In the present scenario of emerging concepts of nano materials and micro technologies, researchers are investigating how and what nano materials can be used to improve different characteristics of conventional concrete. With increase in trend towards the wider use of concrete for prestressed concrete and high rise buildings there is a growing demand concrete with higher strength. In the present research, the effect of nano silica on high performance concrete has for been studied. Nano silica is an ultrafine airborne material with spherical particles less than 20 nm in diameter, the average being about 15 nm. Concrete mixes prepared by replacing portland cement with nano silica at 1%, 1.5%, 2%, 2.5%, 3% with curing age of 28 days. The mechanical tests like-compressive strength, flexural strength, modulus of elasticity, splitting tension test and rapid chloride permeability test of high performance concrete were studied. The micro analyses were studied using scanning electron microscope and energy dispersive spectroscopy to know the effect of nano silica on high performance concrete. The experiment result shows that, at 3% of nano silica has better mechanical properties, voids were also reduced because of that denser matrix was formed in the high performance concrete.
