Hydrophobic-photocatalytic composite cementitious material and method of making

Abstract

The application discloses a hydrophobic-photocatalytic composite cement material and a preparation method, and relates to the technical field of inorganic non-metallic materials, and comprises the following steps: S1, taking 89wt% of a silicate cement matrix, 10wt% of a TiO2 photocatalyst and 1.0wt% of a stearic acid hydrophobic agent according to the mass percentage; S2, the silicate cement, the TiO2 photocatalyst and the stearic acid hydrophobic agent are preliminarily mixed by mechanical stirring to obtain a mixture; S3, the mixture is added into a ball mill for ball milling modification, grinding balls with different diameters are matched according to a certain proportion, the rotating speed of the ball mill and the ball milling time are controlled, the overall hydrophobic property and the photocatalytic property of the composite cement material are endowed, and the hydrophobic-photocatalytic composite cement material is obtained after discharging. The application realizes the uniform dispersion of the TiO2 photocatalyst in the cement matrix through ball milling, and simultaneously makes the stearic acid hydrophobic agent fully dispersed in the cement particles, so that the overall hydrophobic property and the photocatalytic property of the composite cement material are endowed, instead of the local hydrophobic property and the photocatalytic property of the surface coating.

Description

Technical Field

[0001] This invention relates to the field of inorganic non-metallic materials technology, and more specifically to the field of a hydrophobic-photocatalytic composite cement material and its preparation method. It is applicable to the production and application of green building cementitious materials. Background Technology

[0002] In the context of green building development, cement-based materials not only need to meet traditional physical and mechanical properties, but are also endowed with functions such as environmental purification, making photocatalytic cement-based materials a research hotspot. These materials use cement as a carrier to immobilize nano-photocatalysts, which can degrade organic pollutants and purify air and water, showing significant application value in urban roads, sewage treatment plants, bridges, and other scenarios.

[0003] However, existing photocatalytic cement-based materials have significant technical defects: during service, the surface is prone to adsorbing stains such as fallen leaves, dust, and algae, which block light and prevent the photocatalyst from being effectively activated, resulting in the failure of photocatalytic activity; at the same time, nano-photocatalysts such as TiO2 will accelerate the carbonization of cement-based materials, reduce the pH value of the matrix, and cause steel corrosion, which seriously affects the durability of reinforced concrete structures and significantly shortens the service life of materials.

[0004] To address the issue of photocatalytic activity failure, researchers have proposed a hydrophobic-photocatalytic composite strategy. This involves introducing hydrophobic modifiers to prepare hydrophobic-photocatalytic cement-based materials, achieving self-cleaning properties. Current preparation methods often employ coatings to combine hydrophobic-photocatalytic materials with cement-based materials, such as spraying or dipping polymethylhydrosiloxane-modified TiO2, or synthesizing hydrophobic TiO2 using a solvothermal method followed by coating. However, these coating methods suffer from weak adhesion and easy detachment, failing to achieve the overall hydrophobic and photocatalytic performance of the material. Other studies have mixed hydrophobic nano-ZnO with white cement to prepare composite pellets, but these only focus on antibacterial properties and do not address the core issue of poor durability in photocatalytic cement-based materials. Furthermore, the preparation and durability optimization technologies for integral hydrophobic-photocatalytic composite cement have not yet been effectively developed.

[0005] The technological bottleneck of existing technologies lies in: 1) Hydrophobic-photocatalytic functions are mostly achieved in the form of coatings, which have poor adhesion to cement substrates, lack overall functional characteristics, and are prone to failure; 2) The photocatalytic performance and the durability of cement-based materials were not taken into account. The nano-photocatalyst accelerated carbonization, leading to steel corrosion. 3) There is a lack of a method for preparing composite cement materials that can be industrially produced and have excellent photocatalytic self-cleaning properties, overall hydrophobicity, and high durability.

[0006] Solving the aforementioned technical problems has become the focus of efforts for those skilled in the art. Summary of the Invention

[0007] The purpose of this invention is to address the technical problems of existing photocatalytic cement-based materials, such as easy surface contamination, easy failure of photocatalytic activity, poor durability, and the fact that hydrophobic-photocatalytic functions are mostly in the form of coatings with weak bonding to the substrate. This invention provides a hydrophobic-photocatalytic composite cement material and its preparation method.

[0008] To achieve the above objectives, the present invention specifically adopts the following technical solution: One aspect of the present invention provides a hydrophobic-photocatalytic composite cement material comprising, by mass percentage: 89 wt% silicate cement matrix, 10 wt% TiO2 photocatalyst, and 1.0 wt% stearic acid hydrophobic agent.

