Modified limestone powder, method for preparing the same, and use thereof

Abstract

The application discloses modified limestone powder and a preparation method and application thereof, and belongs to the technical field of building materials. The application provides a preparation method of modified limestone powder, and the preparation method comprises the following steps: mixing and grinding limestone raw materials and grinding aids. The grinding aids comprise sodium pyrophosphate, sodium gluconate, sodium citrate, an alcohol amine compound and water. According to the preparation method, the particle size of the obtained modified limestone powder can be effectively reduced, the sphericity of the modified limestone powder can be improved, and the content of free calcium ions in the modified limestone powder can be reduced. The application further provides the modified limestone powder prepared by the above preparation method and application of the obtained modified limestone powder.

Description

Technical Field

[0001] This invention relates to the field of building materials technology, and in particular to a modified limestone powder, its preparation method, and its application. Background Technology

[0002] The cement industry is a major energy-consuming industry. To achieve energy conservation and environmental protection, it is urgent to reduce cement usage without compromising the strength and other properties of cement-based building materials. To address these technical challenges, researchers have attempted to use admixtures to replace a portion of the cement.

[0003] Admixtures include active and inactive admixtures. Active admixtures include fly ash, which is currently a mature admixture used in concrete. It is widely popular because it participates in the hydration process and improves strength. However, the uneven distribution of fly ash production and the increased transportation costs of concrete necessitate the development of new admixtures. Therefore, the aforementioned inactive admixtures have emerged, specifically including limestone powder, dolomite powder, and mineral powder. Their mechanism of action in concrete mainly includes morphological effects, activity effects, and nucleation effects. Specifically, small particle sizes can fill the gaps in concrete and act as nuclei to accelerate the hydration process. Small amounts of inactive admixtures have extremely low activity. Based on the above analysis, it is clear that as inactive admixtures, their particle size needs to be reduced to better exert their effects.

[0004] To reduce the particle size of inactive admixtures, they are usually ground before use. However, due to limitations in grinding equipment and the potential for further agglomeration of small particles, it is difficult to further reduce the particle size of the resulting inactive admixtures. Furthermore, admixtures such as limestone powder may generate free calcium ions, which can degrade the carbonation performance of the resulting concrete, thereby worsening its strength and impermeability.

[0005] In summary, existing admixtures such as limestone powder have limited particle size reduction potential, and the calcium ions they contain may degrade the overall performance of concrete. Summary of the Invention

[0006] The present invention aims to at least solve one of the technical problems existing in the prior art. To this end, the present invention proposes a method for preparing modified limestone powder, which can effectively reduce the particle size of the obtained modified limestone powder, improve its sphericity, and at the same time reduce the content of free calcium ions therein.

[0007] The present invention also provides modified limestone powder prepared by the above preparation method.

[0008] The present invention also provides a method for preparing concrete using the above-mentioned modified limestone powder as a raw material.

[0009] The present invention also provides a method for mixing the above-mentioned concrete.

[0010] The present invention also provides applications of the above-mentioned concrete.

[0011] According to an embodiment of a first aspect of the present invention, a method for preparing modified limestone powder is provided, the method comprising mixing and grinding limestone raw materials and grinding aids;

[0012] The grinding aid comprises sodium pyrophosphate (CAS: 7722-88-5), sodium gluconate (CAS: 527-07-1), sodium citrate (CAS: 68-04-2), an alcohol amine compound, and water.

[0013] The preparation method according to embodiments of the present invention has at least the following beneficial effects:

[0014] The grinding aid used in this invention includes sodium pyrophosphate and an alkanolamine compound, which can significantly improve the dispersion performance of limestone powder and prevent the finely ground limestone powder from re-agglomerating.

[0015] The grinding aid used in this invention includes sodium gluconate, which can significantly improve the flowability of limestone powder, improve grinding efficiency, and improve the sphericity of the resulting modified limestone powder.

[0016] The grinding aid provided by this invention includes sodium pyrophosphate, sodium gluconate, and sodium citrate. The three work synergistically to maximize the fixation of free calcium ion content in modified limestone powder, thereby improving the carbonation resistance of concrete containing the modified limestone powder.

