Hydration of blended cement with high volume iron-rich slag from non-ferrous metallurgy

The hydration of blended cements with up to 70 wt% iron-rich slag was investigated. Isothermal calorimetry revealed a retarding effect of the slag on Portland cement hydration during the first day, while from 2 days onwards the reaction extent of C3S, C3A and C4AF increased. The slag reacted to 20–30% after 150 days resulting in AFm phases, as well as a new phase with a layered double hydroxide structure with (Mg + Fe)/Al around 3. Fe was also detected in the C-S-H phase of the blended cements, whereas no clear increase of Fe(III)-containing hydrates was observed. The Ca/Si atomic ratio of C-(A)-S-H in the blended cements decreased with increasing slag content, while the Al/Ca ratio increased only slightly. This study elucidated the fate of iron in cements blended with iron-rich slags and showed the suitability of the latter as SCM with a reactivity similar to the one of siliceous fly ash.