Method for preparing hydrophobic aeolian sand mortar from wet-process modified fly ash doped with stearic acid

Abstract

The invention provides a method for preparing hydrophobic aeolian sand mortar by internally doping stearic acid wet-process modified fly ash, and belongs to the field of building materials.The preparation method comprises the steps that firstly, a hydrophobic layer is formed on the surface of fly ash through stearic acid wet-process modification, the stearic acid wet-process modified fly ash is prepared, then part of cement is replaced according to the proportion, and the hydrophobic aeolian sand mortar is prepared. And mixing with aeolian sand and the like, pulping, curing and forming. The hydrophobic aeolian sand mortar has the beneficial effects that the prepared hydrophobic aeolian sand mortar has efficient hydrophobicity and air permeability, water seepage can be blocked, the interior is kept dry, the hydrophobic surface endows the characteristics of stain resistance and easy cleaning, and the maintenance cost is reduced. Meanwhile, high-valued utilization of solid wastes such as fly ash and aeolian sand is realized, and durability such as erosion resistance and freeze thawing resistance is enhanced through synergism of active components and a gel system. The process is simple, convenient and controllable, is suitable for industrial production, is suitable for rigorous waterproof scenes such as hydraulic engineering, underground engineering and ocean engineering, provides a new scheme for high-performance green mortar, and has environment-friendly and engineering application values.

Description

Technical Field

[0001] The invention relates to the technical field of building mortar materials, in particular to a method for preparing hydrophobic aeolian sand mortar by internally adding stearic acid to wet-process modified fly ash. Background Art

[0002] In the construction industry, mortar, as a core bonding and filling material, is widely used in key processes such as wall construction, floor leveling, and wall plastering. Its performance directly determines the stability, durability, and safety of building structures. However, traditional mortars generally suffer from water-resistance shortcomings, allowing moisture to easily penetrate the material through the pore system, causing a series of degradation problems: First, moisture significantly reduces the mortar's bond strength, weakening the interfacial connection between bricks and blocks, and increasing the risk of wall cracking, deformation, and even collapse. Second, moisture within the pores generates cyclical expansion and contraction stresses during freeze-thaw cycles. Repeated action causes microcracks within the mortar to expand, exacerbating flaking and powdering, significantly shortening its service life. Furthermore, moisture, as a transmission medium, carries corrosive components such as chloride and sulfate ions, accelerating steel corrosion and chemical erosion of building materials, further threatening the durability of the structure.

[0003] Existing mortar waterproofing modification technologies mainly rely on the addition of waterproofing agents or surface coating treatments, but there are obvious technical bottlenecks: the addition of waterproofing agents may lead to deterioration of mortar working performance, such as reduced fluidity and prolonged setting time, and the compatibility issues between different types of waterproofing agents and cement-based materials have not yet been fully resolved; surface coating protection faces problems such as uneven coating and hollowing during construction, as well as peeling and failure of the coating due to environmental erosion after long-term service, making it difficult to provide a long-lasting and stable waterproofing effect. Therefore, the development of new mortars with excellent hydrophobic properties, through material surface structure design and component optimization, essentially constructs a low surface energy waterproof interface and a dense internal pore structure to achieve active barrier to water intrusion. This has important engineering value and broad application prospects for improving the mortar's anti-seepage performance, extending the building's service life, and ensuring structural safety. Summary of the Invention

[0004] In order to solve the technical problems of insufficient waterproof performance, poor durability and traditional waterproof limitations of existing mortars, the present invention discloses a method for preparing hydrophobic aeolian sand mortar by wet-process modified fly ash with stearic acid. This method, through the dual innovation of material modification and process optimization, gives the mortar excellent and long-lasting stable hydrophobic properties, and simultaneously improves its anti-seepage performance, compressive strength and interface bonding strength, fundamentally breaking through the bottleneck of traditional mortar waterproof durability and meeting the stringent technical requirements of modern construction projects for high-performance and long-life mortar materials.

[0005] To achieve the above object, the present invention adopts the following technical solutions:

[0006] The present invention discloses a method for preparing hydrophobic aeolian sand mortar by wet-process modified fly ash mixed with stearic acid, characterized in that the raw materials, calculated by weight, include:

[0007] 20-80 parts of stearic acid wet-process modified fly ash;

[0008] 120-180 parts of cement;

[0009] 400-600 parts of aeolian sand;

[0010] 90-100 parts of water.

