Reinforced waterproof agent for gypsum-based composite cementing material as well as preparation method and application of reinforced waterproof agent

Abstract

The invention discloses an enhanced waterproof agent for a gypsum-based composite cementing material as well as a preparation method and application of the enhanced waterproof agent. The enhanced waterproof agent has a nano layered structure, a calcium-aluminum double hydroxide layer is used as a main layer, and chain-shaped waterproof agent molecules are adsorbed between the layers. The problem that a traditional waterproof agent is insufficient in compatibility is solved, and the mechanical property of a cementing material can be improved while the water resistance of the cementing material is improved. When the enhanced waterproof agent is applied to a gypsum-based composite cementing material, the 1d compressive strength of the gypsum-based cementing material can be increased by 28%-160%, the 28d compressive strength can be increased by 39%-75%, the 28d softening coefficient can be increased by 54%-90%, and the 28d water absorption can be reduced by 43%-77% under the condition that the mixing amount of the enhanced waterproof agent is 2%-8% of the mass of the gypsum-based cementing material.

Description

Technical Field

[0001] The present invention relates to the technical field of building material admixtures, and particularly relates to an enhanced waterproofing agent for gypsum-based composite cementitious materials, a preparation method thereof, and an application thereof. Background Art

[0002] Gypsum-based composite cementitious materials are a type of cementitious materials based on gypsum, added with a small amount of admixtures such as cement and mineral powder, and having both air-hardening and water-hardening properties. Such composite materials usually have good construction performance, low production cost, environmental protection advantages, and excellent fire protection performance, and have broad application prospects. However, the mechanical properties and water resistance of gypsum-based composite cementitious materials are poor. The main reason is that the hydration products of such composite cementitious materials are mainly gypsum dihydrate (CaSO 4 ·2H 2 O), which is also the main source of its mechanical strength. And the CaSO 4 ·2H 2 O crystal itself has certain solubility, and long-term contact with water will cause the crystal to dissolve, soften the hardened body, and damage the structure; secondly, the morphology of CaSO 4 ·2H 2 O is needle-like, resulting in a large number of pores when it forms a skeleton, forming free water flow channels and affecting its performance. Especially in a humid environment, the lack of its water resistance becomes an important factor restricting its application.

[0003] In order to improve the waterproof performance of gypsum-based composite cementitious materials, researchers have tried various modification techniques, such as coating a waterproof layer on the surface of the hardened body or adding some waterproofing agents internally. However, the externally applied waterproofing agent is prone to failure of its waterproof layer due to long-term exposure; while the internally added waterproofing agent will have problems such as poor water compatibility or interfering with the hydration reaction of the cementitious material to a certain extent, affecting its hardening speed and final strength. Therefore, although the existing technology has improved the waterproof performance of gypsum-based composite cementitious materials to a certain extent, how to ensure the mechanical strength of the hardened body while improving the waterproof effect is still the main challenge in current research. Summary of the Invention

[0004] In view of this, the present invention aims to provide an enhanced waterproofing agent for gypsum-based composite cementitious materials to solve the problems of low strength and poor water resistance of existing gypsum slag composite cementitious materials.

[0005] To achieve the above object, the technical solution of the present invention is realized as follows:

[0006] An enhanced waterproofing agent for gypsum-based composite cementitious materials, the molecular structural formula of the enhanced waterproofing agent being a nano-layered structure; the main layer of the nano-layered structure being a calcium-aluminum double hydroxide layer, and the interlayer being chain-like waterproofing agent molecules, and its specific molecular structural formula being as follows:

[0007]

[0008] Optionally, the median particle size of the enhanced waterproofing agent is 50-400 nm, and the solid content is 25%-45%.

[0009] The second object of the present invention is to provide a method for preparing the above-mentioned enhanced waterproofing agent for gypsum-based composite cementitious materials. The preparation method includes the following steps:

[0010] 1) Mix a high-performance water reducer, citric acid, and triisopropanolamine in a mass ratio of 1:(0.05-0.2):(0.01-0.1), and prepare an aqueous solution A with a mass fraction of 0.1%-0.5%, and put it into a reaction vessel;

[0011] 2) Introduce nitrogen or argon into the reaction vessel, add a mixture of calcium oxide and aluminum hydroxide with a molar ratio of (4.5-6.5):1 to the reaction vessel, control the mass ratio of the calcium oxide to the aqueous solution A to be 1:(4.5-15), and stir and react at 5-20 °C at 150-800 rpm for 12-84 h, and then freeze-dry for 12-48 h to obtain a calcium-aluminum-based precursor;

