Maria A. Founti

Gypsum boards are widely used as passive fire protection materials due to their ability to delay heat transfer through endothermic dehydration of calcium sulfate dihydrate (CaSO ₄ ·2 H ₂ O). Understanding the temperature-dependent evolution of porosity and pore size distributions in gypsum board is essential for defining microstructural parameters used in fire-scale thermal transport models. In particular, the evolution of pore structure during dehydration and high-temperature degradation influences heat transfer within the material and therefore affects its fire protection capability. Quantitative data describing how the pore structure evolves at high temperatures remain scarce, limiting the accuracy of multi-physics fire simulations. This work experimentally characterizes the temperature-dependent evolution of porosity and pore size distributions in gypsum board exposed to temperatures up to 1000°C. Samples subjected to controlled thermal treatments were analyzed using mercury intrusion porosimetry, optical microscopy, and large-area optical scanning in order to capture pore structures across multiple length scales. The resulting dataset provides a comprehensive description of pore structure evolution associated with dehydration, fragmentation, and high-temperature sintering processes. The experiments reveal a bimodal pore system consisting of micro-pores (< 10 μm) formed during dehydration and stable meso-/macro-pores (10–100 μm) generated by foaming agents. Total porosity increases with temperature, while the average pore diameter decreases, indicating pore multiplication rather than coalescence. The experimentally measured pore characteristics were incorporated into a microstructure-informed thermal transport model (GPRO: Gypsum PROperties) in order to evaluate the influence of representative pore length scales on the radiative component of heat transfer and to assess their impact on the effective thermal conductivity (k _eff ). Model predictions were compared with literature data for the effective thermal conductivity of gypsum board at elevated temperatures to assess the consistency of the derived microstructural parameters with independently measured macroscopic properties. The results show that the evolution of total porosity strongly affects the conductive component of heat transfer, while the radiative conductivity predicted by diffusion-based radiation models is primarily controlled by pore lengths in the meso-scale range identified in the experimental measurements. Sensitivity analysis indicates that variations in representative pore diameter between 1 μm and 100 μm lead to changes in predicted effective thermal conductivity below 3%. Within diffusion-based radiative heat-transfer formulations, this behaviour reflects the dominance of meso-scale pore lengths in the radiative contribution. The temperature-resolved microstructural dataset presented in this work provides experimentally grounded parameters for thermal modelling of gypsum-based fire protection materials and contributes to improved representation of porous insulation behaviour in fire safety engineering simulations. The resulting temperature-resolved microstructural dataset, linking dehydration, microstructural evolution and temperature-dependent porosity, delivers experimentally grounded parameters for thermal modelling of gypsum-based fire protection materials and contributes to improved representation of porous insulation behavior in fire safety engineering simulations.

Methanol (CH₃OH) combustion under supercritical CO₂ (s-CO₂) conditions could be an attractive solution for reducing greenhouse gas emissions (GHG) in engineering applications, such as gas turbines and dual-fuel marine engines. In this work, a computational study was conducted to characterize the fundamental thermochemistry of CH₃OH combustion in s-CO₂ and to compare it with ”conventional” nitrogen (N₂) environments. First, the reduced order ACR55 mechanism was assessed against predictions obtained with the detailed Updated HP-Mech. mechanism and relevant experimental data for canonical problems, including ignition of homogeneous mixtures, combustion at Perfectly Stirred Reactor (PSR) conditions, and premixed laminar flames. The overall assessment has shown very good performance of the ACR55 mechanism. Next, the role of CO₂ as a diluent was investigated for the ignition of homogeneous mixtures and premixed laminar flames, by comparing two cases: (a) N₂ as diluent, and (b) s-CO₂ as diluent, for conditions of initial pressure and temperature P=175-250 atm and T=600–1800 K, and equivalence ratio of φ=0.4–2.0, relevant to gas turbine and dual-fuel marine engine operation. Compared to N₂, s-CO₂ dilution consistently reduced ignition delay times for lean and stoichiometric mixtures (φ=0.5-1.0), while N₂ yielded higher laminar flame speeds across the full pressure and temperature range. Representative cases were further analyzed using Rate of Production (ROP) analysis: (i) ignition of homogeneous mixture at T=1700 K, P=220 bar, φ=0.8; and (ii) premixed laminar flame at Tun=700 K, P=220 atm, φ=0.5. ROP analysis identified key chemical pathways and helped interpret the observed differences between the two diluents.