[0011] Furthermore, the specific steps of the method include:

[0012] (1) Add a certain amount of stearic acid to anhydrous ethanol, heat at 60°C, and stir with a magnetic stirrer to prepare a stearic acid solution;

[0013] (2) Mixing ordinary fly ash with water, then pouring the stearic acid solution into it, stirring at room temperature to obtain a uniform and stable slurry;

[0014] (3) transferring the slurry into an oven and drying it at 60° C. to remove moisture and obtain stearic acid wet-process modified fly ash;

[0015] (4) Cement, aeolian sand, and stearic acid wet-process modified fly ash are weighed according to the mass ratio and added to the mixing equipment. The mixture is initially dry-mixed and then a certain amount of water is slowly added for wet mixing. After the mixture is evenly mixed, the mortar slurry is injected into the mold, vibrated and shaped, and cured to obtain a hydrophobic aeolian sand mortar specimen.

[0016] Furthermore, in step (1), the mass ratio of anhydrous ethanol to stearic acid is 1:4 to 1:6, and the added amount of stearic acid is 1% to 7% of the mass of ordinary fly ash.

[0017] Furthermore, in step (1), the stirring conditions are: the first stirring rate is 600 to 1500 r / min, and the stirring time is 5 to 8 min;

[0018] In step (2), the stirring conditions are: the second stirring rate is 1000-1500 r / min, and the stirring time is 30-60 min.

[0019] Furthermore, in step (2), the solid-liquid ratio of ordinary fly ash to water is g:mL=1:(4-6).

[0020] Furthermore, in step (3), the drying temperature is 40 to 60° C., and the drying time is 12 to 24 hours.

[0021] Furthermore, in step (4), the cement is selected from 42.5 grade ordinary Portland cement, and the water-cement ratio is 0.4 to 0.5;

[0022] In step (4), the particle size of the aeolian sand is in the range of 0.06 to 0.24 mm.

[0023] Furthermore, in step (4), the dry mixing time is 1 to 3 minutes, the wet mixing time is 2 to 8 minutes, and the vibration time is 1 to 2 minutes.

[0024] Furthermore, the curing conditions of step (4) are: temperature 20±2° C., relative humidity 95±5%, and curing time is 7 days.

[0025] Furthermore, the contact angle of the hydrophobic aeolian sand mortar specimen can reach 125°, the cumulative water absorption rate is ≤2.3%, and the 28d compressive strength is ≥10MPa.

[0026] The beneficial effects of the present invention are that, compared with the prior art, it has the following advantages:

[0027] (1) Significantly improved hydrophobic performance

[0028] According to static contact angle measurement, the hydrophobic aeolian sand mortar prepared by the present invention has a static contact angle of up to 125°, showing typical hydrophobic interface characteristics. This excellent performance is due to the low surface energy micro-nano structure constructed by stearic acid wet-process modified fly ash in the mortar matrix. The stearic acid molecular chain forms a hydrophobic adsorption layer on the surface of the fly ash particles through wet modification, interacting with the aeolian sand aggregate and cement hydration products to construct a hydrophobic interface with a hierarchical structure on the mortar surface. When water contacts the mortar surface, the interface has extremely low surface energy and special geometric morphology, making it difficult for water droplets to spread and infiltrate. They only exist in an approximately spherical form and can roll down quickly when tilted at a small angle, thereby effectively inhibiting water adhesion and penetration. This characteristic fundamentally cuts off the channel for water to invade the interior of the mortar, not only blocking the penetration of liquid water, but also significantly reducing the diffusion and transmission of water vapor, thereby preventing corrosive media such as chloride ions and sulfates from migrating into the mortar matrix with water, achieving a substantial improvement in waterproof performance from the perspective of material interface behavior.

[0029] (2) Enhanced mechanical properties

[0030] Compared with traditional mortar, the hydrophobic aeolian sand mortar with stearic acid wet-process modified fly ash of the present invention has not shown any strength attenuation, but has actually improved its compressive strength and bonding strength. This performance advantage stems from the multiple reinforcement effects of the modified fly ash in the mortar system: on the one hand, its particle grading characteristics can effectively fill the internal pores of the mortar, optimize the micropore structure of the matrix, and reduce the connected porosity; on the other hand, the hydrophobic interface formed by stearic acid modification improves the compatibility of fly ash and cement paste, while its surface active groups can participate in the cement hydration reaction, generating additional cementitious products and enhancing the bonding strength of the aggregate-paste interface transition zone; at the same time, the incorporation of stearic acid wet-process modified fly ash promotes the formation of a more uniform three-phase structure within the mortar, improves the matrix density and interfacial bonding strength, and enhances the synergistic force effect between the various components of the mortar when it is subjected to load, thereby achieving systematic optimization of mechanical properties. This modification mechanism breaks the technical bottleneck of "waterproofness and mechanical properties are antagonistic" in traditional waterproof mortar, and provides a new path for the synergistic improvement of hydrophobic function and mechanical properties.

