Morphological and microstructural analysis of sustainable concrete with crumb rubber and SCMs

Abstract The environmental burden of Portland cement production, a major contributor to global CO 2 emissions, calls for innovative material solutions in concrete technology. This study examines the morphological and microstructural characteristics of sustainable concrete incorporating crumb rubber (CR), fly ash (FA), silica fume (SF), and marble slurry powder (MSP). Fifteen hybrid mix designs were prepared and characterized using X-ray diffraction, Fourier transform infrared spectroscopy, field emission scanning electron microscopy, and energy dispersive X-ray spectroscopy to investigate phase composition, hydration products, and interface morphology. The optimal mix containing 5% SF, 10% MSP, and 15% FA exhibited significant portlandite reduction (∼22–25%) and enhanced amorphous C–S–H gel formation, indicating strong pozzolanic interaction. MSP contributed to pore refinement and improved interfacial bonding, while CR, despite its non-reactive nature, enhanced the ductility and energy absorption potential of the matrix. Elemental mapping confirmed uniform distribution of Ca and Si, supporting improved hydration product formation and microstructural integrity. These findings demonstrate the synergistic effect of CR and supplementary cementitious materials in improving concrete’s internal structure and contribute to ongoing efforts to reduce the construction industry’s carbon footprint.