This work presents a combined experimental and numerical investigation into the fire performance of gypsum boards enhanced with hydrated inorganic salt additives. Furnace tests were conducted on formulations containing aluminium trihydrate, magnesium hydroxide, calcium aluminium sulphate, and magnesium sulphate heptahydrate, covering temperatures up to 500 °C to assess their thermal buffering capacity. Each additive exhibited characteristic dehydration inflection that delayed temperature rise and provided additional thermal inertia. The experimental data were used to calibrate a coupled heat and mass transfer model, highlighting two critical formulation-dependent parameters: the mass transfer correction coefficient (f _mass ) and the crystal aspect ratio (L/d) _cyl . Empirical correlations linking these parameters with fundamental material properties such as bulk density, chemically bound water content, and carbonate loss were established. These correlations enable predictive modelling of new gypsum formulations based solely on recipe data, eliminating the need for extensive recalibration and experimentation. The proposed framework demonstrates strong predictive capability and provides a practical tool for virtual design and optimisation of gypsum-based systems for fire safety applications.

Gypsum-based fire protection relies on thermally activated dehydration, where chemically bound water is released and evaporated, thereby providing an endothermic heat sink that delays heat penetration through assemblies. In parallel, inorganic hydrated salts are increasingly used as flame-retardant additives in gypsum-based systems to enhance heat absorption over specific temperature ranges. Fire simulation tools and performance-based fire engineering approaches require reliable kinetic data and reaction enthalpies that can be implemented as coupled thermal–chemical source terms. However, additive-specific kinetic datasets remain limited, particularly under restricted vapor exchange conditions representative of porous construction materials. This work investigates the thermal decomposition behavior and dehydration kinetics of Aluminum Trihydrate (Al(OH)₃, ATH), Magnesium Hydroxide (Mg(OH)₂, MDH), Calcium Aluminate Sulfate (3CaO·Al₂O₃·3CaSO₄·32H₂O, CAS), and Magnesium Sulfate Heptahydrate (MgSO₄·7H₂O, ESM) with emphasis on vapor-restricted conditions representative of confined porous systems. Differential scanning calorimetry (DSC) experiments were conducted at three heating rates (2, 10, and 20 K/min for MDH, CAS and ESM and 20, 40 and 60 K/min for GB-ATH) up to 600 °C using pinhole crucibles to simulate autogenous vapor pressure. The thermal analysis indicates that ATH and MDH exhibit predominantly single-step dehydration behavior, while ESM shows a complex multi-step mechanism. Although CAS presents a single dominant thermal peak in the DSC signal, the isoconversional analysis reveals a multi-stage reaction behavior, demonstrating that peak-based interpretation alone may be insufficient for such systems. Kinetic parameters were determined using both model-free (Starink) and model-fitting approaches in accordance with the recommendations of the Kinetics Committee of the International Confederation for Thermal Analysis and Calorimetry (ICTAC). All reactions were consistently described using the Avrami–Erofeev model as an effective phenomenological representation of the conversion behavior. The extracted kinetic triplets were validated through numerical simulations, showing good agreement with experimental conversion and reaction rate data. The resulting kinetic parameters and dehydration enthalpies provide a physically consistent dataset for the description of dehydration processes under restricted vapor exchange. These results support the development of thermochemical models for gypsum-based systems; however, their transferability to full-scale assemblies remains subject to validation under coupled heat- and mass-transfer conditions.

Gypsum based fire protection relies on thermally activated dehydration, where chem-ically bound water is released and evaporated, producing an endothermic heat sink and delaying heat penetration through assemblies. In parallel, non-organic hydrated salts are increasingly used as flame retardant additives in gypsum-based systems to enhance heat absorption over targeted temperature ranges. Fire simulation tools and performance-based fire engineering methods require dehydration kinetics and reaction enthalpies that can be implemented as coupled thermal chemical source terms. How-ever, additive specific kinetic datasets suitable for such implementation remain limited, especially under restricted vapor exchange conditions representative of porous con-struction materials. The present study investigates the thermal decomposition behavior and dehydration kinetics of selected non-organic hydrated salts—aluminium trihydrate (ATH), magne-sium hydroxide (MDH), calcium aluminate sulphate (CAS), and magnesium sulphate heptahydrate (ESM)—commonly used as flame-retardant additives in gypsum-based construction materials. Differential scanning calorimetry (DSC) experiments were conducted at three heating rates (10, 20, and 30 K/min for MDH, CAS and ESM and 20, 40 and 60 K/min for GB-ATH) up to 600 °C using pinhole crucibles to simulate autogenous vapor pressure. Thermal analysis revealed that ATH, MDH, and CAS undergo single-step dehydration, while ESM exhibits a complex multi-step mechanism involving the formation of in-termediate meta-stable hydrates. Kinetic parameters were determined using both model-free (Starink) and model-fitting approaches. The derived activation energy profiles confirmed the single-step nature of ATH and MDH and identified CAS and ESM as multi-stage systems. All reactions were well described using the Avrami–Erofeev model, indicating nucleation-and-growth mechanisms. The extracted kinetic triplets were validated through numerical simulation, showing close agreement with experimental α(t) and dα/dt(T) data. The resulting kinetic triplets and dehydration enthalpies form a directly usable dataset for coupled heat transfer and dehydration models of gypsum-based assemblies, enabling improved parameter-ization of endothermic heat sinks and bound water release in fire safety engineering simulations.

