Enhancing the properties of high-performance concrete using micro and nano palm oil fuel ash

This study investigates the influence of palm oil fuel ash (POFA), in micro- and nanoparticle sizes, as a partial cement substitute in high-strength concrete (HSC). Thirteen mixtures incorporating varying proportions of micro-POFA (10%–30%) and nano-POFA (2%–8%) were assessed for workability, mechanical properties, durability, and microstructural characteristics. The optimal formulation—10% micro-POFA combined with 4% nano-POFA—yielded a peak compressive strength of 100.7 MPa at 91 days, alongside enhanced tensile, flexural, and elastic properties, with markedly reduced water permeability. Thermal resistance evaluations confirmed adequate strength retention up to 800 °C. Scanning electron microscopy identified a denser matrix and refined interfacial transition zone, attributed to heightened pozzolanic reactivity. Ensemble machine learning models accurately predicted compressive strength outcomes, complemented by a graphical user interface enabling real-time strength estimation for practical engineering applications. These findings affirm the viability of optimized micro–nano POFA blends in sustainable, high-performance concrete development.