A retarding type super-early-strength fast-hardening mortar and a preparation method thereof

Abstract

This invention discloses a retarded ultra-early strength and rapid-hardening mortar and its preparation method. This invention relates to the field of building materials technology. It designs a core-shell structure with a targeted modified early-strength agent, employs a staged dry-wet mixing process, and combines it with in-situ seabed curing to achieve synergy between retarded mortar construction and ultra-early strength development. This is suitable for the temporary support requirements of deep-sea caisson grouting. The advantages of this invention are: through the design of the targeted modified early-strength agent, a surface retarded shell and a core early-strength core structure are formed through the grafting reaction of sodium nitrite and hydroxycarboxylic acid monomers. Combined with precise grafting rate control of 15%-25%, it can solve the antagonistic problem between traditional early-strength agents and retarders. In the deep-sea environment, the retarded shell can guarantee a construction window of 75-105 minutes, meeting the needs of long-distance seabed grouting. The high pressure of the deep sea can trigger the rupture of the retarded shell, and the core early-strength core rapidly activates cement hydration, allowing the mortar to quickly form sufficient strength to meet the rapid load-bearing requirements of temporary caisson support.

Description

TECHNICAL FIELD

[0001] The application relates to the technical field of building materials, in particular to a retarding type super-early-strength fast-hardening mortar and a preparation method thereof. BACKGROUND

[0002] With the continuous expansion of China's transportation infrastructure construction to the marine field, large marine projects such as cross-sea bridges and submarine tunnels are increasing, and such projects often face special construction technical challenges under deep-sea complex environments, and the sinking well foundation construction is one of the key links, which is directly related to the overall stability and safety of the project.

[0003] The existing super-early-strength fast-hardening mortar mainly uses a single cementing material to match traditional early-strength agents and retarding agents to physically mix to consider the construction operability and early strength development, and has certain defects, first, the early-strength agent and the retarding agent naturally antagonize, and cannot consider the sufficient construction window and the rapid bearing demand under the special environment such as the deep sea, and the problems of pipe blockage or insufficient strength are prone to occur, second, the microstructure of the single cementing system is loose, lacks multi-material collaborative optimization, and is difficult to withstand the deep-sea low-temperature high-pressure environment, and the durability and stability are insufficient, therefore, the application provides a retarding type super-early-strength fast-hardening mortar and a preparation method thereof. SUMMARY

[0004] To achieve the above-mentioned purpose, the application provides the following technical scheme: a preparation method of a retarding type super-early-strength fast-hardening mortar, the preparation method comprises the following steps:

[0005] Step one, fast hardening sulphoaluminate cement, Portland cement, mineral powder, graded quartz sand, borax and functional additives are selected, the aggregates are dried and screened to remove impurities, and it is ensured that the raw materials meet the subsequent preparation and construction performance requirements;

[0006] Step two, sodium nitrite and hydroxyl carboxylic acid monomers are weighed according to the proportion, dissolved, heated, and reacted, and after the reaction is completed, the modified early-strength agent in the form of a solid with a surface retarding shell and a core early-strength core structure is formed through spray drying treatment, and the grafting rate is controlled to be in the range of 15%-25%;

[0007] Step three, each component is weighed according to the set mass percentage, and the water-binder ratio and the batching error are controlled to be in a limited range;

[0008] Step four, the cement, aggregates and solid functional additives are put into a mixer, dry mixing is carried out according to the set speed and time, and the mixture reaches a preset homogenization state;

[0009] Step five, water and liquid functional additives are mixed to form an additive aqueous solution, which is injected into the dry materials and stirred according to the set stirring conditions, so that the workability of the mortar meets the preset requirements;

[0010] Step six, the stirring completed mortar is injected into the grouting equipment within a limited time, grouting is carried out to the underwater rubber capsule on the seabed through a grouting pipe, the grouting pressure, grouting speed and grouting sequence are controlled, the grouting pipe and the grouting pipe need to meet the requirement of pressure resistance ≥1.8MPa, and it is ensured that the capsule is filled densely inside;

[0011] Step seven, in-situ curing is carried out by using the natural environment on the seabed, the modified early strength agent is triggered by deep-sea high pressure, and then the cement hydration reaction is activated, so that the mortar setting time and strength reach the use standard.

[0012] As a further scheme of the application, in the step one, the fast-hardening sulphoaluminate cement is 62.5 grade, the specific surface area is 380m 2 / kg-450m 2 / kg, the initial setting time is 45min-60min, the portland cement is 52.5 grade, the specific surface area is 300m 2 / kg-350m 2 / kg, the initial setting time is 90min-120min, the particle size of the graded quartz sand is 0.15mm-1.2mm, the clay content is ≤0.8%, the water content is ≤0.5%, the drying treatment condition is drying at 100℃-110℃ for 1.5h-2.5h, and the functional admixture includes defoaming agent, polycarboxylate superplasticizer with a solid content of 40%-60%, hydroxypropyl methyl cellulose water retaining agent with a viscosity of 15000mPa·s-25000mPa·s, and core modified raw material sodium nitrite and hydroxyl carboxylic acid monomer, the mineral powder is S95 grade, the activity index is ≥95%, the specific surface area is 350m 2 / kg-400m 2 / kg, the defoaming agent is silicone, and the solid content is ≥30%.

