Petrology and stability of steel slags

The constitution and microstructure of steelmaking slags is described and reviewed following 50 years of research since the classic Iron and Steel Institute accounts. Particular attention is given to the susceptibility of some slags of calcic composition to volumetric instability that is caused by the hydration of the lime phase and periclase. The relative propensity for expansion of the various crystalline and textural forms of these phases is discussed. The occurrence of such steel slags is a matter for concern, e.g. where old iron- and steelmaking sites are being redeveloped. The study by means of optical microscopy of appropriate samples taken during site investigations provides a practical method of assessing the types and amounts of the various steel slags and other materials that are present. The utilisation of modern steel slags depends on appropriate conditioning (such as weathering) and on careful monitoring of their quality and consistency.