Method for preparing hydrophobic aeolian sand mortar by internally doping palmitic acid wet-process modified fly ash

Abstract

The invention provides a method for preparing hydrophobic aeolian sand mortar from palmitic acid-doped wet-process modified fly ash, and belongs to the technical field of building materials. The preparation process comprises the following steps: firstly, forming a hydrophobic layer on the surface of fly ash particles through palmitic acid wet modification to obtain palmitic acid wet modified fly ash; and replacing part of cement with palmitic acid wet modified fly ash according to a mixing ratio, mixing with the aeolian sand and other raw materials to prepare slurry, and demolding and curing to obtain the hydrophobic aeolian sand mortar test block. The hydrophobic aeolian sand mortar has the beneficial effects that the prepared hydrophobic aeolian sand mortar has excellent hydrophobicity, stain resistance, air permeability and permeability resistance, and the durability of the mortar is remarkably improved while high-value utilization of solid wastes such as the fly ash and the aeolian sand is realized. The preparation process is simple and convenient, the cost can be effectively controlled, the strict requirements of modern constructional engineering on high-performance and long-life mortar can be met, and the mortar is suitable for the fields with strict waterproof requirements, such as hydraulic structures, underground engineering and ocean engineering, and has relatively high engineering application value.

Description

Technical Field

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

[0002] With the rapid development of the global construction industry, the overreliance of traditional mortars on river sand aggregates has triggered a serious resource and environmental crisis. According to statistics, the global construction industry consumes approximately 40 to 50 billion tons of natural river sand annually. River sand prices in emerging economies such as China and India have soared by over 300% over the past decade. In some regions, illegal river sand mining has even emerged, leading to secondary disasters such as river ecological damage, riverbed subsidence, and embankment collapse. Meanwhile, desert regions possess vast reserves of aeolian sand (for example, over 20 billion tons in northwest China). However, its particle size distribution is extremely uneven (80% of the particles are concentrated in the 0.06 to 0.24 mm range), its surface is smooth, and its gradation is uniform. When used directly as an aggregate, mortar porosity can reach as high as 25 to 30%, significantly reducing interfacial bonding strength and increasing drying shrinkage by 40 to 60% compared to river sand mortar, severely restricting its application in structural engineering.

[0003] On the other hand, fly ash, a major industrial solid waste generated by coal-fired power plants, produces over 1.5 billion tons annually worldwide. However, China's comprehensive fly ash utilization rate has long been below 70%. Large-scale accumulation not only occupies land but also poses a threat to the ecological environment through the leaching risk of heavy metals (such as arsenic and lead) and dust pollution. Although fly ash can be used as a mineral admixture to partially replace cement (typically at a dosage of 10% to 30%), its dense vitreous structure and low pozzolanic activity (activity index of only 65% ​​to 75%) mean that its direct incorporation can significantly reduce the early strength of mortar (with a 30% fly ash addition, the strength decreases by more than 50% after three days). Existing activation technologies, such as mechanical grinding (which consumes up to 30-50 kWh / t) or alkaline activation (which requires the use of NaOH solutions with concentrations >5 mol / L), can enhance activity, but they face high energy consumption, complex processes, and construction safety and environmental risks posed by a highly alkaline environment.

[0004] In the field of hydrophobic functional modification, there are two main technical routes in the existing technology:

[0005] (1) Surface coating method: Fluorine-containing resin (such as polytetrafluoroethylene (PTFE)) or silicone coating is used to form a hydrophobic layer on the mortar surface by spraying, dipping, etc., with a contact angle of 150-160°. However, the thickness of such coating is only 10-50 μm, and it is easy to peel off under mechanical wear (such as 50 cycles of ASTM D968 sand abrasion test) or freeze-thaw cycles, and the contact angle drops sharply to below 90°. In addition, fluorine-containing materials are bioaccumulative and toxic, and do not comply with environmental regulations such as RoHS.