[0031] (3) Durability and impermeability are greatly improved

[0032] This is due to the hydrophobic interface constructed on the mortar surface and the optimized dense structure within it. This material exhibits dual protective advantages against water erosion and freeze-thaw damage: On the one hand, the hydrophobic surface, through its low surface energy and micro-nano hierarchical structure, makes it difficult for liquid water to adhere and infiltrate, significantly reducing the initial amount of water adsorbed on the mortar surface. On the other hand, the internal addition of stearic acid wet-process modified fly ash optimizes the matrix pore structure, reducing the interconnected porosity and increasing the density of the interfacial transition zone, forming a synergistic "surface water repellent and internal permeability barrier" that fundamentally blocks the path of water penetration. When faced with freeze-thaw cycles, this dual-action protective mechanism effectively reduces the amount of freezable water within the mortar, reduces the mechanical damage to the matrix caused by ice expansion stress, and significantly reduces the mass loss and strength decay rate after freeze-thaw compared to traditional mortars.

[0033] At the same time, the improvement in impermeability directly inhibits the migration and transmission of corrosive media such as chloride and sulfate ions. With water, the primary carrier of ion diffusion, blocked, corrosive ions find it difficult to penetrate the dual barrier of the hydrophobic interface and the dense matrix, thereby slowing the chemical attack of cement paste and the corrosion of steel bars. This synergistic modification based on the optimization of the material's surface interface behavior and internal structure not only achieves a systematic improvement in impermeability and frost resistance, but also cuts off the multi-factor coupled damage path at the root of durability degradation, providing key material-level support for extending the service life of building structures.

[0034] (4) Solving the defects of existing technologies

[0035] This invention overcomes the inherent flaws of traditional surface coating waterproofing technology. By modifying the material itself, rather than relying on an external protective layer, the mortar matrix itself constructs a stable hydrophobic interface and internal permeation barrier structure. This integrated modification strategy avoids the degradation of waterproofing performance caused by adhesion failure, aging, and flaking of traditional coating materials. The hydrophobic function is derived from the chemical compatibility and microstructural synergy between the stearic acid wet-process modified fly ash and the cement-based system, forming a permanent hydrophobic interface that is deeply integrated with the matrix, rather than simply an isolation layer attached to the surface. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 Shown are SEM images of the micromorphology of fly ash before and after modification; (left) SEM image of the micromorphology of ordinary fly ash (before modification); (right) SEM image of the micromorphology of fly ash modified by stearic acid wet method with a stearic acid mass of 5% of the fly ash mass and a stirring time of 1 hour (Y5%-1h);

[0037] Figure 2 Shown is the contact angle test result of stearic acid wet-process modified fly ash powder in Example 1;

[0038] Figure 3 Shown are the morphologies of water droplets / ice crystals on the surface of fly ash powder modified by stearic acid wet method in Example 1; (left) morphology of 3% NaCl solution, (center) morphology of 3% NaCl solution after 1 hour, and (right) morphology of ice beads;

[0039] Figure 4 Shown are the water droplet morphology images on the surface of fly ash powder modified by stearic acid wet method in Example 1 before and after standing for 1 hour; (left) before standing, (right) after standing;

[0040] Figure 5 Shown is the water drop morphology on the surface of the hydrophobic aeolian sand mortar specimen of stearic acid wet-process modified fly ash in Example 2;

[0041] Figure 6 Shown is the contact angle test result of the hydrophobic aeolian sand mortar specimen of stearic acid wet-process modified fly ash in Example 2;

[0042] Figure 7 Shown is a graph of the cumulative water absorption of the hydrophobic aeolian sand mortar specimens of the stearic acid wet-process modified fly ash in Example 2;

[0043] Figure 8 The graph shows the cumulative water absorption of the hydrophobic aeolian sand mortar test block mixed with stearic acid wet-process modified fly ash under the condition of a mass ratio of stearic acid wet-process modified fly ash to cement of 4:6 in Example 2;

