Alkali-free, chlorine-free and fluorine-free liquid accelerator as well as preparation process and application thereof

Abstract

The invention discloses an alkali-free chlorine-free fluorine-free liquid accelerator which is prepared from the following raw materials: polyaluminum sulfate, alkylol amine, a dissolution promoter, a reinforcing agent A, a reinforcing agent B, a complexing agent, a pH regulator, a compound stabilizer and water. The preparation method comprises the following steps: S1, adding water and polyaluminum sulfate into a reaction container, and stirring and heating to completely dissolve the polyaluminum sulfate; s2, adding alcohol amine and a dissolution promoter, reacting at 55-65 DEG C for 30-120 minutes, and respectively adding a reinforcing agent A, a reinforcing agent B, a complexing agent and a compound stabilizer after reacting for a certain time; and S3, adding the pH regulator, and stirring for 1-2 hours to obtain the accelerator. The alkali-free chlorine-free fluorine-free liquid accelerator has the advantages of short setting time, high stability and good mechanical properties, and has a good application prospect.

Description

Technical Field

[0001] The invention relates to the technical field of building materials, and in particular to an alkali-free, chlorine-free and fluorine-free liquid quick-setting agent, a preparation process and an application thereof. Background Art

[0002] Accelerators, as an additive, can promote the rapid coagulation and hardening of cement concrete, cement mortar and cement paste. Its core function is to accelerate the hydration process of cement paste and promote its coagulation and hardening process. Early accelerators mostly relied on ingredients such as alkali metal aluminum salts and metaaluminates. Although they performed well in the rapid setting effect, they were prone to cause a series of problems due to their high alkalinity and chlorine content. Specifically, these alkaline components are prone to alkali-aggregate reactions with active aggregates inside the concrete to generate substances with expansion properties such as alkali silicate gel, calcium carbonate crystals, and magnesium hydroxide crystals, thereby causing self-expansion stress inside the concrete, which in turn causes cracking, which has an adverse effect on the later strength improvement and durability of the concrete. At the same time, chloride ions pose a serious corrosion threat to the steel bars and other metal embedded parts inside the concrete. Due to the chloride ion (Cl - ) has a small ion radius, which can easily penetrate the passivation film on the surface of the steel bar, causing electrochemical corrosion, destroying the passivation layer, and accelerating the rust process of the steel bar.

[0003] In view of this, the development of accelerators is gradually tending towards alkali-free and chlorine-free. At present, the main accelerating component of alkali-free and chlorine-free accelerators is aluminum sulfate. 3+ To achieve its accelerating effect. However, due to the relatively low solubility of aluminum sulfate (Al2(SO4)3), it is easy to undergo hydrolysis and produce flocculent precipitation. As the storage time increases, crystallization and precipitation become more and more obvious, which poses a severe challenge to the stability and use effect of liquid accelerating setting agent.

[0004] In order to increase Al 3+ The current common method is to introduce HF or other fluorine-containing substances to complex with aluminum ions to form aluminum fluoride. However, in order to obtain more stable Al 3+ , it is often necessary to add a large amount of fluoride, which leads to a high fluorine content in the accelerator. Fluoride is extremely toxic and corrosive, which not only causes serious harm to the environment, but also poses a serious threat to the health of workers who work on the construction site for a long time. Therefore, how to reduce the toxicity and corrosiveness of the accelerator while ensuring the rapid setting effect has become a problem that needs to be solved urgently. Summary of the invention

[0005] The present invention aims to provide an alkali-free, chlorine-free and fluorine-free liquid accelerating setting agent, a preparation process and a use method thereof, so as to solve the technical problems existing in the above-mentioned prior art.

[0006] In order to achieve the above technical objectives, the present invention adopts the following technical solutions:

[0007] The invention discloses an alkali-free, chlorine-free and fluorine-free liquid quick-setting agent, which is prepared from the following raw materials in percentage by mass: 46-60% of polyaluminium sulfate, 2-8% of alcohol amine, 1-4% of a dissolution promoter, 1-6% of an enhancer A, 3-7% of an enhancer B, 1.2-2.3% of a complexing agent, 1-2% of a pH regulator, 1-3% of a composite stabilizer and the balance is water.

[0008] Furthermore, the alcohol amine is diethanolamine or triethanolamine; and the solubilizing agent is propanol.

[0009] Furthermore, the enhancer A is lithium sulfate; and the enhancer B is calcium formate.

[0010] Furthermore, the pH regulator is dilute sulfuric acid.

[0011] Furthermore, the composite stabilizer comprises the following components: ethylenediaminetetraacetic acid, polyacrylamide, and boric acid.

[0012] Furthermore, in the composite stabilizer, the composite stabilizer is made of ethylenediaminetetraacetic acid: polyacrylamide: boric acid in a mass ratio of 5:3:2.

