Risk of environmental contamination arising from concrete structures, Part II: Toxic substance

Abstract

The present study concerns the immobilisation of hexavalent chromium (Cr (VI)) ions in the cement matrix. Both the water-soluble and acid-soluble Cr (VI) ions in cement were measured using the spectrophotometer. As a result, the concentration of water-soluble Cr (VI) in cement ranged from 12.3 to 19.0 mg/kg-cem, and the dissolution of acid soluble Cr (VI) was strongly dependent on the pH of solvent, ranging from 172.4 to 318.2 mg/kg-cem. Simultaneously, the influence of cement hydration on the Cr (VI) solubility was investigated. After a cement hydration for 28 days, the water-soluble Cr (VI) was sharply decreased to about 2.0 mg/kg-cem, whilst no particular change in the acid-soluble Cr (VI) was observed. The reduction of water-soluble Cr (VI) may be attributed to a physical adorption of Cr (VI) ions in the cement matrix then to immobilise them, rather than chemical reaction with C(3)A or ettringite, being postulated in previous studies.