Low-carbon cement clinker, preparation method and application thereof

Abstract

The present application relates to the technical field of cement clinker preparation, and particularly relates to a low-carbon cement clinker, a preparation method and application thereof. The low-carbon cement clinker provided by the present application comprises the following components in parts by mass: 55-60 parts of limestone, 20-25 parts of fly ash, 8-10 parts of rich aluminum converter steel slag, 12-17 parts of carbonated calcium carbide slag, and 1.5-2.5 parts of gradient response modifier. The low-carbon cement clinker provided by the present application has the advantages of low calcination temperature, short setting time, fast hardening speed, high early strength, continuous growth of late strength, and low carbon emission. The preparation process is simple, the preparation cost and energy consumption are low, the maintenance time is short, and the present application has important economic and environmental benefits.

Description

Technical Field

[0001] This invention relates to the field of cement clinker preparation technology, specifically to a low-carbon cement clinker, its preparation method, and its application. Background Technology

[0002] With the slowdown in urbanization and industrialization, the pursuit of high-quality development has become a trend in contemporary society. Environmental issues are receiving increasing attention, and global warming is a major challenge facing societal development. Greenhouse gas carbon dioxide is the primary cause of global warming. The cement industry is one of the world's largest sources of carbon dioxide emissions, accounting for 5%-8% of global emissions.

[0003] Low-carbon cement clinker has become a research hotspot in recent years. Its main mineral composition consists of low-calcium minerals C3S2, CS, β-C2S, and γ-C2S. Compared with silicate cement clinker, which is mainly composed of C3S minerals, it requires less limestone in its batching, has a lower calcination temperature, and can absorb a large amount of CO2 gas. This reduces carbon emissions from the cement industry in many ways and can also be used to prepare building materials with excellent physical properties.

[0004] To date, domestic and international researchers have conducted extensive research on cement clinker with belite as the main mineral (dicalcium silicate-based silicate cement clinker). For example, patent application number 20121002240.1 describes cement clinker containing 25-30% -C2S; 28-40% C4A3S; 4-12% C4AF; and 4-8% amorphous phase substances. This cement improves early strength by generating a large amount of -C2S, but the formation conditions are difficult to control. Patent application number 200610045503.6 describes belite-barium calcium sulfoaluminate cement, a composite of barium calcium sulfoaluminate mineral and belite mineral, but its large-scale production is impossible due to limited barium sulfate resources. Other studies have shown that the low hydration activity of belite minerals results in cement strengths that do not meet engineering requirements at 3 days and 28 days.

[0005] Therefore, developing a low-carbon cement clinker that can solve the above-mentioned defects is not only of great environmental significance, but also of great economic value.

[0006] Purpose of the invention To overcome the shortcomings of existing technologies, the present invention aims to provide a low-carbon cement clinker, its preparation method, and its application. The low-carbon cement clinker provided by the present invention comprises the following components by weight: 55-60 parts limestone, 20-25 parts fly ash, 8-10 parts alumina-rich converter steel slag, 12-17 parts carbonated carbide slag, and 1.5-2.5 parts gradient-responsive modifier. The low-carbon cement clinker provided by the present invention has advantages such as low calcination temperature, short setting time, fast hardening speed, high early strength, continuous strength growth in later stages, and low carbon emissions. Furthermore, the preparation process is simple, with low preparation cost and energy consumption, and short curing time, resulting in significant economic and environmental benefits.

[0007] To achieve the above objectives, the present invention provides the following technical solution: A low-carbon cement clinker comprises the following components by weight: 55-60 parts limestone, 20-25 parts fly ash, 8-10 parts alumina-rich converter steel slag, 12-17 parts carbonated carbide slag, and 1.5-2.5 parts gradient-responsive modifier.

[0008] Preferably, the gradient-responsive modifier includes a low-temperature active component and a high-temperature catalytic component.

[0009] Preferably, in the gradient-responsive modifier, the mass ratio of the low-temperature active component to the high-temperature catalytic component is 4-5:6-8.

