Quaternary ammonium salt cement moisture-proof agent as well as preparation method and application thereof

Abstract

The invention discloses a quaternary ammonium salt cement moisture-proof agent as well as a preparation method and application thereof. The preparation method comprises the following steps: dispersing polyol amine in a solvent, and heating to 70-90 DEG C under a stirring condition; dropwise adding halogenated hydrocarbon and a pH regulator at the same time, and reacting for 4-8 hours under the condition that the pH is 9-10; cooling, purifying to remove the solvent, inorganic salt and unreacted materials, and adding water to adjust the concentration to 30-60wt% to obtain the quaternary ammonium salt cement moisture-proof agent. The quaternary ammonium salt cement moisture-proof agent is stable in structure, has excellent alkali resistance, has no adverse effect on cement performance, has an excellent moisture-proof effect on cement, and can effectively solve the problem that the working performance and the mechanical performance are reduced after cement absorbs moisture.

Description

Technical Field

[0001] This invention belongs to the field of materials technology, specifically relating to a cement moisture-proofing agent, its preparation method, and its application. Background Technology

[0002] Cement, as a basic material for infrastructure and housing construction, is of great significance to human civilization and economic development.

[0003] Cement (taking the most common silicate cement as an example) is a hydraulic cementitious material made by calcining appropriate proportions of main raw materials at high temperatures to form clinker, then adding gypsum and other admixtures and grinding them together. It undergoes a hydration reaction upon contact with water. Cement is a powder aggregate composed of various particles, typically smaller than 100 μm, with a specific surface area generally not less than 300 m². 2 / kg. Due to its fine particles and active components, cement has strong hygroscopic properties. When exposed to air, cement easily absorbs moisture, resulting in a moisture-absorbing phenomenon: on the one hand, moisture generates strong cohesion between particles through surface adsorption, capillary condensation, and liquid bridging, leading to decreased powder flowability and agglomeration; on the other hand, moisture absorption triggers localized and irregular hydration reactions in the active components of cement (mainly tricalcium silicate C3S and tricalcium aluminate C3A), affecting its normal hydration process, resulting in incomplete gel structure development, and consequently causing problems such as significantly reduced strength, abnormal setting time, poor flowability, and increased water demand. Cement moisture absorption has serious adverse effects on the production process, transportation, storage, and engineering applications; therefore, it is essential to strictly control moisture absorption.

[0004] Chemical modification is a simple and effective way to improve the moisture absorption properties of cement. Its core mechanism involves introducing specific chemical additives to regulate the surface properties of cement particles at the microscopic level, thereby reducing the contact between water molecules in the air and the cement. Currently, grinding aids widely used in cement grinding (such as polyol amines and polyol organic compounds) contain a large number of hydroxyl groups in their molecules, exhibiting strong hydrophilicity. Furthermore, polyol amines also promote hydration, thus not only failing to improve the moisture absorption problem of cement but potentially exacerbating it.

[0005] Existing technologies indicate that cement can be hydrophobically treated with organic compounds containing hydrophobic groups such as long-chain alkyl groups (e.g., stearic acid, stearates, oleates, and certain silanes). These substances can form a hydrophobic film on the surface of cement particles, physically blocking the contact between water and minerals, thereby improving moisture resistance. However, this method also has significant drawbacks: the hydrophobic film hinders normal hydration reactions, leading to a lower degree of hydration and insufficient formation of cementitious products; its air-entraining effect increases the porosity of the system; and it competitively occupies adsorption sites on the surface of cement particles, affecting the adsorption efficiency of water-reducing agent molecules. Therefore, although these organic compounds can effectively alleviate moisture absorption, they can adversely affect cement strength, setting behavior, and compatibility with water-reducing agents.

[0006] CN116023060 discloses a moisture-absorbing and agglomerating cement grinding aid, the main grinding aid component of which includes N The solvent is water. The substance used in this invention to improve the moisture resistance of cement is N. tert-Butoxycarbonyl diethanolamine contains two hydroxyl groups in its molecule, giving it a certain degree of hygroscopicity and allowing it to absorb moisture from the air. Furthermore, the tert-Butoxycarbonyl (Boc) group in its molecular structure contains an ester group. The moisture introduced after absorbing moisture, combined with the alkaline environment of cement, leads to decomposition, causing it to lose its moisture-resistant properties for cement. Therefore, this invention has limited effectiveness in improving the long-term moisture resistance of cement.

