EFFECTS OF THE CATHODIC CURRENT ON ALKALI-SILICA AGGREGATE REACTION

Abstract

In this study, we investigated whether the cathodic current accelerates the alkali-silica aggregate reaction. Variables considered were the water/cement (w/c) ratio, initial alkali content, and cathodic current. The crack initiation time, crack mouth opening history, and microhardness values were monitored to examine the effect of the cathodic current on crack initiation and propagation due to the alkali-silica aggregate reaction. In addition, chemical titration was performed to determine the amount of accumulated sodium and potassium ions to support our viewpoints. The results showed that the crack initiation time shortened with an increase in the initial alkali content, w/c ratio, and/or cathodic current density. Furthermore, the crack opening rate increased in the same manner. Micro-hardness values indicated that the Calcium-Silicate-Hydrate (CSH) gel near the rebar (cathode) had the strongest softening effect. Moreover, the microhardness value for the concrete near the rebar was related to the influencing parameter, phi, which is defined as the product of the cathodic current density and polarization time. Chemical titration proved that the total amount of accumulated potassium and sodium ions increased with an increase in phi The relation between phi and the crack initiation time was investigated when the w/c ratio and the initial alkali content were maintained as constants. The crack initiation time shortened with an increase in phi. In addition, the crack growth rate increased with an increase in phi. The microhardness value decreased linearly with an increase in phi. Thus, the cathodic protection on the reinforced concrete (RC) structure should be carefully applied, particularly for concrete with high potential of the alkali-silica aggregate reaction.