Sustainable self-compacting concrete: A study on the combined effects of waste glass powder and metakaolin as cement replacements

Partial replacement of cement with eco-friendly pozzolanic materials, such as waste glass powder (WGP) and metakaolin (MK), offers a sustainable approach to improving the service life of self-compacting concrete (SCC). This study evaluates the effects of WGP and MK, individually (binary) and combined (ternary), as partial replacements for cement. Concrete mixes were assessed for workability, mechanical properties, and microstructure. Workability tests showed WGP enhances flow properties, while MK reduces them; however, their combined use at 15% replacement maintained performance. The ternary mix with 5% MK and 10% WGP (5MK+10WGP) exhibited superior mechanical properties, surpassing the control by 7.7% in compressive strength and 3.8% in split tensile strength at 56 days. SEM analysis revealed refined pores, reduced porosity, a denser microstructure, and well-formed C-S-H gels. XRD confirmed these findings with a pronounced broad hump in the 29°–34° 2θ range, indicative of well-developed C-S-H phases. This research demonstrates that incorporating 5MK+10WGP optimally balances workability, strength, and microstructure, providing a sustainable alternative for cementitious materials in SCC, reducing cement consumption, CO₂ emissions, and conserving natural resources.