Effect of Incorporating Rice Husk Ash as Cement Blend and Iron Filings Aggregate as Partial Sand Replacement on Concrete Properties

The objective of this paper is to investigate the effect of incorporating rice husk ash (RHA) as a cement blend and iron filings aggregate (IFA) as a partial sand replacement on concrete properties using appropriate standard procedures. Mechanical and durability properties, including density, compressive strength, ultrasonic pulse velocity (UPV), and water absorption, were evaluated. Results reveal that blending RHA with cement extends the initial setting time and shortens the final setting time in fresh concrete. Additionally, RHA reduces density and enhances compressive strength by forming additional calcium-silicate-hydrate (C-S-H) gel, which fills pores and creates a denser, more compact matrix. The optimal RHA replacement level was identified as 10%. Meanwhile, IFA, found to be uniformly graded and suitable as fine aggregate, increases concrete density and enhances compressive strength, ultrasonic pulse velocity (UPV), and water resistance. These improvements are attributed to better particle packing and stronger bonding at the aggregate-cement paste interface, with 20% replacement as the optimal level. Therefore, a mix of 10% RHA and 20% IFA achieves the best balance for strength, durability, and sustainability in structural concrete.