EP3768651A1

EP3768651A1 - Method for the preparation of fresh concrete and fresh concrete obtained by this method

Info

Publication number: EP3768651A1
Application number: EP20713822.3A
Authority: EP
Inventors: Frantisek POLAK; Lucie SLAVICKOVE; Jiri Fiala
Original assignee: Erc Tech AS
Current assignee: Erc-Tech AS
Priority date: 2019-06-14
Filing date: 2020-02-20
Publication date: 2021-01-27
Also published as: CZ2019375A3; AR119145A1; CZ308833B6; WO2020249141A1

Abstract

The invention relates to a method for the preparation of 1 m³ of fresh concrete using recyclate made from inert construction and demolition waste, by which 1000 to 2300 kg of aggregate, 30 % by weight to 100 % by weight of which consists of recyclate from inert construction and demolition waste is mixed with 10 to 27.9 kg of microsilica or its substituent(s) or a mixture of microsilica and at least one substituent thereof, in an industrial mixer for 5 to 39.9 seconds, whereby due to the friction of the aggregate grains the grains of the recyclate from the inert construction and demolition waste are rubbed intensively, which consequently results in an increase in the specific surface area of the recyclate and production of fine pozzolanic powder, whereby the microsilica and/or substituent(s) thereof, together with the pozzolanic powder, coat the aggregate particles and fill the pores in them. After thorough mixing, 135 to 400 kg of cement is added to the mixture thus prepared under constant mixing within 1 to 20 seconds, with advantage within 1 to 9.9 seconds, or cement, and at least one substituent thereof in a total amount of 135 to 600 kg is added to it one by one in any order or simultaneously under constant mixing within 1 to 20 seconds, and the mixture thus prepared is mixed for a further 5 to 39.9 seconds, whereupon it is sprinkled with 50 to 300 kg of mixing water under constant mixing within 5 to 39.9 seconds, or it is sprayed with this amount of the mixing water within 5 to 39.9 seconds, whereby the surface of the cement and optionally of its substituent(s) is gradually moistened and the resulting cement paste is gradually adhered to the aggregate particles already coated with the mixture of microsilica and/or of its substituent(s) and pozzolanic powder, and after an additional 5 to 160 seconds of mixing, fresh concrete is prepared. The invention also relates to fresh concrete prepared by this method.

Description

METHOD FOR THE PREPARATION OF FRESH CONCRETE AND FRESH CONCRETE OBTAINED BY THIS METHOD

Technical field

The invention relates to a method for preparing fresh concrete using 5 recyclate from inert construction and demolition waste.

The invention also relates to fresh concrete prepared by this method.

Background art

According to qualified estimates, approximately 6.5 billion tons of inert 10 construction and demolition waste is produced worldwide every year. A

substantial majority of this waste accumulates in landfills and dumps, and only a relatively small part is used or processed - most often, however, in a way that does not exploit the full potential of this material, when it serves as a matter of fact merely to fill some empty space. Crushed or ground inert construction and 15 demolition waste is used mainly for packs and backfills of utility lines (a substitute for sorted gravel), as a sub-base for parking lots, roads, concrete structures of floors of buildings and halls, backfills of forefields of bridges, for the consolidation and levelling of forest and field roads (a substitute for a crusher-run materials), or as a sub-base filler of ground bodies of driveways and 20 roads, trackbeds, flood protection barriers (as a substitute for soil), etc.

In addition, procedures for the preparation of concrete in which crushed or ground inert construction and demolition waste is used as replacement of part of aggregate are also known. A common disadvantage of these procedures, typical of which are, for example, the procedures described in CN 25 101942869, CN 202055143, CN 105036660, CN 106431493, CZ 1994-2635,

CZ 2007-0206, CZ 028669, WO 2007013803, US 20090288582 or AU 2010224346, which are based on conventional procedures for the preparation of conventional concretes, is especially the fact that the concretes prepared by them either do not achieve the required mechanical-physical parameters or 30 achieve them only at the cost of large additions of cement (and associated increase in production costs).

It is therefore the object of the present invention to provide a method for the preparation of concretes by replacing the largest possible part of aggregate with recyclate produced by grinding or crushing inert construction and demolition waste, which would enable to prepare concretes with mechanical and physical parameters comparable to conventional concretes, while not requiring an extra addition of cement or any other component. Furthermore, the object of the invention is to provide fresh concrete in which the largest possible part of the aggregate is made up of recycled material produced by grinding or crushing inert construction and demolition waste.

Principle of the invention

The method for the preparation of concrete according to the invention is based on a combination of a specific composition of the concrete and a specific procedure of mixing and dosing its components, which in mutual combination allow to replace up to 100 % by weight of the aggregate in the concrete with recyclate made from inert construction and demolition waste (i.e. ground or crushed inert construction and demolition waste) while achieving mechanical and physical parameters which are at least comparable to or even better than, conventional concretes.

The fresh concrete thus prepared contains in 1 m³ 50 to 300 kg of water, 135 to 400 kg of cement or 135 to 600 kg of a mixture of cement and at least one substituent thereof, 10 to 27.9 kg of microsilica (preferably compacted) or at least one substituent thereof or a mixture of microsilica and at least one substituent thereof, 1000 to 2300 kg of aggregate, whereby 30 to 100 % by weight of the aggregate is formed by brick or ceramic or mixed recyclate made from inert construction and demolition waste, 0 to 40 % by weight of the aggregate consists of natural aggregate and another 0 to 40 % by weight of the aggregate consists of lightweight artificial aggregate (such as agloporite, ceramsite, expandit, expanded perlite, etc.) and/or cinder and/or scoria and/or polystyrene and/or at least one organic filler (such as wood sawdust, shavings, rice husks, shives, etc.) and/or another component for improving thermal and/or acoustic and/or fire resistance properties of hardened concrete.

The used recyclate from inert construction waste can have substantially any fraction depending on the use of the concrete and requirements for its texture - it may be, for example, one-fractional, preferably having a fraction of 0 to 20 mm, two-fractional, preferably having fractions of 0 to 8 mm and 8 to 20 mm, or three-fractional, preferably having fractions of 0 to 4 mm, 4 to 8 mm and 8 to 20 mm. In addition, recyclate and aggregate with a fraction of up to 16 mm or up to 8 mm can be used.