[0009] In one embodiment, the stearic acid is a non-fluorinated hydrophobic agent.

[0010] In one embodiment, the photocatalyst is TiO2.

[0011] Specifically, TiO2 is a photocatalyst, stearic acid is a non-fluorinated hydrophobic agent, and all raw materials are commonly used in industry, with wide availability and low cost.

[0012] The second aspect of the present invention provides a method for preparing a hydrophobic-photocatalytic composite cement material, which is used to prepare the above-mentioned hydrophobic-photocatalytic composite cement material. Ordinary silicate cement is used as the base material, and composite TiO2 photocatalyst and stearic acid hydrophobic agent are added. The hydrophobic-photocatalytic composite cement material is prepared by proportioning and mixing and ball milling modification process.

[0013] In one embodiment, a hydrophobic-photocatalytic composite cement material is prepared by using ordinary silicate cement as a base material, adding a composite TiO2 photocatalyst and a stearic acid hydrophobic agent, and then mixing and ball milling to obtain the material. The specific steps are as follows: S1. Raw material ratio: By mass percentage, take 89 wt% silicate cement matrix, 10 wt% TiO2 photocatalyst and 1.0 wt% stearic acid hydrophobic agent; S2. Raw material mixing: Silicate cement, TiO2 photocatalyst and stearic acid hydrophobic agent are mechanically stirred to initially mix and obtain a mixture. S3. Ball milling modification: The mixture is added to a ball mill for ball milling modification. Grinding balls of different diameters are matched in a certain proportion. The speed and milling time of the ball mill are controlled to achieve uniform dispersion of TiO2 photocatalyst in silicate cement matrix. At the same time, the stearic acid hydrophobic agent is fully dispersed in silicate cement matrix, giving the composite cement material overall hydrophobic and photocatalytic properties. The hydrophobic-photocatalytic composite cement material is obtained when the material is discharged.

[0014] Specifically, ball milling modification is the core of the process. Through ball milling, TiO2 photocatalyst is uniformly dispersed in the cement matrix, while stearic acid hydrophobic agent is fully dispersed in the cement particles, giving the composite cement material overall hydrophobic and photocatalytic properties, rather than the local hydrophobic and photocatalytic properties of the surface coating.

[0015] The performance of the hydrophobic-photocatalytic composite cement material meets the requirements of the national standard for silicate cement PO42.5. It has excellent photocatalytic performance, overall hydrophobic self-cleaning performance and durability. The degradation rate of Rhodamine B in 300 minutes is close to 100%. The contact angle of the unhydrated powder is ≥120° and the contact angle of the hydrated paste is ≥110°. The strength loss rate after freeze-thaw and sulfate attack is ≤11%. It can effectively protect the internal steel bars from corrosion.

[0016] In this material, stearic acid hydrophobic agent and TiO2 photocatalyst work synergistically. The introduction of stearic acid does not affect the photocatalytic activity of TiO2, and can improve the impermeability of cement-based materials, prevent corrosive ions and moisture from entering the matrix, alleviate the problem of accelerated carbonization caused by photocatalyst, and achieve a balance between photocatalytic performance, hydrophobicity and durability.

[0017] This material can be applied to green building projects in urban roads, sewage treatment plants, river and ocean bridges, etc., as a cementing material that combines environmental purification, self-cleaning and high durability.

[0018] In one embodiment, in step S3, the grinding balls are mixed in a ratio of 3cm large ball: 2.5cm medium ball: 1.5cm small ball = 3:3:4.

[0019] In one embodiment, in step S3, the rotational speed of the ball mill is controlled at 35 r / min. - ¹, Set the ball milling time to 60 minutes.

[0020] In one embodiment, in step S1, the silicate cement matrix is ​​prepared by mixing it into neat paste, mortar, or concrete using conventional processes.

[0021] In one embodiment, the silicate cement matrix is ​​prepared by selecting a water-cement ratio of 0.3, and after mixing, it is cured in an environment with a standard temperature of 20℃±1℃ and a humidity of 95%RH±2%RH to obtain silicate cement matrix products.

[0022] The beneficial effects of this invention are as follows: 1. The hydrophobic-photocatalytic composite cement material prepared by this invention meets the national standard requirements for silicate cement PO42.5, with 3-day flexural strength ≥ 5.0 MPa and compressive strength ≥ 22.0 MPa, 28-day flexural strength ≥ 6.5 MPa and compressive strength ≥ 42.5 MPa, and has qualified stability. It can be used as an engineering cementitious material for large-scale application.

