FR2753964A1 - MATERIAL, IN PARTICULAR CONSTRUCTION AND MANUFACTURING METHOD THEREOF - Google Patents

Abstract

The invention concerns a material, in particular for building and its method of manufacture, this material being obtained by mixing (10) quick lime (12) and wet gypsum (14) such as an industrial by-product containing residual gypsum, and by partly burning (18) this mixture at a low temperature to obtain a material essentially formed of calcium sulphate hemihydrate, dead lime and non-calcinated parts forming accelerating admixtures.

Description

 Material, in particular of construction and its manufacturing process.

 The invention relates to a material, in particular a building material, its use for the manufacture of building elements and its manufacturing method.

 European patent 0 290 571 discloses building blocks made of a material consisting essentially of plaster and an inert filler such as sand, having very good resistance to compression due to their molding in a closed mold. during hydration of the plaster which counteracts the natural expansion of the plaster and causes a densification of its crystal lattice. According to this known process, a mixture of plaster, water and an inert filler such as sand is compressed and then kept in a closed mold and is therefore subjected to a high internal pressure resulting from the hydration of the plaster, the duration of this can vary quite widely depending on the temperature and the type of plaster used, so that the molding operation generally lasts a few minutes.

 The plasters available on the market are complex products of good quality, relatively expensive and almost all containing setting retarders which facilitate the practical use of plaster in conventional processes but which lengthen the time during which the mixture of plaster, water and inert filler should be kept in a closed mold in the counter expansion process described above. The extension of this duration reduces the production rate of the construction elements and has a significant impact on their cost price.

 The present invention particularly relates to a new material which does not have this drawback.

 It also relates to a new material, which makes it possible to produce construction elements according to the process known as "thwarted expansion" with performances even better than those obtained so far.

 It also relates to a new material and its manufacturing process, which make it possible to use as raw material not plaster, but by-products of the chemical industry which we do not know what to do until now.

 The invention therefore provides, for this purpose, a material, in particular of construction, characterized in that it consists essentially of calcium sulphate hemihydrate, gypsum and slaked lime.

 Since calcium sulphate hemihydrate is the main component of plaster, such a material can be used as a conventional plaster or a mixture of conventional plaster and an inert filler for the manufacture of building elements according to the expansion process described in European Patent 0 290 571, but with the advantage that the gypsum it contains, being a setting accelerator, makes it possible to significantly increase the rate of manufacture of construction elements, by reducing the duration of their molding. In addition, the lime contained in this material has the long-term effect of increasing the surface hardness of the building elements and their resistance to water, ambient humidity, air and alkaline products.

 Advantageously, the material according to the invention is obtained by mixing wet gypsum and quicklime and partial cooking of the mixture.

 The wet gypsum can be, at least in part, residual gypsum and in particular a by-product of the chemical industry such as for example phosphogypsum (by-product of processes for the preparation of acid, production of boron and borates) or sulfogypsum (by-product of the desulfurization of fumes, in particular fumes from thermal power plants), which are products naturally containing moisture and which the prior art does not allow to use without prior drying.

 Quick lime mixed with these wet gypsums has the effect of absorbing the free water they contain, and raising the temperature, which can, depending on the nature of the mixtures, lead to the formation of nascent hemihydrate calcium sulfate (particularly active).

 Typically, the new material according to the invention comprises by weight from 3 to 15% approximately of slaked lime for 97 to 85% approximately of calcium sulphate hemihydrate and gypsum.

 The invention also provides a method of manufacturing this new material, characterized in that it consists in mixing quicklime and wet gypsum and in subjecting this mixture to partial cooking in order to obtain a material consisting essentially of hemihydrate of calcium sulphate, slaked lime and "incuits" forming setting accelerators.

 This process makes it possible to use wet gypsum without it being necessary to dry them completely beforehand, which saves energy, and to obtain a building material by partial firing of gypsum, hence another energy saving.

 This partial cooking is carried out at a relatively low temperature, for example of the order of 90 to 120 ° C.

 Advantageously, it is possible to use, for making and for cooking the mixture of quicklime and gypsum, a rotary drying oven of the type used for the manufacture of road mixes based on gravel and bitumen.

 These materials are already available and well known to those skilled in the art, so that the manufacture of the new construction material according to the invention requires very little investment and makes it possible to use by-products with little energy expenditure. of the chemical industry we didn't know what to do with.

 Furthermore, the product obtained by mixing wet gypsum and quicklime (a mixture of gypsum and slaked lime) can be used (before or after the above-mentioned partial cooking) for various purposes such as soil amendment (flocculation of clay soil, liming and gypsum, the slaked lime of this mixture being assimilated by plants), and the sulfo-calcium activation of road binders based on slag or hydraulic or pozzolanic binders in general.

 The invention will be better understood and other characteristics, details and advantages thereof will appear more clearly on reading the description which follows, given by way of example with reference to the appended drawings which schematically represent the different stages of the process for manufacturing the material according to the invention.

 The first stage of this process, designated by the reference 10, is a mixing of quicklime 12 and wet gypsum 14, the latter advantageously being made up partly or entirely of residual gypsum such as phosphogypsum, borogypsum or sulfogypsum for example, which are naturally wet byproducts of the chemical industry.

 If necessary, add dry natural gypsum to the residual gypsum as indicated in 16, depending on the water content that one wishes to obtain for the gypsum to be mixed with quicklime.

 As a variant, and in particular when the wet gypsum contains a lot of free water (from 10 to 20% by weight for example), this gypsum or the gypsum-lime mixture can be subjected to partial drying.

