Enhancing the Performance and Sustainability of High-Strength Concrete: A Comprehensive Investigation into the Microstructural and Mechanical Effects of Rice Husk Ash as a Supplementary Cementitious Material

The global construction industry faces immense pressure to reduce its carbon footprint, driven largely by the high carbon dioxide (CO2) emissions associated with Ordinary Portland Cement (OPC) production. Simultaneously, agricultural nations like Vietnam generate massive quantities of rice husk, a byproduct that poses significant disposal challenges. This paper investigates the viability of Rice Husk Ash (RHA) as a green Supplementary Cementitious Material (SCM) in the production of High-Strength Concrete (HSC). Specifically, the study evaluates the fresh properties, mechanical strength (compressive and flexural), and long-term durability characteristics (rapid chloride permeability) of HSC mixtures where cement is partially replaced by RHA at 0%, 5%, 10%, 15%, and 20% by weight. The experimental results demonstrate that an optimum replacement level of 10% to 15% RHA significantly enhances the compressive strength, achieving up to 76.4 MPa at 28 days compared to 65.2 MPa for the control mixture. Furthermore, the incorporation of RHA drastically reduces chloride ion permeability, shifting the durability classification from 'Moderate' to 'Very Low', making it highly suitable for marine infrastructure. Microstructural analysis via Scanning Electron Microscopy (SEM) reveals that the amorphous silica in RHA triggers a robust secondary pozzolanic reaction, densifying the Interfacial Transition Zone (ITZ) and refining the pore network. This study concludes that utilizing RHA not only delivers superior mechanical and durability performance in HSC but also presents a highly sustainable, eco-friendly solution aligned with global net-zero emission goals.