Development and performance analysis of a modified polyurea hydrophobic coating for improving water conveyance efficiency in concrete channel linings

Development and performance analysis of a modified polyurea hydrophobic coating for improving water conveyance efficiency in concrete channel linings | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Article Development and performance analysis of a modified polyurea hydrophobic coating for improving water conveyance efficiency in concrete channel linings Lingyun Feng, Jingjing Liu, Chunli Liu, Ai-Jiu Chen This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-6544642/v1 This work is licensed under a CC BY 4.0 License Status: Posted Version 1 posted You are reading this latest preprint version Abstract The water conveyance capacity of a channel depends heavily on the roughness coefficient of the flow surface, which is challenging to maintain in concrete linings due to construction limitations, skill variability, and water erosion. Applying surface coatings has proven effective in reducing roughness, improving conveyance efficiency, and ensuring durability. This study aims to develop and evaluate a novel hydrophobic coating, the modified polyurea hydrophobic coating (MPHC), to overcome the performance limitations of traditional coatings. The MPHC was formulated using polyurea, polydimethylsiloxane, and silicon dioxide in a specific mass ratio and was designed to combine strong adhesion, high hydrophobicity, and excellent durability. The coating’s performance was assessed through contact angle measurements, tensile bond strength tests, and environmental pretreatment evaluations, including immersion, heat resistance, and freeze-thaw cycling. Experimental results reveal that the MPHC achieves a surface contact angle of 131.2°, demonstrating strong hydrophobicity. The coating incorporates a “binary structure” formed by the combination of polydimethylsiloxane and microsilica powder, which creates a hydrophobic-rough surface. This structure minimizes the flow-solid interface area and adhesion, enhancing drag reduction performance. The bond strength of the MPHC decreases by only 0.1 MPa compared to unmodified polyurea, demonstrating that polydimethylsiloxane minimally affects bonding performance. Furthermore, durability tests—including immersion, high-temperature exposure, and freeze-thaw cycles—show no significant deterioration in either the contact angle or bond strength, confirming the coating’s robustness. Drag reduction tests conducted on channel model linings demonstrate that the MPHC reduces the roughness coefficient by 10.0–11.6% compared to ordinary concrete and by 7.4–7.5% compared to ordinary polyurea coatings. In conclusion, the findings of this study highlight the suitability of the MPHC for channel concrete linings. Its superior hydrophobicity, durability, and drag reduction performance make it a promising solution for improving the water conveyance efficiency of concrete-lined channels. Physical sciences/Materials science Physical sciences/Materials science/Structural materials/Composites Modified polyurea Hydrophobic coating Channel lining Roughness coefficient Binary structure Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Figure 8 Figure 9 Figure 10 Figure 11 Figure 12 Figure 13 Figure 14 1. Introduction Hydraulic engineering frequently employs the Chezy and Manning formulas to calculate the flow capacity of channels (Ma and Shi, 2007; Niazkar et al., 2019; Yang et al., 2007). The flow rate of a channel cross-section can be determined using the equation: \(\:Q=\frac{1}{n}A{R}^{2/3}{i}^{1/2}\) , where Q is the cross-sectional flow, n is the roughness coefficient, A is the cross-sectional area, R is the hydraulic radius, i is the channel slope, and C is the Chezy coefficient. During channel operation, parameters such as A , R , and i generally remain constant. Consequently, the roughness coefficient n becomes the most critical parameter influencing the flow capacity of the channel. For example, in the Middle Route Project of the South-to-North Water Diversion, reducing n by just 0.001 could save project costs by several hundred million yuan (Yang and Wang, 2013). The surface roughness coefficient of channel concrete is closely associated with factors such as construction technology, workers’ skills, and curing conditions (Fatxulloyev et al. 2020, Tian and Niu 2012). For large channels, achieving a smooth and flat concrete surface requires stringent quality control during construction, posing significant challenges (as illustrated in Fig. 1). Concrete surfaces that meet relevant construction specifications typically exhibit a roughness coefficient of approximately 0.0150, with design values for concrete channels in China generally ranging between 0.0150 and 0.0170 (Zeng et al., 1999). However, under harsh operational conditions—such as regions with severe cold or sections with steep slope gradients—external factors like climate and water flow scouring often lead to surface deterioration, including freeze-thaw damage and abrasion (as illustrated in Fig. 2). These adverse conditions can substantially increase the roughness coefficient, greatly reducing the channel's flow capacity (Mo and Lou, 2020; Li et al., 2022; Shi et al. 2015). In extreme cases, such degradation may even compromise the structural integrity of the channel. Sealing coatings effectively reduce the roughness coefficient, improve flow capacity, and protect concrete against freeze-thaw damage. This approach not only improves the durability of channel linings but also extends their service life. Currently, concrete coatings used in engineering applications can be categorized into two main types: traditional sealing coatings and advanced hydrophobic coatings. Traditional sealing coatings generally include polyureas (Li et al. 2024, Guo et al. 2024, Huang et al. 2024), epoxy resins (Fame et al. 2024, Szewczak and Łagód 2024), and polyurethanes (Dong et al. 2024, Ummin et al. 2024, Wu et al. 2024). These coatings exhibit high bonding strength and excellent waterproofing properties. However, they provide limited reductions in roughness coefficient after curing and demonstrate poor frost resistance. In contrast, advanced hydrophobic coatings incorporate binders such as epoxy resin, acrylic acid, and polyurethane, combined with low-surface-energy reagents like silane and siloxane. These coatings retain the high bonding strength and waterproofing properties of traditional coatings while offering superior hydrophobicity. The water contact angle on the surface of hydrophobic coatings exceeds 110° (Zhang et al., 2023), which reduces the fluid's shear strain force on the wall, increases the thickness of the laminar boundary layer, and effectively lowers the wall roughness coefficient (Qin et al., 2018; Tian and Xue, 1999). Additionally, these coatings demonstrate excellent anti-condensation properties and freeze-thaw durability (Liu et al., 2017; Zhang et al., 2021). Liu et al. (2017) developed a translucent superhydrophobic coating using polydimethylsiloxane (PDMS) and polymethyl methacrylate, achieving a contact angle of 157.5° on a rough glass substrate. Similarly, Zhang et al. (2021) prepared a suspension containing silicon micropowder, nano-silica, epoxy resin, and PDMS. When sprayed onto various substrates, this suspension formed superhydrophobic surfaces with micro-nano rough structures and low surface energy. While numerous concrete coatings are available, their performance and suitability for specific applications differ considerably. For channel lining applications, the coating must meet several critical requirements: it must be environmentally friendly, non-toxic, and odorless, while maintaining reliable adhesion to concrete and robust hydrophobicity under adverse conditions, including immersion, high temperatures, and freeze-thaw cycles. However, most existing research on concrete coatings focuses primarily on their initial bonding and hydrophobic performance, with limited experimental studies addressing their performance under harsh environmental conditions. As a result, while many concrete coating products are commercially available, few are suitable for channel lining applications, often leading to suboptimal engineering outcomes. To address these challenges, this study optimally selected polyurea coatings based on their superior properties and developed a novel modified polyurea hydrophobic coating (MPHC) tailored to the performance requirements of channel lining concrete. The hydrophobicity and bond strength of MPHC were experimentally evaluated under conditions of immersion, high temperatures, and freeze-thaw cycles. Among the various concrete coatings, polyurea stands out as a solvent-free, environmentally friendly material with excellent wear resistance, impermeability, frost resistance, corrosion resistance, aging resistance, and mechanical properties. These characteristics make polyurea highly suitable for water conservancy projects (Hu, 2019; Liang et al., 2023; Sun et al., 2019). 2. Testing program 2.1 Materials and preparation of modified polyurea hydrophobic coating The MPHC was prepared using three primary materials: polyurea, PDMS, and silicon dioxide (SiO 2 ). The polyurea, sourced from a chemical reagent company in Beijing, is gray and closely resembles cement mortar (Fig. 3). PDMS, a polymer with the formula (C 2 H 6 OSi) n , was procured from a chemical reagent company in Guangdong. This colorless, high-viscosity liquid is non-toxic, odorless, and exhibits notable properties such as heat, cold, and water resistance, as well as low surface tension and remarkable chemical stability (Fig. 4). The SiO 2 used in this study, also obtained from a chemical reagent company in Guangdong, consists of spherical particles with a particle size of 1 µm, as shown in Fig. 5. The MPHC was formulated with polyurea, PDMS, and SiO 2 powder in a mass ratio of 20:5:1, with polyurea serving as the primary component. The preparation process, illustrated in Fig. 6 , involved several steps. First, polyurea and PDMS were combined and mixed uniformly with a magnetic stirrer for 30 minutes. SiO 2 powder (1 µm; mass ratio 20:1) was then added and stirred for an additional 60 minutes to achieve uniform dispersion. The resulting MPHC is gray, resembling the natural color of concrete (Fig. 7). It has a glossy and oily surface. On a microscopic level, silica microparticles are evenly distributed within the polyurea substrate, forming a micro-rough structure consistent with the Cassie-Baxter theoretical model. 