Chloride-induced steel corrosion in concrete: Part 1 - Corrosion rates, corrosion activity, and attack areas

This paper presents results from a major long-term study on chloride-induced steel corrosion in concrete. The performance of a set of 50 reinforced concrete slabs made with a range of portland and blended cement binders was evaluated, Two portland cements, a high C(3)A and a low C(3)A, a blended fly ash cement, and a blended blast furnace slag cement were used. All reinforced concrete slabs were exposed to high chloride conditions by partial immersion in a three percent NaCl solution modeling seawater conditions. The reinforcement was cleaned and weighed prior to inclusion into the concrete slabs. Periodic nondestructive measurements of concrete performance included half cell potential monitoring, concrete resistivity and electrochemical measurements of rates of corrosion of steel in concrete using potentiodynamic anodic procedures. Individual slabs were broken for reinforcement recovery at predetermined times during the study. Measurements were made of the area of corrosion and the weight loss of steel through corrosion. This information was related to the nondestructive data acquired on the slabs. Because of the large amounts of information acquired in this study, information has been published in two parts. In Part I, estimated corrosion current (I-c) data and areas under the I, versus time envelope (Acr) for reinforcement within concrete slabs is presented. These data were obtained using potentiodynamic anodic polarization techniques. Measurements of the reinforcement corroded area in concrete are also presented and related to the electrochemical measurements taken. It was found that concrete water:binder ratio significantly influenced the corrosion rate of steel in concrete. Relationships were established between corrosion activity and the area of chloride-induced steel corrosion. Observed relationships were different for reinforcement within portland cement concretes and blended cement concretes considered. Work described in Part 2 focuses on relationships between electrochemical data on chloride-induced reinforcement corrosion and gravimetric weight losses of steel in the concrete slabs. In addition, the relative performance of the portland and blended cement concretes is evaluated.