Low-carbon low-shrinkage early-strength cementing material and preparation method thereof

Abstract

The invention relates to a low-carbon low-shrinkage early-strength cementing material and a preparation method thereof. The cementing material comprises red mud, carbide slag, slag powder, fly ash, water glass, sulfate, anhydrite and halloysite nanotubes. According to the technical scheme, solid waste resources are adopted as main raw materials, a large number of chemical excitants are not used, a high-temperature and high-pressure process is not adopted in related processes, the limitation on specific components of the raw materials is low, and the selection range of the raw materials is wider; according to the technical scheme, a large amount of solid waste is mainly used, accumulation of solid waste can be reduced, and the method has the advantages of being low in carbon, environmentally friendly, good in economic benefit and the like and has very high application and popularization value. Most importantly, according to the technical scheme, early shrinkage and later shrinkage of the cementing material are improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of building materials, and particularly relates to a low-carbon, low-shrinkage and early-strength gelling material and a preparation method thereof. Background Art

[0002] The cement industry has a large carbon emission, so it is of great significance to actively develop new low-carbon gelling materials to replace traditional cement.

[0003] Red mud is an alkaline industrial waste residue discharged during the production of alumina from bauxite. The amount of red mud produced varies with the type of bauxite and the production process. For the Bayer process, 0.8 - 1.5 tons of red mud is produced per ton of alumina, and for the sintering process, 1.5 - 2.5 tons of red mud is produced per ton of alumina. The global annual red mud emission exceeds 130 million tons, and the cumulative stockpile exceeds 400 million tons. Red mud has high alkalinity and low activity. The large-scale stacking of red mud not only occupies a large amount of land resources, but also seriously pollutes the surrounding ecological environment. Therefore, researching the large-scale utilization technology of red mud and industrializing it can bring huge economic, social and environmental benefits. Making new low-carbon gelling materials from red mud is a good utilization direction because red mud contains a large amount of SiO 2 、Al 2 O 3 and alkalis, and has the potential to make alkali-activated gelling materials.

[0004] However, the following problems exist in the popularization and application of red mud-based alkali-activated gelling materials:

[0005] 1. Large shrinkage deformation (according to different time stages, the main shrinkage deformations of concrete and mortar can be divided into plastic shrinkage, chemical shrinkage, drying shrinkage, etc.). Under the same mixing ratio conditions, the shrinkage deformation of concrete and mortar prepared with red mud-based alkali-activated gelling materials is much larger than that of concrete and mortar prepared with ordinary Portland cement. This situation leads to potential safety hazards in the use of red mud-based alkali-activated gelling materials.

[0006] 2. When the red mud content is relatively high, the strength of red mud-based alkali-activated gelling materials, especially the early strength, is low; while when the red mud content is low, red mud-based alkali-activated gelling materials have problems of poor economic efficiency and difficulty in popularization.

[0007] 3. Currently, during the research on red mud-based alkali-activated gelling materials, a large amount of chemical activators are used, which does not conform to the concept of low-carbon environmental protection and has poor economic efficiency at the same time.

[0008] Patent publication CN 112694292 A discloses a low-shrinkage and high-strength red mud-slag geopolymer and its preparation method. This technical solution uses an alkali activator (sodium silicate) with a modulus of 1.92. At the same time, by strictly controlling the composition ratio of the effective components of slag powder and red mud, the shrinkage rate of the prepared mortar material is effectively controlled. However, the raw material components, modulus, and quantity of the activator in this technical solution are strictly limited. For example, the modulus of the alkali activator solution prepared in this technical solution is 1.92; the slag used in this technical solution is S95 grade slag, and the quality requirement of the slag is that the CaO content is less than 35%, SiO 2 content is less than 36%, Al 2 O 3 content is less than 16%. The quality requirement of the red mud used in this technical solution is that the CaO content is less than 15%, SiO 2 content is less than 22%, Al 2 O 3 content is less than 30%. The application limitations are relatively large,

[0009] Patent publication CN 109399975 A discloses a red mud desulfurized ash steel slag powder coupled excitation cementitious material and its application. This technical solution uses three solid wastes, namely red mud, desulfurized ash, and steel slag, for coupled excitation to prepare a cementitious material. In the early stage of hydration, ettringite generated by the reaction of calcium hydroxide (or free calcium oxide) in the solid waste, dissolved aluminum ions, and sulfate radicals in the desulfurized ash is used to improve the shrinkage performance and strength. However, in this technical solution, ettringite is the early hydration product of this cementitious material, which can improve the early plastic shrinkage and chemical shrinkage of the cementitious material, but cannot improve the later drying shrinkage of the cementitious material; in addition, the amount of red mud used in this technical solution is small (10% - 50%), and it cannot be applied on a large scale.

