Basic oxygen furnace (BOF) slag cementitious binder activated by Na4EDTA

Basic oxygen furnace (BOF) slag contains two potentially hydraulically reactive phases, belite (C2S) and brownmillerite (C2(A,F)), yet exhibits low reactivity. This study proposes ethylenediaminetetraacetic acid tetrasodium salt (Na4EDTA) as a hydration activator and investigates its effects on BOF slag phase evolution, early hydration kinetics, microstructural development, mechanical properties, and leaching behaviors. The EDTA4− chelation mechanism in the BOF slag system is also discussed. Results show that Na4EDTA significantly enhances BOF slag hydration, producing a stand-alone binder with high compressive strength (38.8 MPa at 28 d, v.s. 8.6 MPa of the reference) and reduced porosity. At 4.8 wt% Na4EDTA, brownmillerite reacts almost completely within one day. Belite hydration is also enhanced, particularly at early ages. The main hydration products are hydrogarnet and C-S-H gel. EDTA itself is likely partially incorporated into the layered double hydroxides (LDHs) structure of hydrotalcite. Heavy metal leaching is below the Dutch legal limits.