[0013] A preparation process of an alkali-free, chlorine-free and fluorine-free liquid accelerating setting agent comprises the following steps:

[0014] S1: Add water and polyaluminium sulfate into a reaction vessel, stir and heat to completely dissolve the polyaluminium sulfate;

[0015] S2: Add alcohol amine and chaotropic agent, react at 55-65℃ for 30-120min, then add enhancer A, enhancer B, complexing agent and composite stabilizer respectively for a certain reaction time;

[0016] S3: Add pH adjuster and stir for 1-2 hours to obtain the accelerating setting agent.

[0017] Furthermore, in S1, polyaluminium sulfate is dissolved by heating at 60°C with stirring for 1 hour.

[0018] Furthermore, in S2, enhancer A, enhancer B, complexing agent and composite stabilizer are added respectively every 30-120 minutes of reaction.

[0019] The alkali-free, chlorine-free and fluorine-free liquid quick-setting agent is used in highway and railway tunnel shotcrete, slope protection, mines, 3D printing, repair and reinforcement projects, and its dosage is 6-9% of cement.

[0020] The preparation technology principle of the alkali-free, chlorine-free and fluorine-free liquid accelerating setting agent of the present invention is as follows:

[0021] 1. The role of the raw material components of the present invention

[0022] Polyaluminium sulfate: The main accelerator, providing aluminium ions to accelerate cement coagulation. Due to its polymeric form, it can react quickly with cement to form a stable gel structure.

[0023] Alcoholamine: a coagulant component and early strength agent. Alcoholamine promotes the coagulation and hardening of cement paste. It can react with Ca 2+ and Fe 3+ Plasma complexation promotes the dissolution of C3A and accelerates its formation of ettringite and AFm, which is beneficial to improving the early strength of concrete.

[0024] Dissolution promoter: Improve the solubility of aluminum ions and make them more evenly dispersed in the system.

[0025] Reinforcer A: Reinforcer A is lithium sulfate, a white crystalline powder with the molecular formula Li2SO4, which has significant accelerating properties. As a key component of accelerators, lithium sulfate can effectively promote the solidification and hardening process of cement at low temperatures, thereby accelerating the initial setting time and final setting time. Lithium sulfate undergoes complex chemical reactions with other components in cement. These reactions not only promote the rapid hydration of cement particles, but also form hydration product crystals with very low solubility, thereby accelerating the setting and hardening of concrete and improving the early strength of concrete.

[0026] Reinforcer B: Calcium formate has a good particle morphology effect, which can effectively fill the internal pores of concrete and increase the structural density, thereby enhancing the mechanical properties and durability of concrete, and at the same time improving the early strength.

[0027] Dilute sulfuric acid: Adjusting the pH value of the liquid accelerator can effectively alleviate the instability problem caused by the hydrolysis-polymerization-precipitation of aluminum ions.

[0028] Complexing agent: Complexing agent can form stable complexes with various metal ions in the accelerator system. These complexes can not only effectively adjust the hardening time of the accelerator, but also significantly improve its early strength and durability. The accelerator made by the complexing agent of the present invention can effectively improve the work efficiency and quality in applications such as highway and railway tunnel shotcrete, slope protection, mines, 3D printing, repair and reinforcement.

[0029] Composite stabilizer: Made of ethylenediaminetetraacetic acid, polyacrylamide, and boric acid; the amino and carboxyl groups in the ethylenediaminetetraacetic acid molecule can react with aluminum ions (Al 3+ ) form a stable coordination bond. These bonds firmly bind aluminum ions to the EDTA molecules through the sharing of electron pairs, thereby preventing the aluminum ions from hydrolyzing. 3+The complex is very stable. Due to the multi-dentate coordination structure formed inside it, EDTA provides multiple coordination sites to bind to aluminum ions. This multi-dentate structure increases the stability of the complex and further improves the stability of aluminum ions. The long chain structure of polyacrylamide can unfold in the solution and attract aluminum ions through electrostatic effects. These electrostatic effects help to evenly disperse aluminum ions in the solution to prevent them from aggregating and precipitating. In addition, polyacrylamide increases the viscosity of the solution to form a colloidal solution, which can further inhibit the aggregation and precipitation of aluminum ions and maintain the stability of the solution. Boric acid can bind to EDTA-Al 3+ The aluminum ions in the complex form weak coordination bonds, which can enhance the complexing ability of EDTA to aluminum ions and improve the stability of the accelerator. The three interact with each other and can synergistically enhance the stability of the accelerator. In the composite stabilizer, EDTA: polyacrylamide: boric acid is made in a ratio of 5:3:2. Too much EDTA complexes too many metal ions, resulting in excessive complexation, affecting the effectiveness of other components, and excessive EDTA may increase the viscosity of the solution, affecting fluidity and construction performance, while too little EDTA cannot fully complex aluminum ions, resulting in aluminum ion hydrolysis and precipitation, reducing the stability of the system, and affecting the setting time and strength development of the accelerator, which is not conducive to engineering application; excessive polyacrylamide may cause the solution viscosity to be too high, affecting construction performance and making it difficult to disperse evenly, while too little polyacrylamide cannot effectively disperse aluminum ions, resulting in precipitation and stratification, reducing the stability of the solution; excessive boric acid may affect the normal hydration reaction of cement and reduce early and late strength; while too little EDTA cannot fully play the role of enhancing complexing ability, affecting the effect of EDTA. Therefore, choosing a reasonable ratio has a significant impact on the effect of the composite stabilizer.

