Risk of environmental contamination arising from concrete structures, Part III: Alkali leaching

Abstract

The present study concerns the leaching of alkali ions in terms of leaching capacity and leaching rate. Tests were performed in two conditions: air-tight and aerated. As a result, it was found that the leaching capacity was strongly dependent on binder type rather than the W/C. 30% PFA and 60% GGBS had lower leaching capacity, compared to OPC. The pH of media was crucial to leaching rate. At 11.4 and 12.4 in the pH, alkali metallic and hydroxyl ions are mainly extracted from the specimen respectively. The alkali leaching converted the pH profile in the cement matrix. After the alkali leaching, the pH in the vicinity of the surface was even lower than in the inner matrix, where no influence of leaching reached. In an aerated condition, the pH of media was increased initially within several hours, but decreased to 8.31-9.08, presumably due to a precipitation of leached ions.