[0012] 3) Dissolve the waterproofing agent in an ethanol-water mixed solution with a volume ratio of 1:(3-10) to obtain a solution B with a concentration of 0.05-0.2 mol / L;

[0013] 4) Add a NaOH solution to the solution B to adjust the pH value of the solution B to 11.0-12.5, and then add a non-ionic surfactant, wherein the dosage of the non-ionic surfactant is 1-5% of the mass of water in the solution B, to obtain a solution C;

[0014] 5) Slowly add the calcium-aluminum-based precursor to the solution C at a rate of 0.5-2 g / min, wherein the dosage of the calcium-aluminum-based precursor is 30-50% of the mass of water in the solution B, and at the same time stir at a high speed at a stirring rate of 800-1500 rpm. After the calcium-aluminum-based precursor is completely added, continue to react for 12-60 h, and control the temperature of the whole reaction process at 15-25 °C. After the reaction is completed, an enhanced waterproofing agent for gypsum-based composite cementitious materials is obtained.

[0015] Optionally, the high-performance water reducer is a polycarboxylate water reducer, and the solid content is 39-41%.

[0016] Optionally, the citric acid is anhydrous citric acid.

[0017] Optionally, the concentration of the triisopropanolamine is 95%.

[0018] Optionally, the water repellent is one of tetradecyl fluoride, dodecyldimethylchlorosilane, octadecyldimethylchlorosilane, dodecyltrichlorosilane, and tetradecyltrichlorosilane.

[0019] Optionally, the molar concentration of the sodium hydroxide solution is 2 - 10 mol / L.

[0020] Optionally, the non-ionic surfactant is polyethylene glycol with a molecular weight of 200 - 600.

[0021] The third object of the present invention is to provide an application of the above-mentioned enhanced water repellent for gypsum-based composite cementitious materials in gypsum-based composite cementitious materials. In this application, the dosage of the enhanced water repellent is 2% - 8% of the mass of the gypsum-based composite cementitious materials.

[0022] The working principle of the enhanced water repellent of the present invention:

[0023] The main hydration products of gypsum-based composite cementitious materials are calcium sulfate dihydrate, trithioaluminate hydrate, and C-S-H gel. The main component of the enhanced water repellent of the present invention is an AFm-like phase, which has a nano-layered structure. The main layer is a calcium-aluminum double hydroxide layer, and the interlayer is a chain-like water repellent molecule. When the enhanced water repellent is applied in gypsum-based composite cementitious materials, since a large amount of sulfate ions will be dissolved out after gypsum is mixed with water, the sulfate ions will undergo an exchange reaction with the chain-like water repellent molecules in the interlayer. This ion exchange reaction has two main effects: First, the strengthening effect. The calcium-aluminum main layer adsorbs sulfate ions to form trithioaluminate hydrate, and the generated hydration products will in turn promote the dissolution and hydration of the high-aluminum phase admixture, thereby promoting the formation of more hydration products and improving the mechanical properties of the hardened body, achieving a strengthening effect; Second, after the chain-like water repellent molecules adsorbed in the interlayer undergo an exchange reaction with sulfate ions, they become free molecules and exist in the mixing water and pore solution. Subsequently, they are adsorbed on the surface of calcium sulfate dihydrate crystals, forming a dense hydrophobic layer on the crystal surface to prevent water infiltration, achieving a waterproof effect, and thus improving the water resistance of gypsum-based composite cementitious materials.

[0024] Compared with the prior art, the enhanced water repellent for gypsum-based composite cementitious materials of the present invention has the following advantages:

[0025] 1. The present invention utilizes the negatively charged property of the selected chain-shaped waterproofing agent molecules to prepare an enhanced waterproofing agent with a layered AFm-like phase structure mainly composed of calcium-aluminum double hydroxide and chain-shaped waterproofing agent molecules adsorbed between the layers. When it is applied to gypsum-based composite cementitious materials, the chain-shaped waterproofing agent molecules between the layers are gradually released through exchange with sulfate ions, act on the surface of gypsum, form a hydrophobic layer, and achieve the waterproof function; the rapid formation of ettringite at an early stage can further promote the hydration of the cementitious material, fill the pores, enhance the mechanical properties of the composite cementitious material, and at the same time further improve the water resistance by improving the pore structure, demonstrating excellent composite functions, that is, when applied to gypsum-slag composite cementitious materials, it can not only significantly improve the water resistance of the cementitious material, but also improve the mechanical properties of the hardened body.

