Method for preparing silane composite nano c-s-h for hydrophobic modification of concrete surface and application thereof

Abstract

The application discloses a preparation method of silane composite nano C-S-H for hydrophobic modification of a concrete surface and application thereof, and relates to the field of building engineering materials. In the prior art, silane is prone to self-polymerization in a strong alkali environment, is difficult to be stably compounded with nano C-S-H, and cannot realize the synergistic effect of hydrophobicity and densification during the construction window period of fresh concrete. The application comprises the following steps: preparing a silane hydrolysis solution A, mixing ethanol, water and n-octyl triethoxysilane in a mass ratio of 50:1:(1.5-2.5), first hydrolyzing in an acid to adjust the pH, and then adjusting to near neutrality by an alkali; preparing a surface aminated dispersion solution B, dispersing nano C-S-H in an alkaline medium, adjusting the solid content and the pH by saturated lime water, and adding gamma-aminopropyl triethoxysilane to react; adding the liquid A into the liquid B to condense, and adjusting the solid content and the pH after alcohol removal. The technical scheme realizes the improvement of hydrophobicity, anti-permeability and chlorine ion resistance, and the obtained suspension is used for concrete surface treatment, so that the synergistic improvement of rapid hydrophobicity and surface layer densification can be realized.

Description

Technical Field

[0001] This invention relates to the field of building materials, and more particularly to a method for preparing silane composite nano-CSH for hydrophobic modification of concrete surfaces and its application. Background Technology

[0002] Concrete, as the most widely used cementitious material in civil engineering, is highly susceptible to erosion by moisture, chlorides, carbon dioxide, and other media during its service life. These media penetrate the matrix through the capillaries and microcracks on the concrete surface, causing a series of deterioration problems such as steel corrosion, freeze-thaw cycle damage, and accelerated concrete carbonation, significantly reducing the durability and service life of concrete structures. To address these issues, hydrophobic surface modification treatment is commonly used in engineering to block the intrusion channels of water and harmful ions. The performance of the surface hydrophobic modification material directly determines the protective effect on the concrete structure. An ideal surface hydrophobic modification material for concrete must possess excellent hydrophobic properties, good interfacial bonding with the concrete matrix, and the ability to improve the microstructure density of the near-surface layer of concrete. It should also be compatible with the early-age process window of concrete construction, achieving efficient protection without affecting the concrete hydration process.

[0003] Currently, organosilane / siloxane penetrants are commonly used for hydrophobic modification of concrete surfaces. These materials mainly achieve hydrophobicity by reducing the surface energy of concrete. However, they have many technical drawbacks in practical applications: Firstly, traditional silane hydrophobic systems are mostly solvent-based or water-emulsion-based. Solvent-based systems have high volatile organic compound (VOC) content, pose a flammability risk, and are prone to pinholes and surface whitening when applied to freshly mixed early-age concrete surfaces. Water-emulsion-based systems rely on surfactants for dispersion and stability, which have poor stability in the strongly alkaline environment formed by concrete hydration. The residue of surfactants can also lead to long-term degradation of the hydrophobic properties of concrete. Secondly, traditional silane hydrophobic systems can only reduce surface energy and cannot improve the micro-density of the near-surface layer of concrete. Their effect on inhibiting capillary water absorption and the migration of harmful ions in concrete in the long term is limited, making it difficult to achieve long-term protection.

