Chromate Ion Transfer Through Mortar by Accelerated Migration Method

Abstract

Chromium (VI) is a highly toxic heavy metal which may be present in cementitious materials (CM) within its constituting elements or external sources and could alter the structure of CM and reduce its compressive strength. Therefore penetration of chromium is an important consideration in environmental engineering concrete structures. For estimating diffusivity of chromium (chromate ion) in cementitious materials, this paper presents an accelerated migration test method for determining the non-steady-state migration coefficient following the simplified Nernst-Planck equation. Likewise, the influence of water-to-cement ratio (w/c), the applied voltage the chromium binding capacity of cement mortar specimen (CMS) and the realistic concentration profile was investigated. For calculation of migration coefficient, the color reagent diphenylamine sulfonate was identified to determine the penetration depth of chromium into the CMS visually. The concentration of chromium was estimated to be about 0.025 percent (wt of CMS) at the discolored border region, and a drop of potential about 3.4 volts was derived. The changes in the microstructure of the CMS due to chromium migration testing were studied. The migration coefficient of CMS obtained between 1.06×10-12 m2/s to 3.25×10-12 m2/s. The w/c of about 0.50 has the highest migration coefficient. The realistic chromium concentration profile in the migration test has a gradual front, and a quadratic curve obeys.