[0006] (2) Internal doping method: Directly adding short-chain fatty acids (such as lauric acid) or nano-hydrophobic particles (such as silica aerogel) can reduce water absorption, but short-chain fatty acids are easy to react with Ca in the high alkaline environment of cement (pH>12.5). 2+ The reaction generates saponified products (such as calcium stearate), which causes the hydrophobicity to decay with age (the contact angle decreases by 30% to 40% after 28 days), and the uneven dispersion of nanomaterials easily causes agglomeration, increases porosity and weakens mechanical properties.

[0007] It is worth noting that long-chain fatty acids (such as palmitic acid C16:0) can theoretically improve their compatibility with cement matrix due to their more stable carbon chain structure and lower critical micelle concentration. However, existing research has mostly focused on long-chain fatty acids such as stearic acid (C18:0), and there has been no report on the systematic study of palmitic acid in the modification of mortar. In addition, although the porous structure of fly ash is conducive to the adsorption of hydrophobic substances, its high specific surface area (300-500m 2 / kg) also exacerbates water adsorption. Direct mixing of palmitic acid in traditional processes can lead to localized enrichment due to uneven dispersion, exacerbating pore defects. Therefore, there is an urgent need to develop an intrinsically hydrophobic technology based on wet-process palmitic acid-modified fly ash. Through the collaborative design of solid waste resource utilization and functionalization, this technology could achieve the combined high strength, durability, and self-cleaning properties of aeolian sand mortar. Summary of the Invention

[0008] In order to solve the above technical problems, the present invention discloses a method for preparing hydrophobic aeolian sand mortar by wet-process modified fly ash with palmitic acid. The surface of the fly ash is modified by palmitic acid to impart hydrophobic properties to the mortar. At the same time, the volcanic ash effect of the fly ash is utilized to improve the later strength of the mortar, thereby achieving the dual goals of solid waste resource utilization and material performance optimization.

[0009] To achieve the above object, the present invention adopts the following technical solutions:

[0010] A method for preparing hydrophobic aeolian sand mortar by adding wet-process modified fly ash with palmitic acid, wherein the raw materials are calculated by weight and include:

[0011] 65-98 parts of cement;

[0012] 300-350 parts of aeolian sand;

[0013] 11-44 parts of palmitic acid wet-process modified fly ash;

[0014] 45-55 parts of water.

[0015] Furthermore, the specific steps of the method include:

[0016] (1) First, a certain amount of palmitic acid was added to anhydrous ethanol, heated at 60°C, and stirred with a magnetic stirrer to obtain a palmitic acid solution;

[0017] (2) Mix ordinary fly ash with water, then pour the palmitic acid solution into it, and stir at room temperature to obtain a uniform and stable slurry;

[0018] (3) transferring the slurry into an oven and drying it at 60-120° C. to remove moisture and obtain palmitic acid wet-process modified fly ash;

[0019] (4) Cement, aeolian sand, and palmitic acid wet-process modified fly ash are weighed according to the mass ratio and added into 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 slurry is injected into the mold, vibrated and shaped, and cured to obtain a hydrophobic aeolian sand mortar specimen.

[0020] Furthermore, in step (1), the mass ratio of the anhydrous ethanol to the palmitic acid is 1:3 to 1:6, and the amount of the palmitic acid added is 1% to 7% of the mass of ordinary fly ash.

[0021] Furthermore, the mixing and stirring conditions in step (1) are as follows: the first stirring rate is 600 to 1500 rpm, and the time is 3 to 5 minutes;

[0022] In step (2), the stirring conditions are: the second stirring rate is 1000-1500 r / min, and the second stirring time is 30-60 minutes.

[0023] Furthermore, in step (2), the solid-liquid ratio of ordinary fly ash to water is g:mL=1:(2-4).

[0024] Furthermore, in step (3), the drying temperature is 60 to 120° C., and the drying time is 2 to 6 hours.

