Study On Mineralized Composite Coating And Durability Of Functionalized Coastal Concrete Surface

With the growing demand for service life of marine engineering structures,the durability of marine concrete becomes increasingly important.In the marine environment,water carrying aggressive ions penetrates into the concrete interior causing material corrosion and structural deterioration.Microbial adhesion also further aggravates corrosion and structural deterioration.Meanwhile,the pore water forms a fatigue stress combining icing pressure and infiltration pressure under the freeze-thaw cycle,causing concrete strength reduction and spalling damage,which seriously affects the durability of concrete structures.Surface coating technology is an effective measure to improve the durability of concrete,and superhydrophobic coatings with waterproof,anti-icing and self-cleaning properties are the current research hotspots.However,traditional hydrophobic coatings face the fatal defects of low strength and low stability,which lead to the application being greatly restricted.The micro-nano-hybrid structure is one of the necessary conditions for the construction of superhydrophobic surfaces,and its structural stability is to some extent decisive for the overall longevity of hydrophobic coatings.The distinctive feature of biomineralization is the control of crystallization and growth of inorganic mineral phases at the molecular level through the interaction of organic macromolecules and inorganic ions at the interface,which results in a special graded structure and assembly of biominerals.Inspired by biomineralization,a functional mineralized layer with a micro-nano-hybrid structure is established by chemical methods,which enhances the applicability and stability of hydrophobic coatings.Based on the biomimetic mineralization approach,this paper synthesized in situ morphologically controllable inorganic minerals（calcium carbonate and silica）to build micro-and nano-scale hybridized structures,which were modified by low surface energy silane compounding to prepare biomimetic superhydrophobic coatings with excellent water repellency and resistance to ionic erosion.The relevant properties were tested and the effects on the durability of marine concrete were analyzed.The specific research contents were as follows:（1）The polydopamine was used to induce calcium carbonate mineralization on the concrete surface and reduce silver ions to nano-silver in situ to build a micro-nano composite rough structure,which was hydrophobically modified by low surface energy silanes to obtain the functionalized calcium carbonate biomimetic superhydrophobic coating.Then,the composite coating samples were tested for hydrophobic and impermeability performance,abrasion resistance,antibacterial performance,and anti-icing performance,and the results showed that the composite coating samples had excellent performance in all of the above.Compared with the untreated samples,the volumetric water absorption rate of the composite coating samples decreased by 90.3%and 93.44%in the normal environment and simulated seawater environment,respectively,showing good waterproof and anti-permeability performance.After repeatedly rubbing the composite coating sample on the sandpaper surface for 5 m equivalent distance,the contact angle of the coating was still greater than 140°,and the decrease was only 6.87%,showing good wear resistance.The composite effect of the antibacterial property of the functional component nanosilver and the self-cleaning property of the superhydrophobic surface could effectively improve the antibacterial effect of the coating,so that the surface of the composite coating was basically free of bacteria and their metabolites,indicating that the composite coating had excellent antibacterial and anti-fouling properties.The coating could also prevent ice condensation,adhesion and accumulation on the surface,making it easier to remove and effectively prolonging the icing time.（2）In order to further improve the structural stability of the superhydrophobic coating,a silica（Si O₂）mineralized layer with higher hardness and strength was synthesized by in situ mineralization on the concrete surface using the sol-gel method（Sol-Gel）.The hydrophobic modification was accomplished simultaneously by introducing low surface energy silanes during the mineralization process,and a stable silica bionanophobic superhydrophobic coating was constructed in one step.The effects of ammonia concentration,tetraethyl silicate（TEOS）concentration,silane concentration and reaction time on the morphology and structure of the silica mineralized layer were investigated using scanning electron microscope（SEM）characterization and single variable control experimental methods.The protective properties of the coating were characterized by porosity tests,hydrophobic and impermeability tests,abrasion resistance tests,and anti-icing tests.The results showed that the ammonia concentration and TEOS concentration were the main factors affecting the particle size and average aggregation of the mineralized Si O₂microspheres.The presence of the hydrophobic modifier silane could improve the structural compactness of the mineralized layer.The size difference of the mineralized Si O₂spheres gradually decreased with the increase of reaction time,and the morphology of the mineralized layer did not change significantly after 6 h of reaction.The results of the protection performance test showed that the Si O₂composite coating obviously reduced the volume ratio of capillary pores and gel pores inside the substrate,and had the effect of double protection.The contact angle of the composite coating surface was 157°,which showed excellent superhydrophobic performance.The composite coating also reduced the contact area of water droplets with the surface,which further prolonged the icing time.Even in the simulated seawater environment,the water absorption rate of the composite coating was less than 1%,indicating that the coating had excellent water and ion penetration resistance.The surface of the composite coating maintained its hydrophobic state after being damaged by tape peeling and sandpaper abrasion,providing excellent structural stability and wear resistance.