[0023] 2. The composite cement material has excellent photocatalytic performance, and the degradation rate of organic pollutants such as Rhodamine B is close to 100% within 300 minutes. It also has good cycle stability. After 5 cycles, the degradation rate can still reach 90%. After wear, the fresh surface inside still maintains 100% degradation effect, and the photocatalytic activity is not easily degraded.

[0024] 3. The composite cement material achieves overall hydrophobicity, with an unhydrated powder contact angle of 123.9°, a hydrated slurry contact angle of 120.4°, and a mortar contact angle of 111.0°. Both the interior and surface of the matrix are hydrophobic, which can effectively prevent the adsorption of moisture and stains, achieve self-cleaning, and solve the problem of surface pollution of photocatalytic materials from the root.

[0025] 4. The composite cement material exhibits excellent durability. After freeze-thaw cycles and sulfate attack, the surface of the specimens showed no obvious damage or spalling, and the strength loss rate was only about 10%, which is much lower than that of ordinary photocatalytic cement-based materials. It also provides good protection for the internal reinforcing steel. After electrochemical corrosion in a 3.5wt% NaCl aqueous solution, the reinforcing steel showed no obvious rust. The corrosion current density was low and the impedance was high, which effectively prevented the intrusion of corrosive ions and alleviated the problem of reinforcing steel corrosion.

[0026] 5. The preparation process is simple, which can be achieved by mechanical stirring and ball milling modification. No complicated equipment is required. The raw materials are cement, TiO2 and stearic acid, which are widely available and inexpensive, and can be industrialized on a large scale.

[0027] 6. The hydrophobic modifier stearic acid works synergistically with the photocatalyst TiO2, which not only does not affect the photocatalytic activity of TiO2, but also makes up for the durability defects of cement-based materials caused by nano-photocatalysts, thus achieving a unity of photocatalytic performance, hydrophobic self-cleaning performance and durability.

[0028] 7. The composite cement prepared by this invention has excellent photocatalytic degradation performance, overall hydrophobic self-cleaning performance and mechanical properties. It can effectively resist freeze-thaw and sulfate erosion, protect the internal steel bars from corrosion, and the preparation process is simple and the raw materials are readily available. It can be industrially applied and meets the requirements of green building for cementitious materials to be multifunctional and highly durable. Attached Figure Description

[0029] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as a limitation of the scope. For those skilled in the art, other related drawings can be obtained from these drawings without creative effort.

[0030] Figure 1These are the contact angle diagram of the Blank sample, the appearance diagram of the Blank sample's resistance to freeze-thaw cycles and sulfate cycles, and the electrochemical corrosion results of the Blank sample.

[0031] Figure 2 These are the contact angle diagram of the B-10TiO2 / PC sample, the appearance diagram of the Blank sample's freeze-thaw resistance and sulfate cycle resistance, and the electrochemical corrosion result diagram of the Blank sample.

[0032] Figure 3 This is a diagram showing the preparation and performance testing of the hydrophobic-photocatalytic composite cement sample in this embodiment.

[0033] Figure 4 The graphs show the photodegradation and mechanical properties of the samples prepared for comparative examples 1 to 3.

[0034] Figure 5 The XRD patterns of the samples prepared in Example 1, Comparative Example 1 and Comparative Example 2 after 3 days and 28 days of hydration are shown.

[0035] Figure 6 These are the FTIR spectra of the samples prepared in Example 1, Comparative Example 1, and Comparative Example 2 after 3 days and 28 days of hydration.

[0036] Figure 7 These are test graphs of the TG curves, Ca(OH)2 and degree of hydration, hydration heat flow curves, and cumulative heat of hydration of the samples prepared in Example 1, Comparative Example 1, and Comparative Example 2.

[0037] Figure 8 This is a graph showing the calcium carbonate (CaCO3) content of the samples prepared in Example 1, Comparative Example 1, and Comparative Example 2 after 3 days and 28 days of hydration.

[0038] Figure 9 The graphs show the water absorption rate and corrosion current density test results for Comparative Examples 1 to Example 1. Detailed Implementation

[0039] To make the technical problems, technical solutions, and technical effects of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. The components of the embodiments of the present invention described and shown in the accompanying drawings can generally be arranged and designed in various different configurations.

[0040] Therefore, the following detailed description of the embodiments of the invention provided in the accompanying drawings is not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments of the invention. All other embodiments obtained by those skilled in the art based on the embodiments of the invention without inventive effort are within the scope of protection of the invention.

