Microstructural characteristics of iron-steel slag concrete: A brief review

The flexibility in the production of concrete permits the incorporation of numerous industrial by-products as a feasible replacement for conventional natural ingredients. Generally, the physicochemical characteristics of the industrial by-products result in variations in the microstructure of concrete. Several petrographic techniques have been used in concrete to understand the alternation in the microstructure of the material instigated by the addition of different industrial by-products. Various petrographic techniques, such as scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS), have been successfully implemented in the field of research in the last decades for microstructural characterization. Currently, the usage of iron-steel slag in concrete has opened an extensive range of potentials for understanding the microstructural behaviour of iron-steel slag as Portland cement (PC), natural coarse and natural fine aggregates (NCA & NFA) replacement in concrete. This paper briefly reviews some of the microstructural features indicating the physical (pore structure, interfacial transition zone (ITZ), shape, etc.) and chemical characteristics of iron-steel slag-based concrete. The effects of different variables, such as slag content, curing conditions, and mixing techniques, on the microstructure are also examined. The microstructure evaluation reveals the complex behaviour of iron-steel slag in concrete, as in some cases its utilization has proved to be beneficial. On the other hand, its presence beyond a certain limit degrades the microstructural behaviour of concretes. This review highlights the general trends in understanding the variation in compressive strength as well as microstructural characteristics over the range of replacement of slag in concrete as a potential replacement of cement, fine and coarse aggregate.