A high durability slag-sulphoaluminate cement and a method for its production

Abstract

The application belongs to the technical field of special cement, and discloses a high-durability slag sulphoaluminate cement and a preparation method thereof. The cement comprises the following components in parts by mass: main granulated blast furnace slag powder; nitrate type LDH-calcium carbonate composite nucleation slag; calcium sulphoaluminate-calcium sulphosilicate composite clinker; anhydrous gypsum or hard gypsum; metakaolin, silica fume or a mixture of the two; calcium nitrate; grinding and dispersing components; wherein the surface of the nitrate type LDH-calcium carbonate composite nucleation slag has an in-situ generated nanometer calcium carbonate inner layer and a nitrate type LDH outer layer from inside to outside. The application uses the main slag powder and the functionalized slag in combination, the main slag powder undertakes the later continuous hydration and low-carbon cementation, and the functionalized slag undertakes the early nucleation, interface filling and ion retardation, so that the high early strength can be maintained under a high slag content.

Description

Technical Field

[0001] This invention belongs to the field of special cement materials technology, specifically relating to a high-durability slag sulfoaluminate cement and its preparation method. Background Technology

[0002] Slag sulfoaluminate cement typically uses granulated blast furnace slag, sulfoaluminate clinker, and gypsum-based sulfate components as main raw materials. It features low clinker content, low heat of hydration, and rapid early strength development, making it suitable for low-carbon cementitious systems. However, under conditions of high slag content and corrosive environments, existing slag sulfoaluminate cement still has the following shortcomings: Firstly, in high slag content systems, the slag reaction is greatly affected by fineness, glass content, alkalinity, and sulfate concentration, resulting in unstable early reaction initiation and fluctuations in early intensity.

[0003] Secondly, the ettringite formed by the reaction of sulfoaluminate clinker and gypsum is greatly affected by changes in sulfate, aluminate and alkalinity in the system. If the hydration process is unbalanced, it can easily lead to insufficient strength growth, decreased volume stability or reduced durability in the later stages.

[0004] Third, ordinary powder compounding is difficult to effectively reduce the proportion of interconnected pores. Chloride ions and sulfate ions can still migrate along the pore channels, resulting in insufficient durability in environments such as marine engineering, salt lakes, underground anti-seepage and sewage treatment structures.

[0005] Fourth, existing methods of externally adding nano-calcium carbonate, LDH, calcium nitrate, or ultrafine slag mostly remain at the level of adding a single component or simple powder mixing, making it difficult to achieve a stable synergistic effect between nucleating components, ion-blocking components, and the slag reaction interface.

[0006] Therefore, there is an urgent need for a highly durable slag sulfoaluminate cement system that can simultaneously regulate the slag reaction interface, ettringite stability, and erosion ion transport channels. Summary of the Invention

[0007] The purpose of this invention is to provide a high-durability slag sulfoaluminate cement and its preparation method, which improves the early strength, later strength stability, chloride ion transport resistance, sulfate attack resistance, impermeability, freeze-thaw resistance and volume stability of the cement while maintaining a high slag content and a low clinker content.

[0008] To achieve the above objectives, the present invention adopts the following technical solution: On the one hand, the present invention provides a high-durability slag sulfoaluminate cement, comprising the following components: 52-68 parts of granulated blast furnace slag powder as the main component; 8-16 parts of nitrate-type LDH-calcium carbonate composite nucleated slag; 7-12 parts of calcium sulfoaluminate-calcium sulfosilicate composite clinker; 10-16 parts of anhydrite or natural anhydrous gypsum; 1-3 parts of metakaolin, silica fume, or a mixture thereof; 0.20-0.70 parts of calcium nitrate; and 0.05-0.20 parts of grinding aid and dispersant components.

[0009] Preferably, the main granulated blast furnace slag powder is S95 or S105 grade slag powder with a specific surface area of ​​400~520m². 2 / kg.

[0010] Preferably, the D50 particle size of the nitrate-type LDH-calcium carbonate composite nucleation slag is 2.0~5.0 μm, and the specific surface area is 750~1100 m². 2 / kg; the surface has an in-situ generated inner layer of nano-calcium carbonate and an outer layer of nitrate-type LDH.

[0011] Preferably, based on the mass of nitrate-type LDH-calcium carbonate composite nucleus slag, the loading of nano-calcium carbonate is 2.5~7.5%, and the loading of nitrate-type LDH is 0.8~3.0%.