[0030] The alkali-free, chlorine-free and fluorine-free liquid accelerator of the present invention is unique in its carefully designed raw material ratio and preparation process, which aims to ensure the high efficiency, environmental protection and stability of the product. The accelerator is carefully formulated with the following raw materials in percentage by mass: polyaluminium sulfate accounts for 46-60%, as a core component, it not only provides the necessary coagulation ability, but also promotes the early strength development of concrete through its unique chemical properties; alcohol amine (specifically diethanolamine or triethanolamine) accounts for 2-8%, as an important regulator, it can effectively improve the fluidity and working performance of concrete, and at the same time enhance the compatibility of the accelerator with the concrete substrate; the solvent propyl alcohol accounts for 1-4%, its function is to accelerate the dissolution and dispersion of other components, improve Reaction efficiency; Enhancer A (lithium sulfate) and Enhancer B (calcium formate) account for 1-6% and 3-7% respectively. The two work synergistically to significantly improve the mechanical properties and durability of concrete; pH adjuster dilute sulfuric acid accounts for 1-2%, which accurately controls the pH of the system to ensure the stable performance of the accelerator in concrete; Composite stabilizer accounts for 1-3%, which is carefully mixed with ethylenediaminetetraacetic acid, polyacrylamide, and boric acid in a mass ratio of 5:3:2. This combination not only enhances the chemical stability of the accelerator, but also improves its adaptability to environmental changes.

[0031] 2. The necessity and importance of controlling the amount of each raw material

[0032] (1) Accurate proportion: The amount of each raw material is strictly calculated to ensure that the overall performance of the accelerator is optimized. The amount of polyaluminium sulfate directly affects the setting time and strength development of concrete, the ratio of amine to solvent is related to the construction performance of concrete, and the amount of enhancer and composite stabilizer added is directly related to the final mechanical properties and long-term stability of concrete.

[0033] (2) Safety and environmental protection considerations: The design of the alkali-free, chlorine-free and fluorine-free formula requires that the selection of raw materials in each step must strictly follow the safety and environmental protection principles to avoid causing harm. The presence of alkali in the accelerator is an issue that cannot be ignored. Alkaline substances can also cause harm to construction workers and the environment. Excessively high alkaline water is irritating to the human body and can reduce the acidity of gastric juice and affect the normal function of the digestive system. Long-term contact with alkaline substances may damage the skin, eyes and other organs of construction workers, and even cause more serious health problems. Chloride ions are another common harmful component in traditional accelerators. Chloride ions not only pollute the construction environment, but also have an adverse effect on the structural properties of concrete. The infiltration of chloride ions will accelerate the corrosion process of concrete and reduce the durability of concrete. At the same time, chloride ions also pose a potential threat to the health of construction workers. Long-term inhalation or contact with chlorine-containing substances may cause health problems such as respiratory diseases and skin inflammation. The presence of fluoride ions in traditional accelerators is also worrying. An appropriate amount of fluoride is beneficial to human health. It helps to enhance the hardness and accelerate bone growth, and also protects teeth. However, long-term excessive intake of fluoride can cause serious harm to the human body. Excessive fluoride can affect the normal metabolism of bones, leading to deformities of joints, spine and limbs, a condition known as skeletal fluorosis. For children, excessive fluoride can also lead to incomplete mineralization of tooth enamel, making teeth brittle and easy to break, and spots of different colors appear on the surface, a condition known as dental fluorosis. In addition, fluoride ions in the sprayed concrete mist may also irritate and damage the respiratory system of operators.

[0034] Therefore, the development and application of alkali-free, chlorine-free and fluorine-free quick-setting agents are particularly important. Accurately controlling the amount of each raw material can not only meet performance requirements, but also minimize the impact on the environment. It not only eliminates the hazards caused by alkali, chlorine and fluorine in traditional quick-setting agents, but also improves the performance and safety of shotcrete. This quick-setting agent has been widely used in highway and railway tunnel shotcrete, slope protection, mines, 3D printing, and repair and reinforcement projects, providing strong protection for the health of construction workers and environmental protection.

[0035] (3) Cost control: Reasonable raw material ratio can not only improve product quality, but also effectively control production costs, achieving a win-win situation in economic and environmental benefits.

[0036] 3. Selection and optimization of preparation process parameters

[0037] In the process of preparing alkali-free, chlorine-free and fluorine-free liquid accelerator, the selection and optimization of process parameters are also crucial, which directly determine the final quality and production efficiency of the product.

[0038] (1) Heating and dissolving stage: Polyaluminium sulfate is heated and stirred at 40-60°C for 1-2 hours to ensure complete dissolution. This step not only improves the reaction efficiency, but also ensures the smooth progress of subsequent reactions. The selection of this temperature is the optimal value obtained through multiple experimental verifications, which can effectively accelerate dissolution without causing raw material decomposition or performance degradation.