2.2 Evaluation methods for coating performance The performance of the MPHC was evaluated through two key tests: contact angle measurement and bonding strength testing. For the contact angle measurement, the MPHC was applied to mortar specimens measuring 70 mm × 70 mm × 20 mm, which were prepared using a cement: sand: water ratio of 1: 2.5: 0.45. These specimens were cured for 28 days under conditions of humidity greater than 95% and a temperature of 20 ± 2°C. The coating thickness was approximately 1 mm. After curing, the specimens were air-dried in a cool place for 60 minutes before testing. The contact angle was measured using a KRUSS DSA100 contact angle measuring instrument, as shown in Fig. 8 . The bonding strength of the MPHC was assessed through a tensile bond strength test. The preparation of bonding test specimens involved applying a uniform layer of MPHC to the surfaces of mortar specimens measuring 70 mm × 70 mm × 20 mm and 40 mm × 40 mm × 10 mm, both prepared with a cement: sand: water ratio of 1:2.5:0.45. These specimens were cured for 28 days under standard conditions of humidity greater than 95% and a temperature of 20 ± 2°C. The coated surfaces of the two specimens were brought into contact, pressed gently, and positioned horizontally. A pressure block measuring 40 mm × 40 mm with a mass of 1.600 ± 0.015 kg was placed on top of the smaller specimen for 30 seconds, and any excess interface agent was scraped off from the sides. The bonded specimens were cured for 14 days under standard conditions. Subsequently, a pull-out joint was affixed to the smaller specimen with a high-strength bonding agent, followed by a 48-hour stabilization period (Fig. 9 ). The tensile bond strength test was conducted by attaching a fixture to the bonded specimen, and connecting it to a tensile testing machine, as shown in Fig. 10 . The tensile test was performed at a speed of 5 ± 1 mm/min until specimen failure occurred, and the failure load was recorded. The tensile bond strength was calculated using Eq. ( 1 ): $$\sigma =\frac{{{F_1}}}{{{A_1}}}$$ 1 Where \(\:\sigma\:\) is the tensile bond strength (MPa), \(\:{F}_{1}\) is the maximum load (N), and \(\:{A}_{1}\) is the adhesive area (mm 2 ). 2.3 Environmental pretreatment of coated specimens The immersion treatment involved specimens coated with the material and cured for seven days under standard test conditions. These specimens were fully immersed in water maintained at a temperature of (23 ± 2) °C. After six days of immersion, the specimens were removed, and surface water stains were gently dried with a cloth to ensure consistency. For the heat resistance treatment, specimens coated with the material and cured for seven days under standard test conditions were placed in an oven maintained at a temperature of (70 ± 2) °C. After seven days of exposure to these elevated temperatures, the specimens were removed from the oven and allowed to cool for four hours under standard test conditions to stabilize their properties. In the freeze-thaw treatment test, specimens were initially cured for seven days under standard test conditions and then immersed in water at (23 ± 2) °C for an additional seven days. After the immersion period, the specimens were removed, and surface water stains were dried using a cloth. The specimens were subsequently subjected to 25 freeze-thaw cycles to evaluate their durability under fluctuating thermal conditions. Each freeze-thaw cycle consisted of two phases: first, the specimens were maintained at (-15 ± 3) °C for 2.0 ± 0.3 hours; subsequently, they were immersed in water at (23 ± 2) °C for 2.0 ± 0.3 hours. 3. Hydrophobicity of modified polyurea hydrophobic coating 3.1 Influence of contact angle on roughness coefficient and drag reduction The contact angle, formed at the interface of solid, liquid, and gas phases, is a key parameter for surface characterization. Solid surfaces are classified based on their contact angle into superhydrophilic surfaces (contact angle 150°) (Vogler, 1998). The contact angle strongly influences both drag reduction and the roughness coefficient of the solid-liquid interface. The relationship between the contact angle and drag reduction rate has been extensively studied, particularly in the context of pipeline coating materials. Experimental results show that a larger contact angle corresponds to higher drag reduction, ranging from 6.8–76.5% (Fu et al., 2012). However, research exploring the relationship between contact angle and roughness coefficient remains limited. Liu (Liu, 2019) investigated this relationship using a rectangular channel with a total length of 25 m, a depth of 50 cm, and a slope of 1/400. The study found that ordinary concrete had a contact angle of 67.2° and a roughness coefficient of 0.01491. In contrast, the superhydrophobic coating had a contact angle of 153.4°—2.28 times higher—and a roughness coefficient of 0.01322, 0.89 times lower. These results demonstrate that increasing the contact angle of a hydrophobic material leads to a reduction in its roughness coefficient. 3.2 Comparative analysis of coating contact angles under various conditions The surface water contact angles of various materials, including cement mortar (saturated), polyurea, and modified polyurea, are illustrated in Fig. 11 . Cement mortar serves as the baseline, representing the uncoated concrete surface. When dry or subjected to heat treatment, the water contact angle of cement mortar cannot be measured due to its high water absorption capacity. However, when saturated, the contact angle is measured at 59.9°. The polyurea coating exhibits a contact angle of 62.9°, comparable to that of cement mortar, indicating limited enhancement in surface hydrophobicity. In contrast, the MPHC contact angle is 131.2°, 2.2 times that of cement mortar and 2.1 times that of ordinary polyurea. These findings demonstrate the significant improvement in hydrophobicity achieved with the modified polyurea. Coatings applied to the bottom of channel linings remain immersed in water, where their operational contact angle affects water conveyance. After immersion, the contact angle of the polyurea coating increases slightly to 75.6°, while the contact angle of the MPHC decreases slightly to 127.9°. The slight reduction in the MPHC contact angle is due to minimal PDMS dissolution, which has negligible impact on hydrophobicity. When the coating is applied to the slope of the channel concrete lining, it is exposed to natural high temperatures during summer when the water level drops. After heat treatment, the contact angle of the polyurea coating remains virtually unchanged at 62.1°. In contrast, the contact angle of the MPHC decreases to 119.0°. Although this value is lower than its pre-heat-treatment contact angle, it remains significantly higher than the contact angles of both ordinary polyurea and cement mortar. In areas of the channel concrete lining subjected to water level fluctuations, the coating experiences freeze-thaw cycles during winter. After 25 freeze-thaw cycles, the contact angle of the cement mortar coating decreases to 46.6%, representing a 22.2% reduction, while its roughness coefficient increases significantly, severely impairing flow capacity. In contrast, the polyurea coating and MPHC are less affected by freeze-thaw cycles, with contact angles of 62.0° and 130.2°, respectively. This demonstrates the MPHC’s superior hydrophobicity and durability under such conditions. 4. Bonding tensile strength As illustrated in Fig. 12, the tensile bond strength of the untreated coatings was measured at 1.3 MPa for the ordinary polyurea coating and 1.2 MPa for the MPHC. Although PDMS improves the coating's contact angle (Liu et al., 2017), it slightly reduces its bond strength. However, this reduction is minimal, with the bond strength decreasing by only 0.1 MPa. Following immersion treatment, the tensile bond strength of the ordinary polyurea coating decreased by 8.7%, while the MPHC showed no reduction. This demonstrates the superior resistance of the MPHC to water-induced degradation in bond strength. Following heat treatment, the tensile bond strength of both coatings increased. The ordinary polyurea coating exhibited a 15.4% increase, while the MPHC showed an 8.3% increase. These findings suggest that a dry environment enhances the bonding performance of polyurea coatings. After exposure to freeze-thaw cycles, the tensile bond strength of the ordinary polyurea coating decreased by 30.7%, while the MPHC experienced a reduction of 25.0%. Despite the decline, the MPHC exhibited superior freeze-thaw resistance compared to ordinary polyurea. Figure 13 shows that tensile failures primarily occurred on fresh mortar surfaces, with some mortar-coating bond surfaces also observed. Additionally, clear signs of freeze-thaw damage were observed in the mortar. Therefore, it can be inferred that the reduction in tensile bond strength after freeze-thaw cycles is primarily attributable to freeze-thaw damage in the mortar specimens rather than the coatings themselves. 