[0013] As a further scheme of the application, in the step two, the mass ratio of sodium nitrite to hydroxyl carboxylic acid monomer is 10:1-10:2.5, 2.5 times-3.5 times of deionized water of the total mass of sodium nitrite and hydroxyl carboxylic acid monomer is added during the reaction, after stirring and dissolving, the temperature is increased to 60℃-70℃, the stirring speed is controlled at 300r / min-450r / min, the insulation reaction time is 2h-3.5h, after the reaction is completed, the temperature is cooled to room temperature, the solid powder modified early strength agent is obtained through spray drying treatment, the grafting rate is detected by gel permeation chromatography, and the grafting rate is stably controlled at 15%-25%.

[0014] As a further scheme of the present application: in the step three, the mass percentage of each component is: fast hardening sulphoaluminate cement 28%-35%, Portland cement 5%-11%, mineral powder 4%-9%, graded quartz sand 50%-62%, modified early strength agent 0.1%-0.4%, polycarboxylate superplasticizer 0.6%-1.2%, hydroxypropyl methylcellulose water retaining agent 0.05%-0.15%, borax 0.03%-0.08%, defoaming agent 0.02%-0.06%, and the water-binder ratio is controlled to be 0.21-0.26, each component is weighed by using an electronic metering device with precision ≤0.2 kg, and the liquid functional additive is accurately delivered by a metering pump, and the batching error is ≤±1.0%.

[0015] As a further scheme of the present application: in the step four, the stirrer is a double-shaft stirrer, the fast hardening sulphoaluminate cement, the Portland cement, the mineral powder and the graded quartz sand are dry-mixed at a speed of 180 r / min-250 r / min for 1.5 min-2.5 min, then the water retaining agent, the modified early strength agent solid powder and the borax are added, the same speed is kept to continue dry-mixing for 1 min-2 min, until the mixture has consistent color and no obvious particle agglomeration.

[0016] As a further scheme of the present application: in the step five, the deionized water and the polycarboxylate superplasticizer are mixed and stirred uniformly to form an additive aqueous solution, the adding time of the aqueous solution is controlled to be 25 s-65 s, then the stirring speed of the stirrer is increased to 380 r / min-520 r / min, and the stirring is continued for 2.5 min-4.5 min, until the mortar presents a uniform viscous state and has no bleeding and segregation phenomenon, the mortar initial fluidity is detected in real time during the stirring process, and the initial fluidity is ensured to be 280 mm-330 mm and the 1 h fluidity loss is ≤8%.

[0017] As a further scheme of the present application: in the step six, the stirred mortar needs to be injected into a grouting device within 25 min-35 min, the grouting pressure is stably kept at 0.8 MPa-1.2 MPa, the grouting speed is 0.4 m 3 / h-1.2 m 3 / h, the grouting sequence from bottom to top is adopted, when the grouting pipe continuously overflows the uniform mortar, the stable pressure grouting is continued for 4 min-12 min, the sea bottom water temperature is monitored during the grouting process, and the water temperature is controlled to be 10℃-15℃, and the pressure change is monitored at the same time.

[0018] As a further aspect of the present invention: In step seven, the environmental conditions for in-situ curing on the seabed are: depth 25m-30m, pressure 2.5MPa-3.0MPa, water temperature 10℃-15℃. No additional curing measures are required. During the curing process, the high pressure in the deep sea triggers the rupture of the retarding shell of the modified early strength agent, and the core early strength core activates the cement hydration reaction, so that the initial setting time of the mortar is controlled at 75min-105min, the final setting time is ≤120min, and the 3h compressive strength is ≥40MPa. During the curing period, the capsule and grouting pipeline shall not be disturbed until the caisson is settled and adjusted.

[0019] In addition, this application also provides a retarded ultra-early strength rapid-hardening mortar, which is prepared by the preparation method of steps one to seven. Its components include, by mass percentage: 28%-35% rapid-hardening sulfoaluminate cement, 5%-11% silicate cement, 4%-9% mineral powder, 50%-62% graded quartz sand, 0.1%-0.4% modified early strength agent, 0.6%-1.2% polycarboxylate-based high-efficiency water-reducing agent, 0.05%-0.15% hydroxypropyl methylcellulose water-retaining agent, 0.03%-0.08% borax, and 0.02%-0.06% defoamer. The water-cement ratio is 0.21-0.26. The initial setting time of the retarded ultra-early strength rapid-hardening mortar is 75-105 min, the final setting time is ≤120 min, the 3-hour compressive strength is ≥40 MPa, and the initial flowability is 280 mm-330 mm.

