Water-resistant building gypsum-based material and preparation method thereof

Abstract

The invention provides a water-resistant building gypsum-based material and a preparation method thereof. The material comprises a building gypsum base body, a hydrophobic film is cured on the surface of the building gypsum base body, and the hydrophobic film is formed by curing waterproof liquid; the building gypsum base body is prepared from four components including desulfurized building gypsum, blast furnace slag, calcium oxide and water, the water-binder ratio is 0.5-0.6, the mass ratio of the blast furnace slag to the desulfurized building gypsum is (1-5): (5-9), and the mass of the calcium oxide is 2%-10% of that of the blast furnace slag; the waterproof liquid comprises water, sodium methyl silicate, tetraethoxysilane, dimethyl silicone oil, sodium hydroxide and sodium silicate. According to the preparation method, a proper waterproof treatment mode is selected according to the size of a workpiece. The blast furnace slag and the calcium oxide are introduced into the desulfurized building gypsum formula, the calcium oxide can effectively excite the activity of the blast furnace slag in a building gypsum matrix, so that the water resistance of a building gypsum-based material is improved, the water resistance of the material is further improved by the waterproof liquid, and meanwhile, the material is endowed with hydrophobicity.

Description

Technical Field

[0001] This application relates to the field of building gypsum technology, and in particular to a water-resistant building gypsum-based material and its preparation method. Background Technology

[0002] Building gypsum is made by calcining industrial by-product gypsum or natural gypsum in a dry environment. As an energy-saving and environmentally friendly cementing material, building gypsum has broad application prospects. However, building gypsum products have the disadvantage of poor water resistance, which limits their application.

[0003] Currently, waterproofing methods for building gypsum products can be divided into two main categories. The first category involves adding modifying materials to improve the water resistance of building gypsum products. The commonly used modifying materials include inorganic minerals and organic reagents.

[0004] The added inorganic minerals are mostly hydraulic materials such as silicate cement and aluminate cement. These materials can effectively improve the density of gypsum blocks by generating products such as hydrated calcium silicate gel, thereby increasing the softening coefficient and reducing water absorption. However, their setting time is relatively fast, and large defects are prone to appear inside the blocks. Furthermore, excessive addition can negatively impact the strength of the material by delaying the formation of ettringite, leading to cracking. Adding organic reagents can also effectively improve the water resistance of gypsum. Commonly used organic reagents are mostly organosilicon waterproofing agents, such as sodium methylsilicate and dimethyl silicone oil. By forming a hydrophobic film on the surface of gypsum crystals, they directly or indirectly reduce the contact between gypsum crystals and water molecules, thus preventing gypsum crystals from being eroded by water molecules. This method is quite effective in improving the softening coefficient of gypsum. However, the added waterproofing agent may affect the growth of dihydrate gypsum crystals and is also costly. The second type of waterproofing method is to apply an external waterproofing layer to improve the water resistance of gypsum. The external waterproofing layer can form an organic or inorganic waterproofing layer on the surface of gypsum products. These waterproofing layers can effectively reduce the number of capillaries on the surface of gypsum test blocks and improve the hydrophobicity of the gypsum surface, thereby increasing the softening coefficient of gypsum. However, if the waterproofing layer falls off, the waterproofing of building gypsum products will be difficult to guarantee.

[0005] Therefore, there is a need to provide an improved technical solution that addresses the shortcomings of the existing technology. Summary of the Invention

[0006] The purpose of this application is to provide a water-resistant building gypsum-based material and its preparation method, so as to solve or alleviate the problems existing in the prior art.

[0007] To achieve the above objectives, this application provides the following technical solution: A water-resistant building gypsum-based material includes a building gypsum matrix, the surface of which is cured with a hydrophobic film formed by curing a waterproofing liquid; the raw materials of the building gypsum matrix consist of four components: desulfurized building gypsum, blast furnace slag, calcium oxide, and water, with a water-cement ratio of 0.5~0.6, and the mass ratio of blast furnace slag to desulfurized building gypsum is (1~5):(5~9), and the mass of calcium oxide is 2%~10% of the blast furnace slag; the waterproofing liquid includes water, 2.4%~2.6% sodium methylsilicate by mass of water, 1.1%~1.4% tetraethyl orthosilicate by mass of water, 1.1%~1.4% dimethyl silicone oil by mass of water, 0.5%~0.6% sodium hydroxide by mass of water, and 0.4%~0.6% sodium silicate by mass of water.

[0008] Furthermore, the waterproofing liquid is composed of water, sodium methylsilicate at a mass of 2.4% to 2.6% of water, tetraethyl orthosilicate at a mass of 1.1% to 1.4% of water, dimethyl silicone oil at a mass of 1.1% to 1.4% of water, sodium hydroxide at a mass of 0.5% to 0.6% of water, sodium silicate at a mass of 0.4% to 0.6% of water, and nano-silica sol at a mass of 0.75% to 1% of water.

