CZ310246B6 - A method of concrete preparation - Google Patents

Abstract

A method of preparation of 1 m3 of fresh concrete consists of the following stepsa) 1000 to 2000 kg of aggregate is mixed in a compulsory mixer for 20 to 40 seconds, whereas 40 to 100 % of aggregate consists of recycled inert construction and demolition waste;b) after mixing 28 to 52 kg of silica fume is added during 10 to 15 seconds while the mixture is being mixed and this mixture is mixed for 40 to 80 seconds;c) after mixing other components are added during 10 to 20 seconds while the mixture is being mixed and this mixture is mixed for another 40 to 80 seconds; andd) after that it is wetted with 135 to 250 kg of mixing water for 40 to 60 seconds while the mixture is being mixed, or such amount of mixing water is sprayed in 40 to 60 seconds and after another 80 to 160 seconds of mixing fresh concrete is prepared,whereas in step c) other components are added, gradually in a random order or at the same time, including cement and at least one cement substitute in the total amount of 135 to 600 kg, and the ratio of concrete and concrete substitute/substitutes is 30:70 to 70:30.

Description

Method for preparing concrete

Technical area

The invention relates to a method for preparing fresh concrete.

State of the art

According to qualified estimates, approximately 6.5 billion tons of inert construction and demolition waste are produced worldwide every year. The vast majority of this is landfilled, and only a relatively small part is further used or processed - most often in a way that does not exploit the full potential of this material, and when this material serves de facto only as a filler for a space. Crushed or ground inert construction and demolition waste is used primarily for backfilling and backfilling of engineering networks (a substitute for sorted gravel sand), for underfilling of parking lots, roads, concrete structures of floors of buildings and halls, backfilling of bridge forecourts, strengthening and leveling of forest and field roads (a substitute for crushed gravel), or for backfilling of earthworks of roads, railways, flood defences (as a substitute for soil), etc.

In addition, methods for preparing concrete are also known in which crushed or ground inert construction and demolition waste is used as a substitute for part of the aggregate. A common disadvantage of these methods, a typical representative of which is, for example, the method described in CN 105036660 A, and which are based on standard methods for preparing standard concretes, is that the concretes prepared by them either do not achieve the required mechanical-physical parameters, or they achieve them only at the cost of a large addition of cement (and the associated increase in production costs).

The aim of the invention is to propose a method for preparing concretes with the replacement of the largest possible part of the aggregate with recycled material created by grinding or crushing inert construction and demolition waste, which would enable the preparation of concretes with mechanical-physical parameters comparable to conventional concretes, while not requiring the addition of extra cement or other components.

The essence of the invention

The aim of the invention is achieved by mixing fresh concrete, which in 1 m ³ contains 135 to 250 kg of water, 135 to 600 kg of a mixture of cement and cement substitute/substitutes in a cement:substitute/cement substitutes ratio of 30:70 to 70:30, 28 to 52 kg of silica fume and 1000 to 2000 kg of aggregate, whereby 40 to 100% by weight of the aggregate is made up of recycled material from inert construction and demolition waste, 0 to 30% by weight of the aggregate is made up of natural aggregate (mined and/or crushed) and 0 to 30% by weight of the aggregate is made up of The aggregate is made up of lightweight artificial aggregate and/or cinder and/or slag and/or polystyrene and/or at least one organic filler, or another component for improving the thermal and/or acoustic and/or fire-resistant properties of hardened concrete.

In a preferred embodiment, this concrete in 1 m ³ contains 180 to 230 kg of water, 170 to 600 kg, preferably 170 to 410 kg of a mixture of cement and cement substitute/substitutes in a cement:substitute/cement substitutes ratio of 30:70 to 70:30, 35 to 45 kg of silica fume and 1355 to 1660 kg of brick recycle, which is a recycle from inert construction and demolition waste, which is entirely or at least more than half composed of brick rubble (with possible addition of rubble from other building materials and/or materials), or ceramic recycle, which is a recycle from inert construction and demolition waste, which is entirely or at least more than half composed of ceramic rubble from ceramic building and equipment elements, such as e.g. paving stones, tiles, ceramic sanitary products, fired tiles, etc. (with possible addition of crushed stone from other

- 1 CZ 310246 B6 building materials and/or materials) or mixed recyclate from inert construction and demolition waste, which is formed by crushed stone from mixed inert construction and demolition waste, which usually contains bricks, concrete and ceramic building and equipment elements in various proportions (with a possible admixture of crushed stone from other building materials and/or materials). The fraction of recycled materials is preferably 0 to 16 mm, or 0 to 8 mm. However, it can also be higher.

In another embodiment, concrete according to the invention is prepared, which has in 1 m ³ 170 to 235 kg of water, 135 to 600 kg, preferably 170 to 455 kg of a mixture of cement and cement substitute/substitutes in a cement:substitute/cement substitutes ratio of 30:70 to 70:30, 35 to 45 kg of silica fume and 945 to 1250 kg of brick or ceramic or mixed recyclate from inert construction and demolition waste, with a recyclate fraction of 0 to 16 mm, respectively. 0 to 8 mm, in combination with 350 to 515 kg of natural aggregate with an upper fraction of up to 16 mm, respectively. up to 8 mm, preferably up to 4 mm, in combination with 450 to 845 kg of concrete recyclate, which is a recyclate from inert construction and demolition waste, which is completely or at least consisting of more than half of concrete crushed stone or crushed stone from another material containing cement, such as cement mortar, concrete screed, etc. (with possible addition of crushed stone from other building materials and/or masses). Concrete recycle preferably has a fraction of 0 to 16 mm, or 0 to 8 mm.

If necessary, it may further contain at least one additive or a mixture of two or more concrete additives in a total amount of up to 5% by weight of the cement batch.

Several different processes can be used to prepare concrete according to the invention, which together form a single inventive idea and differ from each other only in the specific amount of raw materials and the type of recycled material used.

According to the invention, a two-fraction brick or ceramic or mixed recyclate from inert construction and demolition waste with recyclate fractions of preferably 0 to 8 mm and 8 to 16 mm is mixed in a forced circulation mixer for 20 to 40 seconds. After mixing, the entire dose of silica fume is added to it with constant stirring within 10 to 15 seconds, and the mixture thus formed is mixed for another 40 to 80 seconds. Then, cement and at least one cement substituent are added to it gradually in any order or simultaneously within 10 to 20 seconds, with constant stirring, the ratio of cement to cement substituent/substituents being 30:70 to 70:30, and the mixture thus formed is mixed for another 40 to 80 seconds. Then, while stirring continuously for 40 to 60 seconds, the entire batch of mixing water is sprinkled on it or the entire batch of mixing water is sprayed on it within 40 to 60 seconds. After another 80 to 160 seconds of mixing, fresh concrete is prepared in which 100% by weight of aggregate is made up of recycled material from inert construction and demolition waste.

The preparation of the dry mix for the preparation of such fresh concrete is carried out analogously, only without the addition of mixing water and using dried recyclate and possibly other components.

In a preferred embodiment, a two-fraction brick or ceramic or mixed recyclate from inert construction and demolition waste with recyclate fractions of preferably 0 to 8 mm and 8 to 16 mm is mixed in a forced circulation mixer for 20 to 40 seconds. After mixing, a two-fraction concrete recyclate with fractions of preferably 0 to 8 mm and 8 to 16 mm or natural aggregate with an upper fraction preferably up to 16 mm (max. up to 30% by weight of the total aggregate) is added to it with constant mixing, and the mixture thus formed is mixed for another 20 to 40 seconds. Then, the entire dose of silica fume is added to it with constant mixing within 10 to 15 seconds, and the mixture thus formed is mixed for another 40 to 80 seconds. After mixing it, cement and at least one cement substitute are added to it gradually in any order or simultaneously within 10 to 20 seconds, with constant stirring, the ratio of cement to cement substitute/substitutes being 30:70 to 70:30, and the mixture thus formed is mixed for a further 40 to 80 seconds. Subsequently, with constant stirring for 40 to 60 seconds, the entire batch of mixing water is sprinkled on it or the entire batch of mixing water is sprayed onto it within 40 to 60 seconds. After a further 80 to 160 seconds of stirring

- 2 CZ 310246 B6 fresh concrete is prepared in which 70 to 100% by weight of aggregate consists of recycled material from inert construction and demolition waste.

The preparation of the dry mix for the preparation of such fresh concrete is carried out analogously, only without the addition of mixing water and using dried recyclate and possibly other components.

In another variant, a two-fraction dedusted concrete recycle with fractions preferably 1 to 8 and 8 to 16 mm is mixed in a forced circulation mixer for 20 to 40 seconds. After mixing it, the entire dose of silica fume is added to it with constant stirring within 10 to 15 seconds, and the mixture thus formed is mixed for another 40 to 80 seconds. After mixing it, cement and at least one cement substitute are added to it gradually in any order or simultaneously with constant stirring within 10 to 20 seconds, with the ratio of cement and cement substitute/substitutes being 30:70 to 70:30, and the dry mixture thus formed is mixed for another 40 to 80 seconds. Subsequently, while stirring continuously for 40 to 60 seconds, the entire batch of mixing water is sprinkled on it or the entire batch of mixing water is sprayed on it within 40 to 60 seconds. After another 80 to 160 seconds of mixing, fresh concrete is prepared, in which 100% by weight of the aggregate is made up of recycled material from inert construction and demolition waste. The preparation of the dry mix for the preparation of such fresh concrete is then carried out analogously, only without the addition of mixing water and using dried recycled material and possibly other components.