[0025] Furthermore, in step (4), the cement is selected from 42.5 grade ordinary Portland cement with a water-cement ratio of 0.4 to 0.5;

[0026] The particle size of the aeolian sand ranges from 0.06 to 0.24 mm.

[0027] 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.

[0028] Furthermore, the curing conditions of step (4) are: temperature of 20±5° C., relative humidity of 90±5%, and curing time of 7 days.

[0029] Furthermore, the contact angle of the hydrophobic aeolian sand mortar specimen can reach 138°, the cumulative water absorption rate is ≤1.5%, and the 28d compressive strength is ≥10MPa.

[0030] The beneficial effects of the present invention are that, compared with the prior art, it has the following advantages:

[0031] (1) Improved hydrophobic effect

[0032] The hydrophobic aeolian sand mortar prepared by the present invention, with the help of the unique effect of wet-method modification of fly ash by palmitic acid, constructs a stable and dense micron-nanoscale rough structure on the mortar surface. At the same time, the long-chain alkyl groups in the palmitic acid molecules are oriented to form a low surface energy interface. This special surface structure and chemical properties are combined to significantly increase the water contact angle on the mortar surface to 138°, showing excellent hydrophobic properties. When moisture contacts the mortar surface, water droplets are formed and roll down quickly, effectively preventing moisture from penetrating into the mortar. This characteristic is crucial for building structures that are exposed to humid environments for a long time or are eroded by rainwater. It can significantly reduce the erosion of moisture on the mortar substrate, prevent problems such as substrate softening, cracking, freeze-thaw damage, etc. caused by moisture penetration, thereby extending the service life of the building and providing long-term dry protection for the building.

[0033] (2) Enhanced mechanical properties

[0034] Palmitic acid-wet-processed fly ash plays multiple reinforcing roles in mortar. Firstly, the highly active fly ash particles undergo a secondary hydration reaction with cement hydration products, generating more gel, which fills the pores within the mortar and makes the mortar more compact. Secondly, the coating formed by the palmitic acid molecules on the fly ash particles improves the interfacial adhesion between the fly ash and the cement paste, strengthening the bond between the aggregate and the cementitious material. Furthermore, the gradation of aeolian sand, the palmitic acid-wet-processed fly ash, and the cement complements the mortar to form a stable skeleton structure. These factors combine to significantly enhance the mechanical properties of the prepared mortar. These excellent mechanical properties enable the mortar to withstand greater loads and stresses, providing a more reliable support for building structures and laying a solid foundation for their safety and stability.

[0035] (3) Improved anti-seepage and durability

[0036] The inherent hydrophobicity strongly impedes the penetration of water and harmful ions, and the densification of the mortar's internal structure further enhances its impermeability. Palmitic acid wet-process modified fly ash reduces the interconnected pores in the mortar and refines the pore size distribution, forming an impenetrable barrier that effectively prevents the penetration of aggressive media such as water, chloride ions, and sulfates. Furthermore, its excellent impermeability significantly enhances the mortar's durability. Over long-term use, it effectively resists the erosion of harsh environments such as acid rain, salt spray, and freeze-thaw cycles, reducing the occurrence of defects such as steel corrosion and mortar pulverization in concrete structures.

[0037] This method has the advantages of easy preparation, environmental protection, non-toxicity, and quick effect, and provides support for the good application of hydrophobic materials in the field of building materials. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] 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 R7-1h palmitic acid wet-process modified fly ash;

[0039] Figure 2 Shown is the contact angle test result of the fly ash powder modified by the palmitic acid wet method in Example 1;

[0040] Figure 3 Shown are the water droplet / ice crystal morphologies on the surface of fly ash powder modified by the palmitic acid wet method in Example 1; (left) 3% NaCl solution morphology, (right) ice bead morphology;

