Discussing the selection and application of concrete corrosion-resistant materials

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Let’s discuss the selection and application of concrete corrosion-resistant materials. As the environments in which concrete is used become increasingly diverse and industrial pollution grows more severe, the degradation of concrete structures due to environmental factors has become an increasingly prominent issue. Generally, the corrosion damage of concrete structures includes the corrosion damage of the concrete itself and the corrosion damage of the steel reinforcement within it. Since the corrosion of concrete and the steel bars within it reinforce each other, in order to extend the service life of reinforced concrete structures, it is necessary to pay attention to the protection of both concrete and steel bars. The selection and application of corrosion-resistant materials play a crucial role in this regard and deserve special attention. 1. Corrosion resistance of concrete: Concrete contains many pores and capillaries, which facilitate the penetration of chemical agents. To improve its durability, efforts can be made to enhance its density and to isolate these agents. On the one hand, it is necessary to select high-quality materials, determine appropriate proportions, improve construction standards, increase the thickness of the concrete appropriately, and incorporate admixtures such as water reducers, air-entraining agents, and waterproofing agents to enhance the concrete’s impermeability. Some new types of concrete have emerged; these are high-performance concretes made by using large amounts of high-performance admixtures to replace cement, or by using high-performance cementing materials such as plasticized cement or cement with low water demand in place of traditional cement. The concrete produced has properties such as high strength, low shrinkage, and high resistance to chemical corrosion. Steel fiber concrete: The incorporation of steel fibers into concrete significantly enhances its bending and tensile strength as well as fracture toughness, thereby endowing concrete, which is otherwise a brittle material, with good plasticity. For example, when the steel fiber diameter is 0.175 mm, the length is 6, and the content (volume fraction) of steel fibers in the concrete is 6%, the compressive strength of the concrete can be increased by 37.5%. Long-life concrete: When diol ether derivatives are added to ordinary concrete under a water pressure ratio of 0.5, its drying shrinkage rate is 50%–60% that of ordinary concrete. The rate of carbonation can be controlled to about 1/3 of that in ordinary concrete, and the chloride ion penetration rate is 1/4; this enables effective control of the penetration of hydrochloric acid and nitric acid into the concrete, thereby suppressing the rusting of steel rebar. As a result, the rates of concrete carbonation and steel rebar rusting are delayed by more than 10 times. Currently, Japan has developed concrete with a durability of over 500 years. On the other hand, coating the surface of concrete structures with a protective coating is an economical and feasible method to isolate the concrete from the surrounding corrosive agents. Its main purpose is to enhance the concrete’s resistance to carbon dioxide penetration, improve its resistance to chloride penetration, and increase the hydrophobicity of the concrete surface. There are many options available for surface sealing coatings, and most of them can meet the requirements. The surface coatings for concrete differ from the protective coatings used on ordinary steel; the requirements for the base coating material are particularly different. The commonly used sealing coatings include epoxy coatings. Some liquid epoxy resins have a low enough molecular weight and the ability to wet concrete, which allows them to penetrate deep into it. When combined with solvents that enhance the wettability of the concrete surface, these epoxy resins react upon contacting the surface, thereby increasing the strength of the penetrated area. Currently, epoxy coatings are widely used on concrete surfaces due to their alkali resistance, compatibility, and strong adhesion to concrete. If a diluted primer is used, their permeability can be further improved, thereby enhancing their adhesion to the concrete. Vinyl coatings: These coatings are resistant to both acids and alkalis, and they possess excellent resilience and toughness; they are thus very good coatings for concrete. Due to their high molecular weight and high viscosity, vinyl coatings require the use of a diluted primer before application. Applying a vinyl-thinned primer gives the paint a certain degree of penetration into the substrate; although it doesn’t reach the level of liquid epoxy resin, it can **improve the adhesion of the vinyl paint. Due to the fast drying speed, the subsequent coating can be applied within a few minutes. Asphalt coatings come in two types: coal tar asphalt coatings offer good water and chemical