Preparation method of underwater anti-dispersion micro-expansion early high-strength cement mortar

Abstract

The application discloses a preparation method of underwater anti-dispersion micro-expansion early high-strength cement mortar, and relates to the technical field of building materials. The method is prepared by dry mixing, composite slurry, wet mixing in stages, curing, precise pouring and hierarchical maintenance, parameters of each link are controlled, underwater anti-dispersion, micro-expansion, early high-strength performance are achieved, and the method is suitable for seabed construction requirements. The application has the advantages that: through the collaborative design of the composite early strength system and the cementitious material system, the antagonistic contradiction between the traditional early strength component and the low alkali performance is broken, the cement hydration process is accelerated, the early strength is quickly formed, the requirements of underwater engineering rapid construction and rapid bearing are met, the content of free alkali substances in the system is reduced, the erosion risk of corrosive medium to the mortar and the matrix interface is reduced, meanwhile, the adaptability design of the cementitious material and the expansion component compensates the shrinkage deformation in the hardening process, avoids the generation of cracks, and guarantees the firm combination of the mortar and the seabed rock.

Description

Technical Field

[0001] This invention relates to the field of building materials technology, specifically to a method for preparing underwater anti-dispersion micro-expansion early high-strength cement mortar. Background Technology

[0002] With the rapid advancement of infrastructure projects such as marine development, cross-river and cross-sea transportation engineering, underwater tunnels, and port and wharf construction in my country, the scale and technical difficulty of underwater casting and reinforcement projects are continuously increasing, placing more stringent requirements on the comprehensive performance of special cement mortars. The underwater construction environment is unique; factors such as water flow disturbance, high salt and high chloride corrosion from seawater, and low temperature and high humidity directly affect the construction effect and long-term service stability of cementitious materials. Therefore, developing special cement mortars suitable for complex underwater working conditions has become a key direction for the industry's development.

[0003] Existing underwater construction cement mortars mainly meet the basic requirements of underwater casting by accelerating the hydration reaction with a single early-strength agent and reducing material loss by simply compounding anti-dispersion agents. However, this approach has certain drawbacks. First, there is an antagonistic contradiction between the early-strength component and the low-alkali performance, and the mortar is prone to shrinkage cracks during the hardening process, making it difficult to balance early strength and long-term stability of the project. Second, the anti-dispersion ability is weak. In the construction of a certain tunnel, ordinary mortar suffered severe dispersion and loss under the action of moving water. Even the grouting of a subway at sea surface failed to form a complete solidified body due to the easy dispersion of the grout. It lacks a dual protection mechanism, has insufficient water resistance and corrosion resistance, cannot adapt to the complex construction environment of the seabed, and has poor adhesion and durability. Therefore, we propose a method for preparing underwater anti-dispersion micro-expansion early high-strength cement mortar. Summary of the Invention

[0004] The purpose of this invention is to provide a method for preparing underwater anti-dispersion micro-expansion early high-strength cement mortar.

[0005] To achieve the above objectives, the present invention provides the following technical solution: a method for preparing underwater anti-dispersion micro-expansion early high-strength cement mortar, comprising the following steps:

[0006] Step 1: Measure the cementitious material system, composite early strength system, anti-dispersion composite system, functional admixture, aggregate and deionized water according to the preset weight parts, and set aside.

[0007] Step 2: Add the cementitious material system into a twin-shaft mixer and stir until uniformly mixed at the set temperature and speed.

[0008] Step 3: Add the composite early strength system, modified water-repellent agent and other functional additives to an independent mixing container, add a small amount of deionized water and stir to prepare a composite functional additive slurry;

[0009] Step 4: Mix the cementitious material base material from Step 2 with the composite functional additive slurry from Step 3, and stir at the set speed and temperature until the preset uniformity is achieved.

[0010] Step 5: Add deionized water to the dried mixture from Step 4 at a uniform rate according to the preset water-to-binder ratio, stir in stages and adjust the flowability to the preset range in real time.

[0011] Step 6: Allow the mixed slurry to mature under the set conditions. After maturation, test the key properties and adjust as needed.

[0012] Step 7: Use a conduit with an anti-backflow device to inject the matured slurry into the construction area, control the pouring speed and the depth of the conduit, and monitor the seawater flow rate.

[0013] Step 8: After pouring, perform graded curing in the natural underwater environment, and test the core performance after curing until it meets the preset requirements.

