Influence of limestone filler on potassium citrate activated BOF slag binder

Basic Oxygen Furnace slag (BOF slag) is a by-product of steelmaking, which is mainly composed of C 2 S and Brownmillerite (C 4 (A, F), which give it cementitious properties. Previous work reveals that citrate salts can activate Brownmillerite to obtain a performant binder based on BOF slag without including any Portland cement. Nevertheless, the C 2 S is still not activated in this system, and its early reactivity remains very low. The effect of limestone on the mechanical properties of the binder and its phase assemblage are investigated and compared to the effect of quartz. The results show that the use of fillers improves the performances of the BOF slag pastes with more hydration products being formed. They highlight the superior effect of fine limestone incorporation, compared to quartz, with a minimum dosage of 9 vol%. The resulting BOF slag binder exhibits an increase in compressive strength of 55 % compared to the reference and a decreased total porosity. • Small amount of filler improves the compressive strength of the activated BOF slag binder, after 7 days. • Fine fillers (d 50 ̴ 4.5 µm) are more effective than coarser fillers (d 50 ̴ 10 µm), improving the binder performance. • The hydration products are mainly hydrogarnets, and C-S-H gel. • Filler use slighlty reduces porosity by increasing the amount of hydration products, mainly C-S-H. • The fillers do not interfere with the tri-potassium citrate activation of brownmillerite.