[0039] (2) Add additives in stages: After reacting at 55-65°C for 30-120 minutes, add enhancer A, enhancer B, chelating agent, and composite stabilizer every 30-120 minutes. This staged addition method can ensure that each additive can fully exert its effect while avoiding mutual interference and achieving the best synergistic effect.

[0040] (3) Time control: Add pH adjuster and stir for 1-2 hours. Time control of this step can maintain the stability of the system.

[0041] By optimizing the above process parameters, not only the production efficiency of the accelerator was improved, but also some performance improvements were unexpectedly discovered, such as stronger impermeability and higher early strength.

[0042] In summary, in the preparation process of alkali-free, chlorine-free and fluorine-free liquid accelerators, precise control of raw material dosage and optimal selection of process parameters are the key to achieving high performance, environmental protection and cost-effectiveness of products. Through continuous research and practice, these parameters can be further explored and optimized to meet the specific needs of different application scenarios and promote the continuous progress and development of concrete technology.

[0043] Compared with the prior art, the present invention has the following technical advantages:

[0044] 1. The present invention uses enhancer A, enhancer B, complexing agent and composite stabilizer in the raw materials to synergistically prepare a liquid accelerator. The alkali content of the accelerator is ≤1.0%, the chlorine content is ≤0.1%, and the fluorine content is ≤0.05%, which meets the relevant standards and is an alkali-free, chlorine-free and fluorine-free liquid accelerator. The accelerator has the advantages of fast setting time, strong stability and high mechanical strength, excellent physical and chemical properties and mechanical properties, can improve the application scenarios of the accelerator, has a simple preparation process, is easy to operate, and has a good market prospect.

[0045] 2. The alkali-free, chlorine-free, and fluorine-free liquid accelerators prepared in Examples 1-5 of the present invention have initial setting times of 3'18", 3'12", 3'48", 3'15", and 3'30", respectively, and final setting times of 6'06", 6'42", 7'12", 6'24", and 7'31", respectively, which meet the requirements of the national standard GB / T 35159-2017 that the initial setting time is less than 5 min and the final setting time is less than 12 min.

[0046] 3. The alkali-free, chlorine-free, and fluorine-free liquid accelerators prepared in Examples 1-5 of the present invention have stable times of 72d, 68d, 65d, 66d, and 69d, respectively, which can significantly improve the stability of the accelerators.

[0047] 4. When the alkali-free, chlorine-free and fluorine-free liquid accelerator prepared in Example 1 of the present invention is applied to concrete, the 1d compressive strength of the concrete is 12.4MPa, the 28d compressive strength is 38.6MPa, and the 28d compressive strength ratio is 106.3%. The accelerator can significantly improve the strength of concrete and make the concrete have excellent mechanical properties. BRIEF DESCRIPTION OF THE DRAWINGS

[0048] Figure 1 This is a picture of the product obtained in Example 1 of the present invention. DETAILED DESCRIPTION

[0049] The present invention will be further described in detail below in conjunction with specific embodiments. It should be emphasized that the following description is merely exemplary and is not intended to limit the scope of the present invention and its application.

[0050] In the implementation of the present invention, an alkali-free, chlorine-free and fluorine-free liquid accelerating setting agent is prepared by the following raw materials in percentage by mass: 46-60% of polyaluminium sulfate, 2-8% of alcohol amine, 1-4% of dissolution promoter, 1-6% of enhancer A, 3-7% of enhancer B, 1.2-2.3% of complexing agent, 1-2% of pH adjusting agent, 1-3% of composite stabilizer, and the balance is water.

[0051] The alcohol amine is diethanolamine or triethanolamine;

[0052] The reinforcing agent A is lithium sulfate.

[0053] The composite stabilizer is prepared from ethylenediaminetetraacetic acid: polyacrylic amine: boric acid in a mass ratio of 3-5:2-4:1-3.

[0054] A preparation process of an alkali-free, chlorine-free and fluorine-free liquid accelerating setting agent comprises the following steps:

[0055] S1: Add water and polyaluminium sulfate into a reaction vessel, and heat with stirring at 40-60°C for 1-2h to completely dissolve the polyaluminium sulfate;

[0056] S2: add alcohol amine and chaotropic agent, react at 55-65°C for 30-120 minutes, then add enhancer A, enhancer B, complexing agent and composite stabilizer respectively for every 30-120 minutes of reaction;

[0057] S3: Add pH adjuster and stir for 1-2 hours to obtain the accelerating setting agent.

[0058] The invention discloses an application of an alkali-free, chlorine-free and fluorine-free liquid accelerating setting agent. The alkali-free, chlorine-free and fluorine-free liquid accelerating setting agent is applied to projects including highway and railway tunnel shotcrete, slope protection, mines, 3D printing, and repair and reinforcement projects, and the dosage thereof is 6-9% of cement.

[0059] In order to make the disclosure of the present invention more complete, it is described below through more specific embodiments.

