Title:
Performance of Steel Reinforcement in Portland Cement and High-Volume Fly Ash Concretes
Author(s):
P. Gu, J. J. Beaudoin, M. H. Zhang, and V. M. Malhotra
Publication:
Materials Journal
Volume:
96
Issue:
5
Appears on pages(s):
551-559
Keywords:
chlorides; concretes; corrosion; fly ash; reinforcing steels
DOI:
10.14359/657
Date:
9/1/1999
Abstract:
This paper describes the performance of steel reinforcement in portland cement and high-volume fly ash (HVFA) concretes. A number of large slabs 833 x 600 x 153 mm in size were cast from six air-entrained concrete mixes. Four of these mixes were made with normal portland cement with the water-cement ratio (w/c) of the mixes ranging from 0.32 to 0.76; the remaining two mixes were made with the HVFA concrete with a w/c + FA of 0.32. The steel reinforcing bars were placed in concrete with cover thickness ranging from 13 to 76 mm. The concrete slabs were ponded with a 3.4 percent sodium chloride solution for a period of 6 months, and half-cell potential, linear polarization, and A.C. impedance techniques were applied to monitor the progress of the corrosion of steel reinforcement. The results indicate that the performance of the reinforcing steel bars in the HVFA concrete after 6 months of ponding with a 3.4 percent sodium chloride solution was excellent. There was no significant steel corrosion taking place on the reinforcing bars embedded in the HVFA concrete, even with a 13-mm concrete cover. This performance of HVFA concrete is equivalent to that of the control concrete with a w/c of 0.32, and is better than the control concrete with w/c 0.43. Significant corrosion rates were observed for the reinforcing bars embedded in control portland cement concrete with w/c 0.43. As expected, the poorest performance was of the control concrete with a w/c of 0.76, where even the reinforcing bars with a 51-mm cover exhibited corrosion.