Synergistic Effects of Fly Ash and Metakaolin on the Performance of Sustainable Concrete

This study examines the development of environmentally sustainable concrete incorporating fly ash (FA) and metakaolin (MK). Concrete mixtures of grade M60 were produced with a fixed replacement of 20% FA to promote long-term matrix densification, alongside varying MK contents of 4%, 8%, 12%, and 16%. Mechanical properties, including compressive, split tensile, and flexural strengths, as well as durability characteristics such as sorptivity, water absorption, chloride permeability, and homogeneity, were assessed at curing ages of 7, 28, and 90 days. The results demonstrate that the mixture containing 20% FA and 12% MK delivered the most favourable performance among the SCM combinations, leading to improvements of approximately 24–28% in compressive strength, 21–25% in split tensile strength, and 22–24% in flexural strength relative to the control concrete. Life cycle assessment indicated notable reductions in global warming potential, ozone depletion potential and acidification offering substantial environmental benefits.