[0060] Example 1

[0061] The invention discloses an alkali-free, chlorine-free and fluorine-free liquid quick-setting agent, which is prepared from the following raw materials in percentage by weight: 60% of polyaluminium sulfate, 4% of diethanolamine, 2% of propanol, 2% of lithium sulfate, 3% of calcium formate, 2% of complexing agent, 1% of dilute sulfuric acid, 2% of composite stabilizer and the balance of water.

[0062] The composite stabilizer is prepared from ethylenediaminetetraacetic acid: polyacrylamide: boric acid in a mass ratio of 5:3:2.

[0063] A preparation process of an alkali-free, chlorine-free and fluorine-free liquid accelerating setting agent comprises the following steps:

[0064] S1: Add water and polyaluminium sulfate into a reaction vessel, and heat with stirring at 60°C for 1 hour to completely dissolve the polyaluminium sulfate;

[0065] S2: Add alcohol amine and solvent, react at 63°C for 30 min, then add lithium sulfate, calcium formate, complexing agent and composite stabilizer respectively for every 30 min of reaction;

[0066] The preparation method of the complexing agent comprises the following steps:

[0067] (1) 42 parts of N-methyl-2-acrylamide, 10 parts of cyclohexylmethyldimethoxysilane, 70 parts of β-aminoethanesulfonic acid, 1.5 parts of cyclohexanone peroxide and 360 parts of water were mixed, and then reacted for 50 minutes under the conditions of controlling the speed to 200 r / min, the microwave power to 300 W, and the temperature to 38° C. to obtain a reaction mixture;

[0068] (2) adding 0.5 parts of carotene and 90 parts of water to the reaction mixture obtained in step (1), and then reacting for 60 minutes at a speed of 300 r / min, a microwave power of 200 W, and a temperature of 42° C., and then cooling to room temperature to obtain a complexing agent;

[0069] S3: Add dilute sulfuric acid and stir for 2 hours to obtain the accelerating setting agent. The product in the beaker is Figure 1 .

[0070] Example 2

[0071] The invention discloses an alkali-free, chlorine-free and fluorine-free liquid quick-setting agent, which is prepared from the following raw materials in percentage by mass: 46% of polyaluminium sulfate, 5% of triethanolamine, 3% of propanol, 4% of lithium sulfate, 7% of calcium formate, 1.2% of complexing agent, 1% of dilute sulfuric acid, 1% of composite stabilizer and the balance of water.

[0072] The preparation method of the complexing agent is the same as that of Example 1.

[0073] The composite stabilizer is prepared from ethylenediaminetetraacetic acid: polyacrylamide: boric acid in a mass ratio of 4:3:1.

[0074] A preparation process of an alkali-free, chlorine-free and fluorine-free liquid accelerating setting agent comprises the following steps:

[0075] S1: Add water and polyaluminium sulfate into a reaction vessel, and heat with stirring at 40°C for 2h to completely dissolve the polyaluminium sulfate;

[0076] S2: Add alcohol amine and solvent, react at 55°C for 1 hour, then add lithium sulfate, calcium formate, complexing agent and composite stabilizer respectively every 2 hours;

[0077] S3: Add dilute sulfuric acid and stir for 108 minutes to obtain the accelerating setting agent.

[0078] Example 3

[0079] The invention discloses an alkali-free, chlorine-free and fluorine-free liquid quick-setting agent, which is prepared from the following raw materials in percentage by weight: 53% of polyaluminium sulfate, 2% of triethanolamine, 1% of propanol, 6% of lithium sulfate, 4% of calcium formate, 1.8% of a complexing agent, 2% of dilute sulfuric acid, 2% of a composite stabilizer, and the balance being water.

[0080] The preparation method of the complexing agent is the same as that of Example 1.

[0081] The composite stabilizer is prepared from ethylenediaminetetraacetic acid: polyacrylamide: boric acid in a mass ratio of 3:2:1.

[0082] A preparation process of an alkali-free, chlorine-free and fluorine-free liquid accelerating setting agent comprises the following steps:

[0083] S1: Add water and polyaluminium sulfate into a reaction vessel, and heat with stirring at 55°C for 2h to completely dissolve the polyaluminium sulfate;

[0084] S2: Add alcohol amine and solvent, react at 60°C for 40 minutes, then add lithium sulfate, calcium formate, complexing agent and composite stabilizer for 48 minutes each;

[0085] S3: Add dilute sulfuric acid and stir for 2 hours to obtain the accelerating setting agent.

[0086] Example 4

[0087] The invention discloses an alkali-free, chlorine-free and fluorine-free liquid quick-setting agent, which is prepared from the following raw materials in percentage by weight: 55% of polyaluminium sulfate, 8% of diethanolamine, 4% of propanol, 3% of lithium sulfate, 5% of calcium formate, 1.9% of a complexing agent, 2% of dilute sulfuric acid, 3% of a composite stabilizer and the balance of water.

[0088] The preparation method of the complexing agent is the same as that of Example 1.