[0004] To compensate for the shortcomings of a single silane hydrophobic system, existing technologies attempt to combine silanes with inorganic nanomaterials, utilizing the filling and nucleation effects of inorganic nanomaterials to improve the microstructure of the concrete surface. Among these, nano-CSH is a preferred composite inorganic phase due to its consistency with cement hydration products and good compatibility. Nano-CSH can act as heterogeneous nucleation sites to promote cement hydration, refine hydration product grains, seal capillary channels on the concrete surface, and improve matrix density. However, when applying nano-CSH and silane composites to hydrophobic modification of concrete surfaces, insurmountable technical challenges remain: First, nano-CSH is prone to flocculation and agglomeration in the strongly alkaline and high ionic strength environment of concrete, exhibiting poor dispersion stability and difficulty in forming a uniform coating layer on the concrete surface, thus failing to fully exert its densifying effect; Second, silanes are prone to rapid self-hydrolysis and self-condensation reactions in alkaline environments, and when simply compounded with nano-CSH, silane self-polymerization and gelation easily occur. The problem of phase separation of nano-CSH makes it impossible to effectively combine organosilanes and inorganic nano-CSH, resulting in poor storage stability and insufficient construction consistency of the composite system. Thirdly, the existing silane-nano-CSH composite process lacks precise control over the reaction process. The hydrolysis and condensation of silane and the surface modification of nano-CSH cannot proceed in synergy. The prepared composite system cannot be adapted to the critical construction window after the initial setting and before the final setting of concrete. If construction is carried out after the final setting of concrete, the composite system is difficult to effectively penetrate to the near-surface layer of concrete, and the interfacial bonding strength is low. If construction is carried out before the initial setting, it will interfere with the normal hydration process of concrete and affect the properties of the concrete itself.

[0005] Furthermore, in existing composite preparation processes of silane and nanomaterials, the preparation of silane hydrolysate often lacks precise pH control. Excessive or insufficient acidity can lead to incomplete hydrolysis of silane or rapid self-polymerization after hydrolysis. In addition, the surface modification of nano-inorganic materials has not been specifically designed for activation, preventing the hydrophobic groups of silane from achieving directional bonding with the nano-inorganic phase. As a result, the prepared composite system cannot guarantee a stable hydrophobic effect, nor can it improve the density and interfacial bonding strength of the concrete surface through the action of the nano-phase. Ultimately, the hydrophobic, impermeable, and interfacial bonding properties of the composite modified material cannot be simultaneously achieved.

[0006] In summary, existing technologies for hydrophobic modification of concrete surfaces suffer from several drawbacks. Single silane systems offer limited protective effects, poor environmental friendliness, and insufficient stability in strongly alkaline environments. Meanwhile, composite systems combining silane and nano-CSH face numerous technical bottlenecks, including unstable nanophase dispersion, uncontrollable silane reaction processes, ineffective integration of organic and inorganic phases, and a lack of suitable processes for early-age concrete construction. Currently, no method has been developed to achieve synergistic effects between the hydrophobic properties of silane and the densification properties of nano-CSH, ensure stable existence in strongly alkaline cement hydration systems, and be suitable for construction within the window from initial setting to final setting of concrete. This makes it difficult to meet the practical needs of engineering projects for efficient and long-lasting hydrophobic modification of concrete surfaces. Summary of the Invention

[0007] The technical problem to be solved and the technical task proposed by this invention is to improve and refine existing technical solutions, and to provide a method for preparing silane composite nano-CSH for hydrophobic modification of concrete surfaces and its application, so as to achieve efficient and long-term protection of concrete surfaces. To this end, this invention adopts the following technical solution.

[0008] Firstly, a method for preparing silane composite nano-CSH for hydrophobic modification of concrete surfaces is provided, comprising the following steps: Preparation of silane hydrolysate A: Ethanol: Deionized water: n-octyltriethoxysilane = 50: 1: (1.5~2.5) by mass ratio. Mix ethanol and deionized water evenly, adjust the pH of the system to acidic with acid, slowly add n-octyltriethoxysilane dropwise, and hydrolyze the system under stirring. After the hydrolysis reaction, adjust the pH of the system to near neutral with alkali to obtain solution A. Preparation of aminated dispersion B on the surface of nano-CSH: Nano-CSH was dispersed in an alkaline medium, and the solid content and pH value of the system were adjusted with saturated lime water. γ-aminopropyltriethoxysilane was slowly added dropwise under stirring to allow γ-aminopropyltriethoxysilane to react with the surface of nano-CSH to obtain liquid B. Composite reaction and post-treatment: Liquid A was added to liquid B, and a condensation reaction occurred under stirring, causing the hydrolysis product of n-octyltriethoxysilane to covalently condense with the nano-CSH surface activated by γ-aminopropyltriethoxysilane; then alcohols were removed, and the solid content and pH of the system were adjusted with saturated lime water to obtain a silane composite nano-CSH suspension.