5. Test of roughness coefficient of the coating in the channel model To evaluate the drag reduction performance of the MPHC, a concrete-lined channel model was utilized. The channel model, illustrated in Fig. 14 , consists of a rectangular channel with a total length of 20 m, a depth of 50 cm, a width of 20 cm, and a longitudinal bottom slope of i = 1/400. The system includes an automatic water circulation mechanism powered by a water pump. Water flows from the inlet pool through a water-stabilizing grid, passes through the rectangular channel, flows over a rectangular weir for measurement, and exits into the retreat pool. The inlet flow rates were set at 0.030 m 3 /s, 0.040 m 3 /s, and 0.050 m 3 /s. The surface roughness coefficients of three types of channel linings—the common concrete lining, the polyurea-coated lining, and the MPHC lining—were calibrated using the Chezy-Manning formula. The experimental results are summarized in Table 1 . Table 1 The relationship between the flow and the water depth of the channel model Flow Common concrete lining Common polyurea coated lining MPHC lining Water depth 1 Water depth 2 Roughness coefficient Water depth 1 Water depth 2 Roughness coefficient Water depth 1 Water depth 2 Roughness coefficient 0.020 0.182 0.185 0.01445 0.178 0.180 0.01404 0.166 0.168 0.01300 0.040 0.326 0.318 0.01462 0.310 0.315 0.01412 0.290 0.295 0.01306 0.050 0.388 0.390 0.01487 0.366 0.370 0.01423 0.343 0.339 0.01315 As shown in Table 1 , under all tested flow rates, roughness coefficients decreased progressively from the common concrete lining to the polyurea-coated lining and, lastly, the MPHC lining. The MPHC roughness coefficient was 10.0–11.6% lower than that of common concrete and 7.4–7.5% lower than the polyurea-coated lining. This reduction in the roughness coefficient can be explained by the Cassie-Baxter theoretical model. The Cassie-Baxter model explains that an air layer forms between the water flow and the MPHC surface, reducing the flow-solid interface area and adhesion. Consequently, the velocity gradient of the water flow is reduced, leading to a decrease in the shear force between the water flow and the channel sidewall. These factors collectively contribute to the smaller surface roughness coefficient observed for the MPHC. 6. Conclusion This study addresses the challenge of achieving a low roughness coefficient in channel linings. Using the Cassie-Baxter model and hydrophobic theory, PDMS and microsilica powder were incorporated to modify ordinary polyurea, creating the non-toxic, odorless, and eco-friendly MPHC. Experimental investigations were conducted to evaluate the hydrophobicity and bond strength of the MPHC after exposure to immersion in water, high-temperature conditions, and freeze-thaw cycles. The key findings are summarized as follows: ( 1 ) Enhanced hydrophobicity and weather resistance: The incorporation of PDMS and microsilica powder creates a “binary structure” on the surface of the MPHC. Compared to the ordinary polyurea coating, the contact angle of the MPHC increases significantly, indicating improved hydrophobicity. After undergoing immersion, high-temperature, and freeze-thaw treatments, the contact angle of the MPHC exhibits minimal variation, demonstrating excellent weather resistance and stable hydrophobic properties. ( 2 ) Bond strength performance: The MPHC bond strength is slightly reduced compared to unmodified polyurea due to the surface presence of PDMS, which slightly hinders bonding performance. However, the improvement in hydrophobicity outweighs this minor drawback. Furthermore, the bonding performance of the MPHC remains stable, with no signs of degradation observed after immersion, high-temperature, and freeze-thaw treatments. ( 3 ) Drag reduction performance: Tests on the channel model lining reveal that the MPHC achieves the lowest roughness coefficient among the tested materials. The roughness coefficient of the MPHC is reduced by 10.0–11.6% compared to ordinary concrete and by 7.4–7.5% compared to the ordinary polyurea coating. This improvement is primarily attributed to the “binary structure” on the MPHC surface, which reduces the flow-solid interface area and adhesion, thereby lowering the shear force between the water flow and the channel sidewall. In summary, the MPHC exhibits superior hydrophobicity, stable bond strength, and exceptional drag reduction, making it a durable and eco-friendly channel lining material. Declarations Conflicts of interest: The authors declare they have no financial interests. Funding This work was supported by National Natural Science Foundation of China (52179133) and College student innovation project of North China University of Water Resources and Electric Power (2023XA012). Availability of data and material The datasets used and/or analyzed during the current study are available from the corresponding author on reasonable request. Author Contribution Lingyun Feng wrote the main manuscript text, Lingyun Feng and Jingjing Liu conducted experimental research and Chunli Liu made the drawing，Aijiu Chen conducted the review. All authors reviewed the manuscript. Acknowledgments I would like to thank my undergraduate students for their help in the experiment. References Ma, J. & Shi, Z. Research on the absolute roughness of the typical channel of the south-to-north water diversion project. J. Hydroelectric Eng. 26 (5), 75–79 (2007). Niazkar, M., Talebbeydokhti, N. & Afzali, S. H. One dimensional hydraulic flow routing incorporating a variable grain roughness coefficient. Water Resour. Management: Int. J. - Published Eur. Water Resour. Association (EWRA) . 33 (3), 4599–4620 (2019). Yang, K., Cao, S. & Liu, X. Flow resistance and its prediction methods in compound channels. Acta. Mech. Sin. 23 (1), 23–31 (2007). Yang, K. & Wang, Y. System identification of channel roughness forMid-Route Project of South-to-NorthWater Diversion. Chin. Eng. science: Engl. Ed. 11 (6), 58–64 (2013). Fatxulloyev, A., Allayorov, D. & Otakhonov, M. Study of hydraulic parameters for concreting channels, IOP Conference Series: Earth and Environmental Science , 614(1): 012054. (2020). Tian, J. L. & Niu, J. G. The performance study of the open channel concrete in cold area. Adv. Mater. Res. 1896 (535–537), 1661–1664 (2012). Zeng, X., Huang, G. & Duan, W. Summarization of investigation on roughness of concrete channels. J. Yangtze River Sci. Res. Inst. 16 (4), 1–4 (1999). Mo, T. & Lou, Z. Numerical simulation of frost heave of concrete lining trapezoidal channel under an open system. Water 12 (2), 335 (2020). Li, Q., Wu, B. & Zhou, H. Damage simulation analysis of canal concrete lining plates based on temperature-stress-water load coupling. Sustainability 14 (15), 9202–9202 (2022). Shi, S., Zuo, M. & Zhou, H. the occurrence and diagnosis of frost damage degradation in concrete open channels. J. agricultural rural Eng. 83 (10), 835–838a832 (2015). (in Japanese). Li, B. et al. Sealing and anti-seepage polyurea coating design method based on nonlinear FEM simulation. Eng. Comput. 41 (8–9), 2289–2309 (2024). Guo, H. et al. Investigation of polyurea coating influence on dynamic mechanical properties of concrete. Structures 69 , 107446–107446 (2024). Huang, C., He, X. & Zhang, J. Cavitation pit evolution process of epoxy and polyurea coatings on mortar substrates. Ultrason. Sonochem. 104 , 106813 (2024). Fame, C. M. et al. Durability of epoxy and vinyl ester polymers in wet, seawater, and seawater sea sand concrete environments: Molecular dynamics simulations. Constr. Build. Mater. 451 , 138645–138645 (2024). Szewczak, A. & Łagód, G. Experimental research on the possibility of changing the adhesion of epoxy glue to concrete. Materials 17 (22), 5398–5398 (2024). Dong, H. et al. Mechanical properties and constitutive model of waterborne polyurethane modified concrete in compression at different temperature. J. Building Eng. 98 , 111357–111357 (2024). Ummin, O. et al. Influence of surface roughness and interfacial agent on the interface bonding characteristics of polyurethane concrete and cement concrete. J. Building Eng. 91 , 109596 (2024). Wu, Y. et al. Multiscale study of the damage evolution mechanism of polyurethane concrete under freeze–thaw conditions. J. Mater. Civ. Eng. , 36 (11). (2024). Zhang, F. et al. A review on the preparation of superhydrophobic coatings and their application in concrete in cold regions. Mater. guide : 1–21. (2023). (in Chinese). Qin, W. et al. Performance analysis of three kinds of low surface energy drag reduction coatings. Mater. Prot. 51 (05), 39–41 (2018). (in Chinese). Tian, J. & Xue, Q. Experimental study on the reduction of fluid noise by the components of low surface energy of the coating. Chin. J. Appl. Mech. , (03): 109–111. (1999). (in Chinese). Liu, H. et al. Robust translucent superhydrophobic PDMS/PMMA film by facile one-step spray for self-cleaning and efficient emulsion separation. Chem. Eng. J. , 330. (2017). Zhang, J., Zhang, L. & Gong, X. Large-scale spraying fabrication of robust fluorine-Free superhydrophobic coatings based on dual-sized silica particles for effective antipollution and strong buoyancy, Langmuir: the ACS journal of surfaces and colloids , 37(19). (2021). Hu, P. The Application of SK hand-scraped polyurea in water transfer and distribution projects in the northwestern cold and high-altitude areas. People's Yellow River . 41 (04), 122–124 (2019). (in Chinese). Liang, H. et al. Research on the UV resistance performance of single-component polyurea coating materials. People's Yangtze River . 54 (03), 205–209 (2023). (in Chinese). Sun, Z. et al. Surface flat-covering flexible water-stop structure for concrete panel joints in cold regions. Hydropower 45 (05), 50–53 (2019). (in Chinese). Vogler, E. A. Structure and reactivity of water at biomaterial surfaces. Adv. Colloid Interface Sci. 74 (1), 69 (1998). Fu, C. S. et al. Fabrication of micro-nano structured super-hydrophobic surface and drag reduction in channels. Key Eng. Mater. 1920 (519–519), 297–302 (2012). Liu, S. Preparation of environmentally friendly superhydrophobic concrete and its application in long-distance water conveyance channels in cold regions, Northwest Agriculture & Forestry University . (in Chinese) (2019). Additional Declarations No competing interests reported. Cite Share Download PDF Status: Posted Version 1 posted You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. We do this by developing innovative software and high quality services for the global research community. Our growing team is made up of researchers and industry professionals working together to solve the most critical problems facing scientific publishing. Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-6544642","acceptedTermsAndConditions":true,"allowDirectSubmit":true,"archivedVersions":[],"articleType":"Article","associatedPublications":[],"authors":[{"id":455143422,"identity":"38867a77-895f-40d9-a6fe-5745c0a7ad3d","order_by":0,"name":"Lingyun 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Power","correspondingAuthor":false,"prefix":"","firstName":"Jingjing","middleName":"","lastName":"Liu","suffix":""},{"id":455143424,"identity":"c1ad8513-7fa0-4689-aea7-708d4cddd80d","order_by":2,"name":"Chunli Liu","email":"","orcid":"","institution":"Henan Key Laboratory of Geomechanics and Structure Engineering","correspondingAuthor":false,"prefix":"","firstName":"Chunli","middleName":"","lastName":"Liu","suffix":""},{"id":455143425,"identity":"6bd19bdd-6b44-4804-bd9a-84c2a76979be","order_by":3,"name":"Ai-Jiu Chen","email":"","orcid":"","institution":"North China University of Water Resources and Electric Power","correspondingAuthor":false,"prefix":"","firstName":"Ai-Jiu","middleName":"","lastName":"Chen","suffix":""}],"badges":[],"createdAt":"2025-04-28 06:53:08","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-6544642/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-6544642/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":82622050,"identity":"66590e6d-2042-4517-9aed-40da52fb6149","added_by":"auto","created_at":"2025-05-13 12:24:03","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":479719,"visible":true,"origin":"","legend":"\u003cp\u003eManual levelling concrete surface (left) and mechanical levelling concrete surface (right)\u003c/p\u003e","description":"","filename":"1.png","url":"https://assets-eu.researchsquare.com/files/rs-6544642/v1/44cb5a9459cb43329f503bd7.png"},{"id":82622048,"identity":"d3f268f9-5f51-4624-9964-da59095f62b2","added_by":"auto","created_at":"2025-05-13 12:24:03","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":234930,"visible":true,"origin":"","legend":"\u003cp\u003eFreeze-thaw damage of concrete surface of channel lining\u003c/p\u003e","description":"","filename":"2.png","url":"https://assets-eu.researchsquare.com/files/rs-6544642/v1/4d8414457bb4c44f60de50c3.png"},{"id":82622065,"identity":"4647f33a-f75c-47df-9572-d1f39e312e90","added_by":"auto","created_at":"2025-05-13 12:24:04","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":100507,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003ePurea\u003c/strong\u003e\u003c/p\u003e","description":"","filename":"3.png","url":"https://assets-eu.researchsquare.com/files/rs-6544642/v1/bc44e392ad3e4a55d8e03877.png"},{"id":82622059,"identity":"21b9a2c2-97f0-4a23-b70d-f481d82a1590","added_by":"auto","created_at":"2025-05-13 12:24:04","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":61792,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003ePDMS\u003c/strong\u003e\u003c/p\u003e","description":"","filename":"4.png","url":"https://assets-eu.researchsquare.com/files/rs-6544642/v1/ba1503c31e6e36e5b2579d5f.png"},{"id":82622055,"identity":"116eb4ca-2ce6-435e-a92a-9226d29f95f3","added_by":"auto","created_at":"2025-05-13 12:24:03","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":179829,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eSilicon dioxide\u003c/strong\u003e\u003c/p\u003e","description":"","filename":"5.png","url":"https://assets-eu.researchsquare.com/files/rs-6544642/v1/21822c638fe1764a98fc6a21.png"},{"id":82621983,"identity":"2aa3540e-639a-4dab-bc11-852c2584f01d","added_by":"auto","created_at":"2025-05-13 12:24:01","extension":"png","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":215677,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003ePreparation process of modified polyurea hydrophobic coating\u003c/strong\u003e\u003c/p\u003e","description":"","filename":"6.png","url":"https://assets-eu.researchsquare.com/files/rs-6544642/v1/54eaf7217748d0ce2977b7cd.png"},{"id":82621988,"identity":"5d4f80f8-5efd-43a0-85eb-5fae0e50962c","added_by":"auto","created_at":"2025-05-13 12:24:01","extension":"png","order_by":7,"title":"Figure 7","display":"","copyAsset":false,"role":"figure","size":258949,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eThe appearance of the modified polyurea hydrophobic coating (left) and the electron microscope image (right, 100 times magnification)\u003c/strong\u003e\u003c/p\u003e","description":"","filename":"7.png","url":"https://assets-eu.researchsquare.com/files/rs-6544642/v1/4aba287d98b8870937450943.png"},{"id":82622057,"identity":"a47c6423-c053-45cf-bdc3-f4d4925ed4a2","added_by":"auto","created_at":"2025-05-13 12:24:03","extension":"png","order_by":8,"title":"Figure 8","display":"","copyAsset":false,"role":"figure","size":89270,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eKRUSS DSA100 contact Angle measuring instrument\u003c/strong\u003e\u003c/p\u003e","description":"","filename":"8.png","url":"https://assets-eu.researchsquare.com/files/rs-6544642/v1/fe895682aecc63866ed2bf4e.png"},{"id":82621984,"identity":"1a56d341-0f6e-47d2-8d3b-40148d8542f2","added_by":"auto","created_at":"2025-05-13 12:24:01","extension":"png","order_by":9,"title":"Figure 9","display":"","copyAsset":false,"role":"figure","size":168939,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eTensile bond strength test specimen\u003c/strong\u003e\u003c/p\u003e","description":"","filename":"9.png","url":"https://assets-eu.researchsquare.com/files/rs-6544642/v1/fcc189378c5180c3d2482af8.png"},{"id":82622047,"identity":"3008e1f1-e3ef-4026-8d2c-cd0ecb9a742e","added_by":"auto","created_at":"2025-05-13 12:24:03","extension":"png","order_by":10,"title":"Figure 10","display":"","copyAsset":false,"role":"figure","size":207120,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eTest of tensile bond strength of coating\u003c/strong\u003e\u003c/p\u003e","description":"","filename":"10.png","url":"https://assets-eu.researchsquare.com/files/rs-6544642/v1/239126c99cc9a19d4183fad1.png"},{"id":82622041,"identity":"87f2f7f9-1372-4003-9faa-0553bac86d7b","added_by":"auto","created_at":"2025-05-13 12:24:02","extension":"png","order_by":11,"title":"Figure 11","display":"","copyAsset":false,"role":"figure","size":119088,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eThe contact angle of the coating surface\u003c/strong\u003e\u003c/p\u003e","description":"","filename":"11.png","url":"https://assets-eu.researchsquare.com/files/rs-6544642/v1/201897d3bdcc5e147dd8ed9c.png"},{"id":82622044,"identity":"2bbb2796-6d1e-4abc-ac5b-2adcd24a343e","added_by":"auto","created_at":"2025-05-13 12:24:03","extension":"png","order_by":12,"title":"Figure 12","display":"","copyAsset":false,"role":"figure","size":11137,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eCoating bond tensile strength\u003c/strong\u003e\u003c/p\u003e","description":"","filename":"12.png","url":"https://assets-eu.researchsquare.com/files/rs-6544642/v1/ac540432e9b5700bfe901adf.png"},{"id":82622061,"identity":"4474f10a-6807-4490-aa34-b094470f2309","added_by":"auto","created_at":"2025-05-13 12:24:04","extension":"png","order_by":13,"title":"Figure 13","display":"","copyAsset":false,"role":"figure","size":155063,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eTensile failure surface of coating after freeze-thaw treatment\u003c/strong\u003e\u003c/p\u003e","description":"","filename":"13.png","url":"https://assets-eu.researchsquare.com/files/rs-6544642/v1/2124b8768ed318d53574bb1f.png"},{"id":82621993,"identity":"3d55c911-308a-4d6d-92e7-71dd489b7712","added_by":"auto","created_at":"2025-05-13 12:24:02","extension":"png","order_by":14,"title":"Figure 14","display":"","copyAsset":false,"role":"figure","size":34287,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eConcrete lined channel model\u003c/strong\u003e\u003c/p\u003e","description":"","filename":"14.png","url":"https://assets-eu.researchsquare.com/files/rs-6544642/v1/65f964f587c1e5803cfd5019.png"},{"id":83476683,"identity":"8604740b-8ec9-4c10-92a3-9cd538bef123","added_by":"auto","created_at":"2025-05-27 04:46:49","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":3688463,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-6544642/v1/7de04593-38f4-49f1-906c-c20289ec1b46.pdf"}],"financialInterests":"No competing interests reported.","formattedTitle":"Development and performance analysis of a modified polyurea hydrophobic coating for improving water conveyance efficiency in concrete channel linings","fulltext":[{"header":"1. Introduction","content":"\u003cp\u003eHydraulic engineering frequently employs the Chezy and Manning formulas to calculate the flow capacity of channels (Ma and Shi, 2007; Niazkar et al., 2019; Yang et al., 2007). The flow rate of a channel cross-section can be determined using the equation:\u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:Q=\\frac{1}{n}A{R}^{2/3}{i}^{1/2}\\)\u003c/span\u003e\u003c/span\u003e, where \u003cem\u003eQ\u003c/em\u003e is the cross-sectional flow, \u003cem\u003en\u003c/em\u003e is the roughness coefficient, \u003cem\u003eA\u003c/em\u003e is the cross-sectional area, \u003cem\u003eR\u003c/em\u003e is the hydraulic radius, \u003cem\u003ei\u003c/em\u003e is the channel slope, and \u003cem\u003eC\u003c/em\u003e is the Chezy coefficient. During channel operation, parameters such as \u003cem\u003eA\u003c/em\u003e, \u003cem\u003eR\u003c/em\u003e, and \u003cem\u003ei\u003c/em\u003e generally remain constant. Consequently, the roughness coefficient n becomes the most critical parameter influencing the flow capacity of the channel. For example, in the Middle Route Project of the South-to-North Water Diversion, reducing n by just 0.001 could save project costs by several hundred million yuan (Yang and Wang, 2013).\u003c/p\u003e \u003cp\u003eThe surface roughness coefficient of channel concrete is closely associated with factors such as construction technology, workers\u0026rsquo; skills, and curing conditions (Fatxulloyev et al. 2020, Tian and Niu 2012). For large channels, achieving a smooth and flat concrete surface requires stringent quality control during construction, posing significant challenges (as illustrated in Fig.