[0041] One aspect of the present invention provides a hydrophobic-photocatalytic composite cement material comprising, by weight percentage: 89 wt% silicate cement matrix, 10 wt% photocatalyst and 1.0 wt% stearic acid hydrophobic agent.

[0042] The stearic acid is a non-fluorinated hydrophobic agent.

[0043] The photocatalyst is TiO2.

[0044] Specifically, TiO2 is a photocatalyst, stearic acid is a non-fluorinated hydrophobic agent, and all raw materials are commonly used in industry, with wide availability and low cost.

[0045] The preparation method of this hydrophobic-photocatalytic composite cement material uses ordinary silicate cement as a base material, adds a composite TiO2 photocatalyst and stearic acid hydrophobic agent, and prepares a hydrophobic-photocatalytic composite cement material through proportioning and mixing and ball milling modification process. The specific steps are as follows: S1. Raw material ratio: By mass percentage, take 89wt% silicate cement matrix, 10wt% TiO2 photocatalyst and 1.0wt% stearic acid hydrophobic agent; prepare silicate cement matrix by mixing according to conventional process to make neat paste, mortar or concrete. Select water-cement ratio of 0.3 for preparing silicate cement matrix. After mixing, cure in an environment with standard temperature of 20℃±1℃ and humidity of 95%RH±2%RH to obtain silicate cement matrix products. S2. Raw material mixing: Silicate cement, TiO2 photocatalyst and stearic acid hydrophobic agent are mechanically stirred to initially mix and obtain a mixture. S3. Ball Milling Modification: The mixture is added to a ball mill for ball milling modification. The grinding balls are mixed in a ratio of 3cm large balls: 2.5cm medium balls: 1.5cm small balls = 3:3:4. The speed of the ball mill is controlled at 35 r / min. - ¹ The ball milling time is set to 60 min to achieve uniform dispersion of TiO2 photocatalyst in silicate cement matrix, while stearic acid hydrophobic agent is fully dispersed in silicate cement matrix, giving the composite cement material overall hydrophobic and photocatalytic properties, and the hydrophobic-photocatalytic composite cement material is obtained upon discharge.

[0046] Specifically, ball milling modification is the core of the process. Through ball milling, TiO2 photocatalyst is uniformly dispersed in the cement matrix, while stearic acid hydrophobic agent is fully dispersed in the cement particles, giving the composite cement material overall hydrophobic and photocatalytic properties, rather than the local hydrophobic and photocatalytic properties of the surface coating.

[0047] The performance of the hydrophobic-photocatalytic composite cement material meets the requirements of the national standard for silicate cement PO42.5. It has excellent photocatalytic performance, overall hydrophobic self-cleaning performance and durability. The degradation rate of Rhodamine B in 300 minutes is close to 100%. The contact angle of the unhydrated powder is ≥120° and the contact angle of the hydrated paste is ≥110°. The strength loss rate after freeze-thaw and sulfate attack is ≤11%. It can effectively protect the internal steel bars from corrosion.

[0048] In this material, stearic acid hydrophobic agent and TiO2 photocatalyst work synergistically. The introduction of stearic acid does not affect the photocatalytic activity of TiO2, and can improve the impermeability of cement-based materials, prevent corrosive ions and moisture from entering the matrix, alleviate the problem of accelerated carbonization caused by photocatalyst, and achieve a balance between photocatalytic performance, hydrophobicity and durability.

[0049] This material can be applied to green building projects in urban roads, sewage treatment plants, river and ocean bridges, etc., as a cementing material that combines environmental purification, self-cleaning and high durability.

[0050] To make the present invention more apparent and understandable, three samples were prepared using the following preferred comparative examples: Blank (pure cement sample), B-10TiO2 / PC (90wt% cement + 10wt% TiO2 comparative sample), and Example M-10TiO2 / PC (hydrophobic-photocatalytic composite cement sample of the present invention). Their performance was uniformly tested and compared, and detailed descriptions are provided below with reference to the accompanying drawings.

