A nano polycarboxylic acid hydrated calcium silicate early strength agent, a preparation method and application thereof

Abstract

The application belongs to the field of concrete admixtures, and particularly relates to a nano-polycarboxylic acid hydrated calcium silicate early strength agent, a preparation method and application thereof. The early strength agent is prepared by continuously synthesizing a comb-shaped polymer dispersant and nano-hydrated calcium silicate crystal nucleus in a single reaction kettle, and has excellent dispersibility and stability. The preparation process includes two steps of polymer solution preparation and in-situ generation of nano-crystal nucleus, and has high process integration degree, mild conditions and low energy consumption. When used in concrete at a low dosage, the early strength can be significantly improved, the fluidity can be improved, and the later performance and durability are not affected, and the early strength agent is suitable for precast components and conventional concrete engineering.

Description

Technical Field

[0001] This invention belongs to the field of concrete admixtures, specifically relating to a nano-polycarboxylic acid hydrated calcium silicate early strength agent, its preparation method, and its application. Background Technology

[0002] With the continuous development of technology, the market is increasingly recognizing the use of lightweight, efficient and easy-to-install precast components in engineering projects such as houses, bridges, tunnels and transportation. As a result, the quality requirements for precast components are getting higher and higher. In order to further reduce costs and increase efficiency, requirements such as shortening the mold cycle and reducing or eliminating steam curing steps have been put forward. Therefore, there is an urgent need for a new type of green early strength agent for precast components.

[0003] A type of nanoparticle containing polycarboxylate superplasticizer as a dispersant and synthetically produced calcium silicate hydrate as the main component, when added to concrete, can rapidly induce the formation of CSH gel, shorten the setting time of the component, and improve its early strength. Furthermore, since the generated substance is consistent with the hydration substances of cement itself, it does not impair the final strength, making it an effective method to solve the aforementioned problems. However, the efficiency of synthetically produced calcium silicate hydrate is too low, and controlling costs cannot guarantee superior performance. Therefore, it is necessary to study a highly efficient, convenient, and performance-efficient one-step method for synthesizing calcium silicate hydrate.

[0004] Patent CN201910291031.X discloses a CSH gel nanocrystal nucleus early strength agent, its preparation method and application. Although the method can obtain CSH nanocrystal nuclei with good dispersion stability, the preparation steps are cumbersome, the self-controllability is poor, and the requirements for raw material quality control are too high.

[0005] Patent CN202010060140.3 discloses an ammonium alkoxide-modified hydrated calcium silicate nanocrystal nucleus early strength agent and its preparation method, which is prepared from a reaction stock solution, a reaction base solution, and a dispersion stabilizing solution. This ammonium alkoxide-modified hydrated calcium silicate nanocrystal nucleus early strength agent has a simple process, good dispersion stability, and good storage resistance, but its water-reducing effect on cement-based materials is poor.

[0006] Patent CN202110378213.8 discloses an ultra-early strength and ultra-high strength inorganic grouting material based on ordinary silicate cement and its preparation method. The concrete prepared by this grouting material has relatively weak later strength.

[0007] Therefore, developing a novel polycarboxylate hydrated calcium silicate composite early strength agent with high stability, good dispersibility, green environmental protection and non-toxicity, and the ability to accelerate mold turnover is an inevitable trend in the development of admixtures. Summary of the Invention

[0008] This invention aims to overcome the shortcomings of existing technologies and provide a nano-polycarboxylic acid hydrated calcium silicate early-strength agent, its preparation method, and its application. This method features a simplified process, short cycle time, low energy consumption, and produces a product with good dispersibility and high stability, significantly improving the early strength of concrete without affecting its later performance.

[0009] The specific technical solution of the present invention is as follows:

[0010] One of the technical solutions of the present invention is to provide a nano-polycarboxylic acid hydrated calcium silicate early strength agent, which is composed of a polymer dispersant and in-situ supported nano-hydrated calcium silicate crystal nuclei;

[0011] The polymer dispersant is synthesized from the following raw materials in parts by weight: 40-50 parts of polyether macromonomer, 20-25 parts of unsaturated carboxylic acid, 3-5 parts of silane coupling agent, 5-7 parts of hydrogen peroxide and 5-10 parts of vitamin C as the initiator system, and 2-3 parts of chain transfer agent.

[0012] The nano-hydrated calcium silicate crystal nuclei are formed by calcium ions and silicate ions in a reaction system, wherein the concentration of calcium ions is 0.8-2.4 mol / L, the concentration of silicate ions is 0.4-1.2 mol / L, and the molar ratio of calcium ions to silicate ions is (1-3):1.

