Synergistic Ternary Binders for High-Performance Low-Carbon Supplementary Cementitious Materials Incorporating Industrial and Agricultural By-Products

Abstract This work proposes and mechanistically validates a low-clinker, high-performance cementitious system in which silica fume (SF), palm oil fuel ash (POFA), and palm ash (PA) are co-optimized as a ternary supplementary cementitious matrix for use in Concrete-Filled Steel Tube (CFST) elements. Rather than treating these by-products as simple volumetric cement replacements, the binder is designed as a reactive, compositionally balanced system: SF governs early nucleation and pore refinement through ultrafine amorphous silica; POFA contributes aluminosilicate phases that participate in delayed secondary gel formation; PA introduces alkali-bearing species that accelerate dissolution and promote C-S-H/C-A-S-H polymerization at later ages. This coupled hydration-pozzolanic regime generates a strong, low-capillary microstructure despite a clinker reduction approaching 45%. At 28 days, the optimized mixes achieved approximately 30 MPa in compressive strength and 2.6 MPa in splitting tensile strength, recovering about 65-70 % of the reference OPC performance while markedly reducing CaO demand. When deployed in CFST specimens, confinement mobilized triaxial confinement hardening and delayed shell instability, increasing axial capacity by 45% relative to the unconfined core and enabling sustainable mixes to approach conventional CFST performance. The study establishes a direct chemical-structural linkage: oxide balance (CaO-SiO 2 -Al 2 O 3 -alkali), hierarchical particle packing, and confinement synergy can be tuned as design variables to deliver structural-grade behaviour from industrial and agricultural waste streams. The outcome is not only a viable structural concrete, but a pathway toward deliberately engineered low-carbon CFST systems in which carbon efficiency is achieved without surrendering mechanical reliability.