[0007] CN116986844 discloses a grinding aid for improving the hygroscopicity of cement. Its components, by mass percentage, are as follows: 6%–15% polyol monofatty acid ester compound, 12%–48% polyol amine monofatty acid ester compound, 1%–6% gypsum dehydration inhibitor, 3%–7% grinding film-forming agent, 0.5%–3.0% titanate coupling agent, 0.1%–0.5% defoamer, and the remainder being water. This invention improves the hygroscopicity of cement by modifying the cement surface with polyol monofatty acid ester compounds and polyol amine monofatty acid ester compounds. Specifically, the polyol monofatty acid ester compound and the polyol amine monofatty acid ester compound have a carbon chain length of 8... The esterification products of fatty acids 18 and polyol amines have the following drawbacks when used as cement moisture-proofing agents: When cement is exposed to high humidity for a long time, the ester groups are easily hydrolyzed in an alkaline environment, leading to structural damage and loss of moisture-proofing effect; polyol monofatty acid ester compounds and polyol amine monofatty acid esters themselves have air-entraining properties, which will lead to an increase in the air content of cement mortar and concrete, resulting in a decrease in cement strength; when water is added to cement, the hydrolysis of polyol monofatty acid ester compounds and polyol amine monofatty acid esters produces 8... Fatty acids of type 18 can hinder normal cement hydration reactions and competitively occupy adsorption sites on the surface of cement particles, affecting the adsorption efficiency of water-reducing agent molecules. This can have adverse effects on cement strength, setting behavior, and compatibility with water-reducing agents.

[0008] CN102643204 discloses a trihydroxyethyl quaternary ammonium salt and its preparation method. Using triethanolamine and C8-C20 alkane halides as reactants and a low-carbon alcohol as a solvent, the reaction is carried out by microwave heating, controlling the reaction temperature at 65℃~120℃. This preparation method is suitable for C8-C20 long-chain alkane halides, but the high reaction temperature and the need for microwave heating make the preparation method complex and difficult to industrialize. Its disclosed applications include washing, industrial cleaning, life science research, medical diagnostic reagents, and biochemical reagent preparation. However, when this product is used in cement, it can cause severe air entrainment and reduce cement strength.

[0009] CN104193510 discloses a quaternary ammonium salt anti-caking agent, a method for preparing quaternary ammonium salt, and its application. The quaternary ammonium salt anti-caking agent is composed of the following components, each component by weight percentage: 20-30% quaternary ammonium salt is compounded with 70-80% vegetable oil or mineral oil to prepare an oily anti-caking agent; or 20-30% quaternary ammonium salt is compounded with 70-80% water to prepare a water-soluble liquid anti-caking agent; or 5-10% quaternary ammonium salt is mixed evenly with 90-95% inert powder to prepare a powdered anti-caking agent, wherein the inert powder is talc, bentonite, diatomaceous earth, or kaolin, etc. The method for preparing quaternary ammonium salt utilizes aliphatic amines or aliphatic amine waste and alkylating reagents to obtain quaternary ammonium salts. These quaternary ammonium salts are compounded with vegetable oil or mineral oil to prepare oily anti-caking agents, water-soluble liquid anti-caking agents, or powdered anti-caking agents for application in the prevention of caking in granular fertilizers such as granular compound fertilizers and blended fertilizers. The aliphatic amine described in this invention is a mixture of one or more of the following substances in any proportion: C6-C22 monoalkyl aliphatic primary amine, C6-C22 dialkyl aliphatic secondary amine, C6-C22 monoalkyl dimethyl tertiary amine, and C6-C22 dialkyl methyl tertiary amine. The quaternary ammonium salt prepared by this invention does not possess functional groups capable of adsorbing onto cement, making it difficult to effectively adsorb onto the cement surface and achieve a moisture-proof effect. Summary of the Invention

[0010] To address the aforementioned problems, this invention provides a quaternary ammonium salt cement moisture-proofing agent. The polyhydroxy structure on one side of its molecular structure can effectively adsorb onto the surface of cement particles, while the alkyl side chain on the other side has good hydrophobicity, effectively blocking the contact between airborne moisture and minerals. Through the matching of polar adsorption groups and non-polar hydrophobic groups, the adverse effects of the cement moisture-proofing agent on setting time, slurry fluidity, water demand, and strength are effectively avoided. Simultaneously, the stable molecular structure can continuously achieve the moisture-proofing effect, effectively improving the long-term moisture resistance of cement.

[0011] To achieve the above objectives, the following technical solution is adopted: A quaternary ammonium salt cement moisture-proofing agent has the following molecular structure: ; In this system, R1, R2, and R3 are either hydrogen or methyl; R4 is a C4-C8 straight-chain alkyl group; and X is chlorine, bromine, or iodine.

