Corrosion of steel reinforcement is one of the main causes of premature deterioration in reinforced concrete (RC) structures. It causes concrete cover cracking, degrades the steel/concrete bond strength, reduces the cross section of steel bars, and consequently reduces the carrying capacity of RC structures. In general, steel corrosion in concrete structures can be divided into two stages: corrosion initiation and corrosion propagation. In this study, the effect of high performance concrete on the corrosion behavior of steel bar in RC specimens are experimentally investigated, particularly during the propagation stage. Concrete specimens with the addition of fly ash, silica fume, and calcium nitrite were fabricated and tested for over 23 years. The corrosion evolution over time was monitored with open circuit potential. During the propagation stage, the corrosion potential, concrete resistivity, and corrosion rate were also measured. Some selected concrete specimens were terminated and visual observation was conducted. Concrete powder was collected above the rebar trace and concrete core samples were drilled and sliced on selected specimens. The chloride concentration was determined. In addition, the steel bars were cleaned and the corrosion morphology was examined. The maximum corrosion pit depth was measured and the cross sectional loss of steel bars was also estimated. Results showed that during the propagation stage, a more negative corrosion potential is related to a higher corrosion rate and a lower concrete resistivity. Localized corrosion was observed on most of the steel bars, with average mass loss ranging from 1.66% to 9.86%, and a pitting factor varying from 1.12 to 2.65, respectively. Addition of fly ash, silica fume, and calcium nitrite reduced the corrosion rate, compared with ordinary Portland cement (OPC). Use of fly ash and silica fume also reduced the chloride concentration at the steel bar surface.
Key words: reinforced concrete, corrosion, chloride, fly ash, silica fume, calcium nitrite