In another embodiment, a two-fraction concrete recycle with fractions preferably 0 to 8 mm and 8 to 16 mm is mixed in a forced circulation mixer for 20 to 40 seconds. After mixing, natural aggregate with an upper fraction preferably up to 16 mm (max. up to 30% by weight of total aggregate) is added to it with constant mixing and the mixture thus formed is mixed for another 20 to 40 seconds. Then, the entire dose of silica fume is added to it with constant mixing within 10 to 15 seconds and the mixture thus formed is mixed for another 40 to 80 seconds. After mixing it, cement and at least one cement substitute are added to it gradually in any order or simultaneously within 10 to 20 seconds, with constant stirring, the ratio of cement to cement substitute/substitutes being 30:70 to 70:30, and the mixture thus formed is mixed for another 40 to 80 seconds. Subsequently, with constant stirring for 40 to 60 seconds, the entire batch of mixing water is sprinkled on it or the entire batch of mixing water is sprayed onto it within 40 to 60 seconds. After a further 80 to 160 seconds of mixing, fresh concrete is prepared, in which at least 70% by weight of the aggregate is made up of recycled material from inert construction and demolition waste.

The preparation of the dry mix for the preparation of such fresh concrete is carried out analogously, only without the addition of mixing water and using dried recyclate and possibly other components.

In the case where recycled material and possibly natural aggregate with a top fraction of up to 8 mm is used, concrete with a finer texture, sometimes referred to as cement or concrete mortar, is prepared using the same procedures.

In all variants, at least one additive or a mixture of two or more concrete additives may be dissolved in the mixing water in a total amount of up to 5% by weight of the cement batch.

In another embodiment, at least one additive or a mixture of several additives is added to the concrete in an amount of up to 5% by weight of the cement batch only after the dry mixture is sprinkled with mixing water or the mixing water is sprayed onto it.

As natural aggregate, quarried and/or crushed natural aggregate with a fraction of 0 to 4 mm is preferably used.

In other variants, the recycled material from inert construction and demolition waste with the upper fraction, preferably up to 16 mm or up to 8 mm of the first composition, is mixed in a forced circulation mixer for 20 to 40 seconds, after which the recycled material from inert construction and demolition waste with the upper fraction, preferably up to 16 mm or up to 8 mm of the second composition, is added to it with constant stirring.

- 3 CZ 310246 B6 and the mixture thus formed is mixed for 20 to 40 seconds and then natural aggregate with an upper fraction preferably up to 16 mm or up to 8 mm is added to it and the mixture thus formed is mixed for another 20 to 40 seconds. Subsequently, 28 to 52 kg of silica fume are added to it within 10 to 15 seconds and the mixture thus formed is mixed for another 40 to 80 seconds and after mixing it, 135 to 400 kg are added to it gradually in any order or simultaneously within 10 to 20 seconds with constant stirring, cement and at least one cement substitute in a total amount of 135 to 600 kg, with the ratio of cement and cement substituent/substituents being 30:70 to 70:30. The mixture thus formed is mixed for another 40 to 80 seconds, after which 135 to 250 kg of mixing water is sprinkled on it with constant mixing for 40 to 60 seconds, or this amount of mixing water is sprayed onto it within 40 to 60 seconds, and after another 80 to 160 seconds of mixing, fresh concrete is prepared in which at least 70% by weight of the aggregate is made up of recycled material from inert construction and demolition waste. In this case, brick or ceramic or mixed recycled material is preferably first dosed into the mixer, then concrete recycled material and then natural aggregate.

All components of the concrete or dry mix are dosed while the mixer is running. However, it is possible to temporarily stop the mixer after mixing the components already added and before adding the next component, or, if the mixer design allows it, to reverse this operation to add the next component. However, these adjustments to the mixer operation have no effect on the properties or consistency of the prepared fresh concrete (or dry mix), nor on the subsequently hardened concrete and its properties.

If necessary, in any procedure, at least one improving admixture may be added to the mixture before the addition of silica fume to improve the thermal and/or acoustic and/or fire-resistant properties of the concrete, such as lightweight artificial aggregate (agloporite, expanded clay, expanded perlite, etc.), slag, slag, at least one organic filler (wood sawdust, shavings, rice husks, husks, etc.), polystyrene, etc. in an amount of up to 30% by weight of the aggregate, preferably up to 20 or 15% by weight of the total aggregate. This component is added with constant stirring and mixed with the other components forming the aggregate for 20 to 40 seconds.

In another embodiment, the first part of the total batch of aggregates formed by the recycle from inert construction and demolition waste is mixed in a forced circulation mixer for 20 to 40 seconds, then the first part of the total batch of silica fume is added to it within 10 to 15 seconds, and the mixture thus formed is mixed for 20 to 60 seconds. Then, with constant mixing, the second part of the total batch of aggregates formed by the recycle from inert construction and demolition waste or natural aggregate is added to it, and the mixture thus formed is mixed for 20 to 40 seconds, and then the second part of the batch of silica fume is added to it within 10 to 15 seconds, whereby the total amount of aggregates in 1 m ³ of fresh concrete is 1000 to 2000 kg and 40 to 100% by weight. of this aggregate is made up of recycled material from inert construction and demolition waste, and the total dose of silica fume in 1 m ³ of fresh concrete is 28 to 52 kg. The mixture thus formed is mixed for 40 to 80 seconds and after mixing, cement and at least one cement substitute are added to it gradually in any order or simultaneously within 10 to 20 seconds with constant mixing, in a total amount of 135 to 600 kg, with the ratio of cement to cement substitute/substitutes being 30:70 to 70:30, and the mixture thus formed is mixed for another 40 to 80 seconds, after which 135 to 250 kg of mixing water is sprinkled on it with constant mixing for 40 to 60 seconds, or this amount of mixing water is sprayed onto it within 40 to 60 seconds, and after another 80 to 160 seconds of mixing, fresh concrete is prepared.

The first and second parts of the total batch of aggregate may be formed by recyclate from inert construction and demolition waste of the same composition and/or fraction, or, conversely, of different composition and/or fraction.

In another variant, the first part of the total batch of aggregates consisting of recycled material from inert construction and demolition waste is mixed in a forced circulation mixer for 20 to 40 seconds, then the first part of the total batch of silica fume is added to it within 10 to 15 seconds, and the mixture thus formed is mixed for 20 to 60 seconds. Then the second part of the total batch is added to it with constant mixing.

- 4 CZ 310246 B6 aggregates consisting of recycled material from inert construction and demolition waste or natural aggregates and the mixture thus formed is mixed for 20 to 40 seconds. Then, within 10 to 15 seconds, the second part of the dose of silica fume is added to it, and the mixture thus formed is mixed for 20 to 60 seconds and then, with constant mixing, the third part of the total dose of aggregates consisting of recycled material from inert construction and demolition waste or natural aggregates is added to it, and the mixture thus formed is mixed for 20 to 40 seconds. Subsequently, within 10 to 15 seconds, the second part of the dose of silica fume is added to it, with the total amount of aggregates in 1 m ³ of fresh concrete being 1000 to 2000 kg and 40 to 100% by weight. of this aggregate is made up of recycled material from inert construction and demolition waste, and the total dose of silica fume in 1 m ^{3 of} fresh concrete is 28 to 52 kg. The mixture thus formed is mixed for 40 to 80 seconds and after mixing, cement and at least one cement substitute are added to it gradually in any order or simultaneously within 10 to 20 seconds with constant stirring in a total amount of 135 to 600 kg, with the ratio of cement and cement substitute/substitutes being 30:70 to 70:30. The mixture thus formed is mixed for another 40 to 80 seconds, after which 135 to 250 kg of mixing water is sprinkled on it for 40 to 60 seconds while stirring continuously, or this amount of mixing water is sprayed onto it within 40 to 60 seconds, and after another 80 to 160 seconds of mixing, fresh concrete is prepared.

At least two parts of the total batch of aggregate may be formed by recyclate from inert construction and demolition waste of the same composition and/or fraction, or, conversely, of different composition and/or fraction.

Examples of implementation of the invention

The method for preparing concrete is based on a combination of a specific concrete composition and a specific procedure, which in combination allow replacing up to 100% by weight of aggregates in concrete with recycled material from inert construction and demolition waste (i.e. ground or crushed inert construction and demolition waste) while achieving mechanical and physical parameters that are at least comparable to standard concretes.

Recyclate from inert construction waste can have essentially any fraction depending on the use and requirements for concrete, but it is advantageous to have a fraction of 0 to 16 mm or 1 to 16 mm (if only concrete recyclate is used as aggregate), or 0 to 8 mm or 1 to 8 mm (if only concrete recyclate is used as aggregate).