[0009] Furthermore, in the waterproofing liquid, the mass of sodium methylsilicate is 2.5% of water, the mass of tetraethyl orthosilicate is 1.25% of water, the mass of dimethyl silicone oil is 1.25% of water, the mass of sodium hydroxide is 0.5% of water, the mass of sodium silicate is 0.5% of water, and the mass of nano silica sol is 1% of water.

[0010] Furthermore, the mass fraction of nano-silica in the nano-silica sol is 30%, and the average particle size of the nano-silica is 7~11nm.

[0011] Furthermore, the mass ratio of the desulfurized building gypsum, blast furnace slag, and calcium oxide is 50:50:2, and the water-cement ratio of the building gypsum matrix raw material is 0.55.

[0012] Furthermore, the viscosity of the dimethyl silicone oil is 100 cs.

[0013] The present invention also proposes a method for preparing the aforementioned water-resistant building gypsum-based material, comprising three steps: preparation of building gypsum matrix, preparation of waterproofing liquid, and waterproofing treatment; The preparation of the building plaster matrix involves first mixing dry materials, then adding water and stirring evenly before pouring into a mold, followed by demolding to obtain the workpiece; the preparation of the waterproofing liquid involves sequentially adding sodium methylsilicate, tetraethyl orthosilicate, dimethyl silicone oil, nano silica (if available), sodium hydroxide, and sodium silicate to water, stirring evenly after each addition, to finally obtain the waterproofing liquid; the waterproofing treatment involves wetting and curing the demolded workpiece with the waterproofing liquid.

[0014] Furthermore, in the preparation of the waterproofing liquid, sodium methylsilicate is first mixed with water and stirred at a medium speed of 300 rpm to 500 rpm for 10 to 15 minutes. Then, tetraethyl orthosilicate is added and stirred at a speed of 800 rpm to 1000 rpm for 30 to 45 minutes to promote the hydrolysis reaction. Subsequently, dimethyl silicone oil is added. After the solution is stirred evenly, nano-silica sol (if available), sodium hydroxide, and sodium silicate are added and stirred at 400 rpm to 600 rpm for 20 to 30 minutes to form a homogeneous solution. At the same time, excessive shearing is avoided to prevent damage to the dispersion of nanoparticles. After standing for 1 to 2 hours, the hydrophobic curing liquid for gypsum-based building materials is obtained. The final standing process is used to mature the solution and promote the stability of intermolecular cross-linking reactions (such as siloxane polycondensation). If the standing time is shortened, the degree of cross-linking may be insufficient, and the hydrophobic film may crack easily. The entire preparation process is usually carried out at room temperature (20℃~25℃). If it is necessary to accelerate the reaction (such as the hydrolysis of tetraethyl orthosilicate), the temperature can be appropriately increased to 30℃~40℃, but high temperatures (>50℃) should be avoided to prevent the volatilization or decomposition of the organosilicon components. The total stirring time for the three stirring steps in the entire preparation process should preferably be controlled within 60min~75min. Insufficient stirring time may lead to incomplete reaction, while excessive stirring time will result in excessively high viscosity of the hydrophobic curing solution.

[0015] Furthermore, in addition to the necessary raw materials mentioned above, the properties of waterproofing liquid can be improved through additives in practical applications, such as dispersants, pH adjusters, defoamers, and stabilizers.

[0016] Furthermore, for small and medium-sized workpieces, the workpieces are soaked in waterproof liquid for 3 to 7 days, and then taken out and air-dried in a cool place. The soaking method can relatively evenly distribute the waterproof liquid to all surfaces of small workpieces. For large workpieces, the workpiece surface is sprayed or coated with waterproof liquid to form a continuous waterproof film, and then covered with a curing film to keep it moist and cured. This process is repeated several times. After the last curing, the curing film is removed and the workpiece is air-dried.

[0017] The principle of this invention is: (1) By replacing part of the building gypsum with blast furnace slag and using calcium oxide as an alkali activator, on the one hand, calcium oxide activates the activity of blast furnace slag, which causes C-(A)-SH gel to be generated inside the desulfurized building gypsum matrix to encapsulate gypsum crystals and fill the pores inside the desulfurized building gypsum matrix, thereby increasing the density of the desulfurized building gypsum matrix. At the same time, ettringite crystals are generated to increase the overlap density between crystals inside the desulfurized building gypsum matrix, thereby improving both the strength of the desulfurized building gypsum matrix and the water resistance of gypsum. On the other hand, the introduction of calcium-based alkali activator can activate the activity of blast furnace slag and reduce the solubility of dihydrate gypsum crystals.

[0018] (2) Curing the building gypsum substrate in a waterproofing solution improves its water resistance and surface properties, maximizing its surface contact angle and further enhancing its water resistance. The use of the waterproofing solution effectively improves the surface properties of the building gypsum, increases the surface contact angle of the desulfurized building gypsum substrate, and improves the water resistance of the desulfurized building gypsum substrate while giving the surface of the desulfurized building gypsum substrate high hydrophobicity. Furthermore, because a hydrophobic film is formed on the surface of the desulfurized building gypsum substrate during the hydration process, the hydrophobic film has a high degree of adhesion to the desulfurized building gypsum substrate and is not easily detached.