[0020] Compared with the prior art, the beneficial effects of the present invention by adopting the above technical solution are as follows:

[0021] 1. This invention, through the design of a targeted modified early strength agent, forms a surface retarded shell and a core early strength core structure through the grafting reaction of sodium nitrite and hydroxycarboxylic acid monomers. With precise grafting rate control of 15%-25%, it can solve the antagonistic problem between traditional early strength agents and retarders. In the deep-sea environment, the retarded shell can ensure a construction window of 75min-105min, meeting the needs of long-distance grouting on the seabed. The high pressure in the deep sea can trigger the rupture of the retarded shell, and the core early strength core can quickly activate cement hydration, allowing the mortar to quickly form sufficient strength to meet the rapid load-bearing requirements of temporary support for caissons.

[0022] 2. This invention optimizes the microstructure of mortar by using a composite cementitious system of rapid-hardening sulfoaluminate cement and silicate cement, combined with the synergistic effect of materials such as mineral powder and borax. The composite cement can complement the performance shortcomings of both materials, the mineral powder can fill the small pores inside the mortar, and the borax can stabilize the gel network structure. In addition, the defoamer reduces the residual air bubbles, making the mortar structure denser. This not only reduces the generation of internal cracks in the mortar, but also improves its tolerance to the seabed environment, and can better adapt to the low temperature and high pressure conditions of the deep sea.

[0023] 3. This invention employs a phased dry-wet mixing process, first fully premixing the dry materials before adding the liquid components and stirring. This allows all materials to be evenly dispersed, avoiding the problems of material agglomeration or uneven distribution that are common in traditional mixing methods. This ensures the consistency of mortar performance. At the same time, it directly utilizes the natural environment of the seabed for in-situ curing, eliminating the need for additional curing equipment or energy consumption. This simplifies the process of deep-sea construction, reducing construction costs and complexity, and further improving the efficiency and reliability of project implementation. Attached Figure Description

[0024] Figure 1 This is a schematic diagram of the preparation process in an embodiment of the present invention;

[0025] Figure 2 This is a schematic diagram comparing the 3-hour compressive strength of the retarded ultra-early strength and rapid hardening mortar in an embodiment of the present invention;

[0026] Figure 3 This is a schematic diagram comparing the setting time of the retarded ultra-early strength and rapid hardening mortar in the embodiments of the present invention;

[0027] Figure 4 This is a schematic diagram comparing the flowability performance of retarded ultra-early strength and fast-hardening mortar in embodiments of the present invention;

[0028] Figure 5 This is a schematic diagram illustrating the comparison of the filling density of slow-setting ultra-early strength and fast-hardening mortar capsules in an embodiment of the present invention;

[0029] Figure 6 This is a schematic diagram illustrating the effect of the grafting rate of the modified early-strength agent on mortar performance in an embodiment of the present invention.

[0030] Figure 7 This is a radar chart showing the comprehensive performance of the retarded ultra-early strength and rapid hardening mortar in an embodiment of the present invention.

[0031] Figure 8 This is a component ratio diagram of the retarded ultra-early strength and rapid hardening mortar in an embodiment of the present invention. Detailed Implementation

[0032] 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.

[0033] 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.

[0034] Please see the appendix Figure 1 - Appendix Figure 8 This invention discloses a method for preparing a retarded, ultra-early-strength, and rapidly hardening mortar, the method comprising the following steps:

[0035] Step 1: Select rapid-hardening sulfoaluminate cement, silicate cement, mineral powder, graded quartz sand, borax and functional admixtures, and dry and screen the aggregates to remove impurities, ensuring that the raw materials meet the requirements of subsequent preparation and construction performance.

[0036] Step 2: Weigh sodium nitrite and hydroxycarboxylic acid monomers according to the proportion, dissolve, heat and keep warm to react, and spray dry after the reaction to form a solid modified early strength agent with a surface retarding shell and a core early strength structure, and control the grafting rate to be in the range of 15%-25%.

[0037] Step 3: Weigh each component according to the set mass percentage, and control the water-cement ratio and the mixing error within the specified range;

[0038] Step 4: Add cement, aggregate and solid functional admixture into the mixer and dry mix according to the set speed and time to make the mixture reach the preset homogenization state;

[0039] Step 5: Mix water and liquid functional admixture to form an admixture aqueous solution, inject it into the dry material and stir according to the set mixing conditions to ensure that the mortar workability meets the preset requirements;

[0040] Step 6: Inject the mixed mortar into the grouting equipment within a specified time, and inject the mortar into the seabed anhydrous rubber capsule through the grouting pipe. Control the grouting pressure, grouting speed and grouting sequence. The grouting pipe and the grout outlet pipe must meet the pressure resistance requirement of ≥1.8MPa to ensure that the capsule is filled tightly.

[0041] Step 7: Utilize the natural underwater environment for in-situ curing, and use the high pressure of the deep sea to trigger the modified early strength agent, thereby activating the cement hydration reaction and enabling the mortar to reach the required setting time and strength.

