Low shrinkage high performance cement and method of making same

Abstract

The application discloses low-shrinkage high-performance cement and a preparation method thereof, and belongs to the technical field of building materials. The cement comprises the following components: mixed gypsum 2-5%, auxiliary cementitious material 5-10%, low-shrinkage high-performance Portland cement clinker 85-93%, and modified shrinkage reducing agent 0.5-1.0% of the total mass of the above components. The application solves the problem that existing ultra-high-performance concrete prefabricated components are prone to shrinkage and cracking by optimizing the clinker composition and cooperating with the modified shrinkage reducing agent, and realizes low shrinkage and high performance of the cement.

Description

Technical Field

[0001] This invention relates to the field of building materials technology, specifically to a low-shrinkage, high-performance cement and its preparation method. Background Technology

[0002] Offshore wind power, as an important component of clean and renewable energy, has experienced rapid development in recent years. As a crucial part of offshore wind power, hybrid wind turbine towers face increasingly stringent performance requirements. The service environments of offshore and onshore hybrid wind turbine towers differ fundamentally. The marine environment, characterized by strong erosion, high dynamic loads, and highly flexible structures, places higher demands on the concrete structures of hybrid wind turbine towers. High-strength, high-durability cement has become key to the successful application of hybrid towers in offshore wind power projects. Furthermore, research indicates that the main structure and foundation platform of hybrid wind turbine towers need to be prefabricated onshore, and then installed at the offshore construction site. To cope with this extreme marine environment, prefabricated concrete components are typically made of ultra-high performance concrete (UHPC). Due to the high amount of adhesives used in UHPC, it is prone to significant self-shrinkage, making prefabricated components susceptible to micro-cracks, thus posing safety hazards to hybrid wind turbine towers.

[0003] CN 117510108 B discloses a high early strength, low shrinkage composite silicate cement and its preparation method. By introducing copper ions, the melting temperature of the iron phase is lowered, as are the formation temperatures of tricalcium silicate and dicalcium silicate, thus increasing the hydration activity of the iron phase and dicalcium silicate and reducing the early shrinkage of the cement. Although this method improves the activity of dicalcium silicate through ion doping technology, it weakens the later strength growth of the cement. CN 114716163 B discloses a low shrinkage, high crack resistance cement and its preparation method and application. By designing the cement particle composition and classifying the particle composition, inert components are used to replace components that significantly affect hydration heat release and volume shrinkage. Through graded grinding and efficient mixing, the contradiction between early strength, hydration heat release, and volume shrinkage cracking is coordinated, achieving the preparation of high crack resistance cement with low hydration heat, low shrinkage, and moderate early strength. However, graded grinding reduces cement production efficiency and increases grinding costs, which is not conducive to large-scale production.

[0004] Therefore, there is an urgent need for a low-shrinkage high-performance cement and its preparation method that can simultaneously ensure the later-stage strength of cement, improve production efficiency, and significantly reduce the risk of shrinkage cracking in ultra-high performance concrete precast components. Summary of the Invention

[0005] To address the aforementioned problems, this invention starts with the mineral crystal structure of cement and prepares low-shrinkage, high-performance cement by optimizing the cement raw material ratio, adding mineralizers, and modifying shrinkage-reducing agents.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows: A low-shrinkage, high-performance cement comprising the following components by weight percentage: Mixed gypsum 2-5%; Auxiliary cementitious materials: 5-10%; Low-shrinkage, high-performance silicate cement clinker accounts for 85-93%; In addition, there is an externally added modified shrinkage reducing agent, the amount of which is 0.5 to 1.0% of the total mass of the mixed gypsum, auxiliary cementitious materials and low-shrinkage high-performance silicate cement clinker.

[0007] Furthermore, the mineral composition of the low-shrinkage high-performance silicate cement clinker, by mass percentage, includes: 22~28% C2S, 30~45% M1 type C3S, 8~16% M3 type C3S, 2~5% C3A, 11~15% C4AF, 5.0~6.5% MgO, and f-CaO≤1.0%.

[0008] Furthermore, low-shrinkage high-performance silicate cement clinker is made from raw materials including calcareous raw materials, silica-alumina raw materials, ferrous raw materials, magnesium raw materials and mineralizers through high-temperature firing; The raw meal proportions should meet the following requirements: MgO content in clinker should be controlled at 6.0~8.0%, lime saturation coefficient KH should be 0.87~0.90, silicon content SM should be 2.3~2.8, and aluminum content IM should be 0.75~0.82.