[0012] This invention also provides a method for preparing the above-mentioned quaternary ammonium salt cement moisture-proof agent, comprising the following steps: The polyol amine was dispersed in a solvent and heated to 70-90℃ under stirring. Simultaneously add haloalkanes and pH adjusters, and react at pH 9-10 for 4-8 hours; After cooling, the solvent, inorganic salts and unreacted materials are removed by purification treatment. Water is added to adjust the concentration to 30-60wt% to obtain quaternary ammonium salt cement moisture-proof agent.

[0013] According to the above scheme, the polyol amine is one or any mixture of triethanolamine, diethanol monoisopropanolamine, hydroxyethyl diisopropanolamine, and triisopropanolamine.

[0014] According to the above scheme, the halogenated hydrocarbon is one or any mixture of straight-chain halogenated hydrocarbons with a carbon chain length of 4-8; the halogen in the halogenated hydrocarbon is one of chlorine, bromine, and iodine.

[0015] According to the above scheme, the solvent is a mixture of water and organic solvent in a volume ratio of 1:(1-2); the organic solvent is either ethanol or isopropanol.

[0016] According to the above scheme, the pH adjuster is either NaOH or Na2CO3 solution.

[0017] According to the above scheme, the molar ratio of the polyol amine to the haloalkane is 1:(1-1.1); the mass ratio of the polyol amine to the solvent is 1:(2-4).

[0018] This invention also provides the application of the above-mentioned quaternary ammonium salt cement moisture-proofing agent as a cement moisture-proofing agent, anti-caking agent, and prehydration inhibitor.

[0019] According to the above scheme, the cement moisture-proofing agent is evenly sprayed onto the cement raw materials entering the mill during the cement grinding process.

[0020] According to the above scheme, the dosage of the cement moisture-proof agent is 0.02-0.05 wt% of the cement raw materials entering the mill.

[0021] This invention successfully prepares quaternary ammonium salts with corresponding structures through a quaternization reaction between polyol amines and straight-chain haloalkanes with carbon chain lengths of 4-8. The reaction mechanism involves the lone pair electrons on the nitrogen atom of the polyol amine acting as a nucleophile, attacking the α-carbon atom of the haloalkane to undergo a nucleophilic substitution reaction. This method is simple to operate, highly efficient, and yields good products.

[0022] A mixed solvent of water and organic solvent is used in the reaction system to ensure that all reactants and products are in a dissolved state, forming a homogeneous system, thereby significantly improving reaction efficiency. The reaction temperature is controlled within the range of 70-90℃. This temperature range ensures sufficient reactivity of short-chain halogenated hydrocarbons while effectively avoiding the oxidation of triethanolamine and the elimination of halogenated hydrocarbons due to excessively high temperatures. Simultaneously, maintaining the pH of the reaction system in a weakly alkaline range of 9-10 neutralizes the acidic byproducts generated during the reaction and prevents the system from becoming increasingly acidic. Under acidic conditions, polyol amines readily form salts with acids, and the quaternization reaction requires a free tertiary amine as a nucleophile; therefore, an acidic environment severely inhibits the reaction.

[0023] The obtained quaternary ammonium salt product has a stable molecular structure, good water solubility, and excellent alkali resistance. This property enables it to maintain its structural integrity for a long time in alkaline environments such as cement, avoiding molecular degradation caused by the alkaline medium formed after cement absorbs moisture, thus providing cement materials with a long-lasting and stable moisture-resistant function.

[0024] The quaternary ammonium salt type cement moisture-proofing agent prepared by this invention has a molecular structure with a clear dual-functional region: one end is a polar polyhydroxy group, which can effectively adsorb onto newly formed surfaces such as Ca-O bond breaks generated during cement grinding to form a stable directional adsorption layer; the other end is a non-polar alkyl chain with a carbon chain length between 4 and 8, which gives the molecule good hydrophobicity and can effectively block the contact between environmental moisture and the cement mineral surface, thereby achieving the anti-moisture absorption function.

[0025] Through systematic experiments, the inventors discovered that when the length of the alkyl side chain is less than 4, the molecular hydrophobicity is insufficient and the moisture-proof effect is significantly weakened; while when the chain length exceeds 8, its moisture-proof performance also decreases significantly. The longer alkyl chain leads to significant steric hindrance, which reduces the amount of moisture-proof agent adsorbed on the surface of cement particles, thereby weakening its covering ability and hydrophobic effect.