[0041] Figure 4 Shown are the water droplet morphology images on the surface of the fly ash powder modified by the wet method of palmitic acid in Example 1 before and after standing for 1 hour; (left) before standing, (right) after standing;

[0042] Figure 5 Shown is the morphology of water droplets / ice beads on the surface of the hydrophobic aeolian sand mortar specimen mixed with palmitic acid wet-process modified fly ash in Example 2;

[0043] Figure 6 Shown is a contact angle test result of a hydrophobic aeolian sand mortar specimen mixed with palmitic acid wet-process modified fly ash powder in Example 2;

[0044] Figure 7 The graph shows the cumulative water absorption of the hydrophobic aeolian sand mortar test piece mixed with palmitic acid wet-process modified fly ash in Example 2;

[0045] Figure 8 It shows the cumulative water absorption of the hydrophobic aeolian sand mortar specimens added with palmitic acid wet-process modified fly ash under the condition of a mass ratio of palmitic acid wet-process modified fly ash to cement of 4:6 in Example 2.

[0046] Figure 9 Shown are the XRD patterns of fly ash before and after modification;

[0047] Figure 10 Shown are the FT-IR images of fly ash before and after modification; DETAILED DESCRIPTION

[0048] 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 shall fall within the scope of protection of the present invention.

[0049] 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 fly ash modification process with palmitic acid, cleverly combining the hydrophobic modification effect of palmitic 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.

[0050] Example 1

[0051] The present invention discloses a preparation process of palmitic acid wet-process modified fly ash, which comprises the following steps:

[0052] 1. Preparation of raw materials for wet-process modified fly ash with palmitic acid:

[0053] Weigh the following components in percentage by mass:

[0054] Palmitic acid: 1g, 3g, 5g, 7g gradient addition;

[0055] Analytical pure anhydrous ethanol: the dosage is 5 times the mass of palmitic acid;

[0056] Ordinary fly ash: 100g / batch;

[0057] 2. Preparation process of palmitic acid wet modified fly ash

[0058] 2.1 Add palmitic acid and anhydrous ethanol in a mass ratio of 1:4 into a container with a stirring and heating device, stir at 1000r / min, heat to 60℃, and stir at constant temperature for 5 minutes to form a transparent palmitic acid solution.

[0059] 2.2 Transfer the transparent solution obtained in step 2.1 into a reaction beaker, add 100g of ordinary fly ash and 350mL of water, adjust the stirring rate to 1500r / min, and continue stirring for 1h to form a palmitic acid wet-process modified fly ash slurry.

[0060] 2.3 Transfer the palmitic acid wet modified fly ash slurry to a vacuum drying oven, set the drying temperature to 80±5℃, dry for 5 hours, and cool and store to obtain palmitic acid wet modified fly ash, which are recorded as R7-0.5h, R7-1h, R5-0.5h, R5-1h, R3-0.5h, R3-1h, R1-0.5h, and R1-1h.

[0061] 2.4 Wettability test:

[0062] ① Contact angle test: Using JCY series contact angle tester, 5 μL of deionized water was dropped on the surface of modified fly ash powder, and the contact angle was measured to be 150°, as shown in Table 1 and Figure 2 shown.

[0063] Table 1

[0064]

[0065] ② Rolling angle test: Adjust the angular velocity of the tilt platform to 1° / s and record the angle of the water droplet when it rolls down. The rolling angle should be less than 5°.

[0066] ③Surface water droplets / ice crystal morphology: The surface water droplets / ice crystal morphology of fly ash powder modified by palmitic acid wet method is as follows Figure 3 shown. Figure 3 It shows that the ice crystals on the surface of the fly ash modified by the wet method of palmitic acid are discrete spherical (diameter ≤ 2 mm).

[0067] ④ Surface water droplet static morphology: The water droplet morphology of the surface of the fly ash powder modified by the palmitic acid wet method 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.