[0010] Patent publication CN 111018435 A discloses a high-strength and high-toughness geopolymer material and its preparation method. This technical solution uses a pre-absorbed superabsorbent resin to generate self-expansion deformation in the geopolymer to offset most of the early shrinkage of the geopolymer. However, this technical solution only improves the early drying shrinkage of the cementitious material and does not improve the later drying shrinkage of the geopolymer cementitious material; in addition, this invention uses a large amount of chemical activators (600 - 800 parts of alkali activators) and nano-modifiers (20 - 40 parts of nano-silica, 20 - 40 parts of nano-aluminum oxide), resulting in a high cost; moreover, the amount of solid wastes such as red mud used is small, and the economic benefits are poor.

[0011] Patent publication CN 112979230 B discloses a polypropylene fiber-reinforced red mud-based geopolymer material and its preparation method. This technical solution utilizes the bridging ability of polypropylene fibers and their firm adhesion to the geopolymer matrix to improve the problem of large drying shrinkage of geopolymer materials. However, this technical solution only improves the late drying shrinkage of the cementitious material, and has less improvement on the early plastic shrinkage and chemical shrinkage of the cementitious material. In addition, this technical solution uses a large amount of metakaolin (200 - 400 parts) and chemical activators (750 - 850 parts), resulting in a high cost and poor economic benefits. Summary of the Invention

[0012] The present invention aims to solve the problems of large shrinkage deformation of the existing red mud-based alkali-activated cementitious material and low strength, especially early strength, under a high red mud content. It provides a low-carbon, low-shrinkage, and early-strength cementitious material and its preparation method. The main raw materials of the technical solution of the present invention all use solid waste resources, do not use a large amount of chemical activators, and the processes involved do not use high-temperature and high-pressure processes. There are relatively low restrictions on the specific components of the raw materials, and the range of raw material selection is wider. The technical solution of the present invention mainly uses bulk solid waste, which can reduce the accumulation of solid waste, has the advantages of low carbon, environmental protection, and good economic benefits, and has high popularization and application value. Most importantly, the technical solution of the present invention improves both the early shrinkage and late shrinkage of the cementitious material.

[0013] To solve the above problems, the present invention is achieved through the following technical solutions:

[0014] The first object of the present invention is:

[0015] To provide a low-carbon, low-shrinkage, and early-strength cementitious material, which includes the following components in parts by weight:

[0016] 35 - 85 parts of red mud, 3 - 20 parts of carbide slag, 10 - 30 parts of slag powder, 0 - 20 parts of fly ash, 0 - 8 parts of water glass, 2 - 5 parts of sulfate, 3 - 10 parts of anhydrous gypsum, and 0.01 - 0.1 parts of halloysite nanotubes.

[0017] The further optimization of the low-carbon, low-shrinkage, and early-strength cementitious material of the present invention is:

[0018] The outer diameter of the halloysite nanotubes is 10 - 60 nm, the inner diameter is 5 - 25 nm, and the length is 0.5 - 3 μm.

[0019] The further optimization of the low-carbon, low-shrinkage, and early-strength cementitious material of the present invention is:

[0020] The two raw materials, red mud and carbide slag, need to be dried first, and then transported to a pulverizer to be ground to 250 - 400 meshes.

[0021] The further optimization of the low-carbon, low-shrinkage and early-strength cementitious material of the present invention is as follows:

[0022] The red mud is one or a combination of several of Bayer process red mud, sintering process red mud, and combined process red mud; and / or

[0023] In the carbide slag (after drying), the effective content of Ca(OH) 2 should be greater than 85%.

[0024] The further optimization of the low-carbon, low-shrinkage and early-strength cementitious material of the present invention is as follows:

[0025] The sulfates include one or a combination of several of sodium sulfate, potassium sulfate, and magnesium sulfate, and the effective content is not less than 90%.

[0026] The further optimization of the low-carbon, low-shrinkage and early-strength cementitious material of the present invention is as follows:

[0027] The slag powder level is not lower than S75 level, and the specific surface area is greater than 300 m 2 / kg.