Fresh concrete prepared in this way contains in 1 m ³ 135 to 250 kg of water, 135 to 400 kg of cement, 28 to 52 kg of silica fume and 1000 to 2000 kg of aggregate, with 40 to 100% by weight of this aggregate consisting of brick or ceramic or mixed recyclate from inert construction and demolition waste with a fraction preferably of 0 to 16 mm (in a preferred variant, it is a two-fraction recyclate with fractions of 0 to 8 mm and 8 to 16 mm), or 0 to mm, and/or concrete recyclate with a fraction preferably of 0 to 16 mm (in a preferred variant, it is a two-fraction recyclate with fractions of 0 to 8 mm and 8 to 16 mm), respectively. 1 to 16 mm (in the preferred variant, it is a two-fraction recyclate with fractions of 1 to 8 mm and 8 to 16 mm), or 0 to mm, or 1 to 8 mm.

For the purposes of this application, brick recyclate is understood to mean recyclate created by crushing or grinding inert construction and demolition waste, which is entirely or at least predominantly composed of bricks, with possible additions of other building materials and/or materials (concrete, ceramic building and furnishing items, mortar residues, plaster, building adhesive, etc.). Brick recyclate is thus entirely or at least predominantly composed of brick rubble, with possible additions of rubble from other building materials and/or materials. Ceramic recyclate is understood to mean recyclate created by crushing or grinding inert construction and demolition waste, which is entirely or at least predominantly composed of ceramic building and furnishing items, such as paving stones, tiles, ceramic sanitary products, fired tiles, etc., with possible additions of other building materials and/or materials (concrete, bricks, mortar residues, plaster, building adhesive, etc.).

- 5 CZ 310246 B6 mortar, plaster, construction adhesive, etc.). Ceramic recyclate is thus entirely or at least more than half composed of ceramic crushed stone, with a possible admixture of crushed stone from other construction materials and/or materials. Concrete recyclate means recyclate created by crushing or grinding inert construction and demolition waste, which is entirely or at least more than half composed of concrete or other material containing cement (e.g. concrete screed, cement mortar, etc.), with possible admixtures of other construction materials or materials (bricks, ceramic construction and equipment items, mortar residues, plaster, construction adhesive, etc.). Concrete recyclate is thus entirely or at least more than half composed of crushed stone from concrete or other material containing cement, with a possible admixture of crushed stone from other construction materials and/or materials. Mixed recyclate is then understood as recyclate created by crushing or grinding mixed inert construction and demolition waste, which is made up of a mixture of various building materials and substances, usually bricks, concrete and ceramic building and equipment items in various proportions, with a possible addition of mortar residues, plasters, gypsum, construction adhesive, etc. Mixed recyclate is thus made up of crushed material from mixed construction and demolition waste.

The fractions of all these recycled materials can be any according to the intended use and requirements for concrete, preferably 0 to 16 mm, or 1 to 16 mm, or 0 to 8 mm, or 1 to 8 mm.

The remaining part of the aggregate, if any - max. up to 30% by weight, is then made up of natural aggregate (mined and/or crushed) with an upper fraction preferably up to 16 mm, or up to 8 mm, or up to 4 mm. Another 0 to 30% by weight of aggregate, preferably 0 to 20 or 0 to 15% by weight of aggregate can then, if necessary, be made up of at least one known improving admixture that improves the thermal and/or acoustic and/or fire-resistant properties of concrete, and which is commonly used in standard concrete. Such improving admixture is, for example, light artificial aggregate (such as agloporite, expanded clay, expanded perlite, etc.), slag, slag, polystyrene or at least one organic filler (such as wood sawdust, shavings, rice husks, husks, etc.), etc.

When using recycled material from inert construction and demolition waste and possibly natural aggregate with a fraction of 0 to 8 mm, fresh concrete with a finer texture is prepared, sometimes referred to as cement or concrete mortar.

In preferred embodiments, fresh concrete in 1 m ³ contains 180 to 230 kg of water, 170 to 210 kg of cement, 35 to 45 kg of silica fume and 1355 to 1660 kg of brick or ceramic or mixed recyclate from inert construction and demolition waste with a recyclate fraction of 0 to 16 mm, or 0 to 8 mm, or 170 to 235 kg of water, 170 to 255 kg of cement, 35 to 45 kg of silica fume and 945 to 1250 kg of brick or ceramic or mixed recyclate from inert construction and demolition waste with a recyclate fraction of 0 to 16 mm, or 0 to 8 mm, in combination with 350 to 515 kg of natural aggregate with an upper fraction of up to 16 mm, or up to 8 mm, or up to 4 mm, or 165 to 250 kg of water, 170 to 255 kg of cement, 35 to 45 kg of silica fume and 685 to 1075 kg of brick or ceramic or mixed recyclate from inert construction and demolition waste with a recyclate fraction of 0 to 16 mm, or 0 to 8 mm, in combination with 450 to 845 kg of concrete recyclate with a fraction of 0 to 16 mm, or 0 to 8 mm, or 155 to 220 kg of water, 170 to 255 kg of cement, 35 to 45 kg of silica fume and 1025 to 1320 kg of concrete recyclate with a fraction of 0 to 16 mm, or 0 to 8 mm, in combination with 450 to 585 kg of natural aggregate with a top fraction of up to 16 mm or up to 8 mm, preferably up to 4 mm.

If necessary, fresh concrete prepared according to the invention in any variant may contain at least one additive or a mixture of two or more concrete additives in a dose of maximum 5% by weight of the cement dose. Such an additive may be any known additive, such as an additive for vibropressed concrete and/or additives according to EN 934-2. These additives include in particular water-reducing (plasticizing) and strongly water-reducing (superplasticizing) additives for improving the consistency of concrete, for reducing the amount of water, improving the strength and some other properties of fresh and hardened concrete, as well as stabilizing, aerating, accelerating the setting and hardening of concrete, retarding the setting, sealing, etc. This/these additive/additives are

- 6 CZ 310246 B6 added to other concrete components dissolved in the mixing water, or separately, preferably after adding the mixing water.

For thorough mixing of the individual components and preparation of concretes (or dry mixtures) of the required structure and properties, any mixer with forced circulation is used, preferably a mixer with radial movement of the mixing arms, or with double simultaneous radial movement of the mixing arms (such as the mixer described in IT 1244970 B or EP 0508962 A1), in which all its internal surfaces are wiped. However, it is necessary to observe not only the above-mentioned composition of the concretes, but also the mixing times and dosing of the individual components into the mixer (see examples 1 to 4 and 8 to 11 below). All components are dosed while the mixer is running. However, it is possible to temporarily stop the mixer after mixing the already added components and before adding the next component, or, if the mixer design allows, to reverse this run to insert some other component and mix it with the other components. However, these adjustments to the mixer operation have no effect on the properties or consistency of the fresh concrete (or dry mix) being prepared, nor on the subsequently hardened concrete and its properties.

Recyclate from inert construction and demolition waste is sanitized before preparing concrete or dry mix, e.g. in a water or steam bath or in another way, which reduces the number of (pathogenic) organisms and microorganisms contained in it.

Silica fume, which serves as a binder in the standard preparation of standard concretes from natural aggregates, serves as a filler in the preparation of concretes according to the invention, when, when following the dosing method described below and the mixing method described above, it fills the overall lattice structure of the concrete, envelops the recycled particles and fills the pores in them. Thanks to this, fine particles do not clump and the resulting concrete has lower porosity and, after hardening, achieves mechanical-physical parameters comparable to standard concretes.

In the embodiment of the method according to the invention, the silica fume is added to the mixer only after the last component of the aggregate, or recyclate from construction and demolition waste. In addition, it is possible to divide the total dose of silica fume and the total dose of aggregate into two or more smaller parts (the same or different), and to gradually add individual parts of the dose of silica fume after adding individual parts of the total dose of aggregate, or recyclate from construction and demolition waste of different types and/or fractions, or to add at least some parts of the dose of silica fume simultaneously with some parts of the total dose of aggregate or recyclate (see e.g. examples 12 to 15). In all variants, cement with a specific surface area of at least 330 m ² .kg ^-1 or greater is used (e.g. cement of class CEM I 42.5, or higher). Its dosage in the manner described below ensures the formation of a suitable bond between the cement and the recyclate already coated with silica fume and very good homogenization of the mixed mixture.

Part of the cement batch is replaced by a cement substitute, such as ground-granulated blast-furnace slag (GGBS or GGBFS) and/or fly ash, or a mixture of at least two such substitutes, with the ratio of cement to cement substitute(s) in the fresh concrete being 30:70 to 70:30. The total amount of cement and cement substitute(s) is then the same as the amount of cement itself, i.e. 135 to 400 kg/ ^m3 of fresh concrete, or up to 600 kg/ ^{m3 of} fresh concrete. The cement and cement substitute(s) are added to the mixture either simultaneously, each separately, or sequentially in any order (it is preferred, but not essential, to add the cement substitute(s) first and then the cement), or in the form of a pre-prepared mixture of the composition described above.

After creating and mixing the dry mixture from the above-mentioned ingredients, this mixture is sprinkled with mixing water in a mixer while constantly stirring, or the mixing water is sprayed onto it. With this method of dosing the mixing water in combination with constant stirring in a mixer with forced circulation, the surface of the cement is gradually moistened and the cement mastic formed gradually sticks to the grains of the recycled material already coated with silica fume, which makes it

- 7 CZ 310246 B6 prevents the agglomeration of fresh concrete particles, the separation of fine particles of the mixture and the separation of water, and ensures the required consistency of fresh concrete. In addition, this method of dosing activates the silicon dioxide contained in the fine particles of the recyclate and silica fume, and thus the latent hydraulicity of these components, which allows concretes prepared in this way to achieve physical and mechanical parameters comparable to standard concretes, even at a cement dosage that may be lower than that of standard concretes (in some variants 190 to 230 kg/m ³ - see e.g. examples 5, 6 and 7).