[0013] The pH value of the reaction system is 11-12, and the molecular weight of the polymer dispersant is 45,000-55,000.

[0014] As a further option for the early strength agent of the present invention, the polyether macromonomer is selected from one of propylene alcohol polyvinyl ether, isopentenyl alcohol polyoxyethylene ether, and polyethylene diene monomethyl ether.

[0015] As a further option for the early strength agent of the present invention, the unsaturated carboxylic acid is selected from at least one of acrylic acid, methacrylic acid, methyl acrylate, ethyl acrylate, methyl methacrylate, and butyl acrylate.

[0016] As a further option for the early strength agent of the present invention, the chain transfer agent is dodecyl mercaptan.

[0017] As a further option for the early strength agent of the present invention, the calcium ions are derived from one of calcium nitrate, calcium formate or calcium chloride.

[0018] As a further option for the early strength agent of the present invention, the silicate ions are derived from one of sodium metasilicate pentahydrate, sodium metasilicate nonahydrate, potassium silicate, or lithium silicate.

[0019] As a further option for the early strength agent of the present invention, the preferred formulation by weight is: 45 parts of isopentenyl polyoxyethylene ether, the macromonomer of the polyether, 22 parts of acrylic acid, the unsaturated carboxylic acid, 6 parts of hydrogen peroxide, 7 parts of vitamin C, 4 parts of silane coupling agent, and 2.5 parts of dodecyl mercaptan, the chain transfer agent.

[0020] The second technical solution of the present invention provides a method for preparing nano-polycarboxylic acid hydrated calcium silicate early strength agent, which is carried out continuously in a single atmospheric pressure reactor, including the following steps:

[0021] The polyether macromonomer was dissolved in water, and a mixture of unsaturated carboxylic acid and silane coupling agent, hydrogen peroxide aqueous solution, and vitamin C and chain transfer agent were added dropwise simultaneously. After the addition was completed, the reaction was kept at a constant temperature to obtain a polymer solution. Water was added to dilute the solution and the pH was adjusted to form the reaction base solution.

[0022] Calcium salt solution and silicate solution were simultaneously added dropwise to the reaction substrate. After the addition was complete, the reaction continued, and a suspension of early strength agent was obtained after post-treatment.

[0023] As a further option for the preparation method of the early strength agent of the present invention, the synthesis temperature of the polymer solution is 45-55°C, the total dropping time is 120-180 minutes, and after the dropping is completed, the reaction continues at 45-55°C for 60-120 minutes.

[0024] As a further option for the preparation method of the early strength agent of the present invention, the polymer concentration in the reaction substrate after dilution with water is 0.5% to 3%.

[0025] As a further option for the preparation method of the early strength agent of the present invention, the total time for adding the calcium salt solution and the silicate solution is 100-150 minutes, and after the addition is completed, the reaction is continued to be stirred at 15-30°C for 180-270 minutes.

[0026] As a further option for the preparation method of the early strength agent of the present invention, during the simultaneous dropwise addition of the calcium salt solution and the silicate solution, the alkali solution is monitored and replenished in real time to maintain the pH value of the reaction system in the range of 11 to 12.

[0027] The third technical solution of the present invention is to provide the application of nano-polycarboxylic acid hydrated calcium silicate early strength agent in concrete. The early strength agent is added to the concrete mixing system based on the total mass of concrete cementitious materials to improve the compressive strength of concrete.

[0028] As a further option for the application of the early strength agent of the present invention, the dosage of the early strength agent is 0.2% to 5.0% of the total mass of concrete cementitious materials.

[0029] As a further option for the application of the early strength agent of the present invention, the early strength agent is added together with the mixing water, or pre-mixed with the polycarboxylate superplasticizer and then added to the concrete mixing system.

[0030] The beneficial effects of the technical solutions provided in this application include at least the following:

[0031] When using this invention, the dosage is 0.2% to 5% of the mass of the cementitious materials in the concrete, and it can be directly mixed with concrete water-reducing agents. The preparation method integrates the preparation of polymer dispersants and the synthesis of nano-polycarboxylic acid hydrated calcium silicate in a single reactor, effectively simplifying the preparation process conditions, shortening the preparation cycle, and improving process integration and controllability. In the preparation process described in this invention, a highly stable nano-suspension can be prepared without additional heating.