[0089] The composite stabilizer is prepared from ethylenediaminetetraacetic acid: polyacrylamide: boric acid in a mass ratio of 5:4:3.

[0090] A preparation process of an alkali-free, chlorine-free and fluorine-free liquid accelerating setting agent comprises the following steps:

[0091] S1: Add water and polyaluminium sulfate into a reaction vessel, and heat with stirring at 48°C for 1 hour to completely dissolve the polyaluminium sulfate;

[0092] S2: add alcohol amine and chaotropic agent, react at 57°C for 100 min, then add lithium sulfate, calcium formate, complexing agent and composite stabilizer respectively for 90 min each reaction;

[0093] S3: Add dilute sulfuric acid and stir for 72 minutes to obtain the accelerating setting agent.

[0094] Example 5

[0095] The invention discloses an alkali-free, chlorine-free and fluorine-free liquid quick-setting agent, which is prepared from the following raw materials in percentage by weight: 48% of polyaluminium sulfate, 6% of diethanolamine, 2% of propanol, 1% of lithium sulfate, 6% of calcium formate, 1.3% of a complexing agent, 2% of dilute sulfuric acid, 1% of a composite stabilizer and the balance is water.

[0096] The preparation method of the complexing agent is the same as that of Example 1.

[0097] The composite stabilizer is prepared from ethylenediaminetetraacetic acid: polyacrylamide: boric acid in a mass ratio of 4:2:2.

[0098] A preparation process of an alkali-free, chlorine-free and fluorine-free liquid accelerating setting agent comprises the following steps:

[0099] S1: Add water and polyaluminium sulfate into a reaction vessel, and heat with stirring at 53°C for 2h to completely dissolve the polyaluminium sulfate;

[0100] S2: Add alcohol amine and solvent, react at 65°C for 35 minutes, then add lithium sulfate, calcium formate, complexing agent and composite stabilizer for 1 hour each;

[0101] S3: Add dilute sulfuric acid and stir for 1 hour to obtain the accelerating setting agent.

[0102] Comparative Example 1

[0103] It is basically the same as Example 1, except that the reinforcing agent A is not added to the alkali-free, chlorine-free and fluorine-free liquid quick-setting agent, and the balance is supplemented with water.

[0104] Comparative Example 2

[0105] It is basically the same as Example 1, except that the reinforcing agent B is not added to the alkali-free, chlorine-free and fluorine-free liquid quick-setting agent, and the balance is supplemented with water.

[0106] Comparative Example 3

[0107] It is basically the same as Example 1, except that no composite stabilizer is added to the alkali-free, chlorine-free and fluorine-free liquid accelerating setting agent, and the balance is supplemented with water.

[0108] Comparative Example 4

[0109] It is basically the same as Example 1, except that in the alkali-free, chlorine-free and fluorine-free liquid accelerating setting agent, the composite stabilizer is made of only ethylenediaminetetraacetic acid.

[0110] Comparative Example 5

[0111] It is basically the same as Example 1, except that in the alkali-free, chlorine-free and fluorine-free liquid accelerating setting agent, the composite stabilizer is made of polyacrylamide only.

[0112] Comparative Example 6

[0113] It is basically the same as Example 1, except that in the alkali-free, chlorine-free and fluorine-free liquid accelerating setting agent, the composite stabilizer is made of only boric acid.

[0114] 1. Accelerator performance test

[0115] The alkali-free, chlorine-free, and fluorine-free liquid setting agents prepared in Examples 1-5 and Comparative Examples 1-6 were tested for initial setting time and final setting time according to the method in GB / T 35159-2017.

[0116] Table 1 Initial setting time and final setting time of accelerating agent

[0117] project Initial setting time Final setting time Example 1 3′18″ 6′06″ Example 2 3′12″ 6′42″ Example 3 3′48″ 7′12″ Example 4 3′15″ 6′24″ Example 5 3′30″ 7′31″ Comparative Example 1 4′54″ 9′18″ Comparative Example 2 4′36″ 8′36″ Comparative Example 3 8′37″ 15′42″ Comparative Example 4 6′24″ 12′19″ Comparative Example 5 7′12″ 13′18″ Comparative Example 6 7′36″ 14′48″

[0118] As can be seen from Table 1, when the alkali-free, chlorine-free and fluorine-free accelerators obtained in Examples 1-5 are added to cement, the initial setting times are 3'18", 3'12", 3'48", 3'15", and 3'30", respectively, and the final setting times are 6'06", 6'42", 7'12", 6'24", and 7'31", respectively, which meet the requirements of the national standard GB / T 35159-2017 that the initial setting time is less than 5 min and the final setting time is less than 12 min. The initial setting time in Comparative Examples 1-6 is 4'54", 4'36", 4'36", 6'24", 7'12", 7'36", respectively, and the final setting time is 9'18", 8'36", 15'42", 12'19", 13'18", 14'48", respectively. Although the initial setting time and final setting time of Comparative Examples 1-2 meet the national standards, they are not as good as Examples 1-5 of the present application, and the initial setting time and final setting time of Comparative Examples 3-6 do not meet the national standards. It can be seen that the addition of enhancer A, enhancer B and composite stabilizer to the accelerator of the present application can significantly reduce the initial setting time and final setting time, and significantly improve the performance of the accelerator.

