Alkali Activation of Ladle Slag from Steel-Making Process

Ladle slag, currently an under-utilized crystalline metallurgical residue, was studied for use as a precursor for alkali activation. An activating solution containing sodium silicate and potassium hydroxide was used in activating the slag with varying compositional ratios in order to optimize the compressive strength. Ladle slag is commonly regarded as having limited reaction with alkalis, and in previous studies, it has been therefore mixed with reactive precursors, such as metakaolin. However, based on our results, ladle slag shows potential as a sole precursor for alkali-activated binders. X-ray diffractometry reveals that the major minerals in the ladle slag were identified to be gamma-dicalcium silicate and mayenite. After alkali activation, the major reaction product was a silicate hydrate according to DRIFT analysis-sodium-substituted calcium aluminosilicate hydrate gel, C-(N)-A-S-H. XRD analysis supports the hypothesis by revealing an amorphous "halo" in the alkali-activated slag. The unconfined compressive strength of the optimized alkali-activated ladle slag paste specimen was 65 MPa at 28 days.