[0044] Figure 9 is the XRD diffraction pattern of fly ash modified by stearic acid wet method;

[0045] Figure 10 This is the FT-IR spectrum of fly ash modified by stearic acid wet method. Specific implementation methods

[0046] To make the purpose, technical solutions, and advantages of the embodiments of the present invention more clear, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0047] Prior art aeolian sand mortars often suffer from poor hydrophobicity, unstable mechanical properties, and poor impermeability and durability, limiting their application in a wide range of fields. The present invention utilizes a wet-process process for modifying fly ash with stearic acid. This cleverly combines the hydrophobic modification effect of stearic acid with the active filling and reinforcing properties of fly ash. Through a rational raw material ratio and preparation process, these technical challenges are successfully addressed.

[0048] Example 1

[0049] The present invention discloses a preparation process of stearic acid wet-process modified fly ash, which comprises the following steps:

[0050] 1. Preparation of raw materials for stearic acid wet modified fly ash:

[0051] Weigh the following components in percentage by mass:

[0052] Stearic acid: 1g, 3g, 5g, 7g added in gradient;

[0053] Analytical grade anhydrous ethanol: the dosage is 5 times the mass of stearic acid;

[0054] Ordinary fly ash: 100g / batch;

[0055] 2. Modified fly ash preparation process

[0056] 2.1 Add stearic acid and anhydrous ethanol in a mass ratio of 1:5 into a beaker placed on a magnetic stirrer, heat to 60°C, stir at 600 r / min, and stir at constant temperature for 5 minutes to form a stearic acid solution.

[0057] 2.2 Transfer the stearic acid solution obtained in step 2.1 into a beaker, add 100g of ordinary fly ash and 400mL of water, stir at a speed of 1500r / min, and continue stirring for 1h to form a stearic acid wet-process modified fly ash slurry.

[0058] 2.3 Transfer the stearic acid wet modified fly ash slurry to an oven, set the drying temperature to 60°C, bake for 24 hours, take out and cool for storage to obtain stearic acid wet modified fly ash, recorded as Y7%-0.5h, Y7%-1h, Y5%-0.5h, Y5%-1h, Y3%-0.5h, Y3%-1h, Y1%-0.5h, Y1%-1h.

[0059] 2.4 Wettability test:

[0060] ① Contact angle test: Using JCY series contact angle tester, 5 μL of deionized water was dropped on the surface of stearic acid wet modified fly ash powder, and the contact angle was measured to be 150°, as shown in Table 1 and Figure 2 (The number Y1%-0.5h is interpreted as: "Y" is interpreted as stearic acid, "1" is interpreted as stearic acid accounting for 1% of the fly ash mass, and "0.5h" is interpreted as the stirring time is 0.5h)

[0061] Table 1

[0062]

[0063] ② Rolling angle test: adjust the angular velocity of the tilt platform to 1° / s, record the angle of the water drop when it rolls down, and the rolling angle is less than 5° (Y5%-1h, Y7%-1h).

[0064] ③Surface water droplets / ice crystal morphology: The surface water droplets / ice crystal morphology of fly ash powder modified by stearic acid wet method is as follows: Figure 3 shown. Figure 3 It shows that the ice crystals on the surface of stearic acid wet-process modified fly ash are discrete spherical.

[0065] ④ Surface water droplet static morphology: The water droplet morphology of the surface of stearic acid wet modified fly ash powder before and after standing for 1 hour is as follows Figure 4 As shown, it proves that the hydrophobic performance is long-lasting and stable.

[0066] 2.5 Characterization of the mechanism of stearic acid wet-process modified fly ash

[0067] 2.5.1 SEM characterization

[0068] The SEM image of the microstructure of the stearic acid wet modified fly ash is as follows: Figure 1 Shown:

[0069] Unmodified ordinary fly ash consists of monodisperse spherical particles with a particle size of 5-100μm. Its surface is rough, with small particles of 1-5μm attached, and visible micro-pits and cracks. During high-temperature combustion, inorganic minerals melt into droplets, which contract under surface tension to form spheres. These spheres solidify after rapid cooling. They have a smooth outline with a roundness coefficient of 0.85-0.95, and are primarily amorphous glass with nanoscale closed pores.

