RU2821626C1 - Method of producing concrete additives and hydraulically hardening compositions based on recycled concrete wastes - Google Patents

Abstract

FIELD: construction.

SUBSTANCE: invention relates to construction industry, in particular, can be used in production of hydraulically hardening construction compositions, commercial concrete based on portland cement by replacing part of the cement with powder of cement-sand stone in the form of a colloidal suspension obtained by mechanochemical activation in a solution of an alkaline agent. Method includes the following stages: 1) mechanical destruction by crushing and screening of concrete structures with production of dispersed powder of dust-like fraction of cement-sand stone (DLFCSS) with particle size of 150 mcm and less; 2) mixing of dispersed powder of DLFCSS with aqueous solution of NaOH activator of concentration from 0.01M to 0.03M in ratio of 1:1.2; 3) mechanochemical activation of dispersed powder of DLFCSS in aqueous solution of NaOH activator by passing through hydrodynamic disperser for 3–5 seconds at room temperature.

EFFECT: creation of a method of producing a colloidal additive based on recycled concrete wastes, namely dispersed powder of dust-like fraction of cement-sand stone (DLFCSS), in order to replace part of portland cement with a colloidal additive in commercial concrete and hydraulically hardening compositions with improved structure and without loss of strength thereof.

3 cl, 3 dwg, 1 tbl

Description

The invention relates to the field of construction production, in particular, it can be used in the production of hydraulically hardening building compositions, ready-mix concrete based on Portland cement by replacing part of the cement with cement-sand stone powder in the form of a colloidal suspension obtained by its mechano-chemical activation in a solution of an alkaline agent.

One of the ways to solve environmental problems is to reuse (recycle) materials extracted from deteriorating human objects. In this regard, close attention is paid to the recycling of old reinforced concrete structures for the purpose of further recycling of their components [New trends in eco-efficient and recycled concrete, 1st Edit. / J. de Brito, F. Agrela, eds., 2018. Elsevier, 632 p., eBook ISBN: 9780081024812; New trends in recycled aggregate concrete / J. de Brito, C.S. Poon, B. Zhan, eds., 2019. Applied Sciences, 280 p. DOI: 10.3390/books978-3-03921-141-8]. This is achieved by mechanical destruction of reinforced concrete with subsequent separation of metal, gravel and sand-like fraction of cement stone. The latter are usually used as fillers for newly produced concrete masses. This technology is simple and convenient, but when recycling concrete structures, a dust-like (less than 150 microns) fraction of cement-sand stone (PFCP) is also obtained in quantities of 20 - 30% [Kasai Y. Recent trends in recycling of concrete waste and use of recycled aggregate concrete in Japan / T.C. Liu, C. Meyer (Eds.), SP219-Recycling Concrete and Other Materials for Sustainable Development, American Concrete Institute International, Farmington Hills, 2004, p. 11-34. DOI:10.14359/13136; X. Chen, J. Zheng. Influence of recycled powder on hydration characteristics of cement paste. // Bull. Chinese Ceram. Soc. 2016. V. 35. P. 2530-2536].

PFCPC is a polymineral mixture, which includes quartz, calcite, ettringite, non-hydrated Portland cement minerals, calcium silicate and aluminate hydrates, feldspars, hydromica minerals, anhydrite, boehmite, goethite, etc. Their ratio depends on the composition of the original concrete, conditions hardening, operating time and many other factors. The chemical and mineralogical composition and the presence of non-hydrated cement particles make PFCPC a promising starting material for the production of cement clinker and mixed cements.

However, simply replacing Portland cement with recycled PFCPC in quantities of more than 10–15% leads to a deterioration in the strength properties of concrete [Xiao J.Z., Ma Z.M., Sui T.B., Akbarnezhad A., Duan Z.H. Mechanical properties of concrete mixed with recycled powder produced from construction and demolition waste // Journal of Cleaner Production. 2018. V.188. P. 720-731. DOI: 10.1016/j.jclepro.2018.03.277; Beppaev Z.U., Astvatsaturova L.Kh., Kolodyazhny S.A., Vernigora S.A., Lopatinsky V.V. Prospects for the use of finely dispersed recycling products of concrete processing as mineral additives for the production of building mortars // Concrete and reinforced concrete. 2023. No. 1 (615). pp. 43-55. DOI: 10.37538/0005-9889-2023-1(615)-43-55]. Therefore, the adhesive properties of PFCPC can be improved only after its activation, leading to a change in the chemical properties of the powder, for example, thermal, mechanical, chemical or hydrothermal.

