Fe incorporation in cement hydrates: experiments and thermodynamic modeling

Abstract

Current understanding of the state of Fe during the hydration of cement is very limited and further studies are necessary to find out the possible incorporation of Fe in cement hydrates. Moreover, it is important to understand the hydration reaction and properties development of ferrite-rich cement. Our previous study [1] reported the hydration reaction and properties of ferrite-rich Portland cement by various experimental techniques and thermodynamic modelling and compared with ordinary Portland cement. However, we could not quantify the Fecontaining hydrates in the cements and the uptake of Fe by C-S-H. Therefore, the objective of this study is to quantify the Fe-containing hydrates during the hydration of ordinary Portland cement and ferrite-rich Portland cement. Ordinary Portland cement and ferrite-rich Portland cement were hydrated for 3 months and the hydration products were quantified with XRD/Rietveld analysis. The selective dissolution was used to determine the amount of Fe-containing phases. It was found that Fe-siliceous hydrogarnet was the primary Fe-containing phase. From the hydration of ferrite and amount of formed Fesiliceous hydrogarnet, the Fe uptake in C-S-H was determined. The distribution ratio for Fe uptake in C-S-H and chemical composition of Fe-siliceous hydrogarnet were incorporated into the thermodynamic model to predict the hydration reaction of ordinary Portland cement and ferrite-rich Portland cement and the results were compared with experimental data of XRD/Rietveld analysis and selective dissolution. The successful agreement of the experimental results with the model demonstrates the state of Fe in the hydrated cements.