The mixing water must be of drinking water quality. If necessary, it may contain (dissolved or undissolved) at least one known standard concrete admixture.

To supplement the recycled material from inert construction and demolition waste, it is possible to use natural aggregate (mined and/or crushed) with an upper fraction preferably up to 16 mm, or up to 8 mm, or possibly even small mined aggregate with a fraction of 0 to 4 mm.

Below are described four exemplary procedures for the preparation of fresh concrete (and dry mixtures for the preparation of this concrete) - the first one for the case where 100% by weight of the aggregate is made up of two-fraction mixed recyclate from inert construction and demolition waste, with recycle fractions of 0 to 8 mm and 8 to 16 mm, the second one for the case where the aggregate is made up of two-fraction mixed recyclate from inert construction and demolition waste, with recycle fractions of 0 to 8 mm and 8 to 16 mm in combination with two-fraction concrete recyclate with fractions of 0 to 8 mm and 8 to 16 mm or natural aggregate with an upper fraction of up to 16 mm (up to 30% by weight of the total aggregate), the third one for the case where 100% by weight of the aggregate is aggregates consisting of two-fraction concrete recycle with fractions of 1 to 8 mm and 8 to 16 mm, and the fourth for the case where the aggregates are formed of two-fraction concrete recycle with fractions of 0 to 8 mm and 8 to 16 mm in combination with natural aggregates with an upper fraction of up to 16 mm (up to 30% by weight of total aggregates). As is clear to the person skilled in the art, the intervals, respectively. times of adding individual components and the amount of these components are given by the technological requirements for hardened concrete and its mechanical-physical parameters, and can range within the entire intervals listed below. Similarly, in other examples, the upper fraction of the recycle/s and/or natural aggregates may be higher than 16 mm.

In other variants, it is possible to combine brick or ceramic or mixed recyclate from inert construction and demolition waste with concrete recyclate and up to 30% by weight of natural aggregate within the aggregate in an analogous manner. In this case, brick or ceramic or mixed recyclate from inert construction and demolition waste is preferably first dosed into the mixer, then concrete recyclate and then natural aggregate. Brick, ceramic or mixed recyclate from inert construction and demolition waste have similar properties and behavior and therefore can be interchanged or mixed with each other.

Between batches of recycled construction and demolition waste of various types and/or fractions, and/or natural aggregate, or simultaneously with them, parts of the total batch of silica fume can be gradually added to the mixer.

Example 1 (prior art)

To prepare the concrete, a two-fraction mixed recyclate from inert construction and demolition waste, with recyclate fractions of 0 to 8 mm and 8 to 16 mm, is mixed in a forced circulation mixer with radial or double simultaneous radial movement of the mixing arms for 20 to 40 seconds. After mixing, the entire dose of silica fume is added to it with constant stirring for 10 to 15 seconds, and the mixture thus formed is mixed for another 40 to 80 seconds. Then, the entire dose of cement is added to it with constant stirring for 10 to 20 seconds, and the mixture thus formed is mixed for another 40 to 80 seconds. Then, while stirring continuously, the entire batch of mixing water (which, if necessary, contains at least one concrete additive) is sprinkled on it within 40 to 60 seconds or the entire batch of mixing water (which, if necessary, contains at least one concrete additive) is sprayed onto it within 40 to 60 seconds. After a further 80 to 160 seconds of mixing,

- 8 CZ 310246 B6 prepares fresh concrete in which 100% by weight of aggregate consists of recycled material from inert construction and demolition waste.

The preparation of the dry mix for the preparation of such fresh concrete is carried out analogously, only without the addition of mixing water and using dried recyclate and possibly other components.

Example 2 (prior art)

To prepare the concrete, a two-fraction mixed recyclate from inert construction and demolition waste, with fractions of recyclate of 0 to 8 mm and 8 to 16 mm, is mixed in a mixer with forced circulation and radial or double simultaneous radial movement of the mixing arms for 20 to 40 seconds. After mixing, a two-fraction concrete recyclate with fractions of 0 to 8 mm and 8 to 16 mm or natural aggregate with an upper fraction of up to 16 mm (max. up to 30% by weight of the total aggregate) is added to it with constant stirring, and the mixture thus formed is mixed for another 20 to 40 seconds. Then, with constant stirring, the entire dose of silica fume is added to it within 10 to 15 seconds, and the mixture thus formed is mixed for another 40 to 80 seconds. After mixing it, the entire batch of cement is added to it with constant stirring within 10 to 20 seconds and the mixture thus formed is mixed for another 40 to 80 seconds. Subsequently, with constant stirring, the entire batch of mixing water (which, if necessary, contains at least one concrete additive) is sprinkled on it within 40 to 60 seconds or the entire batch of mixing water (which, if necessary, contains at least one concrete additive) is sprayed onto it within 40 to 60 seconds. After a further 80 to 160 seconds of mixing, fresh concrete is prepared in which 70 to 100% by weight of aggregate is made up of recycled material from inert construction and demolition waste.

The preparation of the dry mix for the preparation of such fresh concrete is carried out analogously, only without the addition of mixing water and using dried recyclate and possibly other components.

Example 3 (prior art)

To prepare the concrete, a two-fraction dedusted concrete recycle with fractions of 1 to 8 and 8 to 16 mm is mixed in a forced circulation mixer with radial or double simultaneous radial movement of the mixing arms for 20 to 40 seconds. After mixing it, the entire dose of silica fume is added to it with constant stirring within 10 to 15 seconds, and the mixture thus formed is mixed for another 40 to 80 seconds. After mixing it, the entire dose of cement is added to it with constant stirring within 10 to 20 seconds, and the dry mixture thus formed is mixed for another 40 to 80 seconds. Subsequently, while stirring continuously, the entire batch of mixing water (which, if necessary, contains at least one concrete additive) is sprinkled on it within 40 to 60 seconds or the entire batch of mixing water (which, if necessary, contains at least one concrete additive) is sprayed onto it within 40 to 60 seconds. After a further 80 to 160 seconds of mixing, fresh concrete is prepared in which 100% by weight of aggregate consists of recycled material from inert construction and demolition waste.

The preparation of the dry mix for the preparation of such fresh concrete is carried out analogously, only without the addition of mixing water and using dried recyclate and possibly other components.

Example 4 (prior art)

To prepare the concrete, a two-fraction concrete recycle with fractions of 0 to 8 mm and 8 to 16 mm is mixed in a mixer with forced circulation and radial or double simultaneous radial movement of the mixing arms for 20 to 40 seconds. After mixing, natural aggregate with an upper fraction of up to 16 mm (max. up to 30% by weight of total aggregate) is added to it with constant stirring and the mixture thus formed is mixed for another 20 to 40 seconds. Then, the entire dose of silica fume is added to it with constant stirring within 10 to 15 seconds and the mixture thus formed is mixed for another 40 to 80 seconds. After mixing it, the entire dose of cement is added to it with constant stirring within 10 to 20 seconds and the mixture thus formed is mixed for another 40 to 80 seconds. Subsequently

- 9 CZ 310246 B6 is sprinkled with the entire batch of mixing water (which, if necessary, contains at least one concrete additive) within 40 to 60 seconds while stirring continuously, or the entire batch of mixing water (which, if necessary, contains at least one concrete additive) is sprayed onto it within 40 to 60 seconds. After a further 80 to 160 seconds of mixing, fresh concrete is prepared in which at least 70% by weight of aggregate is made up of recycled material from inert construction and demolition waste.

The preparation of the dry mix for the preparation of such fresh concrete is carried out analogously, only without the addition of mixing water and using dried recyclate and possibly other components.

In all cases, after adding the last aggregate component (i.e. recycled or natural aggregate) and at the same time before adding silica fume, it is possible to add at least one known improving admixture to the formed mixture, which improves the thermal and/or acoustic and/or fire-resistant properties of the concrete, and which is commonly used in standard concretes. Such improving admixture is, for example, lightweight artificial aggregate (such as agloporite, expanded clay, expanded perlite, etc.), slag, slag, polystyrene or at least one organic filler (such as wood sawdust, shavings, rice husks, husks, etc.), etc. This component then constitutes up to 30% by weight of the aggregate, preferably up to 20% by weight or up to 15% by weight of the total aggregate.

Below are 11 specific examples of fresh concrete with test results of these fresh and subsequently hardened concretes (after 7 and 28 days). The ratio of the recycled fractions in these examples is 40% by weight of the fraction 0 to 8 mm, or 1 to 8 mm, and 60% by weight of the fraction 8 to 16 mm, but in general their ratio can be 30:70 to 50:50. Recycled material from construction and demolition waste of fraction 0 to 8 mm, or 1 to 8 mm, can be made up of two recycled fractions, e.g. 0 to 4 mm and 4 to 8 mm, or 1 to 4 mm and 4 to 8 mm; recycled material from construction and demolition waste of fraction 0 to 16 mm, or 1 to 16 mm can be made up of two recycled fractions, e.g. 0 to 8 mm and 8 to 16 mm, or 1 to 8 mm and 8 to 16 mm, or three fractions of this recyclate, e.g. 0 to 4 mm, 4 to 8 mm and 8 to 16 mm, or even more fractions.

