Stability study and impact of the Cr (VI) reducing additives on cement performance

Abstract

A potentially serious condition could occur when cement containing Cr (VI) comes into contact with the skin causing irritations and eczema.

The objective of the present research work is to evaluate the effectiveness of various Cr (VI) additives to Portland cement on its storage for longer periods of time. The cement samples containing various additives were stored in polythene bags and periodically their Cr (VI) levels were tested using the 1,5- diphenylcarbazide method at 540 nm on an UV-Visible spectrophotometer.

The Difference in Cr (VI) amount in freshly prepared and stored samples for different duration helped to assess the change in efficacy. The physical testing of these cement mortar samples were also carried out to understand the effect of these additives on cement quality.

The stannous sulfate (SnSO₄) was found to be the best additive for reducing Cr (VI) in cement and also, it was observed to be relatively stable for longest period. XRD, TG-DSC and Electron microscopic studies were further used to understand effect of SnSO₄ on cement when added as reducing agent for Cr (VI).

Except sodium borohydride (NaBH₄), no other additive investigated in this study showed adverse impact on the strength of the cement. Both SnSO₄ and MnSO₄ exhibited improvement in the compressive strengths of the cement mortars.

Key words:  Cr (VI), SEM, XRD, compressive strengths, TG-DSC.