Corrosion of Steel in Blended Concretes Containing OPC, PFA, GGBS and SF

The chloride threshold level (CTL) in mixed concrete containing, ordinary Portland cement (OPC), pulverized fuel ash (PFA) ground granulated blast furnace slag (GGBS), and silica fume (SF) is important for study on corrosion of reinforced concrete structures. The CTL is defined as a critical content of chloride at the steel depth of the steel which causes the breakdown of the passive film. The criterion of the CTL represented by total chloride content has been used due to convenience and practicality. In order to demonstrate a relationship between the CTL by total chloride content and the CTL by free chloride content, corrosion test and chloride binding capacity test were carried out. In corrosion test, Mortar specimens were cast using OPC, PFA, GGBS and SF, chlorides were admixed ranging 0.0, 0.2, 0.4, 0.8, 1.0, 1.5, 2.0, 2.5 and 3.0% by weight of binder. All specimens were cured 28 days, and then the corrosion rate was measured by the Tafel's extrapolation method. In chloride binding capacity, paste specimens were casting using OPC, PFA, GGBS and SF, chlorides were admixed ranging 0.1, 0.2, 0.3, 0.5, 1.0, 1.5, 2.0, 2.5 and 3.0% by weight of binders. At 28days, solution mixed with the powder of ground specimens was used to measure binding capacity. All specimens of both experiments were wrapped in polythene film to avoid leaching out of chloride and hydroxyl ions. As a result, the CTL by total chloride content ranged from 0.36-1.44% by weight of binders and the CTL by free chloride content ranged from 0.14-0.96%. Accordingly, the difference was ranging, from 0.22 to 0.48% by weight of binder. The order of difference for binder is OPC > 10% SF > 30% PFA > 60% GGBS.