[0019] This application has the following beneficial effects: By incorporating blast furnace slag and calcium oxide into a desulfurized building gypsum matrix, calcium oxide can activate the blast furnace slag, leading to the formation of C-(A)-SH gel and, consequently, more ettringite. The formation of ettringite and C-(A)-SH gel is significantly affected by moisture. These substances exhibit stronger water resistance than gypsum crystals. The interconnected structural system greatly enhances the water resistance of the sample, thus improving the water resistance of the building gypsum matrix specimen. The waterproofing liquid, a mixture of organic and inorganic components, forms a complete and uniform hydrophobic film on the surface of the desulfurized building gypsum matrix, further improving the material's water resistance while imparting hydrophobicity. The alkaline environment provided by sodium hydroxide and sodium silicate facilitates the polymerization and bonding of the hydrophobic film. The addition of nano-silica promotes crystal formation and growth. Dimethyl silicone oil and tetraethyl orthosilicate both contribute to increasing the contact angle, and the addition of dimethyl silicone oil helps reduce water evaporation from the waterproofing liquid. In summary, the surface of gypsum dihydrate crystals is coated with a hydrophobic film or C-(A)-SH gel, which provides good protection for the gypsum dihydrate crystals. Attached Figure Description

[0020] The accompanying drawings, which form part of this application, are used to provide a further understanding of this application. The illustrative embodiments and descriptions of this application are used to explain this application and do not constitute an undue limitation of this application. Wherein: Figure 1 The images show the surface morphology of the water-resistant gypsum-based building material specimen in Example 1, with the left and right images showing the surface morphology of the water-resistant gypsum-based building material specimen at 3d and 7d, respectively.

[0021] Figure 2 The images show the surface morphology of the water-resistant gypsum-based building material specimen in Example 2, with the left and right images showing the surface morphology of the water-resistant gypsum-based building material specimen at 3d and 7d, respectively.

[0022] Figure 3The images show the surface morphology of the water-resistant gypsum-based building material specimen in Comparative Example 1, with the left and right images showing the surface morphology of the water-resistant gypsum-based building material specimen at 3d and 7d, respectively.

[0023] Figure 4 The images show the surface morphology of the water-resistant gypsum-based building material specimens in Comparative Example 2, with the left and right images showing the surface morphology of the water-resistant gypsum-based building material specimens at 3d and 7d, respectively.

[0024] Figure 5 The images show the surface morphology of the water-resistant gypsum-based building material specimen in Comparative Example 3, with the left and right images showing the surface morphology of the water-resistant gypsum-based building material specimen at 3d and 7d, respectively.

[0025] Figure 6 The images show the surface morphology of the water-resistant gypsum-based building material specimens in Comparative Example 4, with the left and right images showing the surface morphology of the water-resistant gypsum-based building material specimens at 3d and 7d, respectively.

[0026] Figure 7 The image shows the XRD pattern of the test block in Embodiment 1 of the present invention.

[0027] Figure 8 The image shows the XRD pattern of the test block of Comparative Example 1 of this invention. Detailed Implementation

[0028] The present application will now be described in detail with reference to the accompanying drawings and embodiments. Various examples are provided by way of explanation and not by way of limitation. In fact, those skilled in the art will recognize that modifications and variations can be made to the present application without departing from the scope or spirit thereof. For example, a feature shown or described as part of one embodiment may be used in another embodiment to produce yet another embodiment. Therefore, it is desirable that the present application encompass such modifications and variations that fall within the scope of the appended claims and their equivalents.

[0029] The raw materials used in the following examples and comparative examples are: Desulfurized building gypsum: It comes from Henan Qiangnai New Materials Co., Ltd. in China. Its main component is hemihydrate gypsum (β-CaSO4•1 / 2H2O). Its main crystal composition is CaSO4•1 / 2H2O, and it also contains a small amount of CaSO4•2H2O and CaSO4•H2O.

[0030] Blast furnace slag: sourced from China Xinxiang Great Wall Blast Furnace Slag Co., Ltd., is blast furnace slag powder that has passed through a 200-mesh sieve, and is S95 grade alkaline blast furnace slag.

[0031] Calcium oxide: derived from Hongyan Reagent Factory, Hedong District, Tianjin, China, analytical grade. This article describes its use as an alkaline activator to activate blast furnace slag. Sodium methylsilicate: sourced from Linyi Lusen Chemical Co., Ltd., with a content of 30%, it is a pollution-free organosilicon waterproofing agent. It has the characteristic of decomposing into methylsilicic acid and sodium hydroxide under weak acid conditions, and can undergo a condensation reaction to generate it again under alkaline conditions.

