Silica aerogel added lightweight cement-based composite mortars for thermal insulation purposes in sustainable structures: A comprehensive study

It has been discovered in recent years that the use of silica aerogel in cement-based materials contributes to the thermal insulation properties of the materials, and studies on this subject have gained importance. However, it was determined that the studies mostly remained at the level of the thermal conductivity coefficient and the main physical and mechanical properties of the materials. In this study, a comprehensive research was carried out with the replacement of micro-sized aerogel particles with quartz sand in different ratios (0, 1, 1.6, 2.4, 3.2, 4 and 4.5 wt%) in lightweight cement-based composite mortar (LCCM) combinations. Specifically, the effect of silica aerogel granules (SAG) on flowability, fresh and hardened densities, porosity, water absorption, compressive strength, macro/microstructural properties (by optic microscope, SEM, XRD analysis), thermal conductivity, specific heat, thermal diffusivity and heat storage capability of LCCMs were investigated. While SAG could increase the flowability (up to 8.4 %) at low using rates, it decreased it at higher rates. It is very effective in reducing fresh and hardened densities. However, it highly increased porosity and water absorption, and greatly decreased compressive strength. On the other hand, generally the poor interfacial properties of the cement matrix and the aerogel were moderately improved in this study. The lowest thermal conductivity was determined as 0.155 W/mK in the highest SAG usage. SAG increased specific heat, decreased thermal diffusivity and decreased heat storage capability of LCCMs up to 45.23 %, 63.49 % and 46.32 %, respectively. As a result of the study, aerogel has been identified as a very suitable material that can be used to highly improve thermal properties in LCCMs.