resistance, while petroleum asphalt coatings provide excellent weathering and light resistance. Both are widely used in concrete coating applications. Typically, a low-viscosity asphalt coating is used as the base coat, followed by a high-viscosity asphalt coating as the top coat to prevent water penetration. Thick-slurry coal tar pitch coatings offer excellent performance in protecting concrete from chemical erosion and water absorption, and can also reduce the resistance in concrete pipes. Chlorinated rubber coating: Chlorinated rubber coatings offer resistance to water and chemical corrosion, as well as the adhesion and weather resistance required of concrete coatings. Since it is a solvent-evaporating paint, its drying speed is relatively fast. Under high humidity conditions, the coating remains intact. Since chlorinated rubber is not resistant to animal and vegetable oils and fats, it is not suitable as a coating for sewers or as a lining for them. In recent years, with advances in coating technology, many new types of concrete sealing coatings have been developed. For example, in modified silicone coatings, the alkoxy groups react with the water in concrete under the action of alkaline substances to form silanol groups; subsequent dehydration and condensation result in the formation of a non-polar hydrophobic layer on the surface of the concrete, which provides excellent corrosion resistance and water resistance. Glass flake coating with highly corrosion-resistant resin ； Powder coatings and similar products with good environmental performance. 2. Selection and application of corrosion-resistant materials for rebar: To address the issue of rebar corrosion, in addition to changing the material of the rebar itself, such as by using corrosion-resistant or stainless steel rebar, the following measures can also be taken: Rebar rust inhibitors. Rebar rust inhibitors are chemical substances that, when added to concrete, can prevent or slow down rebar corrosion. Some of these inhibitors are used directly in the concrete, while others are applied to the surface of the concrete; they penetrate into the concrete through osmosis and then reach the surface of the rebar to exert their effect. Based on their mechanism of action, rebar rust inhibitors can be classified into anodic, cathodic, and mixed types. The anodic type forms a passivation film on the surface of steel; nitrites are commonly used for this purpose ； Cathodic rust inhibitors prevent or slow down the cathodic process by adsorption or film formation ； Mixed-type rust inhibitors are a class that inhibit both anodic and cathodic reactions simultaneously. Adding a rebar rust inhibitor delays the time at which rebar starts to rust and slows down the rate of rebar corrosion. At present, the RI series of steel corrosion inhibitors in our country have been successfully used in hundreds of projects. Coated steel bars and coated rebar: Coated steel bars are primarily galvanized steel bars, which utilize the fact that zinc has a lower electrical potential than iron to provide cathodic protection for the steel bars. Coated rebar refers to rebar whose surface is coated to prevent contact between the rebar and corrosive agents. In countries such as the United States, Japan, and Canada, spraying epoxy powder coatings on the surface of rebar has become a standard practice. However, in order to reduce production costs, China tends to use the method of spraying high-solid-content epoxy coatings on-site. The test methods and evaluation criteria for steel bar corrosion in concrete can follow GBJ82 \"Test Methods for Long-Term Performance and Durability of Ordinary Concrete\", but at present, there are no suitable methods and standards in China for the selection of anti-corrosion coatings for steel bars. Cathodic protection technology: Cathodic protection is an electrochemical method used to reduce the rate of corrosion of rebar. It is relatively easy to apply cathodic protection to reinforced concrete structures in water or moist soil ； In the atmosphere, concrete has a very high resistance value, which makes the anode material and its installation method major issues. The successfully developed auxiliary anodes include: conductive concrete, trench anodes, cable anodes, conductive coatings, distributed grid anodes, etc. A prerequisite for applying cathodic protection to a structure is that all the rebar in the concrete must be electrically connected; otherwise, stray current corrosion will occur. Cathodic protection requires strict control of the protective potential range to prevent a decrease in clamping force and the occurrence of hydrogen embrittlement caused by hydrogen evolution. To effectively address the corrosion prevention issues of concrete structures, it is necessary to employ a variety of protective measures, while also continuously advancing the development and use of new materials and technologies as well as enhancing monitoring at construction sites, to ensure that concrete structures achieve the desired level of durability.