Shahriar Shahbazpanahi - Department of Civil Engineering, Islamic Azad University, Sanandaj Branch, Iran
Chia Paknahad - Bachelor Student of Civil Engineering, Islamic Azad University Sanandaj branch
Saman Toloei - Bachelor Student of Civil Engineering, Islamic Azad University Sanandaj branch
Nima Farzadnia - Housing Research Center, University Putra Malaysia, Malaysia

Concrete consists of three phases of cement paste, aggregates and interfacial transition zone. The mechanical properties of concrete, such as compressive strength, depend on content and dimensions of calcium silicate hydrate, Calcium hydroxide and the bonds between the aggregates and the paste in the matrix. Adding nano-materials to cement paste accelerate cement hydration and increases the wall effect. This process improves the mechanical properties and durability of concrete. Nano modified concrete will be more resistant against tensile and compression forces, abrasion and water diffusivity. Nano materials increase the rate of calcium hydroxide consumption and densify concrete matrix by filling up the pores. This process increases the abrasion resistance, compressive strength and reduces the permeability of concrete. This paper summarizes the application of nano silica in concrete. It investigates the benefits of using nano silica on concrete strength, and concrete permeability as well as the challenges.

nano silica (nS), concrete , strength