[0014] As a further aspect of the present invention: in step one, the raw materials are measured in the following parts by weight:

[0015] The cementitious material system consists of 580-620 parts of R·SAC42.5 cement, 330-370 parts of P.Ⅰ52.5 cement, 30-70 parts of mineral powder, 40-60 parts of nano silica fume, and 5-15 parts of anhydrous calcium sulfoaluminate expansive agent. The particle size of the anhydrous calcium sulfoaluminate expansive agent is 10-50μm.

[0016] The composite early strength system consists of 1.8-2.2 parts lithium sulfate and 0.2-0.3 parts hydroxyapatite, with lithium sulfate purity ≥90% and hydroxyapatite particle size of 50-100 nm.

[0017] The anti-dispersion composite system consists of 1.8-2.2 parts of cellulose ether with a viscosity of 100,000 and 0.9-1.1 parts of cationic polyacrylamide.

[0018] The functional admixtures include 6-8 parts of polycarboxylate high-performance water-reducing agent, 2.4-2.8 parts of quaternized montmorillonite and 5.6-6.2 parts of multi-component copolymerized organosilicon modified water-repellent agent, 0.7-0.9 parts of tartaric acid, 0.4-0.6 parts of defoamer, 220-270 parts of 70-140 mesh quartz sand as aggregate, and deionized water calculated according to a water-cement ratio of 0.3-0.35.

[0019] As a further aspect of the present invention: In step two, the stirring speed of the twin-shaft mixer is 300-400 r / min, the stirring time is 10-15 min, the stirring ambient temperature is 20-25℃, and the mixer is stopped every 3 min during the stirring process to check the uniformity of material mixing, requiring that the material has no obvious color difference or clumping.

[0020] As a further aspect of the present invention: in step three, the stirring speed is 500-600 r / min, the stirring time is 5-8 min, the stirring temperature is controlled at 20-25℃, and the amount of deionized water added is 5-8 parts. The components in the composite functional additive slurry form a stable synergistic phase without antagonistic effects.

[0021] As a further aspect of the present invention: in step four, the stirring mode is high-speed stirring, the rotation speed is 800-1000 r / min, the stirring time is 8-12 min, and the material temperature does not exceed 30℃ during the stirring process.

[0022] As a further aspect of the present invention: In step five, the deionized water is added at a rate of 10-15 parts / min. First, the mixture is stirred at a low speed of 400-500 r / min for 3-5 min, and then stirred at a medium speed of 600-700 r / min for 5-8 min. The fluidity of the slurry is maintained at 200-220 mm. When the fluidity is lower than 200 mm, 0.1-0.3 parts of polycarboxylate high-performance water-reducing agent are added. When the fluidity is higher than 220 mm, 1-2 parts of dried mixture are added.

[0023] As a further aspect of the present invention: In step six, the curing environment temperature is 20-25℃, the curing time is 5-10 min, and during the curing period, the mixture is slowly stirred along the container wall with a glass rod for 10 seconds every 2 min. After curing, the initial setting time of the slurry is controlled at 15-18 min, and the final setting time is controlled at 18-23 min. The underwater anti-dispersion property meets the requirement that there is no obvious loss or stratification after standing for 30 min. If the initial setting time is <15 min, 0.1-0.2 parts of tartaric acid are added. If the initial setting time is >18 min, 0.2-0.3 parts of the composite early strength system are added. If the underwater anti-dispersion loss rate is >5% after standing for 30 min, 0.2-0.3 parts of cationic polyacrylamide are added.

[0024] As a further aspect of the present invention: in step seven, the pouring speed is controlled at 0.5-1.0 m / s². 3 / h, the depth of the conduit buried in the grout is maintained at 1.0-1.5m. During the pouring process, the seawater flow velocity in the pouring area is monitored. If the flow velocity is >0.3m / s, the pouring is suspended and temporary flow blocking measures are taken.

[0025] As a further aspect of the present invention: In step eight, the graded curing includes the first stage of 1-2 hours monitoring the heat release changes of the slurry, with the temperature rise controlled within 10-15℃; the second stage of 2-24 hours maintaining the stability of the seawater environment around the slurry; and the core performance testing after 24 hours of curing: underwater compressive strength ≥15MPa, expansion rate 0.05%-0.1%, free hydroxide ion reduction rate ≥60%, and chloride ion diffusion coefficient reduction ≥50%. The strength and bonding stability are rechecked after 7 days of curing.