For the purposes of this application, under the term“brick recyclate” we understand a recycled material produced by crushing or milling inert construction and demolition waste, which consists entirely or of at least a majority of bricks and possibly contains other building materials and/or substances (concrete, ceramic building elements and fittings, mortar, plaster and adhesive residues, etc.). Thus, brick recyclate consists entirely or of at least of a majority of crushed brick, possibly with the addition of rubble from other building materials and/or substances.

Under the term“ceramic recyclate” we understand a recycled material produced by crushing or milling inert construction and demolition waste, which consists entirely or of at least a majority of ceramic building and fitting elements, such as floor and wall tiles, sanitary ceramic products, clay roofing tiles, etc., and possibly contains other building materials and/or substances (concrete, bricks, mortar, plaster and adhesive residues, etc.). Thus, ceramic recyclate consists entirely or of at least a majority of crushed ceramics, possibly with the addition of rubble from other building materials and/or substances.

Under the term “concrete recyclate” we mean a recycled material produced by crushing or milling inert construction and demolition waste, which consists entirely or of at least a majority of concrete or another cement containing material (concrete screed, cement mortar, etc.), and possibly with admixtures of other building materials and/or substances (bricks, ceramic building and fitting objects, mortar, plaster and adhesive residues, etc.). Thus, concrete recyclate consists entirely or of at least a majority of crushed concrete or other cement containing materials, possibly with the addition of rubble from other building materials and/or substances.

Finally, under the term “mixed recyclate” we understand a recycled material produced by crushing or milling mixed inert construction and demolition waste, which is composed of a mixture of different building materials and substances, usually bricks, concrete and ceramic building elements and fittings in various ratios, possibly with admixtures of mortar, plaster and adhesive residues, etc., or recyclate produced by mixing two or more above-mentioned recyclates (brick, ceramic, concrete) Thus, mixed recyclate is composed of mixed rubble made from construction and demolition waste.

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

Experience with the use of industrial mixing machines shows that the grain friction of the aggregate surprisingly results in considerably more intensive abrasion of the grains of recyclate from inert construction demolition waste than expected, which not only leads to an increase in the specific surface area of the recyclate, but also to an intense formation of fine pozzolanic powder which in the next stages of concrete production works both as a filler and a binder, when, together with microsilica and/or substituent(s) thereof, encapsulates the particles of the recyclate and fills the pores therein and fills up the overall lattice structure of the concrete, and by suitable addition of the mixing water, the silicon dioxide contained therein is activated, thereby activating its latent hydraulicity (see below). If necessary, the fresh concrete according to the invention may contain in any variant at least one additive for concrete in a total amount of up to 10 % by weight of a dose of cement or of a dose of cement and substituent(s) thereof. As such additive, any known additive can be used, for example additive for vibro-pressed concrete and/or additives according to EN 934-2. These additives include especially water- reducing (plasticizing) and strongly water-reducing (superplasticizing or hyperplasticizing) additives, additives for improving the consistency of concrete, water- reducing additives, additives for improving the strength and some other properties of fresh and hardened concrete, as well as stabilizing additives, air-entraining admixtures, foaming agents, additives accelerating hardening and solidification of concrete, additives for retarding hardening and solidification of concrete, sealing agents, corrosion inhibiting additives, etc. This additive/these additives is/are added to the other components of concrete dissolved in mixing water or separately, preferably after the addition of the mixing water.

To mix the individual components thoroughly and to prepare concretes of the desired structure and properties, any industrial mixers can be used, for example planetary mixers, rotor mixers, single shaft mixers, dual shaft mixers or triple shaft mixers, trough mixers, continuous mixers, etc. Using a mixer with a forced circulation is especially advantageous, preferably a mixer with radial movement of mixing arms or with double simultaneous radial movement of mixing arms (such as the mixer described in IT 1244970 or in EP 0508962), in which all its interior surfaces are wiped. Nevertheless, it is necessary to observe not only the above-mentioned concrete composition, but also the mixing and dosing times of the individual components. All the components are dosed while the mixer is running. However, it is possible to temporarily stop the operation of the mixer after the components already added have been thoroughly mixed together and before adding the next component, or, if the mixer design allows it, to reverse the running of the mixer so as to add another component and mix it together with the other components. These adjustments to the mixer operation, however, have no effect on the properties or consistency of the fresh concrete being prepared (or of the dry mixture being prepared), nor on the subsequently hardened concrete and its properties.

Prior to the preparation of the concrete or dry mixture according to the invention, recyclate made from inert construction and demolition waste is hygienized, e.g. by water or steam bath or otherwise, thereby reducing the number of (pathogenic) organisms and microorganisms present in it or completely eliminating the presence of these organisms and microorganisms.

Microsilica and/or substituent(s) thereof which serves as a binder in the conventional production of conventional concretes from natural aggregates, serves as a filler in the preparation of concrete according to the invention, provided that the below-described dosing method and the above-described mixing method is observed, filling the overall lattice structure of the concrete, together with the pozzolanic powder produced by rubbing the grains of the recyclate from construction and demolition waste, covering the particles of the recyclate with coating and filling up intensively the pores therein. Thanks to that, there is no clustering of fine particles and the resulting concrete has a lower porosity and after hardening achieves mechanical and physical parameters comparable to conventional concretes.

In a preferred variant of embodiment, compacted microsilica having a smaller volume is used.

Part of the dose or the whole dose of microsilica may be replaced by at least one microsilica substituent, such as metakaolin or shale with a silica content of at least 45 %. For example, it is advantageous if a mixture of microsilica and substituent(s) thereof containing 30 % to 70 % by weight of microsilica is used.

In a preferred variant of embodiment, microsilica and/or substituent(s) thereof is added to the mixer only after the last part of the aggregate. In addition, it is also possible to divide the whole dose of microsilica and/or substituent(s) thereof as well as the whole dose of the aggregate into two or more smaller parts (of the same or different sizes), and the individual parts of microsilica and/or substituent(s) thereof can be added successively after the addition of the individual parts of the whole dose of the aggregate, or at least some parts of microsilica and/or substituent(s) thereof can be added simultaneously with some parts of the whole dose of the aggregate - see, e.g., examples 1 1 and 12 below.