[0012] Preferably, the nitrate-type LDH is one or more of calcium aluminum nitrate-type LDH, magnesium aluminum nitrate-type LDH, or calcium magnesium aluminum nitrate-type LDH.

[0013] Preferably, in the calcium sulfoaluminate-calcium sulfosilicate composite clinker, the calcium sulfoaluminate mineral content is 35-55%, the calcium sulfosilicate mineral content is 8-25%, the belite content is 20-45%, and the free calcium oxide content is ≤3%.

[0014] Preferably, the grinding aid dispersing component is one or more of the following: polycarboxylate powder dispersant, triethanolamine, triisopropanolamine, calcium glycoside, and lignin sulfonate.

[0015] On the other hand, the present invention also provides a method for preparing the above-mentioned high-durability slag sulfoaluminate cement, comprising the following steps: S1. Mix ultrafine slag, calcium hydroxide and water to form a wet powder system; introduce CO2 gas into the wet powder system and react to cause calcium hydroxide to carbonize in situ on the surface of ultrafine slag to generate nano-calcium carbonate, thus obtaining micro-carbonized slag with nano-calcium carbonate loaded on the surface.

[0016] S2. Add calcium nitrate, magnesium nitrate and sodium aluminate solution, or magnesium nitrate and aluminum nitrate solution, to the obtained micro-carbonized nucleus slag wet powder system, and control the pH of the system with an alkaline regulator to control the molar ratio of divalent metal ions to trivalent aluminum ions to be 2.0~3.0. After the reaction, a nitrate-type LDH outer layer is formed on the surface of the slag. Then filter or press filter and dry to a moisture content ≤1.0% to obtain nitrate-type LDH-calcium carbonate composite nucleus slag.

[0017] S3. Grind together calcium sulfoaluminate-calcium sulfosilicate composite clinker, anhydrite or natural anhydrous gypsum, calcium nitrate, and 40-70% nitrate-type LDH-calcium carbonate composite crystal nucleus slag to obtain a composite activator.

[0018] S4. The main granulated blast furnace slag powder, the remaining nitrate-type LDH-calcium carbonate composite crystal nucleus slag, the composite activator, metakaolin or silica fume, and the grinding aid and dispersing components are put into a mixing device for homogenization to obtain high-durability slag sulfoaluminate cement.

[0019] Preferably, in S1, the mass ratio of ultrafine slag, calcium hydroxide and water is 100:(3~8):(25~45).

[0020] Preferably, in S1, the volume fraction of CO2 in the introduced gas is 8-18%.

[0021] Preferably, the CO2-containing gas can be cement kiln tail gas, lime kiln tail gas, steel plant CO2-containing tail gas, simulated flue gas, or industrial pure CO2 dilution gas.

[0022] Preferably, in S1, after the gas is introduced, the reaction conditions are as follows: reaction at 20~40°C for 45~120 minutes.

[0023] Preferably, in S2, the pH of the system after adjustment with an alkaline regulator is 9.8~11.2.

[0024] Preferably, in S2, the reaction conditions are as follows: reaction at 25~45°C for 30~90 minutes.

[0025] Preferably, in step S3, the powder is ground to a specific surface area of ​​520~680 m². 2 / kg.

[0026] The mechanism of action of this invention is as follows: Calcium sulfoaluminate-calcium sulfosilicate composite clinker reacts rapidly with anhydrite to generate ettringite, providing early strength. The inner layer of nano-calcium carbonate acts as a heterogeneous nucleation site, making the formation of ettringite more uniform and reducing the risk of pore connectivity caused by coarse crystals. The outer layer of nitrate-type LDH inhibits chloride ion migration through anion exchange and, together with calcium nitrate, regulates the aluminate hydration environment, improving the stability of ettringite. The main slag continuously reacts to generate aluminum-containing hydrated calcium silicate gel, filling the gaps in the ettringite framework and reducing the proportion of interconnected pores. Ultimately, a cement system with synergistic improvements in early strength, low permeability, chloride resistance, sulfate resistance, and volume stability is formed.

[0027] The key to this invention lies in constructing the inner layer of nano-calcium carbonate and the outer layer of nitrate-type LDH in situ on the surface of the same ultrafine slag particles, so that the functional particles can simultaneously undertake the functions of nucleation, filling, ion retardation and hydration regulation in the cement system.