[0026] 2. When the enhanced waterproofing agent of the present invention is applied to gypsum-based composite cementitious materials, at a dosage of 2% - 8% of the mass of the gypsum-based cementitious material, the 1-day compressive strength of the gypsum-based cementitious material can increase by 28% - 160%, the 28-day compressive strength can increase by 39% - 75%, the 28-day softening coefficient can increase by 54% - 90%, and the 28-day water absorption rate can decrease by 43% - 77%. Specific embodiments

[0027] To enable those skilled in the art to better understand the technical solutions and technical effects of the present invention, several embodiments will be provided below. Obviously, what is described below is only an embodiment, which does not limit the protection scope of the present invention.

[0028] In the following embodiments, the components of the gypsum-based composite cementitious material are selected as 85% of phosphogypsum and 15% of slag powder, and their chemical compositions are shown in Table 1; the purity of the calcium oxide used is 99%; the purity of the aluminum hydroxide is 99%; the high-performance water reducer is a commercially available KH-6 type polycarboxylate water reducer (PCE) with an effective solid content of 39%; the citric acid is commercially available anhydrous citric acid; the concentration of triisopropanolamine is 95%.

[0029] Table 1

[0030] Raw materials CaO <![CDATA[SO 3 > <![CDATA[SiO 2 > <![CDATA[Al 2 O 3 > MgO <![CDATA[Fe 2 O 3 > <![CDATA[TiO 2 > Loss on ignition Phosphogypsum 34.36％ 50.69％ 5.23％ 0.98％ 0.08％ 0.22％ 0.09％ 6.81％ Slag 36.82％ 2.65％ 26.75％ 19.66％ 11.1％ 0.32％ 0.94％ 0.11％

[0031] Example 1

[0032] A preparation method of an enhanced waterproofing agent for gypsum-based composite cementitious materials, comprising the following steps:

[0033] 1) After mixing 1 part of high-performance water reducer, citric acid, and triisopropanolamine with a mass ratio of 1:0.05:0.01 with 1000 parts of water evenly, an aqueous solution A with a mass fraction of 0.1% is obtained and put into a reaction kettle;

[0034] 2) Continuously introduce nitrogen into the reaction kettle, and at the same time add 222.4 parts of calcium oxide and 68.8 parts of aluminum hydroxide into the reaction kettle. Stir and react at 150 rpm at 20 °C for 12 h, and then freeze-dry for 12 h to obtain a calcium-aluminum-based precursor;

[0035] 3) Add 11 parts of tetradecyl fluoride into 1000 parts of an ethanol-water mixed solution with a volume ratio of 1:3 to obtain solution B with a concentration of 0.05 mol / L;

[0036] 4) Add 2 mol / L NaOH solution to solution B to make the pH of solution B 11.5. Then, add 10 parts of polyethylene glycol to prepare solution C, where the molecular weight of polyethylene glycol is 200;

[0037] 5) Slowly add 225 parts of the calcium-aluminum-based precursor to solution C at a rate of 2 g / min, and at the same time stir at a high speed at a stirring rate of 800 rpm. After the calcium-aluminum-based precursor is completely added, continue to react for 12 h. The temperature of the whole reaction process is controlled at 15 °C. After the reaction is completed, an enhanced waterproofing agent for gypsum-based composite cementitious materials is obtained.

[0038] The structural formula of the enhanced waterproofing agent is as follows:

[0039]

[0040] Example 2

[0041] A preparation method of an enhanced waterproofing agent for gypsum-based composite cementitious materials, comprising the following steps:

[0042] 1) Mix 2 parts of high-performance water reducer, citric acid, and triisopropanolamine with a mass ratio of 1:0.08:0.03 evenly with 1000 parts of water to obtain aqueous solution A with a mass fraction of 0.2%, and put it into the reaction kettle;

[0043] 2) Continuously introduce nitrogen into the reaction kettle, and at the same time add 125 parts of calcium oxide and 34.8 parts of aluminum hydroxide into the reaction kettle. Stir and react at 300 rpm at 15 °C for 24 h, and then freeze-dry for 14 h to obtain a calcium-aluminum-based precursor;