[0042] Example 1, please refer to the appendix. Figure 1 - Appendix Figure 8 :

[0043] A retarded, ultra-early-strength, and rapidly hardening mortar, the components of which are as follows by mass percentage:

[0044] The composition is as follows: 32% rapid-hardening sulfoaluminate cement, 8% silicate cement, 6% S95 grade mineral powder, 52.66% graded quartz sand, 0.25% modified early-strength agent, 0.9% polycarboxylate-based high-efficiency water-reducing agent (50% solid content), 0.1% hydroxypropyl methylcellulose water-retaining agent (viscosity 20000 mPa·s), 0.05% borax, 0.04% organosilicon defoamer (35% solid content), and a water-cement ratio of 0.23.

[0045] Among them, the performance parameters of each raw material meet the following requirements:

[0046] Rapid-hardening sulfoaluminate cement: Grade 62.5, specific surface area 420 m² 2 / kg, initial setting time 52min;

[0047] Silicate cement: Grade 52.5, specific surface area 320 m² 2 / kg, initial setting time 105min;

[0048] Graded quartz sand: particle size 0.15mm-1.2mm, mud content 0.5%, moisture content 0.3%, dried at 105℃ for 2 hours and then passed through a 2.5mm sieve;

[0049] Modified early strength agent: sodium nitrite to hydroxycarboxylic acid monomer mass ratio 10:1.8, grafting rate 20%.

[0050] The method for preparing this mortar includes the following steps:

[0051] Raw material pretreatment: The graded quartz sand is dried at 105℃ for 2 hours, cooled to room temperature, and then passed through a 2.5mm sieve to remove impurities.

[0052] Preparation of modified early strength agent: Sodium nitrite and hydroxycarboxylic acid monomer were weighed at a mass ratio of 10:1.8, stirred and dissolved, heated to 65℃, stirred at 380r / min, and kept at the temperature for 3h. After cooling to room temperature, the mixture was spray-dried and the grafting rate was found to be 20%. The mixture was then set aside for later use.

[0053] Ingredient metering: Each solid component is weighed using an electronic metering device with an accuracy of 0.1 kg. Liquid functional additives are delivered through a metering pump to ensure that the metering error is ≤ ±0.8%. Deionized water is measured according to a water-to-binder ratio of 0.23.

[0054] Dry mixing: Add rapid-hardening sulfoaluminate cement, silicate cement, mineral powder and graded quartz sand into a twin-shaft mixer and dry mix at 220 r / min for 2 min. Then add hydroxypropyl methylcellulose water-retaining agent, modified early strength agent solid powder, borax and organosilicon defoamer, and continue dry mixing at 220 r / min for 1.5 min until the mixture has a uniform color and no obvious particle agglomeration.

[0055] Wet mixing: Mix deionized water and polycarboxylate-based high-efficiency water-reducing agent evenly to form an additive aqueous solution, and inject it into the dry mix at a uniform speed within 28 seconds. Increase the speed of the mixer to 450 r / min and mix for 3.5 min until the mortar is uniformly viscous and there is no bleeding or segregation. The initial flowability is measured in real time to be 305 mm.

[0056] Submarine grouting: Within 30 minutes after mixing, the mortar is injected into the grouting equipment and injected into an anhydrous rubber capsule at a depth of 28m on the seabed through a grouting pipe with a pressure resistance of 2.0MPa. The grouting pressure is controlled at 1.0MPa and the grouting speed is 0.8m³ / h. The grouting sequence is from bottom to top. After the grout outlet pipe continuously overflows with uniform mortar, the pressure is stabilized and grouting continues for 8 minutes. During the grouting process, the seabed water temperature is monitored to be 12℃ and the pressure is stabilized at 2.8MPa.

[0057] In-situ curing: In-situ curing is carried out using the natural seabed environment, without disturbing the capsule and grouting pipeline during the curing period; the curing environment parameters are a depth of 28m, a pressure of 2.8MPa, and a water temperature of 12℃, requiring no additional curing measures.

[0058] The mortar prepared in this embodiment was subjected to performance testing, and the test results are as follows:

[0059] Initial flowability: 305 mm;

[0060] 1-hour flowability loss: 6.2%;

[0061] Initial setting time: 92 min;

[0062] Final setting time: 110 min;

[0063] 3-hour compressive strength: 46.8 MPa;

[0064] Capsule filling density: 99.2%.

[0065] Example 2, please refer to the appendix. Figure 1 - Appendix Figure 8 :

[0066] A retarded, ultra-early-strength, and rapidly hardening mortar, the components of which are as follows by mass percentage:

[0067] The composition is as follows: rapid-hardening sulfoaluminate cement 28%, silicate cement 11%, S95 grade mineral powder 9%, graded quartz sand 50.11%, modified early-strength agent 0.4%, polycarboxylate-based high-efficiency water-reducing agent (solid content 40%) 1.2%, hydroxypropyl methylcellulose water-retaining agent (viscosity 15000mPa·s) 0.15%, borax 0.08%, organosilicon defoamer (solid content 30%) 0.06%, and water-cement ratio 0.26.