[0009] Furthermore, the high-temperature firing of low-shrinkage high-performance silicate cement clinker is as follows: The calcium-based raw materials, silica-alumina-based raw materials, iron-based raw materials, magnesium-based raw materials, and mineralizers are ground to a residue of <10% on an 80µm standard sieve and then homogenized to obtain raw meal. The raw material was heated to 1000℃ at a uniform rate for 50 minutes; held at 1000℃ for 30 minutes; then heated to 1450℃ at a uniform rate for 30 minutes; and then held at 1450℃ for 60 minutes. After cooling, low-shrinkage high-performance silicate cement clinker was obtained. Furthermore, the calcareous raw materials include one or more of limestone, marble, marl, or chalk; the siliceous-aluminous raw materials include one or more of clay, shale, or mudstone; the ferrous raw materials include one of iron tailings, sulfuric acid slag, or copper slag; the magnesian raw materials include dolomite; and the mineralizing agents are anhydrous calcium sulfate and magnesium oxide.

[0010] Furthermore, the amount of anhydrous calcium sulfate added reduces the excess sulfur coefficient in the raw meal. µ The range is 80~240. µ Calculate using the following formula:

[0011] Wherein, SO3, K2O, and Na2O are the mass fractions of the corresponding components in the raw material; 80.06, 94.20, and 61.98 are the molar masses of SO3, K2O, and Na2O, respectively.

[0012] Excess sulfur coefficient µ This reflects the relative level of sulfur remaining in the clinker that can be dissolved in the calcium silicate mineral lattice after removing thermodynamically preferentially formed alkali sulfates (such as K2SO4). µ The value ranges from 80 to 240, and is a positive value. µ This indicates the presence of excess sulfur in the system, which will dissolve into the C3S or C2S lattice, promoting the formation of highly active M1-type C3S.

[0013] Furthermore, the amount of magnesium oxide added makes the mass ratio of SO3 to MgO in the raw material 0.2~0.25.

[0014] By controlling the excess sulfur coefficient µ The mass ratio of SO3 to MgO synergistically regulates the mineral crystal form of C3S in clinker, promotes the formation of M1-type C3S with high lattice distortion and high hydration activity, thereby improving the early strength of cement; at the same time, the CSH gel generated by the hydration of M1-type C3S can effectively fill the internal pores of cement stone and reduce the shrinkage rate of cement.

[0015] Furthermore, the calcium sulfate content of the mixed gypsum is 90-95%, and the mixed gypsum includes at least dihydrate gypsum and anhydrite, with a mass ratio of dihydrate gypsum to anhydrite of 1:1; the auxiliary cementitious material is one or more of silica fume, slag, or high-calcium fly ash, and the particle size range of the auxiliary cementitious material is 0.15-3µm, with a median diameter D... 50 It is 1.36µm.

[0016] Furthermore, the modified shrinkage reducing agent is prepared by the following method: a monohydric alcohol shrinkage reducing agent is dissolved in water at a mass ratio of 1:1, stirred evenly, and then dried sodium alginate is added to completely immerse the sodium alginate in the solution. The solution is sealed and allowed to stand for 24 hours. The excess aqueous solution is then filtered out to obtain the modified shrinkage reducing agent.

[0017] A method for preparing low-shrinkage, high-performance cement, comprising: Low-shrinkage high-performance silicate cement clinker is mixed with mixed gypsum and auxiliary cementitious materials, and a shrinkage-reducing modifier is added externally to obtain low-shrinkage high-performance cement.

[0018] Compared with the prior art, the present invention has the following beneficial effects: 1. This invention increases the f-MgO content in clinker by controlling the MgO content in the clinker to 6.0~8.0%, and optimizing the three ratios of raw meal (KH = 0.87~0.90, SM = 2.3~2.8, IM = 0.75~0.82) and the firing regime, while ensuring that f-CaO ≤ 1.0%. Cement clinker with high MgO content expands during hydration, thereby compensating for the autogenous shrinkage of cement.

[0019] 2. This invention introduces an excess sulfur coefficient. µ (Values ​​range from 80 to 240), and the mass ratio of SO3 to MgO in the raw meal is adjusted to 0.2 to 0.25, so that sulfur and magnesium elements dissolve into the C3S lattice to produce lattice distortion, promote the formation of highly active M1 type C3S in the clinker (its content reaches 30 to 45%), improve the hydration activity of C3S minerals, and thus improve the early strength of cement.

