LIGHTWEIGHT COMPOSITION AND METHOD FOR PRODUCING A LIGHTWEIGHT MIXTURE

The invention relates to a lightening composition, mixable with clay mixtures for making lightened products, in particular building products such as bricks, hollow flat tiles, tiles and panels, and a method for producing a lightened clay mixture.

Lightening materials are known, such as, for example, wood flour, expanded polystyrene or expanded perlite, which can be mixed in variable quantities with the clay so as to obtain lightened clay mixtures. These latter enable building products to be made that are provided with a reduced specific weight and suitable mechanical properties. A drawback of known lightening materials consists of the fact that, as clay is a plastic and compact material, it is possible to add to a clay mixture only reduced quantities of the aforesaid lightening materials, for example small polystyrene balls . Consequently, it is significantly difficult to obtain a clay mixture, and a sufficiently lightened successive product. If, on the other hand, the lightening object is added to the mixture in significant quantities, the mixture is dishomogeneous and gives rise to products that disintegrate during extrusion, drying and/or firing. Another drawback consists of the fact that harmful volatile compounds are generated during firing of products manufactured using known lightening materials, such as wood flour, polystyrene and various other organic products. Consequently, using the known lightening materials is substantially polluting for the environment and potentially hazardous for the operators engaged in manufacturing the products .

An object of the invention is to improve the lightening materials usable for preparing lightened clay mixtures . Another object is to improve known methods for preparing lightened clay mixtures.

A further object is to provide a lightening material usable for preparing a lightened clay mixture with which to produce a building product.

Another further object is to provide a lightening material usable for preparing a lightened clay mixture with which to produce a product and such as to substantially prevent the product disintegrating during extrusion, drying and/or firing. A further other object is to provide a lightening material that is usable for preparing a lightened clay mixture with which to manufacture a product and such as not to emit harmful volatile compounds when the product is fired. Still another object is to provide a lightening material that is usable for preparing a lightened clay mixture with which to produce a building product, for example a brick, having a substantially reduced specific weight and suitable mechanical properties.

In a first aspect of the invention, there is provided a composition, usable for preparing a lightened mixture with which to manufacture products comprising: aluminium oxide, silicon dioxide, expanded silica.

In . a second aspect of the invention, there is provided a method for preparing a lightened clay mixture, comprising mixing clay with a lightening composition, said composition comprising: aluminium oxide, silicon dioxide, expanded silica.

Owing to these aspects, a lightening composition and a method for preparing lightened clay mixtures are made available. By using the composition and the method according to the invention it is possible to make products for building, such as bricks, tiles, hollow flat tiles or panels, that can be dried and fired using known procedures and apparatuses . The composition and the method according to the invention enable a substantially homogenous lightened mixture to be prepared by means of which it is thus possible to produce a

product that does not disintegrate during extrusion, drying and/or firing. In this manner, it is possible to add significant quantities of the aforesaid composition to a clay mixture to be lightened, so as to produce a building product that, although it has mechanical properties that are suitable and conform to current regulations, is also provided with a specific reduced weight.

The aluminium oxide (Al ₂ O ₃ ) , or alumina, increases the mechanical properties of the product obtained from the clay mixture incorporating the composition according to the invention. This is because when the product is fired to 850 ⁰ C, the alumina forms inside the clay mass of the product a sort of metallic structure that increases the mechanical properties thereof. Further, during firing of the product the alumina is transformed into metal aluminium, thus contributing to reducing the specific weight of the product. By using as a lightening material the composition according to the invention, harmful substances are not emitted during firing of the products. This enables the products to be produced working in a manner that is substantially non- polluting and non-hazardous for the operators. The lightening composition according to the invention has a percentage average formula (anhydrous) expressed in the following table 1: Table 1

In an embodiment, the aluminium oxide (Al ₂ O ₃ ) , or alumina, is equal to about 75% of the composition.

In an embodiment, the silicon dioxide (SiO ₂ ) is equal to about 15% of the composition. "Expanded silica" is defined as a material comprising: expanded pumice, expanded cellular glass, expanded sodium silicate, silica fume.

In an embodiment, the expanded silica is equal to about 10% of the composition.

In an embodiment, the lightening composition of Table 1 is hydrated and has a water percentage equal to about 10%. The lightening composition is obtained by mechanically mixing the various components, obtained by known methods and some of which are recoverable as residues of other industrial processes and/or by recycling of waste. For example, the expanded cellular glass is obtained by treating recycled glass at high temperatures. Once the various components have been mixed together, the resulting mix is possibly ground mechanically and/or screened so as to obtain a final composition having a granulometry comprised between 10 and 100 μm. Using processing residues and/or materials obtained from recycling waste to produce the lightening composition makes the latter significantly less costly to produce than other known lightening materials. Further, using processing residues to produce the composition according to the invention enables substantial energy savings to be made, as it is not necessary to resort to processing procedures and/or use plants that require a significant energy consumption, as is required for producing known lightening materials. In order to prepare a lightened clay mixture by means of the lightening composition, a percentage of the latter comprised between 0.1% and 20% is mixed mechanically with a proportional quantity of wet clay. The lightened clay mixture thus obtained is then used for loading an extruding apparatus of known type by means of which lightened products are produced, for example bricks, having desired shapes and sizes. The latter are then dried and fired using known methods and apparatuses . The fired products that are thus obtained were subjected to numerous laboratory tests, and these have demonstrated that these lightened products are provided with mechanical

properties that are suitable and conformant to legal requirements .

In particular, laboratory tests have demonstrated that, in the products obtained by using the composition according to the invention, an average percentage reduction of specific weight of 4.98% is obtained compared with non-lightened products .

Further, the lightened products manufactured by using the composition according to the invention have (once fired) an average mechanical resistance value (flexure resistance) of approximately 135 kg/cm ² , against an average value of approximately 121 kg/cm ² that is measurable in lightened products using known lightening materials (for example, sand) . As the lightened products manufactured by means of the composition according to the invention also have good heat- insulating properties the use in building of these lightened products enables further energy savings to be obtained. Using the lightening material of the composition according to the invention as lightening material enables clay mixtures to be obtained that have suitable plasticity and give rise to products having mechanical properties' that are similar, or superior, to those of products that are obtained using known lightening materials. The composition according to the invention can further be used instead of sand to degrease clay, so as to make the clay more easily dryable.