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, C(3)A and C(4)AF 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.

Automated summary

The study found that iron-rich slag has a retarding effect on the hydration of ordinary Portland cement, but as time progresses, the reaction extent of different components in blended cements increases. Iron interacts with other components in blended cements, forming different forms of iron presence. The Ca/Si atomic ratio of C-S-H in blended cements decreases with increasing slag content, while the Al/Ca ratio increases slightly.