[0028] The further optimization of the low-carbon, low-shrinkage and early-strength cementitious material of the present invention is as follows:

[0029] The fly ash is Class I ash or Class II ash, and the SiO 2 content is greater than 45%.

[0030] The further optimization of the low-carbon, low-shrinkage and early-strength cementitious material of the present invention is as follows:

[0031] The water glass has a modulus of 1.0 - 2.5, is in powder form, and the effective content is not less than 90%.

[0032] The further optimization of the low-carbon, low-shrinkage and early-strength cementitious material of the present invention is as follows:

[0033] The anhydrous gypsum has a fineness greater than 200 mesh.

[0034] The second object of the present invention is:

[0035] To provide a preparation method of the low-carbon, low-shrinkage and early-strength cementitious material described above (including the optimized technical solution), which includes the following preparation steps:

[0036] S1. Convey the red mud and carbide slag to a drying device at 105°C - 120°C and dry until constant weight;

[0037] S2. Convey the dried red mud and carbide slag to a pulverizer and grind them to 250 - 400 mesh, then sieve and reserve;

[0038] S3. Weigh the red mud, carbide slag, slag powder, fly ash, water glass, sulfate, anhydrous gypsum, and halloysite nanotubes obtained after the treatment in step S2 according to the raw material ratio, pour them into the mixing equipment in sequence, and stir until uniform to prepare the low-carbon, low-shrinkage, and early-strength cementitious material.

[0039] The technical solution of the present invention improves both the early shrinkage and the late shrinkage of the cementitious material.

[0040] The low-carbon, low-shrinkage, and early-strength cementitious material prepared by the present invention can completely replace ordinary Portland cement and be applied to cement concrete or cement mortar. Specific Embodiments

[0041] In order to make the application, technical solution, and advantages of the present invention clearer, the content of the present invention will be described in detail in combination with specific embodiments. It should be understood that the embodiments are only used to illustrate the present invention and do not limit the protection scope of the present invention. Any simple improvement to the preparation method of the present invention under the premise of the inventive concept of the present invention belongs to the protection scope of the present invention.

[0042] Example 1 A Low-Carbon, Low-Shrinkage, and Early-Strength Cementitious Material and Its Preparation Method

[0043] A low-carbon, low-shrinkage, and early-strength cementitious material, which comprises the following components in parts by weight:

[0044] 35 - 85 parts of red mud, 3 - 20 parts of carbide slag, 10 - 30 parts of slag powder, 0 - 20 parts of fly ash, 0 - 8 parts of water glass, 2 - 5 parts of sulfate, 3 - 10 parts of anhydrous gypsum, and 0.01 - 0.1 parts of halloysite nanotubes.

[0045] A preparation method of the low-carbon, low-shrinkage, and early-strength cementitious material described above, which comprises the following preparation steps:

[0046] S1. Transport the red mud and carbide slag to a drying equipment at 105°C - 120°C and dry until constant weight;

[0047] S2. Transport the dried red mud and carbide slag to a pulverizer and grind them to 250 - 400 meshes, and sieve them for standby;

[0048] S3. Weigh the red mud, carbide slag, slag powder, fly ash, water glass, sulfate, anhydrous gypsum, and halloysite nanotubes obtained after the treatment in step S2 according to the raw material ratio, pour them into the mixing equipment in sequence, and stir until uniform to prepare the low-carbon, low-shrinkage, and early-strength cementitious material.

[0049] The outer diameter of the halloysite nanotubes is 10 - 60 nm, the inner diameter is 5 - 25 nm, and the length is 0.5 - 3 μm.

[0050] The two raw materials, namely red mud and carbide slag, need to be dried first and then conveyed to a pulverizer to be ground to 250 - 400 mesh.

[0051] The red mud mentioned is a mixture between Bayer red mud and sintered red mud.

[0052] The Ca(OH) 2 in the carbide slag (after drying) should have an effective component greater than 85%.

[0053] The sulfates mentioned include one or a combination of several of sodium sulfate, potassium sulfate, and magnesium sulfate, and the effective component is not less than 90%.

[0054] The slag powder is not less than S75 grade, and the specific surface area is greater than 300 m 2 / kg.

[0055] The fly ash mentioned is grade I ash or grade II ash, and the SiO 2 content is greater than 45%.

[0056] The water glass has a modulus of 1.0 - 2.5, is in powder form, and the effective component is not less than 90%.