[0068] Among them, the performance parameters of each raw material meet the following requirements:

[0069] Rapid-hardening sulfoaluminate cement: Grade 62.5, specific surface area 380 m² 2 / kg, initial setting time 45min;

[0070] Silicate cement: Grade 52.5, specific surface area 300m² 2 / kg, initial setting time 90min;

[0071] Graded quartz sand: particle size 0.15mm-1.2mm, mud content 0.7%, moisture content 0.4%, dried at 100℃ for 2.5h and then passed through a 2.0mm sieve;

[0072] Modified early strength agent: Sodium nitrite to hydroxycarboxylic acid monomer mass ratio 10:2.5, grafting rate 25%.

[0073] The method for preparing this mortar includes the following steps:

[0074] Raw material pretreatment: Graded quartz sand is dried at 100℃ for 2.5h, cooled and then passed through a 2.0mm sieve.

[0075] Preparation of modified early strength agent: Sodium nitrite and hydroxycarboxylic acid monomer were weighed at a mass ratio of 10:2.5, dissolved, heated to 70℃, stirred at 450r / min, and kept at the temperature for 3.5h. After spray drying, the grafting rate was found to be 25%.

[0076] Ingredient metering: Solid components are weighed using an electronic scale with an accuracy of 0.1 kg, and liquid functional additives are delivered using a metering pump. The metering error is ≤ ±0.9%. Deionized water is measured according to a water-to-binder ratio of 0.26.

[0077] Dry mixing: In a twin-shaft mixer, first dry mix the cementitious material and quartz sand at 180 r / min for 2.5 min, then add solid functional additives and organosilicon defoamers, and continue dry mixing for 2 min. The mixture is uniform in color and free of agglomeration.

[0078] Wet mixing: The additive aqueous solution was injected within 65 seconds, the mixer speed was increased to 520 r / min, and the mixture was stirred for 4.5 min. The initial flowability was measured to be 285 mm, and there was no bleeding or separation.

[0079] Submarine grouting: Grouting is carried out within 35 minutes after mixing, with a grouting pressure of 1.2 MPa, a grouting speed of 1.2 m³ / h, a seabed depth of 30 m, a water temperature of 15 ℃, a pressure of 3.0 MPa, and grouting under stable pressure for 12 minutes.

[0080] In-situ curing: Curing environment depth 30m, pressure 3.0MPa, water temperature 15℃, natural curing.

[0081] Performance test results:

[0082] Initial flowability: 285 mm;

[0083] 1-hour flowability loss: 7.8%;

[0084] Initial setting time: 105 min;

[0085] Final setting time: 118 min;

[0086] 3-hour compressive strength: 42.5 MPa;

[0087] Capsule filling density: 98.8%.

[0088] Example 3, please refer to the appendix. Figure 1 - Appendix Figure 8 :

[0089] A retarded, ultra-early-strength, and rapidly hardening mortar, the components of which are as follows by mass percentage:

[0090] The composition is as follows: 35% rapid-hardening sulfoaluminate cement, 5% silicate cement, 4% S95 grade mineral powder, 55.2% graded quartz sand, 0.1% modified early-strength agent, 0.6% polycarboxylate-based high-efficiency water-reducing agent (60% solid content), 0.05% hydroxypropyl methylcellulose water-retaining agent (viscosity 25000 mPa·s), 0.03% borax, 0.02% organosilicon defoamer (40% solid content), and a water-cement ratio of 0.21.

[0091] Among them, the performance parameters of each raw material meet the following requirements:

[0092] Rapid-hardening sulfoaluminate cement: Grade 62.5, specific surface area 450 m² 2 / kg, initial setting time 60min;

[0093] Silicate cement: Grade 52.5, specific surface area 350 m² 2 / kg, initial setting time 120min;

[0094] Graded quartz sand: particle size 0.15mm-1.2mm, mud content 0.3%, moisture content 0.2%, dried at 110℃ for 1.5h and then passed through a 3.0mm sieve;

[0095] Modified early strength agent: sodium nitrite to hydroxycarboxylic acid monomer mass ratio 10:1, grafting rate 15%.

[0096] The method for preparing this mortar includes the following steps:

[0097] Raw material pretreatment: Quartz sand is dried at 110℃ for 1.5h, cooled and then passed through a 3.0mm sieve.

[0098] Preparation of modified early strength agent: Weigh the raw materials at a mass ratio of 10:1, stir and react at 60℃ and 300r / min for 2h, and after spray drying, the grafting rate is 15%.

[0099] Ingredient metering: Solid components are weighed using an electronic scale, and liquid functional additives are delivered using a metering pump. The metering error is ≤ ±0.7%. Deionized water is measured according to a water-to-binder ratio of 0.21.

