Study on the Speciation and Distribution of Cr in Hardened Cement Paste-Modified Tessier Sequential Extraction Procedure

摘要

A modified Tessier sequential extraction procedure was employed to investigate the speciation of Cr in hardened Portland cement. The amount of Cr in extracting solution was determined by atomic absorption spectrophotometer and extraction residue was analyzed based on the results of XRD, SEM and EDS. The distribution of Cr in cement was discussed also. The results show that: 7-35% of Cr in hydrated cement exists in the form of exchangeable or bound to carbonates, which is adsorbed or deposited on the surface of hydrate grains and easy to leach out. The leaching of these two species Cr was accompanied by the dissolution of Ca(OH)2 and incongruent dissolution of C-S-H. 65-93% of Cr exists as species bound to Fe-Mn oxides, bound to sulfide compounds or residue, which leached out with the decomposition of hydration products such as AFt, C-S-H and unhydrate phases. Cr existing as species exchangeable or bound to carbonates increases with curing age gradually.