[0057] The anhydrous gypsum has a fineness of 300 mesh.

[0058] The preparation methods of Examples 2 - 5 are the same as that of the Example, and the main difference lies in partial differences in the specific raw material compositions.

[0059] The specific raw material compositions of each experimental group in Examples 1 - 5 of the low - carbon, low - shrinkage, early - strength gelling material of the present invention are shown in Table 1:

[0060] Table 1 Specific raw material compositions of each experimental group in Examples 1 - 5 (parts by weight)

[0061] Project Red mud Calcium carbide slag Ground granulated blast-furnace slag Fly ash Sodium silicate Sodium sulfate Anhydrous gypsum Halloysite nanotubes Example 1 62 6 23 4 4 3 4 0.03 Example 2 78 5 15 0 3 2 3 0.01 Example 3 71 4 10 3 5 2 3 0.05 Example 4 66 7 25 2 4 3 6 0.04 Example 5 60 12 17 9 6 4 7 0.03

[0062] To further illustrate the performance of the above - mentioned gelling material, its performance was tested with reference to the following test methods.

[0063] 1. Compressive strength performance test: Specimens were molded using GB / T 17671 - 2021 "Test Method for Cement Mortar Strength", and then cured at (20 ± 1)°C and a relative humidity of not less than 90% until the test age.

[0064] 2. Shrinkage rate performance test: Referring to JC / T 603 "Test Method for Dry Shrinkage of Cement Mortar", after the specimens were cured for 1 d at (20 ± 1)°C and a relative humidity of not less than 90% and then demolded, after measuring the initial length, they were cured in an environment with a temperature of (23 ± 2)°C and a relative humidity of (50 ± 5)% until the corresponding age to measure the shrinkage value.

[0065] 3. Test mix ratios, in terms of cementitious materials:

[0066] Example 1: The cementitious material refers to Example 1 in Table 1;

[0067] Comparative Example 1: The cementitious material does not add halloysite nanotubes, and the rest is the same as Example 1 in Table 1;

[0068] Comparative Example 2: The cementitious material does not add anhydrous gypsum (replacing anhydrous gypsum with an equal amount of 300-mesh heavy calcium), and the rest is the same as Example 1 in Table 1;

[0069] Comparative Example 3: The cementitious material does not add halloysite nanotubes and anhydrous gypsum (replacing anhydrous gypsum with an equal amount of 300-mesh heavy calcium), and the rest is the same as Example 1 in Table 1;

[0070] Comparative Example 4: The cementitious material does not add sodium sulfate (replacing sodium sulfate with an equal amount of 300-mesh heavy calcium), and the rest is the same as Example 1 in Table 1;

[0071] Comparative Example 5: The mix ratio of the cementitious material is as follows: 62 parts of red mud, 23 parts of slag powder, 4 parts of fly ash, 8 parts of water glass (modulus 1.5), and 3 parts of sodium hydroxide (analytical pure). All the activators used in this comparative example are chemical activators;

[0072] Comparative Example 6: The cementitious material uses ordinary Portland cement 425;

[0073] Mortar mix ratio, cement-sand ratio 1:2, and the sand used is 20 - 140 mesh river sand; the water-cement ratio is determined according to the mortar fluidity, and the fluidity range is controlled at (160 ± 5) mm.

[0074] The relevant test data are shown in Table 2:

[0075] Table 2 Test Data of Each Example and Comparative Example

[0076]

[0077]

[0078] It can be seen from Example 1 and Comparative Examples 1, 2, and 3 in the above table that both halloysite nanotubes and anhydrous gypsum can reduce the late shrinkage rate of the cementitious material, but the combined addition of the two has a better effect; in addition, halloysite nanotubes have a positive impact on the strength of the cementitious material, especially the late strength.

[0079] It can be seen from Example 1 and Comparative Example 4 in the above table that adding sodium sulfate can improve the early strength and early shrinkage rate of the cementitious material.

[0080] As can be seen from Example 1 and Comparative Example 5 in the above table, the shrinkage rate of the cementitious material prepared by the system of the present invention is much lower than that of the pure chemically activated cementitious material at all ages, and the shrinkage performance has been greatly improved.

[0081] As can be seen from Example 1 and Comparative Example 6 in the above table, the shrinkage rate of the cementitious material prepared by the present invention is lower than that of 42.5-grade ordinary Portland cement at all ages; at the same time, both the early strength and the late strength are higher than those of 42.5-grade ordinary Portland cement.

