Abstract

This study investigated the potential of pumpkin shell ash (PSA) and sugar beet ash (SBA) as partial replacements for fly ash (FA) in self-compacting geopolymer concrete (SCGC). Twenty-one mixtures were produced using a constant binder content of 550 kg/m³ , an alkaline solution-to-binder ratio of 0.47, and 2 % superplasticizer. The concrete performance was evaluated in terms of fresh properties, mechanical strength, transport behavior, thermal resistance, and microstructure. Higher PSA and SBA contents reduced workability due to their increased surface area and water demand, whereas FA improved both flowability and mechanical strength. The 90FA–5PSA–5SBA mixture achieved the best overall performance, with a 28-day compressive strength of 110.7 MPa, splitting tensile strength of 9.1 MPa, flexural strength of 14.5 MPa, and a modulus of elasticity of 46.09 GPa. This mixture also exhibited low chloride ion penetration (275 Coulombs), minimal water permeability (1.43 × 10⁻¹¹ cm/s), and a low sorptivity coefficient (2.76 × 10⁻⁴ mm/s⁰·⁵). The compressive strength increased slightly at 200 °C (114.9 MPa) but decreased to 35.2 MPa at 800 °C. Correlation analysis identified FA as the most influential binder, while PSA and SBA enhanced performance when incorporated at optimal proportions. SEM observations confirmed a denser and more homogeneous matrix in ternary blends, demonstrating the synergistic effects of PSA and SBA on microstructural refinement. Overall, PSA and SBA demonstrated strong potential as sustainable supplementary binders for producing high-performance SCGC with improved mechanical and durability characteristics.