All variants use cement of strength class CEM I to CEM V with binding capacity 32.5 N, R, 42.5 N, R, 52.5 N, R. Its dosing as described below ensures an appropriate bond between the cement and the aggregate, in particular the recyclate already coated with a mixture of microsilica and/or substituent(s) thereof and pozzolanic powder, as well as very good homogenization of the mixture being mixed. At the same time, a part of the transit zone (C-S-H phases) is transferred into the pores of the aggregate and thus strengthens, which results in fortification of recyclate grains - see Fig. 1 , which shows a SEM image of a grain of the recyclate from inert construction and demolition waste with microparticles of microsilica deposited on its surface and in its pores at a magnification of 1000 times, Fig. 2, which shows a SEM image of the surface of the recyclate grain with the emerging transit zone, where it is possible to see also the resulting Ca(OFI) - portlandite, produced by the reaction of CaO contained in the aggregate and free water, at a magnification of 10,000 times, and Fig. 3 shows a SEM image of the surface of the recyclate grain of Fig. 2 at 20,000 times magnification.

Part of the dose of cement may be replaced with a substituent of cement, e.g., with ground-granulated blast-furnace slag - GGBS or GGBFS and/or with fly ash, ground-calcium carbonate - GCC, stone powder (dust from aggregate mining and processing), or, optionally, with a mixture of at least two such substituents, whereby the ratio of cement to substituents of cement in the fresh concrete is from 30:70 to 70:30. This means that the total amount of cement and substituents of cement is the same as the amount of the cement alone, i.e. 135 to 400 kg/m³ of fresh concrete, or up to 600 kg/m³ of fresh concrete. Cement and the substituent(s) of cement are added to the mixture at the same time, separately, or successively in any order (adding substituent(s) of cement first and then cement is preferred, but is not necessary), or in the form of a pre- formed mixture of the above-described composition.

After the preparation of the dry mixture from the above-mentioned components and after thorough mixing, this mixture is sprinkled with mixing water in a mixer under constant mixing, or the mixing water is sprayed on it. When using this method of dosing the mixing water, the surface of the cement is gradually moistured and the cementing paste being formed gradually adheres to the grains of the recyclate already coated with a mixture of microsilica and pozzolanic powder, which prevents the agglomeration of fresh concrete particles, separation of the fine particles of the mixture as well as separation of water and ensures the required consistency of the fresh concrete. In addition, this dosing method activates the silica present in the microsilica and/or substituent(s) thereof and in pozzolanic powder and thereby latent hydraulicity of these components, which allows the concretes prepared by this method to achieve physical and mechanical parameters comparable to conventional concretes, this being achieved even at a dose of cement which may be lower than that for conventional concretes. Due to the unexpectedly large amount of pozzolanic powder, it is possible to shorten the mixing times compared to other processes and significantly reduce the required amount of microsilica and/or substituent(s) thereof. The mixing water quality must correspond to the drinking water. If required, it may contain at least one known standard additive (dissolved or undissolved) for concrete.

To supplement the recyclate made from inert construction and demolition waste, it is possible to use natural aggregate (extracted and/or crushed) with an upper fraction of preferably up to 20 mm (with possible technological admixture up to 5 % by weight of larger particles), or up to 8 mm, or even fine extracted aggregates with a fraction of 0 to 4 mm.

In the preparation of 1 m³ of fresh concrete according to the invention, 1000 to 2300 kg of aggregate, which is from 30 % by weight to 100 % by weight composed of recyclate made from inert construction and demolition waste, is mixed with 10 to 27.9 kg of microsilica or its substituent(s) or a mixture of microsilica and at least one substituent thereof in an industrial mixer for 5 to 39.9 seconds. The friction of the aggregate grains intensively rubs the grains of the recyclate from the inert construction and demolition waste and consequently increases the specific surface area of the recyclate and creates a fine pozzolanic powder, whereby the microsilica and/or substituent(s) thereof, together with the pozzolanic powder, coat/coats the aggregate particles and fill the pores in them. After mixing, 135 to 400 kg of cement are added to the mixture thus obtained, under constant mixing within 1 to 20 seconds, preferably within 1 to 9.9 seconds, or cement and at least one substituent thereof in a total amount of 135 to 600 kg is added to it sequentially in any order or at the same time, under constant mixing within 1 to 20 seconds, and the mixture thus formed is mixed for a further 5 to 39.9 seconds, whereupon the mixture is sprinkled with 50 to 300 kg of mixing water under constant mixing within 5 to 39.9 seconds, or this amount of mixing water is sprayed onto it within 5 to 39.9 seconds, whereby the surface of the cement and, optionally, of its substituent(s) is gradually moistened and the paste formed gradually adheres onto the particles of the aggregate already coated with a mixture of microsilica and/or substituent(s) thereof and pozzolanic powder, and after a further 5 to 160 seconds of mixing, fresh concrete is prepared. Description of drawings

In the accompanying drawings, Fig. 1 is a SEM image of a grain of recyclate made from inert construction and demolition waste in the structure of fresh concrete produced by the method according to the invention at a magnification of 1 ,000 times; Fig. 2 is a SEM image of a grain of recyclate made from inert construction and demolition waste in the structure of fresh concrete produced by the method according to the invention at a magnification of 10,000 times, and Fig. 3 is a SEM image of the grain of recyclate made from inert construction and demolition waste in the structure of fresh concrete produced by the method according to the invention at a magnification of 20,000 times.

Examples of embodiment

Exemplary variants of the preparation of fresh concrete according to the invention are described below, the first of which for the case when 100 % by weight of the aggregate is formed by one type of recyclate made from inert construction and demolition waste (examples 1 and 2), the second variant for the case when the aggregate is formed by recyclate from inert construction and demolition waste in combination with concrete recyclate or with natural aggregate (up to 40 % by weight of the total aggregate) (examples 3 and 4), the third variant for the case when 100 % by weight of the aggregate is formed by a combination of two types of recyclate from inert construction and demolition waste (examples 5 and 6), the fourth variant for the case when the aggregate is formed by a combination of three types of recyclate from inert construction and demolition waste or by a combination of two types of recyclate from inert construction and demolition waste and natural aggregate (up to 40 % by weight of the total aggregate) (examples 7 and 8), the fifth variant for the case when the aggregate is formed by concrete recyclate in combination with natural aggregate, and the sixth variant for the case when individual doses of the aggregate and microsilica and/or substituent(s) thereof are divided into smaller doses (examples 1 1 a 12). As is apparent to a person skilled in the art, the intervals or, more specifically, the periods of time during which individual components are added, as well as the amounts of these components, are determined by the technological requirements for hardened concrete and its mechanical and physical parameters and may vary within the whole intervals stated below. Likewise, the upper fraction of the recyclate(s) and/or of the natural aggregate in other examples may be higher or lower than 20 mm.

