Relationship between Chloride/hydroxide ratio and corrosion rate of steel in concrete

Just as water/cement ratio is an important parameter controlling the strength of concrete, alkali/chloride relationship is an important aspect influencing the performance of steel embedded in concrete. In the past, several studies have been cam’ed out to determine the threshold limit for chloride and it has been established that the tolerable limit for chloride increases with alkalinity. However; in practice, the chloride level is invariably in excess of the tolerable limit and thus is bound to accelerate corrosion. No clear relationship between chloride/hydroxide ratio and corrosion rate of steel has been established so far This paper addresses this important aspect by carrying out some systematic long term evaluation studies. Two diflerent concrete mixes (lean/rich) and two difjerent exposure conditions (immersion/ atmosphere) were used in this investigation. Initial sodium chloride content in the concrete was varied in the range 0, 0.01, 0.05, 0.1, 0.5, 1 and 3.5% N by weight of cement. Corrosion rate was evaluated by conventional gravimetric method. The investigation revealed that even with adequate oxygen availability, the corrosion rate of steel embedded in concrete increases steeply with the Cl/OH ratio, and no such relationship is found to exist when the exposure conditions restricts the availability of oxygen