[0044] 3) Add 30 parts of dodecyldimethylchlorosilane into 1000 parts of an ethanol-water mixed solution with a volume ratio of 1:5 to obtain solution B with a concentration of 0.11 mol / L;

[0045] 4) Add 4 mol / L NaOH solution to solution B to make the pH of solution B 11.7. Then, add 20 parts of polyethylene glycol to prepare solution C, where the molecular weight of polyethylene glycol is 300;

[0046] 5) Slowly add 292 parts of the calcium-aluminum-based precursor to solution C at a rate of 1.5 g / min, while stirring at a high speed of 1000 rpm. After the calcium-aluminum-based precursor is completely added, continue the reaction for 24 h. The temperature throughout the reaction process is controlled at 18 °C. After the reaction is completed, an enhanced waterproofing agent for gypsum-based composite cementitious materials is obtained.

[0047] The structural formula of the enhanced waterproofing agent is as follows:

[0048]

[0049] Example 3

[0050] A preparation method of an enhanced waterproofing agent for gypsum-based composite cementitious materials includes the following steps:

[0051] 1) Mix 3 parts of high-performance water reducer, citric acid, and triisopropanolamine with a mass ratio of 1:0.1:0.05 with 1000 parts of water evenly to obtain aqueous solution A with a mass fraction of 0.3%, and put it into a reaction kettle.

[0052] 2) Continuously introduce nitrogen into the reaction kettle, and at the same time add 100 parts of calcium oxide and 25.3 parts of aluminum hydroxide to the reaction kettle. Stir and react at 500 rpm at 10 °C for 48 h, and then freeze-dry for 18 h to obtain a calcium-aluminum-based precursor.

[0053] 3) Add 42 parts of octadecyl dimethyl chlorosilane to 1000 parts of an ethanol-water mixed solution with a volume ratio of 1:7 to obtain solution B with a concentration of 0.12 mol / L.

[0054] 4) Add 5 mol / L NaOH solution to solution B to make the pH of solution B 12.0, and then add 30 parts of polyethylene glycol to prepare solution C, where the molecular weight of polyethylene glycol is 400.

[0055] 5) Slowly add 350 parts of the calcium-aluminum-based precursor to solution C at a rate of 1.0 g / min, while stirring at a high speed of 1200 rpm. After the calcium-aluminum-based precursor is completely added, continue the reaction for 48 h. The temperature throughout the reaction process is controlled at 15 °C. After the reaction is completed, an enhanced waterproofing agent for gypsum-based composite cementitious materials is obtained.

[0056] The structural formula of the enhanced waterproofing agent is as follows:

[0057]

[0058] Example 4

[0059] A preparation method of an enhanced waterproofing agent for gypsum-based composite cementitious materials includes the following steps:

[0060] 1) After uniformly mixing 4 parts of high-performance water reducer, citric acid, and triisopropanolamine with a mass ratio of 1:0.15:0.1 and 1000 parts of water, an aqueous solution A with a mass fraction of 0.4% is obtained and put into a reaction kettle.

[0061] 2) Continuously introduce nitrogen into the reaction kettle. At the same time, add 80 parts of calcium oxide and 20 parts of aluminum hydroxide into the reaction kettle. Stir and react at 5°C at 700 rpm for 56 h and then freeze-dry for 24 h to obtain a calcium-aluminum-based precursor.

[0062] 3) Dissolve 45.5 parts of dodecyltrichlorosilane in 1000 parts of an ethanol-water mixed solution with a volume ratio of 1:8 to obtain a solution B with a concentration of 0.15 mol / L.

[0063] 4) Add a 7 mol / L NaOH solution to solution B to make the pH of solution B 12.0. Then, add 40 parts of polyethylene glycol to prepare solution C, where the molecular weight of polyethylene glycol is 500.

[0064] 5) Slowly add 400 parts of the calcium-aluminum-based precursor to solution C at a rate of 0.8 g / min, and at the same time stir at a high speed at a stirring rate of 1500 rpm. After the calcium-aluminum-based precursor is completely added, continue to react for 60 h. The temperature of the whole reaction process is controlled at 25°C. After the reaction is completed, an enhanced waterproofing agent for gypsum-based composite cementitious materials is obtained.