Example 1

To prepare concrete according to the invention, brick, ceramic, concrete or mixed recyclate made from inert construction and demolition waste with an upper fraction of 20 mm (e.g. one-fractional recyclate with a fraction of 0 to 20 mm, two-fractional recyclate with fractions of 0 to 8 mm and 8 to 20 mm, or three-fractional recyclate with fractions of 0 to 4 mm, 4 to 8 mm and 8 to 20 mm) is mixed in an industrial mixer for 5 to 39.9 seconds (preferably for 5 to 19.9 seconds). After thorough mixing, the whole dose of microsilica and/or substituent(s) thereof is added to it under constant mixing within 1 to 15 seconds, preferably within 1 to 9.9 seconds, and the mixture thus prepared is mixed for a further 5 to 39.9 seconds. After that, the whole dose of cement or the whole dose of cement and substituent(s) thereof is added to the mixture under constant mixing within 1 to 20 seconds, preferably within 1 to 9.9 seconds, and the mixture thus prepared is mixed for a further 5 to 39.9 seconds. Subsequently, this mixture is sprinkled with the whole dose of mixing water (which, if appropriate, contains at least one additive for concrete) under constant mixing within 5 to 39,9 seconds or the whole dose of mixing water (which, if appropriate, contains at least one additive for concrete) is sprayed on it within 5 to 39,9 seconds. After another 5 to 160 seconds of mixing, fresh concrete is prepared, in which 100 % by weight of the aggregate is composed of recyclate from inert construction and demolition waste.

Example 2

10 samples of fresh concrete according to the invention were prepared by the method described in example 1 , whereby the composition of 1 m³ of each of them is described in Table 1. Table 1

The fresh concretes thus prepared were subjected to consistency tests by a method according to EN 12350-2 and air content was measured by a method according to EN 12350-7.

From these fresh concretes, 150 mm cubes were created for the compressive strength test according to EN 12390-3, 100 mm x 100 mm x 400 mm prisms were formed for testing flexural strength according to EN 12390-5, for the measurement of volume changes according to CSN (Czech Technical Standard) 73 1320, for the measurement of static modulus of elasticity according to ISO 1920-10 and 200 mm x 200 mm x 50 mm boards were formed for thermal conductivity test. After the hardening of concrete, the test bodies were removed from the molds on the following day and stored for the appropriate tests in an air-conditioned chamber at a temperature of 20 ± 2 ° C and a relative humidity above 95 %. Parameters measured during these tests are summarized in Table 2.

Table 2

In addition, chloride content in this concrete was determined by calculation according to EN 196-2 and EN 1744-1 , the content of natural radionuclides and mass activity index were determined according to the procedure of Regulation No. 307/2002 Coll of the State Office for Nuclear Safety on radiation protection, as amended, whereby both these parameters meet the requirements of this Regulation for use for buildings with residential rooms or spaces (mass activity ²²⁶Ra < 150 Bq.kg ¹, mass activity index I < 0.5). According to the procedure of EN 12457 and Regulation of the Ministry of the Environment No. 294/2005 Coll its ecotoxicity was found to be complying with the requirements. The criteria for the determination of ecotoxicity are shown in Table 3.

Table 3

Table 4 shows the strength classes of concrete to which the respective concretes belong due to their mechanical-physical parameters and the classification classes of specification of use of these concretes according to CSN (Czech Technical Standard) EN 206 (see Table 5). Table 4

Table 5

Example 3

To prepare concrete according to the invention, brick, ceramic or mixed recyclate from inert construction and demolition waste with an upper fraction of 20 mm (e.g. one-fractional recyclate with a fraction of 0 to 20 mm, two-fractional recyclate with fractions of 0 to 8 mm and 8 to 20 mm, or three-fractional recyclate with fractions of 0 to 4 mm, 4 to 8 mm and 8 to 20 mm) is mixed in an industrial mixer for 5 to 39.9 seconds (preferably for 5 to 19.9 seconds). After thorough mixing, concrete recyclate with an upper fraction of 20 mm (e.g., one- fractional concrete recyclate with a fraction of 0 to 20 mm, two-fractional concrete recyclate with fractions of 0 to 8 mm and 8 to 20 mm, or three- fractional concrete recyclate with fractions of 0 to 4 mm, 4 to 8 mm and 8 to 20 mm) or natural aggregate with an upper fraction of 20 mm, preferably 8 mm, or fine aggregate with an upper fraction of 4 mm (up to 40 % by weight of the total aggregate in the concrete) is added to it under constant mixing and the mixture thus obtained is mixed for a further 5 to 39.9 seconds. After that, the whole dose of microsilica and/or substituent(s) thereof is added to it under constant mixing within 1 to 15 seconds, preferably within 1 to 9.9 seconds, and the mixture thus prepared is mixed for an additional 5 to 39.9 seconds. After that, the whole dose of cement or the whole dose of cement and substituent(s) thereof is added to it under constant mixing within 1 to 20 seconds, preferably within 1 to 9.9 seconds, and the mixture thus prepared is mixed for a further 5 to 39.9 seconds. Subsequently, this mixture is sprinkled with the whole dose of mixing water (which, if necessary, contains at least one additive for concrete) under constant mixing within 5 to 39.9 seconds or the whole dose of the mixing water (which, if necessary, contains at least one additive for concrete) is sprayed on it within 5 to 39.9 seconds. After another 5 to 160 seconds of mixing, fresh concrete is prepared, in which 60 to 100 % by weight of the aggregate is composed of recyclate from inert construction and demolition waste. Example 4

8 samples of fresh concrete according to the invention were prepared by the method described in example 3, whereby the composition of 1 m³ of each of them is described in Table 6.