[0009] As a preferred technical means: In the step of preparing silane hydrolysate A, the pH of the system is adjusted to 4.5~5.5 with glacial acetic acid, and n-octyltriethoxysilane is slowly added dropwise. After the addition is completed, stirring is continued, and then the pH of the system is adjusted to 6.5~7.0 with triethylamine to obtain solution A.

[0010] As a preferred technical means: In the step of preparing nano-CSH surface aminated dispersion B, 100 parts by weight of nano-CSH based on solids are added, the solid content is adjusted to 8 wt% with saturated lime water, the pH is adjusted to 10.8~11.2, and 0.4~0.5 parts by weight of γ-aminopropyltriethoxysilane are slowly added dropwise. After the addition is completed, stirring is continued to obtain liquid B.

[0011] As a preferred technical means: in the step of preparing the nano-CSH surface aminated dispersion B, the volume median diameter D of the nano-CSH is... 50 The wavelength range is 80~150nm, and the solid content is 8~12wt%.

[0012] As a preferred technical means, the nano-CSH is prepared by the following method: at room temperature, 32-48 parts by weight of 4 mol / L sodium silicate solution and 32-48 parts by weight of 4 mol / L calcium nitrate solution are simultaneously added dropwise to 100 parts by weight of 10-15 wt% polycarboxylate superplasticizer solution, and the mixture is stirred continuously. After the addition is completed, the pH of the system is adjusted to 11.2-12.2, and the mixture is stirred continuously to obtain a nano-CSH suspension.

[0013] As a preferred technical means: in the composite reaction and post-processing steps, liquid A is added at a rate of 0.3~0.5 vol%·min. - ¹ is added to liquid B at a dropping rate of 1, the stirring speed is 800~1200 rpm, and the condensation reaction time is 100~150 min.

[0014] As a preferred technical means: in the composite reaction and post-treatment steps, the removal of alcohols is carried out by depressurized deethanolination, so that the residual alcohol content is ≤1wt%; the adjustment of the solid content and pH value of the system is carried out by adjusting the solid content to 8wt% and the pH to 10.8~11.2 with saturated lime water.

[0015] Secondly, an application of silane composite nano-CSH prepared by the aforementioned method in hydrophobic modification of concrete surface is provided. The concrete surface is sprayed after the initial setting and before the final setting of the concrete, and the spraying amount is 200~300g / m², based on the mass of the suspension.

[0016] Beneficial effects: In a weakly acidic environment of ethanol / water, octyltriethoxysilane (OTES) undergoes controlled hydrolysis to generate active silanol (Si-OH). The system is then adjusted to near neutrality with triethylamine to stabilize its condensable state. Simultaneously, nano-CSH is dispersed in an alkaline medium of saturated limewater. Its surface is rich in Si-OH / Si-O-Ca active sites. γ-aminopropyltriethoxysilane (APTES) undergoes initial alcoholysis / hydrolysis and condenses with the nano-CSH surface to form Si-O-Si / Si-O-Ca covalent bonds, achieving amination and activation of the nano-CSH particle surface and providing Lewis basic sites to catalyze subsequent condensation reactions. When silanol-containing liquid A is added to the activated liquid B, the silanol obtained from acidic hydrolysis preferentially undergoes directional condensation and crosslinking with the silane groups introduced by APTES and the surface silanol at the CSH interface, constructing an organic-inorganic synergistic network with inorganic nano-CSH as the framework and siloxanes as bridges. The hydrophobic octyl segments are oriented outward to form a low surface energy layer. An alkaline environment and sufficient shear force make interfacial condensation preferential over bulk self-condensation. Reduced pressure de-alcoholization pushes the reaction equilibrium to generate more Si-O-Si / Si-O-Ca bonds by removing ethanol / water, resulting in a dense, alkali-resistant, and covalently bonded layer that is compatible with the cement hydration system. This layer simultaneously achieves chemical low surface energy and physical sealing on the micro- and nano-pore walls of concrete, significantly reducing the surface energy of the pore walls and the effective cross-section of the interconnected pores, thereby inhibiting capillary water absorption and chloride ion migration, and ensuring long-term bonding stability with the concrete matrix.