\u0026nbsp;1). Concrete surfaces that meet relevant construction specifications typically exhibit a roughness coefficient of approximately 0.0150, with design values for concrete channels in China generally ranging between 0.0150 and 0.0170 (Zeng et al., 1999). However, under harsh operational conditions\u0026mdash;such as regions with severe cold or sections with steep slope gradients\u0026mdash;external factors like climate and water flow scouring often lead to surface deterioration, including freeze-thaw damage and abrasion (as illustrated in Fig.\u0026nbsp;2). These adverse conditions can substantially increase the roughness coefficient, greatly reducing the channel's flow capacity (Mo and Lou, 2020; Li et al., 2022; Shi et al. 2015). In extreme cases, such degradation may even compromise the structural integrity of the channel.\u003c/p\u003e \u003cp\u003eSealing coatings effectively reduce the roughness coefficient, improve flow capacity, and protect concrete against freeze-thaw damage. This approach not only improves the durability of channel linings but also extends their service life. Currently, concrete coatings used in engineering applications can be categorized into two main types: traditional sealing coatings and advanced hydrophobic coatings. Traditional sealing coatings generally include polyureas (Li et al. 2024, Guo et al. 2024, Huang et al. 2024), epoxy resins (Fame et al. 2024, Szewczak and Łag\u0026oacute;d 2024), and polyurethanes (Dong et al. 2024, Ummin et al. 2024, Wu et al. 2024). These coatings exhibit high bonding strength and excellent waterproofing properties. However, they provide limited reductions in roughness coefficient after curing and demonstrate poor frost resistance.\u003c/p\u003e \u003cp\u003eIn contrast, advanced hydrophobic coatings incorporate binders such as epoxy resin, acrylic acid, and polyurethane, combined with low-surface-energy reagents like silane and siloxane. These coatings retain the high bonding strength and waterproofing properties of traditional coatings while offering superior hydrophobicity. The water contact angle on the surface of hydrophobic coatings exceeds 110\u0026deg; (Zhang et al., 2023), which reduces the fluid's shear strain force on the wall, increases the thickness of the laminar boundary layer, and effectively lowers the wall roughness coefficient (Qin et al., 2018; Tian and Xue, 1999). Additionally, these coatings demonstrate excellent anti-condensation properties and freeze-thaw durability (Liu et al., 2017; Zhang et al., 2021). Liu et al. (2017) developed a translucent superhydrophobic coating using polydimethylsiloxane (PDMS) and polymethyl methacrylate, achieving a contact angle of 157.5\u0026deg; on a rough glass substrate. Similarly, Zhang et al. (2021) prepared a suspension containing silicon micropowder, nano-silica, epoxy resin, and PDMS. When sprayed onto various substrates, this suspension formed superhydrophobic surfaces with micro-nano rough structures and low surface energy.\u003c/p\u003e \u003cp\u003eWhile numerous concrete coatings are available, their performance and suitability for specific applications differ considerably. For channel lining applications, the coating must meet several critical requirements: it must be environmentally friendly, non-toxic, and odorless, while maintaining reliable adhesion to concrete and robust hydrophobicity under adverse conditions, including immersion, high temperatures, and freeze-thaw cycles. However, most existing research on concrete coatings focuses primarily on their initial bonding and hydrophobic performance, with limited experimental studies addressing their performance under harsh environmental conditions. As a result, while many concrete coating products are commercially available, few are suitable for channel lining applications, often leading to suboptimal engineering outcomes.\u003c/p\u003e \u003cp\u003eTo address these challenges, this study optimally selected polyurea coatings based on their superior properties and developed a novel modified polyurea hydrophobic coating (MPHC) tailored to the performance requirements of channel lining concrete. The hydrophobicity and bond strength of MPHC were experimentally evaluated under conditions of immersion, high temperatures, and freeze-thaw cycles. Among the various concrete coatings, polyurea stands out as a solvent-free, environmentally friendly material with excellent wear resistance, impermeability, frost resistance, corrosion resistance, aging resistance, and mechanical properties. These characteristics make polyurea highly suitable for water conservancy projects (Hu, 2019; Liang et al., 2023; Sun et al., 2019).\u003c/p\u003e"},{"header":"2. Testing program","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e \u003ch2\u003e2.1 Materials and preparation of modified polyurea hydrophobic coating\u003c/h2\u003e \u003cp\u003eThe MPHC was prepared using three primary materials: polyurea, PDMS, and silicon dioxide (SiO\u003csub\u003e2\u003c/sub\u003e). The polyurea, sourced from a chemical reagent company in Beijing, is gray and closely resembles cement mortar (Fig.\u0026nbsp;3). PDMS, a polymer with the formula (C\u003csub\u003e2\u003c/sub\u003eH\u003csub\u003e6\u003c/sub\u003eOSi)\u003csub\u003en\u003c/sub\u003e, was procured from a chemical reagent company in Guangdong. This colorless, high-viscosity liquid is non-toxic, odorless, and exhibits notable properties such as heat, cold, and water resistance, as well as low surface tension and remarkable chemical stability (Fig.\u0026nbsp;4). The SiO\u003csub\u003e2\u003c/sub\u003e used in this study, also obtained from a chemical reagent company in Guangdong, consists of spherical particles with a particle size of 1 \u0026micro;m, as shown in Fig.\u0026nbsp;5.\u003c/p\u003e \u003cp\u003eThe MPHC was formulated with polyurea, PDMS, and SiO\u003csub\u003e2\u003c/sub\u003e powder in a mass ratio of 20:5:1, with polyurea serving as the primary component. The preparation process, illustrated in Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e6\u003c/span\u003e, involved several steps. First, polyurea and PDMS were combined and mixed uniformly with a magnetic stirrer for 30 minutes. SiO\u003csub\u003e2\u003c/sub\u003e powder (1 \u0026micro;m; mass ratio 20:1) was then added and stirred for an additional 60 minutes to achieve uniform dispersion. The resulting MPHC is gray, resembling the natural color of concrete (Fig.\u0026nbsp;7). It has a glossy and oily surface. On a microscopic level, silica microparticles are evenly distributed within the polyurea substrate, forming a micro-rough structure consistent with the Cassie-Baxter theoretical model.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec4\" class=\"Section2\"\u003e \u003ch2\u003e2.2 Evaluation methods for coating performance\u003c/h2\u003e \u003cp\u003eThe performance of the MPHC was evaluated through two key tests: contact angle measurement and bonding strength testing. For the contact angle measurement, the MPHC was applied to mortar specimens measuring 70 mm \u0026times; 70 mm \u0026times; 20 mm, which were prepared using a cement: sand: water ratio of 1: 2.5: 0.45. These specimens were cured for 28 days under conditions of humidity greater than 95% and a temperature of 20\u0026thinsp;\u0026plusmn;\u0026thinsp;2\u0026deg;C. The coating thickness was approximately 1 mm. After curing, the specimens were air-dried in a cool place for 60 minutes before testing. The contact angle was measured using a KRUSS DSA100 contact angle measuring instrument, as shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e8\u003c/span\u003e.\u003c/p\u003e \u003cp\u003eThe bonding strength of the MPHC was assessed through a tensile bond strength test. The preparation of bonding test specimens involved applying a uniform layer of MPHC to the surfaces of mortar specimens measuring 70 mm \u0026times; 70 mm \u0026times; 20 mm and 40 mm \u0026times; 40 mm \u0026times; 10 mm, both prepared with a cement: sand: water ratio of 1:2.5:0.45. These specimens were cured for 28 days under standard conditions of humidity greater than 95% and a temperature of 20\u0026thinsp;\u0026plusmn;\u0026thinsp;2\u0026deg;C. The coated surfaces of the two specimens were brought into contact, pressed gently, and positioned horizontally. A pressure block measuring 40 mm \u0026times; 40 mm with a mass of 1.600\u0026thinsp;\u0026plusmn;\u0026thinsp;0.015 kg was placed on top of the smaller specimen for 30 seconds, and any excess interface agent was scraped off from the sides. The bonded specimens were cured for 14 days under standard conditions. Subsequently, a pull-out joint was affixed to the smaller specimen with a high-strength bonding agent, followed by a 48-hour stabilization period (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e9\u003c/span\u003e).\u003c/p\u003e\u003cp\u003eThe tensile bond strength test was conducted by attaching a fixture to the bonded specimen, and connecting it to a tensile testing machine, as shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e10\u003c/span\u003e. The tensile test was performed at a speed of 5\u0026thinsp;\u0026plusmn;\u0026thinsp;1 mm/min until specimen failure occurred, and the failure load was recorded. The tensile bond strength was calculated using Eq.\u0026nbsp;(\u003cspan refid=\"Equ1\" class=\"InternalRef\"\u003e1\u003c/span\u003e):\u003c/p\u003e \u003cp\u003e \u003cdiv id=\"Equ1\" class=\"Equation\"\u003e \u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equ1\" name=\"EquationSource\"\u003e\n$$\\sigma =\\frac{{{F_1}}}{{{A_1}}}$$\u003c/div\u003e \u003cdiv class=\"EquationNumber\"\u003e1\u003c/div\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003eWhere \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:\\sigma\\:\\)\u003c/span\u003e\u003c/span\u003e is the tensile bond strength (MPa), \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:{F}_{1}\\)\u003c/span\u003e\u003c/span\u003e is the maximum load (N), and \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:{A}_{1}\\)\u003c/span\u003e\u003c/span\u003e is the adhesive area (mm\u003csup\u003e2\u003c/sup\u003e).