[0032] Based on the above process characteristics, this technical solution significantly improves the preparation efficiency of nano-polycarboxylic acid hydrated calcium silicate, effectively reduces the cost of raw materials and energy consumption, and provides a feasible technical path for the integrated and large-scale preparation of concrete admixtures.

[0033] Furthermore, when the nano-polycarboxylate hydrated calcium silicate early-strength agent prepared in this invention is applied to concrete systems, it can significantly enhance the early strength of concrete even at relatively low dosages, without adversely affecting the later workability of the concrete. This application not only reduces the curing requirements for precast concrete components but also accelerates the turnover cycle of production molds, ultimately achieving the green manufacturing goal of energy conservation and emission reduction in the production of precast concrete components. Detailed Implementation

[0034] The technical solutions in the embodiments of this application will be clearly and completely described below with reference to the embodiments of this application. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments in this application, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of this application.

[0035] This invention provides a nano-polycarboxylic acid hydrated calcium silicate early-strength agent, its integrated preparation method, and its application in concrete. The early-strength agent is continuously synthesized in a single reactor using a polymer dispersant of a specific composition and nano-hydrated calcium silicate crystal nuclei. It features uniform dispersion, high stability, low dosage, and significant early-strength effect, making it suitable for improving the early strength of concrete and maintaining its long-term performance.

[0036] First, the composition of the nano-polycarboxylic acid hydrated calcium silicate early strength agent is explained in detail.

[0037] The raw materials for preparing the early strength agent, by weight, include the following components:

[0038] Polymer dispersant synthesis section:

[0039] Polyether macromonomer: 40-50 parts;

[0040] Unsaturated carboxylic acids: 20-25 parts;

[0041] Initiator system: 5-7 parts hydrogen peroxide, 5-10 parts vitamin C;

[0042] Silane coupling agent: 3-5 parts;

[0043] Chain transfer agent: 2-3 parts of dodecyl mercaptan;

[0044] Water: as needed, used for dissolving and diluting.

[0045] Nanocrystal nucleus synthesis section:

[0046] Calcium salt solution: calcium ion concentration is 0.8–2.4 mol / L;

[0047] Silicate solution: Silicate concentration is 0.4–1.2 mol / L;

[0048] pH adjusters: sodium hydroxide and nitric acid, used to maintain the pH of the reaction system at 11-12.

[0049] In this invention, the polyether macromonomer is selected from one of propylene glycol polyvinyl ether, isopentenyl alcohol polyoxyethylene ether, and polyethylene diene monomethyl ether. The ether bonds and double bonds in its molecular structure can form a comb-like structure during polymerization, exerting steric hindrance and ensuring the dispersion stability of the nanoparticles.

[0050] The unsaturated carboxylic acid is selected from at least one of acrylic acid, methacrylic acid, methyl acrylate, ethyl acrylate, methyl methacrylate, and butyl acrylate. Its carboxyl group can provide charge repulsion and interact with calcium ions, assisting in the formation and stabilization of crystal nuclei.

[0051] The initiator system is a redox system. Hydrogen peroxide and vitamin C can generate active free radicals at room temperature, which can initiate polymerization reactions, reduce energy consumption, and improve reaction controllability.

[0052] Silane coupling agents can introduce siloxane groups into polymer molecules, enhance the interfacial bonding between polymers and inorganic silicates, and improve the structural stability of the final product.

[0053] Chain transfer agents are used to regulate the molecular weight of polymers, keeping it within the range of 45,000 to 55,000, ensuring that the polymer has sufficient dispersibility without its diffusion and adsorption in the system being affected by excessively large molecular weight.

[0054] The calcium salt is a soluble calcium salt, selected from calcium nitrate, calcium formate, and calcium chloride. The silicate is a soluble complex silicate, selected from sodium metasilicate pentahydrate, sodium metasilicate nonahydrate, potassium silicate, and lithium silicate. The molar ratio of calcium salt to silicate is controlled between 1:1 and 3:1 to match the standard stoichiometric range of hydrated calcium silicate.

[0055] pH adjusters are used to maintain the pH of the reaction system at a strongly alkaline environment of 11-12, which is conducive to the nucleation and growth of hydrated calcium silicate nanocrystals and inhibits the formation of aggregates.

[0056] The preparation method of nano-polycarboxylic acid hydrated calcium silicate early strength agent is described in detail.

[0057] The preparation method provided by this invention includes the following steps:

[0058] Step 1: Preparation of polymer dispersant solution.

