Lightweight geopolymer-based mortars for the structural and energy retrofit of buildings

•Many existing buildings need both structural and energy retrofitting.•Geopolymer-based materials are a promising solution to develop innovative materials.•A new geopolymer-based mortar was assessed and investigated.•Recycled and waste materials were involved in the mix design of the new mortar.•The mechanical and energy efficiency of the mortar were discussed. The interest in materials and techniques for the structural and energy retrofitting of existing buildings has steadily grown in recent years. Nowadays, geopolymer binders are considered a promising solution to substitute, partially or totally, cement and lime-based mortars. In particular, the suitability of geopolymers as an alternative to cement matrix for use in fabric-reinforced (FR) systems, is investigated. In this work, a geopolymer mortar incorporating fly ash and expanded glass aggregate was researched with respect to rheological behavior, as well as mechanical and thermal properties. Evaluation of listed properties is supported with a detailed analysis of the underlying microstructure and phase composition, which were assessed with Scanning Electron Microscopy, Thermal Gravimetry, and X-ray diffraction. Additionally, the effect of moisture content on the thermal performance of investigated mortars is quantified. Given sufficient reactivity of fly ash, the direct comparison with standard lime-based mortar used in masonry applications shows non-inferior mechanical performance. Moreover, approximately two-fold reduction in thermal conductivity is observed in geopolymer-based mortars, which makes it a promising solution for energetic retrofitting. Quantitative metrics evaluated in this work can aid engineers in the design of a geopolymer FR-system with adequate thermo-mechanical compatibility with the masonry substrate.