[0010] Preferably, the low-temperature active component is prepared by the following steps: S11. Disperse nano-SiO2 with a particle size of 50-80nm in a 2-4wt% silane coupling agent ethanol solution and sonicate for 30-40min to obtain a SiO2 suspension. S12. At room temperature, precursor solution A and precursor solution B are added alternately to the SiO2 suspension every 30 min, and the cycle is repeated 5-6 times to form an amorphous gel layer. S13. The solution treated in step S12 is kept at 120-150℃ for 4-6 hours, then cooled to room temperature, centrifuged, washed, and dried to obtain the low-temperature active component.

[0011] Preferably, the precursor solution A is a 0.5-0.6 mol / L calcium nitrate tetrahydrate solution; the precursor solution B is a mixture of a 0.3-0.4 mol / L aluminum nitrate solution and a 0.4-0.5 mol / L sodium silicate solution in a mass ratio of 1:1.

[0012] Preferably, the high-temperature catalytic component is prepared by the following steps: S21. Mix zirconium oxynitrate dihydrate, boric acid, and diammonium hydrogen phosphate in a molar ratio of 1:2:3, dissolve in deionized water, and adjust the pH of the solution to 9-10 with ammonia water to form a precursor solution; S22. The precursor solution is hydrothermally reacted at 180-200℃ for 24-28h, then cooled to room temperature, centrifuged, washed and dried to obtain zirconium borophosphate support; S23. The zirconium borophosphate support is impregnated in a mixed solution of nickel nitrate solution and cobalt nitrate solution, ultrasonically dispersed for 30-40 min, heated to 500-600℃ and held for 2-3 h under a protective atmosphere, and then cooled to room temperature to obtain the high-temperature catalytic component.

[0013] Preferably, in step S23, in the mixed solution of nickel nitrate solution and cobalt nitrate solution, Ni 2+ and Co 2+ The molar ratio is 3:1; the protective atmosphere is a mixture of hydrogen and argon in a mass ratio of 5:95.

[0014] Preferably, the carbonated carbide slag is obtained by placing carbide slag in a CO2 atmosphere and maintaining it at 800-900℃ for 1-3 hours.

[0015] A method for preparing low-carbon cement clinker, comprising the following steps: S1. The gradient-responsive modifier is mixed with limestone, fly ash, alumina-rich converter steel slag, and carbonated carbide slag in proportion and then mechanically ball-milled for 30-40 minutes to obtain raw meal; S2. The raw material is heated to 800-1100℃ and calcined for 1-2 hours, then heated to 1150-1250℃ and calcined for 0.5-1 hours, then heated to 1250-1350℃ and calcined for 1-2 hours, and finally cooled to room temperature to obtain the low-carbon cement clinker.

[0016] An application of the low-carbon cement clinker in the field of concrete preparation.

[0017] Compared with the prior art, the beneficial effects of the present invention are as follows: 1. This invention replaces traditional raw materials with a high proportion of fly ash, alumina-rich converter steel slag, and carbonated calcium carbide slag, directly reducing limestone usage by 15-20%, thereby significantly reducing CO2 emissions from limestone mining and high-temperature decomposition. Simultaneously, carbonation treatment of the calcium carbide slag at 800-900℃ in a CO2 atmosphere achieves two objectives: firstly, stabilizing free CaO in the calcium carbide slag to prevent subsequent volume expansion defects; secondly, consolidating CO2 from industrial waste gas within the calcium carbide slag to form stable carbonates, thus realizing the resource utilization of greenhouse gases. 2. This invention further optimizes calcination energy consumption through the innovative application of a gradient-responsive modifier. This modifier is composed of a low-temperature active component and a high-temperature catalytic component in a ratio of 4-5:6-8, and their synergistic effect lasts throughout the calcination process. The low-temperature active component, through alternating loading of Ca / Al / Si composite oxides on a nano-SiO2 support, reduces the activation energy of limestone decomposition in the 800-1100℃ range, promotes CSH formation, shortens the CaCO3 decomposition path, and significantly reduces the calcination temperature in the low-temperature section. Meanwhile, the high-temperature catalytic component, based on Ni-Co nanoparticles supported on a Zr-BP support, can accelerate the formation of tricalcium silicate crystal nuclei at 1250-1350℃, significantly reducing the overall energy consumption in the high-temperature section. Attached Figure Description

[0018] Figure 1 This is a process flow diagram for preparing the low-carbon cement clinker described in this invention; Figure 2 This is a flow chart of the preparation process of the low-temperature active component described in this invention; Figure 3 This is a flow chart of the preparation process of the high-temperature catalytic component described in this invention. Detailed Implementation

