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Building materials are responsible for significant CO2 emissions and energy consumption, both during production and operational phases. Earth as a building material offers a valuable alternative to conventional materials, as it naturally provides high hygrothermal comfort and air quality even with passive conditioning systems. However, disadvantages related to high density, conductivity, and wall thickness prevent its effective inclusion in the mainstream. This research explores enhancing the thermophysical properties of compressed earth blocks (CEBs) by using locally sourced natural materials. The study is framed in the Portuguese context and the natural materials involved are wheat straw (WS) as a by-product of wheat harvesting, cork granules (CGs) from bottle caps, and ground olive stone (GOSs) residues from olive oil production. Blocks were produced with different mixtures of these materials and the thermal response was examined in a hot box apparatus. Best results include a 20 and 26% reduction in thermal conductivity for mixtures with 5v.% CG and 10v.% GOS, respectively, and an associated reduction in bulk density of 3.8 and 5.4%. The proposed approach therefore proves to be effective in improving the key thermophysical characteristics of CEBs. The article includes a comparative analysis of the experimental data from this study with those from the literature. The study contributes to the growing knowledge of sustainable materials, providing insights for researchers and practitioners looking for innovative solutions for low-carbon and energy-efficient materials. [ABSTRACT FROM AUTHOR]

Cubic boron nitride (cBN) has been used as a tool material for several decades due to its high hardness and thermal stability. Various binders are commonly added to cBN to synthesise cBN composites for better cutting performance. However, most studies have only investigated properties such as hardness and bulk modulus, without comprehensively studying elastic properties through experiments. In this study, the sound velocities and elastic properties of cBN with AlN binder were determined by using the ultrasonic interferometry technique. The bulk and shear moduli with their pressure dependence were determined as B 0 = 351 (3) GPa, G 0 = 344 (3) GPa, B 0 ′ = 4.32 (4) and G 0 ′ = 1.74 (2) using the finite strain equation-of-state approaches. Elasticity-related thermal properties, such as Debye temperature, Grüneisen parameter, thermal conductivity and coefficient of thermal expansion were also estimated. The results show that the elastic properties of the cBN composite with vol. 8.8% AlN-binder are comparable to the pure cBN compact. Additionally, the thermal conductivity and coefficient of thermal expansion have little effect on cBN composite with AlN binder compared to pure cBN. [ABSTRACT FROM AUTHOR]

New composites produced with recycled waste are needed to manufacture more sustainable construction materials. This paper aimed to analyze the hygrothermal and mechanical performance of plasterboard with a polymethylhydrosiloxane (PMHS) content, incorporating recycled PET microplastic waste and varying factors such as PMHS dose, homogenization time, and drying temperature after setting. A cube-centered experimental design matrix was performed. The crystal morphology, porosity, fluidity, water absorption, flexural strength, and thermal conductivity of plasterboards were measured. The results showed that incorporating recycled PET microplastics does not produce a significant difference in the absorption and flexural strength of plasterboards. However, the addition of recycled PET reduced the thermal conductivity of plasterboards by around 10%. [ABSTRACT FROM AUTHOR]

Epoxy resins are used in electronic packaging. However, its low thermal conductivity is a disadvantage and the high moisture absorption leads to defects such as cracking and delamination. In this work, the effect of thermo‐mechanical properties of epoxy resins under moisture‐heat coupling is investigated by molecular dynamics (MD) simulations. The diglycidyl ether of bisphenol A (DGEBA) and polyetheramine D230 are used as epoxy resin matrix and curing agents, respectively. The degree of cross–linking is set from 0% to 98% and the moisture mass fraction is set from 0 wt.% to 10 wt.%. The radius distribution function(RDF) shows that water molecules tend to appear ≈2.75 Å from the epoxy resin. The thermal conductivity of the epoxy resin increases by 54.55% for the maximum cross–linking degrees studied. And it increases by 19.23% when the moisture mass fraction is increased from 0 wt.% to 10 wt.%. The deformation of the epoxy resin is calculated which includes the coefficient of thermal expansion(CTE), coefficient of moisture expansion(CME), and coefficient of linear expansion. It is found that moisture expansion predominated at low temperatures and thermal expansion dominates at high temperatures. The analysis provides a theoretical basis for the study of hygrothermal coupling effects. [ABSTRACT FROM AUTHOR]