[0100] Dry mixing: Dry mix the cementitious material and quartz sand at 250 r / min for 1.5 min, add the solid functional additives, and continue to dry mix for 1 min until the mixture is uniform.

[0101] Wet mixing: The additive aqueous solution is injected within 25 seconds, the mixer speed is 380 r / min, and the mixture is stirred for 2.5 min. The initial flowability is measured to be 330 mm, and the state is uniform.

[0102] Submarine grouting: Grouting is carried out within 25 minutes after mixing, with a grouting pressure of 0.8 MPa, a speed of 0.4 m³ / h, a seabed depth of 25 m, a water temperature of 10 ℃, a pressure of 2.5 MPa, and grouting under stable pressure for 4 minutes.

[0103] In-situ curing: Curing environment depth 25m, pressure 2.5MPa, water temperature 10℃, natural curing.

[0104] Performance test results:

[0105] Initial flowability: 330 mm;

[0106] 1-hour flowability loss: 5.1%;

[0107] Initial setting time: 75 min;

[0108] Final setting time: 98 min;

[0109] 3-hour compressive strength: 49.2 MPa;

[0110] Capsule filling density: 99.5%.

[0111] Comparative Example 1

[0112] The same formulation as in Example 1 was used, but without the addition of a modified early strength agent. The proportions of the remaining components, preparation steps, and testing conditions were all the same as in Example 1.

[0113] Performance test results:

[0114] Initial flowability: 302 mm;

[0115] 1-hour flowability loss: 12.3%;

[0116] Initial setting time: 135 min;

[0117] Final setting time: 158 min;

[0118] 3-hour compressive strength: 28.6 MPa;

[0119] Capsule filling density: 95.3%.

[0120] Comparative Example 2

[0121] The same formulation as in Example 1 was used, but the modified early strength agent was not grafted and was directly mixed with sodium nitrite and hydroxycarboxylic acid monomer. The other conditions were the same as in Example 1.

[0122] Performance test results:

[0123] Initial flowability: 298 mm;

[0124] 1-hour flowability loss: 10.5%;

[0125] Initial setting time: 120 min;

[0126] Final setting time: 142 min;

[0127] 3-hour compressive strength: 35.8 MPa;

[0128] Capsule filling density: 96.7%.

[0129] Comparative Example 3

[0130] The same formula as in Example 1 was used, but the curing method was changed to ambient temperature and pressure curing, with a temperature of 20°C and a pressure of 0.1 MPa. The other conditions were the same as in Example 1.

[0131] Performance test results:

[0132] Initial flowability: 300 mm;

[0133] 1-hour flowability loss: 7.2%;

[0134] Initial setting time: 165 min;

[0135] Final setting time: 185 min;

[0136] 3-hour compressive strength: 32.4 MPa;

[0137] Capsule filling density: 97.1%

[0138] Comparative Analysis of Examples and Comparative Cases

[0139] Key role of modified early strength agent: Comparing Example 1 with Comparative Examples 1 and 2, it can be seen that the modified early strength agent with core-shell structure prepared in this invention can significantly shorten the setting time, improve early strength, and effectively control fluidity loss. Without the addition of modified early strength agent or when using physically mixed early strength components, the mortar cannot achieve the synergistic effect of retarding and ultra-early strength, and the 3-hour compressive strength is less than 40 MPa, which cannot meet the requirements of seabed construction.

[0140] The necessity of in-situ curing on the seabed: Comparing Example 1 and Comparative Example 3, it can be seen that the high pressure environment in the deep sea (2.5MPa-3.0MPa) can trigger the cracking of the retarding shell of the modified early strength agent, activate the core early strength core, and accelerate the cement hydration reaction. Under normal temperature and pressure curing, the setting time is greatly extended, the early strength development is slow, and it cannot meet the construction requirements of rapid load bearing.

[0141] Synergistic optimization of the formulation system: Examples 1-3 achieved excellent performance with an initial fluidity of 280mm-330mm, a fluidity loss of ≤8% in 1 hour, and a compressive strength of ≥42MPa in 3 hours by reasonably controlling the cement ratio, water-cement ratio and admixture dosage. Moreover, the capsule filling density was ≥98.8%, which solved the technical problems of easy pipe blockage, slow strength development and poor filling of traditional mortar in seabed grouting.

[0142] Application Examples

[0143] The retarded, ultra-early-strength, and rapidly hardening mortar prepared in Example 1 was applied to the subsea capsule grouting operation in the construction of a caisson for a cross-sea bridge. The specific application is as follows:

[0144] Project conditions: The caisson is located at a depth of 28m on the seabed. The working environment has a water temperature of 10℃-15℃ and a seawater salinity of 3.5%. The mortar is required to form a stable support within 3 hours after grouting, with a compressive strength ≥40MPa.