[0032] Tetraethyl orthosilicate: Sourced from Tianjin Kemei Chemical Reagent Co., Ltd., density range 0.931-0.934ρ / (g / ml) (20℃), acidity (as HCl) ≤0.02ω / %, colorless transparent liquid with an ether-like aroma. It readily hydrolyzes in water, producing silicic acid and ethanol.

[0033] Dimethyl silicone oil: Imported silicone oil from Dow Corning, with a viscosity of 100 cs.

[0034] Sodium hydroxide: sourced from Hongyan Reagent Factory, Hedong District, Tianjin, analytical grade.

[0035] Sodium silicate: analytical grade.

[0036] Nano silica sol: sourced from Shandong Linyi Kehan ​​Silicon Products Co., Ltd., product code JN-1430-A1. It contains 30% nano silica by mass, with an average particle size range of 7-11 nm. Testing revealed a small amount of Na₂O (0.35% by mass) in this nano silica sol, whose main function is to maintain sol stability and control particle growth by adjusting the pH and ionic environment of the system.

[0037] Example 1 A water-resistant building gypsum-based material includes a building gypsum matrix, wherein a hydrophobic film is cured on the surface of the building gypsum matrix, and the hydrophobic film is formed by curing a waterproof liquid; The raw materials of the building gypsum matrix are composed of four components: desulfurized building gypsum, blast furnace slag, calcium oxide and water, with a water-to-binder ratio of 0.55. The mass ratio of the blast furnace slag, desulfurized building gypsum and calcium oxide is 50:50:2. In the waterproofing liquid, the mass of sodium methylsilicate is 2.5% of water, the mass of tetraethyl orthosilicate is 1.25% of water, the mass of dimethyl silicone oil is 1.25% of water, the mass of sodium hydroxide is 0.5% of water, and the mass of sodium silicate is 0.5% of water.

[0038] A method for preparing a water-resistant building gypsum-based material for the purpose of making test blocks includes the following steps: Preparation of waterproofing solution: Measure 1000ml of deionized water and 25g of sodium methylsilicate and mix them. After stirring evenly, add 12.5g of tetraethyl orthosilicate, followed by 12.5g of dimethyl silicone oil. After stirring the solution evenly, add 5g of sodium hydroxide and 5g of sodium silicate. Stir evenly to obtain the waterproofing solution. Preparation and waterproofing of building gypsum substrate: Blast furnace slag, building gypsum and calcium oxide are poured into a slurry mixing pot. The slurry mixing pot is started to mix the dry materials evenly. Then an appropriate amount of water is poured into the mixing pot and mixed evenly to obtain a uniform slurry. The slurry is then poured into a 40mm×40mm×40mm mold. After 2 hours, the mold is removed and the mold is soaked in waterproofing liquid. After reaching the required curing period, the test block is taken out and air-dried naturally.

[0039] Example 2 The only difference between Example 2 and Example 1 is that the waterproofing liquid contains nano-silica sol, and the mass of the nano-silica sol is 1% of the water.

[0040] Preparation of waterproofing solution: Measure 1000ml of deionized water and 25g of sodium methylsilicate and mix them. After stirring evenly, add 12.5g of tetraethyl orthosilicate, followed by 12.5g of dimethyl silicone oil. After stirring the solution evenly, add 5g of sodium hydroxide, 10g of nano silica sol and 5g of sodium silicate. Stir evenly to obtain the waterproofing solution.

[0041] The test block was prepared according to the method of Example 1.

[0042] Comparative Example 1 Compared to Example 2, Comparative Example 1's waterproofing liquid does not contain sodium hydroxide or sodium silicate. The test blocks were prepared in the same manner as in Example 1.

[0043] Comparative Example 2 Compared to Example 2, Comparative Example 2's waterproofing liquid does not contain sodium methylsilicate. The test blocks were prepared in the same manner as in Example 1.

[0044] Comparative Example 3 Compared to Example 2, Comparative Example 3's waterproofing liquid did not contain dimethyl silicone oil. The test blocks were prepared in the same manner as in Example 1.

[0045] Comparative Example 4 Compared to Example 2, Comparative Example 4's waterproofing liquid contains only tetraethyl orthosilicate and sodium methylsilicate. The test block was prepared in the same manner as in Example 1.

[0046] Comparative Example 5 Compared to Example 2, Comparative Example 5's waterproofing liquid contains only sodium methylsilicate. The test block was prepared in the same manner as in Example 1.

[0047] The composition of the waterproofing liquid in the above embodiments and comparative examples is summarized in Table 1. The percentages in Table 1 represent the weight ratio of each substance to the water in the waterproofing liquid.

