https://www.hindawi.com/journals/amse/2016/8453567/

Article Influence of nano materials on flexural behavior and compres...

https://josbrouwers.bwk.tue.nl/publications/Other37.pdf

Good question

Following

Nano-particles silica are widely used in concrete today, leading to further improvements in compressive strength and physical and chemical properties of concrete.

Addition of NS in cement paste and in concrete can lead to completely different effects. One is size effect, i.e. primarily based on their particle nature, which makes it useful as filling material and the second is the commerce Pozzolanic activity of the cluster compounds. NS in cement mortar not only increases the compressive strength, but also results in a finer pore structure, and then reduces overall permeability of hardened concrete.

All of the above responses are generally very good. I would question that "they are widely used in concrete." Nano materials are expensive and really only specified for the niche high performance concrete. Also, there are environmental factors that are of concern because if dispersions of nano-particles were to dry during handling and become airborne, they can easily penetrate skin and become a health issue. Furthermore, one needs to be aware of how the nano-admixture impacts concrete workability.

Thanks to all

Dear prof. Dr. Ara Jeknavorian , Thank you so much for your valuable comment.

Reactive nano-silica role in concrete is a reactive filler or a functional materials, meaning it enters into the intricate pore structure of concrete, reacted and forms tight structure at nano level. For example the ITZ the region around the aggregate (usually coarse), which is coated by cement paste or in reaction term, hydrated cement paste is responsible for many long term characteristics of concrete for example permeability or transport of fluid and ions. Nano-silica (if reactive) has ability to fill the ITZ and reacted that will make strong bond between aggregate and the paste. Hence, it improves compression strength, permeability and durability.

Also, some nano fillers like graphene oxide has ability of self-sensing and portray piezo-resistive charcter

I completely agree with the comment of prof. Dr. Nasir Shafiq

Yes, the role of nano-silica (NS) in cement mortar and concrete is a reactive filler or a functional materials, meaning it enters into the intricate pore structure of concrete, reacted and forms tight structure at nano level. For example the ITZ the region around the aggregate (usually coarse), which is coated by cement paste or in reaction term, hydrated cement paste is responsible for many long term characteristics of concrete for example permeability or transport of fluid and ions. Nano-silica (if reactive) has ability to fill the ITZ and reacted that will make strong bond between aggregate and the paste.

Dear prof. Dr. Isam Issa Omran , Thank you so much for your valuable comment.

It will improve the properties of concrete

Very interesting discussion, thanks to all.

In salt sampels we have some results / depend NaCl vs SiO2 %

I have done number of trials with NS in concrete but I am yet to see any positive results.

Slump flow of concrete gets reduced drastically (which is understandable) but compressive strength also got reduced compared to control concrete.

NS is very good as bleed reducing agent but for increase in compressive strength? I haven't seen this effect.

NS in cement mortar not only increases the compressive strength, but also results in a finer pore structure, and then reduces overall permeability of hardened concrete.

Very useful discussion

I am quite agree with the answer of Nasir Shafiq