There is a known method for processing concrete waste [US7258737, 2006-11-23, C04B11/036]. The thermal method involves the production of recycled cement by dehydration of PFCPC at 400 - 500 ° C, intermediate grinding and correction of the CaO content in the resulting mixture, its re-firing at 600 - 700 ° C and grinding to a cement fraction of less than 80 microns.

Obviously, this method is quite energy-consuming.

A simple approach to increasing the astringent properties of PFCPC could be its mechanical activation in a ball mill, leading to an increase in the specific surface area of the powder. However, experimental results on 10% replacement of cement in concrete with recycling PFTsPK [Meng T., Hong Y., Ying K., Wang Z. Comparison of technical properties of cement pastes with different activated recycled powder from construction and demolition waste // Cement and Concrete Composites. 2021. V. 120. 104065. DOI: 10.1016/j.cemconcomp.2021.104065] showed that grinding in a ball mill PFTsPK, which has a bimodal particle size distribution (3 - 90 μm and 90 - 1000 μm), to a powder with a particle size 1 - 100 µm (with a broad maximum at 4 - 20 µm) only slightly, by approximately 5%, increased the strength of 28-day concrete while maintaining in both cases a strength close to that of the comparative sample without additives. At the same time, a further increase in the PFCPC content caused a significant drop in the strength of concrete, regardless of the grinding quality of the PFCPC. However, when using finely ground PFCPC, the strength turned out to be 20 - 25% higher compared to samples with coarse PFCPC.

This means that the chemical activity of the PFCPC surface after grinding in a ball mill is still insufficient for strong adhesion to the filler and particles of hydrating cement.

Relatively universal is the well-known and widely used method of alkaline activation, which makes it possible to convert various minerals, slags, fly ash and PFC into binders and geopolymers used in the production of building materials and various structures [Handbook of Alkali-activated Cements, Mortars and Concretes / F. Pacheco-Torgal, JA Labrincha, C. Leonelli, A. Palomo, P. Chindaprasirt, eds., 2015, Elsevier, 830 p., https://doi.org/10.1016/C2013-0-16511-7]. The method involves the action of fairly concentrated (5 - 15 M) solutions of alkalis, for example, NaOH or KOH, on these materials with the formation of gels that harden after some time. As a consequence, the total alkali metal content in the final product is relatively high and is calculated in percentages. This not only worsens the economic performance of concrete production using this technology due to the high cost of alkaline agents, but can also cause low resistance of concrete based on composite binders to corrosion and destruction due to self-expansion due to the occurrence of an alkaline reaction with silica and calcium carbonates, known like “cancer of concrete.” The latter imposes, for example, a restriction on the sodium content in cement, which should not exceed 0.6% (in terms of Na ₂ O) [EN 197-1 European Standard. Cement – Part 1: Composition, specifications and conformity criteria for common cements].

Thus, despite the effectiveness of using alkaline activators for the production of binders, the development of approaches to reducing the total content of alkali metals in the resulting concrete is required to increase their functional life. One of the known approaches to mitigate the negative effect of using an alkaline additive is the introduction of pozzolan, amorphous silica or metakaolin, which can bind excess alkali.

It should be noted that alkaline activation can be used not only to create binders, causing volumetric changes in the components, but also to chemically modify the surface of other concrete components: gravel (SU1100265, published 06/30/1984) or sand (RU2223241, published 02/10/2004) . For this, alkali solutions with relatively low concentrations are used, and the main task is to create a sufficient number of hydroxyl groups on the surface of the filler grains, which enhance the adhesion of the filler to the binder.

A close technical solution to the claimed one is the method of preparing recycled concrete [Ren P., Li B., Yu J.-G., Ling T.-C. Utilization of recycled concrete fines and powders to produce alkaliactivated slag concrete blocks // J. Cleaner Production. 2020. V. 267. P. 122115. DOI: 10.1016/j.jclepro.2020.122115] based on a complex binder obtained by mixing fine powders (less than 100 microns) of blast furnace slag and cement stone, taken in different weight ratios, with a hydroxide solution and sodium silicate (SiO ₂ /Na ₂ O = 3.33). When replacing 20% of slag with cement stone, the strength of the resulting 28-day concrete was 12-15% higher, and with a 30% replacement it could remain close to that for concrete produced using only blast furnace slag.

However, the resulting concretes contained up to 10% alkaline activator in terms of Na ₂ O.