Example 5 (prior art)

Using the procedure described in Example 1, 1 ^m3 of concrete was prepared, which contained 1505 kg of two-fraction mixed recyclate from inert construction and demolition waste with a recyclate fraction of 0 to 8 mm and 8 to 16 mm, 40 kg of silica fume (MICROSILICA-SIOXID®, manufacturer OFZ, as, Istebné, Slovak Republic), 190 kg of cement and 205 kg of water.

The fresh concrete prepared in this way was subjected to a consistency test according to EN 12350-2, with a measured slump of 35 mm corresponding to grade S1. In addition, it was also subjected to air content measurements according to EN 12350-7, with an average air content of 3.4% corresponding to standard non-aerated concrete.

From this fresh concrete, cubes with an edge of 150 mm were formed for the compressive strength test according to EN 12390-3, prisms with dimensions of 100 mm x 100 mm x 400 mm for the bending tensile strength test according to EN 12390-5, for the measurement of volume changes according to ČSN 73 1320, the measurement of the static modulus of elasticity according to ISO 1920-10 and plates with dimensions of 200 mm x 200 mm x 50 mm for the thermal conductivity test. After the concrete had hardened, the test specimens were demolded the next day and stored in an air-conditioned chamber at a temperature of 20 ±2 °C and a relative humidity above 95% for the relevant tests. The following parameters were measured in these tests: compressive strength (average of three measurements) after 7 days 19.7 MPa, compressive strength (average of three measurements) after 28 days 32.0 MPa, flexural tensile strength after 28 days 2.6 MPa, volume changes of concrete 1.278%o (after 28 days), static modulus of elasticity 12.5 GPa, thermal conductivity 0.46 W/(m.K).

In addition, the chloride content of this concrete was determined by calculation according to EN 196-2 and EN 1744-1, which was 0.118%, the content of natural radionuclides was determined by the procedure according to Decree No. 307/2002 Coll. of the State Office for Nuclear Safety on radiation protection, as amended, which was 27 Bq/kg, and the mass activity index was determined by 0.40, both of which parameters correspond to

- 10 CZ 310246 B6 the requirements of this Decree for use in buildings with residential or living rooms (mass activity ²²⁶ Ra <150 Bq.kg ^-1 , mass activity index I <0.5). Its ecotoxicity was determined as satisfactory by the procedure according to EN 12457 and Decree of the Ministry of the Environment No. 294/2005 Coll. The criteria for determining ecotoxicity are given in Table 1.

Table 1

Test organism Duration of action [hours] I II On the aquatic arthropod Daphnia magna 48 Maximum immobilization 30% Max. immobilization 30% On the aquatic vertebrate Poecillia reticulata 96 without death and change in behavior without death and change in behavior On the alga Desmodesmus subspicatus 72 Max. inhibition 30% Max. growth change 30% On the seeds of the Sinapis alba plant 72 Max. inhibition 30% Max. growth change 30%

With its mechanical-physical parameters, this particular concrete corresponds to standard 10 concrete of strength class C 20/25 and the classification classes of the use specification X0, XC1 and XC2 according to ČSN EN 206 - see Table 2.

Table 2

Classification class Description of the degree of environmental impact Example of the occurrence of the degree of environmental influence for concrete without risk of corrosion or deterioration X0 For concrete without reinforcement or embedded metal inserts. All influences except freezing and thawing, abrasion or chemically aggressive environments Concrete inside buildings with very low humidity For concrete with reinforcement or embedded metal inserts: Very dry for concrete with a risk of corrosion due to carbonation XC1 Dry or still wet. Concrete inside buildings with low humidity; Concrete permanently immersed in water. XC2 Wet, sometimes dry. Concrete surface exposed to long-term water exposure; Most foundations. XC3 Moderately wet, humid. Concrete inside buildings with medium or high humidity; Outdoor concrete protected from rain. XC4 Alternating wet and dry Concrete surfaces in contact with water, not included in the environmental impact level XC2 for concrete with a risk of corrosion due to chlorides, but not from sea water XD1 Moderately wet, humid. Concrete surfaces exposed to chlorides dispersed in the air. XD2 Wet, sometimes dry. Swimming pools. Concrete exposed to

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Classification class Description of the degree of environmental impact Example of the occurrence of the degree of environmental influence industrial waters containing chlorides. for concrete exposed to freezing and thawing, without chemical de-icing agents XF1 Slightly saturated with water without de-icing agents. Vertical concrete surfaces exposed to rain and frost.

Example 6 (prior art)

A total of 7 fresh concrete samples were created using the method described in Example 2, with 5 compositions of 1 m ³ of each described in Table 3.

Table 3

Sample Folder CB 1/1 CB 1/2 CB 1/4 CB 1/7 CB 1/9 CB 1/10 CB 1/11 Natural aggregate, fraction 0 to 4 mm [kg] 420 390 0 465 0 450 0 Mixed recycled material from inert construction and demolition waste, fractions 0 to 8 and 8 to 16 mm [kg] 1,125 1,135 865 1,135 765 1,055 975 Concrete recycle, fractions 0 to 8 and 8 to 16 mm [kg] 0 0 660 0 765 0 460 Silica drift [kg] 40 40 40 40 40 40 40 Cement [kg] 230 230 230 190 190 230 230 Plasticizing or superplasticizing admixture for concrete [kg] 0 0 0 0.95 0.92 1.17 1.31 Water [kg] 200 205 195 190 185 210 235 Bulk density of 7-day-old concrete [kg/m ³ ] 1960 1970 1950 2010 1950 - - Bulk density of concrete aged 28 days [kg/m ³ ] 1950 1980 1990 1970 1950 - -

These concretes were subsequently subjected to the tests described in Example 5 and some of them additionally to the pressure water seepage test according to EN 12390-8, meeting the requirement for a maximum seepage of 50 mm, the frost resistance test according to ČSN 73 1322 at 100 cycles, meeting the requirement of min. 0.75, and the alkali-silica expansion test according to ASTM C 1260-94 (prisms measuring 25 mm x 25 mm x 250 mm). The results of these tests are given in Table 4.

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Table 4

Sample Parameter CB 1/1 CB 1/2 CB 1/4 CB 1/7 CB 1/9 CB 1/10 CB 1/11 Consistency of fresh concrete cone slump [mm] 35 30 40 100 60 160 55 Air content in fresh concrete [%] 3.4 3.6 2.8 1.8 2.2 5.8 4.7 Compressive strength [MPa] After 7 days - After 28 days 20.1 24.0 18.7 14.2 14.9 16.7 22.6 32.9 35.7 41.9 28.2 26.8 28.5 33.5 Bending tensile strength after 28 days [MPa] 3.2 - 2.5 1.9 3.2 - - Pressure water penetration depth [mm] 31 - 39 32 30 - - Volume changes of concrete [%o] 1,115 - 0.964 - - - - Frost resistance [-] - 1.07 0.82 - 0.90 0.89 0.98 100 cycles Static modulus of elasticity |GPa| - 17.5 16.0 17.5 16 Chloride content [%] 0.125 0.125 0.138 0.112 0.125 0.122 0.126 Alkali-silica expansion [%] - - - - - 0.037 0.028 Content of natural radionuclides Mass activity ²²⁶ Ra [Bq.kg ^-1 ] - Mass activity index [-] - 24 20 - - - - - 0.41 0.32 - - - - Ecotoxicity conforms conforms conforms conforms conforms Complies conforms

Table 5 then lists the concrete strength classes to which the given concretes fall due to their mechanical-physical parameters and the classification classes of the specification of the use of these concretes according to ČSN EN 206 (see Table 2).

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Table 5

Sample CB 1/1 CB 1/2 CB 1/4 CB 1/7 CB 1/9 CB 1/10 CB 1/11 Concrete strength class C 20/25 C 25/30 C 30/37 C 16/20 C 16/20 C 20/25 C 20/25 Concrete usage specifications X0 XC1 XC2 X0 XC1 XC2 XC3 XC4 XD1 XD2 XF1 X0 XC1 XC2 XC3 XC4 XD1 XD2 XF1 X0 XC1 X0 XC1 X0 XC1 XC2 X0 XC1 XC2

Example 7 (prior art)

Using the method described in Example 4, 3 samples of fresh concrete were created, the composition of 1 m ³ of each being described in Table 6.

Table 6

Sample Folder CB 1/5 CB 1/6 CB 1/8 Natural aggregates, 500 515 530 fraction 0 to 4 mm [kg] Concrete recycle, fractions 0 to 8 and 8 to 16 mm [kg] 1165 1200 1140 Silica drift [kg] 40 40 40 Cement [kg] 230 190 190 Plasticizing or superplasticizing admixture for concrete [kg] 0 0 0.86 Water [kg] 200 185 175 Bulk density of 7-day-old concrete [kg/m ³ ] 2050 2100 2030 Bulk density of concrete aged 28 days [kg/m ³ ] 2080 2110 2030

These concretes were subsequently subjected to the tests described in Examples 5 and 6, with 50 cycles for the frost resistance test. The results of these tests are given in Table 7.

