Aggregates, manufacturing processes for such aggregates and their uses

Abstract

The intention relates to a process for preparing coated aggregates comprising the following steps: a) loading raw aggregates into a mixer; b) distributing a coating composition into the mixer, the coating composition comprising sand and cement; c) mixing the contents of the mixer for a period sufficient to form a film around the raw aggregates. Such aggregates are particularly useful for the production of concrete as well as for other applications.

Description

2

[0010] Aggregates play an essential role in concrete design, both in terms of their diversity and their contribution to the final material properties. Their selection, based on criteria of particle size, origin, and technical characteristics, is a key step in ensuring the success of any construction project.

[0011] The properties of aggregates, such as their shape, density, mechanical strength, and absorption capacity, greatly influence the final performance of the concrete. Concrete intended for structures requiring high strength or increased durability demands high-quality aggregates that are well-calibrated and free of impurities. Conversely, less demanding aggregates may be suitable for more basic applications.

[0012] These aggregates are first classified according to their size. Sands, called fine aggregates, consist of particles whose diameter is less than 5 mm. They can be obtained naturally, like river sand, or manufactured by crushing. Gravel, or coarse aggregates, are made up of particles whose size is greater than 5 mm and can reach up to 80 mm.These materials include gravel, pebbles, and crushed stone, used to give concrete its structure and strength.15

[0013] Regarding their origin, aggregates can be natural or artificial. Natural aggregates come directly from deposits, rivers, or quarries, where they are extracted without major transformation. On the other hand, artificial aggregates are produced by industrial processes, such as the recycling of construction waste, particularly concrete, or the use of industrial by-products such as slag.20

[0014] Artificial aggregates are granular materials manufactured or transformed, often from industrial by-products or specially treated raw materials. Unlike natural aggregates, artificial aggregates are the result of industrial processes designed to give them specific properties or to valorize waste. Their increasing use in construction is driven by their unique technical characteristics and their contribution to more sustainable practices.

[0015] These aggregates can come from different sources.Industrial by-products are a prime example. For instance, blast furnace slag, a byproduct of steelmaking, is cooled and ground to become dense and resistant aggregates, often used in technical concretes. Fly ash, a residue from coal combustion in thermal power plants, can be agglomerated to form lightweight aggregates. Expanded clay (known, for example, as ARGEX), obtained by firing specific clays at high temperatures, produces porous aggregates particularly well-suited to the manufacture of lightweight or insulating concretes. Granulated lay-up, another by-product of metallurgy, also finds application in concretes requiring increased durability. BE2024 / 5846 3

[0016] Besides industrial by-products, certain artificial aggregates are specifically produced for particular applications. For example, recycled glass aggregates, obtained by crushing used glass, can be integrated into decorative or technical concretes.Similarly, recycled concrete, made from crushed construction debris, is an increasingly popular material for sustainable construction projects.5

[0017] These aggregates offer numerous advantages. By valorizing industrial waste or replacing natural resources, they contribute to reducing the environmental footprint of the construction sector. Moreover, their specific properties, such as reduced density, particular mechanical resistance, or better thermal insulation, allow them to meet a variety of needs.10

[0018] Artificial aggregates, with their diversity and qualities, therefore play a key role in the evolution towards higher-performing and more environmentally friendly construction materials. Their integration into construction projects demonstrates the importance growth of sustainable practices in this sector.

[0019] However, their use sometimes requires adaptations in the concrete formulations to guarantee the desired performance.

[0020] The prior art already includes solutions that have been proposed for coating aggregate particles to give them desired properties. These processes always include a step of soaking the aggregates before coating. Such soaking does indeed increase the adhesion of the coating composition.20 However, soaking has many disadvantages. Some very porous aggregates must be saturated with water. Otherwise, these aggregates tend to absorb water from the mix and degrade the properties of the concrete. These waterlogged aggregates present other problems; they can release some of the water they contain and influence the quality of the concrete obtained. Another common problem is that after coating, the water is found25 trapped in the porosity of the aggregates and may require a very long time to be eliminated.

[0021] It would therefore be desirable to provide a solution allowing us to overcome the constraints concerning the aggregates.Furthermore, we would like to be able to have aggregates with a strength perfectly corresponding to the user's requirements (i.e., 30 with a custom-made strength). We would also like to be able to use any type of aggregate for high value-added applications. Ideally, the technology implemented should be non-polluting and not directly involve fossil fuels producing greenhouse gases.

[0022] Inventory Description

[0023] The invention that is the subject of this patent application aims to solve this technical problem. To achieve this, a process for preparing coated aggregates is proposed, comprising the following steps: -a) loading raw aggregates into a mixer; -b1) distributing a coating composition into the mixer, the coating composition comprising sand and grain; -c) mixing the contents of the mixer for a period of time allowing the formation of a film around the raw aggregates.

