Strategies to increase the compressive strength of ultra-lightweight foamed concrete

Foamed concrete is a special lightweight concrete characterized by the presence of a stable preformed foam in the mix proportion that give rise to the development of a system of air voids in the material. Its physical and mechanical properties are strongly influenced by microstructural properties, in turn linked to various parameters such as the amount of foam, the presence of mineral additions or chemical additives, the characteristics of the mixing process and so on. Since ultra-lightweight foamed concrete is characterized by excellent functional properties (thermal insulation, sound absorption, fire resistance) but very poor mechanical properties (compressive strength), in this contribution three different ways to improve the compressive strength of this material without worsening its lightness are discussed. More specifically, the three different strategies (improve the consistency of the fresh lightweight cementitious paste through the addition of a viscosity enhancing agent, add silica fume and increase the rotational speed of the vertical mixer) lead to appreciable improvement in the compressive strength of the produced foamed concrete. The most significant increases in compressive strength are associated with the addition of silica fume in the mix, in proportion to 10% of the cement weight.