PSI - Issue 64

Barbara Klemczak et al. / Procedia Structural Integrity 64 (2024) 1126–1133 Author name / Structural Integrity Procedia 00 (2019) 000 – 000

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1. Introduction The European climate law mandates meeting the EU's emission reduction target of at least 55% by 2030, with a broader goal of achieving climate neutrality by 2050. To fulfil this obligation, extensive efforts are underway to reduce the energy consumption associated with heating and cooling in buildings, a major source of energy use. A notable trend in these efforts involves developing new materials with lower carbon footprints and innovative functionalities related to heat storage and release, aimed at enhancing building energy efficiency. One approach towards this objective is the development of porous cementitious composites as a sustainable alternative to traditional building materials like Autoclaved Aerated Concrete (AAC) or foamed concrete (FC). AAC, renowned for its superb thermal insulation, fire resistance, and acoustic properties, is composed of sand, cement, lime, and water aerated with aluminium powder to achieve a cellular structure containing up to 80% air (Chen et al., 2017) . Its lightweight nature facilitates easy transportation and handling during construction, reducing labour and transportation costs. AAC's energy efficiency also contributes to lower heating and cooling expenses due to its insulating properties, while its fire resistance and acoustic insulation enhance safety and comfort for occupants. However, AAC can be more costly initially compared to conventional concrete, attributed to its energy-intensive production process involving steam curing at high temperatures and pressures (ranging from 180°C to 210°C and 4 to 16 MPa), leading to increased electricity consumption and greenhouse gas emissions. Importantly, producing autoclaved aerated concrete (AAC) on a building site is not feasible due to the specialized equipment and processes required. Due to the need for specialized equipment like autoclaves and precise control over the curing process, AAC production is typically carried out in dedicated manufacturing facilities. Thus, transporting the produced AAC panels or blocks from the manufacturing facility to the construction site is a common practice. Despite these challenges, AAC remains a compelling choice for sustainable construction (Jasiński and Drobiec, 2016) , albeit its availability may be limited in certain regions. A more environmentally friendly solution could be foamed concrete (FC), which also exhibits a cellular microstructure, resulting in a relatively low weight per unit volume and good performance in terms of fire resistance and thermal insulation (Falliano et al., 2021; Gencel et al., 2022a; Gołaszewski et al., 2022) . FC is commonly produced by mixing separately manufactured foam with the base material, which is typically cement mortar or paste. Alternatively, the base paste components, water and foaming agent can be mixed simultaneously using ultra-fast mixers or specialized FC generators, although this method is less common. Once placed in the mould, foamed concrete hardens under normal atmospheric conditions. Therefore, foamed concrete (FC) is a material with a straightforward production process that is relatively cost-effective compared to autoclaved aerated concrete (AAC). It can be produced not only in prefabrication but also on a construction site. By carefully adjusting the composite's density, it is possible to achieve the necessary mechanical strength while maintaining the desired insulating properties. Typically, the density of foamed concrete ranges from 400 to 1600 kg/m³, with lightweight variants categorized below 600 to 800 kg/m³, and densities below 400 to 500 kg/m³ considered ultralight (Amran et al., 2015; Falliano et al., 2018) . Like AAC, FC incorporates at least 20% volume of mechanically generated foam mixed into the base cement paste or mortar. Furthermore, FC can incorporate embedded Microencapsulated Phase Change Materials (MPCMs) that can store or release energy through reversible chemical phase changes from solid to liquid states (Caggiano et al., 2019; Erkizia et al., 2023; Fachinotti et al., 2020; Klemczak et al., 2023; Zhilyaev et al., 2023) . The phase transition process of MPCMs, involving melting and solidifying, enables them to function as a thermal comfort system. As room temperature rises, MPCMs absorb energy in the liquid state and, upon cooling, release this stored energy as they solidify, contributing to maintaining comfortable temperatures within buildings (Gencel et al., 2022b; Lim et al., 2015) . This process enhances the insulating properties of foamed concrete and its capacity for heat storage and release. Importantly, this feature gives foamed concrete an advantage over AAC, as AAC cannot contain MPCMs due to its high-temperature production process. This work explores relatively new research using phase change materials (PCMs) in lightweight foam concrete. Incorporating microencapsulated (MPCMs) in foam concrete (FC) can enhance thermal energy storage and release, thereby improving its insulating properties and contributing to energy efficiency in buildings. Although there has been significant recent interest in phase change materials and their integration into cement composites, the number of studies in this area remains limited, with most focusing on the properties of MPCM mortars. Research on light composites such as foam concrete is sparse, and existing studies primarily address either heavy or ultralight foam