Aerogel-based materials for building applications: Influence of granule size on thermal and acoustic performance

Aerogel was one of the most promising nano-materials for use in buildings and its thermal performance was widely discussed in the literature while an accurate study of acoustic properties was never provided. The aim of the paper is to investigate experimentally the influence of granules size on both thermal and acoustic properties of granular aerogels and aerogel-based solutions (a plaster and a translucent polycarbonate panel) for energy saving in buildings. Several kinds of aerogels were investigated, ranging from small granules (0.01-1.2 mm) to large granules (1-4 mm). For each kind of aerogel, the absorption coefficient (α) and Transmission Loss (TL) were measured at normal incidence in a traditional impedance tube, taking into account 5 thicknesses (15, 20, 25, 30 e 40 mm) and thermal conductivity (λ) was evaluated by the Heat Flux Meter, setting up an appropriate methodology because of the sample nature. The aerogel granules outperformed the conventional insulating materials: depending on the particle sizes, λ varies in 19-23 × 10^(-3) W/(mK) range at 10 °C. The smallest granules (highest density) had the best performance, both in terms of thermal and acoustic insulation: α-values and TL better than the ones of rock wool were achieved (α = 0.95 and TL = 15 dB at about 1700 Hz). The good acoustic behaviour was confirmed also considering the two aerogel-based solutions for buildings: the peak of the absorption coefficient of the aerogel-based plaster was 0.29 at about 1050 Hz, compared to a value of about 0.1 of conventional plasters; simultaneously, λ diminished from 0.7 W/mK to 0.05 W/mK.