[0019] The present invention will now be clearly and completely described in conjunction with embodiments thereof. Obviously, the described embodiments are merely some, not all, of the embodiments of the present invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0020] Please see Figure 1-3 The present invention provides a technical solution: In this embodiment of the invention, the original chemical composition information of limestone raw material, fly ash raw material, alumina-rich converter steel slag raw material, and carbide slag raw material is as follows: Example 1 A method for preparing low-carbon cement clinker: S1. The gradient-responsive modifier is mixed with limestone, fly ash, alumina-rich converter steel slag and carbonated carbide slag in proportion and then mechanically ball-milled for 30 minutes (particle size D50=12μm) to obtain raw meal; S2. The raw material is heated to 800℃ and calcined for 1 hour, then heated to 1250℃ and calcined for 0.5 hours, then heated to 1350℃ and calcined for 1 hour, and then cooled to room temperature to obtain the low-carbon cement clinker; A low-carbon cement clinker, the raw materials for its preparation include the following components by mass (one mass part is defined as 100g): The carbonated carbide slag is obtained by placing carbide slag under a CO2 atmosphere and maintaining it at 800°C for 1 hour. The gradient-responsive modifier comprises a low-temperature active component and a high-temperature catalytic component; the mass ratio of the low-temperature active component to the high-temperature catalytic component is 5:8. The low-temperature active component is prepared through the following steps: S11. Disperse nano-SiO2 with a particle size of 50-80nm in a 2wt% silane coupling agent ethanol solution (solid-liquid ratio 1:10), and sonicate for 30min (power 300W, frequency 40kHz) to functionalize the surface hydroxyl groups, and prepare a SiO2 suspension. Adjust the pH of the SiO2 suspension to 9 by ammonia water. The amino group (-NH2) in KH-550 combines with the hydroxyl group on the surface of SiO2 to form a graft structure (≡Si-O-Si-(CH2)3-NH2), which enhances the adhesion of the subsequent aluminosilicate coating layer. S12. At room temperature, precursor solution A and precursor solution B are alternately added to the SiO2 suspension every 30 minutes, and the cycle is repeated 5 times to form an amorphous gel layer; the amorphous gel layer is prepared by the following chemical reaction: Ca 2+ +2Al(OH)4 - +2HSiO3 - +2OH − →CaAl2Si2O7·3H2O↓+ 3H2O; S13. The solution treated in step S12 is kept at 120°C for 4 hours, then cooled to room temperature, centrifuged, washed, and dried to obtain the low-temperature active component; when the temperature is ≥80°C, amorphous CaAl2Si2O7·3H2O begins to reconstruct, and the following reaction occurs: CaAl2Si2O7·3H2O→CaAl2Si2O7·H2O+ 2H2O; At the same time, a dense γ-type aluminosilicate crystal network will form on the surface of nano-SiO2; The silane coupling agent is model KH-550; the precursor solution A is a 0.5 mol / L calcium nitrate tetrahydrate solution, and the amount added each time is 5% of the SiO2 suspension; the precursor solution B is a mixture of 0.3 mol / L aluminum nitrate solution and 0.4 mol / L sodium silicate solution in a mass ratio of 1:1, and the amount added each time is 10% of the SiO2 suspension; When the clinker is calcined to 800℃, the outer shell of CaAl2Si2O7·H2O in the low-temperature active component will crack, releasing nano-SiO2 which reacts with Ca(OH)2 in the carbonated carbide slag to form CSH gel, filling the pores, reducing sintering resistance, and simultaneously activating Al in the alumina-rich converter slag. 3+ The calcium aluminum yellow feldspar intermediate phase is formed.

