Chloride thresholds for initiation of corrosion of steel reinforcement in concrete

A study was performed of variables that affect the chloride threshold for corrosion of reinforcement, including pore water alkalinity, water-to-cement ratio, the use of Florida aggregate, and the addition of fly ash. To accomplish this, specimens were subjected to a periodic wet-dry ponding cycle using 15% by weight NaCl solution. Half cell potential and macrocell current measurements were taken to determine the time to corrosion. Upon active corrosion, the specimens were removed from the ponding cycle and dissected. Powder samples were collected from the concrete at the steel depth to ascertain the total chloride concentration. The determination of the pore water pH was attempted using a leaching method. To date only a portion of the specimens have displayed corrosion. The role of cement alkalinity and water-to-cement ratio in affecting corrosion resistance is reported and the results are discussed within the context of designing concrete structures for corrosion resistance.