[0065] The structural formula of the enhanced waterproofing agent is as follows:

[0066]

[0067] Example 5

[0068] A preparation method of an enhanced waterproofing agent for gypsum-based composite cementitious materials, comprising the following steps:

[0069] 1) After uniformly mixing 5 parts of high-performance water reducer, citric acid, and triisopropanolamine with a mass ratio of 1:0.08:0.1 and 1000 parts of water, an aqueous solution A with a mass fraction of 0.5% is obtained and put into a reaction kettle.

[0070] 2) Continuously introduce nitrogen into the reaction kettle. At the same time, add 67 parts of calcium oxide and 14.5 parts of aluminum hydroxide into the reaction kettle. Stir and react at 5°C at 800 rpm for 84 h and then freeze-dry for 48 h to obtain a calcium-aluminum-based precursor.

[0071] 3) Dissolve 66.2 parts of tetradecyltrichlorosilane in 1000 parts of an ethanol-water mixed solution with a volume ratio of 1:10 to obtain a solution B with a concentration of 0.2 mol / L.

[0072] 4) Add a 10 mol / L NaOH solution to Solution B to adjust the pH of Solution B to 12.5. Then, add 45 parts of polyethylene glycol to prepare Solution C, where the molecular weight of the polyethylene glycol is 600;

[0073] 5) Slowly add 454 parts of the calcium-aluminum-based precursor to Solution C at a rate of 0.5 g / min, while stirring at a high speed of 1500 rpm. After the calcium-aluminum-based precursor is completely added, continue the reaction for 60 h. The temperature during the entire reaction process is controlled at 15 °C. After the reaction is completed, an enhanced waterproofing agent for gypsum-based composite cementitious materials is obtained.

[0074] The structural formula of the enhanced waterproofing agent is as follows:

[0075]

[0076] The median particle size and effective solid content of the enhanced waterproofing agents in Examples 1-5 obtained in the present invention are shown in Table 2.

[0077] Table 2

[0078] Example Median particle size (nm) Effective solid content (%) Example 1 350 26 Example 2 150 32 Example 3 270 38 Example 4 180 42 Example 5 130 40

[0079] The enhanced waterproofing agents in Examples 1-5 are used to prepare gypsum-based composite cementitious materials. The composite cementitious materials selected in the present invention include phosphogypsum, slag, and the enhanced waterproofing agent. The specific application method is as follows: Mix the enhanced waterproofing agent in the mixing water, then add phosphogypsum and slag, fully stir, and pour the mixture into a mold of 40×40×40 mm. After vibrating and compacting, seal it and place it in a standard curing room for curing. Among them, the total mass of phosphogypsum and slag is 100%, phosphogypsum and slag account for 85% and 15% respectively, and the dosage of the enhanced waterproofing agent is 2% - 8% of their total mass. During the preparation process, the water-cement ratio of the cementitious material is 0.4, and a commercially available polycarboxylate water reducer (solid content 39%) is used to adjust the fluidity of the slurry to be consistent.

[0080] Comparative Example 1

[0081] The gypsum-based composite cementitious material in Comparative Example 1 only includes phosphogypsum and slag, which account for 85% and 15% respectively, and does not contain the enhanced admixture described in the present invention. During the preparation process, the water-cement ratio of the cementitious material is 0.5.

[0082] The mechanical properties and water resistance of the gypsum-based composite cementitious material of Comparative Example 1 and the enhanced waterproofing agent incorporated with Examples 1-5 of the present invention were determined. Among them: The mechanical properties were tested with reference to GB / T 17671-2021 "Test Method for Strength of Cement Mortar (ISO Method)". The test method for the softening coefficient was: The compressive strength of the test sample before and after soaking in water for 24 h was tested. The compressive strength before soaking was named dry compressive strength, and the compressive strength after soaking was named wet compressive strength. The softening coefficient was the ratio of the wet compressive strength to the dry compressive strength; the test method for water absorption was: The mass of the sample before and after soaking in water for 24 h was weighed, and the water absorption was calculated according to the following formula:

[0083]

[0084] The dosages of the enhanced waterproofing agent of Comparative Example 1 and Examples 1-5 of the present invention in the gypsum-based composite cementitious material and the test results are shown in Table 3.