[0017] This invention achieves APTES interface activation and controlled hydrolysis-condensation of OTES in an alkaline saturated lime water system, constructing an organic-inorganic synergistic network chemically bonded to the concrete matrix. This results in high compatibility between the product and the cement hydration system, with rapid effectiveness during the initial to final setting period: a stable hydrophobic layer (water contact angle ≥100°) is formed within 24 hours after spraying. By reducing the surface energy of the pore walls and partially sealing and connecting capillaries, the capillary water absorption coefficient decreases by ≥30% after 7 days compared to the untreated control; simultaneously, it significantly inhibits chloride ion migration, showing an increase in chloride ion permeability of ≥50% after 28 days of salt spray. The pH is matched to the cement hydration environment, and the residual alcohol content is ≤1wt%, reducing the adverse effects on early concrete hydration and interfacial bonding. The nano-CSH framework provides the composite system with excellent water and alkali resistance stability and long-term adhesion. Attached Figure Description

[0018] Figure 1 This is a schematic diagram comparing the water contact angle of concrete surfaces in embodiments, comparative examples, and untreated groups according to the present invention. Detailed Implementation

[0019] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings.

[0020] This invention relates to silane composite nano-CSH surface-modified materials suitable for alkaline liquid phase environments and their application methods. Unless otherwise specified, "parts" refers to parts by mass, wt% to mass fraction; vol% to volume fraction; pH is determined at 25±2°C; "saturated lime water" refers to a saturated Ca(OH)2 aqueous solution; particle size D... 50 This is the median diameter of the volume.

[0021] This invention provides a method for preparing silane composite nano-CSH for hydrophobic modification of concrete surfaces, comprising the following steps: Preparation of silane hydrolysate A: Ethanol: Deionized water: n-octyltriethoxysilane = 50: 1: (1.5~2.5) by mass ratio. Mix ethanol and deionized water evenly, adjust the pH of the system to acidic with acid, slowly add n-octyltriethoxysilane dropwise, and hydrolyze the system under stirring. After the hydrolysis reaction, adjust the pH of the system to near neutral with alkali to obtain solution A. Preparation of nano-CSH surface aminated dispersion B: Nano-CSH was dispersed in an alkaline medium, and the solid content and pH value of the system were adjusted with saturated lime water. γ-aminopropyltriethoxysilane was slowly added dropwise under stirring to allow APTES to react with the nano-CSH surface to obtain liquid B. Composite reaction and post-treatment: Liquid A was added to liquid B, and a condensation reaction occurred under stirring, causing the hydrolysis product of n-octyltriethoxysilane to covalently condense with the nano-CSH surface activated by γ-aminopropyltriethoxysilane; then alcohols were removed, and the solid content and pH of the system were adjusted with saturated lime water to obtain a silane composite nano-CSH suspension.

[0022] Preparation of nano-CSH (basic raw materials) The volume median diameter D of the nano-CSH used in this embodiment 50 With a wavelength of 80-150 nm and a solid content of 8-12 wt%, this nano-CSH was prepared using a co-precipitation method. The specific steps are as follows: At room temperature (25±2℃), 32–48 parts of 4 mol / L sodium silicate solution and 32–48 parts of 4 mol / L calcium nitrate solution were simultaneously added dropwise to 100 parts of 10–15 wt% polycarboxylate superplasticizer (PCE) solution using two dropper pumps. The dropping rate was controlled at 2–3 mL / min (based on the volume of sodium silicate solution), with continuous stirring (500 rpm). After the addition was complete, the pH of the system was adjusted to 11.7 with saturated lime water, and stirring was continued for 24 h to obtain a nano-CSH suspension. The particle size of nano-CSH can be controlled by adjusting the mass ratio of sodium silicate to calcium nitrate. Table 1 lists the particle size and solid content parameters of nano-CSH obtained under several typical ratios.

[0023] Table 1. CSH preparation process parameters

[0024] Example 1 (1) Preparation of silane hydrolysate A: Weigh out 500 parts anhydrous ethanol, 10 parts deionized water, and 15 parts OTES according to a mass ratio of ethanol:deionized water:OTES = 50:1:1.5. Add the ethanol and deionized water to the reaction flask and stir well. Adjust the pH of the system to 5.0 with glacial acetic acid, and then slowly add OTES dropwise while stirring, controlling the dropwise addition rate to about 1 part / min. After the addition is complete, continue stirring for 30 min. Then adjust the pH of the system to 6.8 with triethylamine to obtain solution A.