\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec5\" class=\"Section2\"\u003e \u003ch2\u003e2.3 Environmental pretreatment of coated specimens\u003c/h2\u003e \u003cp\u003eThe immersion treatment involved specimens coated with the material and cured for seven days under standard test conditions. These specimens were fully immersed in water maintained at a temperature of (23\u0026thinsp;\u0026plusmn;\u0026thinsp;2) \u0026deg;C. After six days of immersion, the specimens were removed, and surface water stains were gently dried with a cloth to ensure consistency.\u003c/p\u003e \u003cp\u003eFor the heat resistance treatment, specimens coated with the material and cured for seven days under standard test conditions were placed in an oven maintained at a temperature of (70\u0026thinsp;\u0026plusmn;\u0026thinsp;2) \u0026deg;C. After seven days of exposure to these elevated temperatures, the specimens were removed from the oven and allowed to cool for four hours under standard test conditions to stabilize their properties.\u003c/p\u003e \u003cp\u003eIn the freeze-thaw treatment test, specimens were initially cured for seven days under standard test conditions and then immersed in water at (23\u0026thinsp;\u0026plusmn;\u0026thinsp;2) \u0026deg;C for an additional seven days. After the immersion period, the specimens were removed, and surface water stains were dried using a cloth. The specimens were subsequently subjected to 25 freeze-thaw cycles to evaluate their durability under fluctuating thermal conditions. Each freeze-thaw cycle consisted of two phases: first, the specimens were maintained at (-15\u0026thinsp;\u0026plusmn;\u0026thinsp;3) \u0026deg;C for 2.0\u0026thinsp;\u0026plusmn;\u0026thinsp;0.3 hours; subsequently, they were immersed in water at (23\u0026thinsp;\u0026plusmn;\u0026thinsp;2) \u0026deg;C for 2.0\u0026thinsp;\u0026plusmn;\u0026thinsp;0.3 hours.\u003c/p\u003e \u003c/div\u003e"},{"header":"3. Hydrophobicity of modified polyurea hydrophobic coating","content":"\u003cdiv id=\"Sec7\" class=\"Section2\"\u003e \u003ch2\u003e3.1 Influence of contact angle on roughness coefficient and drag reduction\u003c/h2\u003e \u003cp\u003eThe contact angle, formed at the interface of solid, liquid, and gas phases, is a key parameter for surface characterization. Solid surfaces are classified based on their contact angle into superhydrophilic surfaces (contact angle\u0026thinsp;\u0026lt;\u0026thinsp;10\u0026deg;), hydrophilic surfaces (contact angle 10\u0026deg;\u0026ndash;65\u0026deg;), hydrophobic surfaces (contact angle 65\u0026deg;\u0026ndash;150\u0026deg;), and superhydrophobic surfaces (contact angle\u0026thinsp;\u0026gt;\u0026thinsp;150\u0026deg;) (Vogler, 1998). The contact angle strongly influences both drag reduction and the roughness coefficient of the solid-liquid interface.\u003c/p\u003e \u003cp\u003eThe relationship between the contact angle and drag reduction rate has been extensively studied, particularly in the context of pipeline coating materials. Experimental results show that a larger contact angle corresponds to higher drag reduction, ranging from 6.8\u0026ndash;76.5% (Fu et al., 2012). However, research exploring the relationship between contact angle and roughness coefficient remains limited. Liu (Liu, 2019) investigated this relationship using a rectangular channel with a total length of 25 m, a depth of 50 cm, and a slope of 1/400. The study found that ordinary concrete had a contact angle of 67.2\u0026deg; and a roughness coefficient of 0.01491. In contrast, the superhydrophobic coating had a contact angle of 153.4\u0026deg;\u0026mdash;2.28 times higher\u0026mdash;and a roughness coefficient of 0.01322, 0.89 times lower. These results demonstrate that increasing the contact angle of a hydrophobic material leads to a reduction in its roughness coefficient.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec8\" class=\"Section2\"\u003e \u003ch2\u003e3.2 Comparative analysis of coating contact angles under various conditions\u003c/h2\u003e \u003cp\u003eThe surface water contact angles of various materials, including cement mortar (saturated), polyurea, and modified polyurea, are illustrated in Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e11\u003c/span\u003e. Cement mortar serves as the baseline, representing the uncoated concrete surface. When dry or subjected to heat treatment, the water contact angle of cement mortar cannot be measured due to its high water absorption capacity. However, when saturated, the contact angle is measured at 59.9\u0026deg;. The polyurea coating exhibits a contact angle of 62.9\u0026deg;, comparable to that of cement mortar, indicating limited enhancement in surface hydrophobicity. In contrast, the MPHC contact angle is 131.2\u0026deg;, 2.2 times that of cement mortar and 2.1 times that of ordinary polyurea. These findings demonstrate the significant improvement in hydrophobicity achieved with the modified polyurea.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eCoatings applied to the bottom of channel linings remain immersed in water, where their operational contact angle affects water conveyance. After immersion, the contact angle of the polyurea coating increases slightly to 75.6\u0026deg;, while the contact angle of the MPHC decreases slightly to 127.9\u0026deg;. The slight reduction in the MPHC contact angle is due to minimal PDMS dissolution, which has negligible impact on hydrophobicity.\u003c/p\u003e \u003cp\u003eWhen the coating is applied to the slope of the channel concrete lining, it is exposed to natural high temperatures during summer when the water level drops. After heat treatment, the contact angle of the polyurea coating remains virtually unchanged at 62.1\u0026deg;. In contrast, the contact angle of the MPHC decreases to 119.0\u0026deg;. Although this value is lower than its pre-heat-treatment contact angle, it remains significantly higher than the contact angles of both ordinary polyurea and cement mortar.\u003c/p\u003e \u003cp\u003eIn areas of the channel concrete lining subjected to water level fluctuations, the coating experiences freeze-thaw cycles during winter. After 25 freeze-thaw cycles, the contact angle of the cement mortar coating decreases to 46.6%, representing a 22.2% reduction, while its roughness coefficient increases significantly, severely impairing flow capacity. In contrast, the polyurea coating and MPHC are less affected by freeze-thaw cycles, with contact angles of 62.0\u0026deg; and 130.2\u0026deg;, respectively. This demonstrates the MPHC\u0026rsquo;s superior hydrophobicity and durability under such conditions.\u003c/p\u003e "},{"header":"4. Bonding tensile strength","content":"\u003cp\u003eAs illustrated in Fig.\u0026nbsp;12, the tensile bond strength of the untreated coatings was measured at 1.3 MPa for the ordinary polyurea coating and 1.2 MPa for the MPHC. Although PDMS improves the coating's contact angle (Liu et al., 2017), it slightly reduces its bond strength. However, this reduction is minimal, with the bond strength decreasing by only 0.1 MPa. Following immersion treatment, the tensile bond strength of the ordinary polyurea coating decreased by 8.7%, while the MPHC showed no reduction. This demonstrates the superior resistance of the MPHC to water-induced degradation in bond strength. Following heat treatment, the tensile bond strength of both coatings increased. The ordinary polyurea coating exhibited a 15.4% increase, while the MPHC showed an 8.3% increase. These findings suggest that a dry environment enhances the bonding performance of polyurea coatings.\u003c/p\u003e \u003cp\u003eAfter exposure to freeze-thaw cycles, the tensile bond strength of the ordinary polyurea coating decreased by 30.7%, while the MPHC experienced a reduction of 25.0%. Despite the decline, the MPHC exhibited superior freeze-thaw resistance compared to ordinary polyurea. Figure\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e13\u003c/span\u003e shows that tensile failures primarily occurred on fresh mortar surfaces, with some mortar-coating bond surfaces also observed. Additionally, clear signs of freeze-thaw damage were observed in the mortar. Therefore, it can be inferred that the reduction in tensile bond strength after freeze-thaw cycles is primarily attributable to freeze-thaw damage in the mortar specimens rather than the coatings themselves.\u003c/p\u003e"},{"header":"5. Test of roughness coefficient of the coating in the channel model","content":"\u003cp\u003eTo evaluate the drag reduction performance of the MPHC, a concrete-lined channel model was utilized. The channel model, illustrated in Fig.