Table 6

These concretes were subsequently subjected to the tests described in example 2. The results of these tests are summarized in Table 7.

Table 7

In addition, chloride content in this concrete was determined by calculation according to EN 196-2 and EN 1744-1 , the content of natural radionuclides and mass activity index were determined following the procedure of Decree No. 307/2002 Coll on radiation protection of the State Office for Nuclear Safety, as amended, whereby all these parameters meet the requirements of this Decree for use in buildings with residential rooms or spaces (mass activity ²²⁶Ra < 150 Bq.kg ¹, mass activity index I < 0.5). According to the procedure in EN 12457 and Decree of the Ministry of Environment No. 294/2005 Coll., the ecotoxicity of this concrete was found to be complying with the requirements. The criteria for determination of ecotoxicity are shown in Table 3, example 2.

Table 8 shows strength classes of concrete to which the respective concretes belong due to their mechanical-physical parameters and the classification classes of specification of the use of these concretes according to CSN (Czech Technical Standard) EN 206 (see Table 5).

Table 8

Example 5

To prepare concrete according to the invention, recyclate made from inert construction and demolition waste with an upper fraction of 20 mm (e.g. one-fractional recyclate with a fraction of 0 to 20 mm, two-fractional recyclate with fractions of 0 to 8 mm and 8 to 20 mm, or three-fractional recyclate with fractions of 0 to 4 mm, 4 to 8 mm and 8 to 20 mm) of the first type (brick, ceramic or mixed recyclate, alternatively concrete recyclate) is mixed in an industrial mixer for 5 to 39.9 seconds (preferably for 5 to 19.9 seconds). After thorough mixing, recyclate from inert construction and demolition waste with an upper fraction of 20 mm (e.g. one-fractional recyclate with a fraction of 0 to 20 mm, two-fractional recyclate with fractions of 0 to 8 mm and 8 to 20 mm, or three-fractional recyclate with fractions of 0 to 4 mm, 4 to 8 mm and 8 to 20 mm) of the second type (brick, ceramic or mixed recyclate, optionally concrete recyclate) is added under constant mixing, whereby the recyclate being added is made from inert construction and demolition waste of a different type than the recyclate to which it is added, and the mixture thus prepared is mixed for a further 5 to 39.9 seconds. Thereafter, the whole dose of microsilica and/or substituent(s) thereof is added to it under constant mixing within 1 to 15 seconds, preferably within 1 to 9.9 seconds and the mixture thus prepared is mixed for a further 5 to 39.9 seconds. After that, the whole dose of cement or the whole dose of cement and substituent(s) thereof is added to it under constant mixing within 1 to 20 seconds, preferably within 1 to 9.9 seconds, and the mixture thus prepared is mixed for a further 5 to 39.9 seconds. Subsequently, this mixture is sprinkled with the whole dose of mixing water (which, if necessary, contains at least one additive for concrete) under constant mixing within 5 to 39.9 seconds or the whole dose of mixing water (which, if necessary, contains at least one additive for concrete) is sprayed on it within 5 to 39.9 seconds. After another 5 to 160 seconds of mixing, fresh concrete is prepared, in which 100 % by weight of the aggregate is composed of recyclate from inert construction and demolition waste. Example 6

3 samples of fresh concrete according to the invention were prepared by the method described in example 5, whereby the composition of 1 m³ of each of them is described in Table 9.

Table 9

These concretes were subsequently subjected to the tests described in example 2. The results of these tests are summarized in Table 10. Table 10

In addition, chloride content in this concrete was determined by calculation according to EN 196-2 and EN 1744-1 , the content of natural radionuclides and mass activity index were determined following the procedure of Decree No. 307/2002 Coll on radiation protection of the State Office for Nuclear Safety, as amended, whereby all these parameters meet the requirements of this Decree for use in buildings with residential rooms or spaces (mass activity ²²⁶Ra < 150 Bq.kg ¹, mass activity index I < 0.5). According to the procedure in EN 12457 and Decree of the Ministry of Environment No. 294/2005 Coll its ecotoxicity was found to be complying with the requirements. The criteria for determination of ecotoxicity are shown in Table 3, example 2.

Table 1 1 shows the strength classes of concretes into which the respective concrete belongs due to its mechanical-physical parameters and classification classes of specification of the use of these concrete according to CSN EN 206 (see Table 5).

Table 11

Example 7

To prepare concrete according to the invention, recyclate made from inert construction and demolition waste having an upper fraction of 20 mm (e.g. one-fractional recyclate with a fraction of 0 to 20 mm, two-fractional recyclate with fractions of 0 to 8 mm and 8 to 20 mm, or three-fractional recyclate with fractions of 0 to 4 mm, 4 to 8 mm and 8 to 20 mm) of the first type (brick, ceramic or mixed recyclate, optionally concrete recyclate) is mixed in an industrial mixer for 5 to 39.9 seconds (preferably for 5 to 19.9 seconds). After thorough mixing, recyclate from inert construction and demolition waste with an upper fraction of 20 mm (e.g. one-fractional recyclate with a fraction of 0 to 20 mm, two-fractional recyclate with fractions of 0 to 8 mm and 8 to 20 mm, or three-fractional recyclate with fractions of 0 to 4 mm, 4 to 8 mm and 8 to 20 mm) of the second type (brick, ceramic or mixed recyclate, optionally concrete recyclate) is added to it under constant mixing, whereby the recyclate being added is made from inert construction and demolition waste of a different type than the recyclate to which it is added, and the mixture thus prepared is mixed for a further 5 to 39.9 seconds. After thorough mixing, recyclate from inert construction and demolition waste with an upper fraction of 20 mm (e.g. one- fractional recyclate with a fraction of 0 to 20 mm, two-fractional recyclate with fractions of 0 to 8 mm and 8 to 20 mm, or three-fractional recyclate with fractions of 0 to 4 mm, 4 to 8 mm and 8 to 20 mm) or natural aggregate with an upper fraction of 20 mm, preferably 8 mm, or fine aggregate with an upper fraction of 4 mm (up to 40 % by weight of the total aggregate in concrete) is added to it under constant mixing and the mixture thus prepared is mixed for a further 5 to 39.9 seconds. Thereafter, the whole dose of microsilica and/or its substituent(s) is added to it under constant mixing within 1 to 15 seconds, preferably within 1 to 9.9 seconds and the mixture thus prepared is mixed for a further 5 to 39.9 seconds. After that, the whole dose of cement or the whole dose of cement and substituent(s) thereof is added to it under constant mixing within 1 to 20 seconds, preferably within 1 to 9.9 seconds, and the mixture thus prepared is mixed for a further 5 to 39.9 seconds. Subsequently, this mixture is sprinkled with the whole dose of mixing water (which, if necessary, contains at least one additive for concrete) under constant mixing within 5 to 39.9 seconds or the whole dose of the mixing water (which, if necessary contains at least one additive for concrete) is sprayed on it within 5 to 39.9 seconds. After another 5 to 160 seconds of mixing, fresh concrete is prepared, in which at least 60 % by weight of the aggregate consists of recyclate from inert construction and demolition waste.