[0059] Polyether macromonomers were added to water at 45–55°C and stirred until completely dissolved to form a premix. Under stirring, a mixture of unsaturated carboxylic acid, silane coupling agent, hydrogen peroxide solution, and a mixture of vitamin C and chain transfer agent were added dropwise simultaneously. The dropping rate and sequence of each material were controlled, with a total dropping time of 120–180 minutes. After the addition was complete, the reaction was continued at 45–55°C for 60–120 minutes to ensure complete polymerization. A comb-like polymer solution with a solid content of approximately 27% and a molecular weight of 45,000–55,000 was obtained. Water was then added to the polymer solution to dilute its concentration to between 0.5% and 3%. Finally, the pH of the solution was adjusted to 11–12 using sodium hydroxide solution and dilute nitric acid to obtain a homogeneous and stable reaction substrate.

[0060] Step 2: Synthesis of nano-hydrated calcium silicate crystal nuclei and preparation of early strength agent.

[0061] Prepare an aqueous solution A with a calcium salt concentration of 0.8–2.4 mol / L and an aqueous solution B with a silicate concentration of 0.4–1.2 mol / L. Transfer the reaction mixture to a reaction vessel, maintain the temperature at 15–30°C, and adjust the stirring rate to 300–1000 r / min. While stirring, add solutions A and B simultaneously dropwise to the reaction mixture at a constant rate according to the preset calcium-silicon molar ratio, with the total addition time controlled at 100–150 minutes. During the dropwise addition, monitor the pH value of the system in real time and maintain the pH within the range of 11–12 by adding sodium hydroxide solution. After the dropwise addition is complete, continue stirring the reaction for 180–270 minutes to allow complete crystal growth. After the reaction is completed, filter and wash to obtain a suspension of nano-polycarboxylic acid hydrated calcium silicate early strength agent with a solid content of 8%–12%.

[0062] The entire preparation process is carried out continuously in a single atmospheric pressure reactor without the need for separation and transfer of intermediate products, and the total reaction time is 780 to 840 minutes.

[0063] The core of this invention lies in utilizing in-situ generated comb-like polymers as dispersants and structure-directing agents to directly synthesize nanoscale hydrated calcium silicate in a strongly alkaline aqueous solution and stably disperse it. This method features high process integration, mild conditions, no need for additional heating, low energy consumption, and stable and uniform product performance.

[0064] After obtaining the nano-polycarboxylic acid hydrated calcium silicate early strength agent, the present invention further provides a method for its application in concrete.

[0065] The specific application methods include:

[0066] The accelerator is added to the concrete mixing system at a dosage of 0.2% to 5.0% of the total mass of the concrete cementitious materials, along with the mixing water. Alternatively, it can be pre-mixed with a polycarboxylate superplasticizer before being added to the concrete. After mixing until homogeneous, it can be poured and cured. Concrete with this accelerator exhibits significantly improved early strength, especially the 1-day and 7-day compressive strength, without adversely affecting the concrete's fluidity, later-stage strength, or durability.

[0067] The early strength agent of the present invention, its preparation method, and its application effects are described in detail below through multiple examples and comparative examples.

[0068] Example 1: Preferred formulation of nano-polycarboxylic acid hydrated calcium silicate early strength agent

[0069] This embodiment provides a nano-polycarboxylic acid hydrated calcium silicate early strength agent, the composition of which is as follows by mass parts:

[0070] Isoprene alcohol polyoxyethylene ether: 45 parts;

[0071] Acrylic acid: 22 parts;

[0072] Hydrogen peroxide: 6 parts;

[0073] Vitamin C: 7 servings;

[0074] Silane coupling agent: 4 parts;

[0075] Dodecyl mercaptan: 2.5 parts;

[0076] Deionized water: 100 parts for initial dissolution and 800 parts for subsequent dilution;

[0077] Calcium nitrate: 59.4 g, for preparing solution A;

[0078] Sodium metasilicate pentahydrate: 48 grams, for preparing solution B;

[0079] Sodium hydroxide and dilute nitric acid: in appropriate amounts, used for pH adjustment.

[0080] Example 2: Optimized process for preparing nano-polycarboxylic acid hydrated calcium silicate early strength agent

[0081] This embodiment provides a method for preparing an early-strength agent as described in Example 1, with the following specific steps:

[0082] Step 1: Preparation of polymer dispersant solution.