 Typically, wet gypsum can contain about 5 to 10 percent by weight of free water and about 3 to 15 percent by weight of quicklime is added to it.

 During mixing, quicklime is hydrated (quenched) by taking free water from the wet gypsum and becomes very fine, its fineness being much greater than that of quicklime obtained by grinding (it passes from 3,000 to 10,000 on a white surface for example). This hydration is accompanied by a release of heat causing a rise in temperature which may be sufficient for the production of semi-hydrate emerging from calcium sulphate.

 The mixture of gypsum and slaked lime is then subjected to partial firing 18, at a temperature which can be of the order of approximately 90 to 120 ° C. (whereas the normal firing temperature of gypsum for the manufacture of plaster is of the order of 150 to 160-C), the gypsum transforming into a mixture of calcium sulphate hemihydrate and incuits which are accelerators for setting calcium sulphate hemihydrate.

 Mixing 10 and partial cooking 18 can be carried out using materials which are traditionally used for the manufacture of road mixes based on gravel and bitumen, these materials being robust, safe and well known in the art.

 The material resulting from partial firing 18 can be stored as indicated in 20, to then be mixed with additives if necessary as indicated in 22 for various uses as indicated in 24, or it can be used immediately for manufacturing of building elements as will be described below. As indicated in the drawing, it is also possible to directly store the material resulting from the mixing 10.

 The material leaving the partial firing 18 is at a temperature close to 100 "C or higher and must be cooled, the cooling being able to be natural (heat exchange with the surrounding medium) or else to be able to occur or continue during the kneading. with an inert filler which is cold and possibly wet.

 Mixing with the inert filler is sufficient in principle to cool the material to a temperature where water can be added to it without vaporization.

 The amount of water added to the material is slightly greater than the optimum Prector to obtain the best possible compactness of the construction elements, and the inert load can be sand or any other load depending on the intended use of the construction elements .

 Optionally, water can be added at the end of mixing of the material and the inert filler, the mixture being for example at a temperature of the order of 60-80 C.

 The final temperature of the mixture can be determined to regulate the setting speed and promote the phenomenon of thwarted expansion.

 At 28, the mixture of material, water and filler is placed in a mold which is closed and which is placed under a press, and is kept in the closed mold for almost the entire duration of l hydration of plaster, as described in detail in European Patent 0 290 571 as well as in European Patent Application 0 619 773 to which a person skilled in the art can refer if necessary, the duration of this retention in the mold being a few minutes (typically two to four minutes) in these previous documents, whereas it can here be reduced to a much shorter duration, for example from ten to thirty seconds approximately, depending on the rate of incuits in the material according to the invention.

 The construction elements which are thus obtained can be used as soon as they are removed from the mold and they have a very high dimensional accuracy (of the order of 0.1 mm) due to the contrared expansion of the hemihydrate during their molding, so they can be used without a joint. The lime contained in these elements carbonates slowly (in a few months) on contact with carbon dioxide naturally present in the surrounding air and forms a surface layer of cullet which has the effect of improving resistance to air, to rain and to the surrounding humidity, as well as to alkaline products (washing or leaching products for example), and to increase the surface hardness of these elements, which allows them to be used under even more severe conditions and for example like good cut stone.

 The present invention has the essential advantage of using as is, in the wet state and very economically, by-products of the industry which are mixed with a small amount of quicklime to manufacture at low cost a new material itself usable in a particularly advantageous way for the manufacture of building elements according to the process of contrarian expansion, or to obtain a product usable for the amendment of soils and for the sulfo-calcium activation of binders.

Claims (11)

 1.- Material, in particular of construction, characterized in that it consists essentially of calcium sulphate hemihydrate, gypsum and slaked lime.  2.- Material according to claim 1, characterized in that it is obtained by mixing (10) wet gypsum (14) and quicklime (12) and by partial cooking (18) of the mixture.  3.- Material according to claim 2, characterized in that the mixture comprises approximately 3 to 15% by weight of lime for 97 to 85% approximately by weight of calcium sulphate hemihydrate and gypsum.  4.- Material according to one of the preceding claims, characterized in that it is mixed with an inert filler such as for example sand.  5.- Use of the material according to one of claims 1 to 4, characterized in that it consists in placing a mixture of this material and water in a mold, in compressing the mixture in the mold, in then opposing an increase in the volume of the mixture in the mold during the hydration of the calcium sulphate hemihydrate, in demolding the product thus obtained and in using it as a building element.  6.- A method of manufacturing a material, in particular of construction, characterized in that it consists of mixing quicklime (12) and wet gypsum (14), then subjecting this mixture to partial cooking ( 18) to obtain a material consisting essentially of calcium sulphate hemihydrate, slaked lime and incuits which are accelerators for setting calcium sulphate hemihydrate.  7.- Method according to claim 6, characterized in that the wet gypsum comprises residual gypsum such as phosphogypsum, borogypsum, sulfogypsum or other industrial by-products based on gypsum.  8.- Method according to claim 6 or 7, characterized in that the wet gypsum comprises natural gypsum (16).  9.- Method according to one of claims 6 to 8, characterized in that the partial cooking (18) is carried out at relatively low temperature, of the order of 90 to 120 "C for example.  10.- Method according to one of claims 6 to 9, characterized in that one uses, to form the mixture of quicklime and gypsum and for baking, a rotary oven of the type used for the manufacture of road mixes based on gravel and bitumen.  11. Material obtained by partial execution of the method according to one of claims 6 to 8, characterized in that it is formed by mixing wet gypsum, such as reductive gypsum and quicklime and is intended for the amendment of soils and the sulfo-calcium activation of binders.