[0028] Compared with the prior art, the present invention has the following beneficial effects: 1. This invention uses a combination of main slag powder and functionalized ultrafine slag. The main slag powder undertakes the role of continuous hydration and low-carbon cementation in the later stage, while the functionalized ultrafine slag undertakes the role of early nucleation, interface filling and ion retardation. It can maintain high early strength even with high slag content.

[0029] 2. This invention loads nano-calcium carbonate in situ onto the surface of ultrafine slag via CO2 micro-carbonation, avoiding the problems of easy agglomeration, difficult dispersion, and insufficient effective nucleation sites when ordinary nano-calcium carbonate is added externally.

[0030] 3. This invention constructs nitrate-type LDH in situ on the outer layer of micro-carbonized slag nuclei, so that chloride ion blocking components and nucleating components are located on the same functional particle surface, which can reduce chloride ion transport capacity and improve the applicability to marine engineering and salt lake environments.

[0031] 4. This invention regulates the formation and stability of ettringite by combining calcium nitrate, nitrate-type LDH and calcium carbonate crystal nuclei, thereby improving the early strength of cement while reducing the risk of later strength reduction, abnormal expansion and shrinkage cracking.

[0032] 5. The technical effects of the present invention can be directly verified by data such as compressive strength, electrical flux, chloride ion migration coefficient, sulfate corrosion resistance coefficient, drying shrinkage rate, impermeability and freeze-thaw performance, without the need for X-ray diffraction patterns, scanning electron microscope images or pore structure patterns as necessary supporting materials. Detailed Implementation

[0033] To enable those skilled in the art to better understand the present application, the technical solutions in specific embodiments of the present application will be clearly and completely described below. Unless otherwise defined, the technical or scientific terms used in this invention should have the ordinary meaning understood by those skilled in the art.

[0034] The raw materials and parameters required in this embodiment of the invention are as follows: The main granulated blast furnace slag powder is S95 grade slag powder with a specific surface area of ​​460 m². 2 / kg. The ultrafine slag is obtained by ultrafine grinding of S105 grade granulated blast furnace slag, with a D50 particle size of 3.4 μm and a specific surface area of ​​920 m². 2 / kg. In the calcium sulfoaluminate-calcium sulfosilicate composite clinker, the calcium sulfoaluminate mineral content is 45%, the calcium sulfosilicate mineral content is 16%, the belite content is 32%, and the free calcium oxide content is 1.5%. The gypsum used is anhydrite, with a specific surface area of ​​410 m². 2 / kg. The specific surface area of ​​metakaolin is 850 m². 2 / kg; the SiO2 content in the silica fume is 92%. The grinding aid and dispersing component is a composite of polycarboxylate powder dispersant and triisopropanolamine, with a mass ratio of 3:1.

[0035] Preparation of nitrate-type LDH-calcium carbonate composite nucleated slag: 100 parts ultrafine slag, 5 parts calcium hydroxide, and 35 parts water were added to a high-speed mixer and stirred for 6 minutes to form a homogeneous wet powder system. Simulated cement kiln exhaust gas with a CO2 volume fraction of 12% was introduced into the wet powder system, and the reaction was carried out at 30℃ for 75 minutes to obtain micro-carbonized nucleated slag. Subsequently, magnesium nitrate and sodium aluminate solutions were added to the micro-carbonized nucleated slag wet powder system, controlling the Mg / Al molar ratio at 2.5, and the pH of the system was adjusted to 10.5 with sodium hydroxide solution. The reaction was carried out at 35℃ for 60 minutes. After the reaction, the mixture was filtered and dried at 65℃ to a moisture content of 0.7% to obtain nitrate-type LDH-calcium carbonate composite nucleated slag. In the obtained nitrate-type LDH-calcium carbonate composite nucleated slag, the loading of nano-calcium carbonate was 5.2%, and the loading of nitrate-type LDH was 1.8%.

[0036] Example 1 Weigh the following raw materials by weight: 66 parts of granulated blast furnace slag powder, 9 parts of nitrate-type LDH-calcium carbonate composite crystal nucleus slag, 8.5 parts of calcium sulfoaluminate-calcium sulfosilicate composite clinker, 14 parts of anhydrite, 2 parts of metakaolin, 0.25 parts of calcium nitrate, and 0.05 parts of grinding aid and dispersant.