[0017] The grinding aid used in this invention includes alkanolamine compounds, which can be used as early strength agents to improve the early strength performance of concrete containing the modified limestone powder.

[0018] In the preparation method provided by the present invention, modified limestone powder with small particle size and high sphericity can be obtained by limiting the type of grinding aid, and the modified limestone powder can improve the carbonation resistance and early strength performance of concrete.

[0019] According to some embodiments of the present invention, the particle size of the limestone raw material is between 0.5 and 3 mm. For example, it can be about 1 mm. Since further grinding is required, the particle size is not strictly limited in actual production, as long as it is compatible with the grinding equipment.

[0020] According to some embodiments of the present invention, the mass ratio of limestone powder to grinding aid is 100:0.05 to 0.5. Specifically, it can be 100:0.15 to 0.25. More specifically, it can be about 100:0.2.

[0021] According to some embodiments of the present invention, the grinding aid, by weight percentage, comprises:

[0022]

[0023] According to some embodiments of the present invention, the sodium pyrophosphate accounts for 11-13% of the mass of the grinding aid. Specifically, it can be about 12%.

[0024] According to some embodiments of the present invention, the sodium gluconate accounts for 3-4% of the mass percentage of the grinding aid. Specifically, it may be about 3.5%.

[0025] According to some embodiments of the present invention, the sodium citrate accounts for 9-12% of the mass percentage of the grinding aid. Specifically, it can be about 10%.

[0026] According to some embodiments of the present invention, the alkanolamine compound is present in a mass percentage of 25% to 35% of the grinding aid. Specifically, it may be about 30% or about 33%.

[0027] According to some embodiments of the present invention, the amine compound includes at least one of triethanolamine (CAS: 102-71-6), triisopropanolamine (CAS: 122-20-3), diethanol monoisopropanolamine (CAS: 6712-98-7), and diisopropylethanolamine (CAS: 96-80-0).

[0028] According to some embodiments of the present invention, the alkanolamine compound includes triethanolamine and diisopropylethanolamine. The molar ratio of triethanolamine to diisopropylethanolamine is 1:0.8 to 1.2. More specifically, it can be about 1:1.

[0029] According to some embodiments of the present invention, the equipment used for the mixing and grinding includes at least one of a vertical mill or a roller mill.

[0030] According to some embodiments of the present invention, the mixing and grinding time is 30 to 60 minutes. Within this time range, the corresponding specific surface area can be achieved, and the time consumption is short, resulting in energy savings.

[0031] According to some embodiments of the present invention, the mixing and grinding time is 40 to 50 minutes. For example, it can be about 45 minutes.

[0032] According to an embodiment of the second aspect of the present invention, a modified limestone powder prepared by the preparation method described above is provided, wherein the modified limestone powder has a sieve residue rate of ≤10% on a 45μm square hole sieve.

[0033] Since the modified limestone powder adopts all the technical solutions of the preparation method in the above embodiments, it has at least all the beneficial effects brought about by the technical solutions in the above embodiments. Furthermore, the modified limestone powder has a small particle size, high uniformity, high sphericity, and low free calcium ion content, thus significantly improving the overall performance of concrete including the modified limestone powder.

[0034] According to some embodiments of the present invention, the modified limestone powder has a calcium carbonate content of ≥75%. Specifically, it may be about 80% or about 85%.

[0035] According to some embodiments of the present invention, the specific surface area of ​​the modified limestone powder is ≥300 m². 2 / kg. For example, it could be approximately 700m³. 2 / kg.

[0036] According to some embodiments of the present invention, the modified limestone powder has a sieve residue of ≤7% on a 45μm square-hole sieve. Specifically, it can be approximately 6.5%.

[0037] According to an embodiment of a third aspect of the present invention, a concrete is provided, the raw materials for preparing the concrete including the modified limestone powder, as well as cement, fly ash, aggregate, polycarboxylate superplasticizer and water; the polycarboxylate superplasticizer is grafted with sulfonic acid groups.

