Experimental and SEM image segmentation analysis to establish the optimum content of ferrochrome slag aggregate in lime activated high-volume GGBS-based concrete

Abstract

This study investigates the synergistic effects of lime-activated high-volume ground granulated blast-furnace slag (GGBS) binder and ferrochrome slag (FCS) coarse aggregate on the mechanical, durability, and microstructural performance of sustainable concrete. Concrete mixes incorporating 60% GGBS, 7% hydrated lime (lime), and FCS replacement levels of 50%, 75%, and 100% were evaluated through mechanical testing, durability assessment, and microstructural characterization using X-ray diffraction with Rietveld refinement, field-emission scanning electron microscopy (FE-SEM), and U-Net-based semantic segmentation of SEM images. The optimized mix containing 75% FCS achieved a comparable 28-day compressive strength of 33.8 MPa, representing a marginal increase of 3.5% over the control mix, along with similar improvements of approximately 3% in split tensile strength and 2.5% in flexural strength. However, significant durability enhancements were observed, including a reduction of 23% in water absorption and 78% in carbonation depth in addition to an improvement of 72% in acid induced strength loss and 73% in abrasion resistance. Rietveld quantification confirmed substantial portlandite consumption, enhanced calcium silicate hydrate (C-S-H) gel generation, and a higher amorphous fraction, indicating intensified pozzolanic reaction and matrix densification. The presence of stable FCS-derived spinel phases such as forsterite, enstatite, and mullite further contributed to microstructural stability. SEM image segmentation of the optimum mix quantified a 43% reduction in porosity, a 20% increase in the degree of hydration, and a significant refinement of the interfacial transition zone thickness in comparison to the control mix. Environmental assessment demonstrated nearly 38% reduction in embodied carbon and 33% cost savings with a significant improvement of 151% in efficiency index, while TCLP results confirmed effective chromium immobilization less than 0.07 mg/L. Overall, the findings establish 75% FCS replacement as an optimal strategy for producing high-performance, eco-efficient concrete and highlight the potential of industrial by-product valorization in sustainable construction.