[0083] Weigh 45 parts by weight of isopentenyl alcohol polyoxyethylene ether and add it to a 2000 mL atmospheric pressure reactor equipped with a stirrer and temperature control. Measure 100 parts by weight of deionized water, heat it to 50 degrees Celsius, and then pour it into the reactor. Turn on the mechanical stirrer and set the speed to 200 rpm. Continue stirring until the polyether macromonomer is completely dissolved, forming a homogeneous and transparent premixed solution.

[0084] Weigh out 22 parts by mass of acrylic acid and 4 parts by mass of silane coupling agent, mix thoroughly, and transfer to the first peristaltic pump reservoir. Weigh out 6 parts by mass of hydrogen peroxide, dilute with 10 parts by mass of deionized water, and transfer to the second peristaltic pump reservoir. Weigh out 7 parts by mass of vitamin C and 2.5 parts by mass of dodecyl mercaptan, mix, and transfer to the third peristaltic pump reservoir.

[0085] Simultaneously start the first and second peristaltic pumps to add the acrylic acid-silane coupling agent mixture and hydrogen peroxide dilution solution dropwise into the reactor. Control the drop rate of the acrylic acid mixture at 0.37 mL / min and the drop rate of the hydrogen peroxide dilution solution at 0.17 mL / min, both to be completed within 60 minutes. Ten minutes after the acrylic acid mixture begins to drop, start the third peristaltic pump to add the vitamin C-chain transfer agent mixture dropwise, controlling the drop rate at 0.14 mL / min, to be completed within 110 minutes.

[0086] After all materials have been added, maintain the reaction temperature at 50 degrees Celsius and the stirring speed at 200 rpm, and continue the reaction at this temperature for 130 minutes to allow the polymerization reaction to proceed fully and obtain a comb-like polymer solution.

[0087] Add 800 parts by mass of deionized water to the reactor and maintain stirring to ensure uniform dispersion of the polymer. At this point, the solution concentration is approximately 1.5%. Adjust the pH of the solution to 11.25 using a 10% sodium hydroxide solution and a 65% dilute nitric acid solution to obtain a stable reaction base solution.

[0088] Step 2: Synthesis of nano-hydrated calcium silicate crystal nuclei and preparation of early strength agent.

[0089] Weigh 59.4 g of calcium nitrate and dissolve it in 100 parts by weight of deionized water to prepare a calcium salt solution A with a concentration of approximately 1.0 mol / L. Weigh 48 g of sodium metasilicate pentahydrate and dissolve it in 100 parts by weight of deionized water to prepare a silicate solution B with a concentration of approximately 1.0 mol / L. Sonicate solutions A and B separately for 5 minutes to remove dissolved gases, then connect them to the fourth and fifth peristaltic pumps, respectively.

[0090] Maintain the temperature of the reaction substrate at approximately 25 degrees Celsius and increase the stirring speed to 500 rpm. Simultaneously turn on the fourth and fifth peristaltic pumps, and add solution A and solution B dropwise to the reaction substrate at a volume ratio of 1:1.2. Control the dropping rate of solution A to 1.2 mL / min and the dropping rate of solution B to 1.0 mL / min, ensuring that both are added within 100 minutes. At this point, the molar ratio of calcium to silicon in the system is approximately 1:1.2.

[0091] During the dropwise addition, the pH value of the system was measured every 10 minutes using a calibrated pH meter. The pH value was maintained within the range of 11.2 ± 0.2 by adding a small amount of 10% sodium hydroxide solution.

[0092] After the addition is complete, maintain a stirring speed of 500 rpm and continue the reaction for 320 minutes to allow the nanocrystal nuclei to grow and mature.

[0093] After the reaction was completed, the resulting white suspension was filtered and the product was washed several times with deionized water to finally obtain a nano-polycarboxylic acid hydrated calcium silicate early strength agent suspension with a solid content of about 10%, which was labeled as sample PCE-CSH-1.

[0094] Example 3: Preparation method of nano-polycarboxylic acid hydrated calcium silicate early strength agent with variable dropping time

[0095] The difference between this embodiment and Example 2 lies in the dropping time of solution A and solution B in the nanocrystal nucleus synthesis step. The dropping rates of solution A and solution B were controlled to extend the total dropping time to 300 minutes; the remaining steps and parameters were identical to those in Example 2. After the reaction was complete, the reaction was stirred for another 1440 minutes. The resulting early-strength agent sample was labeled PCE-CSH-2.