[0026] Compared with the prior art, the beneficial effects of the present invention by adopting the above technical solution are as follows:

[0027] 1. This invention overcomes the antagonistic contradiction between traditional early-strength components and low-alkali properties through the synergistic design of a composite early-strength system and a cementitious material system. In the composite early-strength system, lithium sulfate can directly accelerate the hydration process of sulfoaluminate cement and silicate cement, achieving rapid improvement in early strength. 50-100nm nano-sized hydroxyapatite can provide a large number of nano-sized hydration nucleation sites due to its ultra-high specific surface area, significantly reducing the nucleation barrier of cement hydration products and accelerating the generation and growth of hydrated calcium silicate gel and ettringite crystals, thus achieving early-strength effect in conjunction with lithium sulfate. At the same time, nano-hydroxyapatite can react with free calcium hydroxide produced by cement hydration, fixing the free alkali in the system and further reducing the alkalinity of the system. In synergy with lithium sulfate, it not only accelerates the cement hydration process and promotes rapid formation of early strength to meet the needs of rapid construction and rapid load-bearing in underwater engineering, but also reduces the content of free alkaline substances in the system, reducing the risk of corrosion from corrosive media to the mortar and matrix interface. Meanwhile, the compatibility design of cementitious materials and expansion components effectively compensates for shrinkage deformation during the hardening process, avoids cracking, ensures a strong bond between the mortar and the seabed rock, and enhances the long-term stability of the project.

[0028] 2. This invention significantly enhances the underwater anti-dispersion ability of mortar by utilizing a dual protection mechanism of an anti-dispersion composite system and a modified water-repellent agent, reducing the loss of effective components during construction and ensuring the uniformity and integrity of underwater pouring. The protective layer formed by the modified water-repellent agent on the mortar surface, combined with the densification effect of the cementitious material, can not only block water penetration but also resist the erosion of harmful ions such as chloride ions, thereby improving the water resistance and corrosion resistance of the mortar. This approach is suitable for complex underwater construction environments, solves the problems of poor adhesion and insufficient durability of traditional underwater mortars, and broadens the engineering application scenarios of special mortars. Attached Figure Description

[0029] Figure 1 This is a scanning electron microscope image of cement mortar after hardening for 24 hours in Example 1 of this invention.

[0030] Figure 2 This is a schematic diagram of the method steps in an embodiment of the present invention. Detailed Implementation

[0031] The specific embodiments of the present invention will be further described below with reference to the accompanying drawings. It should be noted that the description of these embodiments is for the purpose of helping to understand the present invention, but does not constitute a limitation of the present invention.

[0032] Furthermore, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0033] Please see the appendix Figure 1 -Appendix Figure 2 The present invention discloses a method for preparing underwater anti-dispersion micro-expansion early high-strength cement mortar, comprising the following steps:

[0034] Step 1: Measure the cementitious material system, composite early strength system, anti-dispersion composite system, functional admixture, aggregate and deionized water according to the preset weight parts, and set aside.

[0035] Step 2: Add the cementitious material system into a twin-shaft mixer and stir until uniformly mixed at the set temperature and speed.

[0036] Step 3: Add the composite early strength system, modified water-repellent agent and other functional additives to an independent mixing container, add a small amount of deionized water and stir to prepare a composite functional additive slurry;

[0037] Step 4: Mix the cementitious material base material from Step 2 with the composite functional additive slurry from Step 3, and stir at the set speed and temperature until the preset uniformity is achieved.

[0038] Step 5: Add deionized water to the dried mixture from Step 4 at a uniform rate according to the preset water-to-binder ratio, stir in stages and adjust the flowability to the preset range in real time.

[0039] Step 6: Allow the mixed slurry to mature under the set conditions. After maturation, test the key properties and adjust as needed.

[0040] Step 7: Use a conduit with an anti-backflow device to inject the matured slurry into the construction area, control the pouring speed and the depth of the conduit, and monitor the seawater flow rate.

[0041] Step 8: After pouring, perform graded curing in the natural underwater environment, and test the core performance after curing until it meets the preset requirements.

[0042] Example 1: Raw Material Measurement: Each component was accurately weighed according to weight parts. The cementitious material system consisted of 600 parts of R·SAC42.5 cement, 350 parts of P.I52.5 cement, 50 parts of mineral powder, 50 parts of nano silica fume, and 10 parts of anhydrous calcium sulfoaluminate expansion agent with a particle size of 30μm, meeting the 10-50μm requirement. The composite early strength system consisted of 2.0 parts of lithium sulfate and 0.25 parts of hydroxyapatite. The anti-dispersion composite system consisted of 2.0 parts of 100,000 viscosity cellulose ether and 1.0 part of cationic polyacrylamide. The functional admixtures consisted of 7 parts of polycarboxylate high-performance water-reducing agent, 2.6 parts of quaternized montmorillonite, 5.9 parts of multi-component copolymerized organosilicon, 0.8 parts of tartaric acid, and 0.5 parts of defoamer. The aggregate consisted of 240 parts of 70-140 mesh quartz sand. The amount of deionized water was calculated based on a water-cement ratio of 0.32, and the dosage was 345.6 parts.