[0025] (2) Preparation of nano-CSH surface aminated dispersion B: Take 100 parts (based on solids) of nano CSH (using CSH-01 formulation), add an appropriate amount of saturated lime water, adjust the solid content of the system to 8 wt%, adjust the pH to 11.2, and stir evenly. Under stirring, slowly add 0.45 parts of APTES dropwise over 20 min, and continue stirring for 30 min after the addition is complete to obtain liquid B.

[0026] (3) Composite reaction and post-treatment: Liquid B was placed in a reaction flask, and under stirring conditions of 25°C and 1000 rpm, liquid A was added at a rate of 0.4 vol%·min. - ¹The solution was added dropwise to solution B at a rate of (based on the total volume of solution A). After the addition was complete, the mixture was stirred for another 120 min. After the reaction was complete, the solution was subjected to reduced pressure at ≤40℃ until the residual alcohol content was ≤1 wt%. Finally, the solid content of the system was adjusted to 8 wt% and the pH was adjusted to 11.0 with saturated lime water to obtain a silane composite nano-CSH suspension.

[0027] Example 2 (1) Preparation of silane hydrolysate A: Weigh out 500 parts of anhydrous ethanol, 10 parts of deionized water, and 25 parts of OTES according to the mass ratio of ethanol:deionized water:OTES = 50:1:2.5. Mix the ethanol and deionized water thoroughly, adjust the pH of the system to 4.8 with glacial acetic acid, add OTES dropwise (approximately 1.5 parts / min), and stir for 30 min after the addition is complete. Then adjust the pH of the system to 7.0 with triethylamine to obtain solution A.

[0028] (2) Preparation of nano-CSH surface aminated dispersion B: Take 100 parts (based on solids) of nano CSH (using CSH-02 formula), adjust the solid content to 8 wt% and pH to 11.0 with saturated lime water, add 0.5 parts of APTES dropwise over 20 min while stirring, and then stir for another 30 min to obtain solution B.

[0029] (3) Composite reaction and post-treatment: Liquid A was dispensed at 0.5 vol%·min - ¹Add dropwise into liquid B, stir at 1000 rpm for 120 min, then de-alcoholize under reduced pressure until residual alcohol is ≤1 wt%, adjust the solid content to 8 wt% and pH to 11.2 with saturated lime water to obtain the product.

[0030] Example 3 (1) Preparation of silane hydrolysate A: Weigh out 500 parts of anhydrous ethanol, 10 parts of deionized water, and 20 parts of OTES according to the mass ratio of ethanol:deionized water:OTES = 50:1:2.0. Mix the ethanol and deionized water thoroughly, adjust the pH of the system to 5.2 with glacial acetic acid, add OTES dropwise (approximately 1.2 parts / min), and stir for 30 min after the addition is complete. Then adjust the pH of the system to 6.5 with triethylamine to obtain solution A.

[0031] (2) Preparation of nano-CSH surface aminated dispersion B: Take 100 parts (based on solids) of nano CSH (using CSH-03 formula), adjust the solid content to 8 wt% and pH to 11.8 with saturated lime water, add 0.4 parts of APTES dropwise over 20 min while stirring, and then stir for another 30 min to obtain solution B.

[0032] (3) Composite reaction and post-treatment: Liquid A was dispensed at 0.3 vol%·min - ¹Add dropwise into liquid B, stir at 1000 rpm for 120 min, then de-alcoholize under reduced pressure until residual alcohol is ≤1 wt%, adjust the solid content to 8 wt% and pH to 11.8 with saturated lime water to obtain the product.

[0033] Example 4 (1) Preparation of silane hydrolysate A: Weigh out 500 parts anhydrous ethanol, 10 parts deionized water, and 25 parts OTES according to the mass ratio of ethanol:deionized water:OTES = 50:1:2.5. Mix the ethanol and deionized water thoroughly, adjust the pH of the system to 5.0 with glacial acetic acid, add OTES dropwise (at a rate of about 1 part / min), stir for 30 minutes after the addition is complete, and then adjust the pH of the system to 6.7 with triethylamine to obtain solution A.