[0037] First, calcium sulfoaluminate-calcium sulfosilicate composite clinker, anhydrite, calcium nitrate, and 60% nitrate-type LDH-calcium carbonate composite nucleation slag are ground together to a specific surface area of ​​560 m².2 / kg, to obtain the composite activator. Then, the composite activator, the main granulated blast furnace slag powder, the remaining nitrate-type LDH-calcium carbonate composite crystal nucleus slag, metakaolin and grinding aid dispersion components are put into a mixer and homogenized for 10 minutes to obtain the cement product.

[0038] Example 2 Weigh the following raw materials by weight: 59 parts of granulated blast furnace slag powder, 13 parts of nitrate-type LDH-calcium carbonate composite crystal nucleus slag, 11.5 parts of calcium sulfoaluminate-calcium sulfosilicate composite clinker, 14 parts of anhydrite, 2 parts of silica fume, 0.45 parts of calcium nitrate, and 0.1 parts of grinding aid and dispersant.

[0039] First, calcium sulfoaluminate-calcium sulfosilicate composite clinker, anhydrite, calcium nitrate, and 65% nitrate-type LDH-calcium carbonate composite nucleation slag are ground together to a specific surface area of ​​640 m². 2 / kg, to obtain the composite activator. Then, the composite activator is homogenized and mixed with the remaining components for 12 minutes to obtain the finished cement product.

[0040] Example 3 Weigh the following raw materials by weight: 60 parts of granulated blast furnace slag powder, 15 parts of nitrate-type LDH-calcium carbonate composite crystal nucleus slag, 9.5 parts of calcium sulfoaluminate-calcium sulfosilicate composite clinker, 12.5 parts of anhydrite, 2 parts of metakaolin, 0.55 parts of calcium nitrate, and 0.1 parts of grinding aid and dispersant.

[0041] First, calcium sulfoaluminate-calcium sulfosilicate composite clinker, anhydrite, calcium nitrate, and 70% nitrate-type LDH-calcium carbonate composite nucleation slag are ground together to a specific surface area of ​​620 m². 2 / kg, to obtain the composite activator. Then, the composite activator is homogenized and mixed with the remaining components for 12 minutes to obtain the finished cement product.

[0042] Example 4 By weight, 62 parts of the main granulated blast furnace slag powder, 12 parts of nitrate-type LDH-calcium carbonate composite nucleated slag, 9 parts of calcium sulfoaluminate-calcium sulfosilicate composite clinker, 13.5 parts of anhydrite, 2.8 parts of a mixture of metakaolin and silica fume, 0.35 parts of calcium nitrate, and 0.1 parts of grinding aid and dispersant are weighed. The mass ratio of metakaolin to silica fume is 2:1.

[0043] First, calcium sulfoaluminate-calcium sulfosilicate composite clinker, anhydrite, calcium nitrate, and 55% nitrate-type LDH-calcium carbonate composite nucleation slag are ground together to a specific surface area of ​​600 m². 2 / kg, to obtain the composite activator. Then, the composite activator is homogenized and mixed with the remaining components for 10 minutes to obtain the finished cement product.

[0044] Comparative Example 1: This comparative example does not use functionalized composite crystal nucleus slag. The difference from Example 3 is that 15 parts of nitrate-type LDH-calcium carbonate composite crystal nucleus slag are replaced with an equal amount of ordinary ultrafine slag, while the other components and preparation process are the same.

[0045] Comparative Example 2 This comparative example only incorporates nano-calcium carbonate and calcium nitrate. The difference from Example 3 is that it does not prepare nitrate-type LDH-calcium carbonate composite nucleus slag; instead, it uses ordinary ultrafine slag, nano-calcium carbonate, and calcium nitrate directly dry-mixed. The total amount of nano-calcium carbonate and calcium nitrate is calculated based on the loading amount corresponding to the composite nucleus slag in Example 3. The remaining components and preparation process are the same.

[0046] Comparative Example 3 This comparative example only uses micro-carbonized slag nuclei and does not construct an LDH outer layer. The difference from Example 3 is that the surface of the ultrafine slag is only loaded with nano-calcium carbonate through CO2 micro-carbonization, without in-situ deposition of nitrate-type LDH. The other components and preparation process are the same.

[0047] Comparative Example 4 This comparative example uses only LDH-modified slag without micro-carbonization treatment. The difference from Example 3 is that the ultrafine slag is not subjected to CO2 micro-carbonization treatment and is directly deposited with nitrate-type LDH. The other components and preparation process are the same.

