# Activation Potential of Various Activators for Ferronickel Slag Under Steam Curing: Characterization of Hydration Products and Mechanical Properties

## TL;DR

This study explores how different activators affect the hydration and strength of ferronickel slag in construction materials under steam curing.

## Contribution

The study reveals that Ca-based activators, especially a Ca(OH)2–gypsum composite, outperform Na- or K-based activators in activating ferronickel slag.

## Key findings

- Finer ferronickel slag particles contain amorphous MgO that reacts with Ca-based activators to form hydrotalcite.
- Ca(OH)2–gypsum composite shows superior activation performance compared to NaOH or KOH.
- KOH activation produces a knotted-fiber-bundle-like K–A–S–H phase that may improve crack resistance.

## Abstract

This study investigates the activation potential of various activators for ferronickel slag (FNS) and the associated phase evolution. First, the existing forms of MgO in FNS were identified by analyzing its phase composition across different particle sizes. Subsequently, FNS was activated using six types of activators—Ca(OH)2, CaO, NaOH, KOH, Na2CO3, and a Ca(OH)2–gypsum composite—under steam curing at 80 °C for 7 days. The setting time, fluidity, hydration products, and mechanical properties of the activated systems were systematically examined. The results show that finer water-cooled FNS particles contain abundant amorphous phases, including amorphous MgO, which can react with Ca-based activators to form hydrotalcite—a reaction not observed with Na- or K-based activators. Compared with Na- or K-based activators, Ca-containing activators, particularly the Ca(OH)2–gypsum combination, exhibited superior activation performance. In addition, distinct microstructures were observed: NaOH activation promoted the formation of a yarn ball-like N–A–S–H gel, while KOH activation led to a knotted-fiber-bundle-like K–A–S–H phase, the latter showing potential for enhancing the crack resistance of cement-based materials. These findings provide new insights into the activator-dependent hydration mechanisms of FNS and support its value-added utilization in sustainable construction materials.