[0034] (2) Preparation of nano-CSH surface aminated dispersion B: Take 100 parts (based on solids) of nano CSH (using CSH-04 formula), adjust the solid content of the system to 8 wt% and the pH to 11.8 with saturated lime water, add 0.45 parts of APTES dropwise over 20 min while stirring, and stir for another 30 min after the addition is complete to obtain solution B.

[0035] (3) Composite reaction and post-treatment: Liquid A was dispensed at 0.4 vol%·min - ¹ is added dropwise to liquid B, and the mixture is stirred at 1000 rpm for 120 min to induce a condensation reaction. Then, the alcohol is removed under reduced pressure until the residual alcohol in the system is ≤1 wt%. The solid content of the system is adjusted to 8 wt% and the pH is adjusted to 11.2 with saturated lime water to obtain the product.

[0036] Example 5 (1) Preparation of silane hydrolysate A: Weigh out 500 parts anhydrous ethanol, 10 parts deionized water, and 15 parts OTES according to the mass ratio of ethanol:deionized water:OTES = 50:1:1.5. Mix the ethanol and deionized water thoroughly, adjust the pH of the system to 5.1 with glacial acetic acid, add OTES dropwise (at a rate of about 1 part / min), stir for 30 min after the addition is complete, and then adjust the pH of the system to 6.9 with triethylamine to obtain solution A.

[0037] (2) Preparation of nano-CSH surface aminated dispersion B: Take 100 parts (based on solids) of nano CSH (using CSH-05 formula), adjust the solid content of the system to 8 wt% and the pH to 11.0 with saturated lime water, add 0.4 parts of APTES dropwise over 20 min while stirring, and stir for another 30 min after the addition is complete to obtain solution B.

[0038] (3) Composite reaction and post-treatment: Liquid A was dispensed at 0.3 vol%·min - ¹ is added dropwise to liquid B, and the mixture is stirred at 1000 rpm for 120 min to induce a condensation reaction. Then, the alcohol is removed under reduced pressure until the residual alcohol in the system is ≤1 wt%. The solid content of the system is adjusted to 8 wt% and the pH is adjusted to 11.0 with saturated lime water to obtain the product.

[0039] Example 9 (1) Preparation of silane hydrolysate A Weigh out 500 parts anhydrous ethanol, 10 parts deionized water, and 25 parts OTES according to a mass ratio of ethanol:deionized water:OTES = 50:1:2.5. Add the ethanol and deionized water to the reaction flask and stir well. Adjust the pH of the system to 5.0 with glacial acetic acid, and then slowly add OTES dropwise while stirring, controlling the dropwise rate to about 1.5 parts / min. After the dropwise addition is complete, continue stirring for 30 min. Then adjust the pH of the system to 6.8 with triethylamine to obtain solution A.

[0040] (2) Preparation of nano-CSH surface aminated dispersion B Take 100 parts (based on solids) of nano CSH (using CSH-09 formulation), add an appropriate amount of saturated lime water, adjust the solid content of the system to 8 wt%, adjust the pH to 11.0, and stir evenly. Under stirring, slowly add 0.45 parts of γ-aminopropyltriethoxysilane (APTES) dropwise over 20 min. After the addition is complete, continue stirring for 30 min to obtain liquid B.

[0041] (3) Composite reaction and post-treatment Liquid B was placed in a reaction flask, and under stirring conditions of 25°C and 1000 rpm, liquid A was added at a rate of 0.3 vol%·min. - ¹The solution was added dropwise to solution B at a rate of (based on the total volume of solution A). After the addition was complete, the mixture was stirred for another 120 min. After the reaction was complete, the solution was subjected to reduced pressure at ≤40℃ until the residual alcohol content was ≤0.8 wt%. Finally, the solid content of the system was adjusted to 8 wt% and the pH was adjusted to 11.2 with saturated lime water to obtain a silane composite nano-CSH suspension.

[0042] Comparative Example 1 (without OTES) (1) Preparation of silane hydrolysate A: The operation steps are the same as in Example 1, except that OTES (i.e., ethanol:deionized water = 50:1, without silane) is not added. All other operations are the same, and solution A (without silane) is obtained.