[0051] Example 1 This embodiment discloses the preparation and performance testing method of M-10TiO2 / PC (the hydrophobic-photocatalytic composite cement sample of this invention), as follows: S1. Raw material preparation: Ordinary silicate cement 42.5 was selected as the base material, TiO2 photocatalyst and stearic acid were selected as functional modifiers, and two samples prepared in Comparative Example 1 and Comparative Example 2 were used as variable controls. S2. Weighing of ingredients: Weigh 0.89 kg of cement, 0.1 kg of TiO2 photocatalyst, and 0.01 kg of stearic acid hydrophobic agent by mass percentage. The total mass is consistent with that of Blank in Comparative Example 1 and B-10TiO2 / PC sample in Comparative Example 2. S3. Mechanical mixing: Add the above three raw materials to the mixer and mix at a speed of 200 r·min. - ¹, Stir for 10 minutes to obtain a preliminarily mixed mixture; S4. Ball milling modification: The ball milling modification parameters were exactly the same as those of Comparative Example 1 (Blank sample) and Example 2 (B-10TiO2 / PC sample). After ball milling, the material was discharged to obtain the hydrophobic-photocatalytic composite cement material M-10TiO2 / PC of the present invention. S5. Performance Testing: Using the same testing standards, methods, and conditions as Comparative Example 1 and Comparative Example 2, test its mechanical properties, photocatalytic properties, hydrophobic properties, and durability.

[0052] Figure 3 These are the preparation and performance testing diagrams of the hydrophobic-photocatalytic composite cement sample in this embodiment; Figure 3 In the figure, a represents the contact angle of the B-10TiO2 / PC sample; b represents the appearance of the B-10TiO2 / PC sample under freeze-thaw and sulfate cycle resistance; and c represents the electrochemical corrosion results of the B-10TiO2 / PC sample.

[0053] Comparative Example 1 This embodiment discloses the preparation and performance testing method of Blank (pure cement sample), as follows: S1. Raw material preparation: Only ordinary Portland cement 42.5 was selected as the base material, without any functional modifiers added, to ensure that the raw materials were consistent with the other two samples and to ensure the accuracy of the test comparison; S2. Ingredient weighing: Accurately weigh 1 kg of cement (consistent with the total mass of other samples for easy performance comparison). S3. Mechanical mixing: Add cement to the mixer and mix at a speed of 200 rpm. - ¹, Stir for 10 minutes to obtain uniform pure cement material; S4. Ball Milling Treatment: Add the above materials to the LHK experimental ball mill. The grinding balls are mixed in a ratio of 3cm large balls: 2.5cm medium balls: 1.5cm small balls = 3:3:4. Set the ball mill speed to 35 r / min. - ¹, ball mill for 60 minutes, and the discharged material is the Blank pure cement sample; S5. Performance Testing: Performance testing will be conducted according to the following unified standards, serving as a blank control: S51. Mechanical properties: Prepare neat cement paste and mortar specimens according to GB / T17671–1999, and test the flexural and compressive strength at 3d and 28d after standard curing; S52. Photocatalytic performance: The photocatalytic degradation rate of Rhodamine B (RhB) by the tested sample was calculated using the formula η=(A0-A...). t ) / A0×100% (A0 is the absorbance of the supernatant before the photocatalytic reaction, A t (Absorbance of supernatant at different reaction times). S53. Hydrophobic properties: The static contact angle of unhydrated powder and hydrated cement paste / mortar was tested using the seat drop method and a contact angle measuring instrument. S54. Durability: Perform freeze-thaw cycles and sulfate corrosion tests according to GB / T50082-2009, and record the strength loss rate and changes in the appearance of the specimens; perform electrochemical corrosion tests on steel bars according to electrochemical test methods, and record the corrosion current density, impedance and corrosion status of the steel bars.

[0054] Figure 1 The attached figures are for Comparative Example 1, where a is the contact angle of the Blank sample; b is the appearance of the Blank sample in terms of freeze-thaw resistance and sulfate cycle resistance; and c is the electrochemical corrosion result of the Blank sample. The contact angles of the unhydrated powder, paste, and mortar of the Blank samples prepared from pure cement were all below 90°, indicating that the Blank samples are hydrophilic. After freeze-thaw resistance and sulfate corrosion resistance, significant peeling and damage appeared at the edges of the Blank surface. In addition, after electrochemical corrosion, the Blank samples showed a large amount of rust on both the inside and outside, and the internal reinforcing steel was severely corroded.

