Alkali-free accelerator and preparation method thereof

Abstract

The invention discloses an alkali-free accelerator and a preparation method thereof, and relates to the technical field of light building materials. The alkali-free accelerator is prepared from the following components in parts by mass: 30 to 50 parts of aluminum sulfate, 5 to 15 parts of organic acid, 8 to 20 parts of alcohol amine compound, 0.5 to 5 parts of stabilizer and 30 to 40 parts of water. Through an alkali-free formula system (aluminum sulfate and organic acid replace traditional alkaline components), health hazards of alkaline substances to constructors are thoroughly avoided, meanwhile, the excessive hydration risk of cement products caused by the alkaline environment is reduced, and the whole process better meets the green construction requirement. Through the dynamic chelation of the stabilizer and the synergistic effect of components, the generation rate and microstructure arrangement of cement hydration products are effectively regulated and controlled, the later strength attenuation caused by disordered hydration of a traditional accelerator is avoided, and the balance between the setting speed and the long-term mechanical property is realized.

Description

Technical Field

[0001] This invention relates to the field of lightweight building materials technology, specifically to an alkali-free quick-setting agent and its preparation method. Background Technology

[0002] In the field of lightweight building materials, accelerators are widely used. Their main function is to accelerate the setting and hardening of cement or its products in a very short time, thereby ensuring construction efficiency and building quality. However, most traditional accelerators contain alkaline components, such as common alkaline accelerators. Although they can achieve the effect of rapid setting to a certain extent, they have many drawbacks that cannot be ignored.

[0003] On the one hand, alkaline accelerators can easily cause excessive hydration of cement, resulting in excessive hydration products within the cement stone structure. The disordered accumulation of these hydration products and the potential volume expansion reaction often lead to a significant decrease in the later strength of cement products. For example, in some shotcrete construction, after using alkaline accelerators, the concrete can set quickly in the short term, but after several days or weeks, its compressive strength and other indicators are difficult to maintain stability, resulting in strength reduction. This greatly affects the durability and reliability of building projects, posing a hidden danger to the long-term safe use of buildings.

[0004] On the other hand, alkaline quick-setting agents also pose a potential threat to the health of construction workers. During construction, alkaline substances are easily volatilized or dispersed in the air as dust. Construction workers who are exposed to this environment for a long time are prone to skin, respiratory tract, and eye irritation and corrosion, which may lead to various skin diseases, respiratory diseases, and eye diseases. This increases the occupational health risks of construction and also increases the difficulty and cost of safety protection during the construction process.

[0005] Furthermore, traditional alkali-based quick-setting agents are quite sensitive to environmental conditions such as humidity and temperature during application. Slight deviations in environmental conditions can cause significant fluctuations in their quick-setting effect, making it difficult to precisely control the construction process and affecting the stability of project progress and quality. Moreover, in some special environments, such as high humidity or low temperature scenarios, the performance of alkali-based quick-setting agents is greatly reduced, making it difficult to meet the needs of modern complex and ever-changing construction projects.

[0006] Given the numerous problems associated with traditional alkali-based quick-setting agents, developing an alkali-free quick-setting agent with superior performance is of great practical significance for promoting technological progress in the lightweight building materials industry, improving the quality and safety of construction projects, and adapting to diverse construction environments. Summary of the Invention

[0007] The purpose of this invention is to address the problems existing in the prior art by providing an alkali-free quick-setting agent and its preparation method, which effectively solves the problems of reduced strength in the later stage, high sensitivity to the construction environment, and high health risks caused by traditional alkali quick-setting agents. At the same time, it has good quick-setting performance and adaptability to better meet the application needs in the field of lightweight building materials.

[0008] To achieve the above objectives, the technical solution adopted by the present invention is: an alkali-free quick-setting agent, composed of the following components in the indicated mass ratios: 30-50 parts aluminum sulfate, 5-15 parts organic acid, 8-20 parts alkanolamine compound, 0.5-5 parts stabilizer, and 30-40 parts water.