[0070] The morphological characteristics of stearic acid wet-process modified fly ash Y7%-1h prepared in this embodiment are as follows: Figure 1 As shown: It is composed of a large number of small-sized block crystals with regular shapes, similar to fish scales, arranged closely and stacked layer by layer, which is in sharp contrast to the single spherical structure of fly ash.

[0071] 2.5.2 XRD characterization

[0072] The XRD pattern of stearic acid wet modified fly ash is as follows: Figure 9 shown.

[0073] Figure 9 The XRD pattern of ordinary fly ash shows a broad "steamed bun peak" at 30°~40°. After being modified with stearic acid, a new diffraction peak appears near 28°, indicating that stearic acid and Ca 2+ The metal ions form calcium stearate through carboxyl coordination.

[0074] 2.5.3 FT-IR characterization

[0075] The FT-IR spectrum of fly ash modified by stearic acid wet method is as follows: Figure 10 shown.

[0076] Figure 10 Medium, modified sample 1700cm -1 The free -COOH peak at the bottom of the fly ash is significantly reduced, indicating that the carboxyl group dissociates and reacts with the fly ash surface Ca 2+ 、Fe 3+ The metal ions coordinate to form carboxylate complexes.

[0077] 2.5.4 Key reaction formula

[0078] ① Stearic acid dissociation:

[0079]

[0080] ② Coordinate with metal ions (Ca 2+ For example):

[0081] 2C 17 H 35 COO - +Ca 2+ →(C 17 H 35 COO)2Ca

[0082] Example 2

[0083] The present invention discloses a method for preparing hydrophobic aeolian sand mortar by wet-process modified fly ash mixed with stearic acid, which comprises the following steps:

[0084] 1. Raw material preparation:

[0085] Stearic acid wet-process modified fly ash: In Example 1, stearic acid wet-process modified fly ash of various specifications was obtained;

[0086] Cement: 42.5 grade ordinary Portland cement;

[0087] Aeolian sand: particle size range is 0.06-0.24mm;

[0088] Mixing water: tap water (pH = 6.5 ~ 7.5);

[0089] 2. Hydrophobic aeolian sand mortar forming process

[0090] 2.1 Ingredients mixing: Weigh the following components according to mass ratio:

[0091] 20-80g of stearic acid wet-process modified fly ash;

[0092] Cement 120-180g;

[0093] 400g of aeolian sand;

[0094] 100g water;

[0095] Among them, the weight ratio of stearic acid wet-process modified fly ash and cement is 4:6, 3:7, 2:8, and 1:9.

[0096] 2.2 Mixing process:

[0097] a. Add cement, stearic acid wet-process modified fly ash and aeolian sand into a planetary mortar mixer at a speed of 300±10r / min and dry mix for 1 minute;

[0098] b. Slowly add water, increase the speed to 400±10r / min, and continue stirring for 5 minutes.

[0099] 2.3 Casting:

[0100] Pour the slurry into the mold and vibrate for 60 to 90 seconds to remove bubbles, and use a scraper to smooth the surface.

[0101] 2.4 Standard maintenance

[0102] The molds were transferred to a standard curing room and cured for 7 days at 20±2°C and 95±5% relative humidity. The resulting hydrophobic aeolian sand mortar specimens were labeled Y3%-1, Y3%-2, Y3%-3, Y3%-4, Y5%-1, Y5%-2, Y5%-3, Y5%-4, Y7%-1, Y7%-2, Y7%-3, and Y7%-4. (The number Y3%-1 indicates: "Y" represents stearic acid, "3%" represents 1% of the mass of the ordinary fly ash, and "1" represents 10% of the mass of the modified fly ash.)

[0103] control group

[0104] The following is a control group experiment, namely the traditional aeolian sand mortar forming process, which includes the following steps:

[0105] 1. Raw material preparation:

[0106] 1.1 Mortar base material

[0107] Ordinary fly ash (i.e., stearic acid content 0%);

[0108] Cement: 42.5 grade ordinary Portland cement;

[0109] Aeolian sand: particle size range is 0.06-0.24mm;

[0110] Mixing water: tap water (pH = 6.5 ~ 7.5);

[0111] 2. Aeolian sand mortar forming process

[0112] 2.1 Ingredients mixing: Weigh the following components according to mass ratio:

[0113] Ordinary fly ash 20-80g;

[0114] Cement 120-180g;

[0115] 400g of aeolian sand;

[0116] 100g water;

[0117] Among them, the weight ratio of ordinary fly ash to cement is 4:6, 3:7, 2:8, and 1:9.

