Strength, sulphate resistance, embodied energy, microstructural features and economic performance of graded concrete made with high-volume fly ash

Abstract

Cement production is a major contributor to global CO2 emissions, prompting the need for sustainable alternatives in construction. This study investigates graded concrete (GC) as a viable solution, comprising two different concrete grades, M30 and M20, arranged in a 1:1 spatial variation using Portland slag cement (PSC) and Portland Pozzolana cement (PPC). To enhance sustainability, PSC in the M30 mix was partially replaced with 40–70 % fly ash (FA) and lime. The mechanical performance of GC was evaluated through compressive and flexural strength tests at 7, 14, 28, 56, 91, and 182 days. Durability was assessed via sulphate resistance test, while ecological and economic aspects were measured through embodied energy and economic index, respectively. Results showed that GC exhibited superior strength and durability compared to standard M30 concrete, even with 50 % cement replaced by 43 % FA and 7 % lime. Additionally, GC demonstrated a 31 % reduction in embodied energy and a 16 % cost savings relative to M30. scanning electron microscopy (SEM) analysis validated the improved microstructure. The study confirms the potential of GC as a high-performance, cost-effective, and environmentally friendly material for structural applications, promoting the beneficial use of industrial by-products like fly ash.