Quantifying the microstructure evolution and phase assemblage of solid waste as construction materials by EDS image analysis: A case study of carbonated basic oxygen furnace slag aggregates

Abstract

The diversities of raw materials and manufacturing techniques lead to large fluctuations in the upcycling potential of solid waste as construction materials. A quantitative energy dispersive X-ray spectroscopy (EDS) image analysis methodology was developed to measure the microstructure evolution and phase assemblage of solid waste. Based on the proposed EDS image enhancement algorithm, the component complexity and structural heterogeneity of basic oxygen furnace slag (BOFS) can be fully revealed by the EDS images. Thereafter, the proportions of major phases (i.e., pores, reaction products, and unreacted components) and the specific composition information of involved phases can be determined. The spatial distributions of reaction products and unreacted components could be studied by the lineal-path distribution function and the phase assemblage of reaction products could be studied by the elemental ratios. The results showed that the effects of subsequent hydration on the microstructural and mineralogical alterations of carbonation products were more prominent than the consumption of unreacted components. The continuous dissolution of the Ca and Si ions upon the hydration significantly promoted the transformation of carbonation products and microstructure densification of BOFS aggregates, which was the main contributor to the development of mechanical performance.