\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e14\u003c/span\u003e, consists of a rectangular channel with a total length of 20 m, a depth of 50 cm, a width of 20 cm, and a longitudinal bottom slope of \u003cem\u003ei\u003c/em\u003e\u0026thinsp;=\u0026thinsp;1/400. The system includes an automatic water circulation mechanism powered by a water pump. Water flows from the inlet pool through a water-stabilizing grid, passes through the rectangular channel, flows over a rectangular weir for measurement, and exits into the retreat pool. The inlet flow rates were set at 0.030 m\u003csup\u003e3\u003c/sup\u003e/s, 0.040 m\u003csup\u003e3\u003c/sup\u003e/s, and 0.050 m\u003csup\u003e3\u003c/sup\u003e/s. The surface roughness coefficients of three types of channel linings\u0026mdash;the common concrete lining, the polyurea-coated lining, and the MPHC lining\u0026mdash;were calibrated using the Chezy-Manning formula. The experimental results are summarized in Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab1\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 1\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eThe relationship between the flow and the water depth of the channel model\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"10\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c6\" colnum=\"6\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c7\" colnum=\"7\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c8\" colnum=\"8\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c9\" colnum=\"9\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c10\" colnum=\"10\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\" morerows=\"1\" rowspan=\"2\"\u003e \u003cp\u003eFlow\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colspan=\"3\" nameend=\"c4\" namest=\"c2\"\u003e \u003cp\u003eCommon concrete lining\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colspan=\"3\" nameend=\"c7\" namest=\"c5\"\u003e \u003cp\u003eCommon polyurea coated lining\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colspan=\"3\" nameend=\"c10\" namest=\"c8\"\u003e \u003cp\u003eMPHC lining\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eWater depth 1\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eWater depth 2\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003eRoughness coefficient\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003eWater depth 1\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c6\"\u003e \u003cp\u003eWater depth 2\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c7\"\u003e \u003cp\u003eRoughness coefficient\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c8\"\u003e \u003cp\u003eWater depth 1\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c9\"\u003e \u003cp\u003eWater depth 2\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c10\"\u003e \u003cp\u003eRoughness coefficient\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e0.020\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e0.182\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e0.185\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e0.01445\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e0.178\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e0.180\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e0.01404\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003e0.166\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c9\"\u003e \u003cp\u003e0.168\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c10\"\u003e \u003cp\u003e0.01300\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e0.040\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e0.326\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e0.318\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e0.01462\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e0.310\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e0.315\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e0.01412\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003e0.290\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c9\"\u003e \u003cp\u003e0.295\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c10\"\u003e \u003cp\u003e0.01306\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e0.050\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e0.388\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e0.390\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e0.01487\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e0.366\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e0.370\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e0.01423\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003e0.343\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c9\"\u003e \u003cp\u003e0.339\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c10\"\u003e \u003cp\u003e0.01315\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003eAs shown in Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e, under all tested flow rates, roughness coefficients decreased progressively from the common concrete lining to the polyurea-coated lining and, lastly, the MPHC lining. The MPHC roughness coefficient was 10.0\u0026ndash;11.6% lower than that of common concrete and 7.4\u0026ndash;7.5% lower than the polyurea-coated lining. This reduction in the roughness coefficient can be explained by the Cassie-Baxter theoretical model. The Cassie-Baxter model explains that an air layer forms between the water flow and the MPHC surface, reducing the flow-solid interface area and adhesion. Consequently, the velocity gradient of the water flow is reduced, leading to a decrease in the shear force between the water flow and the channel sidewall. These factors collectively contribute to the smaller surface roughness coefficient observed for the MPHC.\u003c/p\u003e"},{"header":"6. Conclusion","content":"\u003cp\u003eThis study addresses the challenge of achieving a low roughness coefficient in channel linings. Using the Cassie-Baxter model and hydrophobic theory, PDMS and microsilica powder were incorporated to modify ordinary polyurea, creating the non-toxic, odorless, and eco-friendly MPHC. Experimental investigations were conducted to evaluate the hydrophobicity and bond strength of the MPHC after exposure to immersion in water, high-temperature conditions, and freeze-thaw cycles. The key findings are summarized as follows:\u003c/p\u003e \u003cp\u003e(\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e) Enhanced hydrophobicity and weather resistance: The incorporation of PDMS and microsilica powder creates a \u0026ldquo;binary structure\u0026rdquo; on the surface of the MPHC. Compared to the ordinary polyurea coating, the contact angle of the MPHC increases significantly, indicating improved hydrophobicity. After undergoing immersion, high-temperature, and freeze-thaw treatments, the contact angle of the MPHC exhibits minimal variation, demonstrating excellent weather resistance and stable hydrophobic properties.\u003c/p\u003e \u003cp\u003e(\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e) Bond strength performance: The MPHC bond strength is slightly reduced compared to unmodified polyurea due to the surface presence of PDMS, which slightly hinders bonding performance. However, the improvement in hydrophobicity outweighs this minor drawback. Furthermore, the bonding performance of the MPHC remains stable, with no signs of degradation observed after immersion, high-temperature, and freeze-thaw treatments.\u003c/p\u003e \u003cp\u003e(\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e) Drag reduction performance: Tests on the channel model lining reveal that the MPHC achieves the lowest roughness coefficient among the tested materials. The roughness coefficient of the MPHC is reduced by 10.0\u0026ndash;11.6% compared to ordinary concrete and by 7.4\u0026ndash;7.5% compared to the ordinary polyurea coating. This improvement is primarily attributed to the \u0026ldquo;binary structure\u0026rdquo; on the MPHC surface, which reduces the flow-solid interface area and adhesion, thereby lowering the shear force between the water flow and the channel sidewall.\u003c/p\u003e \u003cp\u003eIn summary, the MPHC exhibits superior hydrophobicity, stable bond strength, and exceptional drag reduction, making it a durable and eco-friendly channel lining material.\u003c/p\u003e"},{"header":"Declarations","content":"\u003ch2\u003eConflicts of interest:\u003c/h2\u003e\n\u003cp\u003eThe authors declare they have no financial interests.\u003c/p\u003e\n\u003ch2\u003eFunding\u003c/h2\u003e\n\u003cp\u003eThis work was supported by National Natural Science Foundation of China (52179133) and College student innovation project of North China University of Water Resources and Electric Power (2023XA012).\u003c/p\u003e\n\u003ch2\u003eAvailability of data and material\u003c/h2\u003e\n\u003cp\u003eThe datasets used and/or analyzed during the current study are available from the corresponding author on reasonable request.\u003c/p\u003e\n\u003ch2\u003eAuthor Contribution\u003c/h2\u003e\n\u003cp\u003eLingyun Feng wrote the main manuscript text, Lingyun Feng and Jingjing Liu conducted experimental research and Chunli Liu made the drawing，Aijiu Chen conducted the review. All authors reviewed the manuscript.\u003c/p\u003e\n\u003ch2\u003eAcknowledgments\u003c/h2\u003e\n\u003cp\u003eI would like to thank my undergraduate students for their help in the experiment.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\u003cli\u003e\u003cspan\u003eMa, J. \u0026amp; Shi, Z. Research on the absolute roughness of the typical channel of the south-to-north water diversion project. \u003cem\u003eJ. Hydroelectric Eng.\u003c/em\u003e \u003cb\u003e26\u003c/b\u003e (5), 75\u0026ndash;79 (2007).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eNiazkar, M., Talebbeydokhti, N. \u0026amp; Afzali, S. H. One dimensional hydraulic flow routing incorporating a variable grain roughness coefficient. \u003cem\u003eWater Resour. Management: Int. J. - Published Eur. Water Resour. Association (EWRA)\u003c/em\u003e. \u003cb\u003e33\u003c/b\u003e (3), 4599\u0026ndash;4620 (2019).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eYang, K., Cao, S. \u0026amp; Liu, X. Flow resistance and its prediction methods in compound channels. \u003cem\u003eActa. Mech. Sin.\u003c/em\u003e \u003cb\u003e23\u003c/b\u003e (1), 23\u0026ndash;31 (2007).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eYang, K. \u0026amp; Wang, Y. System identification of channel roughness forMid-Route Project of South-to-NorthWater Diversion. \u003cem\u003eChin. Eng. science: Engl. Ed.\u003c/em\u003e \u003cb\u003e11\u003c/b\u003e (6), 58\u0026ndash;64 (2013).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eFatxulloyev, A., Allayorov, D. \u0026amp; Otakhonov, M. Study of hydraulic parameters for concreting channels, \u003cem\u003eIOP Conference Series: Earth and Environmental Science\u003c/em\u003e, 614(1): 012054. (2020).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eTian, J. L. \u0026amp; Niu, J. G. The performance study of the open channel concrete in cold area. \u003cem\u003eAdv. Mater. Res.\u003c/em\u003e \u003cb\u003e1896\u003c/b\u003e (535\u0026ndash;537), 1661\u0026ndash;1664 (2012).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eZeng, X., Huang, G. \u0026amp; Duan, W. Summarization of investigation on roughness of concrete channels. \u003cem\u003eJ. Yangtze River Sci. Res. Inst.\u003c/em\u003e \u003cb\u003e16\u003c/b\u003e (4), 1\u0026ndash;4 (1999).