[0021] The Al in the CaAl2Si2O7·H2O shell 3+ and Si 4+ Preferential adsorption of Ca from clinker through electrostatic attraction 2+ This leads to the formation of localized high concentrations of Ca. 2+ The region. Based on the negative charge characteristics of silicates, this promotes the earlier nucleation of tricalcium silicate (C3S) during the calcination stage at 800℃, significantly increasing the formation rate of C3S. The reaction equation is shown below: 2CaO + SiO2 → C2S, which further transforms into C3S at high temperatures; The outer shell of CaAl2Si2O7·H2O undergoes gradual dissociation during the initial stage of hydration (pH>12), releasing AlO2. - and HSiO3 - Based on the cation exchange capacity of silicates, these ions react with free Ca²⁺ in the system to form hydrated calcium aluminate (C₃A·CaCO₃·H⁺). 12 The intermediate phase, which can bridge the generated CSH gel with unhydrated particles, significantly improves the 3-day compressive strength. The reaction equation is shown below: AlO2⁻ + 3Ca²+ + CO3²⁻ + 12H2O → C3A·CaCO3·12H2O↓; The high-temperature catalytic component is prepared through the following steps: S21. Mix zirconium oxynitrate dihydrate, boric acid, and diammonium hydrogen phosphate in a molar ratio of 1:2:3, dissolve in deionized water (solid-liquid ratio 1:10), and adjust the pH of the solution to 9 with ammonia water to form a precursor solution; S22. The precursor solution was subjected to hydrothermal reaction at 180°C for 24 hours, then cooled to room temperature, centrifuged, washed, and dried to obtain zirconium borophosphate support; S23. The zirconium borophosphate support is impregnated in a mixed solution of nickel nitrate solution and cobalt nitrate solution (solid-liquid ratio 1:5), ultrasonically dispersed for 30 min, heated to 500℃ and held for 2 h under a protective atmosphere, and then cooled to room temperature to obtain the high-temperature catalytic component; In step S23, in the mixed solution of nickel nitrate solution and cobalt nitrate solution, Ni 2+ and Co 2+The molar ratio is 3:1; the protective atmosphere is a mixture of hydrogen and argon in a mass ratio of 5:95. When the clinker is calcined to 1250℃, ZrBPO7 in the high-temperature catalytic component forms a heterojunction with Ni-Co nanoparticles, catalyzing the reconstruction of the aluminoferrite phase (C4AF) and promoting the uniform distribution of minerals. The reaction equation is shown below: C2A + Fe2O3 + CaO → C4AF; When the clinker is calcined to 1350℃, the BPO network remaining in the high-temperature catalytic component reacts with CaO and dissolves into the C3S lattice, thereby increasing the phase transition temperature of β-C2S→α'-C2S. The reaction equation is shown below: 3CaO + B2O3 + P2O5 → Ca3(BPO5)2.

[0022] Example 2: Example 2 differs from Example 1 in that, in Example 2, the raw materials used in the preparation include the following components by mass (one mass part is defined as 100g): The remaining steps are exactly the same as in Example 2 and Example 1.

[0023] Example 3: Example 3 differs from Example 1 in that, in Example 3, the mass ratio of the low-temperature active component to the high-temperature catalytic component in the gradient-responsive modifier is 4:6. The remaining steps are exactly the same in Example 3 and Example 1.

[0024] Example 4: Example 4 differs from Example 1 in that, in Example 4, the mass ratio of the low-temperature active component to the high-temperature catalytic component in the gradient-responsive modifier is 4:8. The remaining steps are exactly the same in Example 4 and Example 1.

[0025] Comparative Example Comparative Example 1: The only difference between Comparative Example 1 and Example 1 is that the use of the low-temperature active component in the gradient-responsive modifier was omitted in Comparative Example 1 and replaced with the same proportion of high-temperature catalytic component. The remaining steps are exactly the same in Comparative Example 1 and Example 1.

[0026] Comparative Example 2: The only difference between Comparative Example 2 and Example 1 is that the high-temperature catalytic component in the gradient-responsive modifier was removed and replaced with the same proportion of low-temperature active component in Comparative Example 2. The remaining steps are exactly the same in Comparative Example 2 and Example 1.

