Insulation efficiency of alkali-activated lightweight mortars containing different ratios of binder/expanded perlite fine aggregate

In the current paper, an attempt has been done to produce insulating materials based on alkali-activated slag (AAS) mortars, free from any foaming/blowing agent, with a good balance between suitable compressive strength and low thermal conductivity. Due to its prospective properties, expanded perlite (EP) was used as a lightweight fine aggregate. For AAS lightweight mortars, different binder/EP ratios of ½, ¼ and 1/6, by volume, were used. Traditional Portland cement mortar (TC) with a binder/siliceous sand ratio of ½ as well as AAS mortar with a binder/siliceous sand ratio of ½, by volume, were prepared for comparison purposes. To obtain more insulating materials, slag in the mixture containing binder/EP ratio of 1/6 was partially replaced with 50% solely metakaolin (MK) and 50% solely fly ash (FA). The bulk density, compressive strength, total porosity, thermal conductivity and thermal resistance for all mortar types were measured. The samples were analyzed by scanning electron microscopy (SEM). The results showed that good insulation materials can be produced without adding any foaming agent, of which low thermal conductivities (0.995–0.158 W/mK), low densities (2080–670 kg/m³), high total porosities (24.22–75.1%) and acceptable compressive strength (21.6–5 MPa) can be obtained.