[0043] Dry mixing of cementitious materials: Put all the above cementitious materials into a twin-shaft mixer, set the mixing environment temperature to 23℃ (within the 20-25℃ range), the mixing speed to 350r / min, and the mixing time to 12min. During the mixing process, stop the machine at 3min, 6min, 9min, and 12min to check the uniformity of the material mixing. Observe that there is no obvious color difference or clumping in the material, and confirm that the mixing meets the standards.

[0044] Preparation of composite functional admixture slurry: Take an independent stirring container, add the composite early strength system, modified water repellent and other functional admixtures in sequence, add 6 parts of deionized water precisely, set the stirring speed to 550 r / min, the stirring time to 6 min, and maintain the ambient temperature at 23℃ during the stirring process to finally form a composite functional admixture slurry with no antagonistic effect among the components and stable synergy.

[0045] Mixing and stirring: Import all the cementitious material base material prepared in step 2 into the mixing equipment, and then slowly add the composite functional additive slurry from step 3. Turn on the high-speed stirring mode, set the speed to 900 r / min, and the stirring time to 10 min. Monitor the material temperature in real time during the stirring process, and control the temperature at 28℃ through the equipment temperature control system, ensuring that it does not exceed the limit requirement of 30℃, so as to ensure that the material mixing reaches the preset uniformity.

[0046] Add water and stir in stages: Add the calculated deionized water to the dried mixture in step 4 at a rate of 12 parts / min. First, stir at a low speed of 450 r / min for 4 min, then switch to a medium speed of 650 r / min for 6 min. Detect the fluidity of the slurry in real time during the stirring process. The final fluidity was measured to be 210 mm, which is within the preset range of 200-220 mm. No additional water-reducing agent or dried mixture needs to be added.

[0047] Maturation adjustment: Transfer the stirred slurry to a maturation container and place it in a 23℃ environment for 8 minutes. During maturation, stir slowly along the container wall with a glass rod for 10 seconds at the 2nd, 4th, 6th and 8th minutes respectively to avoid local solidification or stratification of the slurry. After maturation, test the key performance: initial setting time 16 minutes, final setting time 20 minutes, no obvious loss or stratification after standing underwater for 30 minutes, loss rate 3.8%, all performance meets the standards, no component adjustment is required.

[0048] Underwater pouring: Pouring is carried out using a duct equipped with an anti-backflow device, with a set pouring speed of 0.8m. 3 / h, the depth of the conduit buried in the grout was maintained at 1.2m by the depth monitoring equipment. During the pouring process, the seawater flow velocity in the pouring area was monitored in real time and the measured flow velocity was 0.2m / s, which did not exceed the limit of 0.3m / s. Therefore, there was no need to stop the pouring. The entire pouring process was stable and orderly.

[0049] Graded curing: After pouring, graded curing is carried out in the natural seabed environment. In the first stage (1-2 hours), the heat release of the slurry is monitored in real time, and the temperature rise is recorded as 12℃. In the second stage (2-24 hours), protective devices are used to maintain the stability of the seawater environment around the slurry, avoiding water flow impact or drastic temperature fluctuations. After 24 hours of curing, the core performance is tested as required. After 7 days of curing, the strength and bond stability are re-checked to ensure that the project meets the requirements for use.

[0050] from Figure 1 (SEM image of cement mortar after 24 hours of hardening in Example 1 of this invention) It can be observed that the cement hydration products have a dense structure, the hydrated calcium silicate gel is continuous and uniform, and the ettringite crystals are regularly dispersed, with no obvious harmful pores or microcracks. This microscopic morphology confirms that this method can precisely control the cement hydration process, effectively improve the early strength and resistance to chloride ion erosion of the mortar, while compensating for hardening shrinkage and ensuring the interfacial bonding stability with the matrix, which completely corresponds to the measured macroscopic properties.

