Q.: For corrosion protection, ACI 318-95, Building Code Requirements for Structural Concrete, specifies maximum water-soluble chloride ion in concrete as percent by weight of cement. What are acceptable levels when measuring chloride-ion content in existing concrete—specifically, by weight of the concrete sample?

A.: For an exact answer you need to know the cement content and unit weight of the concrete. For instance, if the cement content is 600 pounds per cubic yard, a maximum allowable chloride-ion content of 0.15% by weight of the cement corresponds to 0.9 pounds of chloride ion per cubic yard. If a cubic yard of concrete weighs 3,800 pounds (about 142 pounds per cubic foot), the level would be 0.9/3,800, or 0.024% by weight of the concrete.