[0038] The concrete according to embodiments of the present invention has at least the following beneficial effects:

[0039] Since the concrete adopts all the technical solutions of the modified limestone powder in the above embodiments, it has at least all the beneficial effects brought about by the technical solutions in the above embodiments.

[0040] In traditional techniques, concrete with added limestone powder has difficulty improving early strength, requiring approximately 200 days to achieve a high strength. However, in this invention, the modified limestone powder and fly ash have a synergistic effect, which, when combined, can improve the early strength of the resulting concrete.

[0041] Furthermore, the sulfonic acid groups on the polycarboxylate superplasticizer have a strong binding ability with free calcium ions, thereby creating a synergistic effect between the polycarboxylate superplasticizer and the modified limestone powder, further improving the carbonation resistance of the resulting concrete.

[0042] According to some embodiments of the present invention, the grade of the cement is not lower than P·O42.5.

[0043] According to some embodiments of the present invention, the mass ratio of the modified limestone powder to cement is 1.5 to 3.5:5. The mass of the modified limestone powder refers only to the mass of the solid product. The mass ratio of the modified limestone powder to cement is 2 to 3:5. For example, it can be approximately 1:2.

[0044] According to some embodiments of the present invention, the mass ratio of the fly ash to the cement is 1 to 3:5. For example, it can be approximately 1:2.

[0045] According to some embodiments of the present invention, the mass ratio of the modified limestone powder, cement, and fly ash to the mass of the aggregate is 1:4.5 to 5.5. For example, it can be approximately 1:5.

[0046] According to some embodiments of the present invention, the residue rate of the fly ash on a 45μm square-hole sieve is ≤30% (Grade II fly ash). For example, it can be ≤12% (Grade I fly ash).

[0047] According to some embodiments of the present invention, the aggregate includes coarse aggregate and fine aggregate.

[0048] According to some embodiments of the present invention, the mass ratio of fine aggregate to coarse aggregate is 0.5 to 0.8:1. For example, it can be approximately 1:1.

[0049] According to some embodiments of the present invention, the fine aggregate includes at least one of river sand and manufactured sand.

[0050] According to some embodiments of the present invention, the fine aggregate comprises river sand and manufactured sand. The mass ratio of the river sand to the manufactured sand is 1:0.8 to 1.2. Specifically, it can be approximately 1:1.

[0051] According to some embodiments of the present invention, the particle size of the fine aggregate is 0.15 to 2.36 mm.

[0052] According to some embodiments of the present invention, the coarse aggregate includes at least one of crushed stone and steel slag.

[0053] According to some embodiments of the present invention, the particle size of the coarse aggregate is 8 to 25 mm.

[0054] According to some embodiments of the present invention, the polycarboxylate superplasticizer accounts for 0.1% to 1% of the total mass of the modified limestone powder, cement, and fly ash. Specifically, it may be about 0.3%.

[0055] According to some embodiments of the present invention, in the concrete, the mass ratio of cement to water is 1.5 to 2.5:1. For example, it can be approximately 2:1.

[0056] According to an embodiment of a fourth aspect of the present invention, a method for mixing the concrete is provided, the method comprising mixing the polycarboxylate superplasticizer, the modified limestone powder and water; and then mixing it with the mixture of cement and aggregate.

[0057] The mixing method according to embodiments of the present invention has at least the following beneficial effects:

[0058] This invention first mixes the polycarboxylate superplasticizer and the modified limestone powder, which facilitates the bonding between the sulfonate groups on the polycarboxylate superplasticizer and the free calcium ions in the modified limestone powder. This further enhances the overall performance of the resulting concrete.

[0059] According to some embodiments of the present invention, the mixing method includes mixing the cement and aggregate to obtain a solid mixture; mixing the polycarboxylate superplasticizer, the modified limestone powder and water to obtain a solid-liquid mixture; and mixing the solid mixture with the solid-liquid mixture.