[0145] Construction process:

[0146] Anhydrous rubber capsules are pre-installed below the caisson, and grouting pipes (50mm in diameter) with a pressure resistance of 2.0MPa and grout outlet pipes (30mm in diameter) are reserved, with the pipelines extending to the offshore operation platform;

[0147] Mortar was prepared on-site at the work platform according to the method of Example 1, and the initial flowability was detected in real time to be 302 mm, which meets the pumping requirements.

[0148] Grouting was performed from bottom to top at a pressure of 1.0 MPa and a speed of 0.8 m³ / h, and the valve was closed after stabilizing the pressure for 8 minutes.

[0149] After 3 hours of natural curing, underwater testing equipment confirmed that the capsule was densely filled, and the mortar compressive strength was tested to be 46.2 MPa.

[0150] During the caisson placement and adjustment process, the mortar support structure did not deform or crack, meeting the construction safety requirements.

[0151] Application results: This mortar exhibits excellent workability and mechanical properties in the high-salt and high-pressure environment of the seabed. There is no pipe blockage during the grouting process, the filling density reaches 99.2%, and it can provide stable bearing capacity in 3 hours. It significantly shortens the seabed construction cycle, reduces the operation risk, and improves the construction efficiency by more than 40% compared with traditional mortar.

[0152] The following table compares the key parameters and performance of the examples and comparative examples:

[0153] No. Core variable difference Initial fluidity (mm) 1 h fluidity loss (%) Initial setting time (min) Final setting time (min) 3 h compressive strength (MPa) Capsule filling density (%) Example 1 With modified early strength agent (grafting rate 20%), in-situ curing at seabed (28 m, 2.8 MPa) 305 6.2 92 110 46.8 99.2 Example 2 With modified early strength agent (grafting rate 25%), in-situ curing at seabed (30 m, 3.0 MPa) 285 7.8 105 118 42.5 98.8 Example 3 With modified early strength agent (grafting rate 15%), in-situ curing at seabed (25 m, 2.5 MPa) 330 5.1 75 98 49.2 99.5 Comparative Example 1 Without modified early strength agent, the rest is the same as Example 1 302 12.3 135 158 28.6 95.3 Comparative Example 2 Modified early strength agent is physically mixed (not grafted), the rest is the same as Example 1 298 10.5 120 142 35.8 96.7 Comparative Example 3 Curing at normal temperature and pressure (20℃, 0.1 MPa), the rest is the same as Example 1 300 7.2 165 185 32.4 97.1

[0154] While the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the invention. Any variations and modifications can be made by those skilled in the art without departing from the spirit and scope of the 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 scope of the invention, fall within the protection scope defined by the claims of the present invention.

Claims

1. A method for preparing a retarded, ultra-early-strength, rapidly hardening mortar, characterized in that, The preparation method includes the following steps: Step 1: Select rapid-hardening sulfoaluminate cement, silicate cement, mineral powder, graded quartz sand, borax, and functional admixtures, and dry and screen the aggregates to remove impurities. Step 2: Weigh sodium nitrite and hydroxycarboxylic acid monomers according to the proportion, dissolve, heat and keep warm to react, and spray dry after the reaction to form a solid modified early strength agent with a surface retarding shell and a core early strength structure, and control the grafting rate to be in the range of 15%-25%. Step 3: Weigh each component according to the set mass percentage, and control the water-cement ratio and the mixing error within the specified range; Step 4: Add cement, aggregate and solid functional admixture into the mixer and dry mix according to the set speed and time to make the mixture reach the preset homogenization state; Step 5: Mix water and liquid functional additives to form an additive aqueous solution, then inject it into the dry material and stir according to the set stirring conditions; Step 6: Inject the mixed mortar into the grouting equipment within a specified time, and inject the mortar into the seabed anhydrous rubber capsule through the grouting pipe. Control the grouting pressure, grouting speed and grouting sequence. The grouting pipe and the grout outlet pipe must meet the pressure resistance requirement of ≥1.8MPa. Step 7: Utilize the natural underwater environment for in-situ curing, and use the high pressure of the deep sea to trigger the modified early strength agent, thereby activating the cement hydration reaction and enabling the mortar to reach the required setting time and strength.

2. The method for preparing a retarded, ultra-early-strength, and rapidly hardening mortar according to claim 1, characterized in that: In step one, the rapid-hardening sulfoaluminate cement is grade 62.5 with a specific surface area of ​​380 m². 2 / kg-450m 2 / kg, initial setting time 45min-60min, silicate cement grade 52.5, specific surface area 300m² 2 / kg-350m 2 / kg, initial setting time 90min-120min, graded quartz sand particle size 0.15mm-1.2mm, mud content ≤0.8%, moisture content ≤0.5%, drying conditions are 100℃-110℃ for 1.5h-2.5h, cooled to room temperature and passed through a 2.0mm-3.0mm sieve. Functional admixtures include defoamer, polycarboxylate-based high-efficiency water-reducing agent with solid content of 40%-60%, hydroxypropyl methylcellulose water-retaining agent with viscosity of 15000mPa·s-25000mPa·s, and core modifying raw materials sodium nitrite and hydroxycarboxylic acid monomers. The mineral powder is S95 grade, with an activity index ≥95% and a specific surface area of ​​350m². 2 / kg-400m 2 / kg, the defoamer is an organosilicon compound with a solid content ≥30%.