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Table 7

Sample Parameter CB 1/5 CB 1/6 CB 1/8 Consistency of fresh concrete - cone slump [mm] 120 140 70 Air content in fresh concrete [%] 2.4 2.5 3.0 Compressive strength [MPa] After 7 days - After 28 days 20.1 21.4 9.6 28.5 31.3 20.1 Bending tensile strength after 28 days [MPa] 1.9 3.2 2.2 Pressure water penetration depth [mm] - - 45 Volume changes of concrete [%o] - 1,226 - Frost resistance [-] 50 cycles 0.85 - 0.90 Static modulus of elasticity [GPa] 14.5 20.5 15.5 Chloride content [%] 0.130 0.117 0.118 Content of natural radionuclides Mass activity ²²⁶ Ra [Bq.kg ^-1 ] - Mass activity index [-] 15 - - 0.31 - - Ecotoxicity conforms conforms conforms

Table 8 then lists the concrete strength classes to which the given concretes fall due to their mechanical-physical parameters and the classification classes of the specification of the use of these concretes according to ČSN EN 206 (see Table 2).

Table 8

Sample CB CB CB 1/5 1/6 1/8 Concrete strength class C 16/20 C 20/25 C 12/15 Concrete usage specifications X0 XC1 X0 XC1 XC2 X0

In the case where brick or ceramic or mixed recyclate from inert construction and demolition waste and/or concrete recyclate with a top fraction of 8 mm is used for concrete preparation, or in combination with natural aggregate with a top fraction of up to 8 mm, preferably with mined aggregate 15 with a fraction of 0 to 4 mm, the concrete preparation is carried out analogously - see the following examples 8 to 11.

The composition of fresh concrete and dry mixes differs from the variants described above only in the fraction of aggregate (recyclate and natural aggregate).

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Below are described four other exemplary procedures for the preparation of concrete (and dry mixtures for the preparation of this concrete) - the first for the case where 100% by weight of the aggregate is made up of mixed recyclate from inert construction and demolition waste with a recyclate fraction of 0 to 8 mm, the second for the case where the aggregate is made up of mixed recyclate from inert construction and demolition waste with a recyclate fraction of 0 to 8 mm in combination with concrete recyclate with a fraction of 0 to 8 mm or natural aggregate with an upper fraction of up to 8 mm (up to 30% by weight of the total aggregate), the third for the case where 100% by weight of the aggregate is aggregates consisting of concrete recycle with a fraction of 1 to 8 mm, and the fourth for the case where the aggregates consist of concrete recycle with a fraction of 0 to 8 mm in combination with natural aggregates with an upper fraction of up to 8 mm (up to 30% by weight of the total aggregates). Here too, it is clear to the person skilled in the art that the intervals, or rather the times of addition of individual components and the amount of these components are given by the technological requirements for hardened concrete and its mechanical-physical parameters, and can range within the entire intervals listed below. These procedures then prepare concretes with a finer texture than in the previous examples, which are sometimes referred to as cement or concrete mortars. Their composition is the same as in the previous examples, with the exception of the recycle fraction/recycles.

In other variants, it is then possible to combine brick or ceramic or mixed recyclate with concrete recyclate and up to 30% by weight of natural aggregate within the aggregate in an analogous manner. In this case, brick or ceramic or mixed recyclate from inert construction and demolition waste is preferably first dosed into the mixer, then concrete recyclate and then natural aggregate. Brick, ceramic or mixed recyclate from inert construction and demolition waste have similar properties and behavior and, as a result, they can be interchanged or mixed.

Example 8 (prior art)

To prepare the concrete, a mixed recyclate from inert construction and demolition waste with a recyclate fraction of 0 to 8 mm is mixed in a forced circulation mixer with radial or double simultaneous radial movement of the mixing arms for 20 to 40 seconds. After mixing, the entire dose of silica fume is added to it with constant stirring for 10 to 15 seconds, and the mixture thus formed is mixed for another 40 to 80 seconds. Then, the entire dose of cement is added to it with constant stirring for 10 to 20 seconds, and the mixture thus formed is mixed for another 40 to 80 seconds. Subsequently, while stirring continuously, the entire batch of mixing water (which, if necessary, contains at least one concrete additive) is sprinkled on it within 40 to 60 seconds or the entire batch of mixing water (which, if necessary, contains at least one concrete additive) is sprayed onto it within 40 to 60 seconds. After a further 80 to 160 seconds of mixing, fresh concrete is prepared in which 100% by weight of the aggregate is made up of recycled material from inert construction and demolition waste.

The preparation of the dry mix for the preparation of such fresh concrete is carried out analogously, only without the addition of mixing water and using dried recyclate and possibly other components.

Example 9 (prior art)

To prepare concrete, mixed recycled material from inert construction and demolition waste, with a recycled material fraction of 0 to 8 mm, is mixed in a mixer with forced circulation and radial or double simultaneous radial movement of the mixing arms for 20 to 40 seconds. After mixing it, concrete recycled material with a fraction of 0 to 8 mm or natural aggregate with an upper fraction of up to 8 mm (max. up to 30% by weight of total aggregate) is added to it and the mixture thus formed is mixed for another 20 to 40 seconds. Then, with constant mixing, the entire dose of silica fume is added to it within 10 to 15 seconds, and the mixture thus formed is mixed for another 40 to 80 seconds. After mixing it, the entire dose of cement is added to it with constant mixing within 10 to 20 seconds, and the mixture thus formed is mixed for another 40 to 80 seconds. Then, while stirring continuously, the entire batch of mixing water (which, if necessary, contains at least one concrete additive) is sprinkled on it within 40 to 60 seconds, or the entire batch of mixing water (which, if necessary, contains at least one concrete additive) is poured onto it within 40 to 60 seconds.

- 16 CZ 310246 B6 is sprayed. After another 80 to 160 seconds of mixing, fresh concrete is prepared, in which 70 to 100% by weight of aggregate consists of recycled material from inert construction and demolition waste.

The preparation of the dry mix for the preparation of such fresh concrete is carried out analogously, only without the addition of mixing water and using dried recyclate and possibly other components.

Example 10 (prior art)

To prepare the concrete, the dedusted concrete recycle with a fraction of 1 to 8 mm is mixed in a forced circulation mixer with radial or double simultaneous radial movement of the mixing arms for 20 to 40 seconds. After mixing it, the entire dose of silica fume is added to it with constant stirring within 10 to 15 seconds, and the mixture thus formed is mixed for another 40 to 80 seconds. After mixing it, the entire dose of cement is added to it with constant stirring within 10 to 20 seconds, and the dry mixture thus formed is mixed for another 40 to 80 seconds. Subsequently, while stirring continuously, the entire batch of mixing water (which, if necessary, contains at least one concrete additive) is sprinkled on it within 40 to 60 seconds or the entire batch of mixing water (which, if necessary, contains at least one concrete additive) is sprayed onto it within 40 to 60 seconds. After a further 80 to 160 seconds of mixing, fresh concrete is prepared in which 100% by weight of the aggregate is made up of recycled material from inert construction and demolition waste.

The preparation of the dry mix for the preparation of such fresh concrete is carried out analogously, only without the addition of mixing water and using dried recyclate and possibly other components.

Example 11 (prior art)

To prepare the concrete, the concrete recycle with a fraction of 0 to 8 mm is mixed in a mixer with forced circulation and radial or double simultaneous radial movement of the mixing arms for 20 to 40 seconds. After mixing, natural aggregate with an upper fraction of up to 8 mm (max. up to 30% by weight of total aggregate) is added to it with constant stirring and the mixture thus formed is mixed for another 20 to 40 seconds. Then, the entire dose of silica fume is added to it with constant stirring within 10 to 15 seconds and the mixture thus formed is mixed for another 40 to 80 seconds. After mixing it, the entire dose of cement is added to it with constant stirring within 10 to 20 seconds and the mixture thus formed is mixed for another 40 to 80 seconds. Subsequently, while stirring continuously, the entire batch of mixing water (which, if necessary, contains at least one concrete additive) is sprinkled on it within 40 to 60 seconds or the entire batch of mixing water (which, if necessary, contains at least one concrete additive) is sprayed onto it within 40 to 60 seconds. After a further 80 to 160 seconds of mixing, fresh concrete is prepared in which at least 70% by weight of the aggregate consists of recycled material from inert construction and demolition waste.

The preparation of the dry mix for the preparation of such fresh concrete is carried out analogously, only without the addition of mixing water and using dried recyclate and possibly other components.

Also in these cases, it is possible, after adding the last aggregate component (i.e. recycled or natural aggregate) and at the same time before adding the silica fume, to add to the formed mixture at least one known improving admixture, which improves the thermal and/or acoustic and/or fire-resistant properties of the concrete, and which is commonly used in standard concretes. Such improving admixture is, for example, light artificial aggregate (such as agloporite, expanded clay, expanded perlite, etc.), slag, slag, polystyrene or at least one organic filler (such as wood sawdust, shavings, rice husks, husks, etc.), etc. This component then constitutes up to 30% by weight of the aggregate, preferably up to 20% by weight or up to 15% by weight of the total aggregate.

The aggregate fraction of 0 to 16 mm described in the above examples is not limiting for the implementation of the invention, since both natural aggregate and recycled material from inert construction and demolition waste may have a higher upper fraction limit.