The closest technical solution (prototype) to the claimed one is the method for producing cement paste [Meng T., Hong Y., Ying K., Wang Z. Comparison of technical properties of cement pastes with different activated recycled powder from construction and demolition waste // Cement and Concrete Composites. 2021. V. 120. 104065. DOI: 10.1016/j.cemconcomp.2021.104065] based on a binder formed by grinding cement stone obtained during demolition of buildings in a ball mill in a solution of triethanolamine with the addition of water. When replacing up to 20% of Portland cement with PFCPC activated in this way, the strength of the resulting 28-day sample was practically no different from that for a comparison sample based on Portland cement, and with a further increase in the proportion of activated PFCPC, it quickly decreased.

In the above prototype, the mechano-chemical activation of PFCPC was carried out in a ball mill with the addition of water and an organic amine - triethanolamine, taken in an amount of 0.1% by weight of PFCPC as a chemical activator that stimulates the hydration of PFCPC particles. The activated powder in suspension was then mixed with the cement.

The disadvantages of this method of activating PFCPC are:

- periodic mode of production of activated PFCPC;

- use of an expensive organic alkaline activator;

- the need for a relatively large load of this activator;

- the low quality of the resulting additive does not allow increasing the degree of cement replacement in mortars and concretes by more than 20%, as this leads to a decrease in the strength of the resulting ready-mixed concrete.

The invention is based on the task of creating a method for producing a colloidal additive based on recycled concrete waste (destroyed concrete buildings and structures) in order to replace part of the Portland cement with a colloidal additive in ready-mixed concrete and hydraulically hardening compositions without losing their strength properties.

The technical result is a method for producing a colloidal additive for concrete and hydraulically hardening compositions based on recycled concrete waste, namely dispersed powder PFTsPK, characterized by:

- continuity of the process of obtaining colloidal additives;

- a significant reduction compared to the prototype in the amount of inorganic alkaline activator used;

- using a cheap inorganic alkaline activator;

- the ability to obtain a colloidal additive, the use of which allows replacing 20 - 30% of Portland cement in ready-mixed concrete and hydraulically hardening compositions and at the same time leads to an improvement in the structure, preservation and improvement of their strength properties.

The proposed method for obtaining a colloidal additive for concrete and hydraulically hardening compositions based on recycled concrete waste includes the following steps:

1) mechanical destruction by crushing and screening concrete structures to obtain dispersed powder of the pulverized fraction of cement-sand stone with particle sizes of 150 microns or less;

2) mixing dispersed powder of the pulverized fraction of cement-sand stone with an aqueous solution of the activator, NaOH, concentration from 0.01 M to 0.03 M in a ratio of 1: 1.2;

3) mechano-chemical activation of dispersed powder of the pulverized fraction of cement-sand stone in an aqueous solution of the activator by passing through a continuous hydrodynamic dispersant for 3-5 seconds or less at room temperature to obtain a colloidal additive, which is a PFCPC powder with a hydroxylated particle surface.

Thus, the present invention proposes a method for producing a colloidal additive based on recycled concrete waste by mechano-chemical activation of PFCPC particles in a dilute solution of an alkaline agent.

The dispersed part of concrete scrap, namely PFCPC, formed during crushing and screening of destroyed concrete structures, is subjected to mechano-chemical activation in a continuous hydrodynamic dispersant, in which ultrafine grinding of PFCPC is carried out in a slightly alkaline environment.

As a result, the sizes of PFCPC particles decrease, calcium carbonates and Si-O-Al bonds are destroyed, and the surface of the particles is hydrated, that is, saturated with hydroxyl groups (-OH groups), which are formed due to the reaction of the surface of the minerals that make up PFCPC with a NaOH solution.

Gels with active -OH groups begin to slowly interact with each other and bonds are formed with the release of water, Si-O-Al bonds are formed, a bridging bond is formed between silicon-silicon, silicon-aluminum through oxygen, then water is involved in the form of crystalline hydrate and the result is - calcium aluminates, silicates.

According to the generally accepted theory of the formation of cement stone (CS), when mixing a cement-sand mixture with water, the metal oxides contained in the cement first transform into the corresponding poorly soluble hydroxides, which over time form a concentrated sol, which gradually turns into a gel. When it ages, chemical reactions occur between the gel fragments and the exchange of mobile cations, in particular, Ca ²⁺ , which are responsible for the electrostatic interaction between the gel fragments. All this increases the cohesion of the gel structure, which in turn initiates the emergence and growth of crystalline hydrate nuclei, among which hydrated C3A and C2S dominate.