[0096] Example 4: Preparation method of nano-polycarboxylic acid hydrated calcium silicate early strength agent with modified polymer macromonomer

[0097] The difference between this embodiment and Example 2 lies in the type of polyether macromonomer used in the polymer dispersant synthesis step. 45 parts by mass of propylene alcohol polyvinyl ether were used instead of isopentenyl alcohol polyoxyethylene ether; the remaining raw material ratios, preparation steps, and process parameters were exactly the same as in Example 2. The resulting early-strength agent sample was labeled PCE-CSH-3.

[0098] Example 5: Preparation method of nano-polycarboxylic acid hydrated calcium silicate early strength agent with varying calcium and silicon sources

[0099] The difference between this embodiment and Example 2 lies in the types of calcium salts and silicates used in the nanocrystal nucleus synthesis step. An equimolar amount of calcium formate is used instead of calcium nitrate as the calcium source, and an equimolar amount of potassium silicate is used instead of sodium metasilicate pentahydrate as the silicon source. The remaining raw material ratios, preparation steps, and process parameters are exactly the same as in Example 2. The resulting early-strength agent sample is labeled PCE-CSH-4.

[0100] Example 6: Preparation method of nano-polycarboxylic acid hydrated calcium silicate early strength agent with varying reaction temperature

[0101] The difference between this embodiment and Example 2 lies in the reaction temperature during the nanocrystal nucleus synthesis step. The temperature of the reaction substrate was controlled at 15 degrees Celsius and maintained throughout the entire dropwise addition and subsequent reaction process. The remaining steps and parameters were exactly the same as in Example 2. The resulting early-strength agent sample was labeled PCE-CSH-5.

[0102] Example 7: Preparation method of nano-polycarboxylic acid hydrated calcium silicate early strength agent with varying stirring speed

[0103] The difference between this embodiment and Example 2 lies in the stirring speed during the nanocrystal nucleus synthesis step. The stirring speed was increased to 800 rpm, while the remaining steps and parameters were exactly the same as in Example 2. The resulting early-strength agent sample was labeled PCE-CSH-6.

[0104] Comparative Example 1: Preparation of Nano-Hydrated Calcium Silicate without Polymer Dispersant

[0105] This comparative example aims to illustrate the crucial role of polymer dispersants. The preparation process did not include the polymer synthesis in step one; instead, a sodium hydroxide aqueous solution with a pH of 11.25 was directly prepared as the base solution. Subsequently, following step two of Example 2, calcium salt solution A and silicate solution B were added dropwise to this base solution to synthesize hydrated calcium silicate. During the dropwise addition, due to the absence of a dispersant, a large amount of flocculent precipitate rapidly formed in the system, failing to form a stable suspension. The final product was filtered and washed under the same conditions, yielding a solid that easily agglomerated, labeled as control sample CP-1.

[0106] Comparative Example 2: Stepwise preparation of nano-polycarboxylic acid hydrated calcium silicate

[0107] This comparative example employs a traditional stepwise process. First, a polymer dispersant solution was prepared in a separate reactor according to step one of Example 2, and then concentrated and dried into a powder. Next, in another reactor, the polymer powder was redissolved in water and the pH was adjusted, followed by the synthesis of nano-hydrated calcium silicate according to step two of Example 2. This process requires extensive equipment, is lengthy, and takes over 1000 minutes in total, with slightly poor redispersibility in the final product. The resulting sample was designated as control sample CP-2.

[0108] Comparative Example 3: Commercially available conventional early-strength agents

[0109] This comparative example uses a commercially available calcium nitrate liquid early strength agent as a reference. The recommended dosage is usually 2% to 4% of the mass of the cementitious material, and it is marked as the comparative sample CP-3.

[0110] Comparative Example 4: Preparation method without pH adjustment

[0111] The difference between this comparative example and Example 2 is that the pH value of the system was not actively controlled during the nanocrystal nucleus synthesis step. During the dropwise addition, the pH value of the system naturally decreased from the initial 11.25. The final product had uneven particle size distribution, poor stability, and stratified after standing, and was labeled as the control sample CP-4.

[0112] Application Example 1:

[0113] This application example is used to test the effect of the early strength agent of the present invention on the early strength and workability of cement mortar.

[0114] 1. Sample preparation:

[0115] The standard cement is used, and the mix proportion is: 800 grams of cement, 200 grams of silica fume, and 1350 grams of ISO standard sand, with a fixed water-cement ratio of 0.2. A polycarboxylate-based high-performance water-reducing agent is used, with a dosage of 0.25% of the total mass of the cementitious materials.