[0068] 2.5 Characterization of the modification mechanism of fly ash modified by palmitic acid wet method

[0069] ①SEM characterization

[0070] The microscopic morphology SEM image of the palmitic acid wet modified fly ash is as follows: Figure 1 As shown:

[0071] Unmodified fly ash has a morphological characteristic: a single, relatively large spherical particle with a rough surface and scattered small particles or protrusions. This spherical structure is due to the high temperature melting and surface tension during the coal combustion process, which causes the particles to tend towards a spherical shape.

[0072] Structural features: The overall outline is relatively smooth, with no obvious regular crystal form, showing the original physical state without modification.

[0073] The morphological characteristics of the palmitic acid wet-process modified fly ash R7%-1h prepared in this embodiment are as follows: Figure 1 As shown, it is composed of a large number of small, blocky crystals with relatively regular shapes (such as square and rectangular), tightly packed, and presenting a polycrystalline aggregate state. Palmitic acid, as a fatty acid, has a typical crystal structure, showing a regular crystal form under an electron microscope.

[0074] Structural characteristics: The crystal boundaries are clear and the size uniformity is high, which is in sharp contrast to the single spherical structure of fly ash, reflecting the characteristics of organic crystal materials.

[0075] ②XRD and FT-IR characterization

[0076] The XRD and FT-IR patterns of fly ash modified by palmitic acid wet method are shown in Figure 9 and Figure 10 Shown:

[0077] As can be seen from the figure, palmitic acid (C 16 H 32 The reaction of O2-modified fly ash is mainly esterification reaction, supplemented by physical adsorption. Its core chemical equation and mechanism of action are as follows:

[0078] (1) Esterification reaction (chemical bonding): The carboxyl group (-COOH) of palmitic acid reacts with the hydroxyl group (-OH, from minerals such as SiO2 and Al2O3) on the surface of fly ash to form an ester bond (COC), achieving chemical fixation.

[0079] Reaction equation:

[0080]

[0081] R: represents the alkyl chain of palmitic acid (C 15 H 31 -).

[0082] (2) Physical adsorption (non-chemical bonding)

[0083] Palmitic acid molecules are adsorbed on the fly ash surface through van der Waals forces (such as dispersion forces and hydrogen bonds between alkyl chains) to form a physical covering layer.

[0084] Example 2

[0085] The present invention discloses a method for preparing hydrophobic aeolian sand mortar by wet-process modified fly ash mixed with palmitic acid, which comprises the following steps:

[0086] 1. Raw material preparation:

[0087] 1.1 Mortar base material

[0088] Palmitic acid wet-process modified fly ash: In Example 1, palmitic acid wet-process modified fly ash of various specifications was obtained;

[0089] Cement: 42.5 grade ordinary Portland cement;

[0090] Aeolian sand: particle size range is 0.06-0.24mm;

[0091] Mixing water: tap water (pH = 6.5 ~ 7.5);

[0092] 2. Hydrophobic aeolian sand mortar forming process

[0093] 2.1 Ingredients mixing: Weigh the following components according to mass ratio:

[0094] Palmitic acid wet-process modified fly ash 11-44g;

[0095] Cement 65-98g;

[0096] 330g of aeolian sand;

[0097] 50g water;

[0098] Among them, the mass ratio of palmitic acid wet-process modified fly ash to cement is 1:9, 2:8, 3:7, and 4:6.

[0099] 2.2 Dry mixing treatment:

[0100] a. Put cement and aeolian sand into a planetary mixer (speed 300±10r / min) and premix for 2 minutes;

[0101] b. Add palmitic acid wet-process modified fly ash and continue dry mixing for 3 minutes.

[0102] 2.3 Wet mixing and molding:

[0103] Slowly add water, increase the speed to 400±10r / min, and wet mix until a homogeneous slurry is formed; inject the slurry into the mold and vibrate for 1 to 2 minutes until it is formed, use a vibrating table to expel bubbles, and use a scraper to level the surface.