[0024] It should be understood that the raw aggregate is loaded dry into the mixer.Of course, some residual natural moisture may persist in these raw aggregates. The moisture content of raw aggregates, in the absence of any soaking operation, depends on several factors, including environmental conditions and the nature of the aggregates themselves. Fine aggregates, such as sand, generally have a higher moisture content than coarse aggregates. This difference is explained by their finer particle size and their increased capacity to retain water on the surface. As a general rule, the moisture content of unsoaked aggregates can vary between 0.5% and 8% by weight. Natural or washed sands, exposed to humid conditions or stored outdoors, often have a moisture content between 2% and 6% by weight. On the other hand, gravel or pebbles, due to their... Coarser texture and lower porosity result in lower moisture values, often between 0.5% and 2% by weight. Storage also plays a determining role.Raw aggregates stored in open air can absorb moisture from the atmosphere or rain, thus increasing their water content. Conversely, aggregates stored under cover or in controlled conditions retain minimal moisture. Thus, when dry, it should be understood that the moisture content does not exceed 8% by weight. This distinguishes so-called dry raw aggregates from raw aggregates that have undergone a soaking process and generally contain more than 25% water by weight.

[0025] Advantageously, the coating composition further comprises one or more components chosen from the group consisting of glass powder, refractory or decarbonated cements, fly ash, and chemical hardeners.

[0026] This allows for the control and drastic reduction of surface porosity.

[0027] Advantageously, the coating composition further comprises one or more additives chosen from the group consisting of water-repellent additives, adhesive additives, and colorants.

[0028] This allows for the imparting of desired properties to the aggregates, such as a particular color.

[0029] It is preferable to adjust the water content of the raw aggregates and the coating composition, and for this purpose, a humidification step (b2) of the raw aggregates is preferably provided after step (b1). This humidification step (b2) is carried out by watering or spraying the raw aggregates with a humidification solution. In the simplest cases, such a humidification solution may simply consist of water. Advantageously, this can be used as an opportunity to incorporate a water-soluble or water-suspended additive. Examples of such additives are water-repellent additives, additives that promote grain dispersion, and sticking additives.

[0030] Moistening the mixture after distribution of the coating composition 5 provides a wide range of properties and ensures the strength of the aggregate.

[0031] To obtain a coated aggregate of a given thickness, the operations of steps b1)etc), and possibly b2) if step 5 is implemented, are repeated until coated aggregates of the desired thickness are obtained.

[0032] According to an advantageous embodiment of the invention, a drying step is provided after the final implementation of step c).

[0033] This drying step allows for precise adjustment of the moisture content of the coated aggregates before their incorporation into concrete.

[0034] Another aspect of the present invention concerns a new mixing installation enabling the implementation of the process described above.

[0035] According to the invention, this mixing installation comprises: - a mixer with a receiving body; - means for supplying and distributing a coating composition comprising sand and cement.

[0036] According to the invention, the receiving body of the mixer is driven in rotation. It advantageously possesses an axis of evolution around which it is driven in rotation. Maison understands that the receiving body does not necessarily have to exhibit a symmetry of revolution as long as it can be driven in rotation. For example, one can provide in its internal space blades, mixing wings or other elements designed to promote mixing.25

[0037] According to the invention, the distribution means have a longitudinal axis parallel to the axis of evolution of the receiving body. It may be, for example, a tube with holes whose axis coincides with or is parallel to the axis of evolution of the receiving body.

[0038] The feeding means may be mechanical, for example, a tube with a screw conveyor or a carrier belt. According to a variant, these feeding means may be pneumatic, the coating composition being driven by a flow of gas, for example, air.

[0039] Examples of distribution means include simple holes in the tube, one or more slots, etc.

[0040] According to one variant of the mixing installation, this also includes means 35 for supplying and distributing liquid. As with the means for distributing the coating composition, the liquid distribution means have a longitudinal axis BE2024 / 5846 6 parallel to the axis of evolution of the receiving body of the mixer. Ideally, the liquid distribution means are arranged on an axis parallel to the distribution means of the coating composition.

[0041] According to another aspect, the invention concerns a film-coated aggregate capable of being obtained by the process described above.5

[0042] The invention concerns film-coated aggregates comprising i) a core made up of raw aggregates; ii) a film comprising cement and sand. According to the invention, the raw aggregates of the core are chosen - either from the group consisting of quarry crushed stone, crushed bricks / bricks / blocks from demolition sites or waste from waste disposal or incineration centers, crushed glass, crushed plaster foam, cellular concrete or foamed concrete and their combinations; -either by the group consisting of crushed expanded clay particles, polystyrene beads or grains, wood chips, plastic particles, perlite and their 15 combinations.

[0043] Advantageously, the film further comprises one or more components selected from the group consisting of glass powder, refractory or decarbonated cements, fly ash and chemical hardeners.

[0044] Advantageously, the film further comprises one or more additives chosen from the group consisting of water-repellent additives, adhesive additives or colorants.

[0045] Another aspect of the invention concerns a concrete comprising cement, sand and film-coated aggregates as described above.

[0046] Another aspect of the invention concerns the use of coated aggregates whose core is made for the manufacture of concrete.

[0047] The inventor of the present invention observed that when these coated aggregates comprise a core made of raw aggregates selected from a group consisting of crushed expanded clay particles, polystyrene beads or grains, wood chips, plastic particles, perlite and combinations thereof, they can advantageously be used for the production of insulating granules for flat roofing.

[0048] Brief description of the figures

[0049] The invention will now be described by means of the accompanying figure, which has no other purpose than to illustrate the present invention.

[0050] TheFig.1 represents a mixing installation with a mixer according to Invenon35

[0051] A detailed presentation of an embodiment is shown using figure BE2024 / 5846 7

[0052] We are schematically represented at l.