[0027] Performance testing: According to the requirements of GB / T 16733-1997 standard, the comprehensive calcination energy consumption of the prepared low-carbon cement clinker was tested; according to the requirements of GB / T 17671-1999 standard, the 3-day compressive strength and 28-day compressive strength of the prepared low-carbon cement clinker were tested; according to the requirements of GB / T 176-2017 standard, the free calcium oxide content of the prepared low-carbon cement clinker was tested; according to the requirements of GB / T 1346-2011 standard, the soundness pass rate of the prepared low-carbon cement clinker was tested; according to the requirements of GB / T 32151.8-2020 standard, the CO2 emission equivalent of the prepared low-carbon cement clinker was tested. The test results are shown below: As can be seen from the performance test data of Examples 1-4 and Comparative Examples 1-2, the overall calcination energy consumption of Examples 1-4 is significantly lower than that of Comparative Example 1. The main reason is that in the low-temperature calcination stage, Examples 1 and 4 introduced a low-temperature active component (nano-SiO2 loaded with Ca / Al / Si composite oxide) to reduce the activation energy of limestone decomposition, promote CSH formation, shorten the CaCO3 decomposition path, and greatly reduce the low-temperature calcination temperature. This study points out that when the mass ratio of low-temperature active component to high-temperature catalytic component is controlled at 5:8 or 4:8, the thermodynamic resistance can be reduced through a synergistic effect. For example, the chemical reaction between SiO2 surface functionalization and calcium aluminum silicate (CaAl2Si2O7·3H2O→CaAl2Si2O7·H2O+ 2H2O) can release moisture and enhance pore filling, reducing heat conduction loss. In the high-temperature calcination stage, Example 1 improved the tricalcium silicate (C3S) formation rate by using a high-temperature catalytic component (Zr-BP carrier loaded with Ni-Co), which reduced the calcination time and energy consumption. This is due to the heterojunction effect of the support material catalyzing the reconstruction of the aluminoferrite phase (C4AF), and stabilizing the mineral structure by dissolving it into the C3S lattice through the BPO network, thus reducing the waste of thermal energy caused by phase transformation lag. In contrast, Comparative Example 1, lacking a low-temperature component, requires an extended calcination time in the low-temperature section to complete the carbonate decomposition, while Comparative Example 2, due to the elimination of the high-temperature catalytic component, suffers from hindered silicate mineral formation, requiring an increase in temperature compensation reaction efficiency. The core reason for the 28-day compressive strength improvement is the synergistic effect of the gradient modifier at different temperature stages. Among the contributions of the low-temperature active components, the dissociation of CaAl2Si2O7·H2O at 800℃ releases AlO2. - and HSiO3 - Ions, these active components, are attracted to Ca in the system via electrostatic attraction. 2+The combination of these components forms calcium aluminum feldspar (C2AS) nuclei and accelerates the transformation of dicalcium silicate (C2S) to tricalcium silicate (C3S). This reaction not only accelerates C3S nucleation but also improves the uniform distribution of the mineral by stabilizing the intermediate phase. For example, the 28-day strength (62.3 MPa) of Example 1 is significantly higher than that of Comparative Example 2 (48.2 MPa) without the use of the low-temperature active component. The high-temperature catalytic component enhances mineral stability by promoting the solid solution of BPO in the C3S lattice. Specifically, Ni-Co nanoparticles supported on the Zr-BP support catalyze the reconstruction of the aluminoferrite phase (C4AF) at 1250–1350 °C, while the solid solution effect of the BPO network inhibits the phase transition from β-C2S to α'-C2S, thereby enhancing the structural strength of the lattice. The achievement of the highest strength of 64.1 MPa in Example 2 verifies the ability of the high-temperature component to repair lattice defects. In Comparative Example 1, due to the lack of low-temperature active components, C3S crystal nuclei could not be effectively generated in the low-temperature range, resulting in a significant reduction in the final C3S proportion. In Comparative Example 2, due to the lack of high-temperature catalytic components, the uniformly distributed C4AF phase could not be formed, and the weakening of the interfacial bonding force between mineral phases directly led to a decrease in strength. The phased action mechanism of gradient modifiers plays a crucial role in controlling free calcium oxide (f-CaO) and improving cement stability. Low-temperature active components effectively fill pores and inhibit calcium oxide particle agglomeration by promoting the formation of hydrated calcium silicate (CSH) gel. For example, at 800℃, the CSH network encapsulates unreacted CaO particles, preventing direct contact with water molecules and thus reducing the risk of subsequent hydration expansion. Simultaneously, high-temperature catalytic components accelerate the reconstruction of silicate minerals (such as the directional growth of active C3S nuclei) at 1250-1350℃, promoting the solidification of free calcium oxide into the mineral lattice. In the examples, the f-CaO content was less than 1%, significantly better than the 1.5% limit specified in GB 175-2020. In contrast, Comparative Example 1, lacking the introduction of low-temperature active components, could not form a sufficiently continuous CSH gel network, resulting in incomplete conversion of Ca(OH)2 to CSH. Unencapsulated CaO particles continued to react during subsequent hydration, increasing their content to 1.65%, exceeding the standard limit, causing volume expansion and resulting in approximately 20% of stability failures.