[0051] Example 2: Raw material measurement: 620 parts of R·SAC42.5 cement, 370 parts of P.I52.5 cement, 70 parts of mineral powder, 60 parts of nano silica fume, 15 parts of anhydrous calcium sulfoaluminate expansion agent, 2.2 parts of lithium sulfate, 0.3 parts of hydroxyapatite; 2.2 parts of cellulose ether with a viscosity of 100,000, 1.1 parts of cationic polyacrylamide; 8 parts of polycarboxylate high-performance water-reducing agent, 2.8 parts of quaternized montmorillonite, 6.2 parts of multi-component copolymerized organosilicon, 0.9 parts of tartaric acid, 0.6 parts of defoamer; 270 parts of 70-140 mesh quartz sand; deionized water, calculated at a water-cement ratio of 0.35, with a dosage of 415.5 parts.

[0052] Dry mixing of cementitious materials: ambient temperature 25℃, speed 400r / min, stir for 15min, stop the machine and check that the mixing uniformity meets the standard.

[0053] Preparation of composite functional additive slurry: Add 8 parts of deionized water, stir at 600 r / min for 8 min, and the slurry is stable and does not separate.

[0054] Mixing and stirring: 1000 r / min speed, 12 min stirring, material temperature 30℃.

[0055] Add water and stir in stages: Add water at a rate of 15 parts / min, stir at low speed for 5 minutes, stir at medium speed for 8 minutes, and maintain a flowability of 220 mm.

[0056] Curing adjustment: Curing at 25℃ for 10 minutes, initial setting time 18 minutes, final setting time 23 minutes, underwater loss rate 4.3%.

[0057] Underwater pouring: pouring speed 1.0m 3 / h, the duct was buried at a depth of 1.5m, the seawater flow velocity was 0.25m / s, and the pouring was successful.

[0058] Graded maintenance: The temperature rises by 15℃ in 1 hour, and the performance is tested after 24 hours.

[0059] Example 3: Raw material measurement: 580 parts of R·SAC42.5 cement, 330 parts of P.I52.5 cement, 30 parts of mineral powder, 40 parts of nano silica fume, 5 parts of anhydrous calcium sulfoaluminate expansion agent; 1.8 parts of lithium sulfate, 0.2 parts of hydroxyapatite; 1.8 parts of cellulose ether with a viscosity of 100,000, 0.9 parts of cationic polyacrylamide; 6 parts of polycarboxylate high-performance water-reducing agent, 2.4 parts of quaternized montmorillonite, 5.6 parts of multi-component copolymerized organosilicon, 0.7 parts of tartaric acid, 0.4 parts of defoamer; 220 parts of 70-140 mesh quartz sand; 294 parts of deionized water calculated at a water-cement ratio of 0.3.

[0060] Dry mixing of cementitious materials: ambient temperature 20℃, speed 300r / min, stir for 10min, mix evenly.

[0061] Preparation of composite functional additive slurry: Add 5 parts of deionized water, stir at 500 r / min for 5 min until the slurry is uniform.

[0062] Mixing and stirring: 800 r / min speed, 8 min stirring, material temperature 25℃.

[0063] Add water and stir in stages: Add water at a rate of 10 parts / min, stir at low speed for 3 minutes, stir at medium speed for 5 minutes, and maintain a flowability of 200 mm.

[0064] Curing adjustment: Curing at 20℃ for 5 minutes, initial setting time 15 minutes, final setting time 18 minutes, underwater loss rate 3.6%.

[0065] Underwater pouring: pouring speed 0.5m 3 / h, duct burial depth 1.0m, seawater flow velocity 0.15m / s, irrigation stable.

[0066] Graded maintenance: Temperature rises by 10℃ in 1 hour, and performance is tested after 24 hours.

[0067] The formulations and process parameters for Examples 1-3 are shown in Table 1:

[0068] The formulation and process parameters for Examples 1-2 are shown in the table below:

[0069] Comparative Example 1

[0070] Compared with Example 1, no 100,000 viscosity cellulose ether and cationic polyacrylamide were added, but the amounts of other raw materials, preparation steps and process parameters were the same as in Example 1;

[0071] Comparative Example 2

[0072] Compared with Example 1, the amount of lithium sulfate used was 3.0 parts, which exceeded the range of 1.8-2.2 parts, and the amount of hydroxyapatite used was 0.4 parts, which exceeded the range of 0.2-0.3 parts, while the other conditions remained unchanged.