Example 8

3 samples of fresh concrete according to the invention were prepared by the method described in example 7, whereby the composition of 1 m³ of each of them is described in Table 12.

Table 12

These concretes were subsequently subjected to the tests described in example 2. The results of these tests are summarized in Table 13.

Table 13

Table 14 shows the strength classes of concrete to which the respective concrete belongs due to its mechanical-physical parameters and classification classes of specification of the use of these concrete according to CSN (Czech Technical Standard) EN 206 (see Table 5).

Table 14

Example 9

To prepare concrete according to the invention, concrete recyclate having an upper fraction of 20 mm (e.g. one-fractional recyclate with a fraction of 0 to 20 mm, two-fractional recyclate with fractions of 0 to 8 mm and 8 to 20 mm, or three-fractional recyclate with fractions of 0 to 4 mm, 4 to 8 mm and 8 to 20 mm) is mixed in an industrial mixer for 5 to 39.9 seconds (preferably for 5 to 19.9 seconds). After thorough mixing, natural aggregate with an upper fraction of 20 mm (up to 40 % by weight of the total aggregate in concrete) is added to it under constant mixing and the mixture thus obtained is mixed for a further 5 to 39.9 seconds (preferably for 5 to 19.9 seconds). Afterwards, the whole dose of microsilica and/or of substituent(s) thereof is added to it under constant mixing within 1 to 15 seconds, preferably within 1 to 9.9 seconds, and the mixture thus obtained is mixed for a further 5 to 39.9 seconds. After that, the whole dose of cement or the whole dose of cement and substituent(s) thereof is added to it under constant mixing within 1 to 20 seconds, preferably within 1 to 9.9 seconds, and the mixture thus prepared is mixed for a further 5 to 39.9 seconds. Subsequently, this mixture is sprinkled with the whole dose of mixing water (which, if necessary contains at least one additive for concrete) under constant mixing for 5 to 39.9 seconds or the whole dose of the mixing water (which, if necessary contains at least one additive for concrete) is sprayed on it within 5 to 39.9 seconds. After another 5 to 160 seconds of mixing, fresh concrete is prepared, in which at least 60 % by weight of the aggregate is composed of recyclate from inert construction and demolition waste. Example 10

5 samples of fresh concrete according to the invention were prepared by the method described in example 9, whereby the composition of 1 m³ of each of them is described in Table 15. Table 15

These concretes were subsequently subjected to the tests described in example 2. The results of these tests are given in Table 16. Table 16

In addition, chloride content in this concrete was determined by calculation according to EN 196-2 and EN 1744-1 , the content of natural radionuclides and mass activity index were determined following the procedure of Decree No. 307/2002 Coll on radiation protection of the State Office for Nuclear Safety, as amended, whereby all these parameters meet the requirements of this Decree for use in buildings with residential rooms or spaces (mass activity ²²⁶Ra < 150 Bq.kg ¹, mass activity index I < 0.5). According to the procedure in EN 12457 and Decree of the Ministry of Environment No. 294/2005 Coll its ecotoxicity was found to be complying with the requirements. The criteria for determination of ecotoxicity are summarized in Table 3, example 2.

Table 17 shows the strength classes of concrete to which the respective concrete belongs due to its mechanical-physical parameters and classification classes of specification of the use of these concretes according to CSN (Czech Technical Standard) EN 206 (see Table 5).

Table 17

In other variants, within the aggregate, it is possible to combine brick or ceramic or mixed recyclate from inert construction and demolition waste with concrete recyclate and with up to 40 % by weight of natural aggregate. In this case, preferably a brick or ceramic or mixed recyclate from inert construction and demolition waste is added to the mixer first, afterwards it is followed by concrete recyclate and then by natural aggregate. Brick, ceramic or mixed recyclate from inert construction and demolition waste have similar characteristics and behavior and can therefore be interchanged or mixed.

In addition to the embodiments described above, in which microsilica and/or substituent(s) thereof is added to the mixer after the last aggregate component, in other variants, the whole dose of microsilica and/or substituent(s) thereof, as well as the whole dose of the aggregate, may be divided into two or more smaller portions (equal or different), whereby the individual portions of the dose of microsilica and/or substituent(s) thereof are added one by one after the addition of the individual portions of the whole dose of the aggregate, or recyclate from inert construction and demolition waste of different types or and/or fractions, or at least some parts of the dose of microsilica and/or substituent(s) thereof may be added simultaneously with some parts of the whole dose of the aggregate or recyclate - see examples 11 and 12 below.