[0026] The quaternary ammonium salt-type cement moisture-proofing agent prepared in this invention is a short-chain alkyl alcoholamine quaternary ammonium salt. The positively charged quaternary ammonium nitrogen head group of the quaternary ammonium salt strongly adsorbs onto the surface of negatively charged cement particles, such as hydration products of C3S. At the same time, the polyhydroxyl groups can complex metal ions, promoting the dissolution of mineral phases. The quaternary ammonium salt molecules adsorbed on the particle surface can serve as heterogeneous nucleation sites for hydration products (such as ettringite AFt, CSH gel), accelerating the precipitation and growth of hydration products, thereby accelerating the overall hydration rate and improving cement strength. The short-chain alkyl groups have weak lipophilicity, resulting in an excessively high overall hydrophilic-lipophilic balance (HLB) value, classifying it as a hydrophilic surfactant. The intermolecular forces (van der Waals forces) between short-chain alkyl groups are very weak, failing to form a strong and elastic protective film on the bubble liquid film. Therefore, it will not introduce bubbles that adversely affect the mechanical properties of mortar and concrete. Short-chain alkyl groups have a large difference in side chain length and opposite charge properties with polycarboxylate superplasticizers, so they will not compete for adsorption with polycarboxylate superplasticizers and will not have an adverse effect on the compatibility of superplasticizers.

[0027] Through systematic experiments, the inventors discovered that when the carbon chain length of the side chain in the alkyl alcoholamine quaternary ammonium salt is greater than 8, it has an adverse effect on the performance of cement: the hydration process is inhibited, the long-chain alkyl group hinders the migration of water molecules into the cement mineral, delays the hydration nucleation and growth process, resulting in a loose and uneven microstructure of the later hydration products, which in turn leads to a prolonged setting time and a decrease in mechanical properties; the long-chain structure enhances its adsorption capacity at the gas-liquid interface, significantly reduces surface tension, and introduces a large number of fine bubbles. At the same time, the strong van der Waals forces between alkyl chains can make the molecules arrange closely at the interface, forming a high-strength composite film and stabilizing the bubble structure. This air-entraining effect will lead to a decrease in the strength of mortar or concrete; the long-chain quaternary ammonium salt will compete with water-reducing agent molecules for adsorption on the cement surface, hindering the water-reducing agent from exerting its due electrostatic repulsion and steric hindrance effect, resulting in the loss of water-reducing effect.

[0028] Therefore, controlling the alkyl chain length within the range of 4-8 can achieve an optimal balance between adsorption, hydrophobicity, and cement hydration performance.

[0029] Compared with the prior art, the beneficial effects of the present invention are as follows: 1. The quaternary ammonium salt type cement moisture-proofing agent provided by the present invention can be effectively and stably adsorbed on the surface of cement powder particles, effectively blocking the contact between environmental moisture and the surface of cement minerals, and has excellent moisture resistance. 2. The quaternary ammonium salt type cement moisture-proofing agent provided by this invention has a stable molecular structure and excellent alkali resistance, and can effectively provide long-term moisture-proofing effect for cement. 3. The quaternary ammonium salt type cement moisture-proofing agent provided by the present invention can effectively complex ions generated during cement hydration, promote cement hydration, and improve cement strength; 4. The quaternary ammonium salt type cement moisture-proofing agent provided by this invention has good compatibility with water-reducing agents and has no adverse effect on the workability of cement; 5. The quaternary ammonium salt type cement moisture-proofing agent provided by the present invention has low air entrainment and has no adverse effect on the mechanical properties of cement mortar and concrete; 6. The preparation method of the quaternary ammonium salt type cement moisture-proof agent provided by the present invention is simple, the raw materials are easy to obtain, the application method is simple, and it can be industrialized. Detailed Implementation

[0030] The following embodiments further illustrate the technical solutions of the present invention, but are not intended to limit the scope of protection of the present invention. The following specific embodiments are only some preferred embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, modifications, substitutions, and improvements made by those skilled in the art without creative effort are all within the scope of protection of the present invention.

[0031] The specific embodiment provides a method for preparing a quaternary ammonium salt cement moisture-proofing agent, including the following steps: adding polyol amine and solvent to a reaction vessel, stirring and heating to 70-90℃ at 200-400 rpm; simultaneously adding halogenated hydrocarbons and pH adjusters, reacting at pH 9-10 for 4-8 hours; after the reaction is completed, cooling to room temperature, removing solvent, inorganic salts and unreacted materials through purification treatment, and adjusting the concentration to 30-60 wt% with water to obtain the quaternary ammonium salt cement moisture-proofing agent.

[0032] Specifically, the polyol amine used is one or any mixture of triethanolamine, diethanolmonoisopropanolamine, hydroxyethyldiisopropanolamine, and triisopropanolamine. The halogenated hydrocarbon used is one or any mixture of straight-chain halogenated hydrocarbons with a carbon chain length of 4-8; the halogen in the halogenated hydrocarbon is one of chlorine, bromine, and iodine. The solvent used is a mixture of water and an organic solvent; the organic solvent is one of ethanol or isopropanol; the volume ratio of water to organic solvent is 1:(1-2). The pH adjuster used is one of a 20wt% NaOH or Na2CO3 solution. The molar ratio of polyol amine to halogenated hydrocarbon is 1:(1-1.1); the mass ratio of polyol amine to solvent is 1:(2-4).