[0048] Comparative Example 5 By weight, 72 parts of the main granulated blast furnace slag powder, 9.5 parts of calcium sulfoaluminate-calcium sulfosilicate composite clinker, 16 parts of anhydrite, 2 parts of metakaolin, 0.4 parts of calcium nitrate, and 0.1 parts of grinding aid and dispersant were weighed and directly homogenized and mixed without the use of ultrafine slag grading activation, CO2 micro-carbonization treatment, and LDH in-situ deposition.

[0049] Comparative Example 6 Compared with Example 3, the components of this comparative example are the same, but the calcium sulfoaluminate-calcium sulfosilicate composite clinker, anhydrite, calcium nitrate and nitrate-type LDH-calcium carbonate composite crystal nucleus slag are not ground together, but are all directly homogenized and mixed.

[0050] Comparative Example 7 Compared with Example 3, this comparative example does not prepare nitrate-type LDH-calcium carbonate composite crystal nucleus slag. Instead, it uses ordinary ultrafine slag, nano-calcium carbonate, nitrate-type LDH powder and calcium nitrate directly dry-mixed. The calculated amount of each functional component is the same as in Example 3.

[0051] Test case This test case involves the following tests conducted on the above embodiments and comparative examples: Mortar strength test: Cement, standard sand and water were mixed in a mass ratio of 1:3:0.50 and the specimen size was 40 mm × 40 mm × 160 mm. The compressive strength was tested at 1d, 3d, 28d and 90d respectively.

[0052] Electrical flux test: 56-day-old mortar specimens were used for testing. The results are expressed as coulombic value C. The lower the electrical flux, the better the resistance to chloride ion penetration.

[0053] Chloride ion migration coefficient: Tested using specimens aged 56 days, results are expressed as m 2 / s indicates that the lower the value, the weaker the chloride ion transport capacity.

[0054] Chloride ion binding capacity test: The specimen is immersed in a 3.5% sodium chloride solution until the specified age. After sampling and grinding, the free chloride ion content and total chloride ion content are determined, and the chloride ion binding rate is calculated according to "chloride ion binding rate = (total chloride ion content - free chloride ion content) / total chloride ion content × 100%".

[0055] Sulfate corrosion resistance test: The compressive strength retention rate was tested after immersion in 5% sodium sulfate solution for 90 days. Sulfate corrosion resistance coefficient = compressive strength of specimen cured in sulfate solution / compressive strength of specimen cured in standard solution.

[0056] Drying shrinkage test: 25 mm × 25 mm × 280 mm mortar specimens were used for testing, and the test age was 180 days.

[0057] Impermeability test: The water pressure method was used to test and record the maximum impermeability pressure.

[0058] Freeze-thaw performance test: The mass loss rate and relative dynamic elastic modulus after 300 freeze-thaw cycles were tested using the rapid freeze-thaw method.

[0059] The test results are shown in the table below. It should be noted that each test result is the average value obtained from three sets of parallel tests under the same test conditions. The deviation of the parallel test results did not affect the performance change trend between each embodiment and the comparative example.

[0060] Table 1: Test Results of Mortar Compressive Strength

[0061] The results showed that Examples 1-4 exhibited high compressive strength at 1d, 3d, 28d, and 90d. Specifically, Example 3 showed compressive strengths of 24.3MPa, 74.8MPa, and 82.6MPa at 1d, 28d, and 90d, respectively, representing increases of 64.2%, 27.0%, and 32.4% compared to Comparative Example 5 (comparative slag sulfoaluminate cement). This indicates that nitrate-type LDH-calcium carbonate composite nucleated slag can simultaneously improve both early-age strength and later-age strength stability. Comparative Example 6, although using the same components as Example 3, did not co-mill the calcium sulfoaluminate-calcium sulfosilicate composite clinker, anhydrite, calcium nitrate, and part of the composite nucleated slag. Its compressive strengths at 1d, 28d, and 90d were all lower than those of Example 3, indicating that the segmented milling process is beneficial for improving the reactivity of the composite activator. Comparative Example 7 uses ordinary ultrafine slag, nano-calcium carbonate, nitrate-type LDH powder and calcium nitrate directly dry mixed. Although its strength is higher than that of Comparative Example 5, it is significantly lower than that of Example 3. This shows that constructing the inner layer of nano-calcium carbonate and the outer layer of nitrate-type LDH in situ on the surface of the same ultrafine slag particles is more conducive to hydration nucleation and strength development than simply adding each functional component externally.