The indicated reactions in the gel volume include the following:

- formation of oxygen bridges between cations of elements M (M = Al, Si) belonging to different gel fragments:

- formation of ionic bridges from calcium cations between oxygen groups belonging to different gel fragments:

or

At its core, this bond between the cations of the elements M (M = Al, Si) is formed by two oxygen bridges through calcium.

From a chemical point of view, if such a gel at the time of formation contains any foreign particles with a surface chemical state close to that in the gel, then they will also be involved in the above processes of interaction with the gel. Consequently, particles of old CK must be activated in such a way that a sufficiently large number of hydroxyl groups appear on their surface. To do this, intensive mechanical grinding and chemical modification with some kind of activator should be used. When these stages are combined, we can talk about the mechano-chemical activation of the old CK.

Since, according to the above reactions, in aged CC there are M–O–M and M–O–Ca–O–M bonds, the activator must break them, that is, hydroxylate the surface. In our opinion, alkalis and acids taken in small quantities are suitable for these purposes. Below are views on the chemical nature of their action on the surface of old CC.

In fig. 1, 2 show schemes for the activation of CK minerals by the action of NaOH, Ca(OH) ₂ and HCl.

In fig. Figure 1 shows a diagram of possible reactions of hydrated C3A with activators.

In fig. Figure 2 shows a diagram of possible reactions of hydrated C2S with activators.

In fig. Figure 3 shows a diagram of the chemical state of the hydroxylated surface of old CC minerals.

From the presented diagrams the following conclusions can be drawn:

- in small doses, all activators can hydroxylate the surface of CC minerals,

- in large doses, activators, except Ca(OH) ₂ , can destroy particles of CC minerals, turning them into salts (HCl) or gels (NaOH),

- the hydroxylated surface of the old CC minerals will have the same surface chemical state as the surface of the gel formed when cement is mixed with water. Therefore, it will have good adhesion to the newly formed particles of new CC due to chemical bonding with them, as shown in the diagram presented in Fig. 3.

Thus, during the mechano-chemical activation of dispersed PFCPC powder in a weak alkaline solution, the surface of PFCPC powder particles becomes chemically identical to the surface of particles of hydrating Portland cement, which ensures good adhesion of cement particles and additives, both among themselves and with the filler.

Moreover, the use of high concentrations of alkali to convert PFCPC into a gel is impractical, since the volume of PFCPC particles already has the structure of hydrated cement, which is partially replaced by activated PFCPC.

Thus, the distinctive features of the claimed method from the known ones are:

- continuity of the process of obtaining an activated colloidal suspension (colloidal additive) in a continuous hydrodynamic dispersant, in which ultrafine grinding of PFCPC is carried out in a weak alkaline environment;

- use of a cheap (10 times less per unit weight) inorganic alkaline activator);

- lower consumption of chemical activator per unit weight of the activated product (at least 2 times);

- significant, up to 30%, savings in cement when preparing concrete and hydraulically hardening compositions with the specified colloidal additive.

As a result, an insignificant increase in the content of sodium ions in the binder is detected, which is less than 0.05%, which does not create the risk of “concrete cancer” in the case of using a small amount of pozzolan additives in the concrete composition.

To experimentally test the proposed solution, 13 compositions of fine-grained concrete mixture were manufactured and tested, from which standard samples were molded in accordance with GOST 10180-2012. Samples, for the preparation of which Portland cement type CEM II/A-Sh 32.5 was used as a binder produced by OJSC “Iskitimcement” (Iskitim, Novosibirsk region), meeting the requirements of GOST 31108-2016, hardened under normal thermal and humidity conditions and were tested in in accordance with GOST R 58527-2019 on the 7th, 14th and 28th days.

The colloidal additive was obtained by mechano-chemical activation of dispersed PFCPC powder under the following parameters:

- activator: weak solution of sodium hydroxide;

- activator concentrations: 0.01, 0.02, 0.03M;

- ratio of activator solution / PFCPC powder (ml/g): 1 / 1.2 ml/g;

- activation temperature: room;

- duration of activation in a hydrodynamic dispersant: 3-5 seconds.

Then they replaced part of the cement, namely 10, 20 and 30%, in concrete mixtures with activated material (in the form of a suspension).

Example 1:

Prototype: Cem. B32.5 - 480 g; 120 g of PFCPK mechanically and chemically activated in a ball mill with the addition of the chemical activator triethanolamine - 0.12 g and water 120 g; sand from Mkr. 2.1-2.2 – 1500 g; additional water 158 g.