[0033] Unless otherwise specified, all raw materials used in the specific implementation methods are obtained through commercial means.

[0034] Example 1 1 mol of triethanolamine and 298.5 g of a 1:1 mixture of water and ethanol were added to a reaction vessel. The mixture was stirred at 200 rpm and heated to 90 °C. Simultaneously, 1 mol of 1-chlorobutane and a 20 wt% NaOH solution were added and reacted at pH 9.0 for 4 h. After the reaction was completed, the mixture was cooled to room temperature. The solvent, inorganic salts, and unreacted materials were removed by purification. Water was added to adjust the concentration to 30 wt% to obtain a quaternary ammonium salt cement moisture-proofing agent.

[0035] Example 2 1 mol of diethanol monoisopropanolamine and 489.7 g of a mixed solvent of water and isopropanol in a volume ratio of 1:1.5 were added to a reaction vessel. The mixture was stirred at 400 rpm and heated to 70 °C. Simultaneously, 1.1 mol of 1-bromopentane and a 20 wt% Na₂CO₃ solution were added, and the reaction was carried out at pH 10 for 8 h. After the reaction was completed, the mixture was cooled to room temperature, and the solvent, inorganic salts, and unreacted materials were removed by purification. The concentration was adjusted to 60 wt% by adding water to obtain the quaternary ammonium salt cement moisture-proof agent.

[0036] Example 3 1 mol of hydroxyethyl diisopropanolamine and 708.8 g of a water-ethanol mixture (volume ratio 1:1.3) were added to a reaction vessel. The mixture was stirred at 218 rpm and heated to 78 °C. Simultaneously, 1.05 mol of 1-iodobutane and a 20 wt% Na₂CO₃ solution were added, and the reaction was carried out at pH 9.5 for 7.2 h. After the reaction was completed, the mixture was cooled to room temperature. The solvent, inorganic salts, and unreacted materials were removed by purification. Water was added to adjust the concentration to 56 wt% to obtain the quaternary ammonium salt cement moisture-proof agent.

[0037] Example 4 1 mol of triisopropanolamine and 401.6 g of a mixed solvent of water and isopropanol in a volume ratio of 1:2 were added to a reaction vessel. The mixture was stirred at 300 rpm and heated to 86 °C. Simultaneously, 1.08 mol of 1-chlorohexane and a 20 wt% NaOH solution were added, and the reaction was carried out at pH 9.7 for 5.3 h. After the reaction was completed, the mixture was cooled to room temperature, and the solvent, inorganic salts, and unreacted materials were removed by purification. The concentration was adjusted to 38 wt% by adding water to obtain the quaternary ammonium salt cement moisture-proof agent.

[0038] Example 5 0.5 mol triethanolamine, 0.5 mol diethanol monoisopropanolamine, and 390.5 g of a 1:1 water-ethanol mixture were added to a reaction vessel. The mixture was stirred at 286 rpm and heated to 81 °C. Simultaneously, 1.01 mol 1-bromoheptane and a 20 wt% Na₂CO₃ solution were added, and the reaction was carried out at pH 9.3 for 4.6 h. After the reaction was completed, the mixture was cooled to room temperature, and the solvent, inorganic salts, and unreacted materials were removed by purification. Water was added to adjust the concentration to 47 wt% to obtain a quaternary ammonium salt cement moisture-proof agent.

[0039] Example 6 0.5 mol of hydroxyethyl diisopropanolamine, 0.5 mol of triisopropanolamine, and 700.1 g of a water-ethanol mixture (volume ratio 1:1.2) were added to a reaction vessel. The mixture was stirred at 319 rpm and heated to 70 °C. Simultaneously, 1.02 mol of 1-iodohexane and a 20 wt% Na₂CO₃ solution were added, and the reaction was carried out at pH 9.6 for 7.8 h. After the reaction was completed, the mixture was cooled to room temperature, and the solvent, inorganic salts, and unreacted materials were removed by purification. Water was added to adjust the concentration to 58 wt% to obtain the quaternary ammonium salt cement moisture-proof agent.