[0009] The stabilizer is a compound represented by Formula 1:

[0010] Formula 1;

[0011] R1 is selected from: methyl, ethyl, tert-butyl, phenyl, furanyl, thiophene.

[0012] Furthermore, the organic acid is at least one of citric acid, tartaric acid, or gluconic acid.

[0013] Furthermore, the alkanolamine compound is at least one of triethanolamine, diethanolamine, or isopropanolamine.

[0014] Furthermore, the aluminum sulfate has a particle size of 200-400 mesh and a purity of ≥95%.

[0015] Furthermore, the stabilizer is any one of the compounds shown in the following structures:

[0016] ;

[0017] .

[0018] Furthermore, the method for synthesizing the stabilizer is as follows:

[0019] ;

[0020] Step 1: Raw material 1 and raw material 2 are subjected to a substitution reaction to synthesize intermediate 1;

[0021] Step 2: Intermediate 1 is synthesized into intermediate 2 via a borate reaction;

[0022] Step 3: Intermediate 2 and raw material 3 are combined via a Suzuki coupling reaction to synthesize a stabilizer.

[0023] A method for preparing an alkali-free quick-setting agent includes the following steps:

[0024] S1. Mix the aluminum sulfate with water in a certain proportion and stir to form a suspension;

[0025] S2. Add the organic acid and the alcohol amine compound sequentially to the suspension, and heat to 40-60°C to react for 1-3 hours;

[0026] S3. Add the stabilizer, continue stirring for 0.5-1 hour, cool to room temperature and filter to obtain an alkali-free quick-setting agent.

[0027] Furthermore, the stirring speed described in S1 is 300-500 r / min, and the stirring time is 20-40 minutes.

[0028] Furthermore, the heating rate described in S2 is 2-5℃ / min, and the reaction temperature is 50-55℃.

[0029] Furthermore, the cooling described in S3 adopts a circulating water cooling system with a cooling rate of 10-15℃ / h.

[0030] Application of an alkali-free quick-setting agent in the field of lightweight building materials.

[0031] The alkali-free formula of this invention regulates the hydration reaction process and reduces the accumulation of disordered hydration products through the synergistic effect of aluminum sulfate and organic acids. Combined with the chelating effect of stabilizers on aluminum ions, a dense and stable cement stone structure is formed, enabling lightweight building materials to achieve rapid setting while simultaneously improving 28-day compressive strength and significantly outperforming traditional products in long-term strength stability. By replacing traditional alkaline activators (such as sodium hydroxide) with alkaline compounds (such as triethanolamine) and using a pH-neutral organic acid system, the irritation of alkaline dust and volatiles to the respiratory tract and skin of construction workers is completely avoided. Through aluminum sulfate and a gradient heating process of 2-5℃ / min, the accelerator maintains a stable setting-promoting effect at ambient temperatures ranging from 5-40℃, significantly superior to traditional products, making it particularly suitable for complex environments such as tunnels and underground engineering projects.

[0032] The coordinating groups in the stabilizer molecule described in this invention can dissociate with Al released from aluminum sulfate. 3+Stable cyclic chelates are formed. This chelation mechanism works by: dynamically controlling the release rate of aluminum ions, slowing down the initial hydration reaction, preventing the instantaneous over-reaction of C3A minerals to form loose ettringite, forming an [Al-stabilizer] complex, and reducing the accumulation of disordered hydration products. The hydrophobic substituents of the stabilizer (such as tert-butyl and phenyl) can be directionally adsorbed onto the surface of cement particles, inhibiting the disordered aggregation of aluminum hydroxide colloids, promoting the directional arrangement of nanosheet-like hydration products, and preventing excessive cross-linking of hydration products through steric hindrance, thus forming a cement stone microstructure with higher density. The conjugated system in the stabilizer molecule (such as furanyl and thiophene groups) can form π-π stacking interactions with organic acids, improving the colloidal stability of the solution, locking free water molecules through an intermolecular hydrogen bond network, reducing the tendency of phase separation during storage, and undergoing gradual dissociation under alkaline conditions to achieve the gradient release of aluminum ions.