[0116] Experimental group: The early-strength agent samples prepared in Examples 2 to 7 were added to the mixing water at a dosage of 0.5% of the cement mass. The amount of mixing water used should be reduced by the water content of the early-strength agent itself.

[0117] Control group 1: Blank mortar without any early strength agent.

[0118] Control group 2: Mortar with 0.5% of commercially available early strength agent CP-3 added to control group 3.

[0119] Each sample was prepared as a 40mm×40mm×160mm prism specimen according to GB / T17671-1999 "Test Method for Strength of Cement Mortar".

[0120] 2. Testing Method:

[0121] The mortar fluidity was tested according to GB / T2419-2005 "Determination of Flowability of Cement Mortar".

[0122] The specimens were cured under standard conditions, and their compressive strength was tested at 1 day, 7 days, and 28 days. In addition, to simulate the production of precast components, a steam curing regimen was added: after the specimens were formed, they were left to stand for 2 hours, and then cured at 65 degrees Celsius and 90% relative humidity for 6 hours, and their strength after steam curing was tested.

[0123] 3. Test Results:

[0124] The performance test results of cement mortar are summarized in Table 1.

[0125] Table 1: Effects of different early-strength agents on the properties of cement mortar

[0126]

[0127] 4. Results Analysis:

[0128] In terms of fluidity, the mortar with the early-strength agent of this invention exhibited a fluidity between 275 and 290 mm, which was significantly improved compared to the 270 mm of the control group. This indicates that the product of this invention has a certain plasticizing effect and good compatibility with water-reducing agents. In contrast, the commercially available early-strength agent CP-3 resulted in a slight decrease in fluidity.

[0129] In terms of early strength, the early strength agent of this invention exhibits significant advantages. The mortar incorporating PCE-CSH-1 achieved a 1-day compressive strength of up to 60.99 MPa, an increase of over 55% compared to the control group; the 7-day strength reached 78.02 MPa, an increase of over 26%. Other sample examples also showed significant improvements in early strength. In contrast, the commercially available early strength agent CP-3 offered limited improvement in 1-day strength.

[0130] Regarding later-stage strength, the 28-day strength of all mortars containing the early-strength agent of this invention was higher than that of the control group, indicating that it had no adverse effect on the later-stage strength development of concrete, and even slightly promoted it. The steam-cured strength was comparable to or slightly higher than that of the control group, indicating that it is suitable for the rapid curing process of precast components.

[0131] In summary, the PCE-CSH-1 sample from Example 2 exhibited the best overall performance in terms of improving early strength, enhancing flowability, and ensuring later strength.

[0132] In summary, the nano-polycarboxylic acid hydrated calcium silicate early-strength agent and its integrated preparation method provided by this invention organically combine polymer dispersant synthesis with the nanocrystal nucleus growth process through molecular design, achieving continuous and controllable production of the product in a single reactor. The prepared early-strength agent possesses a uniform nanoscale structure and excellent dispersion stability. In concrete applications, it exhibits outstanding characteristics of low dosage, high early strength, no impact on later performance, and a slight improvement in the workability of concrete mixtures. This technology simplifies the process flow, reduces energy consumption and costs, and provides an innovative solution for the efficient and green manufacturing of concrete admixtures, especially precast concrete components.

[0133] The basic principles of this application have been described above with reference to specific embodiments. However, it should be noted that the advantages, benefits, and effects mentioned in this application are merely examples and not limitations, and should not be considered as essential features of each embodiment of this application. Furthermore, the specific details disclosed above are for illustrative and facilitative purposes only, and are not limitations. These details do not limit the application to the necessity of employing the aforementioned specific details for implementation.

[0134] The above description of the disclosed aspects is provided to enable any person skilled in the art to make or use this application. Various modifications to these aspects will be readily apparent to those skilled in the art, and the general principles defined herein can be applied to other aspects without departing from the scope of this application. Therefore, this application is not intended to be limited to the aspects shown herein, but rather to be carried out within the widest scope consistent with the principles and novel features of the invention herein.

