Synthesis of nano-silica at low temperatures and its application in concrete

Nowadays, the two most important commercial processes in the production of nano-silica are the thermal route (also known as flame hydrolysis) and the wet route (e.g., the neutralization of sodium silicate solutions). A high temperature process is involved in both production methods. The production of nano-silica by the dissolution of olivine is an interesting alternative to the existing commercial methods because of the good quality of the resulting silica and low energy requirements and CO2 emissions. The produced nano-silica has a specific surface area between 100 and 400 m2/g; a primary particle size between 10 and 25 nm, which are agglomerated in clusters; and an impurity content below 5 wt.%. In addition, olivine nano-silica can be classified as a pozzolanic material with an activity index of 101 %. The optimum replacement level of olivine nano-silica in conventional vibrated concrete is around 5% by volume resulting in: 1) a compressive strength increase of 20 %; 2) a CO2 emission reduction of 3 %. Therefore, the use of the olivine nano-silica in CVC does not only improve the compressive strength but also reduces the CO2 emissions.