[0060] According to some embodiments of the present invention, in the mixing method, the mixing process in each step includes stirring. The specific stirring time can be determined according to the equipment conditions in actual production, as long as uniform mixing is achieved.

[0061] According to an embodiment of the fifth aspect of the present invention, the application of the concrete described herein is provided in the construction of mine shafts, railway tunnels, water diversion culverts, and underground engineering projects.

[0062] Since the application adopts all the technical solutions of the concrete in the above embodiments, it has at least all the beneficial effects brought about by the technical solutions in the above embodiments.

[0063] Unless otherwise specified, the term "about" in this invention actually means that the error is allowed to be within ±2%, for example, about 100 is actually 100 ± 2% × 100.

[0064] Unless otherwise specified, "between" in this invention includes the number itself, for example, "between 2 and 3" includes the endpoint values ​​2 and 3.

[0065] Other features and advantages of the invention will be set forth in the description which follows, and will be apparent in part from the description, or may be learned by practicing the invention. Detailed Implementation

[0066] The following will describe the concept and technical effects of the present invention clearly and completely with reference to embodiments, so as to fully understand the purpose, features and effects of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are all within the scope of protection of the present invention.

[0067] In the description of this invention, the terms "one embodiment," "some embodiments," "illustrative embodiment," "example," "specific example," or "some examples," etc., refer to specific features, structures, materials, or characteristics described in connection with that embodiment or example, which are included in at least one embodiment or example of the invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0068] Unless otherwise specified, the parameters of the raw materials used in the specific implementation method are as follows:

[0069] The limestone raw material was purchased from Yunnan Highway Investment and Construction Co., Ltd., with a calcium carbonate content of 82% and an average particle size (DV50) of approximately 1 mm; the calcium carbonate content is ≥82%.

[0070] The amine compound is a mixture of triethanolamine and diisopropylethanolamine in a 1:1 molar ratio.

[0071] The cement grade is P·O42.5;

[0072] The fly ash is Grade II fly ash produced by Shenhua Guohua Shouguang Power Generation Co., Ltd.; the residue rate on a 45μm square mesh sieve is ≤25%.

[0073] The coarse aggregate is crushed stone, with a particle size continuously distributed between 8 and 25 mm.

[0074] The fine aggregate is a mixture of river sand and manufactured sand in a 1:1 mass ratio; the fine aggregate has a continuous particle size distribution of 0.15 to 2.36 mm.

[0075] The polycarboxylate superplasticizer was purchased from Qingdao Dingchang New Materials Manufacturer. The model is aminosulfonate high-efficiency superplasticizer (ASP), which is an aromatic aminosulfonate polymer.

[0076] Example 1

[0077] This example demonstrates the preparation of a modified limestone powder. The specific preparation method is as follows:

[0078] The limestone raw material and grinding aid were mixed at a mass ratio of 100:0.2 and then ground into powder in a vertical grinding mill for 45 minutes.

[0079] The modified limestone powder had a residue of approximately 7% on a 45μm square-hole sieve; its specific surface area (BET test) was approximately 700 m². 2 / kg. The composition of the grinding aid used in this example is shown in Table 1.

[0080] SEM analysis showed that the particles had high uniformity in size and were mostly spherical or near-spherical.

[0081] Example 2 and Comparative Examples 1-3 each prepared a modified limestone powder, the specific difference from Example 1 being:

[0082] The composition of the grinding aid used is slightly different, and the specific composition is shown in Table 1.

[0083] Table 1. Composition (mass percentage) of the grinding aids used in Examples 1-2 and Comparative Examples 1-3

[0084] Example 1 Example 2 Comparative Example 1 Comparative Example 2 Comparative Example 3 Sodium pyrophosphate 13 11 25 13 / Sodium gluconate 3 4 3 / 3 Sodium citrate 12 9 / 15 12 Alkylamine compounds 30 35 30 30 43 water margin margin margin margin margin

[0085] Example 3

[0086] This example demonstrates the preparation of a type of concrete, with the following specific steps:

[0087] A solid-liquid mixture was obtained by mixing polycarboxylate superplasticizer, modified limestone powder (from Example 1), and water.