[0073] Test methods

[0074] Based on relevant standards and industry specifications, the following test items and conditions were established to comprehensively evaluate the material properties:

[0075] Anti-dispersion loss rate: According to the "Test Procedure for Underwater Non-dispersible Concrete" (DL / T5117-2000), simulate seawater environment (flow velocity 0.3m / s), and calculate the loss rate after standing for 30 minutes. The formula is: Anti-dispersion loss rate = (mass of lost solids / mass of initial slurry solids) × 100%, ambient temperature 25±1℃.

[0076] Setting time: According to the "Test Methods for Standard Consistency Water Requirement, Setting Time and Soundness of Cement" (GB / T1346-2011), the initial setting and final setting times were determined using a Vicat apparatus at a test temperature of 20±2℃ and a relative humidity of ≥90%.

[0077] 1-hour underwater compressive strength: According to the "Test Method for Strength of Cement Mortar" (GB / T17671-2021), 40×40×160mm specimens were prepared and tested after underwater curing for 1 hour at an ambient temperature of 20±2℃.

[0078] 24h expansion rate: According to "Concrete Expansion Agent" (GB / T23439-2017), the 24h expansion rate was determined using a length comparator. The specimen size was 25×25×280mm, and the standard curing conditions were used.

[0079] Free hydroxide reduction rate: The concentration of free hydroxide in the slurry was determined by potentiometric titration, and the reduction rate was calculated by comparing it with that of the reference silicate cement.

[0080] Chloride ion diffusion coefficient: The rapid chloride ion migration coefficient method (RCM method, NTBUILD492) was used to prepare 100×50mm cylindrical specimens, which were tested after standard curing for 28 days. The sodium chloride solution concentration was 3.5%, and the test temperature was 20±2℃.

[0081] Exothermic changes: Temperature changes are monitored in real time within 1-2 hours of curing using temperature sensors, and the rate of temperature rise is recorded.

[0082] Flowability: According to the "Method for Determining the Flowability of Cement Paste", the truncated cone mold method is used for determination, and the test temperature is 25±1℃.

[0083] Table 2 shows the performance test results of the examples and comparative examples:

[0084] Results Analysis

[0085] Anti-dispersion properties

[0086] The anti-dispersion loss rates of Examples 1-3 were all between 3.6% and 4.3%, which were much lower than the 28.5% of Comparative Example 1. Comparative Example 1 lacked cellulose ether with a viscosity of 100,000 and cationic polyacrylamide, so it could not form a stable three-dimensional network structure, and the slurry was easily lost underwater. This proves that the anti-dispersion composite system is the core component to ensure underwater anti-dispersion. In the examples, the two anti-dispersion agents worked synergistically. Cellulose ether improved the viscosity of the slurry, and cationic polyacrylamide enhanced the cohesion, effectively inhibiting the loss in the seawater environment.

[0087] Setting time and early strength properties

[0088] In the example, the initial setting time was controlled at 15-18 minutes, and the final setting time at 18-23 minutes, meeting the design requirements. Furthermore, the underwater compressive strength at 1 hour was ≥15.8 MPa, satisfying the rapid load-bearing requirement. In contrast, in Comparative Example 2, due to excessive use of the accelerator, the initial setting time was shortened to 12 minutes, and the final setting time to 15 minutes. This excessively rapid setting resulted in a short construction window, and the underwater compressive strength at 1 hour was only 14.3 MPa. In Comparative Example 2, the amount of hydroxyapatite exceeded the set range of 0.2-0.3 parts, causing nanoparticles to agglomerate and become unevenly distributed. When dispersed in the hydration system, the loss of the nanonucleation effect actually disrupts the structural density of the hydration products, leading to a decrease in early strength. This indicates that the amounts of lithium sulfate and hydroxyapatite must be strictly controlled within the set range. Excessive lithium sulfate will directly cause the cement hydration reaction to be too violent, the setting time to be too fast, and the construction window to be significantly shortened. Excessive hydroxyapatite, on the other hand, will not be evenly dispersed in the hydration system due to the agglomeration effect of nanoparticles, thus losing the nanonucleation effect and disrupting the structural continuity of the hydration products. Excessive amounts of both will affect the workability and strength development of the slurry.

[0089] Expansion rate and low alkalinity

[0090] The 24-hour expansion rate of the examples was between 0.05% and 0.10%, precisely meeting the micro-expansion requirements, effectively compensating for slurry shrinkage, and avoiding cracking. The expansion rate of Comparative Example 1 was only 0.03%, and the lack of an anti-dispersion system led to the loss of the effective components of the expansion agent. The expansion rate of Comparative Example 2 was 0.12%, exceeding the design range and easily causing structural deformation. The free hydroxide reduction rate of the examples was between 63% and 67%, and met the standard of ≥60%, while that of Comparative Example 1 was only 25%. This shows that the synergistic effect of the cementitious material system and the modified water-repellent agent can effectively reduce the alkalinity of the slurry and improve its adhesion to the rock base layer.