[0062] Table 2: Test Results of Chloride Ion Transport Resistance

[0063] The results showed that the 56-day electrical flux and 56-day chloride ion migration coefficient of Examples 1-4 were significantly lower than those of the comparative examples, indicating that the cement of the present invention has better resistance to chloride ion transport. Specifically, the 56-day electrical flux of Example 3 was 510C, and the chloride ion migration coefficient was 3.3 × 10⁻⁶. -12 m 2 / s, which is a reduction of 60.2% and 61.6% compared to Comparative Example 5, respectively. Comparative Example 3, which only uses micro-carbonized slag nuclei without constructing an LDH outer layer, has a chloride ion migration coefficient of 5.4 × 10⁻⁶. -12 m 2 / s; Comparative Example 4, using only LDH-modified slag without micro-carbonization treatment, had a chloride ion migration coefficient of 5.9 × 10⁻⁶. -12 m 2 The values ​​of / s were significantly higher than those in Example 3, indicating that the synergistic presence of the inner layer of nano-calcium carbonate and the outer layer of nitrate-type LDH resulted in better resistance to chloride ion transport. Comparative Example 6, which did not employ a segmented grinding process, had an electrical flux of 720C and a chloride ion migration coefficient of 5.1 × 10⁻⁶. -12 m 2 / s indicates that segmented grinding is beneficial for improving the activity of the composite activator and the density of the hardened body. Comparative Example 7 uses direct external doping of each functional component, but its resistance to chloride ion transport is still weaker than that of Example 3. This shows that the advantage of the present invention does not come from the simple superposition of nano-calcium carbonate, LDH and calcium nitrate, but from the in-situ construction structure of the composite crystal nucleus slag and its synergistic effect with the segmented grinding process.

[0064] Table 3: Test results of resistance to sulfate attack, shrinkage and impermeability

[0065] The results showed that the 90-day sulfate corrosion resistance coefficients of Examples 1-4 were all no less than 0.97, the 180-day drying shrinkage rates were all no higher than 528 με, the maximum impermeability pressure was all no less than 1.6 MPa, and the 90-day sulfate erosion length change rate was all less than 0.060%, indicating that the cement of the present invention has good comprehensive durability in terms of sulfate erosion, long-term shrinkage, and impermeability. Among them, the 90-day sulfate corrosion resistance coefficient of Example 3 reached 1.01, the 180-day drying shrinkage rate was 462 με, the maximum impermeability pressure was 2.0 MPa, and the 90-day sulfate erosion length change rate was only 0.036%; compared with Comparative Example 5, its 180-day drying shrinkage rate decreased by 35.4%, the maximum impermeability pressure increased by 100%, and the 90-day sulfate erosion length change rate decreased by 71.9%. Comparative Example 3 only has a nano-calcium carbonate inner layer, and Comparative Example 4 only has an LDH outer layer. Their sulfate corrosion resistance coefficient, shrinkage rate, impermeability pressure, and sulfate erosion length change rate are all lower than those of Example 3, indicating that the nucleation effect of nano-calcium carbonate and the ion blocking effect of nitrate-type LDH need to work synergistically on the surface of the same functionalized slag particles. Comparative Examples 6 and 7 have better performance than the ordinary Comparative Example 5, but lower than Example 3, further demonstrating that both the segmented grinding process and the in-situ composite nucleus structure are beneficial for reducing the proportion of interconnected pores, improving impermeability, and enhancing volume stability under sulfate erosion conditions.

[0066] Table 4: Freeze-thaw performance test results

[0067] The results showed that after 300 freeze-thaw cycles, the mass loss rate of Examples 1-4 was no higher than 2.9%, and the relative dynamic elastic modulus was no lower than 86%, significantly better than the comparative examples. Among them, Example 4 showed the best freeze-thaw resistance with a mass loss rate of only 1.8% and a relative dynamic elastic modulus of 92% after 300 freeze-thaw cycles. The mass loss rate of Example 3 was 2.1%, and the relative dynamic elastic modulus was 91%, also significantly better than Comparative Example 5, which was made of ordinary slag sulfoaluminate cement. Although Comparative Examples 6 and 7 showed some improvement over Comparative Example 5 due to the presence of composite nucleus slag or functional components, their mass loss rates were still 3.6% and 3.9%, respectively, and their relative dynamic elastic moduli were 84% and 82%, respectively, both weaker than Example 3. These results indicate that the in-situ construction structure of composite nucleus slag and the segmented preparation method of partial co-grinding and partial final homogenization are beneficial in reducing the proportion of interconnected pores in the hardened body, mitigating internal damage during freeze-thaw cycles, and thus improving durability under freeze-thaw conditions.