[0082] In summary, the low-carbon, low-shrinkage and early-strength cementitious material prepared by the present invention can completely replace ordinary Portland cement and be applied to cement concrete or cement mortar.

[0083] In conclusion, the above are only the preferred examples of the present invention, and there is no any formal limitation to the present invention; any equivalent changes, modifications and evolutions made by those skilled in the art within the scope of the technical solution of the present invention by using the disclosed technical content are regarded as the equivalent examples of the present invention; at the same time, any equivalent changes, modifications and evolutions made to the above embodiments according to the essence of the present invention still fall within the protection scope of the technical solution of the present invention.

[0084] The technical features of the above-described embodiments can be combined arbitrarily. For the sake of concise description, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, it should be considered that the scope described in this specification.

[0085] The experimental methods without specific conditions in the present invention are usually carried out under conventional conditions or according to the conditions recommended by the manufacturer.

[0086] For various optimized technical solutions in the present invention, unless otherwise stated, the various optimized technical solutions can be combined with each other.

[0087] Unless otherwise stated, the percentages and parts are weight percentages and weight parts.

[0088] The experimental methods without specific conditions in the specification and embodiments are usually carried out under conventional conditions or according to the conditions recommended by the manufacturer.

[0089] Unless otherwise defined, all professional and scientific terms used herein have the same meaning as those familiar to those skilled in the art. In addition, any methods and materials similar or equivalent to the described content can be applied to the method of the present invention.

Claims

1. A low-carbon, low-shrinkage and early-strength cementitious material, characterized in that: it comprises the following components by weight: 35-85 parts of red mud, 3-20 parts of carbide slag, 10-30 parts of slag powder, 0-20 parts of fly ash, 0-8 parts of water glass, 2-5 parts of sulfate, 3-10 parts of anhydrous gypsum, 0.01-0.1 parts of halloysite nanotubes.

2. The low-carbon, low-shrinkage and early-strength cementitious material according to claim 1, characterized in that: the outer diameter of the halloysite nanotubes is 10-60 nm, the inner diameter is 5-25 nm, and the length is 0.5-3 μm.

3. The low-carbon, low-shrinkage and early-strength cementitious material according to claim 1, characterized in that: the two raw materials of red mud and carbide slag need to be dried first, and then transported to a pulverizer to be ground to 250-400 meshes.

4. The low-carbon, low-shrinkage and early-strength cementitious material according to claim 1, characterized in that: the red mud is one or a combination of several of Bayer process red mud, sintering process red mud, and combined process red mud; and / or The Ca(OH) in the carbide slag mentioned above 2 The effective component content should be greater than 85%.

5. The low-carbon, low-shrinkage and early-strength cementitious material according to claim 1, characterized in that: the sulfate includes: one or a combination of several of sodium sulfate, potassium sulfate, and magnesium sulfate, and the active ingredient is not less than 90%.

6. The low-carbon, low-shrinkage and early-strength cementitious material according to claim 1, characterized in that: The slag powder mentioned above is not lower than S75 grade, and the specific surface area is greater than 300 m 2 / kg.

7. The low-carbon, low-shrinkage and early-strength cementitious material according to claim 1, characterized in that: The fly ash described is Class-I fly ash or Class-II fly ash, with the SiO 2 content being greater than 45%.

8. The low-carbon, low-shrinkage and early-strength cementitious material according to claim 1, characterized in that: the water glass has a modulus of 1.0-2.5, is a powder, and the active ingredient is not less than 90%.

9. The low-carbon, low-shrinkage and early-strength cementitious material according to claim 1, characterized in that: the anhydrous gypsum has a fineness greater than 200 meshes.

10. A preparation method of the low-carbon, low-shrinkage and early-strength cementitious material according to claim 1, characterized in that: it comprises the following preparation steps: S1. Transport the red mud and carbide slag to a drying device at 105°C - 120°C and dry to constant weight; S2. Transport the dried red mud and carbide slag to a pulverizer to grind to 250-400 meshes, and sieve for standby; S3. Weigh the red mud, carbide slag, slag powder, fly ash, water glass, sulfate, anhydrous gypsum, and halloysite nanotubes obtained after the treatment in step S2 respectively according to the raw material ratio, pour them into a mixing device in sequence, and stir until uniform to prepare the low-carbon, low-shrinkage and early-strength cementitious material.

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