[0104] 2.4 Standard maintenance

[0105] The mold was transferred to a standard curing room and cured for 7 days at a temperature of 20±5°C and a relative humidity of 90±5% to obtain hydrophobic aeolian sand mortar specimens, which were recorded as R7-1h1:9, R7-1h2:8, R7-1h3:7, R7-1h4:6, R7-0.5h4:6, R5-0.5h4:6, R5-1h4:6, R3-0.5h4:6, R3-1h4:6, R1-0.5h4:6, and R1-1h4:6.

[0106] The following is a control group experiment, namely the traditional aeolian sand mortar forming process, which includes the following steps:

[0107] 1. Raw material preparation:

[0108] 1.1 Mortar base material

[0109] Ordinary fly ash (i.e., palmitic acid content 0%);

[0110] Cement: 42.5 grade ordinary Portland cement;

[0111] Aeolian sand: particle size range is 0.06-0.24mm;

[0112] Mixing water: tap water (pH = 6.5 ~ 7.5);

[0113] 2. Aeolian sand mortar forming process

[0114] 2.1 Ingredients mixing: Weigh the following components according to mass ratio:

[0115] Ordinary fly ash 11-44g;

[0116] Cement 65-98g;

[0117] 330g of aeolian sand;

[0118] 50g water;

[0119] Among them, the mass ratio of ordinary fly ash to cement is 1:9, 2:8, 3:7, and 4:6.

[0120] 2.2 Dry mixing treatment:

[0121] a. Put cement and aeolian sand into a planetary mixer (speed 300±10r / min) and premix for 2 minutes;

[0122] b. Add ordinary fly ash and continue dry mixing for 3 minutes.

[0123] 2.3 Wet mixing and molding:

[0124] Slowly add water, increase the speed to 400±10r / min, and wet mix until a homogeneous slurry is formed; inject the slurry into the mold and vibrate for 1 to 2 minutes until it is formed, use a vibrating table to expel bubbles, and use a scraper to level the surface.

[0125] 2.4 Standard maintenance

[0126] The mold was transferred to a standard curing room and cured for 7 days at a temperature of 20±5°C and a relative humidity of 90±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.

[0127] 3. Wettability of hydrophobic aeolian sand mortar:

[0128] ① Contact angle: Using JCY series contact angle tester, 5μL deionized water was dropped on the surface of the mortar specimen, and the contact angle was measured to be 138°, as shown in Table 2 and Figure 6 shown.

[0129] Table 2

[0130] Mortar test blocks R7-1h2:8 R5-1h3:7 R7-1h3:7 R3-1h4:6 R5-1h4:6 R7-1h4:6 contact angle 124.3° 123.3° 124.5° 125.9° 136.7° 138.6°

[0131] ② Water droplet / ice crystal morphology: The water droplet / ice crystal morphology on the surface of hydrophobic aeolian sand mortar with wet modified fly ash mixed with palmitic acid is as follows: Figure 5 shown.

[0132] 4. Water absorption test of hydrophobic aeolian sand mortar:

[0133] 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 ≤1.5% (the water absorption rate of the control group was ≥5.6%).

[0134] The water absorption rate variation trend curves of the test blocks prepared in Example 2 are presented in Figure 7 and Figure 8 .

[0135] exist Figure 7 In the experiment, the palmitic acid content was kept constant, and only the mass ratio of palmitic acid-modified fly ash (using ordinary fly ash as a control) to cement was adjusted. The experimental results showed that as the proportion of palmitic acid-modified fly ash in the mixture gradually increased, the water absorption rate of the hydrophobic aeolian sand mortar specimens containing palmitic acid-modified fly ash showed a significant downward trend.

[0136] Figure 8 The results show that while the mass ratio of palmitic acid-modified fly ash (the control group still used ordinary fly ash) to cement was fixed at 4:6, the palmitic acid content was varied and compared with the control group without palmitic acid. The results show that the water absorption rate of the hydrophobic aeolian sand mortar specimens with the addition of palmitic acid-modified fly ash was also significantly reduced.