[0043] (2) Preparation of nano-CSH surface aminated dispersion B: Same as the operation steps in Example 1, without adjustment.

[0044] (3) Combination reaction and post-processing: The operation steps are the same as in Example 1, without any adjustment, to obtain the product (silane without OTES modification).

[0045] Comparative Example 2 (without APTES activation) (1) Preparation of silane hydrolysate A: Same as the operation steps in Example 3, without adjustment.

[0046] (2) Preparation of nano CSH dispersion B: Take 100 parts (based on solids) of nano CSH (using CSH-03 formula), adjust the solid content of the system to 8wt% and pH to 11.8 with saturated lime water, stir evenly, and do not add APTES for surface activation to obtain liquid B (unaminated).

[0047] (3) Composite reaction and post-processing: The operation steps are the same as in Example 3, without any adjustment, to obtain the product (nano CSH without APTES activation).

[0048] The core process parameters of the above embodiments and comparative examples are shown in Table 2. To avoid redundancy, the detailed steps of Examples 6-8 are omitted, and only the key process parameters are recorded in Table 2.

[0049] Table 2 Process parameters for examples and comparative examples

[0050] The main performance results of the embodiments and comparative examples of this invention were obtained using the same age and environment.

[0051] The suspensions obtained from the above examples and comparative examples were used for concrete surface treatment, and their performance was tested. All examples and comparative examples were tested under the same conditions of 20±2°C and 50–60% relative humidity, with the same mixing, curing, and age.

[0052] 1. Concrete slab preparation: C30 concrete was used to form 100mm×100mm×50mm slabs. After standard curing for 24 hours, the slabs were demolded and then cured under standard conditions until initial setting but before final setting (approximately 4-6 hours). Spraying was then performed. The spraying amount was 250±20g / m², applied in two coats with an interval of 10-15 minutes. The nozzle diameter was 1.3mm, the pressure was 0.20-0.25MPa, and the spraying distance was 20-25cm. After spraying, standard curing continued until the specified age for testing.

[0053] 2. Water contact angle test: The static drip method was used. 5 μL of deionized water was dropped, and the reading was taken 5 seconds after dropping. Five points were tested on each test plate and the average value was taken.

[0054] 3. Capillary water absorption coefficient test: Refer to ASTM C1585, test the capillary water absorption curve within 7 days, and take the slope of the initial linear segment as the capillary water absorption coefficient.

[0055] 4. Chloride ion permeability test: Refer to ASTM C1202 (RCPT method) to test the 6-hour electrical flux of 28-day-old specimens.

[0056] 5. Surface Pull-out Strength Test: Following ASTM C1583, a 50mm diameter metal pull-out head is bonded to the surface of the test plate. A 5mm deep annular groove is cut along the perimeter. A load is applied at a rate of 0.06 MPa / s, and the failure load is recorded. The pull-out strength is calculated, and only data from internal matrix failure are statistically analyzed. The strength calculation formula is as follows:

[0057] in, Where is the drawing strength (MPa), and D is the diameter of the drawing head (mm). The maximum destructive load (N).

[0058] The test results are shown in Table 3.

[0059] Table 3 Performance test results of the examples and comparative examples

[0060] As shown in Table 3, the silane composite nano-CSH suspensions prepared in Examples 1-9 of this invention, when used for hydrophobic modification and densification treatment of concrete surfaces, exhibit significantly better overall performance than the untreated group: 24h water contact angle ≥104° (maximum 116°), 7d capillary water absorption coefficient reduced by 36.0%~53.6% compared to the untreated group, 24h pull-out at 5mm relatively increased by 75.0%~115.0%, and 28d RCPT electrical flux reduced by 52.4%~66.7%. Among them, Example 9 showed the best overall performance (24h contact angle reached 116°, capillary water absorption coefficient decreased by 53.6%, 5mm pull-out increased by 115.0%, and 28d RCPT electrical flux decreased by 66.7%); Example 6 also achieved a 115.0% improvement in concrete surface pull-out, demonstrating excellent performance.