[0055] Comparative Example 2 This embodiment discloses the preparation and performance testing method of B-10TiO2 / PC (90wt% cement + 10wt% TiO2 comparative sample), as follows: S1. Raw material preparation: Ordinary silicate cement 42.5 was selected as the base material, low-cost TiO2 photocatalyst was selected as the modifier, and no stearic acid hydrophobic agent was added. The sample was compared with the sample of Example 1. S2. Weighing of ingredients: Weigh 0.9 kg of cement and 0.1 kg of TiO2 photocatalyst accurately according to the mass percentage. The total mass is consistent with the Blank sample of Comparative Example 2 and the sample of Example 1. S3. Mechanical mixing: Add the above two raw materials to the mixer and mix at a speed of 200 r·min. - ¹, Stir for 10 minutes to obtain a preliminarily mixed mixture; S4. Ball milling modification: The ball milling modification parameters were exactly the same as those of Comparative Example 1 (Blank sample), and the ball mill output was B-10TiO2 / PC comparative sample. S5. Performance Testing: Using the same testing standards, methods, and conditions as Comparative Example 1 (Blank sample), its mechanical properties, photocatalytic properties, hydrophobic properties, and durability were tested. The focus was on comparing the changes in photocatalytic properties and durability to highlight the role of stearic acid hydrophobic agent.

[0056] Figure 2 In the figure, a represents the contact angle of the B-10TiO2 / PC sample; b represents the appearance of the B-10TiO2 / PC sample under freeze-thaw and sulfate cycle resistance; and c represents the electrochemical corrosion results of the B-10TiO2 / PC sample. The contact angles of the unhydrated powder, paste, and mortar of the B-10TiO2 / PC sample prepared by adding pure cement and the photocatalyst TiO2 were all below 90°, indicating that the B-10TiO2 / PC sample is hydrophilic. After freeze-thaw and sulfate corrosion tests, significant peeling and damage appeared at the surface edges of the B-10TiO2 / PC. Furthermore, after electrochemical corrosion, the Blank sample showed extensive rust on both the internal and external surfaces of the B-10TiO2 / PC, and the internal reinforcing steel was severely corroded. This indicates that adding the photocatalyst TiO2 to cement did not improve the hydrophilicity and durability of the cement.

[0057] Figure 4 The figures show the photodegradation and mechanical properties of the samples prepared in Comparative Examples 1 to 3. In the figures, a represents the photodegradation properties of the Blank, B-10TiO2 / PC, and M-10TiO2 / PC samples; b represents the mechanical properties of the Blank, B-10TiO2 / PC, and M-10TiO2 / PC samples.

[0058] Under illumination, Blank without the photocatalyst TiO2 exhibited almost the same RhB degradation effect as RhB self-degradation, indicating that Blank lacks photocatalytic degradation capability. The Blank sample, after adding the photocatalyst TiO2, namely B-10TiO2 / PC, showed excellent photodegradation of RhB. The sample M-10TiO2 / PC, obtained by hydrophobic modification of B-10TiO2 / PC, also showed excellent photocatalytic activity, indicating that stearic acid does not significantly affect the photocatalytic activity of B-10TiO2 / PC. The mechanical properties of both M-10TiO2 / PC and B-10TiO2 / PC decreased at 3 days and 28 days, which may be related to the reduced cement content and the addition of the hydrophobic agent. However, the mechanical properties of M-10TiO2 / PC still meet the basic mechanical requirements of ordinary Portland cement.

[0059] Figure 5 These are the XRD patterns of samples prepared in Example 1, Comparative Example 1, and Comparative Example 2 at 3 days and 28 days of hydration. All samples contain typical hydrated phases (ettringite AFt, monosulfide calcium aluminate AFm, calcium hydroxide) and unhydrated phases (tricalcium silicate C3S, dicalcium silicate C2S, tetracalcium aluminoferrite C4AF, and tricalcium aluminate C3A). The results indicate that the addition of the photocatalyst TiO2 and stearic acid does not chemically react with cement to produce new phases. Furthermore, characteristic diffraction peaks of TiO2 were found in B-10TiO2 / PC and M-10TiO2 / PC cement pastes, indicating that the photocatalyst TiO2 was successfully incorporated into the cement paste.

[0060] Figure 6These are the FTIR spectra of the samples prepared in Example 1, Comparative Example 1, and Comparative Example 2 after 3 days and 28 days of hydration. The photocatalyst TiO2 is analyzed at 3600–3300 cm⁻¹. -1 The wavelength range exhibits a distinct broad band, which is typical of Ti-O characteristic absorption peaks. 3600–3300 cm⁻¹ was observed in both 3-day and 28-day B-10TiO₂ / PC and M-10TiO₂ / PC pastes. -1 The range exhibits similar broad bands. Apart from this, no other new Ti-containing absorption peaks were found in B-10TiO2 / PC and M-10TiO2 / PC, indicating that the photocatalyst TiO2 does not directly react with the hydration products and no new bonds are formed. Stearic acid is bound to the surface of cement particles through physical adsorption and electrostatic interactions; therefore, the -CH3 asymmetric stretching vibration of stearic acid (2918.2 cm⁻¹) was observed in the hydrated M-10TiO2 / PC. -1 ) and -CH2 symmetric stretching vibration (22849.2cm) -1 The absorption peak of M-10TiO2 / PC indicates that the hydrated M-10TiO2 / PC has hydrophobic groups.

