Long-term thermal conductivity of aerogel-enhanced insulating materials under different laboratory aging conditions Umberto Berardi * , Roya Hamideh Nosrati Department of Architectural Science, Ryerson University, 350 Victoria street, Toronto, ON, M5B2K3, Canada article info Article history: Received 12 August 2017 Received in revised form 6 January 2018 Accepted 9 January 2018 Available online xxx Keywords: Insulating materials Long-term performance Aging Aerogel Thermal conductivity Laboratory testing abstract Aerogel-enhanced materials are known to have significantly lower thermal conductivity than traditional insulating materials. However, given the lack of long-term experiences with aerogel-enhanced products, the consistency of their superior thermal performance under the effect of the various climatic aging processes is still unknown. This study describes the effects of accelerated aging processes in laboratory conditions over the thermal performance of aerogel-enhanced insulating materials. Several products including aerogel-enhanced plasters, blankets, and boards, were exposed to different climatic accelerated stresses, which exceeded typical use conditions. The tests included freeze-thaw cycles, elevated tem- perature, high humidity levels, and the exposure to cycles of high UV levels alternated to high tem- perature and moisture levels. The thermal properties of the products before, during, and after the accelerated aging periods were measured. The Peck model, Arrhenius equation, and Coffin-Manson relation were hence employed to correlate the accelerated aging results with the corresponding real service conditions. The paper discusses the acceleration factors of the aging tests and their calculation methods. The long-term performance of the products is quantified through the changes of their thermal conductivity measured over wide temperature ranges. The results show that for the different investi- gated materials, the increase in the thermal conductivity over the pristine conditions is typically below 10% for aging exposure corresponding to 20 years in typical conditions. Finally, this study suggests that despite some aging-driven degradation, the thermal conductivity of aerogel-enhanced materials after aging remains significantly lower than that of non-aged traditional insulating materials. Crown Copyright © 2018 Published by Elsevier Ltd. All rights reserved. 1. Introduction Aerogel-enhanced products are increasingly spreading into the insulation market with the promise to reduce the energy losses with minimum thickness layers. In fact, aerogel-enhanced products provide significantly higher thermal resistance per unit of thickness than traditional insulating materials [1e3]. The aerogels are dried gels with an exceptionally high porosity, which permits them to have a lower thermal conductivity than air [4]. Nanopores with diameters of a few tens nanometers occupy more than 90% of the total volume of the aerogel, whose bulk density often ranges between 70 kg/m 3 and 150 kg/m 3 [5]. The aerogels reach an extremely low thermal conductivity (~0.01e0.02 W/mK) as a result of the well-balanced relationship among the low solid skeleton conductivity, the low gaseous con- ductivity, and the low radiative infrared transmission [6]. Meanwhile, researchers are trying to reduce the thermal conduc- tivity of aerogel even further to reach values below 0.01 W/(mK) [7]. The high light transmissibility and good sound absorption properties of new commercial aerogels have recently suggested new uses of aerogels [7e9]. In general, the advantage of aerogel-enhanced products for thermal insulation is in their space-saving benefit which has been proved also using aerogel insulation films [10]. Several years ago, the introduction of aerogel in glazing systems was proposed using both monolithic aerogels and granular ones in the glazing inter- space [11e 13]. Monolithic silica aerogels have higher solar trans- mittance than granular ones but their fragility challenges the possibility of using insulating glazing aerogels although their ad- vantages have been demonstrated in both warm and cold climates [13e15]. For example, 10 mm thick monolithic aerogel windows have shown a solar transmittance up to 0.9, whereas granular silica aerogel windows have maximum solar transmittance around 0.5 [16e18]. Buratti and Moretti showed that, compared to a double * Corresponding author. Contents lists available at ScienceDirect Energy journal homepage: www.elsevier.com/locate/energy https://doi.org/10.1016/j.energy.2018.01.053 0360-5442/Crown Copyright © 2018 Published by Elsevier Ltd. All rights reserved. Energy 147 (2018) 1e15