Sodium metabisulfite, with the chemical formula Na2S2O5, usually abbreviated as SMBS, is a widely used chemical substance in the concrete industry. It has multiple functions, including reducing bubbles, extending initial and final setting times, and improving corrosion resistance, thereby significantly improving the performance of concrete. However, attention must be paid to controlling its dosage during use to avoid negative effects.
When mixing concrete, adding an appropriate amount of sodium metabisulfite can effectively reduce the formation of bubbles. This is mainly because sodium metabisulfite has excellent defoaming performance. It can quickly react with water and other components in concrete, producing liquid with strong surface tension, thereby quickly pulling bubbles into the liquid and eliminating them. This bubble elimination effect can make the concrete more dense, thereby improving its compressive strength and durability.
In addition to eliminating bubbles, sodium metabisulfite also has a significant retarding effect. In high-temperature environments, the initial and final setting times of concrete can be shortened, which may lead to cracking and deformation of the structure. After adding sodium metabisulfite, the initial and final setting times of concrete can be significantly extended, thereby avoiding these problems. This retarding effect is mainly achieved by inhibiting the cement hydration reaction. Sodium metabisulfite reacts with certain components in cement to form substances with high viscosity, thereby slowing down the evaporation rate of water and prolonging the initial setting time. In addition, it can also reduce the temperature of concrete by suppressing the heat generated by the cement hydration reaction, thereby further extending the final setting time.
In addition to the above two properties, sodium metabisulfite can also improve the corrosion resistance of concrete. It can react with certain components in concrete to form a dense oxide film, thereby preventing the infiltration of water and harmful substances. This corrosion resistance is particularly important for preventing the erosion of chloride ions and other harmful substances, thereby improving the durability of concrete. Especially concrete structures working in marine environments and other harsh conditions require this type of protection.