The pulverized fraction of cement-sand stone (PFCPS) is loaded into a ball mill, with the ratio balls : PFCPS = 3 : 1, water is added to obtain a suspension with a moisture content of 60%, triethanolamine in the amount of 0.1% by weight of PFCPS, and mechano-chemical activation is carried out in within 2 hours. The resulting colloidal additive is introduced into the composition of fine-grained concrete instead of 20% cement.

Experiment 1. Mechano-chemical activation of PFCPC with 0.01 M NaOH solution.

Example 2:

Composition K1 (control): Cem. B32.5 - 600 g; sand microdistrict 2.1-2.2 – 1500 g; water 278g.

Example 3:

Composition 11: (Replacement of 10% cement with mechanically-chemically activated PFTsPK) Cem. B32.5 - 540 g; 60 g of PFCPC mechanically and chemically activated in a hydrodynamic activator together with 92 g of 0.01 M NaOH solution; sand from Mkr. 2.1-2.2 – 1500 g; additional water - 186 g; metakaolin – 40 g.

Example 4:

Composition 12: (Replacement of 20% cement with mechanically-chemically activated PFTsPK) Cem. B32.5 - 480 g; 120 g of PFCPC mechanically and chemically activated in a hydrodynamic activator together with 183 g of 0.01 M NaOH solution; sand from Mkr. 2.1-2.2 – 1500 g; water additional 95 g; metakaolin – 60 g.

Example 5:

Composition 13: (Replacement of 30% cement with mechanically-chemically activated PFTsPK) Cem. B32.5 - 420 g; 180 g of PFCPC mechanically and chemically activated in a hydrodynamic activator together with 335 g of 0.01 M NaOH solution; sand from Mkr. 2.1-2.2 – 1500 g; water additional 3 g; metakaolin – 80 g.

In experiment 1, the dusty fraction of cement-sand stone was mixed with a 0.01 M NaOH solution in a ratio of 1:1.2 and mechanically and chemically activated by passing through a hydrodynamic dispersant. Activation time is 3-5 seconds. The resulting suspension was introduced into the composition of fine-grained concrete instead of 10, 20 and 30% cement.

Experiment 2. Mechano-chemical activation of PFCPC with 0.02 M NaOH solution.

Example 6:

Composition K2 (control): Cem. B32.5 - 600 g; sand microdistrict 2.1-2.2 – 1500 g; metakaolin – 40; water 278 g.

Example 7:

Composition 21: (Replacement of 10% cement with mechanically-chemically activated PFTsPK) Cem. B32.5 - 540 g; 60 g of PFCPC mechanically and chemically activated in a hydrodynamic activator together with 91 g of 0.02 M NaOH solution; sand from Mkr. 2.1-2.2 – 1500 g; water additional 187 g; metakaolin – 40 g.

Example 8:

Composition 22: (Replacement of 20% cement with mechanically-chemically activated PFTsPK) Cem. B32.5 - 480 g; 120 g of PFCPC mechanically and chemically activated in a hydrodynamic activator together with 182 g of 0.02 M NaOH solution; sand from Mkr. 2.1-2.2 – 1500 g; water additional 96 g; metakaolin – 60 g.

Example 9:

Composition 23: (Replacement of 30% cement with mechanically-chemically activated PFTsPK) Cem. B32.5 - 420 g; 180 g of PFCPC mechanically and chemically activated in a hydrodynamic activator together with 274 g of 0.02 M NaOH solution; sand from Mkr. 2.1-2.2 – 1500 g; water additional 4 g; metakaolin – 80 g.

In experiment 2, the dusty fraction of cement-sand stone was mixed with a 0.02 M NaOH solution in a ratio of 1:1.2 and mechanically and chemically activated by passing through a hydrodynamic dispersant. Activation time is 3-5 seconds. The resulting suspension was introduced into the composition of fine-grained concrete instead of part, 10, 20 or 30%, of cement.

Experiment 3. Mechano-chemical activation of PFCPC with 0.03 M NaOH solution.

Example 10:

Composition K3 (control): Cem. B32.5 - 600 g; sand from Mkr. 2.1-2.2 – 1500 g; metakaolin – 60; water 278 g.

Example 11:

Composition 31: (Replacement of 10% cement with mechanically-chemically activated PFTsPK) Cem. B32.5 - 540 g; 60 g of PFCPC mechanically and chemically activated in a hydrodynamic activator together with 91 g of 0.03 M NaOH solution; sand from Mkr. 2.1-2.2 – 1500 g; water additional 188 g; metakaolin – 40 g.