[0135] The above description is merely a preferred embodiment of this application and is not intended to limit this application. Any modifications or equivalent substitutions made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. A nano-polycarboxylic acid hydrated calcium silicate early strength agent, characterized in that, It consists of a polymer dispersant and in-situ supported nano-hydrated calcium silicate crystal nuclei; The polymer dispersant is synthesized from the following raw materials in parts by weight: 40-50 parts of polyether macromonomer, 20-25 parts of unsaturated carboxylic acid, 3-5 parts of silane coupling agent, 5-7 parts of hydrogen peroxide and 5-10 parts of vitamin C as the initiator system, and 2-3 parts of chain transfer agent. The nano-hydrated calcium silicate crystal nuclei are formed by calcium ions and silicate ions in a reaction system, wherein the concentration of calcium ions is 0.8-2.4 mol / L, the concentration of silicate ions is 0.4-1.2 mol / L, and the molar ratio of calcium ions to silicate ions is (1-3):

1. The pH value of the reaction system is 11-12, and the molecular weight of the polymer dispersant is 45,000-55,000.

2. The nano-polycarboxylic acid hydrated calcium silicate early strength agent as described in claim 1, characterized in that, The polyether macromonomer is selected from one of propylene alcohol polyoxyethylene ether, isopentenyl alcohol polyoxyethylene ether, and polyethylene monomethyl ether.

3. The nano-polycarboxylic acid hydrated calcium silicate early strength agent as described in claim 1, characterized in that, The unsaturated carboxylic acid is selected from at least one of acrylic acid, methacrylic acid, methyl acrylate, ethyl acrylate, methyl methacrylate, and butyl acrylate.

4. The nano-polycarboxylic acid hydrated calcium silicate early strength agent as described in claim 1, characterized in that, The chain transfer agent is dodecyl mercaptan.

5. The nano-polycarboxylic acid hydrated calcium silicate early strength agent as described in claim 1, characterized in that, The calcium ions are derived from one of calcium nitrate, calcium formate, or calcium chloride.

6. The nano-polycarboxylic acid hydrated calcium silicate early strength agent as described in claim 1, characterized in that, The silicate ions are derived from one of sodium metasilicate pentahydrate, sodium metasilicate nonahydrate, potassium silicate, or lithium silicate.

7. The nano-polycarboxylic acid hydrated calcium silicate early strength agent as described in claim 1, characterized in that, The preferred formulation, by weight, is: 45 parts of isopentenyl polyoxyethylene ether, the macromonomer of the polyether, 22 parts of acrylic acid, the unsaturated carboxylic acid, 6 parts of hydrogen peroxide, 7 parts of vitamin C, 4 parts of silane coupling agent, and 2.5 parts of dodecyl mercaptan, the chain transfer agent.

8. A method for preparing the nano-polycarboxylic acid hydrated calcium silicate early strength agent as described in claim 1, characterized in that, The process is carried out continuously in a single atmospheric pressure reactor, including the following steps: The polyether macromonomer was dissolved in water, and a mixture of unsaturated carboxylic acid and silane coupling agent, hydrogen peroxide aqueous solution, and vitamin C and chain transfer agent were added dropwise simultaneously. After the addition was completed, the reaction was kept at a constant temperature to obtain a polymer solution. Water was added to dilute the solution and the pH was adjusted to form the reaction base solution. Calcium salt solution and silicate solution were simultaneously added dropwise to the reaction substrate. After the addition was complete, the reaction continued, and a suspension of early strength agent was obtained after post-treatment.

9. The preparation method according to claim 8, characterized in that, The polymer solution is synthesized at a temperature of 45–55°C, with a total dropping time of 120–180 minutes. After the dropping is completed, the reaction continues at 45–55°C for 60–120 minutes.

10. The preparation method according to claim 8, characterized in that, After dilution with water, the polymer concentration in the reaction substrate is 0.5% to 3%.

11. The preparation method according to claim 8, characterized in that, The total time for adding the calcium salt solution and silicate solution is 100-150 minutes. After the addition is complete, the reaction is continued to be stirred at 15-30°C for 180-270 minutes.

12. The preparation method according to claim 8, characterized in that, During the simultaneous addition of the calcium salt solution and the silicate solution, the alkali solution was monitored and replenished in real time to maintain the pH value of the reaction system within the range of 11 to 12.

13. The application of the nano-polycarboxylic acid hydrated calcium silicate early-strength agent as described in claim 1 in concrete, characterized in that: The amount of early-strength agent added to the concrete mixing system, based on the total mass of concrete cementitious materials, is used to improve the compressive strength of concrete.

14. The application as described in claim 13, characterized in that, The dosage of the early strength agent is 0.2% to 5.0% of the total mass of concrete cementitious materials.

15. The application as described in claim 13, characterized in that, The early strength agent is added together with the mixing water, or it is added to the concrete mixing system after being premixed with the polycarboxylate superplasticizer.

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