[0119] This is because: lithium sulfate, a white crystalline powder with the molecular formula Li2SO4, has significant accelerating properties. As a key component of the accelerator, lithium sulfate can effectively promote the solidification and hardening process of cement at low temperatures, thereby accelerating the initial and final setting times; calcium formate can also accelerate the hydration reaction of C3A, accelerating the initial and final setting times; ethylenediaminetetraacetic acid in the composite stabilizer forms a stable complex with aluminum ions to prevent the hydrolysis and precipitation of aluminum ions. This ensures that the active ingredients of the accelerator can quickly participate in the hydration reaction of cement, thereby accelerating the setting process; polyacrylamide can effectively disperse polyaluminum sulfate, ensuring that it acts evenly on the cement paste and improving the reaction efficiency; the presence of boric acid helps maintain the appropriate pH value of the solution, ensuring that the reaction is carried out under optimal conditions.

[0120] 2. Accelerator stability test

[0121] Accelerators were prepared from Examples 1-5 and Comparative Examples 1-6. The stability test of the accelerators was carried out with reference to the method in standard GB / T35159-2017. The state in the measuring cylinder was observed at the prescribed time. If more than 5 mL of precipitation or stratification and segregation occurred at the bottom of the measuring cylinder, the liquid accelerator was considered to be unstable. The time from the start of the test to the instability of the solution was recorded as the stability time.

[0122] Table 2 Accelerator Stability Time

[0123]

[0124]

[0125] As can be seen from Table 2, the quick-setting agent using enhancer A, enhancer B and composite stabilizer in the present application has a stabilization time of 72d, 68d, 65d, 66d and 69d, respectively, while the comparative examples 1-2 which do not use the enhancer A and enhancer B of the present application, and the comparative examples 3-6 which do not use the composite stabilizer of the present application and do not fully use the composite stabilizer components of the present application, have a stabilization time of 56d, 59d, 12d, 30d, 25d and 17d, respectively. The stabilization time of comparative examples 1-6 is not as good as that of embodiments 1-5 of the present application, indicating that the quick-setting agent prepared by using enhancer A, enhancer B and composite stabilizer in the present application can significantly improve the stability of the quick-setting agent.

[0126] This is due to:

[0127] (1) Lithium sulfate will undergo partial hydration reaction in the solution to form lithium sulfate hemihydrate (Li2SO4·H2O). This hydrate will form a stable crystal structure in the solution, which can play a bridging role, prevent the components from aggregating and precipitating, and improve the uniformity and stability of the entire system; calcium formate will dissociate in the solution to form calcium ions (Ca 2+ ) and formate ions (HCO2 - ), calcium ions can react with silicates and aluminates in cement to form stable hydrates, thereby improving the stability of the accelerator.

[0128] (2) The amino and carboxyl groups in the EDTA molecule can form stable coordination bonds with aluminum ions (Al3+). These bonds allow aluminum ions to be firmly bound to the EDTA molecule through the sharing of electron pairs, thereby preventing the aluminum ions from hydrolyzing. 3+ The complex is very stable. Due to the multi-dentate coordination structure formed inside it, EDTA provides multiple coordination sites to bind to aluminum ions. This multi-dentate structure increases the stability of the complex and further improves the stability of aluminum ions. The long chain structure of polyacrylamide can unfold in the solution and attract aluminum ions through electrostatic effects. These electrostatic effects help to evenly disperse aluminum ions in the solution to prevent them from aggregating and precipitating. In addition, polyacrylamide increases the viscosity of the solution to form a colloidal solution, which can further inhibit the aggregation and precipitation of aluminum ions and maintain the stability of the solution. Boric acid can bind to EDTA-Al 3+ The aluminum ions in the complex form weak coordination bonds, which can enhance the complexing ability of EDTA to aluminum ions and improve the stability of the accelerator. The three interact with each other and can synergistically enhance the stability of the accelerator.

[0129] 3. Mechanical strength test of accelerating agent

[0130] The accelerators prepared in Example 1 and Comparative Examples 1-6 were applied to concrete in an amount of 6% according to the method in GB / T35159-2017, and the mechanical properties of the concrete were tested.

[0131] Table 3 Mechanical properties of concrete

[0132]

[0133]

[0134] It can be seen from Table 3 that in Example 1, the 1d compressive strength is 12.4MPa, the 28d compressive strength is 38.6MPa, and the 28d compressive strength ratio is 106.3%, while the 1d compressive strengths of Comparative Examples 1-6 are 10.1MPa, 9.6MPa, 10.3MPa, 10.5MPa, 10.9MPa, and 11.2MPa, respectively, and the 28d compressive strengths are 32.1MPa, 30.3MPa, 33.7MPa, and 34.6MPa, respectively. The 1d compressive strength, 28d compressive strength and 28d compressive strength ratio of comparative examples 1-6 are not as good as those of embodiment 1 of the present application, indicating that the mechanical properties of concrete can be significantly improved by adding reinforcer A, reinforcer B and composite stabilizer in embodiment 1 of the present application.