[0048] Table 1. Composition of the waterproofing liquid in the examples and comparative examples

[0049] The surface contact angle, strength, softening coefficient, apparent morphology, XRD patterns, and porosity of the specimens from each embodiment and comparative example were tested, and the results are as follows: Table 2. Effect of each embodiment and comparative example on the surface contact angle of water-resistant building gypsum-based materials

[0050] As shown in Table 2, the surface contact angle of the gypsum-based building material specimens increased with the addition of sodium methylsilicate. The surface contact angle increased with only sodium methylsilicate and tetraethyl orthosilicate compared to the sodium methylsilicate-only treatment in Comparative Example 5. Without the introduction of sodium hydroxide and sodium silicate, the specimens exhibited high surface contact angles at both 3 and 7 days of curing. At 3 days, the surface contact angle was 122.49°, and at 7 days, it reached 144.00°. This increase in surface contact angle is mainly attributed to the hydrophobic film formed by sodium methylsilicate and tetraethyl orthosilicate. The main reaction during curing is the polymerization of the hydrophobic film, which is primarily affected by alkalinity. Under suitable alkalinity, the hydrophobic film continuously polymerizes. Although sodium hydroxide and sodium silicate were not introduced under these conditions, calcium oxide was introduced during specimen molding as an alkaline activator for blast furnace slag, thus providing a certain degree of alkalinity. Under these alkaline conditions, the hydrophobic film could still polymerize effectively. When sodium methylsilicate was not introduced into the system, the 3-day contact angle of the test block was only 123.75°, significantly lower than the 147.80° of the system containing sodium methylsilicate. This difference stems from the synergistic effect of sodium methylsilicate and tetraethyl orthosilicate, which effectively regulates the surface enrichment of hydrophobic groups. Without dimethyl silicone oil, the contact angle at 3 days was 132.75°, and at 7 days it was 134.25°. The 7-day contact angle was slightly higher than the 3-day contact angle, but the change was not significant. Its maximum contact angle was lower than that of other waterproofing liquid formulations, indicating that dimethyl silicone oil plays an important role in improving the surface contact angle of the test block in the waterproofing liquid. The reason is that, firstly, as a hydrophobic modifier, the -CH3 groups in the molecular structure of dimethyl silicone oil can effectively reduce the surface energy of the material. When silicone oil is combined with organosilicon, silicone oil molecules can migrate to the surface of the cured film and align, forming a dense, low-surface-energy hydrophobic layer. The system without added silicone oil relies solely on the self-crosslinking reaction of organosilicon, resulting in a low density of methyl groups on the surface, which limits the improvement of the contact angle. The sample without nano-silica achieved contact angles of 147.80° and 148.75° at 3 and 7 days, respectively. The stability of the data indicates that the waterproofing liquid already possesses excellent hydrophobicity, attributed to the alkaline environment provided by the composite alkaline system. Notably, the increase in contact angle narrowed to 0.95° at 7 days, consistent with the kinetic characteristics of hydrophobic modification: when the contact angle exceeds 145°, the surface energy decreases to below 20 mN / m, at which point the Cassie-Baxter non-wetting state is essentially formed, and further improvement is limited by the surface roughness saturation effect. The surface enrichment process of hydrophobic groups was largely completed by 3 days. The surface contact angle of the most complete waterproof liquid (Example 2) specimen reached 149° at 3 days and 153° at 7 days. The contact angle of the specimen was greater than 150°, which is considered a superhydrophobic material. Compared with the case without the addition of nano silica, the contact angle was further improved, which also indirectly proves the role played by nano silica.

[0051] In summary, sodium methylsilicate and tetraethyl orthosilicate play an important role in improving the surface contact angle of building gypsum-based materials. Sodium hydroxide and sodium silicate help maintain and further improve the surface contact angle of the hydrophobic film by adjusting the alkalinity of the waterproofing liquid. The presence of nano-silica and silicone oil can improve the morphology and composition of the hydrophobic film, which is more conducive to enhancing the connection between the hydrophobic film and the surface of the test block.

[0052] Tables 3 and 4 show the strength and softening coefficient of water-resistant building gypsum-based material specimens treated with different proportions of waterproofing liquid.

[0053] Table 3. 3d strength and softening coefficient of test blocks treated with waterproofing liquids of different ratios

[0054] Table 4. 7-day strength and softening coefficient of test blocks treated with waterproofing liquids of different proportions.