[0040] Example 7 0.3 mol triethanolamine, 0.4 mol diethanol monoisopropanolamine, 0.3 mol hydroxyethyl diisopropanolamine, and 571.2 g of a water-ethanol mixture (volume ratio 1:1.9) were added to a reaction vessel. The mixture was stirred at 389 rpm and heated to 90 °C. Simultaneously, 1.09 mol 1-bromooctane and a 20 wt% NaOH solution were added, and the reaction was carried out at pH 10 for 6.2 h. After the reaction was completed, the mixture was cooled to room temperature. The solvent, inorganic salts, and unreacted materials were removed by purification. Water was added to adjust the concentration to 37 wt% to obtain a quaternary ammonium salt cement moisture-proofing agent.

[0041] Example 8 0.1 mol triethanolamine, 0.5 mol diethanol monoisopropanolamine, 0.3 mol hydroxyethyl diisopropanolamine, 0.2 mol triisopropanolamine, and 469.9 g of a 1:1 water-isopropanol mixture were added to a reaction vessel. The mixture was stirred at 352 rpm and heated to 75 °C. Simultaneously, 1 mol 1-bromobutane and a 20 wt% Na₂CO₃ solution were added, and the reaction was carried out at pH 9.1 for 4.3 h. After the reaction was completed, the mixture was cooled to room temperature. The solvent, inorganic salts, and unreacted materials were removed by purification. Water was added to adjust the concentration to 44 wt% to obtain a quaternary ammonium salt cement moisture-proofing agent.

[0042] Example 9 1 mol of triethanolamine and 417.7 g of a water-ethanol mixture (volume ratio 1:2) were added to a reaction vessel. The mixture was stirred at 367 rpm and heated to 73 °C. Simultaneously, 1.1 mol of 1-chloroheptane and a 20 wt% NaOH solution were added, and the reaction was carried out at pH 9.2 for 7.2 h. After the reaction was completed, the mixture was cooled to room temperature. The solvent, inorganic salts, and unreacted materials were removed by purification. Water was added to adjust the concentration to 49 wt% to obtain the quaternary ammonium salt cement moisture-proof agent.

[0043] Example 10 1 mol of triisopropanolamine and 650.3 g of a water-ethanol mixture (volume ratio 1:1.5) were added to a reaction vessel. The mixture was stirred at 216 rpm and heated to 87 °C. Simultaneously, 1.05 mol of 1-iodooctane and a 20 wt% NaOH solution were added, and the reaction was carried out at pH 9.5 for 7.8 h. After the reaction was completed, the mixture was cooled to room temperature. The solvent, inorganic salts, and unreacted materials were removed by purification. Water was added to adjust the concentration to 55 wt% to obtain the quaternary ammonium salt cement moisture-proof agent.

[0044] Comparative Example 1 Repeat Example 1, but replace 1-chlorobutane with chloroethane, keeping other conditions unchanged, to obtain Comparative Sample 1.

[0045] Comparative Example 2 Repeat Example 2, but replace 1-bromopentane with 1-bromolauran, keeping other conditions unchanged, to obtain Comparative Sample 2.

[0046] Comparative Example 3 Repeat Example 3, but replace 1-iodobutane with 1-chlorooctadecane, keeping other conditions unchanged, to obtain Comparative Sample 3.

[0047] The performance of the quaternary ammonium salt cement moisture-proofing agent prepared in Examples 1 to 10, the samples obtained in Comparative Examples 1 to 3, triethanolamine monooctanoate, triethanolamine monooleate, and commercially available cement grinding aids with polyol amines as the main component were tested and evaluated.

[0048] 1. Water solubility test Take 100 mL of sample and distilled water in a colorimetric tube according to a 1:2 mixing ratio, seal the tube tightly, and shake well. Place the tube in a 20℃ constant temperature apparatus and record the time. After 30 minutes, remove the colorimetric tube and place it together with another colorimetric tube containing 100 mL of distilled water against a black background. Simultaneously, use a spectrophotometer to observe the water solubility test results of the sample axially, as shown in Table 1.

[0049] Table 1

[0050] As shown in Table 1, the prepared quaternary ammonium salt cement moisture-proofing agent has good water solubility, while the water solubility is poor when the side chain is an alkyl or ester substance with a chain length of 18. The cement surface has hydrophilic properties, so the prepared quaternary ammonium salt cement moisture-proofing agent can be better adsorbed onto the surface of cement particles.

[0051] 2. Alkali resistance The sample was thoroughly dried. 20g of the sample was mixed with NaOH at a 1:1 mass ratio and placed in a petri dish. The dish was then placed in a constant temperature and humidity chamber at 20℃ and 80%RH. The time was recorded. Samples were taken after 3, 7, and 28 days and analyzed by high-performance liquid chromatography (HPLC). The decomposition rate of the sample was calculated based on the peak area. The results are shown in Table 2.

