Improved compressive strength of alkali activated slag upon heating

• Thermal stability of alkali activated steel slag was investigated.
• Alkali activated slag exhibits improved strength in a high temperature environment.
• Strengthening is described based on the microstructural modifications.
• Mineralogical transformation of wüstite into magnetite was observed to and above 600 °C.

This paper presents a study on thermal stability of alkali activated slag (AAS) prepared from electric arc furnace slag (EAFS) using a mixture of alkaline sodium hydroxide and sodium silicate solutions. The samples were investigated by means of XRD, SEM, TG/DTA and porosity analysis. Compressive strengths of AAS samples before and after exposure to elevated temperatures ranging from 600 °C to 1000 °C were determined. The significant microstructural modifications highlighted by changes in porosity due to the sintering process are responsible for the strengthening of AAS sample after heating at 600,800 and 1000 °C. Moreover, in AAS sample after heating to and above 600 °C wüstite transforms to spinel.