[0055] Tables 3 and 4 show that, compared to the samples without sodium hydroxide and sodium silicate, the strength and softening coefficient of the test blocks were significantly improved, demonstrating the activating effect of sodium hydroxide and sodium silicate on the activity of blast furnace slag. Combined with their microstructure, it can be seen that under the activation of multiple activators, the outer surface of the test blocks contained more hydration products and had higher density. The main function of sodium hydroxide and sodium silicate is to provide an alkaline environment, thereby activating the activity of blast furnace slag. The combined activating effect of calcium oxide can effectively activate the activity of blast furnace slag, thus effectively improving the water resistance of building gypsum-based materials. Simultaneously, because the hydration process of blast furnace slag is relatively slow, the hydration products can be effectively and tightly bonded to the hydrophobic film during the hydration process. This plays an important role in protecting the hydrophobic film and greatly improves the water resistance of building gypsum-based materials, but it will reduce the hydrophobic effect of the film to some extent. Adding nano-silica to the curing solution can improve the strength of gypsum-based building materials to some extent, but the improvement effect is not significant. The strength improvement mainly comes from the amount of blast furnace slag added and the degree of activation of the blast furnace slag activity. This is because the main role of nano-silica is not to improve the strength of the specimen, but to improve the bonding strength of the hydrophobic layer and optimize the internal microstructure of the specimen. During the hydration process of the gypsum-based building materials, the nano-silica also generates hydrated calcium silicate gel, and this reaction proceeds from the outside to the inside of the specimen. The reaction occurs simultaneously with the formation and adhesion of the hydrophobic film. At this time, the hydrated calcium silicate gel and the gypsum-based building materials play their role as inorganic binders, greatly improving the bonding strength of the hydrophobic layer, and thus greatly improving the water resistance of the specimen, and the strength is also improved to a certain extent.

[0056] Figures 1 to 6The images show the surface morphology of the test blocks from Examples 1-2 and Comparative Examples 1-4, respectively. From... Figure 1 It can be seen that when no nano-silica is introduced into the solution, the morphology of the hydrophobic film does not change significantly. Due to the presence of sodium hydroxide, sodium silicate and calcium hydroxide, the hydration products C-(A)-SH gel and ettringite, which are activated after the activity of blast furnace slag is activated, can be clearly seen. As the curing age increases, the hydrophobic film can be seen to wrap the hydration products more tightly, and the cracks are relatively reduced. The hydrophobic film is mainly formed by sodium methylsilicate and tetraethyl orthosilicate. It is combined with the C-(A)-SH gel, a hydration product of blast furnace slag, and plays an important protective role for the gypsum dihydrate crystals.

[0057] from Figure 2 It can be seen that the most complete waterproofing liquid curing helps to form a sheet-like hydrophobic film on the surface of the test block, covering the surface of the test block, thereby giving the test block hydrophobic properties, which is beneficial to improving the contact angle of the test block surface, giving the test block a self-cleaning function, greatly reducing the moisture absorption rate of the test block, and improving its durability. It can be seen that the hydrophobic film and the C-(A)-SH gel in the test block are connected, which is beneficial to the connection strength between the hydrophobic film and the test block, and the hydrophobic film is tightly connected to the surface of the test block.

[0058] from Figure 3 It can be seen that even without the addition of sodium hydroxide and sodium silicate, a distinct hydrophobic film is still visible on the surface of the test block. This film encapsulates gypsum crystals and ettringite crystals. At 3 days, the degree of crystal encapsulation is relatively low, with some crystals still exposed outside the hydrophobic film. Low-polymerization hydrophobic substances are scattered on the test block surface, but due to the lack of an effective hydrophobic network, the hydrophobicity is relatively poor. For the surface morphology of the test block at 7 days, the hydrophobic film encapsulates the crystals better, resulting in a better hydrophobic effect, consistent with the static contact angle test. Furthermore, it can be observed that there are many large cracks on the test block surface at 3 days, while fewer cracks are present at 7 days, indicating that the hydrophobic film formed on the test block surface fills the cracks to some extent.

[0059] from Figure 4It can be seen that even without the introduction of sodium methylsilicate, a hydrophobic film is still generated and covers the surface of the test block under the action of tetraethyl orthosilicate. In the presence of sodium hydroxide, sodium silicate, and calcium oxide, the activity of blast furnace slag inside the test block is activated and a hydration reaction occurs. In the presence of calcium sulfate, ettringite crystals are also generated, and the strength of the test block is significantly improved under these conditions. However, a certain number of cracks also appear. As the curing age increases, nano-silica generates CSH gel under alkaline conditions, and blast furnace slag also generates C-(A)-SH gel under alkaline conditions. It, together with the hydrophobic film, encapsulates the calcium sulfate dihydrate crystals and ettringite crystals, and the cracks also shrink. As the curing age is extended to 7 days, nano-silica generates nano-CSH gel in the alkaline medium through a dissolution-precipitation mechanism. At the same time, the C-(A)-SH gel formed by the secondary hydration of blast furnace slag produces a synergistic encapsulation effect with the hydrophobic organosilicon film.

[0060] from Figure 5 It can be seen that without the introduction of dimethyl silicone oil, the morphology of the hydrophobic film at 3d and 7d is relatively changed. At 3d, the morphology is plate-like, with the plates connecting to form the early hydrophobic film, giving the sample surface high hydrophobicity. As the curing time increases, the plate-like hydrophobic films gradually connect and form a solid structure, with the degree of connection between the individual hydrophobic films increasing, eventually fusing into a single unit, and the hydrophobic film finally takes shape, with the contact angle reaching its maximum value. The gypsum crystals covered by the hydrophobic film can be seen through it, indicating the protective effect of the hydrophobic film on the sample. C-(A)-SH gel produced by the hydration of blast furnace slag can also be seen on the sample surface. The organic hydrophobic layer and the inorganic gel, combined together, protect the dihydrate gypsum crystals from water erosion, greatly improving the hydrophobicity and water resistance of the sample.

