III is used.

3. Method according to one of the preceding claims, characterized in that it is reacted with 3 to 5 moles of anhydrite III with 2 to 4 moles of alumina.

4. Method according to one of the preceding claims, characterized in that the anhydrite III and alumina have a particle size less than 400 microns.

5. Method according to one of the preceding claims, characterized in that after reacting the anhydrite III and alumina, the resulting calcium sulfoaluminate-based composition is milled to obtain a granular composition of which the particle size is less than 400 μm.

6. Method according to one of the preceding claims, characterized in that is used as a source of anhydrite III, a hydraulic binder based on anhydrite III.

7. Method according to one of the preceding claims, characterized in that one uses as a source of alumina, the minerals following alone or in combination: calcined bauxite, tabular alumina, calcined alumina, calcined refractory clay, fireclay refractory, perlite, vermiculite, bentonite, magnesite, dolomite, slag, white or brown corundum, kerphalite, alumina hydrate, recycled asbestos, aluminous fused cement, magnesia alumina spinel, andalusite.

8. Process according to one of the preceding claims, characterized in that the anhydrite III and the alumina are reacted at a temperature of between 1000 ^° C. and 1300 ^° C.

9. Process according to one of the preceding claims, characterized in that the anhydrite III and the alumina are reacted by heating with ramp temperature rise.

10. The method of claim 9, characterized in that the temperature rise is 20O ⁰ C to a temperature between 1000 ° C and 1300 ⁰ C for a period of between 30 and 45 minutes.

11. Method according to one of claims 1 to 8, characterized in that the anhydrite III and alumina are reacted by a direct calcination by means of a flame.

12. Method according to one of claims 1 to 8, characterized in that the anhydrite III and alumina are reacted by direct aeraulic calcination.

13. Method according to one of claims 1 to 8, characterized in that the anhydrite III and alumina are reacted by direct heating using electrical resistances.

14. Method according to one of claims 1 to 8, characterized in that the anhydrite III and alumina are reacted by cooking using microwaves.

15. Method according to one of claims 1 to 8, characterized in that the anhydrite III is reacted with alumina by hybrid cooking of previously heating the mixture with the aid of electrical resistances then to complete the reaction using the microwaves.

16. Method according to one of the preceding claims, characterized in that: a) dry mixing an anhydrite powder III, a powder based on alumina and / or an anhydrite-based powder II and / or hydraulic lime, b) the mixture of step a) is reacted in temperature to obtain a granular composition based on calcium sulfoaluminate.

17. A method according to claim 16, characterized in that if the anhydrite powder II or the hydraulic lime is not mixed during step a), they are mixed with the sulfonated granular composition. calcium aluminate of step b).

18. Method according to one of claims 16 or 17, characterized in that if one mixes the hydraulic lime during step a), is reacted between 1200 ⁰ C and 1300 ⁰ C the mixture of said step a) .

19. Method according to one of claims 16 to 18, characterized in that one mixes between 5 and 40% by weight of hydraulic lime.

20. Method according to one of claims 1 to 15, characterized in that: a) a powder based on anhydrite III, an alumina powder and / or an anhydrite powder II is mixed with water to form a pasty mixture, b) the pasty mixture is dried. from step a) until it hardens, c) the hardened mixture of step b) is ground to obtain a granular mixture, d) the granular mixture of step c) is reacted in temperature; to obtain a granular composition based on calcium sulfoaluminate.

21. Process according to claim 20, characterized in that if the anhydrite powder II is not mixed during step a), it is mixed with the granular mixture of step c) or with the composition granular sulpho aluminate calcium of step d).

22. Method according to one of claims 20 or 21, characterized in that adding hydraulic lime to the granular mixture of step c) or the granular composition of step d).

23. Method according to one of claims 16 to 19 or according to claim 22, characterized in that the hydraulic lime is replaced by a powder based limestone.

24. Method according to one of claims 19 to 23, characterized in that the proportion of anhydrite III is greater than the proportion of anhydrite II.

25. Composition based on calcium sulfoaluminate, characterized in that it is obtained by the method according to one of the preceding claims.

26. Composition according to claim 25, characterized in that it comprises more than 80% by weight of calcium sulfoaluminate.

27. Use of the composition according to one of claims 25 or 26 as an active ingredient for the preparation of a material of the mortar or concrete type.

28. Use according to claim 27, for the preparation of a mortar type material or refractory concrete.

29. Use according to claim 27 or 28, as a hydraulic binder or active filler.

30. Use according to claim 29 as a refractory hydraulic binder or refractory active filler.