[0052] Table 2

[0053] Table 2 shows that the prepared quaternary ammonium salt cement moisture-proofing agent exhibits good alkali resistance, showing almost no decomposition in a humid alkaline environment, while triethanolamine monooctanoate and triethanolamine monooleate decompose rapidly in a humid alkaline environment. Therefore, the prepared quaternary ammonium salt cement moisture-proofing agent can provide better long-term moisture-proofing for cement.

[0054] 3. Comparison of moisture-proof effect and cement performance Sample preparation: 5 kg of various cement raw materials were added to the test mill according to the PO 42.5 cement mix ratio: clinker 80%, slag 5%, coal slag 5%, limestone 5%, and desulfurized gypsum 5%. Before grinding, the sample was added to the cement raw materials at a dosage of 0.03%. The grinding time was fixed at 25 min to obtain the PO 42.5 cement sample. Performance tests and evaluations were conducted on the quaternary ammonium salt cement moisture-proofing agents prepared in Examples 1 to 10, the samples obtained in Comparative Examples 1 to 3, triethanolamine monooctanoate, triethanolamine monooleate, commercially available cement grinding aids with polyol amines as the main component, and the blank group.

[0055] (1) Moisture-proof effect test 1.5 kg of the prepared PO 42.5 cement was spread evenly in a sample pan and placed in a constant temperature and humidity chamber at 20℃ and 80%RH. The time was recorded simultaneously. The samples were weighed after 3 days, 7 days, and 28 days, and the water absorption rate was calculated based on the change in cement mass. After 28 days, the samples were sieved using a 0.8 mm square-hole sieve, and the agglomeration rate of the samples was calculated based on the sieve residue, as shown in Table 3.

[0056] Table 3

[0057] Table 3 shows that the blank group of cement absorbs moisture in humid environments, leading to an increase in water absorption and ultimately severe caking. After adding the quaternary ammonium salt cement moisture-proofing agents prepared in Examples 1 to 10, the water absorption rate of the cement decreased significantly at different times. Excluding the influence of adsorbed water (physical adsorption), it achieved virtually no moisture absorption or caking within 28 days. In Comparative Example 1, changing the carbon chain length in the quaternary ammonium salt cement moisture-proofing agent to 2 resulted in a significant increase in water absorption and caking rates at different times, indicating poor moisture-proofing performance. In Comparative Examples 2 and 3, changing the carbon chain length in the quaternary ammonium salt cement moisture-proofing agents to 12 and 18 respectively resulted in significant increases in water absorption and caking rates at different times, indicating poor moisture-proofing performance. Triethanolamine monooctanoate and triethanolamine monooleate exhibit good moisture-proof effects in the early 3 and 7 days, but their alkali resistance is poor in humid environments, leading to decomposition and ultimately a significant increase in water absorption and agglomeration rate after 28 days. This indicates that their long-term moisture-proof effect is far inferior to the quaternary ammonium salt cement moisture-proof agents prepared in Examples 1 to 10. Cement grinding aids with polyol amines as the main component, due to their strong hydrophilicity and ability to significantly promote cement hydration, not only lack moisture-proof effect but also exacerbate cement moisture absorption and agglomeration.

[0058] (2) Cement workability test The workability of the prepared PO 42.5 cement after milling and the cement placed in a constant temperature and humidity chamber at 20℃ and 80%RH for 28 days were tested. The results are shown in Table 4. The air content test was conducted according to JGJ / T 70-2009 "Standard for Test Methods of Basic Properties of Building Mortar"; the mortar fluidity test was conducted according to GB / T 2419-2005 "Determination Method of Flowability of Cement Mortar"; the cement paste fluidity test was conducted according to GB / T 8077-2012 "Test Method of Homogeneity of Concrete Admixtures". The dosage of polycarboxylate superplasticizer was fixed at 0.15% of the cement content.

[0059] Table 4

[0060] Table 4 shows that after 28 days of moisture absorption in a humid environment, the prehydration reaction altered the surface properties of cement particles and the microstructure of the slurry, producing a flocculating gel. This resulted in a slight decrease in the air content of the mortar, while the mortar flowability and the flowability of the neat cement paste with water-reducing agent significantly decreased, indicating a severe decline in the workability of the cement after moisture absorption. After adding the quaternary ammonium salt cement moisture-proofing agents prepared in Examples 1 to 10, the air content, mortar flowability, and flowability of the neat cement paste with water-reducing agent showed little difference from the control, and the changes before and after moisture absorption were minimal, indicating no adverse effect on the cement workability. Furthermore, these agents effectively prevented prehydration, maintaining good workability. In Comparative Examples 1, 2, and 3, changing the carbon chain length in the quaternary ammonium salt cement moisture-proofing agents to 2, 12, and 18 respectively significantly reduced the cement workability retention effect, failing to achieve the same results. Triethanolamine monooctanoate and triethanolamine monooleate increased the air content of the cement mortar, and their cement workability retention effects were inferior to those of the quaternary ammonium salt cement moisture-proofing agents. Commercially available cement grinding aids have no moisture-proof effect and degrade the workability of cement.