- 17 CZ 310246 B6

In any of the above-mentioned embodiments, it is possible to replace part of the cement batch with a cement substitute, such as ground-granulated blast-furnace slag (GGBS or GGBFS) and/or fly ash, or a mixture of at least two such substitutes, with the ratio of cement to cement substitute/substitutes in fresh concrete being 30:70 to 70:30. The total amount of cement and cement substitute/substitutes is then the same as the amount of cement itself given in the relevant examples, i.e. 135 to 400 kg/m ³ of fresh concrete, or higher, up to 600 kg/m ³ of fresh concrete. The cement and cement substitute/substitutes are added to the mixture either simultaneously, each separately, or sequentially in any order (it is preferred, but not essential, to add the cement substitute/substitutes first and then the cement), or in the form of a pre-prepared mixture of the composition described above.

In addition to the above-described embodiment variants, in which the silica fume is added to the mixer only after the last aggregate component, in other variants it is possible to divide the total dose of silica fume and the total dose of aggregate into two or more smaller parts (the same or different), and to gradually add individual parts of the silica fume dose after adding individual parts of the total dose of aggregate, or recyclate from construction and demolition waste of various types and/or fractions, or to add at least some parts of the silica fume dose simultaneously with some parts of the total dose of aggregate or recyclate.

Example 12 (according to the invention)

To prepare the concrete according to the invention, the recycled material from inert construction and demolition waste of the first composition and/or the first fraction (e.g. fraction 0 to 8 mm) is mixed in a forced circulation mixer for 20 to 40 seconds, then the first part of the total dose of silica fume is added to it within 10 to 15 seconds, and the mixture thus formed is mixed for 20 to 60 seconds. Then, the recycled material from inert construction and demolition waste of the second composition and/or the second fraction (e.g. fraction 8 to 16 mm) or natural aggregate is added to it with constant mixing, and the mixture thus formed is mixed for 20 to 40 seconds, and then the second part of the dose of silica fume is added to it within 10 to 15 seconds, the total dose of aggregate being 1000 to 2000 kg/m ³ of fresh concrete and the total dose of silica fume is 28 to 52 kg. The mixture thus formed is further mixed for 40 to 80 seconds and then 135 to 400 kg of cement or a total of 135 to 600 kg of cement combined with at least one cement substitute, such as ground-granulated blast-furnace slag (GGBS or GGBFS) and/or fly ash in a ratio of 30:70 to 70:30, is added to it with constant mixing for 10 to 20 seconds. The mixture thus formed is mixed for another 40 to 80 seconds, after which 135 to 250 kg of mixing water is sprinkled on it with constant mixing for 40 to 60 seconds, or this amount of mixing water is sprayed onto it for 40 to 60 seconds, and after another 80 to 160 seconds of mixing, fresh concrete is prepared, in which up to 100% by weight. aggregates made from recycled inert construction and demolition waste.

Cement and at least one cement substituent are added to the mixture simultaneously, each separately, or sequentially in any order (it is preferred, but not necessary, to add the cement substituent(s) first and then the cement), or in the form of a pre-prepared mixture with a cement to cement substituent(s) ratio of 30:70 to 70:30.

The quantities of other concrete components and their fractions in this variant are the same as in examples 1 to 11.

In variants in which recycled material from construction and demolition waste of one composition, or one fraction, is used, its quantity can be divided analogously into two or more batches (identical or different), and these batches can be supplied to the mixer together or alternately with two or more batches of silica fume (see e.g. examples 13 and 15).

- 18 CZ 310246 B6

Example 13 (according to the invention)

To prepare the concrete according to the invention, the first part of the total batch of aggregates consisting of recycled inert construction and demolition waste is mixed in a forced circulation mixer for 20 to 40 seconds, then the first part of the total batch of silica fume is added to it within 10 to 15 seconds, and the mixture thus formed is mixed for 20 to 60 seconds. Then, with constant stirring, the remaining part of the aggregates consisting of recycled inert construction and demolition waste or natural aggregate is added to it, and the mixture thus formed is mixed for 20 to 40 seconds, and then the second part of the batch of silica fume is added to it within 10 to 15 seconds, with the total batch of aggregates being 1000 to 2000 kg/m ^{3 of} fresh concrete and the total batch of silica fume is 28 to 52 kg/m ³ of fresh concrete. The mixture thus formed is further mixed for 40 to 80 seconds and then 135 to 400 kg of cement or a total of 135 to 600 kg of cement combined with at least one cement substitute, such as ground-granulated blast-furnace slag (GGBS or GGBFS) and/or fly ash in a ratio of 30:70 to 70:30, is added to it with constant mixing for 10 to 20 seconds. The mixture thus formed is mixed for another 40 to 80 seconds, after which 135 to 250 kg of mixing water is sprinkled on it with constant mixing for 40 to 60 seconds, or this amount of mixing water is sprayed onto it for 40 to 60 seconds, and after another 80 to 160 seconds of mixing, fresh concrete is prepared, in which up to 100% by weight. aggregates made from recycled inert construction and demolition waste.

Cement and at least one cement substituent are added to the mixture simultaneously, each separately, or sequentially in any order (it is preferred, but not necessary, to add the cement substituent(s) first and then the cement), or in the form of a pre-prepared mixture with a cement to cement substituent(s) ratio of 30:70 to 70:30.

The quantities of other concrete components and their fractions in this variant are the same as in examples 1 to 11.

Example 14 (according to the invention)

To prepare the concrete according to the invention, the recycled material from inert construction and demolition waste of the first composition and/or the first fraction (e.g. fraction 0 to 4 mm) is mixed in a forced circulation mixer for 20 to 40 seconds, then the first part of the total dose of silica fume is added to it within 10 to 15 seconds, and the mixture thus formed is mixed for 20 to 60 seconds. Then, with constant stirring, the recycled material from inert construction and demolition waste of the second composition and/or the second fraction (e.g. fraction 4 to 8 mm) or part of the total dose of natural aggregate is added to it, and the mixture thus formed is mixed for 20 to 40 seconds. Then, the second part of the total dose of silica fume is added to it within 10 to 15 seconds, and the mixture thus formed is mixed for another 20 to 60 seconds. Then, with constant mixing, a recycle from inert construction and demolition waste of the third composition and/or the third fraction (e.g. fraction 8 to 16 mm) or the remaining part of the natural aggregate batch is added to it and the mixture thus formed is mixed for 20 to 40 seconds and then a third part of the total batch of silica fume is added to it within 10 to 15 seconds, whereby the total batch of aggregate is 1000 to 2000 kg/m ³ of fresh concrete and the total batch of silica fume is 28 to 52 kg/m ³ of fresh concrete. The mixture thus formed is mixed for 40 to 80 seconds and then 135 to 400 kg of cement or a total of 135 to 600 kg of cement in combination with at least one cement substitute is added to it within 10 to 20 seconds, with constant mixing, such as ground-granulated blast-furnace slag (GGBS or GGBFS) and/or fly ash, with the ratio of cement to substituent(s) in the fresh concrete being 30:70 to 70:30. The mixture thus formed is mixed for a further 40 to 80 seconds, after which 135 to 250 kg of mixing water is sprinkled on it with constant mixing for 40 to 60 seconds, or this amount of mixing water is sprayed onto it within 40 to 60 seconds, and after a further 80 to 160 seconds of mixing, fresh concrete is prepared in which up to 100% by weight of aggregate is made up of recycled material from inert construction and demolition waste.

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Cement and at least one cement substituent are added to the mixture simultaneously, each separately, or sequentially in any order (it is preferred, but not necessary, to add the cement substituent(s) first and then the cement), or in the form of a pre-prepared mixture with a cement to cement substituent(s) ratio of 30:70 to 70:30.

The quantities of other concrete components and their fractions in this variant are the same as in examples 1 to 11.

Example 15 (according to the invention)

To prepare the concrete according to the invention, the first part of the total batch of aggregates consisting of recycled material from inert construction and demolition waste is mixed in a forced circulation mixer for 20 to 40 seconds, then the first part of the total batch of silica fume is added to it within 10 to 15 seconds, and the mixture thus formed is mixed for 20 to 60 seconds. Then, with constant mixing, the second part of the total batch of aggregates consisting of recycled material from inert construction and demolition waste of the same composition and/or fraction as the first part of the total batch of aggregates or natural aggregate is added to it and the mixture thus formed is mixed for 20 to 40 seconds. Then, the second part of the total batch of silica fume is added to it within 10 to 15 seconds. The mixture thus formed is further mixed for 20 to 60 seconds. Then, with constant mixing, a third part of the total batch of aggregates is added to it, consisting of recycled material from inert construction and demolition waste of the same composition and/or fraction as the first part of the total batch of aggregates or natural aggregates, and the mixture thus formed is mixed for 20 to 40 seconds. Then, within 10 to 15 seconds, a third part of the total batch of silica fume is added to it, whereby the total batch of aggregates is 1000 to 2000 kg/m ³ of fresh concrete and the total batch of silica fume is 28 to 52 kg/m ³ of fresh concrete. The mixture thus formed is mixed for 40 to 80 seconds, and then, with constant mixing, within 10 to 20 seconds, 135 to 400 kg of cement or a total of 135 to 600 kg of cement in combination with at least one cement substitute, such as ground-granulated blast-furnace slag (GGBS or GGBFS) and/or fly ash, with the ratio of cement to substituent(s) in the fresh concrete being 30:70 to 70:30. The mixture thus formed is mixed for a further 40 to 80 seconds, after which 135 to 250 kg of mixing water is sprinkled on it with constant mixing for 40 to 60 seconds, or this amount of mixing water is sprayed onto it within 40 to 60 seconds, and after a further 80 to 160 seconds of mixing, fresh concrete is prepared in which up to 100% by weight of aggregate is made up of recycled material from inert construction and demolition waste.

