Influence of rice husk ash and rice tiller ash along with chromate reducing agents on strength and hydration properties of Ordinary Portland Cement

Six blended cement samples were prepared by adding either reducing agents (1% SnCl2·2H2O and FeSO4·2H2O) only or reducing agents along with agricultural waste (rice husk ash, RHA and rice tiller ash, RTA). Cr (VI) leachability of pure Ordinary Portland Cement, OPC (S1) and blended samples (S2-S7) was checked using the standard diphenylcarbazide (DPC) method. It has been observed that blended cement samples with 1% stannous chloride (S3, S5 and S7) are more effective in reducing Cr(VI) content than cement samples with 1% ferrous sulfate (S2, S4 and S6). Addition of reducing agents only (S2 and S3) delayed the initial hydration process, as reducing agents might be reacted with Ca(OH)2 to form ettringite phases and decreases Ca(OH)2 content. Initial as well later age hydration improved on addition of rice husk ash or rice tiller along with reducing agents (S4-S7). Amorphous silica of RHA and RTA reacted with Ca(OH)2 to form calcium silicate hydrate which provides strength to the cement and improve the hydration. Microstructural changes in these samples were analyzed by thermo gravimetric analysis (TGA), scanning electron microscopy (SEM) and X-ray diffraction (XRD).