The use of lime as a binder in hemp–lime considerably increases the drying time of hemp–lime after casting. Furthermore, lime is a non-renewable mineral resource. As such, this paper explores the effectiveness of using an alternative non-mineral binder instead of lime to formulate a novel hemp–shive insulation. The moisture-dependent thermal conductivity, adsorption isotherm, vapour diffusion resistance factor, and in-built hygrothermal performance of four variants of a novel bio-based insulation were investigated. The hygrothermal performance of the novel hemp–shive insulation was compared with that of a previously developed novel hemp–lime insulation. No significant variation in thermal conductivity of hemp–shive insulations between the equilibrium moisture contents (EMC) at 0% and 50% relative humidity (RH) was observed, but there was a substantial increase in thermal conductivity hemp–shive insulations when the material reached the EMC at 98% RH. The average dry thermal conductivity values of hemp–shive and hemp–lime insulations were also similar. The adsorption isotherms of hemp–shive insulations were determined at 0%, 20%, 50%, 70%, 90%, and 98% relative humidity steps. At 98% RH, the moisture adsorption capacity of hemp–shive insulations was 4-to-5-times higher than that of hemp–lime insulation. Hemp–shive insulations' vapour diffusion resistance factor (µ value) was about double the µ value of hemp–lime insulation. Hemp–shive insulations exhibited 4-to-5-times higher water absorption resistance than that of hemp–lime insulation. Numerically determined porosity values of hemp–shive agree with the values of wood-based insulation materials of similar density. Finally, using all experimentally acquired data as inputs, dynamic whole-building hygrothermal simulations were carried out and the results show that novel hemp–shive insulation materials perform at a similar level to the hemp–lime insulation in terms of heating and cooling energy demand but require 45% less energy for humidification. However, the relative humidity inside the hemp–shive wall remains higher than 70%, which can potentially induce mould growth. [ABSTRACT FROM AUTHOR]

Recycled aggregate concrete has great significance from the environmental protection perspective. However, the current research findings on its hygrothermal properties are sparse. In this study, the apparent density, thermal conductivity, mass moisture content, water vapor permeability coefficient, water absorption coefficient, and liquid water diffusion coefficient of recycled aggregate concrete were determined by experimental methods. The effect of temperature and humidity on thermal conductivity was also studied. Furthermore, the fitting relations of the thermal conductivity of recycled aggregate concrete with the two variables of temperature and relative humidity were presented. The isothermal moisture absorption curve and the fitting relationship of water vapor permeability coefficient with relative humidity were also developed. The results indicate that the thermal conductivity of the eight recycled concrete specimens in the dry state at 25°C ranges from 0.994 to 1.242 W/(m·K). The thermal conductivity increases with the increase in temperature. When the temperature rises from 25°C to 35°C, the thermal conductivity of recycled aggregate concrete increases by 3.8%–13.5%. With the increase of relative humidity, the thermal conductivity of recycled aggregate concrete shows an increasing trend, followed by a steady state, and finally the increasing trend, showing a cubic function relationship between them. When the relative humidity increases from 0% to 95%, the thermal conductivity increases by about 20%. The mass moisture content and the water vapor permeability coefficient increase with relative humidity. The results of this study can provide basic information for the study on the heat and moisture transfer of recycled aggregate concrete, and enhance the database of hygrothermal properties of building materials. [ABSTRACT FROM AUTHOR]

