During the last 30 years, lightweight concretes (LCs) have been developed in order to decrease the volume of load-bearing components, reduce the consumption of raw materials and obtain better thermal properties than those of conventional concrete. Several production processes can be employed. Lightweight aggregates can be used to decrease the density (lightweight aggregate concrete) or gas can be introduced by various methods (foam concrete (FC)). A wide range of properties can be achieved depending on several parameters (production process, binder choice, water/cement mass ratio, porous structure, admixture or surfactant content etc.). This paper reviews the influence of these parameters on the compressive strength and thermal conductivity of FC, bringing the information together in two overview graphics. Special attention is paid to LC made with calcium sulfate (gypsum) binders. This study shows that the gypsum lightweight materials present acceptable thermomechanical performances.

The mineral foams studied were mainly composed of a reactive, partially anhydrous calcium sulphate (90%) and Portland cement (10%), mixed with a low water-to-binder ratio (W/B = .35) leading to a highly concentrated suspension. The foaming method used allowed a wide foam density range (250 < ρ < 820 kg/m³) to be obtained after hardening and drying, with the same mineral suspension composition. To ensure that foam formed and remained stable until the material had set, six surfactants were chosen. The influence of the surfactants on paste properties in the fresh state was evaluated and the thermal and mechanical performances of gypsum–cement products (foamed and unfoamed) were analysed. The thermal conductivity of gypsum–cement foams evolved linearly with density but compressive strength values were widely dispersed and depended on the porous structure, which was strongly dependent on surfactant type and content. The performance levels of gypsum–cement foams were compared with those of lightweight foam concrete from litterature. The most efficient surfactants and the optimum content range leading to the best thermomechanical compromise were identified. They ensured a minimal compressive strength of 2 MPa, and thermal conductivity lower than .2 W/(m.K).