[0091] Durability and heat dissipation performance

[0092] The chloride ion diffusion coefficients in all examples are ≤2.4×10⁻⁶. -12 m 2 / s, far lower than the 5.8 × 10 in Comparative Example 1. -12 m 2 / s, meeting the requirement of a ≥50% reduction in chloride ion diffusion coefficient, indicating that the component design of this invention can effectively improve the resistance to chloride ion corrosion and ensure long-term service stability. The exothermic rise is controlled between 10-15℃, which meets the design requirements. In contrast, due to excessive early strength agent, the exothermic rise in Comparative Example 2 reached 18℃, which easily led to internal temperature stress cracking of the slurry.

[0093] Flowability

[0094] The fluidity of the embodiment is between 200-220 mm, which meets the construction and grouting requirements. In contrast, the fluidity of Comparative Example 1, which does not contain an anti-dispersant, reaches 235 mm, and the slurry is too thin, resulting in serious loss.

[0095] Summarize

[0096] This invention successfully solves the technical problems of poor anti-dispersion properties, insufficient early strength, uncontrolled expansion rate, and substandard low alkalinity in traditional underwater cement mortar through precise component synergistic design and process optimization. The synergistic effect of the cementitious material system, composite early strength system, anti-dispersion composite system, and functional admixtures achieves a balance between anti-dispersion properties, early strength, micro-expansion properties, and low alkalinity of the mortar. The preparation process, including dry mixing pre-homogenization, high-speed stirring, staged water addition, and maturation adjustment, ensures the stability and consistency of material properties.

[0097] The test results of the examples show that the cement mortar of the present invention has an anti-dispersion loss rate of ≤4.3%, an underwater compressive strength of ≥15.8MPa after 1 hour, an expansion rate of 0.05%-0.10% after 24 hours, a free hydroxide ion reduction rate of ≥63%, and a chloride ion diffusion coefficient of ≤2.4×10⁻⁶. -12 m 2 / s, all performance characteristics are suitable for harsh underwater construction scenarios such as seabed rock sub-layer grouting, and comparative verification has verified the necessity of key components and process parameters. The absence of core components or deviation from the process range will lead to a significant decrease in performance.

[0098] Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make possible changes and modifications without departing from the spirit and scope of the present invention. Therefore, any modifications, equivalent changes and alterations made to the above embodiments based on the technical essence of the present invention without departing from the content of the technical solution of the present invention shall fall within the protection scope defined by the claims of the present invention.

Claims

1. A method for preparing underwater anti-dispersion micro-expansion early high-strength cement mortar, characterized in that, Includes the following steps: Step 1: Measure the cementitious material system, composite early strength system, anti-dispersion composite system, functional admixture, aggregate and deionized water according to the preset weight parts, and set aside. The corresponding raw materials are measured in the following parts by weight: The cementitious material system consists of 580-620 parts of R·SAC42.5 cement, 330-370 parts of P.Ⅰ52.5 cement, 30-70 parts of mineral powder, 40-60 parts of nano silica fume, and 5-15 parts of anhydrous calcium sulfoaluminate expansive agent. The particle size of the anhydrous calcium sulfoaluminate expansive agent is 10-50μm. The composite early strength system consists of 1.8-2.2 parts lithium sulfate and 0.2-0.3 parts hydroxyapatite, with lithium sulfate purity ≥90% and hydroxyapatite particle size of 50-100 nm. The anti-dispersion composite system consists of 1.8-2.2 parts of cellulose ether with a viscosity of 100,000 and 0.9-1.1 parts of cationic polyacrylamide. The functional admixtures include 6-8 parts of polycarboxylate high-performance water-reducing agent, 2.4-2.8 parts of quaternized montmorillonite and 5.6-6.2 parts of multi-component copolymerized organosilicon modified water-repellent agent, 0.7-0.9 parts of tartaric acid, 0.4-0.6 parts of defoamer, 220-270 parts of 70-140 mesh quartz sand as aggregate, and deionized water calculated according to a water-cement ratio of 0.3-0.