[0020] 3. This invention uses sodium alginate as a carrier. Leveraging the water absorption and release properties of sodium alginate, monohydric alcohol-based shrinkage-reducing agents are controllably released into cement, thus improving the shrinkage-reducing effect. Furthermore, the water absorption and release properties of sodium alginate also promote cement hydration, continuously providing moisture during the hydration process, increasing the degree of cement hydration, making the cement stone structure denser, and thereby endowing the cement with superior durability. Detailed Implementation

[0021] In this invention, the dosage of anhydrous calcium sulfate is determined according to the following steps: (1) Determine the mass fractions of SO3, K2O, and Na2O in the calcium, silicon-aluminum, iron, and magnesium raw materials used; (2) Set the target value of the excess sulfur coefficient µ (80~240), and calculate the target SO3 mass fraction required in the raw meal according to the following formula: ; (3) Subtract the mass fraction of SO3 contained in the calcium raw materials, silicon-aluminum raw materials, iron raw materials and magnesium raw materials to obtain the mass fraction of SO3 that needs to be supplemented by anhydrous calcium sulfate. (4) Based on the mass fraction of SO3 in anhydrous calcium sulfate, the mass fraction of the additional SO3 is converted into the mass fraction of anhydrous calcium sulfate in the total mass of raw material, and then the amount of anhydrous calcium sulfate is obtained.

[0022] In this invention, the amount of magnesium oxide added is determined according to the following steps: (1) Add the SO3 supplemented by anhydrous calcium sulfate to the SO3 contained in the calcium raw materials, silicon-aluminum raw materials, iron raw materials and magnesium raw materials to obtain the total SO3 mass fraction in the raw materials; (2) Based on the set SO3 to MgO mass ratio of 0.2 to 0.25, calculate the required total MgO mass fraction using the following formula: ; The sulfur-to-magnesium ratio is between 0.2 and 0.25. (3) Determine the mass fraction of MgO in calcium-based raw materials, silica-alumina-based raw materials, iron-based raw materials, and magnesium-based raw materials; (4) Subtract the MgO mass fraction in the calcium raw materials, silicon-aluminum raw materials, iron raw materials and magnesium raw materials from the required total MgO mass fraction to obtain the MgO mass fraction that needs to be added, and then obtain the amount of magnesium oxide added.

[0023] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments. Obviously, the described embodiments are merely some embodiments of this invention, and not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0024] In this embodiment of the invention, both anhydrous calcium sulfate and magnesium oxide are industrial-grade raw materials.

[0025] Examples 1-4, the group assignments of each example are shown in Table 1.

[0026] Table 1. Component ratios for Examples 1-4

[0027] The mineral composition of the low-shrinkage high-performance silicate cement clinker in each embodiment is shown in Table 2.

[0028] Table 2 Mineral composition of low-shrinkage high-performance silicate cement clinker in Examples 1-4

[0029] Comparative Examples 1-3, and the group assignments for each comparative example are shown in Table 3-5.

[0030] Table 3. Component ratios of Comparative Example 1

[0031] Table 4. Component ratios of Comparative Example 2

[0032] Table 5. Component ratios of Comparative Example 3

[0033] For the test examples, the cement in the embodiments and comparative examples was tested using conventional testing methods in the art, and the results are shown in Table 6.

[0034] Table 6 Performance Test Results

[0035] As shown in Table 6, compared with ordinary medium-heat silicate cement (Comparative Example 1), the low-shrinkage high-performance cement of the present invention has increased the mortar strength by 10-30% at 3 days, increased the mortar strength by 6-20% at 7 days, increased the mortar strength by 10-15% at 28 days, and reduced the drying shrinkage rate by 41-56% at 28 days.

[0036] Under the same conditions of low-shrinkage high-performance silicate cement clinker, mixed gypsum, and auxiliary cementitious materials as described in this invention, Example 1, which uses a modified shrinkage-reducing agent, exhibits a 28-day drying shrinkage rate of 0.048%, which is approximately 30% lower than that of Comparative Example 2 (0.069%), which uses a common monohydric alcohol-based shrinkage-reducing agent. The 3-day, 7-day, and 28-day compressive strengths are increased by approximately 2%, 10.5%, and 7.8%, respectively. This demonstrates that the sodium alginate-loaded modified shrinkage-reducing agent of this invention can significantly improve the shrinkage-reducing effect and synergistically enhance the mechanical properties of cement.

