Corrosion effects of stabilized backfill on steel reinforcement

Cement stabilization of backfill has been used for some time in mechanically stabilized earth type retaining walls. However, there has been no data on the corrosion life of galvanized steel reinforcement in this environment, which is intermediate in pH between normal soil and pure concrete. Field observations had indicated a potential corrosion problem at a particular site in Deer Park, Texas. Cement addition to backfill in the usual quantities (i.e., 7 percent or more) raised the pH environment to values close to that of normal concrete. At these levels corrosion rates of zinc coatings were not significantly accelerated - if anything, corrosion rates were less than for unstabilized fill. Very small amounts of cement addition, in the order of 1 to 4 percent producing pH values significantly less than 12, could cause limited acceleration of corrosion. It is, therefore, advisable to control minimum cement levels and to encourage efficient mixing. The use of crushed concrete as backfill did not accelerate corrosion. This material, therefore, appears to be acceptable for this application.