[0068] Table 5: Results of Chloride Ion Binding Ability Test

[0069] The results showed that the free chloride ion content of Example 3 at 28 days was 0.043%, and the chloride ion binding rates at 28 days and 56 days were 72.5% and 78.6%, respectively, which were significantly better than those of the comparative examples. This indicates that the present invention can effectively reduce the free chloride ion content in the hardened body and improve the chloride ion binding capacity. Comparative Example 3 used only micro-carbonized slag without constructing an LDH outer layer, and its chloride ion binding rate at 56 days was 61.8%; Comparative Example 4 used only LDH-modified slag without micro-carbonization treatment, and its chloride ion binding rate at 56 days was 68.2%, both lower than that of Example 3. This indicates that the nitrate-type LDH outer layer has a significant contribution to chloride ion binding and inhibition, while the nucleation and pore refinement effects formed by the nano-calcium carbonate inner layer can further improve the anti-chloride ion transport effect. Comparative Example 7 used ordinary ultrafine slag, nano-calcium carbonate, nitrate-type LDH powder, and calcium nitrate directly dry-mixed. Its 56-day chloride ion binding rate was 70.3%, lower than that of Example 3. This indicates that in-situ construction of the LDH outer layer on the surface of the composite crystal nucleus slag is more beneficial for its dispersion and effective function in the cement system than direct external addition of LDH powder. Combined with the results of electrical flux and chloride ion migration coefficient in Table 2, it can be seen that this invention not only reduces the chloride ion migration rate but also improves the chloride ion binding capacity through the anion exchange effect of nitrate-type LDH, thereby enhancing the durability of cement materials in marine, salt lake, and chloride-eroded environments.

[0070] The above embodiments and comparative examples demonstrate that the technical effects of the present invention stem from the synergistic effect of nitrate-type LDH-calcium carbonate composite nucleation slag, calcium sulfoaluminate-calcium sulfosilicate composite clinker, calcium nitrate, and the segmented grinding process. First, the inner layer of nano-calcium carbonate provides heterogeneous nucleation sites, promoting the uniform formation of early hydration products, improving early strength, and refining the pore structure. Second, the outer layer of nitrate-type LDH enhances chloride ion binding capacity and reduces chloride ion migration rate through interlayer anion exchange. Third, calcium nitrate and nitrate-type LDH jointly regulate the aluminate hydration environment, which is beneficial for the formation and stability of ettringite. Finally, the participation of some composite nucleation slag in the co-grinding of the composite activator enhances the activator's reactivity, while the remaining composite nucleation slag is added in the final homogenization stage, which helps retain its surface composite structure. Compared with the common method of externally adding nano-calcium carbonate, LDH powder or calcium nitrate, the present invention achieves the synergistic effect of nucleation, filling, ion retardation and hydration regulation by constructing an inner layer of nano-calcium carbonate and an outer layer of nitrate-type LDH in situ on the surface of the same ultrafine slag particles. This results in comprehensive improvement of cement materials in terms of strength, resistance to chloride ion transport, resistance to sulfate attack, impermeability, freeze-thaw resistance and volume stability.

[0071] Finally, it should be noted that the described embodiments are merely some, not all, of the embodiments of the present invention. Those skilled in the art will understand that various changes, modifications, substitutions, and variations can be made to these embodiments without departing from the principles and spirit of the present invention. The scope of the present invention is defined by the claims and their equivalents; that is, all other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

Claims

1. A high-durability slag sulfoaluminate cement, characterized in that, By weight, it includes the following components: 52-68 parts of granulated blast furnace slag powder as the main component; 8-16 parts of nitrate-type LDH-calcium carbonate composite crystal nucleus slag; 7-12 parts of calcium sulfoaluminate-calcium sulfosilicate composite clinker; 10-16 parts of anhydrite or natural anhydrous gypsum; 1-3 parts of metakaolin, silica fume, or a mixture thereof; and 0.20-0.70 parts of calcium nitrate. 0.05~0.20 parts of grinding aid and dispersant component; The surface of the nitrate-type LDH-calcium carbonate composite crystal nucleus slag has an in-situ generated inner layer of nano-calcium carbonate and an outer layer of nitrate-type LDH from the inside out.

