Nanosilica in Lightweight Foamed Concrete

lightweight foamed concrete (LFC) or aircrete is a type of alternative lightweight concrete that contains no coarse aggregate and is made by mixing water, cement and foam. It has a lower self-weight, greater workability and superior insulating properties but less strength than normal-strength concrete. It can be used in load bearing structural applications with the right mixture design and production methods.

This paper is a comprehensive evaluation of the effects of nanosilica (NS) on the compressive strength, drying shrinkage, thermal conductivity and the sorption of ultra-lightweight foamed concretes (ULFCs) with a density lower than 350 kg/m3. The experiments were conducted in a 50 L Eirich mixer using a shear intensity up to 1000 rpm. The fine materials were dry-mixed for 30 s and then water, superplasticizer and stabiliser were added to form the cement slurry. Air was then injected to produce the foamed mass.

The results of the investigation indicated that the addition of NS improved the fresh and hardened characteristics of the ULFCs, particularly its compressive strength. In general, the solid structure of ULFC specimens with NS contained thicker walls, which contributed to its higher compression strength.

It was also found that the hydration process of ULFCs with NS takes place faster than in the case of SF due to its smaller particle size. The NS incorporated in the ULFCs also modifies their pore structure and increases the connectivity between the voids. This significantly reduces the drying shrinkage of ULFC.