###### Abstract  
The construction industry involves some of the activities with the highest consumption of raw materials and significant waste production. According to the European Commission, it requires large quantities of resources, representing approximately 50% of all extracted materials, and accounting for over 35% of the EU's total waste production. In particular, the production and use of concrete, as well as that of EPS (expanded polystyrene), largely exploited for energy-efficient buildings, involve a substantial amount of extracted raw materials and waste. This study focuses on the development of construction materials, such as lightweight and thermally efficient mortars and concretes, incorporating recycled EPS (R-EPS) instead of fine aggregates. Mixtures were designed by partially or completely replacing the fine aggregate with R-EPS on a volume basis. All designed mortars exhibit compressive strength exceeding the minimum values required by Italian legislation and show thermal performance improvements of up to 89.49% compared to the reference mortar. Similarly, the concretes demonstrate strengths compliant with regulations and exhibit thermal characteristic enhancements, ranging from 27.68% for structural lightweight mixes to 74.58% for non-structural ones. concrete; recycled EPS; waste materials; material characterization +
Footnote †: journal: Applied Sciences  
the sustainability of a material that can be transformed into a new resource, commonly referred to as secondary raw material. In this regard, expanded polystyrene, widely used for its low cost, versatility, and performance properties, is completely recyclable [25]. Furthermore, in recent years, the construction sector has experienced a significant increase in energy consumption, currently contributing to approximately 40% of the total primary energy consumption in the United States and the European Union. This trend has emphasized the importance of designing, constructing, and managing buildings efficiently to achieve a net-zero energy balance. This goal is crucial for addressing the energy crisis, reducing climate-altering emissions, and mitigating serious environmental threats [26]. This is particularly relevant considering the climate change, involving a long-term increase in global energy demand [27]. Numerous studies and experiments have focused on the use of sustainable raw materials, particularly the valorization and reuse of waste materials in the production of mortars and cements. This approach aims to optimize the properties of construction materials, especially mechanical and thermal ones, while reducing the extraction and use of raw materials and minimizing landfill waste disposal [28; 29; 30; 31; 32; 33; 34; 35; 36; 37; 38; 39; 40; 41; 42; 43]. In various studies, waste products, such as fly ash (FA) [28; 32], plastic waste [33], green pozzolan (GP) [34], waste paper sludge ash (WPSA) [35], food waste [36; 40], and wood biomass ash (WBA--wood bottom ash) from power plants [38; 39] have been added to concrete or mortar mixes. The use of EPS and recycled expanded polystyrene (R-EPS), as a replacement for aggregate in concrete and mortar formulations, has been extensively experimented with, successfully achieving lightweight and thermally efficient mortars. Lightweight concrete with EPS has been proposed for several decades. EPS is used to reduce the structural weight of materials for both on-site and prefabricated constructions, resulting in improved thermal and acoustic insulation. The experiments involve the partial replacement of both fine and coarse aggregates with EPS beads. The EPS content in concrete and mortar mixtures can vary from partial replacement to complete replacement (100%). Mechanical performance, particularly compressive strength, progressively and linearly decreases with the increasing percentage of replaced EPS. Additionally, discussions have covered the performance related to moisture insulation, thermal insulation, and acoustic insulation of the material.