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eMo, T. \u0026amp; Lou, Z. Numerical simulation of frost heave of concrete lining trapezoidal channel under an open system. \u003cem\u003eWater\u003c/em\u003e \u003cb\u003e12\u003c/b\u003e (2), 335 (2020).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eLi, Q., Wu, B. \u0026amp; Zhou, H. Damage simulation analysis of canal concrete lining plates based on temperature-stress-water load coupling. \u003cem\u003eSustainability\u003c/em\u003e \u003cb\u003e14\u003c/b\u003e (15), 9202\u0026ndash;9202 (2022).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eShi, S., Zuo, M. \u0026amp; Zhou, H. the occurrence and diagnosis of frost damage degradation in concrete open channels. \u003cem\u003eJ. agricultural rural Eng.\u003c/em\u003e \u003cb\u003e83\u003c/b\u003e (10), 835\u0026ndash;838a832 (2015). (in Japanese).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eLi, B. et al. Sealing and anti-seepage polyurea coating design method based on nonlinear FEM simulation. \u003cem\u003eEng. Comput.\u003c/em\u003e \u003cb\u003e41\u003c/b\u003e (8\u0026ndash;9), 2289\u0026ndash;2309 (2024).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eGuo, H. et al. Investigation of polyurea coating influence on dynamic mechanical properties of concrete. \u003cem\u003eStructures\u003c/em\u003e \u003cb\u003e69\u003c/b\u003e, 107446\u0026ndash;107446 (2024).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eHuang, C., He, X. \u0026amp; Zhang, J. Cavitation pit evolution process of epoxy and polyurea coatings on mortar substrates. \u003cem\u003eUltrason. Sonochem.\u003c/em\u003e \u003cb\u003e104\u003c/b\u003e, 106813 (2024).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eFame, C. M. et al. Durability of epoxy and vinyl ester polymers in wet, seawater, and seawater sea sand concrete environments: Molecular dynamics simulations. \u003cem\u003eConstr. Build. Mater.\u003c/em\u003e \u003cb\u003e451\u003c/b\u003e, 138645\u0026ndash;138645 (2024).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eSzewczak, A. \u0026amp; Łag\u0026oacute;d, G. Experimental research on the possibility of changing the adhesion of epoxy glue to concrete. \u003cem\u003eMaterials\u003c/em\u003e \u003cb\u003e17\u003c/b\u003e (22), 5398\u0026ndash;5398 (2024).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eDong, H. et al. Mechanical properties and constitutive model of waterborne polyurethane modified concrete in compression at different temperature. \u003cem\u003eJ. Building Eng.\u003c/em\u003e \u003cb\u003e98\u003c/b\u003e, 111357\u0026ndash;111357 (2024).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eUmmin, O. et al. Influence of surface roughness and interfacial agent on the interface bonding characteristics of polyurethane concrete and cement concrete. \u003cem\u003eJ. Building Eng.\u003c/em\u003e \u003cb\u003e91\u003c/b\u003e, 109596 (2024).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eWu, Y. et al. Multiscale study of the damage evolution mechanism of polyurethane concrete under freeze\u0026ndash;thaw conditions. \u003cem\u003eJ. Mater. Civ. Eng.\u003c/em\u003e, \u003cb\u003e36\u003c/b\u003e(11). (2024).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eZhang, F. et al. A review on the preparation of superhydrophobic coatings and their application in concrete in cold regions. \u003cem\u003eMater. guide\u003c/em\u003e : 1\u0026ndash;21. (2023). (in Chinese).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eQin, W. et al. Performance analysis of three kinds of low surface energy drag reduction coatings. \u003cem\u003eMater. Prot.\u003c/em\u003e \u003cb\u003e51\u003c/b\u003e (05), 39\u0026ndash;41 (2018). (in Chinese).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eTian, J. \u0026amp; Xue, Q. Experimental study on the reduction of fluid noise by the components of low surface energy of the coating. \u003cem\u003eChin. J. Appl. Mech.\u003c/em\u003e, (03): 109\u0026ndash;111. (1999). (in Chinese).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eLiu, H. et al. Robust translucent superhydrophobic PDMS/PMMA film by facile one-step spray for self-cleaning and efficient emulsion separation. \u003cem\u003eChem. Eng. J.\u003c/em\u003e, 330. (2017).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eZhang, J., Zhang, L. \u0026amp; Gong, X. Large-scale spraying fabrication of robust fluorine-Free superhydrophobic coatings based on dual-sized silica particles for effective antipollution and strong buoyancy, \u003cem\u003eLangmuir: the ACS journal of surfaces and colloids\u003c/em\u003e, 37(19). (2021).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eHu, P. The Application of SK hand-scraped polyurea in water transfer and distribution projects in the northwestern cold and high-altitude areas. \u003cem\u003ePeople's Yellow River\u003c/em\u003e. \u003cb\u003e41\u003c/b\u003e (04), 122\u0026ndash;124 (2019). (in Chinese).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eLiang, H. et al. Research on the UV resistance performance of single-component polyurea coating materials. \u003cem\u003ePeople's Yangtze River\u003c/em\u003e. \u003cb\u003e54\u003c/b\u003e (03), 205\u0026ndash;209 (2023). (in Chinese).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eSun, Z. et al. Surface flat-covering flexible water-stop structure for concrete panel joints in cold regions. \u003cem\u003eHydropower\u003c/em\u003e \u003cb\u003e45\u003c/b\u003e (05), 50\u0026ndash;53 (2019). (in Chinese).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eVogler, E. A. Structure and reactivity of water at biomaterial surfaces. \u003cem\u003eAdv. Colloid Interface Sci.\u003c/em\u003e \u003cb\u003e74\u003c/b\u003e (1), 69 (1998).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eFu, C. S. et al. Fabrication of micro-nano structured super-hydrophobic surface and drag reduction in channels. \u003cem\u003eKey Eng. Mater.\u003c/em\u003e \u003cb\u003e1920\u003c/b\u003e (519\u0026ndash;519), 297\u0026ndash;302 (2012).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eLiu, S. Preparation of environmentally friendly superhydrophobic concrete and its application in long-distance water conveyance channels in cold regions, \u003cem\u003eNorthwest Agriculture \u0026amp; Forestry University\u003c/em\u003e. (in Chinese) (2019).\u003c/span\u003e\u003c/li\u003e\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":true,"highlight":"","institution":"","isAcceptedByJournal":false,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true},"keywords":"Modified polyurea, Hydrophobic coating, Channel lining, Roughness coefficient, Binary structure","lastPublishedDoi":"10.21203/rs.3.rs-6544642/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-6544642/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eThe water conveyance capacity of a channel depends heavily on the roughness coefficient of the flow surface, which is challenging to maintain in concrete linings due to construction limitations, skill variability, and water erosion. Applying surface coatings has proven effective in reducing roughness, improving conveyance efficiency, and ensuring durability. This study aims to develop and evaluate a novel hydrophobic coating, the modified polyurea hydrophobic coating (MPHC), to overcome the performance limitations of traditional coatings. The MPHC was formulated using polyurea, polydimethylsiloxane, and silicon dioxide in a specific mass ratio and was designed to combine strong adhesion, high hydrophobicity, and excellent durability. The coating\u0026rsquo;s performance was assessed through contact angle measurements, tensile bond strength tests, and environmental pretreatment evaluations, including immersion, heat resistance, and freeze-thaw cycling. Experimental results reveal that the MPHC achieves a surface contact angle of 131.2\u0026deg;, demonstrating strong hydrophobicity. The coating incorporates a \u0026ldquo;binary structure\u0026rdquo; formed by the combination of polydimethylsiloxane and microsilica powder, which creates a hydrophobic-rough surface. This structure minimizes the flow-solid interface area and adhesion, enhancing drag reduction performance. The bond strength of the MPHC decreases by only 0.1 MPa compared to unmodified polyurea, demonstrating that polydimethylsiloxane minimally affects bonding performance. Furthermore, durability tests\u0026mdash;including immersion, high-temperature exposure, and freeze-thaw cycles\u0026mdash;show no significant deterioration in either the contact angle or bond strength, confirming the coating\u0026rsquo;s robustness. Drag reduction tests conducted on channel model linings demonstrate that the MPHC reduces the roughness coefficient by 10.0\u0026ndash;11.6% compared to ordinary concrete and by 7.4\u0026ndash;7.5% compared to ordinary polyurea coatings. In conclusion, the findings of this study highlight the suitability of the MPHC for channel concrete linings. Its superior hydrophobicity, durability, and drag reduction performance make it a promising solution for improving the water conveyance efficiency of concrete-lined channels.\u003c/p\u003e","manuscriptTitle":"Development and performance analysis of a modified polyurea hydrophobic coating for improving water conveyance efficiency in concrete channel linings","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2025-05-13 12:23:50","doi":"10.21203/rs.3.rs-6544642/v1","editorialEvents":[{"type":"communityComments","content":0}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"023ecc0c-2874-4b7e-b901-68cbfc2451af","owner":[],"postedDate":"May 13th, 2025","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"posted","subjectAreas":[{"id":48380461,"name":"Physical sciences/Materials science"},{"id":48380462,"name":"Physical sciences/Materials science/Structural materials/Composites"}],"tags":[],"updatedAt":"2025-05-27T04:38:39+00:00","versionOfRecord":[],"versionCreatedAt":"2025-05-13 12:23:50","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-6544642","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-6544642","identity":"rs-6544642","version":["v1"]},"buildId":"8U1c8b4HqxoKbykW_rLl7","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}