[0061] Figure 7 This is a schematic diagram of the TG curves, Ca(OH)2 and degree of hydration, hydration heat flow curves, and cumulative heat of hydration for the samples prepared in Example 1, Comparative Example 1, and Comparative Example 2. In the figure, (a) is the TG curve for Blank, B-10TiO2 / PC, and M-10TiO2 / PC, (b) is the Ca(OH)2 and degree of hydration, (c) is the hydration heat flow curve, and (d) is the cumulative heat of hydration.

[0062] Depend on Figure 7 As shown in (a) and (b), for 3d M-10TiO2 / PC, the large surface area of ​​the TiO2 catalyst provides more active sites for hydration, thus accelerating hydration. The 3d hydration degree of B-10TiO2 / PC is higher than that of the Blank sample. However, after hydrophobic modification, the inherent hydrophobicity of M-10TiO2 / PC hinders hydration to some extent. Therefore, the hydration degree of M-10TiO2 / PC is higher than that of Blank but lower than that of B-10TiO2 / PC. The heat flow curves and cumulative heat effects of cement hydration heat are shown below. Figure 7 As shown in (c) and (d). In Figure 7 (c) All samples showed essentially the same performance during the dissolution phase. After the addition of the photocatalyst, the heat flow curves of B-10TiO2 / PC and M-10TiO2 / PC were significantly higher than those of Blank during both the induction and acceleration phases, while those of M-10TiO2 / PC were lower than those of B-10TiO2 / PC. This further confirms that the photocatalyst TiO2 can accelerate early hydration, while stearic acid can hinder hydration to some extent.

[0063] Figure 8 This is a graph showing the calcium carbonate (CaCO3) content of the samples prepared in Example 1, Comparative Example 1, and Comparative Example 2 after 3 days and 28 days of hydration. At 3 days and 28 days, the CaCO3 content of B-10TiO2 / PC was higher than that of Blank, indicating that the addition of a photocatalyst accelerates carbonation and generates more CaCO3. However, the CaCO3 content in the hydrophobically modified M-10TiO2 / PC was significantly lower than that in B-10TiO2 / PC. This demonstrates that the hydrophobically modified cementitious material can prevent water and other liquids from entering its interior, thereby hindering CO2 from the air from reacting and generating CaCO3.

[0064] Figure 9 In the middle: (a) Immersion water absorption of samples prepared in Comparative Examples 1, 2 and 3 at 3d(a) and 28d(b); (c) Potential kinetic polarization curves in 3.5wt% NaCl aqueous solution at 3d; and (d) Electrochemical impedance spectroscopy (EIS) spectra. L R is the resistance of the electrolyte. c R is the resistance of the mortar layer, C is the capacitance of the mortar layer, and R is the capacitance of the mortar layer. ct Q is the charge transfer resistance of the reinforcing bar, Q is the non-ideal double-layer capacitance of the reinforcing bar / mortar interface region, and W is the Warburg element that diffuses with the corrosion zone. Depend on Figure 9 As shown in (a) and (b), after hydrophobic modification, the water absorption rate of the M-10TiO2 / PC specimen initially increased rapidly at 3 days and then gradually slowed down with no significant change at 28 days. Compared with unmodified Blank and B-10TiO2 / PC, the water absorption rate of M-10TiO2 / PC was significantly lower. This phenomenon indicates that the hydrophobic properties of M-10TiO2 / PC effectively prevented water from entering the interior of the specimen. Figure 9 From (c) and (d), we can see that Blank (2.32 × 10) -7 A·cm -2 ) and B-10TiO2 / PC (5.13×10 - 7 A·cm -2 The corrosion current density of M-10TiO2 / PC was significantly higher than that of M-10TiO2 / PC (8.01×10) at 3d. -8 A·cm -2The corrosion current density of M-10TiO2 / PC is generally considered to be higher than that of B-10TiO2 / PC. Generally, the higher the corrosion current density, the faster the corrosion rate of the reinforcing steel. The response in the high-frequency region is information from the cement mortar layer and solution, while the response in the low-frequency region is the interface signal between the mortar and the reinforcing steel. The electrolyte impedance Rc of M-10TiO2 / PC with the mortar is much greater than that of Blank and B-10TiO2 / PC. The hydrophobicity of M-10TiO2 / PC increases the resistance of corrosive ions to entering the interior of the cementitious material, leading to increased resistance in the mortar layer. The lower corrosion current density and higher corrosion potential and impedance explain the important reason why M-10TiO2 / PC can protect the reinforcing steel. Therefore, compared with Blank and B-10TiO2 / PC, M-10TiO2 / PC can provide longer-term and more effective protection for the reinforcing steel, helping to extend the life of the cementitious material.