[0118] 2.2 Mixing process:

[0119] a. Put cement, ordinary fly ash and aeolian sand into a planetary mortar mixer at a speed of 300±10r / min and dry mix for 1 minute;

[0120] b. Slowly add water, increase the speed to 400±10r / min, and continue stirring for 5 minutes to obtain a slurry.

[0121] 2.3 Casting:

[0122] Pour the slurry into the mold and vibrate for 60 to 90 seconds to remove bubbles, and use a scraper to smooth the surface.

[0123] 2.4 Standard maintenance

[0124] The mold was transferred to a standard curing room and cured for 7 days at a temperature of 20±2°C and a relative humidity of ≥95±5% to obtain a control group of hydrophobic aeolian sand mortar test blocks with a ratio of 1:9, 2:8, 3:7, and 4:6.

[0125] 3. Wettability of hydrophobic aeolian sand mortar:

[0126] ① Contact angle: Using JCY series contact angle tester, take 5μL deionized water droplets and drop them on the surface of the mortar specimen. The measured contact angle can reach 125°, as shown in Table 2 and Figure 6 As shown. ( Figure 6 The arrangement order corresponds to the test block number in Table 2)

[0127] Table 2

[0128] Test block number Y3％-1 Y3％-2 Y3％-3 Y3％-4 contact angle 52.83° 96.63° 99.99° 114.39° Test block number Y5％-1 Y5％-2 Y5％-3 Y5％-4 contact angle 94.13° 113.61° 119.80° 116.84° Test block number Y7％-1 Y7％-2 Y7％-3 Y7％-4 contact angle 97.85° 125.19° 109.93° 105.89°

[0129] ② Water drop shape: The water drop shape on the surface of hydrophobic aeolian sand mortar with stearic acid wet modified fly ash is as follows: Figure 5 shown.

[0130] 4. Water absorption test of hydrophobic aeolian sand mortar:

[0131] The test piece obtained in Example 2 was dried to constant weight and immersed in a water tank. The cumulative water absorption rate was recorded for 7 days and was ≤2.3% (the water absorption rate of the control group was ≥5.6%).

[0132] The water absorption rate variation trend curves of the test blocks prepared in Example 2 are shown in Figure 7 and Figure 8 .

[0133] Figure 7 In the experiment, the stearic acid content was kept constant, and only the mass ratio of stearic acid-modified fly ash (using ordinary fly ash as a control) to cement was adjusted. The experimental results showed that as the proportion of stearic acid-modified fly ash in the mixture gradually increased, the water absorption rate of the hydrophobic aeolian sand mortar specimens containing stearic acid-modified fly ash showed a significant downward trend.

[0134] Figure 8The results show that, while maintaining a fixed mass ratio of stearic acid-modified fly ash (the control group still used ordinary fly ash) to cement at 4:6, only the stearic acid content was varied, and a comparative analysis was conducted with a control group without stearic acid. The results show that the water absorption rate of hydrophobic aeolian sand mortar specimens with the addition of stearic acid-modified fly ash also significantly decreased.

[0135] comprehensive Figure 7 and Figure 8 Experimental data indicates that when the stearic acid content is between 5% and 7%, the cumulative water absorption of fly ash hydrophobic aeolian sand mortar specimens containing this modifier is significantly reduced. This phenomenon strongly demonstrates that stearic acid wet-process modified fly ash effectively blocks pores in the mortar system and creates a hydrophobic barrier on the pore surface, significantly improving the mortar's hydrophobic properties.

[0136] This invention innovatively employs a wet-process fly ash modification process with stearic acid. By scientifically regulating the raw material ratio and preparation process, it organically integrates the hydrophobic modification efficiency of stearic acid with the active filling and strengthening effect of fly ash, effectively overcoming the bottleneck of existing technologies. Compared with traditional surface hydrophobic coating processes, this invention breaks through the limitations of single surface modification, taking into account the optimization of the mortar's internal structure and the improvement of surface properties, achieving long-lasting and stable hydrophobic properties from the material's intrinsic level, and avoiding the technical drawbacks of traditional coatings such as easy shedding and insufficient durability. At the same time, the composite modification technology compensates for the shortcomings of mortar strength degradation and short service life caused by the use of only aeolian sand as an aggregate. This preparation process has the remarkable characteristics of a simple process and controllable operation, adapting to the needs of large-scale industrial production, and opening up a new technical path for the efficient utilization of aeolian sand, a rich natural resource, in the construction field. Its application not only creates significant economic benefits and reduces the consumption of natural sand and gravel resources, but also produces positive environmental benefits, promoting the transformation and upgrading of the building materials industry towards a green and low-carbon direction. The technical achievements of this invention are applicable to scenarios with high waterproof performance requirements, such as hydraulic structures, underground projects, and marine environments, and provide reliable technical support for improving the durability of construction projects under complex service conditions.