Example 12:

Composition 32: (Replacement of 20% cement with mechanically-chemically activated PFTsPK) Cem. B32.5 - 480 g; 120 g of PFCPC mechanically and chemically activated in a hydrodynamic activator together with 180 g of 0.03 M NaOH solution; sand from Mkr. 2.1-2.2 – 1500 g; water additional 98 g; metakaolin – 60 g.

Example 13:

Composition 33: (Replacement of 30% cement with mechanically-chemically activated PFTsPK) Cem. B32.5 - 420 g; 180 g of PFCPC mechanically and chemically activated in a hydrodynamic activator together with 272 g of 0.03 M NaOH solution; sand from Mkr. 2.1-2.2 – 1500 g; water additional 6 g; metakaolin – 80 g.

In experiment 3, the dusty fraction of cement-sand stone was mixed with a 0.03 M NaOH solution in a ratio of 1:1.2 and mechanically and chemically activated by passing through a hydrodynamic dispersant. Activation time is 3-5 seconds. The resulting suspension was introduced into the composition of fine-grained concrete instead of 10, 20 and 30% cement.

In the table the results are presented, namely the density, flexural and compressive strength of concrete samples aged 7, 14 and 28 days for examples 1-13, illustrating the influence of colloidal additives obtained by the claimed method on the quality of concrete when replacing part of Portland cement.

Examples 3-5 are examples of replacing part of the cement in fine-grained concrete with a colloidal additive mechanically and chemically activated by PFCPC in a 0.01 M NaOH solution.

Examples 7-9 are examples of replacing part of the cement in fine-grained concrete with a colloidal additive mechanically and chemically activated by PFCPC in a 0.02 M NaOH solution.

Examples 11-13 are examples of replacing part of the cement in fine-grained concrete with a colloidal additive mechanically and chemically activated by PFCPC in a 0.03 M NaOH solution.

The following were used as control compositions with which the studied compositions were compared:

- example 2 : Cem. B32.5 - 600 g; sand microdistrict 2.1-2.2 – 1500 g; water 278g;

- example 6: composition according to example 2 , but with the addition of 6.6% metakaolin;

- example 10 : composition according to example 2 , but with the addition of 10% metakaolin.

Metakaolin was added to neutralize the effect of sodium ions.

Examples of the studied compositions in comparison with the control ones show the influence of the colloidal additive together with the addition of metakaolin on the physical and mechanical characteristics of fine-grained concrete.

Analysis of the results given in the table showed that the colloidal additive, obtained by mechano-chemical activation of the dusty fraction of cement-sand stone during the processing of old reinforced concrete structures, can replace part of the Portland cement (20 - 30%) in ready-mixed concrete and hydraulically hardening compositions, improving them structure due to an increase in the density of the samples, and with the preservation and improvement of strength properties.

Thus, the proposed method makes it possible to obtain a colloidal additive based on recycled concrete waste, the use of which to replace 20 - 30% of Portland cement in ready-mixed concrete and hydraulically hardening compositions does not lead to a loss of their strength.

The method makes it possible to obtain raw materials for recycling, that is, it promotes the renewal of resources, the return of construction waste to economic circulation in order to reduce the costs of new construction, preserve natural resources, as well as land plots, excluding their use for the placement of new landfills.

Claims (6)

1. A method for producing an additive for concrete and hydraulically hardening compositions based on recycled concrete waste, characterized in that the method includes the following steps: 1) mechanical destruction of concrete structures to produce dispersed powder of the pulverized fraction of cement-sand stone PFTsPK with particle sizes of 150 microns or less; 2) mixing dispersed powder of the pulverized fraction of cement-sand stone with an aqueous solution of the NaOH activator with a concentration of 0.01 M to 0.03 M in a ratio of 1: 1.2; 3) mechanochemical activation of dispersed powder of the pulverized fraction of cement-sand stone in an aqueous solution of the NaOH activator for 3-5 seconds at room temperature to obtain a colloidal additive, which is a PFCPC powder with a hydroxylated particle surface. 2. The method according to claim 1, characterized in that concrete structures are destroyed by crushing and screening. 3. The method according to claim 1, characterized in that the mechanochemical activation of dispersed powder of the pulverized fraction of cement-sand stone in an aqueous solution of the NaOH activator is carried out in a continuous hydrodynamic dispersant.