Nanoconcrete

Nanoconcrete (also spelled nano concrete or nano-concrete) is a form of concrete that contains Portland cement particles that are no greater than 100 μm^[1] and particles of silica no greater than 500 μm, which fill voids that would otherwise occur in normal concrete, thereby substantially increasing the material's strength.^[2] It is also a product of high-energy mixing (HEM) of conventional cement, sand and water which is a bottom-up approach of nano technology.^[3]

Decorative plate made of Nano concrete with High-Energy Mixing (HEM)

Two-layered pavers, pigmented top layer made of HEM nanoconcrete

Role of nano particles

Incorporating ultra-fine particles into a Portland-cement paste within a concrete mixture in accordance with top-down approach of nano technology reduces the void space between the cement and aggregate in the cured concrete. This improves strength, durability, shrinkage and bonding to steel reinforcing bars.^[2]

Manufacture

To ensure the mixing is thorough enough to create nanoconcrete, the mixer must apply a total mixing power to the mixture of 30–600 watts per kilogram of the mix. This mixing must continue long enough to yield a net specific energy expended upon the mix of at least 5000 joules per kilogram of the mix.^[4] and may be increased to 30–80 kJ per kilogram. A superplasticizer is then added to the activated mixture which can later be mixed with aggregates in a conventional concrete mixer. In the HEM process, the intense mixing of cement and water with or without sand in conditions of queasy laminar flow, Reynolds number 20-800 provides dissipation and absorption of energy by the mixture and increases shear stresses on the surface of cement particles. As a result, the temperature of the mixture increases by 20–25 and more degrees Celsius. This intense mixing serves to deepen hydration process inside the cement particles. The nano-sized colloid Calcium Silicate Hydrate (C-S-H) formation increased several times compared with conventional mixing. Thus, the ordinary concrete transforms to nanoconcrete. The initial natural process of cement hydration with formation of colloidal globules about 5 nm in diameter^[5] spreads into the entire volume of cement–water matrix as the energy expended upon the mix.^[6] The liquid activated mixture can be used by itself for casting small architectural details and decorative items, or expanded with gas-forming admixture for making Aerated HEM Nanoconcrete ^[7] as a lightweight concrete. HEM Nanoconcrete hardens in low and subzero temperature conditions because the liquid phase inside the nano-pores of C-S-H gel doesn't freeze at temperatures from −8 to −42 degrees Celsius.^[8] The increased volume of gel reduces capillarity in solid and porous materials.