Lightweight alkali-activated composites containing sintered fly ash aggregate and various amounts of silica aerogel

Abstract

The use of silica aerogel as a replacement for natural aggregate in cement composites makes it possible to obtain a material with a much lower bulk density and a significantly reduced thermal conductivity coefficient. Unfortunately, this usually leads to a decrease in the mechanical performance of the composite due to the deterioration of adhesion between the silica aerogel and the binder. Lowering the thermal conductivity coefficient is also possible by using lightweight aggregate, which is inherently characterized by increased porosity. Therefore, the combined use of lightweight aggregate and silica aerogel can improve the adverse effect of using aerogel alone. The aim of this study was to design composites based on lightweight sintered aggregate and silica aerogel using alkali-activated ground granulated blast furnace slag as binding material. The effects of silica aerogel at 10, 20 and 30 vol% on bulk density, water absorption, flexural and compressive strength, resistance to temperatures of 450 and 1050 °C, were studied. In addition, the thermal conductivity coefficient, thermal diffusivity and volumetric specific heat of the produced composites were determined. Silica aerogel added at 30 vol% resulted in a reduction of the thermal conductivity coefficient from 0.7 to 0.51 W/(m·K) while maintaining compressive strength of 15.2 MPa. In addition, good resistance to elevated temperature was obtained, the composite with the addition of 20 vol% aerogel subjected to 450 °C was characterized by a compressive strength of 17.8 MPa. A higher proportion of silica aerogel and especially a higher exposure temperature resulted in a drastic decrease in mechanical parameters.