EFFECT OF NANO SILICA AND MICRO SILICA ON THE STRENGTH AND MICROSTRUCTURE OF HIGH STRENGTH CONCRETE

Abstract

High-strength concrete (HSC) plays a vital role in modern civil engineering due to its superior mechanical performance and durability. However, achieving enhanced strength and dense microstructure requires the incorporation of advanced mineral admixtures. This study investigates the combined and individual effects of nano silica and micro silica on the mechanical properties and microstructural characteristics of high-strength concrete. Nano silica, with its extremely fine particle size and high pozzolanic reactivity, improves early-age strength and refines pore structure, while micro silica enhances bonding between cement paste and aggregates through improved packing density and secondary C-S-H gel formation. Experimental results demonstrate a significant increase in compressive strength, split tensile strength, and flexural strength with optimal replacement levels of cement by nano silica (1–3%) and micro silica (5– 10%). Scanning Electron Microscopy (SEM) and X-ray Diffraction (XRD) analyses indicate reduced microcracking and a denser, more homogeneous matrix. The synergistic use of nano and micro silica substantially enhances the performance and durability of HSC compared to conventional mixes. These findings suggest that nano-modified concrete offers promising potential for high-performance structural applications requiring long-term strength and durability.