Cement and at least one cement substituent are added to the mixture simultaneously, each separately, or sequentially in any order (it is preferred, but not necessary, to add the cement substituent(s) first and then the cement), or in the form of a pre-prepared mixture with a cement to cement substituent(s) ratio of 30:70 to 70:30.

The quantities of other concrete components and their fractions in this variant are the same as in examples 1 to 11.

All concretes according to the invention are intended for manual and machine processing (including shotcrete) and are suitable for common concrete structures made of plain and reinforced concrete. In addition to fresh concrete (ready-mix concrete) for the construction of family houses, hotels, residential buildings, office buildings, industrial buildings, production halls, special-purpose facilities, medical facilities, etc., or their parts such as pillars, floors, shorter lintels (up to approx. 6 m), foundation slabs or footings, base concrete, etc., they can also be used for the production of concrete products and prefabricated elements - e.g. concrete blocks and bricks, paving stones, slabs, blocks, curbs, various elements of garden architecture, ceiling beams and inserts, etc.

In addition, all variants are concretes that are 100% recyclable in the same way they were created.

Claims (12)

1. A method for preparing 1 m ³ of fresh concrete, comprising the steps of: a) 1000 to 2000 kg of aggregate is mixed in a forced circulation mixer for 20 to 40 seconds, with 40 to 100% of the aggregate consisting of recycled material from inert construction and demolition waste; b) after mixing it, 28 to 52 kg of silica fume is added to it with constant stirring within 10 to 15 seconds, the mixture thus formed is stirred for 40 to 80 seconds; c) after mixing it, other ingredients are added to it with constant stirring for 10 to 20 seconds and the mixture thus formed is mixed for a further 40 to 80 seconds; and d) after which 135 to 250 kg of mixing water is sprinkled on it with constant mixing for 40 to 60 seconds, or this amount of mixing water is sprayed on it within 40 to 60 seconds, and after another 80 to 160 seconds of mixing, fresh concrete is prepared, characterized in that in step c) cement and at least one cement substitute are added as further components, successively in any order or simultaneously, in a total amount of 135 to 600 kg, the ratio of cement to cement substitute/substitutes being 30:70 to 70:30. 2. A method for preparing 1 m ³ of fresh concrete according to claim 1, characterized in that in step a) 1000 to 1740 kg of two-fraction brick recyclate, which is entirely or at least more than half composed of brick rubble, or ceramic recyclate, which is entirely or at least more than half composed of ceramic rubble from ceramic construction and equipment items, or mixed recyclate from inert construction and demolition waste, which is composed of rubble from mixed construction and demolition waste, with recyclate fractions of 0 to 8 mm and 8 to 16 mm and a mutual ratio of these fractions of 30:70 to 50:50, are mixed in a forced circulation mixer for 20 to 40 seconds. 3. A method for preparing 1 m ³ of fresh concrete according to claim 1, characterized in that in step a) 1000 to 1800 kg of two-fraction concrete recycle, which is entirely or at least more than half composed of concrete crushed stone or crushed stone from another cement-containing material, with recycle fractions of 1 to 8 mm and 8 to 16 mm and a mutual ratio of these fractions of 30:70 to 50:50, are mixed in a forced circulation mixer for 20 to 40 seconds. 4. A method for preparing 1 m ³ of fresh concrete according to any one of claims 1 to 2, characterized in that before step a) the recycled material from inert construction and demolition waste of the first composition is mixed in a forced circulation mixer for 20 to 40 seconds, after its mixing, the recycled material from inert construction and demolition waste of the second composition or natural aggregate is added to it with constant mixing and the mixture thus formed is mixed in step a) for 20 to 40 seconds. 5. A method for preparing 1 m ³ of fresh concrete according to claim 4, characterized in that before step a) 695 kg to 1395 kg of brick recycle, which is entirely or at least more than half composed of brick rubble, or ceramic recycle, which is entirely or at least more than half composed of ceramic rubble of ceramic construction and equipment items, or mixed recycle from inert construction and demolition waste, which is composed of rubble from mixed construction and demolition waste, with a recycle fraction of 0 to - 21 CZ 310246 B6 8 mm, after mixing it, 260 to 570 kg of natural aggregate with an upper fraction of up to 8 mm is added to it with constant stirring, and the mixture thus formed is mixed in step a) for 20 to 40 seconds. 6. A method for preparing 1 m ³ of fresh concrete according to claim 4, characterized in that before step a) 525 kg to 1090 kg of two-fraction brick recycle, which is entirely or at least more than half composed of brick rubble, or ceramic recycle, which is entirely or at least more than half composed of ceramic rubble from ceramic construction and equipment items, or mixed recycle from inert construction and demolition waste, which is composed of rubble from mixed construction and demolition waste, with recycle fractions of 0 to 8 mm and 8 to 16 mm and a mutual ratio of these fractions of 30:70 to 50:50, are mixed in a forced circulation mixer for 20 to 40 seconds, after which 450 to 1065 kg of two-fraction concrete recycle, which is entirely or at least more than half composed of the majority of which consists of concrete crushed stone or crushed stone from another cement-containing material, with recycled fractions of 0 to 8 mm and 8 to 16 mm and a mutual ratio of these fractions of 30:70 to 50:50, and the mixture thus formed is mixed in step a) for 20 to 40 seconds. 7. A method for preparing 1 m ³ of fresh concrete according to claim 4, characterized in that before step a) 525 kg to 1090 kg of brick recycle, which is entirely or at least more than half composed of brick rubble, or ceramic recycle, which is entirely or at least more than half composed of ceramic rubble from ceramic construction and equipment items, or mixed recycle from inert construction and demolition waste, which is composed of rubble from mixed construction and demolition waste, with a recycle fraction of 0 to 8 mm, are mixed in a forced circulation mixer for 20 to 40 seconds, after mixing it, 450 to 1065 kg of concrete recycle, which is entirely or at least more than half composed of concrete rubble or rubble from another cement-containing material, with a recycle fraction of 0 to 8 mm, are added to it with constant stirring, and the mixture thus formed is mixed for 20 to 40 seconds in step a). 8. A method for preparing 1 m ³ of fresh concrete according to claim 4, characterized in that before step a) 820 kg to 1525 kg of two-fraction concrete recycle, which is entirely or at least more than half composed of concrete crushed stone or crushed stone from another cement-containing material, with recycled fractions of 0 to 8 mm and 8 to 16 mm and a mutual ratio of these fractions of 30:70 to 50:50, after mixing it, 350 to 600 kg of natural aggregate with an upper fraction of up to 16 mm is added to it with constant stirring, and the mixture thus formed is mixed in step a) for 20 to 40 seconds. 9. A method for preparing 1 m ³ of fresh concrete according to claim 4, characterized in that before step a) 820 kg to 1525 kg of concrete recycle, which is entirely or at least more than half composed of concrete crushed stone or crushed stone from another cement-containing material, with a recycled fraction of 0 to 8 mm, are mixed in a forced circulation mixer for 20 to 40 seconds, after mixing it, 350 to 600 kg of natural aggregate with an upper fraction of up to 8 mm are added to it with constant stirring, and the mixture thus formed is mixed in step a) for 20 to 40 seconds. 10. A method for preparing 1 m ³ of fresh concrete according to any one of claims 1 to 2, characterized in that before step a) the recycled material from inert construction and demolition waste of the first composition is mixed in a forced circulation mixer for 20 to 40 seconds, after its mixing the recycled material from inert construction and demolition waste of the second composition is added to it with constant stirring and the thus formed - 22 CZ 310246 B6 the mixture is mixed for 20 to 40 seconds, then natural aggregate is added to it and the mixture thus formed is mixed in step a) for another 20 to 40 seconds. 11. A method for preparing 1 m ³ of fresh concrete according to claim 1, characterized in that before step a) the recyclate from inert construction and demolition waste of the first composition is mixed in a forced circulation mixer for 20 to 40 seconds, after its mixing, the recyclate from inert construction and demolition waste of the second composition or natural aggregate is added to it with constant stirring and the mixture thus formed is mixed in step a) for 20 to 40 seconds, after its mixing, at least one improving admixture is added to it with constant stirring before step b) for improving the thermal and/or acoustic and/or fire-fighting properties of the concrete and the mixture thus formed is mixed for 20 to 40 seconds. 12. A method for preparing 1 m ³ of fresh concrete according to claim 1, characterized in that before step a) the recycle from inert construction and demolition waste of the first composition is mixed in a forced circulation mixer for 20 to 40 seconds, after its mixing, the recycle from inert construction and demolition waste of the second composition is added to it with constant stirring and the mixture thus formed is mixed for 20 to 40 seconds, then natural aggregate is added to it and the mixture thus formed is mixed in step a) for another 20 to 40 seconds, after its mixing, at least one improving admixture is added to it with constant stirring to improve the thermal and/or acoustic and/or fire-fighting properties of the concrete before step b), and the mixture thus formed is mixed for 20 to 40 seconds.