[0135] This is because: lithium sulfate undergoes complex chemical reactions with other components in cement. These reactions not only promote the rapid hydration of cement particles, but also form hydration product crystals with very low solubility, thereby accelerating the coagulation and hardening of concrete, which can significantly improve the early strength and compressive strength of concrete. Calcium formate dissolves rapidly in cement paste and releases calcium ions, which can accelerate the hydration reaction of C3S and C3A. The hydration reaction of C3S generates CSH gel, which improves the early strength of concrete; in addition, calcium ions can react with aluminum ions and silicates to form stable hydrates, which can effectively fill the pores of concrete and improve the density and mechanical properties of concrete. Calcium formate has a good particle morphology effect, which can effectively fill the internal pores of concrete, increase the structural density, and thus enhance the mechanical properties and durability of concrete; it has a very significant improvement effect on early strength, and at the same time has a significant enhancement effect on the later compressive strength.

[0136] Ethylenediaminetetraacetic acid can prevent excessive hydrolysis and precipitation of aluminum ions, ensure that aluminum ions participate in the hydration reaction of cement, generate stable hydration products, and improve strength; polyacrylamide, as a polymer dispersant, can effectively disperse cement particles and other components, ensure uniform reaction, prevent component aggregation, and improve early and late strength; boric acid can adjust the pH value and buffer solution, maintain the stability of the reaction environment, prevent component inactivation and precipitation caused by pH fluctuations, ensure the stability of the entire hydration process, and improve mechanical properties.

[0137] The above content cannot be used to determine that the specific implementation of the present invention is limited to these descriptions. For ordinary technicians in the technical field to which the present invention belongs, they can make several simple deductions or substitutions without departing from the concept of the present invention, which should be regarded as belonging to the scope of patent protection of the present invention determined by the submitted claims.

Claims

1. An alkali-free, chlorine-free and fluorine-free liquid accelerating agent, characterized in that: The invention is made of the following raw materials in percentage by mass: 46-60% of polyaluminium sulfate, 2-8% of alcohol amine, 1-4% of a dissolution promoter, 1-6% of an enhancer A, 3-7% of an enhancer B, 1.2-2.3% of a complexing agent, 1-2% of a pH regulator, 1-3% of a composite stabilizer and the balance is water.

2. The alkali-free, chlorine-free, and fluorine-free liquid quick-setting agent according to claim 1, characterized in that: The alcohol amine is diethanolamine or triethanolamine; the solubilizing agent is propanol.

3. The alkali-free, chlorine-free, and fluorine-free liquid quick-setting agent according to claim 1, characterized in that: The reinforcing agent A is lithium sulfate; the reinforcing agent B is calcium formate.

4. The alkali-free, chlorine-free, and fluorine-free liquid quick-setting agent according to claim 1, characterized in that: The pH regulator is dilute sulfuric acid.

5. The alkali-free, chlorine-free, and fluorine-free liquid accelerating setting agent according to claim 1, characterized in that: The composite stabilizer comprises the following components: ethylenediaminetetraacetic acid, polyacrylamide and boric acid.

6. The alkali-free, chlorine-free, and fluorine-free liquid accelerating setting agent according to claim 5, characterized in that: In the composite stabilizer, the composite stabilizer is prepared from ethylenediaminetetraacetic acid: polyacrylamide: boric acid in a mass ratio of 3-5:2-4:1-3.

7. A process for preparing the alkali-free, chlorine-free and fluorine-free liquid accelerating setting agent according to any one of claims 1 to 6, characterized in that: The following steps are involved: S1: Add water and polyaluminium sulfate into a reaction vessel, stir and heat to completely dissolve the polyaluminium sulfate; S2: Add alcohol amine and chaotropic agent, react at 55-65℃ for 30-120min, then add enhancer A, enhancer B, complexing agent and composite stabilizer respectively for a certain reaction time; S3: Add pH adjuster and stir for 1-2 hours to obtain the accelerating setting agent.

8. The preparation process of an alkali-free, chlorine-free and fluorine-free liquid accelerating setting agent according to claim 6, characterized in that: In S1, polyaluminium sulfate is dissolved by heating at 40-60°C with stirring for 1-2 hours.

9. The preparation process of an alkali-free, chlorine-free and fluorine-free liquid accelerating setting agent according to claim 6, characterized in that: In S2, enhancer A, enhancer B, complexing agent and composite stabilizer are added respectively every 30-120 minutes of reaction.

10. An application of an alkali-free, chlorine-free, and fluorine-free liquid accelerating setting agent prepared according to the process described in any one of claims 7 to 9, characterized in that: The alkali-free, chlorine-free and fluorine-free liquid quick-setting agent is used in highway and railway tunnel shotcrete, slope protection, mines, 3D printing, repair and reinforcement projects, and its dosage is 6-9% of cement.

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