[0033] The aluminum sulfate-based alkali-free system described in this invention, combined with organic acids such as citric acid, forms a neutral buffer environment, eliminating the health threat posed by alkaline volatiles to construction workers; alcohol amine compounds react with Al through hydroxyl groups. 3+ The directional coordination activates the hydration of cement minerals, while the stabilizer with a specific structure dynamically regulates the release rate of aluminum ions through chelation, inhibiting the explosive formation of ettringite. Its steric hindrance effect guides the hydration products to form a dense layered structure, thereby increasing the 28-day compressive strength. The gradient heating and step-by-step feeding process further optimizes the molecular assembly of components, and combined with circulating water cooling to control crystallization kinetics, comprehensively achieving a balance between rapid setting performance, long-term strength, and construction safety.

[0034] Compared with the prior art, the beneficial effects of the present invention are:

[0035] 1. Significantly improved environmental friendliness and safety: By using an alkali-free formula system (aluminum sulfate + organic acids to replace traditional alkaline components, such as sodium hydroxide), the health hazards of alkaline substances to construction workers are completely avoided, while reducing the risk of excessive hydration of cement products caused by alkaline environments. The overall process is more in line with the requirements of green construction.

[0036] 2. Significantly optimized long-term strength stability: The dynamic chelating effect and component synergistic effect of the stabilizer effectively regulate the generation rate and microstructure arrangement of cement hydration products, avoiding the later strength decay caused by disordered hydration of traditional accelerators, and achieving a balance between setting speed and long-term mechanical properties.

[0037] 3. Enhanced adaptability to construction environment: Through gradient heating process and specific stabilizer design, the sensitivity to environmental conditions such as temperature and humidity is reduced. It can still maintain a stable quick-setting effect in complex construction scenarios (such as low temperature and high humidity environments), thus broadening the application scope of quick-setting agents. Attached Figure Description

[0038] Figure 1 This is a method for synthesizing the stabilizer described in this invention. Detailed Implementation

[0039] The technical solution of the present invention will now be clearly and completely described with reference to the accompanying drawings. Obviously, the described embodiments are merely some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0040] Synthesis example 1

[0041] Synthesis of Stabilizer 1:

[0042] ;

[0043] Step 1: Under a nitrogen atmosphere, 20 g of raw material 1 and 13.36 g of aluminum trichloride were added sequentially to the reaction system, followed by 150 g of dichloromethane. A 50 g dichloromethane solution containing 4.72 g of raw material 2 was slowly added dropwise at 0°C. The reaction was allowed to proceed at room temperature for 8 hours. After the reaction was complete, the reaction solution was slowly poured into 500 ml of 0.1 mol / L HCl at 0°C. The mixture was stirred for 30 minutes, allowed to stand, and separated. The organic phase was retained, and the aqueous phase was washed three times with 50 ml of dichloromethane. The organic phases were combined, and 100 ml of 0.1 mol / L sodium bicarbonate solution was added. The mixture was stirred and shaken to adjust the pH to neutral. The organic phase was retained, dried over anhydrous magnesium sulfate, filtered, rotary evaporated, and dried to obtain 16.49 g of intermediate 1. MS [MS+1]: 441.

[0044] Step 2: Under a nitrogen atmosphere, 16.49 g of intermediate 1 and 200 g of ultra-dry tetrahydrofuran were added sequentially to the reaction system. The temperature was lowered to -70°C, and 2.51 g of n-butyllithium was added dropwise. After the addition was complete, the mixture was stirred for 1 hour, and then 10.54 g of triisopropyl borate was added dropwise. After the addition was complete, the mixture was allowed to rise naturally to room temperature and reacted for 10 hours. The solvent was then evaporated to obtain 10.66 g of intermediate 2. MS [MS+1]: 407.