[0137] Of course, the above description is not a limitation of the present invention, and the present invention is not limited to the above examples. Changes, modifications, additions or substitutions made by technicians in this technical field within the essential scope of the present invention should also fall within the scope of protection of the present invention.

Claims

1. A method for preparing hydrophobic aeolian sand mortar by adding stearic acid to wet-process modified fly ash, characterized in that: Raw materials are calculated by weight and include: 20-80 parts of stearic acid wet-process modified fly ash; 120-180 parts of cement; 400-600 parts of aeolian sand; 90-100 parts of water.

2. The method for preparing hydrophobic aeolian sand mortar by wet-process modified fly ash mixed with stearic acid as claimed in claim 1, characterized in that: The specific steps include: (1) Add a certain amount of stearic acid to anhydrous ethanol, heat at 60°C, and stir with a magnetic stirrer to prepare a stearic acid solution; (2) Mixing ordinary fly ash with water, then pouring the stearic acid solution into it, stirring at room temperature to obtain a uniform and stable slurry; (3) transferring the slurry into an oven and drying it at 60° C. to remove moisture and obtain stearic acid wet-process modified fly ash; (4) Cement, aeolian sand, and stearic acid wet-process modified fly ash are weighed according to the mass ratio and added to the mixing equipment. The mixture is initially dry-mixed and then a certain amount of water is slowly added for wet mixing. After the mixture is evenly mixed, the mortar slurry is injected into the mold, vibrated and shaped, and cured to obtain a hydrophobic aeolian sand mortar specimen.

3. The method for preparing hydrophobic aeolian sand mortar by wet-process modified fly ash mixed with stearic acid according to claim 2, wherein: In step (1), the mass ratio of anhydrous ethanol to stearic acid is 1:4 to 1:6, and the added amount of stearic acid is 1% to 7% of the mass of ordinary fly ash.

4. The method for preparing hydrophobic aeolian sand mortar by wet-process modified fly ash mixed with stearic acid according to claim 4, wherein: In step (1), the stirring conditions are: the first stirring rate is 600 to 1500 r / min, and the stirring time is 5 to 8 min; In step (2), the stirring conditions are: the second stirring rate is 1000-1500 r / min, and the stirring time is 30-60 min.

5. The method for preparing hydrophobic aeolian sand mortar by wet-process modified fly ash mixed with stearic acid according to claim 4, wherein: In step (2), the solid-liquid ratio of ordinary fly ash to water is g:mL=1:(4-6).

6. The method for preparing hydrophobic aeolian sand mortar by wet-process modified fly ash mixed with stearic acid according to claim 5, wherein: In step (3), the drying temperature is 40 to 60° C., and the drying time is 12 to 24 hours.

7. The method for preparing hydrophobic aeolian sand mortar by wet-process modified fly ash mixed with stearic acid according to claim 6, wherein: In step (4), the cement is 42.5 grade ordinary Portland cement with a water-cement ratio of 0.4 to 0.5; In step (4), the particle size of the aeolian sand is in the range of 0.06 to 0.24 mm.

8. The method for preparing hydrophobic aeolian sand mortar by wet-process modified fly ash mixed with stearic acid according to claim 7, wherein: In step (4), the dry mixing time is 1 to 3 minutes, the wet mixing time is 2 to 8 minutes, and the vibration time is 1 to 2 minutes.

9. The method for preparing hydrophobic aeolian sand mortar by adding stearic acid to wet-process modified fly ash according to claim 8, characterized in that: The curing conditions of step (4) are: temperature 20±2° C., relative humidity 95±5%, and curing time is 7 days.

10. The method for preparing hydrophobic aeolian sand mortar by adding stearic acid to wet-process modified fly ash according to claim 9, characterized in that: The contact angle of the hydrophobic aeolian sand mortar specimen can reach 125°, the cumulative water absorption rate is ≤2.3%, and the 28d compressive strength is ≥10MPa.

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