Corrosion Performance of Plain and Epoxy-Coated MMFX Bars

Abstract

The corrosion resistance of ASTM A1035 Type CL (2% Cr), CM (4% Cr), and CS (9% Cr) steel bars produced by MMFX Technologies were evaluated in both cracked and uncracked concrete as well as in the rapid macrocell test. Uncoated bars with 4% and 9% chromium were tested both in the condition received and after pickling at the University of Kansas; coated bars with 2% and 4% chromium were also evaluated after simulating damage typical to that which would occur during normal handling and placement at a construction site. Bars were compared to the performance of conventional (ASTM A615) and epoxy-coated (ASTM A775) reinforcement from previous studies, and a life-cycle cost analysis over a 75-year design life was performed.

The uncoated MMFX bars with 4% and 9% chromium exhibited approximately three times the chloride threshold and between 30-66% of the corrosion rate of uncoated conventional reinforcement, with the 9% chromium bars exhibiting better performance than the 4% chromium bars. Pickling of 9% chromium bars significantly improved its corrosion resistance, while pickling the 4% chromium bars provided only mild benefit. Both epoxy-coated bars tested (2% and 4% chromium) exhibited reduced disbondment of the coating at the end of testing compared to conventional epoxy-coated reinforcement. The 4% chromium coated bars also exhibited significantly lower corrosion rates relative to conventional epoxy-coated reinforcement, with corrosion rates between 15 and 30% of that of conventional ECR. Coated bars with 2% chromium performed comparably or slightly better than conventional epoxy-coated reinforcement (depending on the test method), but the differences were not statistically significant. The life-cycle cost analysis found that epoxy-coated MMFX with 4% chromium was the most cost-effective reinforcement of the bars in this study.