The production of Fischer–Tropsch liquid biofuels from the supercritical water gasification (SCWG) of lignocellulosic biomass is energetically and environmentally assessed by coupling process modelling with Life-Cycle Assessment. A conceptual process model has been developed comprising the following stages: (a) the thermochemical conversion of lignocellulosic biomass in a supercritical water gasification (SCWG) reactor, (b) syngas upgrade through dry reforming (DRR), (c) liquid biofuel production from Fischer–Tropsch synthesis (FTS) and (d) FT product upgrade and refinement, so that diesel-like (FT—Diesel), gasoline-like (FT—Gasoline), and jet fuel-like (FT Jet Fuel) yields are predicted. Parametric studies have been performed, highlighting the effect of biomass concentration and SCWG temperature on end-product yields. Furthermore, alternative scenarios have been examined with respect to: (a) maximizing FT liquid biofuel yields and (b) minimizing heat requirements to potentially achieve a thermally self-sustained process. The results of the simulated process, including liquid biofuel yield and heat-demand predictions, are used as inputs in the inventories compiled for the Life-Cycle Assessment of the overall process. Agricultural and feedstock transportation stages have also been considered. Energetic and environmental benefits and challenges are highlighted through the quantification of Global Warming Potential (GWP), while special importance is assigned to following the REDII sustainability methodology and reference data.

This Special Issue compiles results of EU H2020 funded projects working on the development of multi-functional envelope solutions for deep renovation of buildings. The projects have a common and aligned objective to develop and demonstrate plug & build smart components, including insulation materials, heating and cooling elements, ventilation, smart windows, energy production, solar harvesting, and storage with necessary connecting and controlling parts to be integrated in a prefabricated envelope system. They highlight that plug & build solutions are suitable for mass production by industry for buildings undergoing deep renovation to NZEB standards. They also underline that the development and implementation of digital based technologies can boost the application of such industrialized concepts.

The residential sector is responsible for the largest share of global energy consumption, while the existing building stock in Europe is relatively old. This issue, in combination with the low rate of new constructions, highlights the necessity for deep renovation of existing buildings to reach NZEB standards. At the same time, in the last decades, off-site prefabricated solutions have gained popularity in the building market, allowing the reliable and effective integration of diverse components and reducing the total renovation cost and occupants’ disturbance. The current study describes three all-in-one “Plug & Play” prefab renovation solutions and their assessment in terms of thermal, static, acoustic, and fire performance. The assessing performance is selected depending on their incorporated element as well as the national regulations of the country where the renovation solution is going to be installed. The assessment aims to ensure their characteristics’ satisfaction with the European and national requirements. In parallel, the assessment identifies the accurate behaviour of prefab façade systems both in passive and active mode and improves/optimises any possible design drawbacks.

Following the need of urban areas to maintain the existing building stock and simultaneously upgrade the overall energy performance, the renovation down-to-nZEB state has already become a necessity. In this regard, a vast range of prefabricated solutions have been developed lately. The main objective of such solutions would be not only to constitute an effective system to tackle building energy consumption but also to be versatile in terms of implementation and economic viability. In this regard, an adaptable off-site prefabricated envelope solution with an embodied HVAC system called “SmartWall” has been developed. The SmartWall can minimise thermal losses through the well-insulated envelope while, at the same time, its integrated HVAC system efficiently maintains indoor thermal comfort conditions. This study examines the virtual implementation of the SmartWall as a “Plug-n-Play” renovation solution to reach the nZEB state of a typical apartment in a multi-family residence in Athens. The analysis considers two SmartWall alternatives using conventional and eco-friendly materials. The results indicate a reduction of 88% in primary energy consumption without affecting thermal comfort conditions and highlighting that the nZEB state can be ensured if the SmartWall application is enhanced with photovoltaic modules.