Degradation of Normal Portland and Slag Cement Concrete Under Load Due to Reinforcement Corrosion

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Title: Degradation of Normal Portland and Slag Cement Concrete Under Load Due to Reinforcement Corrosion

Author(s): K. E. Philipose, J. J. Beaudoin, and R. F. Feldman

Publication: Special Publication

Volume: 132

Issue:

Appears on pages(s): 1491-1508

Keywords: chloride ions; corrosion; degradation; microcracking; polarization; reinforcing steels; slag cements; Materials Research

Date: 5/1/1992

Abstract:
Corrosion of reinforcement is one of the major degradation mechanisms of reinforced concrete elements. The majority of studies published on concrete-steel corrosion have been conducted on unstressed specimens. Structural concrete, however, is subjected to substantial strain near the steel reinforcing bars that resist tensile loads, which results in a system of microcracks. Report presents the initial results of an investigation to determine the effect of applied load and microcracking on the rate of ingress of chloride on and corrosion of steel in concrete. Simply supported concrete beam specimens were loaded to give a maximum strain of about 600 æî on the tension face. Chloride ion ingress on cores taken from loaded specimens was monitored using energy-dispersive x-ray analysis techniques. Corrosion current and rate measurements using linear polarization electrochemical techniques were also obtained on the same loaded specimens. Variables investigated included two concrete types, two steel cover depths, three applied load levels, bonded and unbonded reinforcing steel, and the exposure to tension and compression beam faces to chloride solution. One concrete mixture was made with Type 10 portland cement, the other with 75 percent blast furnace slag, 22 percent Type 50 cement, and 3 percent silica fume. The rate of chloride ion ingress into reinforced concrete and hence the time for chloride ion to reach the reinforcing steel is shown to be dependent on applied load and the concrete quality. The dependence of corrosion process descriptors--passive layer formation, initiation period, and propagation period--on level of applied load is discussed.