[0045] Step 3: Under a nitrogen atmosphere, 10.66 g of intermediate 2, 19.42 g of starting material 3, 7.25 g of anhydrous potassium carbonate, 0.9 g of tetra(triphenylphosphine)palladium, and 150 g of a mixed solution of toluene, ethanol, and water (volume ratio 2:1:1) were added sequentially to the reaction system. The mixture was heated to 75°C and refluxed for 10 hours. The heating was then turned off, and the mixture was cooled to room temperature. The mixture was allowed to stand and separated. The aqueous phase was extracted twice with ethyl acetate. The organic phases were combined, washed three times with water, evaporated to dryness, and subjected to column chromatography using a mixture of petroleum ether and dichloromethane as eluent to obtain 19.03 g of stabilizer 1. MS [MS+1]: 900.

[0046] Stabilizer 1 1 ¹H NMR (deuterated chloroform): δ 8.79-8.74 (m, 1H), 8.58-8.53 (m, 1H), 8.04-7.97 (m, 1H), 7.88 (dd, 1H), 7.72-7.60 (m, 2H), 7.41 (d, 1H), 7.19 (m, 1H), 7.18-7.07 (m, 2H), 5.48 (d, 1H), 4.86 (t, 1H), 4.30 (t, 2H), 4.1 2(dd,1H),3.89(dd,1H),3.79(m,2H),3.73-3.60(m,4H),2.64(s,3H),2.21(m,2H),1.96(m,2H), 1.80-1.69(m,2H),1.73-1.60(m,4H),1.60-1.39(m,2H),1.42-1.19(m,8H),0.95-0.85(m,27H).

[0047] Synthesis Example 2-Synthesis Example 6

[0048] Synthesis Example 2 – In this synthesis example, stabilizers 2 to 6 were synthesized sequentially, following the same synthesis method as in Synthesis Example 1, except that raw material 2 was replaced, while the rest remained the same as in Synthesis Example 1. The specific structures of raw material 2, stabilizers 2 to 6, and their MS [MS+1] data are shown in the table below.

[0049]

[0050] Example 1

[0051] A method for preparing an alkali-free quick-setting agent, the specific steps of which are as follows:

[0052] Raw material ratio (parts by mass): 40 parts aluminum sulfate (300 mesh, 96% purity), 10 parts organic acid (citric acid), 15 parts alkanolamine compound (triethanolamine), 2 parts stabilizer (stabilizer 1 obtained from synthesis example 1), and 35 parts water.

[0053] Preparation steps:

[0054] S1. Add 40 parts aluminum sulfate and 35 parts water to the reactor and stir continuously at a stirring speed of 400 r / min for 30 minutes to form a suspension.

[0055] S2. Add 10 parts of citric acid and 15 parts of triethanolamine to the suspension in sequence, control the heating rate to 3℃ / min, raise the system temperature to 50℃ and keep the temperature constant for 2 hours.

[0056] S3. Add 2 parts of stabilizer 1 to S2 and continue stirring for 45 minutes. Then turn on the circulating water cooling system and cool the system to room temperature at a rate of 12℃ / h. Filter to remove undispersed particles to obtain a transparent viscous liquid, which is the alkali-free quick-setting agent.

[0057] Examples 2-6

[0058] The preparation of an alkali-free quick-setting agent is carried out by referring to the preparation method of Example 1, except that the stabilizer is replaced sequentially with stabilizer 2-stabilizer 6 prepared in Synthesis Examples 2-6, and the rest is the same as in Example 1.

[0059] Comparative Example 1

[0060] The preparation of an alkali-free quick-setting agent is the same as in Example 1, except that no stabilizer is added.

[0061] Comparative Example 2

[0062] The preparation of an alkali-free quick-setting agent is carried out by referring to the preparation method of Example 1, except that the mass part of aluminum sulfate is changed from 40 parts to 60 parts, and the rest is the same as in Example 1.

[0063] Comparative Example 3

[0064] The preparation of an alkali-free quick-setting agent is carried out by referring to the preparation method of Example 1, except that the mass part of aluminum sulfate is changed from 40 parts to 20 parts, and the rest is the same as in Example 1.

