ACI 318-11, Building Code Requirements for Structural Concrete, provides minimum coverage requirements that help protect embedded metals from corrosive materials. Chloride ions are the most extensively documented pollutant that can cause corrosion of metals in concrete. To mitigate corrosion of steel reinforcement, corrosion-inhibiting additives, coating the reinforcement with an epoxy resin, and using sealants and membranes on the concrete surface are some of the measures that can be taken. We will look at some of these measures and go beyond the most popular topic of corrosion, iron (Fe) and steel, to include aluminum (Al), zinc (Zn), and concrete.
Embedded prestressing cords, cables, lifting anchors, fixtures, rack angles and galvanized rebar can corrode enough to crack your concrete and masonry coatings. It accelerates the hydration of cement, which accelerates the development of strength and generates heat that can even prevent the concrete from initially freezing. The destruction of the passive layer occurs when the alkalinity of concrete is reduced or when the chloride concentration in concrete increases to a certain level. Edison patented portland cement mixtures in aluminum powder because subsequent reactions with the alkalis in portland cement release hydrogen gas creating foamed concrete useful for insulation purposes.
Electrons stay in the rod and flow to places called cathodes, where they combine with water and oxygen in concrete. As for stainless steel, type 316 is widely used for integrated reinforcing bars, and rebar suppliers should be able to advise on its relative advantages. Acidic solutions can cause attack and corrode steel, and regardless of pH it can cause corrosion in some grades of stainless steel, galvanized steel (by definition, galvanized coating is zinc) and aluminum. Work at FHWA (Clear 197) found that the conversion factor of acid-soluble chlorides to water-soluble chlorides could vary from 0.35 to 0.90, depending on the constituents and history of the concrete.
The amount of carbonation increases significantly in particular with a high water-cement ratio, low cement content, short curing period, low strength and highly permeable or porous paste. Specifically high quality, it has been estimated that carbonation will be carried out at a rate of up to 0.04 inches per year. In conclusion, it is important to take measures to protect embedded metals from corrosive materials such as chloride ions. Contacting a supplier of galvanized and stainless rebar is a good place to start as they have a wealth of experience in this issue. Additionally, corrosion-inhibiting additives, coating the reinforcement with an epoxy resin, and using sealants and membranes on the concrete surface are some other measures that can be taken.
