Microstructural and mechanical evaluation of HVFAC incorporating recycled plastic flakes and pozzolanic additives for environmental sustainability

This research examines the microstructural behaviour of High-Volume Fly Ash Concrete (HVFAC) in both plastic and hardened states, highlighting how constituent materials influence performance characteristics. As microstructure governs mechanical strength, durability, and long-term stability, the study evaluates the impact of admixtures on structural integrity. It emphasizes mix design modifications to tailor microstructural properties and enhances concrete performance through engineered material combinations. Eleven M-30 grade concrete mixes were developed over eight days using Ordinary Portland Cement (OPC), Pozzo Crete 100 (processed fly ash), Silica Fume (SF), and Waste Plastic Bottle Flakes (PBFs) in varying ratios, with 1 % superplasticizer by weight of cementitious material. After 28 days of water curing, compressive strength and non-destructive testing (NDT) assessed mechanical performance. Microstructural analysis via Scanning Electron Microscopy (SEM) and Energy-Dispersive X-ray Spectroscopy (EDS) was performed on powdered samples from each mix. The studies revealed diverse morphological features, including dense, refined matrices; porous Interfacial Transition Zones (ITZ); spherical fly ash particles; glassy textures; and partially unreacted pozzolanic materials. A denser microstructure correlated with improved durability, including reduced permeability and enhanced resistance to chloride ingress and chemical attack, suggesting suitability for aggressive environments. Additionally, including plastic waste supports sustainability goals and presents potential for non-structural or moderately loaded applications, balancing mechanical performance with environmental considerations. This study highlights the potential of synergistic material combinations to optimize concrete for targeted performance and sustainability outcomes.