[0028] As can be seen from the above, the low-carbon cement clinker provided by the present invention has the advantages of low calcination temperature, short setting time, fast hardening speed, high early strength, continuous growth of later strength, and low carbon emissions. Moreover, the preparation process involved is simple, with low preparation cost and energy consumption, and short curing time, which has significant economic and environmental benefits.

[0029] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and variations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A low-carbon cement clinker, characterized in that, The composition by weight includes the following components: 55-60 parts limestone, 20-25 parts fly ash, 8-10 parts alumina-rich converter steel slag, 12-17 parts carbonated carbide slag, and 1.5-2.5 parts gradient-responsive modifier. The gradient-responsive modifier includes a low-temperature active component and a high-temperature catalytic component; In the gradient-responsive modifier, the mass ratio of the low-temperature active component to the high-temperature catalytic component is 4-5:6-8; The low-temperature active component is prepared through the following steps: S11. Disperse nano-SiO2 with a particle size of 50-80nm in a 2-4wt% silane coupling agent ethanol solution and sonicate for 30-40min to obtain a SiO2 suspension. S12. At room temperature, precursor solution A and precursor solution B are added alternately to the SiO2 suspension every 30 min, and the cycle is repeated 5-6 times to form an amorphous gel layer. S13. The solution treated in step S12 is kept at 120-150℃ for 4-6 hours, then cooled to room temperature, centrifuged, washed, and dried to obtain the low-temperature active component; The high-temperature catalytic component is prepared through the following steps: S21. Mix zirconium oxynitrate dihydrate, boric acid, and diammonium hydrogen phosphate in a molar ratio of 1:2:3, dissolve in deionized water, and adjust the pH of the solution to 9-10 with ammonia water to form a precursor solution; S22. The precursor solution is hydrothermally reacted at 180-200℃ for 24-28h, then cooled to room temperature, centrifuged, washed and dried to obtain zirconium borophosphate support; S23. The zirconium borophosphate support is impregnated in a mixed solution of nickel nitrate solution and cobalt nitrate solution, ultrasonically dispersed for 30-40 min, heated to 500-600℃ and held for 2-3 h under a protective atmosphere, and then cooled to room temperature to obtain the high-temperature catalytic component; The precursor solution A is a 0.5-0.6 mol / L calcium nitrate tetrahydrate solution; the precursor solution B is a mixture of a 0.3-0.4 mol / L aluminum nitrate solution and a 0.4-0.5 mol / L sodium silicate solution in a mass ratio of 1:

1.

2. The low-carbon cement clinker according to claim 1, characterized in that, In step S23, in the mixed solution of nickel nitrate solution and cobalt nitrate solution, Ni 2+ and Co 2+ The molar ratio is 3:1; the protective atmosphere is a mixture of hydrogen and argon in a mass ratio of 5:

95.

3. The low-carbon cement clinker according to claim 1, characterized in that, The carbonated carbide slag is obtained by placing carbide slag under a CO2 atmosphere and maintaining it at 800-900℃ for 1-3 hours.

4. A method for preparing low-carbon cement clinker, used to prepare the low-carbon cement clinker according to any one of claims 1-3, characterized in that, Includes the following steps: S1. The gradient-responsive modifier is mixed with limestone, fly ash, alumina-rich converter steel slag, and carbonated carbide slag in proportion and then mechanically ball-milled for 30-40 minutes to obtain raw meal; S2. The raw material is heated to 800-1100℃ and calcined for 1-2 hours, then heated to 1150-1250℃ and calcined for 0.5-1 hours, then heated to 1250-1350℃ and calcined for 1-2 hours, and finally cooled to room temperature to obtain the low-carbon cement clinker.

5. The application of the low-carbon cement clinker according to any one of claims 1-3 in the field of concrete preparation.

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