Innovative graded application of high-volume fly ash and lime with blended cements for enhanced elastic modulus, bond strength, microstructure and sustainability of concrete

Cement production is a leading source of global CO₂ emissions, highlighting the need for sustainable construction materials and practices. This study explores graded concrete (GC) as an eco-efficient alternative, consisting of two concrete grades, M30 and M20, arranged in a 1:1 spatial configuration using Portland slag cement and Portland pozzolana cement. To enhance sustainability, PSC in the M30 mix was partially replaced 40–70% with 33–63% fly ash (FA) and 7% lime. The properties of GC were assessed through compressive strength, modulus of elasticity, bond strength and abrasion resistance tests, supported with analysis of variance and stress distribution analyses. GC incorporating high-volume FA achieved superior strength and durability compared to M30 concrete, even with 50% cement replaced by 43% FA and 7% lime. While the scanning electron microscopy analysis validated macro-level results, the embodied energy and cost-benefit analyses of GC established the sustainability. The enhanced performance is attributed to a dense interfacial layer between the two grades, ensuring effective stress distribution. GC reduced embodied energy by 31% and cost by 16%, while SEM analysis confirmed a refined microstructure. The findings establish GC as a high-performance, economical, and low-energy construction material utilizing high volume FA supporting the United Nations’ sustainable development goals 9, 11 and 12.