Development of Green Ultra High Performance Concrete with low cement content using mineral powders and nano-silica extracted from rice husk ash

In this study, GUHPC with a low cement content (≤ 450 kg/m 3 ) was developed through an optimized mix design that combined the physical and chemical effects of a binder system incorporating nano-silica (NS) extracted from rice husk ash. Six GUHPC mixtures were prepared with 0%, 1%, 2%, 3%, 4%, and 5% NS contents. Experimental results showed that incorporating NS significantly enhanced the mechanical properties of GUHPC compared to the control mix. The most effective performance was achieved with 4% NS, which remarkably increased compressive strength, particularly at early ages. Direct tensile tests confirmed substantial improvements in the tensile capacity of GUHPC. Furthermore, incorporating NS enhanced stress–strain behavior, which is characterized by higher peak stress and greater ductility. Microstructural observations indicated that NS refined hydration products and promoted the development of a denser C-S-H gel network, thereby reducing microcracking and improving the homogeneity of the matrix.