[0065] Test Comparison Explanation: Through parallel preparation and unified performance testing of the above three samples, the following conclusions can be clearly drawn: The Blank sample has no photocatalytic and hydrophobic properties, and its durability against freeze-thaw cycles and sulfate attack is poor; the B-10TiO2 / PC sample has photocatalytic properties, but no hydrophobic function, and the introduction of TiO2 accelerates the carbonization of the cement matrix, resulting in a significant decrease in the durability against steel corrosion and sulfate attack; the M-10TiO2 / PC sample (this invention) achieves excellent photocatalytic performance, overall hydrophobic self-cleaning properties, and high durability (resistance to freeze-thaw cycles, sulfate attack, carbonation, and steel corrosion) through the synergistic effect of stearic acid, TiO2, and cement, effectively solving many technical defects of the prior art and highlighting the inventiveness, practicality, and advancement of this invention.

Claims

1. A hydrophobic-photocatalytic composite cement material, characterized in that, The product comprises the following components by weight percentage: 89 wt% silicate cement matrix, 10 wt% photocatalyst, and 1.0 wt% stearic acid hydrophobic agent.

2. The hydrophobic-photocatalytic composite cement material according to claim 1, characterized in that, The stearic acid is a non-fluorinated hydrophobic agent.

3. The hydrophobic-photocatalytic composite cement material according to claim 1, characterized in that, The photocatalyst is TiO2.

4. A method for preparing a hydrophobic-photocatalytic composite cement material, used to prepare the hydrophobic-photocatalytic composite cement material according to any one of claims 1 to 3, characterized in that, A hydrophobic-photocatalytic composite cement material was prepared by adding composite TiO2 photocatalyst and stearic acid hydrophobic agent to ordinary silicate cement as the base material, through proportioning and mixing and ball milling modification process.

5. The method for preparing a hydrophobic-photocatalytic composite cement material according to claim 4, characterized in that, A hydrophobic-photocatalytic composite cement material was prepared by adding a composite TiO2 photocatalyst and stearic acid hydrophobic agent to ordinary silicate cement as the base material, through proportioning and mixing and ball milling modification processes. The specific steps are as follows: S1. Raw material ratio: By mass percentage, take 89 wt% silicate cement matrix, 10 wt% TiO2 photocatalyst and 1.0 wt% stearic acid hydrophobic agent; S2. Raw material mixing: Silicate cement, TiO2 photocatalyst and stearic acid hydrophobic agent are mechanically stirred to initially mix and obtain a mixture. S3. Ball milling modification: The mixture is added to a ball mill for ball milling modification. Grinding balls of different diameters are matched in a certain proportion. The speed and milling time of the ball mill are controlled to achieve uniform dispersion of TiO2 photocatalyst in silicate cement matrix. At the same time, the stearic acid hydrophobic agent is fully dispersed in silicate cement matrix, giving the composite cement material overall hydrophobic and photocatalytic properties. The hydrophobic-photocatalytic composite cement material is obtained when the material is discharged.

6. The method for preparing a hydrophobic-photocatalytic composite cement material according to claim 5, characterized in that, In step S3, the grinding balls are mixed in a ratio of 3cm large ball: 2.5cm medium ball: 1.5cm small ball = 3:3:

4.

7. The method for preparing a hydrophobic-photocatalytic composite cement material according to claim 5, characterized in that, In step S3, the rotational speed of the ball mill is controlled at 35 r / min. - ¹, Set the ball milling time to 60 minutes.

8. The method for preparing a hydrophobic-photocatalytic composite cement material according to claim 5, characterized in that, In step S1, the silicate cement matrix is ​​prepared by mixing it into neat paste, mortar, or concrete using conventional processes.

9. The method for preparing a hydrophobic-photocatalytic composite cement material according to claim 8, characterized in that, A water-cement ratio of 0.3 was selected for preparing silicate cement matrix.

10. The method for preparing a hydrophobic-photocatalytic composite cement material according to claim 8, characterized in that, After mixing, silicate cement matrix is ​​cured in an environment with a standard temperature of 20℃±1℃ and a humidity of 95%RH±2%RH to obtain silicate cement matrix products.

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