[0037] Finally, it should be noted that the above embodiments are merely preferred embodiments of the present invention used to illustrate the technical solutions of the present invention, and are not intended to limit the invention, nor are they intended to limit the patent scope of the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. These modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention. That is to say, any changes or refinements made to the main design concept and spirit of the present invention that are not of substantial significance, but whose technical problems are still consistent with the present invention, should be included within the protection scope of the present invention. In addition, the direct or indirect application of the technical solutions of the present invention to other related technical fields are similarly included within the patent protection scope of the present invention.

Claims

1. A low-shrinkage, high-performance cement, characterized in that, Includes the following components by mass percentage: Mixed gypsum 2-5%; Auxiliary cementitious materials: 5-10%; Low-shrinkage, high-performance silicate cement clinker accounts for 85-93%; In addition, there is an externally added modified shrinkage reducing agent, the amount of which is 0.5 to 1.0% of the total mass of the mixed gypsum, auxiliary cementitious materials and low-shrinkage high-performance silicate cement clinker.

2. The low-shrinkage high-performance cement according to claim 1, characterized in that, The mineral composition of low-shrinkage high-performance silicate cement clinker, by mass percentage, includes: 22~28% C2S, 30~45% M1 type C3S, 8~16% M3 type C3S, 2~5% C3A, 11~15% C4AF, 5.0~6.5% MgO, and f-CaO≤1.0%.

3. The low-shrinkage high-performance cement according to claim 1, characterized in that, Low-shrinkage, high-performance silicate cement clinker is made from raw materials including calcareous raw materials, silica-alumina raw materials, ferrous raw materials, magnesium raw materials and mineralizers through high-temperature firing. The raw meal proportions should meet the following requirements: MgO content in clinker should be controlled at 6.0~8.0%, lime saturation coefficient KH should be 0.87~0.90, silicon content SM should be 2.3~2.8, and aluminum content IM should be 0.75~0.

82.

4. The low-shrinkage high-performance cement according to claim 3, characterized in that, The high-temperature firing process for low-shrinkage, high-performance silicate cement clinker is detailed below: The calcium-based raw materials, silica-alumina-based raw materials, iron-based raw materials, magnesium-based raw materials, and mineralizers are ground to a residue of <10% on an 80µm standard sieve and then homogenized to obtain raw meal. The raw material was heated at a constant rate to 1000℃ for 50 minutes; held at 1000℃ for 30 minutes; then heated at a constant rate to 1450℃ for 30 minutes; and then held at 1450℃ for 60 minutes. After cooling, low-shrinkage high-performance silicate cement clinker was obtained.

5. The low-shrinkage high-performance cement according to claim 3, characterized in that, The calcareous raw materials include one or more of limestone, marble, marl, or chalk; the silica-alumina raw materials include one or more of clay, shale, or mudstone; the ferrous raw materials include one of iron tailings, sulfuric acid slag, or copper slag; the magnesian raw materials include dolomite; and the mineralizing agents are anhydrous calcium sulfate and magnesium oxide.

6. The low-shrinkage high-performance cement according to claim 5, characterized in that, The amount of anhydrous calcium sulfate added reduces the excess sulfur coefficient in the raw meal. µ The range is 80~240. µ Calculate using the following formula: ； SO3, K2O, and Na2O represent the mass fractions of the corresponding components in the raw material.

7. The low-shrinkage high-performance cement according to claim 5, characterized in that, The amount of magnesium oxide added makes the mass ratio of SO3 to MgO in the raw material 0.2~0.

25.

8. The low-shrinkage high-performance cement according to claim 1, characterized in that, The mixed gypsum has a calcium sulfate content of 90-95%, and includes at least dihydrate gypsum and anhydrite, with a mass ratio of dihydrate gypsum to anhydrite of 1:

1. The auxiliary cementitious material is one or more of silica fume, slag, or high-calcium fly ash, and the particle size range of the auxiliary cementitious material is 0.15-3µm, with a median diameter D... 50 It is 1.36µm.

9. The low-shrinkage high-performance cement according to claim 1, characterized in that, The modified shrinkage reducing agent is prepared by the following method: a monohydric alcohol shrinkage reducing agent is dissolved in water at a mass ratio of 1:1, stirred evenly, and then dried sodium alginate is added to completely immerse the sodium alginate in the solution. The solution is sealed and left to stand for 24 hours. The excess aqueous solution is then filtered out to obtain the modified shrinkage reducing agent.

10. A method for preparing low-shrinkage high-performance cement as described in any one of claims 1 to 9, characterized in that, include: Low-shrinkage high-performance silicate cement clinker is obtained by mixing it with gypsum and auxiliary cementitious materials, and adding a shrinkage-reducing modifier.

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