Example 11

To prepare concrete according to the invention, the first part of the whole dose of aggregate composed of recyclate made from inert construction and demolition waste is mixed in an industrial mixer for 5 to 39.9 seconds (preferably for 5 to 19.9 seconds), whereupon the first part of the whole dose of microsilica and/or of substituent(s) thereof is added to it within 1 to 15 seconds, preferably within 1 to 9.9 seconds, and the mixture thus obtained is mixed for 5 to 39.9 seconds (preferably for 5 to 19.9 seconds). Subsequently, the remaining part of the aggregate consisting of recyclate from inert construction and demolition waste or natural aggregate is added to it under constant mixing and the mixture thus obtained is mixed for 5 to 39.9 seconds (preferably for 5 to

19.9 seconds) and then the second part of the dose of microsilica and/or of substituent(s) thereof is added to it within 1 to 15 seconds, preferably within 1 to

9.9 seconds. The whole dose of the aggregate is 1000 to 2300 kg/m³ of fresh concrete and the whole dose of microsilica and/or of substituent(s) thereof is 10 to 27.9 kg/m³ of fresh concrete. The mixture thus obtained is mixed for a further 5 to 39.9 seconds. After thorough mixing, the whole dose of cement or of cement and substituent(s) thereof is added to it under constant mixing within 1 to 20 seconds, preferably within 1 to 9.9 seconds, and the mixture thus prepared is mixed for another 5 to 39.9 seconds. Subsequently, the mixture is sprinkled with the whole dose of mixing water (which, if necessary, contains at least one addition for concrete) under constant mixing within 5 to 39.9 seconds or the whole dose of the mixing water (which, if necessary, contains at least one addition for concrete) is sprayed on it within 5 to 39.9 seconds. After a further 5 to 160 seconds of mixing, fresh concrete is prepared, in which 100 % by weight of the aggregate is composed of recyclate made from inert construction and demolition waste.

Both parts of the whole dose of the aggregate may consist of the same type of recyclate made from inert construction and demolition waste or may differ in fraction and/or the type of recyclate. Example 12

To prepare concrete according to the invention, the first part of the whole dose of the aggregate composed of recyclate made from inert construction and demolition waste is mixed in an industrial mixer for 5 to 39.9 seconds (preferably for 5 to 19.9 seconds). Thereafter, the first part of the whole dose of microsilica and/or of substituent(s) thereof is added to it within 1 to 15 seconds, preferably within 1 to 9.9 seconds, and the mixture thus obtained is mixed for 5 to 39.9 seconds (preferably for 5 to 19.9 seconds). After that, the second part of the whole dose of the aggregate composed of recyclate from inert construction and demolition waste or natural aggregate is added to it under constant mixing and the mixture thus obtained is mixed for 5 to 39.9 seconds (preferably for 5 to 19.9 seconds), whereupon the second part of the dose of microsilica and/or of substituent(s) thereof is added to it within 1 to 15 seconds, preferably 1 to 9.9 seconds, and the mixture thus obtained is mixed for 5 to 39.9 seconds (preferably for 5 to 19.9 seconds). Subsequently, the third part of the aggregate composed of recyclate from inert construction and demolition waste or natural aggregate is added to it under constant mixing and the mixture thus obtained is mixed for 5 to 39.9 seconds (preferably for 5 to 19.9 seconds) and then the third part of the dose of microsilica and/or substituent(s) thereof is added to it within 1 to 15 seconds, preferably within 1 to 9.9 seconds, and the mixture thus obtained is mixed for 5 to 39.9 seconds (preferably for 5 to 19.9 seconds). The whole dose of the aggregate is 1000 to 2300 kg/m³ of fresh concrete and the whole dose of microsilica and/or substituent(s) thereof is 10 to 27.9 kg/m³ of fresh concrete. The mixture thus obtained is further mixed for 5 to 39.9 seconds. After thorough mixing, the whole dose of cement or cement and substituent(s) thereof is added to it under constant mixing within 1 to 20 seconds, preferably within 1 to 9.9 seconds, and the mixture thus prepared is mixed for a further 5 to 39.9 seconds. Subsequently, this mixture is sprinkled with the whole dose of mixing water (which, if necessary, contains at least one additive for concrete ) under constant mixing wihin 5 to 39.9 seconds or the whole dose of the mixing water (which, if necessary, contains at least one additive for concrete,) is sprayed on it within 5 to 39.9 seconds. After another 5 to 160 seconds of mixing, fresh concrete is prepared, in which at least 100 % by weight of the aggregate is composed of recyclate from inert construction and demolition waste.

Different parts of the whole dose of the aggregate may consist of the same type of recyclate from inert construction and demolition waste or may differ from each other in fraction and/or the type of recyclate.

In all the above cases, it is possible to replace up to 40 % by weight, preferably up to 20 % by weight or up to 15 % by weight of the total aggregate in the concrete with artificial aggregate (such as agloporite, ceramsite, expandit, expanded perlite, etc.) and/or cinder and/or scoria and/or polystyrene and/or at least one organic filler (such as wood sawdust, shavings, rice husks, shives, etc.) and/or another component for improving thermal and/or acoustic and/or fire resistance properties of hardened concrete. Preferably, this material is added prior to the addition of microsilica and/or substituent(s) thereof. In all these cases, recyclate from inert construction and demolition waste constitutes at least 30 % by weight of the total aggregate in the concrete.

If necessary, it is possible to add to any of the concretes described above reinforcement fibers of at least one type which reinforce the structure of the concrete and thereby improve some of its properties, e.g. tensile strength and flexural strength. Suitable reinforcing fibers are, e.g., polypropylene (PP) fibers, polyvinyl alcohol (PVA) fibers, blends of polypropylene and polyethylene (PLV) fibers, cellulose fibers, steel fibers, glass fibers, carbon fibers, Kevlar fibers etc. These fibers are preferably added to the concrete mixture after the addition of microsilica and/or substituent(s) thereof and after thorough mixing of the mixture obtained. The total amount of all reinforcing fibers is 0.6 to 1.2 kg/m³ of fresh concrete, in the case of steel and similar fibers the total amount is up to 25 kg/m³ of fresh concrete. The reinforcing fibers are added to the concrete mixture under constant mixing within 5 to 30 seconds, which ensures their uniform distribution in the concrete.

If all the components of the aggregate used have an upper fraction of 8 mm, fresh concrete with a finer texture is prepared using the same processes, sometimes referred to as cement mortar or concrete mortar.

The 0 to 20 mm aggregate fraction described in the above examples is not limiting for the implementation of the invention, since both natural aggregate and recyclate from inert construction and demolition waste may have a higher limit of the upper fraction.

Moreover, all variants are concretes which are 100% recyclable in the same way they were produced.

All the concretes according to the invention are designed for both manual and machine processing (including shotcrete) and are suitable for conventional concrete structures from both plain concrete and ferroconcrete. In addition to fresh concrete (transport concrete) for the construction of houses, hotels, residential buildings, office buildings, industrial buildings, production halls, special purpose facilities, medical facilities, etc., or for their parts, such as pillars and posts, floors, lintels in lengths up to approximately 6 m, base plates or bases, foundation concrete, etc., these concretes can be also used for the production of concrete products and prefabricated elements, e.g., concrete blocks and bricks, paving cobbles, slabs, blocks, curbs, various elements of garden architecture, ceiling beams and inserts, etc.

