Physical, mechanical and thermal properties of lightweight insulating mortar with recycled Etna volcanic aggregates

The study concerns the reuse of pyroclastic products generated by volcano Etna eruptions for the production of lightweight insulating mortar. Fourteen mixtures, grouped into three families, with three types of natural binder were designed. The first family (CEM) contains Portland cement and calcium hydroxide, the second Natural Hydraulic Lime (NHL), the third (POZZ) combines pozzolanic sand and calcium hydroxide, to form a cementitious compound. The effect of the presence of an Air Entraining Agent (AEA), added in three different ratio with respect to the dry mixture (0.02%, 0.05% 0.1%) to increase the porosity, was investigated. In the mixtures containing the 0.1% of AEA, a breathable resin in the ratio 0.1% of the binder was added, to compensate for the degradation of the mechanical strength due to the AEA. On the basis of the mechanical and physical properties of the composites (flexural and compressive strength, density, porosity, water absorption) and of the thermal conductivity, always within the range of 0.154–0.266 W/mK, the mixtures suitable for lightweight and thermal mortar are identified. The correlation between density and porosity and between thermal conductivity and pososity is discussed. A numerical simulation, based on a numerical homogenization technique at the mesoscale, is used to show how the thermal properties of the constituents of the mixture influence the equivalent thermal conductivity of the composite.