[0065] Performance testing:

[0066] The alkali-free accelerator obtained from the examples and comparative examples was tested for setting time of cement paste and mortar, and mortar compressive strength, according to the requirements of GB / T35159-2017 "Accelerators for Shotcrete". The dosage of the accelerator was calculated as a percentage of the cement mass. The test results are shown in the table below:

[0067] Accelerator dosage / % Initial setting time / min Final setting time / min 1d compressive strength / MPa 28-day compressive strength / MPa 90-day compressive strength retention rate / % Example 1 3.0 4.2 8.5 12.3 38.7 105.2 Example 2 3.0 4.5 9.1 11.8 36.9 102.8 Example 3 3.0 3.9 7.8 13.1 39.5 106.5 Example 4 3.0 4.8 9.6 10.9 35.4 98.7 Example 5 3.0 5.1 10.2 10.2 34.1 95.4 Example 6 3.0 3.6 7.2 14.5 41.2 108.9 Comparative Example 1 3.0 15.6 28.3 6.8 24.5 82.3 Comparative Example 2 3.0 8.1 12.5 9.9 27.8 71.6 Comparative Example 3 3.0 22.7 39.4 4.3 18.2 68.9

[0068] The examples showed a significant performance improvement compared to the comparative examples. With the appropriate introduction of stabilizers and precise control of aluminum sulfate content, the setting time of the examples was significantly shortened, the initial compressive strength formed rapidly and steadily increased, and the long-term strength retention rate was better than the baseline system, with no later-stage strength decay. In contrast, the comparative examples suffered from uncontrolled setting time (too fast or too slow) due to component imbalances (such as lack of stabilizers, excessive or insufficient aluminum sulfate), accompanied by long-term strength deterioration or structural loosening. Furthermore, the pH values ​​of all examples remained stable within the neutral range, verifying the environmental friendliness and safety of the alkali-free system and demonstrating the synergistic effect of the formulation design and the controllability of the process.

[0069] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. An alkali-free quick-setting agent, characterized in that, It is composed of the following components in the indicated mass ratios: 30-50 parts aluminum sulfate, 5-15 parts organic acid, 8-20 parts alkanolamine compound, 0.5-5 parts stabilizer, and 30-40 parts water. The stabilizer is a compound represented by Formula 1: Formula 1; R1 is selected from: methyl, ethyl, tert-butyl, phenyl, furanyl, thiophene.

2. The alkali-free quick-setting agent according to claim 1, characterized in that, The organic acid is at least one of citric acid, tartaric acid, or gluconic acid.

3. The alkali-free quick-setting agent according to claim 1, characterized in that, The alkanolamine compound is at least one of triethanolamine, diethanolamine, or isopropanolamine.

4. The alkali-free quick-setting agent according to claim 1, characterized in that, The aluminum sulfate has a particle size of 200-400 mesh and a purity of ≥95%.

5. The alkali-free quick-setting agent according to claim 1, characterized in that, The stabilizer is any one of the compounds shown in the following structures: ； 。 6. A method for preparing an alkali-free quick-setting agent according to any one of claims 1-5, characterized in that, Includes the following steps: S1. Mix the aluminum sulfate with water in a certain proportion and stir to form a suspension; S2. Add the organic acid and the alcohol amine compound sequentially to the suspension, and heat to 40-60°C to react for 1-3 hours; S3. Add the stabilizer, continue stirring for 0.5-1 hour, cool to room temperature and filter to obtain an alkali-free quick-setting agent.

7. The method for preparing an alkali-free quick-setting agent according to claim 6, characterized in that, The stirring speed described in S1 is 300-500 r / min, and the stirring time is 20-40 minutes.

8. The method for preparing an alkali-free quick-setting agent according to claim 6, characterized in that, The heating rate described in S2 is 2-5℃ / min, and the reaction temperature is 50-55℃.

9. The method for preparing an alkali-free quick-setting agent according to claim 6, characterized in that, The cooling described in S3 uses a circulating water cooling system with a cooling rate of 10-15℃ / h.

10. The application of an alkali-free quick-setting agent according to any one of claims 1-5 in the field of lightweight building materials.

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