Claims

PATENT CLAIMS

1. A method for the preparation of 1 m³ of fresh concrete using recyclate made from inert construction and demolition waste, characterized in that 1000 to 2300 kg of aggregate, 30 % to 100 % by weight of which consists of recyclate from inert construction and demolition waste, is mixed in an industrial mixer for 5 to 39.9 seconds with 10 to 27.9 kg of microsilica or substituent(s) thereof or a mixture of microsilica and at least one substituent thereof, whereby due to the rubbing of aggregate grains, the grains of the recyclate from inert construction and demolition waste are subject to intensive abrasive action which consequently results in an increase in the specific surface area of the recyclate and production of fine pozzolanic powder, whereby the aggregate particles are coated and pores in them are filled with the microsilica and/or substituent(s) thereof, together with the pozzolanic powder, and after thorough mixing, 135 to 400 kg of cement is added to the mixture thus obtained under constant mixing within 1 to 20 seconds, or cement and at least one substituent thereof in a total amount of 135 to 600 kg is added to it one by one in any order or simultaneously under constant mixing within 1 to 20 seconds, and the mixture thus obtained is mixed for a further 5 to 39.9 seconds, whereupon it is sprinkled with 50 to 300 kg of mixing water under constant mixing within 5 to 39.9 seconds, or it is sprayed with this amount of the mixing water within 5 to 39.9 seconds, whereby the surface of cement and, optionally, the surface of substituent(s) thereof is gradually moistened and the resulting cement paste is gradually adhered to the aggregate particles already coated with the mixture of microsilica and/or substituent(s) thereof and pozzolanic powder, and after an additional 5 to 160 seconds of mixing, fresh concrete is prepared.

2. The method according to claim 1 , characterized in that first, the aggregate is mixed in an industrial mixer for 5 to 39.9 seconds and after thorough mixing, the whole dose of microsilica and/or substituent(s) thereof is added to it within 1 to 15 seconds and the mixture thus obtained is mixed for a further 5 to 39.9 seconds.

3. The method according to claim 1 , characterized in that cement or cement and substituent(s) thereof is/are added to the mixture obtained within 1 to 9.9 seconds.

4. The method according to claim 2, characterized in that microsilica and/or substituent(s) thereof is/are added to the aggregate within 1 to 9.9 seconds.

5. The method according to claim 1 or 2, characterized in that the aggregate has an upper fraction of 20 mm.

6. The method according to claim 5, characterized in that the aggregate is two-fractional with fractions of 0 to 8 mm and 8 to 20 mm.

7. The method according to claim 5, characterized in that the aggregate is three-fractional with fractions of 0 to 4 mm, 4 mm to 8 mm and 8 to 20 mm.

8. The method according to claim 1 or 2, characterized in that recyclate made from inert construction and demolition waste is brick recyclate, which consists entirely or of at least a majority of crushed brick, or ceramic recyclate, which consists entirely or of at least a majority of crushed ceramics from ceramic building and fitting elements, or concrete recyclate, which consists entirely or of at least a majority of crushed concrete or another cement containing material, or mixed recyclate, which consists of crushed mixed construction and demolition waste.

9. The method according to claim 1 or 2, characterized in that the substituent of microsilica is metakaolin or shale with a content of silica of at least 45 % by weight.

10. The method according to any of claims 1 to 7, characterized in that up to 40 % by weight of the total aggregate is formed by natural aggregate.

11. The method according to claim 1 to 7 or 10, characterized in that up to 40 % by weight of the total aggregate is formed by lightweight artificial aggregate and/or cinder and/or scoria and/or polystyrene and/or at least one organic filler and/or another component for improving thermal and/or acoustic and/or fire resistance properties of hardened concrete.

12. The method according to claim 1 , characterized in that at least one additive for concrete is added to the mixture being prepared simultaneously with mixing water, or after the mixing water has been added, whereby the total amount of all the additives for concrete added is up to 10 % by weight of the dose of cement or the dose of cement and substituent(s) thereof.

13. The method according to claim 1 , characterized in that the microsilica is compacted.

14. The method according to claim 1 , characterized in that after the addition of microsilica and/or substituent(s) thereof and after thorough mixing of the mixture obtained, reinforcing fibers of at least one type are added to this mixture under constant mixing within 5 to 30 seconds, the total amount of all reinforcing fibers being in the range from 0.6 to 25 kg/m³ of fresh concrete.

15. Fresh concrete prepared by the method according to claim 1 to 14, characterized in that it contains in 1 m³ 50 to 300 kg of water, 135 to 400 kg of cement or 135 to 600 kg of a mixture of cement and at least one substituent thereof, 10 to 27.9 kg of microsilica, at least one substituent thereof or a mixture of microsilica and at least one substituent thereof and 1000 to 2300 kg of aggregate, whereby 30 to 100 % of the aggregate is composed of recyclate from inert construction and demolition waste, 0 to 40 % of the aggregate is composed of natural aggregate and 0 to 40 % of the aggregate is composed of lightweight artificial aggregate and/or cinder and/or scoria and/or polystyrene and/or at least one organic filler and/or another component for improving thermal and/or acoustic and/or fire resistance properties of hardened concrete.

16. Fresh concrete according to claim 15, characterized in that 70 to 100 % of the aggregate is formed by recyclate from inert construction and demolition waste.

17. Fresh concrete according to claim 15 or 16, characterized in that up to 40 % by weight of the total aggregate is composed of lightweight artificial aggregate and/or cinder and/or scoria and/or polystyrene and/or at least one organic filler and/or another component for improving thermal and/or acoustic and/or fire resistance properties of hardened concrete.

18. Fresh concrete according to claim 15, characterized in that it further contains at least one additive for concrete, whereby the total amount of all added additives for concrete is up to 10 % by weight of the dose of cement or the dose of cement and substituent(s) thereof.

19. Fresh concrete according to claim 15, characterized in that it further contains reinforcing fibers in an amount of 0.6 to 25 kg/m³ of fresh concrete.