Use of nano-silica in cement-based materials – a comprehensive review

Recently, nano silica (NS) has gained the attraction of academic researchers and the construction industry because of enhancing the properties of cementitious composites. Although there have been some related reviews, the comprehensiveness and advancedness need to be further improved. This paper is a detailed review of previously conducted studies to explore the influence of NS in cementitious composites for evaluating mechanical properties and durability. The impact of NS on the fresh state, i.e. setting time and workability, and in the hardened state, i.e. compressive, flexural, and split tensile strengths is considered. Besides, the long-term durability is discussed that include permeability, resistance against acid and base attack, abrasion resistance, and carbonation resistance. Furthermore, volume stability and microstructure of concrete with NS are presented. A huge number of studies showed the positive effect of NS with optimized content for improving the concrete properties, while a negative effect was observed with the use of excess NS content. The inclusion of NS in cementitious composites substantially enhances the mechanical properties, durability and microstructure. Meanwhile, better dispersibility is the key to ensure the strengthening effect of NS, which can be improved by changing the morphology/size of NS, optimizing the stirring method, and adding surfactants. Further investigation of the application of NS in special concrete is its development direction, and the effect of NS on the microstructure of main hydration products needs to be further explored.