[0137] comprehensive Figure 7 and Figure 8 Experimental data indicates that when the palmitic acid content is between 5% and 7%, the cumulative water absorption of hydrophobic aeolian sand mortar specimens containing modified fly ash is significantly reduced. This phenomenon strongly demonstrates that palmitic 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.

[0138] The present invention adopts the process of wet-process modified fly ash with internal palmitic acid, cleverly combines the hydrophobic modification effect of palmitic acid with the active filling and reinforcement effect of fly ash, and successfully solves these technical difficulties through reasonable raw material ratio and preparation process. Compared with methods such as traditional surface coating hydrophobic coating, the present invention is optimized from two aspects of mortar internal structure and surface performance, making hydrophobicity more durable and stable, avoiding problems such as coating shedding; At the same time, it overcomes the shortcomings of insufficient mortar strength and poor durability caused by simply using aeolian sand as aggregate. The preparation method is simple in process and easy to operate, suitable for industrial large-scale production, and has opened up new ways for the efficient utilization of aeolian sand, a rich natural resource, in the field of construction, with significant economic and environmental benefits, and has effectively promoted the technological innovation and sustainable development of the building materials industry. It is particularly suitable for scenes with high requirements for waterproof performance, such as hydraulic structures, underground projects and marine environments.

[0139] 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 wet-process modified fly ash with palmitic acid, characterized in that: The raw materials are calculated by weight and include: 65-98 parts of cement; 300-350 parts of aeolian sand; 11-44 parts of palmitic acid wet-process modified fly ash; 45-55 parts of water.

2. The method for preparing hydrophobic aeolian sand mortar by wet-process modified fly ash mixed with palmitic acid as claimed in claim 1, characterized in that: The specific steps include: (1) First, a certain amount of palmitic acid was added to anhydrous ethanol, heated at 60°C, and stirred with a magnetic stirrer to obtain a palmitic acid solution; (2) Mix ordinary fly ash with water, then pour the palmitic acid solution into it, and stir at room temperature to obtain a uniform and stable slurry; (3) transferring the slurry into an oven and drying it at 60-120° C. to remove moisture and obtain palmitic acid wet-process modified fly ash; (4) Cement, aeolian sand, and palmitic acid wet-process modified fly ash are weighed according to the mass ratio and added into 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 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 palmitic acid as claimed in claim 2, characterized in that: In step (1), the mass ratio of the anhydrous ethanol to the palmitic acid is 1:3 to 1:6, and the added amount of the palmitic 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 palmitic acid as claimed in claim 3, characterized in that: The mixing and stirring conditions in step (1) are as follows: the first stirring rate is 600 to 1500 rpm and the time is 3 to 5 minutes; In step (2), the stirring conditions are: the second stirring rate is 1000-1500 r / min, and the second stirring time is 30-60 minutes.

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

6. The method for preparing hydrophobic aeolian sand mortar by wet-process modified fly ash mixed with palmitic acid as claimed in claim 5, characterized in that: In step (3), the drying temperature is 60-120° C., and the drying time is 2-6 hours.

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

8. The method for preparing hydrophobic aeolian sand mortar by wet-process modified fly ash mixed with palmitic acid as claimed in claim 7, characterized in that: 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 wet-process modified fly ash mixed with palmitic acid as claimed in claim 8, characterized in that: Step (4) curing conditions: temperature of 20±5°C, relative humidity of 90±5%, and curing time of 7 days.

10. The method for preparing hydrophobic aeolian sand mortar by wet-process modified fly ash mixed with palmitic acid as claimed in claim 9, characterized in that: The contact angle of the hydrophobic aeolian sand mortar specimen can reach 138°, the cumulative water absorption rate is ≤1.5%, and the 28d compressive strength is ≥10MPa.

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