35. Step 2: Add the cementitious material system into a twin-shaft mixer and stir until uniformly mixed at the set temperature and speed. Step 3: Add the composite early strength system, modified water-repellent agent and other functional additives to an independent mixing container, add a small amount of deionized water and stir to prepare a composite functional additive slurry; Step 4: Mix the cementitious material base material from Step 2 with the composite functional additive slurry from Step 3, and stir at the set speed and temperature until the preset uniformity is achieved to obtain a dry mixture. Step 5: Add deionized water to the dried mixture from Step 4 at a uniform rate according to the preset water-to-binder ratio, stir in stages and adjust the flowability to the preset range in real time. Step 6: Allow the mixed slurry to mature under the set conditions. After maturation, test the key properties and adjust as needed. Step 7: Use a conduit with an anti-backflow device to inject the matured slurry into the construction area, control the pouring speed and the depth of the conduit, and monitor the seawater flow rate. Step 8: After pouring, perform graded curing in the natural underwater environment, and test the core performance after curing until it meets the preset requirements.

2. The method for preparing underwater anti-dispersion micro-expansion early high-strength cement mortar according to claim 1, characterized in that: In step two, the stirring speed of the twin-shaft mixer is 300-400 r / min, the stirring time is 10-15 min, the stirring ambient temperature is 20-25℃, and the mixer is stopped every 3 min during the stirring process to check the uniformity of the material mixing. The material should have no obvious color difference or clumping.

3. The method for preparing underwater anti-dispersion micro-expansion early high-strength cement mortar according to claim 1, characterized in that: In step three, the stirring speed is 500-600 r / min, the stirring time is 5-8 min, the stirring temperature is controlled at 20-25℃, and the amount of deionized water added is 5-8 parts. The components in the composite functional additive slurry form a stable synergistic phase without antagonistic effects.

4. The method for preparing underwater anti-dispersion micro-expansion early high-strength cement mortar according to claim 1, characterized in that: In step four, the stirring mode is high-speed stirring, the speed is 800-1000 r / min, the stirring time is 8-12 min, and the material temperature does not exceed 30℃ during the stirring process.

5. The method for preparing underwater anti-dispersion micro-expansion early high-strength cement mortar according to claim 1, characterized in that: In step five, the deionized water is added at a rate of 10-15 parts / min. First, stir at a low speed of 400-500 r / min for 3-5 min, then stir at a medium speed of 600-700 r / min for 5-8 min. The fluidity of the slurry is maintained at 200-220 mm. If the fluidity is lower than 200 mm, add 0.1-0.3 parts of polycarboxylate high-performance water-reducing agent. If the fluidity is higher than 220 mm, add 1-2 parts of dried mixture.

6. The method for preparing underwater anti-dispersion micro-expansion early high-strength cement mortar according to claim 1, characterized in that: In step six, the curing temperature is 20-25℃, the curing time is 5-10 minutes, and during curing, the mixture is slowly stirred along the container wall with a glass rod for 10 seconds every 2 minutes. After curing, the initial setting time of the slurry is controlled at 15-18 minutes, and the final setting time is controlled at 18-23 minutes. The underwater anti-dispersion property meets the requirement that there is no obvious loss or stratification after standing for 30 minutes. If the initial setting time is <15 minutes, 0.1-0.2 parts of tartaric acid are added. If the initial setting time is >18 minutes, 0.2-0.3 parts of the composite early strength system are added. If the loss rate of the underwater anti-dispersion property after standing for 30 minutes is >5%, 0.2-0.3 parts of cationic polyacrylamide are added.

7. The method for preparing underwater anti-dispersion micro-expansion early high-strength cement mortar according to claim 1, characterized in that: In step seven, the pouring speed is controlled between 0.5 and 1.0 m / s. 3 / h, the depth of the conduit buried in the grout is maintained at 1.0-1.5m. During the pouring process, the seawater flow velocity in the pouring area is monitored. If the flow velocity is >0.3m / s, the pouring is suspended and temporary flow blocking measures are taken.

8. The method for preparing underwater anti-dispersion micro-expansion early high-strength cement mortar according to claim 1, characterized in that: In step eight, the graded curing includes the first stage of 1-2 hours monitoring the heat release changes of the slurry, with the temperature rise controlled within 10-15℃; the second stage of 2-24 hours maintaining the stability of the seawater environment around the slurry; and the core performance testing after 24 hours of curing: underwater compressive strength ≥15MPa, expansion rate 0.05%-0.1%, free hydroxide ion reduction rate ≥60%, and chloride ion diffusion coefficient reduction ≥50%. The strength and bonding stability are rechecked after 7 days of curing.

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