[0061] (3) Cement mechanical property testing Mechanical properties were tested on the prepared PO 42.5 cement after milling and the cement after being placed in a constant temperature and humidity chamber at 20℃ and 80%RH for 28 days. The results are shown in Table 5. The cement strength test was performed in accordance with GB / T 17671-2021 "Test Method for Strength of Cement Mortar (ISO Method)".

[0062] Table 5

[0063] Table 5 shows that after 28 days of moisture absorption in a humid environment, the pre-hydration reaction caused irregular and localized reactions of the active components in the cement on the surface, consuming their activity. When water was added and stirred, they could no longer fully hydrate to form a complete gel structure, resulting in a significant decrease in the strength of the cement mortar. Adding the quaternary ammonium salt cement moisture-proofing agent prepared in Examples 1 to 10 resulted in an increase in strength compared to the blank, while its significant moisture-proofing effect maintained the cement strength well. Comparative Examples 1, 2, and 3, which changed the carbon chain length in the quaternary ammonium salt cement moisture-proofing agent to 2, 12, and 18 respectively, showed a significant decrease in cement strength, failing to achieve the same effect. Triethanolamine monooctanoate and triethanolamine monooleate increased the air content of the cement mortar and did not provide long-term moisture-proofing; after long-term moisture absorption, the cement strength decreased significantly. Commercially available cement grinding aids had no moisture-proofing effect and promoted moisture absorption, significantly reducing cement strength.

Claims

1. A quaternary ammonium salt cement moisture-proofing agent, characterized in that... It has the following molecular structure: ； In this system, R1, R2, and R3 are either hydrogen or methyl; R4 is a C4-C8 straight-chain alkyl group; and X is chlorine, bromine, or iodine.

2. The preparation method of the quaternary ammonium salt cement moisture-proofing agent according to claim 1, characterized in that... Includes the following steps: The polyol amine was dispersed in a solvent and heated to 70-90℃ under stirring. Simultaneously add haloalkanes and pH adjusters, and react at pH 9-10 for 4-8 hours; After cooling, the solvent, inorganic salts and unreacted materials are removed by purification treatment. Water is added to adjust the concentration to 30-60wt% to obtain quaternary ammonium salt cement moisture-proof agent.

3. The preparation method of the quaternary ammonium salt cement moisture-proofing agent as described in claim 2, characterized in that... The polyol amine is one or any mixture of triethanolamine, diethanol monoisopropanolamine, hydroxyethyl diisopropanolamine, and triisopropanolamine.

4. The preparation method of the quaternary ammonium salt cement moisture-proofing agent as described in claim 2, characterized in that... The halogenated hydrocarbon is one or any mixture of straight-chain halogenated hydrocarbons with a carbon chain length of 4-8; the halogen in the halogenated hydrocarbon is one of chlorine, bromine, and iodine.

5. The preparation method of the quaternary ammonium salt cement moisture-proofing agent as described in claim 2, characterized in that... The solvent is a mixture of water and an organic solvent in a volume ratio of 1:(1-2); the organic solvent is either ethanol or isopropanol.

6. The preparation method of the quaternary ammonium salt cement moisture-proofing agent as described in claim 2, characterized in that... The pH adjuster is either NaOH or Na2CO3 solution.

7. The preparation method of the quaternary ammonium salt cement moisture-proofing agent as described in claim 2, characterized in that... The molar ratio of the polyol amine to the haloalkane is 1:(1-1.1); the mass ratio of the polyol amine to the solvent is 1:(2-4).

8. The application of the quaternary ammonium salt cement moisture-proofing agent according to claim 1 as a cement moisture-proofing agent, anti-caking agent, and prehydration inhibitor.

9. The application of the quaternary ammonium salt cement moisture-proofing agent as described in claim 8 as a cement moisture-proofing agent, anti-caking agent, and prehydration inhibitor, characterized in that... This includes uniformly spraying the cement moisture-proofing agent onto the cement raw materials entering the mill during the cement grinding process.

10. The application of the quaternary ammonium salt cement moisture-proofing agent as described in claim 9 as a cement moisture-proofing agent, anti-caking agent, and prehydration inhibitor, characterized in that... The dosage of the cement moisture-proofing agent is 0.02-0.05 wt% of the cement raw materials fed into the mill.

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