Mechanical behavior of Angular Fly Ash Aggregates in Lightweight Concrete: Strength Development Properties

This research investigates the viability of using angular fly ash aggregates (AFAA) as a partial or complete replacement for natural coarse aggregates in lightweight concrete production. Experimental analysis evaluated five different replacement proportions (0%, 25%, 50%, 75%, and 100%) with compressive strength measurements conducted at 7, 14, 21, and 28 days of curing. Physical characterization of aggregates revealed that AFAA exhibited higher impact value, crushing value, abrasion value, and water absorption compared to natural aggregates, while having lower specific gravity (1.33 vs 2.55). Fresh concrete properties showed decreasing workability (measured by slump values) with increasing AFAA content. Compressive strength results demonstrated a consistent strength development pattern across all mixtures, with strength inversely proportional to AFAA content. The optimal replacement level was identified at 50% AFAA, achieving a 28-day compressive strength of 25.93 MPa while maintaining satisfactory workability. A regression-based mathematical model was developed to predict strength evolution over time, showing high correlation (R² values between 0.914-0.992) across all mixture proportions. Beyond mechanical performance, AFAA incorporation offers significant environmental benefits through waste utilization, natural resource conservation, and reduced carbon footprint compared to traditional aggregates. The findings suggest that appropriately proportioned AFAA can serve as a viable alternative in lightweight concrete applications, supporting sustainable construction practices while maintaining adequate structural performance.