[0088] Cement, coarse aggregate, and fine aggregate are mixed to obtain a solid mixture;

[0089] The above solid-liquid mixture and solid mixture are further mixed to obtain the final concrete.

[0090] The composition of the raw materials prepared in this example is as follows (by weight):

[0091]

[0092]

[0093] The weight of the modified limestone powder refers only to the mass of the solid product in Example 1.

[0094] Example 4

[0095] This example prepared a type of concrete, which differs from Example 3 in that:

[0096] The modified limestone powder used was from Example 2.

[0097] Comparative Example 4

[0098] This example prepared a type of concrete, which differs from Example 3 in that:

[0099] The modified limestone powder used was from Comparative Example 1.

[0100] Comparative Example 5

[0101] This example prepared a type of concrete, which differs from Example 3 in that:

[0102] The modified limestone powder used was from Comparative Example 2.

[0103] Comparative Example 6

[0104] This example prepared a type of concrete, which differs from Example 3 in that:

[0105] The modified limestone powder used was from Comparative Example 3.

[0106] Comparative Example 7

[0107] This example prepared a type of concrete, which differs from Example 3 in that:

[0108] The raw materials used in the preparation do not include fly ash, and the amount of cement used is increased; the details are as follows:

[0109]

[0110] Comparative Example 8

[0111] This example demonstrates the preparation of a type of concrete. The composition of the raw materials used in this preparation is the same as in Example 1, and the preparation steps are as follows:

[0112] Polycarboxylate superplasticizer and water are mixed to obtain a solid-liquid mixture;

[0113] Modified limestone powder (from Example 1), cement, coarse aggregate and fine aggregate are mixed to obtain a solid mixture; the above solid-liquid mixture and solid mixture are further mixed to obtain the mixed concrete.

[0114] The modified limestone powder used in this example is from the examples or comparative examples.

[0115] Test case

[0116] The first aspect of this example tested the morphology and sieve residue of the modified limestone powder obtained in Examples 1-2 and Comparative Examples 1-3; the morphology was tested using SEM, mainly observing its morphological uniformity and sphericity. The test results are shown in Table 2.

[0117] Table 2. Morphology and sieve residue of modified limestone powder obtained in Examples 1-2 and Comparative Examples 1-3 on a 45 μm square mesh sieve.

[0118]

[0119] Table 3 shows that the modified limestone powder prepared by the method provided in this embodiment of the invention has the characteristics of small particle size, good dispersibility, uniform distribution, and high sphericity. When added to concrete, it is expected to improve its workability and strength. If sodium citrate is not included, the morphology is not significantly affected, but the sieve residue rate will increase slightly, indicating that sodium citrate also has a certain dispersing effect. If sodium gluconate is omitted, the fluidity of the mixture during grinding may be reduced, not only decreasing grinding efficiency but also decreasing the sphericity of the obtained modified limestone powder, with obvious burrs appearing on the surface. If sodium pyrophosphate is omitted, the dispersibility of the mixture during grinding decreases, therefore the small-particle-size product obtained during grinding will agglomerate again, and the sieve residue rate will increase significantly.

[0120] The second aspect of this example tested the performance of the concrete obtained in Examples 3-4 and 4-8, specifically workability (slump, spread, segregation, and seepage), compressive strength at different ages, and carbonation resistance. Workability was tested according to the national standard GB / T50080-2002; compressive strength was tested according to the national standard GB / T50107-2010; and carbonation testing was conducted according to the method in GB / T 50082-2009 "Standard for Test Methods of Long-Term Performance and Durability of Ordinary Concrete". Concrete specimens were placed in a carbonation chamber with a CO2 volume concentration of (20±3)%, a temperature of (20±2)℃, and a relative humidity of (70±5)%. The carbonation depth of the concrete at 28 days was measured using vernier calipers. The grade of carbonation resistance of the concrete was evaluated according to GB 50164-2011 "Standard for Quality Control of Concrete". The results of the above tests are shown in Table 3.