[0085] It can be seen from the test results in Table 3 that the gypsum-based composite cementitious material incorporated with the enhanced waterproofing agent of Examples 1-5 of the present invention compared with the gypsum-based composite cementitious material in Comparative Example 1, the 1-day compressive strength increased by 28% - 160%, the 28-day compressive strength increased by 39% - 75%, the 28-day softening coefficient increased by 54% - 90%, and the 28-day water absorption decreased by 43% - 77%. It shows that the addition of the enhanced waterproofing agent not only significantly improves the water resistance of the gypsum-based cementitious material, but also has a certain promoting effect on the mechanical properties of the composite cementitious material.

[0086] Table 3

[0087]

[0088] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. An enhanced waterproofing agent for gypsum-based composite cementitious materials, characterized in that: The molecular structure of the enhanced waterproofing agent is a nano-layered structure; the main layer of the nano-layered structure is a calcium-aluminum double hydroxide layer, and the interlayer is a chain-like waterproofing agent molecule, and its molecular structure is as follows:

2. The enhanced waterproofing agent for gypsum-based composite cementitious materials according to claim 1, characterized in that: The median particle size of the enhanced waterproofing agent is 50 to 400 nm.

3. A method for preparing the enhanced waterproofing agent for gypsum-based composite cementitious materials according to any one of claims 1 to 2, characterized in that: The following steps are involved: 1) High-performance water reducing agent, citric acid and triisopropanolamine are mixed in a mass ratio of 1: (0.05-0.2): (0.01-0.1) to prepare an aqueous solution A with a mass fraction of 0.1% to 0.5%, and put it into a reaction container; 2) introducing nitrogen or argon into a reaction container, adding a mixture of calcium oxide and aluminum hydroxide in a molar ratio of (4.5-6.5) : 1 into the reaction container, controlling the mass ratio of the calcium oxide to the aqueous solution A to be 1 : (4.5-15), stirring the reaction at 150-800 rpm at 5-20° C. for 12-84 hours, and freeze-drying for 12-48 hours to obtain a calcium-aluminum-based precursor; 3) dissolving the waterproofing agent in a mixed solution of ethanol and water in a volume ratio of 1:(3-10) to obtain a solution B with a concentration of 0.05-0.2 mol / L; 4) adding NaOH solution to the solution B to adjust the pH value of the solution B to 11.0-12.5, and then adding a non-ionic surfactant, wherein the amount of the non-ionic surfactant is 1-5% of the mass of water in the solution B, to obtain a solution C; 5) slowly adding the calcium aluminum-based precursor to the solution C at a rate of 0.5 to 2 g / min, wherein the amount of the calcium aluminum-based precursor is 30 to 50% of the mass of water in the solution B, and stirring at a high speed of 800 to 1500 rpm. After the calcium aluminum-based precursor is completely added, the reaction is continued for 12 to 60 hours. The temperature of the entire reaction process is controlled at 15 to 25°C. After the reaction is completed, an enhanced waterproofing agent for gypsum-based composite cementitious materials is obtained.

4. The method for preparing an enhanced waterproofing agent for gypsum-based composite cementitious materials according to claim 3, characterized in that: The high-performance water-reducing agent is a polycarboxylate water-reducing agent with a solid content of 39-41%.

5. According to the method for preparing the enhanced waterproofing agent for gypsum-based composite cementitious materials as claimed in claim 3, the citric acid is anhydrous citric acid.

6. The method for preparing an enhanced waterproofing agent for gypsum-based composite cementitious materials according to claim 3, wherein the concentration of the triisopropanolamine is 95%.

7. The method for preparing an enhanced waterproofing agent for gypsum-based composite cementitious materials according to claim 3, wherein the waterproofing agent is one of tetradecyl fluoride, dodecyldimethylchlorosilane, octadecyldimethylchlorosilane, dodecyltrichlorosilane and tetradecyltrichlorosilane.

8. The method for preparing an enhanced waterproofing agent for gypsum-based composite cementitious materials according to claim 3, wherein the molar concentration of the sodium hydroxide solution is 2 to 10 mol / L.

9. The method for preparing an enhanced waterproofing agent for gypsum-based composite cementitious materials according to claim 3, wherein the nonionic surfactant is polyethylene glycol with a molecular weight of 200 to 600.

10. The enhanced waterproofing agent for gypsum-based composite cementitious materials according to claim 1 is used in gypsum-based composite cementitious materials, characterized in that: The dosage of the enhanced waterproofing agent is 2% to 8% of the mass of the gypsum-based composite gelling material.

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