[0061] The above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A method for preparing silane composite nano-CSH for hydrophobic modification of concrete surfaces, characterized in that, Includes the following steps: Preparation of silane hydrolysate A: Ethanol: Deionized water: n-octyltriethoxysilane = 50: 1: (1.5~2.5) by mass ratio. Mix ethanol and deionized water evenly, adjust the pH of the system to acidic with acid, slowly add n-octyltriethoxysilane dropwise, and hydrolyze the system under stirring. After the hydrolysis reaction, adjust the pH of the system to near neutral with alkali to obtain solution A. Preparation of aminated dispersion B on the surface of nano-CSH: Nano-CSH was dispersed in an alkaline medium, and the solid content and pH value of the system were adjusted with saturated lime water. γ-aminopropyltriethoxysilane was slowly added dropwise under stirring to allow γ-aminopropyltriethoxysilane to react with the surface of nano-CSH to obtain liquid B. Composite reaction and post-treatment: Liquid A was added to liquid B, and a condensation reaction occurred under stirring, causing the hydrolysis product of n-octyltriethoxysilane to covalently condense with the nano-CSH surface activated by γ-aminopropyltriethoxysilane; then alcohols were removed, and the solid content and pH of the system were adjusted with saturated lime water to obtain a silane composite nano-CSH suspension.

2. The method for preparing silane composite nano-CSH for hydrophobic modification of concrete surfaces according to claim 1, characterized in that: In the step of preparing silane hydrolysate A, the pH of the system is adjusted to 4.5-5.5 with glacial acetic acid, and n-octyltriethoxysilane is slowly added dropwise. After the addition is complete, stirring is continued, and then the pH of the system is adjusted to 6.5-7.0 with triethylamine to obtain solution A.

3. The method for preparing silane composite nano-CSH for hydrophobic modification of concrete surfaces according to claim 1, characterized in that: In the step of preparing nano-CSH surface aminated dispersion B, 100 parts by weight of nano-CSH (based on solids) are added, the solid content is adjusted to 8 wt% with saturated lime water, the pH is adjusted to 10.8~11.2, and 0.4~0.5 parts by weight of γ-aminopropyltriethoxysilane are slowly added dropwise. After the addition is complete, stirring is continued to obtain liquid B.

4. The method for preparing silane composite nano-CSH for hydrophobic modification of concrete surfaces according to claim 1, characterized in that: In the step of preparing the nano-CSH surface-aminated dispersion B, the volume median diameter D of the nano-CSH is... 50 The wavelength range is 80~150nm, and the solid content is 8~12wt%.

5. The method for preparing silane composite nano-CSH for hydrophobic modification of concrete surfaces according to claim 4, characterized in that: The nano-CSH was prepared by the following method: at room temperature, 32-48 parts by weight of 4 mol / L sodium silicate solution and 32-48 parts by weight of 4 mol / L calcium nitrate solution were simultaneously added dropwise to 100 parts by weight of 10-15 wt% polycarboxylate superplasticizer solution, and the mixture was stirred continuously. After the addition was completed, the pH of the system was adjusted to 11.2-12.2, and the mixture was stirred continuously to obtain a nano-CSH suspension.

6. The method for preparing silane composite nano-CSH for hydrophobic modification of concrete surfaces according to claim 1, characterized in that: In the combined reaction and post-treatment steps, liquid A is reacted at a rate of 0.3~0.5 vol%·min. - ¹ is added to liquid B at a dropping rate of 1, the stirring speed is 800~1200 rpm, and the condensation reaction time is 100~150 min.

7. The method for preparing silane composite nano-CSH for hydrophobic modification of concrete surfaces according to claim 1, characterized in that: In the combined reaction and post-treatment steps, the removal of alcohols is carried out by depressurized deethanolination, so that the residual alcohol content is ≤1wt%; the solid content and pH of the system are adjusted by using saturated lime water to adjust the solid content to 8wt% and the pH to 10.8~11.

2.

8. The application of silane composite nano-CSH prepared by the preparation method according to any one of claims 1 to 7 in the hydrophobic modification of concrete surfaces, characterized in that: The concrete surface is sprayed after the initial setting and before the final setting of the concrete, with a spraying amount of 200~300g / m², based on the mass of the suspension.

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