[0061] from Figure 6 It can be seen that although a hydrophobic film can be formed on the surface of the test block by introducing only tetraethyl orthosilicate and sodium methylsilicate waterproofing solution, the polymerization effect of the hydrophobic film is relatively poor and the hydrophobic film is relatively dispersed. As the age of the test block increases, the hydrophobic film on the surface of the test block gradually cracks, indicating that the durability of the hydrophobic film is relatively poor when only tetraethyl orthosilicate and sodium methylsilicate are used. The reason is that when sodium hydroxide and sodium silicate are not added, the alkalinity in the curing solution is relatively low, and the polymerization of the hydrophobic film requires a certain alkalinity to maintain, so its polymerization degree is poor, and as the curing time is prolonged, the hydrophobic film gradually shows large cracks. Similarly, because the waterproofing solution lacks alkaline substances, the activation of blast furnace slag activity is also limited to a certain extent.

[0062] Figure 7 To investigate the impact of the absence of nano-silica in the waterproofing liquid on the phase composition of building gypsum-based cementitious materials, from... Figure 7As can be seen from the XRD pattern, the content of ettringite inside the sample increases significantly with age, while the intensity of the dihydrate gypsum crystal diffraction peak also decreases significantly. Since alkali-activated blast furnace slag itself cannot produce ettringite, this indicates that there is a process of transformation from dihydrate gypsum crystal to ettringite crystal during this process. This is consistent with the XRD pattern of the sample from Comparative Example 1. Figure 8 It can be seen that sodium hydroxide and sodium silicate play an important role in activating the activity of blast furnace slag. Calcium sulfate dihydrate has high solubility, which causes sulfate ions to be generated in the curing solution, and then reacts with monosulfide hydrated calcium sulfoaluminate to form ettringite. However, the relative content of ettringite is not as high as that of curing with water. At the same time, it was found that when no nano silica was added, the diffraction peaks of gypsum dihydrate crystals changed significantly at 3d and 7d, indicating that the morphology of gypsum crystals changed significantly during curing without the addition of nano silica. Combined with the surface morphology and strength changes of the test block, it can be seen that the addition of nano silica is conducive to the formation of CSH gel on the surface of the test block, connecting and protecting the hydrophobic film. Macroscopically, this means that while retaining hydrophobicity, its strength is also improved.

[0063] from Figure 8 It can be seen that if sodium hydroxide and sodium silicate are not added to the waterproofing solution, almost no ettringite is formed in the building gypsum-based material, and its strength is low, indicating that sodium hydroxide and sodium silicate play an important role in curing the test blocks. This is because sodium hydroxide and sodium silicate have an activating effect on the activity of blast furnace slag. OH- breaks the Si-O-Si and Si-O-Al bonds in the blast furnace slag, causing them to re-bond and form a cementing effect. Under alkaline conditions and the action of silicate anions, the blast furnace slag gradually dissolves into silicon-oxygen tetrahedra and aluminum-oxygen tetrahedra, and gradually re-bonds to form a new network structure.

[0064] Table 5 shows the effect of different examples and comparative examples of waterproofing liquid on the porosity of water-resistant building gypsum-based material test blocks.

[0065] Table 5. Effect of waterproofing liquid on porosity of test blocks in the same examples and comparative examples.

[0066] As can be seen from Table 5, the specimen of Example 2 has the lowest porosity, indicating that the addition of nano-silica plays an important role in improving the compactness of the specimen. By reducing the porosity of the specimen surface, it can effectively reduce the intrusion of water into the specimen, thereby protecting the internal structural network of the specimen to a certain extent and thus improving the water resistance of the specimen.

[0067] The waterproofing liquid of this invention not only modifies the surface of materials but also promotes the activation of blast furnace slag activity, leading to the formation of C-(A)-SH gel, a hydration product with higher density. This results in a more dense, hydrophobic surface and significantly reduced internal porosity. When the waterproofing liquid of Example 2 was used for curing, the contact angle of the gypsum-based building material was 153°, and the 7-day dry and wet strengths were 38.72 MPa and 37.95 MPa, respectively, with a water resistance coefficient of 0.98, indicating the best waterproofing effect. Each component in the waterproofing liquid contributes to improving the water resistance of the test blocks, and the blast furnace slag and calcium oxide components in the gypsum matrix are also essential. The addition of dimethyl silicone oil helps reduce the surface tension of the hydrophobic liquid, improving the penetration effect of the solution on the material surface. The addition of sodium hydroxide and sodium silicate helps activate the blast furnace slag on the outer surface of the material, thereby promoting the formation of hydration products with better water resistance, such as C-(A)-SH gel and ettringite. Sodium methylsilicate and tetraethyl orthosilicate facilitate the formation of a hydrophobic film on the material's outer surface, thereby modifying the surface from hydrophilic to hydrophobic, achieving a maximum contact angle of 153°. This imparts a self-cleaning function. The weakly alkaline environment created by sodium hydroxide and sodium silicate promotes the formation of the hydrophobic film. The composite activation conditions formed by incorporating calcium oxide into the sodium hydroxide and sodium silicate composite material are conducive to activating the activity of blast furnace slag within the material. Simultaneously, immersion in a hydrophobic curing solution promotes the transformation of dihydrate gypsum crystals into ettringite crystals. Combined with the resulting C-(A)-SH gel, the material exhibits both high water resistance and high strength.