2. The high-durability slag sulfoaluminate cement according to claim 1, characterized in that, The main granulated blast furnace slag powder is S95 or S105 grade slag powder with a specific surface area of ​​400~520 m². 2 / kg; the D50 particle size of nitrate-type LDH-calcium carbonate composite nucleated slag is 2.0~5.0 μm, and the specific surface area is 750~1100 m² / kg. 2 / kg.

3. The high-durability slag sulfoaluminate cement according to claim 1, characterized in that, Based on the mass of nitrate-type LDH-calcium carbonate composite crystal nucleus slag, the loading of the inner layer of nano-calcium carbonate is 2.5~7.5%, and the loading of the outer layer of nitrate-type LDH is 0.8~3.0%.

4. The high-durability slag sulfoaluminate cement according to claim 1, characterized in that, Nitrate-type LDH can be one or more of calcium-aluminum nitrate-type LDH, magnesium-aluminum nitrate-type LDH, or calcium-magnesium-aluminum nitrate-type LDH.

5. The high-durability slag sulfoaluminate cement according to claim 1, characterized in that, In the calcium sulfoaluminate-calcium sulfosilicate composite clinker, the calcium sulfoaluminate mineral content is 35-55%, the calcium sulfosilicate mineral content is 8-25%, the belite content is 20-45%, and the free calcium oxide content is ≤3%; the grinding aid and dispersing component is one or more of the following: polycarboxylate powder dispersant, triethanolamine, triisopropanolamine, calcium sugar, and lignin sulfonate.

6. A method for preparing high-durability slag sulfoaluminate cement as described in any one of claims 1 to 5, characterized in that, Includes the following steps: S1. Mix ultrafine slag, calcium hydroxide and water to form a wet powder system. Introduce CO2 gas into the wet powder system to cause calcium hydroxide to carbonize in situ on the surface of ultrafine slag to generate nano-calcium carbonate, thus obtaining micro-carbonized slag with a nano-calcium carbonate inner layer on the surface. S2. Add a solution containing nitrate, divalent metal ions and trivalent aluminum ions to the wet powder system of micro-carbonized crystal nucleus slag obtained in S1, and adjust the pH of the system to form a nitrate-type LDH outer layer on the surface of the micro-carbonized crystal nucleus slag in situ. After filtration or pressure filtration and drying, nitrate-type LDH-calcium carbonate composite crystal nucleus slag is obtained. S3. Grind together calcium sulfoaluminate-calcium sulfosilicate composite clinker, anhydrite or natural anhydrous gypsum, calcium nitrate, and 40-70% nitrate-type LDH-calcium carbonate composite crystal nucleus slag to obtain a composite activator. S4. Mix and homogenize the main granulated blast furnace slag powder, the remaining nitrate-type LDH-calcium carbonate composite crystal nucleus slag, the composite activator, metakaolin and / or silica fume, and the grinding aid and dispersing components to obtain high-durability slag sulfoaluminate cement.

7. The preparation method according to claim 6, characterized in that, In S1, the mass ratio of ultrafine slag, calcium hydroxide and water is 100:(3~8):(25~45); the CO2-containing gas is cement kiln tail gas, lime kiln tail gas, steel plant CO2-containing tail gas, simulated flue gas or industrial pure CO2 dilution gas, and the CO2 volume fraction is 8~18%.

8. The preparation method according to claim 6, characterized in that, In S1, the in-situ carbonization reaction temperature is 20~40℃ and the reaction time is 45~120 minutes; in S2, the system pH is 9.8~11.2, the molar ratio of divalent metal ions to trivalent aluminum ions is 2.0~3.0, the reaction temperature is 25~45℃, and the reaction time is 30~90 minutes.

9. The preparation method according to claim 6, characterized in that, In step S2, the solution containing divalent metal ions and trivalent aluminum ions is a solution of calcium nitrate, magnesium nitrate and sodium aluminate, or a solution of magnesium nitrate and aluminum nitrate; the moisture content of the dried nitrate-type LDH-calcium carbonate composite crystal nucleus slag is ≤1.0%.

10. The preparation method according to claim 6, characterized in that, In step S3, the specific surface area of ​​the composite activator after co-milling is 520~680 m². 2 / kg; In step S4, the mixing and homogenization time is 5~15 minutes.

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