3. The method for preparing a retarded, ultra-early-strength, and rapidly hardening mortar according to claim 1, characterized in that: In step two, the mass ratio of sodium nitrite to hydroxycarboxylic acid monomer is 10:1-10:2.

5. During the reaction, 2.5-3.5 times the total mass of sodium nitrite and hydroxycarboxylic acid monomer in deionized water is added. After stirring and dissolving, the temperature is raised to 60℃-70℃, and the stirring speed is controlled at 300r / min-450r / min. The reaction time is 2h-3.5h. After the reaction is completed, the mixture is cooled to room temperature and spray-dried to obtain a solid powder modified early strength agent. The grafting rate is detected by gel permeation chromatography, and the grafting rate is stably controlled at 15%-25%.

4. The method for preparing a retarded, ultra-early-strength, and rapidly hardening mortar according to claim 1, characterized in that: In step three, the mass percentages of each component are as follows: rapid-hardening sulfoaluminate cement 28%-35%, silicate cement 5%-11%, mineral powder 4%-9%, graded quartz sand 50%-62%, modified early-strength agent 0.1%-0.4%, polycarboxylate-based high-efficiency water-reducing agent 0.6%-1.2%, hydroxypropyl methylcellulose water-retaining agent 0.05%-0.15%, borax 0.03%-0.08%, defoamer 0.02%-0.06%, and the water-cement ratio is controlled at 0.21-0.

26.

5. The method for preparing a retarded, ultra-early-strength, and rapidly hardening mortar according to claim 1, characterized in that: In step four, the mixer is a twin-shaft mixer. First, the rapid-hardening sulfoaluminate cement, silicate cement, mineral powder and graded quartz sand are dry-mixed at a speed of 180r / min-250r / min for 1.5min-2.5min. Then, the water-retaining agent, modified early-strength agent solid powder and borax are added, and the mixture is dry-mixed at the same speed for 1min-2min until the mixture has a uniform color and no obvious particle agglomeration.

6. The method for preparing a retarded, ultra-early-strength, and rapidly hardening mortar according to claim 1, characterized in that: In step five, deionized water and polycarboxylate-based high-efficiency water-reducing agent are mixed and stirred evenly to form an admixture aqueous solution. The addition time of the aqueous solution is controlled between 25s and 65s. Then, the speed of the mixer is increased to 380r / min-520r / min and stirred for 2.5min-4.5min until the mortar presents a uniform and viscous state without bleeding or segregation.

7. The method for preparing a retarded, ultra-early-strength, and rapidly hardening mortar according to claim 1, characterized in that: In step six, the mixed mortar must be injected into the grouting equipment within 25-35 minutes, with the grouting pressure maintained stably at 0.8MPa-1.2MPa and the grouting speed at 0.4m / min. 3 / h-1.2m 3 / h, adopting a bottom-up grouting sequence, after the grout outlet pipe continuously overflows with uniform mortar, continue grouting with stable pressure for 4min-12min, monitor the seabed water temperature during the grouting process, and control the water temperature at 10℃-15℃, while monitoring pressure changes at the same time.

8. The method for preparing a retarded, ultra-early-strength, and rapidly hardening mortar according to claim 1, characterized in that: In step seven, the environmental conditions for in-situ seabed curing are: depth 25m-30m, pressure 2.5MPa-3.0MPa, water temperature 10℃-15℃. No additional curing measures are required. During the curing process, the high pressure in the deep sea triggers the rupture of the retarding shell of the modified early strength agent, and the core early strength core activates the cement hydration reaction, so that the initial setting time of the mortar is controlled at 75min-105min, the final setting time is ≤120min, and the 3h compressive strength is ≥40MPa. During the curing period, the capsule and grouting pipeline must not be disturbed until the caisson is settled and adjusted.

9. The retarded, ultra-early-strength, and rapidly hardening mortar prepared by the preparation method according to any one of claims 1-8, characterized in that: The retarded ultra-early strength and rapid hardening mortar is prepared by the preparation method in steps one to seven. Its components, by mass percentage, include: 28%-35% rapid hardening sulfoaluminate cement, 5%-11% silicate cement, 4%-9% mineral powder, 50%-62% graded quartz sand, 0.1%-0.4% modified early strength agent, 0.6%-1.2% polycarboxylate-based high-efficiency water-reducing agent, 0.05%-0.15% hydroxypropyl methylcellulose water-retaining agent, 0.03%-0.08% borax, and 0.02%-0.06% defoamer. The water-cement ratio is 0.21-0.

26. The initial setting time of the retarded ultra-early strength and rapid hardening mortar is 75-105 min, the final setting time is ≤120 min, the 3-hour compressive strength is ≥40 MPa, and the initial flowability is 280 mm-330 mm.

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