[0068] The above description is merely a preferred embodiment of this application and is not intended to limit this application. Various modifications and variations can be made to this application by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. A water-resistant building gypsum-based material, characterized in that: The product includes a building gypsum matrix, the surface of which is cured with a hydrophobic film formed by curing a waterproofing liquid; the raw materials of the building gypsum matrix consist of four components: desulfurized building gypsum, blast furnace slag, calcium oxide, and water, with a water-to-binder ratio of 0.5-0.6, and the mass ratio of blast furnace slag to desulfurized building gypsum is (1-5):(5-9), and the mass of calcium oxide is 2%-10% of the blast furnace slag; the waterproofing liquid includes water, 2.4%-2.6% sodium methylsilicate by mass of water, 1.1%-1.4% tetraethyl orthosilicate by mass of water, 1.1%-1.4% dimethyl silicone oil by mass of water, 0.5%-0.6% sodium hydroxide by mass of water, and 0.4%-0.6% sodium silicate by mass of water.

2. The water-resistant building gypsum-based material according to claim 1, characterized in that: The waterproofing solution is composed of water, sodium methylsilicate (2.4%~2.6% by weight of water), tetraethyl orthosilicate (1.1%~1.4% by weight of water), dimethyl silicone oil (1.1%~1.4% by weight of water), sodium hydroxide (0.5%~0.6% by weight of water), sodium silicate (0.4%~0.6% by weight of water), and nano-silica sol (0.75%~1% by weight of water).

3. The water-resistant building gypsum-based material according to claim 2, characterized in that: In the waterproofing liquid, the mass of sodium methylsilicate is 2.5% of water, the mass of tetraethyl orthosilicate is 1.25% of water, the mass of dimethyl silicone oil is 1.25% of water, the mass of sodium hydroxide is 0.5% of water, the mass of sodium silicate is 0.5% of water, and the mass of nano silica sol is 1% of water.

4. The water-resistant building gypsum-based material according to claim 2, characterized in that: The nano-silica sol contains 30% nano-silica by mass, and the average particle size of the nano-silica is 7-11 nm.

5. The water-resistant building gypsum-based material according to claim 1, characterized in that: The mass ratio of the desulfurized building gypsum, blast furnace slag, and calcium oxide is 50:50:2, and the water-cement ratio of the building gypsum matrix raw material is 0.

55.

6. The water-resistant building gypsum-based material according to claim 1, characterized in that: The viscosity of the dimethyl silicone oil is 100 cs.

7. A method for preparing a water-resistant building gypsum-based material as described in any one of claims 1 to 6, characterized in that: It includes three steps: preparation of building plaster substrate, preparation of waterproofing liquid, and waterproofing treatment; The preparation of the building plaster matrix involves first mixing dry materials, then adding water and stirring evenly before pouring into a mold, followed by demolding to obtain the workpiece; the preparation of the waterproofing liquid involves sequentially adding sodium methylsilicate, tetraethyl orthosilicate, dimethyl silicone oil, sodium hydroxide, and sodium silicate to water, stirring evenly after each addition, to finally obtain the waterproofing liquid; the waterproofing treatment involves wetting and curing the demolded workpiece with the waterproofing liquid.

8. The method for preparing water-resistant building gypsum-based material according to claim 7, characterized in that: In the preparation of the waterproofing liquid, sodium methylsilicate is first mixed with water and stirred at a medium speed of 300 rpm to 500 rpm for 10 min to 15 min. Then, tetraethyl orthosilicate is added and stirred at a speed of 800 rpm to 1000 rpm for 30 min to 45 min to promote the hydrolysis reaction. Then, dimethyl silicone oil is added. After the solution is stirred evenly, sodium hydroxide and sodium silicate are added and stirred at 400 rpm to 600 rpm for 20 min to 30 min. After standing for 1 h to 2 h, the waterproofing liquid is obtained.

9. The method for preparing water-resistant building gypsum-based material according to claim 7, characterized in that: For small and medium-sized workpieces, soak them in waterproof liquid for 3 to 7 days, then remove them and let them air dry in a cool place. For large workpieces, spray or coat the surface of the workpiece with waterproof liquid to form a continuous waterproof film, then cover it with a curing film to keep it moist and cure. Repeat this process several times. After the last curing, remove the curing film and let the workpiece air dry.

Images