[0121] Table 3. Properties of concrete obtained in Examples 3-4 and 4-8

[0122]

[0123]

[0124] Table 3 shows that the concrete obtained in the embodiments of the present invention has excellent workability, strength and carbonation resistance.

[0125] The comparison of workability results shows that if the composition of the grinding aid is not within the range provided by this invention, the workability is deteriorated due to the deterioration of the morphology of the resulting modified limestone powder. Overall, the workability tends to improve with the increase of particle size uniformity and fineness. Furthermore, in this invention, the combination of fly ash and modified limestone powder also improves the workability of the resulting concrete to a certain extent.

[0126] The comparison of strength results shows that the particle size and morphology of modified limestone powder have a certain influence on the strength, and the smaller the particle size and the higher the uniformity, the better the strength. In addition, a synergistic effect occurred between fly ash and modified limestone powder, which can improve the early strength of the resulting concrete. If fly ash is omitted, the early strength of the resulting concrete will decrease significantly, and the strength will gradually increase after 90 days.

[0127] The comparison of carbonation depth results shows that the preparation method of the modified limestone powder provided by the present invention and the mixing method of concrete both affect the carbonation depth. Specifically, if the grinding aid components are not within the range provided by the present invention, or if the modified limestone powder and polycarboxylate superplasticizer are not mixed first, the free calcium ions cannot be well fixed, which will lead to an increase in carbonation depth.

[0128] In summary, the modified limestone powder preparation method provided by this invention, which combines modified limestone powder with fly ash and optimizes the preparation process, can significantly improve the overall performance of the resulting concrete. The resulting concrete is expected to be used in mine shafts, railway tunnels, water diversion culverts, and underground engineering construction.

[0129] The embodiments of the present invention have been described in detail above. However, the present invention is not limited to the above embodiments. Within the scope of knowledge possessed by those skilled in the art, various changes can be made without departing from the spirit of the present invention. Furthermore, the embodiments of the present invention and the features thereof can be combined with each other unless otherwise specified.

Claims

1. A method for preparing modified limestone powder, characterized in that, The preparation method includes mixing and grinding limestone raw materials and grinding aids; The mass ratio of the limestone raw material to the grinding aid is 100:0.05~0.5; The grinding aid, by weight percentage, comprises: Sodium pyrophosphate 10-15%; Sodium gluconate 1-5%; Sodium citrate 8~15%; Alkylamine compounds: 15-40%; Water balance.

2. A modified limestone powder prepared by the method described in claim 1, characterized in that, The modified limestone powder has a sieve residue rate of ≤10% on a 45μm square hole sieve.

3. The modified limestone powder according to claim 2, characterized in that, The modified limestone powder has a calcium carbonate content of ≥75%; and / or, the modified limestone powder has a specific surface area of ​​≥300 m². 2 / kg.

4. A type of concrete, characterized in that, The raw materials for preparing the concrete include the modified limestone powder as described in claim 2 or 3, as well as cement, fly ash, aggregate, polycarboxylate superplasticizer and water; the polycarboxylate superplasticizer is grafted with sulfonic acid groups.

5. The concrete according to claim 4, characterized in that, The mass ratio of the modified limestone powder to cement is 1.5 to 3.5:5; and / or, the mass ratio of the fly ash to the cement is 1 to 3:

5.

6. The concrete according to claim 4, characterized in that, The mass ratio of the modified limestone powder, cement, and fly ash to the aggregate is 1:4.5~5.5; and / or, the polycarboxylate superplasticizer accounts for 0.1~1% of the mass ratio of the modified limestone powder, cement, and fly ash.

7. A method for mixing concrete as described in any one of claims 4 to 6, characterized in that, This includes mixing the polycarboxylate superplasticizer, the modified limestone powder, and water; and then mixing it with the mixture of cement and aggregates.

8. The application of concrete as described in any one of claims 4 to 6 in the construction of mine shafts, railway tunnels, water diversion culverts, and underground engineering projects.

Images