This article investigates the static analysis of functionally graded electromagnetic nanocomposite sandwich plates reinforced with graphene platelets (GPLs) under hygrothermal loads. The upper and lower layers of nanocomposite face sheets are made of piezoelectromagnetic material with randomly oriented and uniformly disseminated or functionally graded (FG) GPLs throughout the thickness of the layers, while the core layer is made of honeycomb structures. The effective Young's modulus of the face sheets of the sandwich plate is derived with the aid of the Halpin–Tsai model. While the rule of mixtures is incorporated to compute Poisson's ratio and electric-magnetic characteristics of the sandwich plate's upper and lower layers. The governing equations are obtained by a refined quasi-3-D plate theory, with regard to the shear deformation as well as the thickness stretching effect, together with the principle of virtual work. Impacts of the various parameters on the displacements and stresses such as temperature, moisture, GPLs weight fraction, external electric voltage, external magnetic potential, core thickness, geometric shape parameters of plates, and GPLs distribution patterns are all illustrated in detail. From the parameterized studies, it is significant to recognize that the existence of the honeycomb core causes the plate to be more resistant to the thermal condition and the external electric voltage because of the weak electricity and thermal conductivity of the honeycomb cells. Consequently, the central deflection decreases with increasing the thickness of the honeycomb core. Moreover, with varying the external electric and magnetic potentials, the deflection behavior of the sandwich structures can be managed; raising the electric and magnetic parameters contribute to an increment and decrement in the deflection, respectively. [ABSTRACT FROM AUTHOR]

In order to meet sustainable development goals, global policies are strongly oriented towards the recovery of local materials such as agricultural waste. In this context, a new biosourced compressed earth brick (CEB) has been produced with bio-shell aggregates of Cocos nucifera (CN) and Canarium schweinfurthii (CS), added in equal proportions for various mixtures. The main objective is to study, on one hand, the effect of CN and CS aggregates on the mechanical behaviour and the thermo-physical properties of the CEB. On the other hand, durability of CEB was investigated in terms of hydric stability, abrasion resistance and hygro-thermomechanical behaviour. Mixtures were prepared using earthen material and 0, 5, 10 and 15 wt% CNCS, with 8 wt% cement CEM II-B-LL 42.5, respectively. Wet and dry compressive strengths are evaluated versus compaction pressure (2.5, 5, 7 and 10 MPa). The increase of CNCS aggregate content induced a reduction of the compressive strength in both wet a\nd dry situations whatever the compaction pressure. The samples with 5 wt % CNCS and 8 wt % cement, however, offered performances close to reference samples without CNCS aggregates. The reverse trend was found for thermal conductivity: thermal conductivity of the bio-sourced CEB is below 1 W·m-2·K-1 which means good insulating performances. It is noted that the modified CEB have relatively low water absorption, which contribute to a good durability. Hygro- and thermo-mechanical tests showed however a quasi-linear decrease of compressive strength when the humidity of the environment increases but also when the temperature rises. At the end, to obtain more accurate properties by prediction, some machine learning models were used. [ABSTRACT FROM AUTHOR]

Rapid thermal charging of the latent heat thermal energy storage unit (LHTESU) based on phase change material (PCM) is restricted by the material's low thermal conductivity. The numerical investigation for the thermal charging process of LHTESU considering a rectangular enclosure under the high-temperature gradient is presented. Constant and variable length fins with different locations are considered inside the enclosure with one vertical sidewall at a constant temperature. For various part-load thermal charging operations, a two-dimensional transient model with enthalpy-porosity technique is employed with natural convection current to evaluate the thermal charging rate and melting characteristics. The simulation outcomes manifest that convective heat transfer significantly impacts PCM melting in the case of variable length fins. Uniform distribution of Variable length fins with the most extended fin near the base of the container has 20% superior thermal charging performance than of constant length in full load thermal charging operations. However, in half-load thermal charging operations, constant-length fins with uniform distribution in the enclosure reduce the maximum thermal charging time and the average temperature of the PCM domain. Further, the result indicates that Cases VF-2 (most extended fins placed significantly close to the bottom and remaining fins inserted with equal gap) and VF-3 (fins insertion only in the lower half of the container) minimized the sensible heating of liquid PCM by directing the heat towards solid PCM. Case VF-3 demonstrated the most robust thermal charging performance by taking the least melting time in all cases for a 90% thermal charging of the system. [ABSTRACT FROM AUTHOR]

Straw bale building construction is attracting a revived public interest because of its potential for reduced carbon footprint, hygrothermal comfort, and energy savings at an affordable price. The present paper aims to summarize the current knowledge on straw bale construction, using available data from academic, industry, and public agencies sources. The main findings on straw fibers, bales, walls, and buildings are presented. The literature shows a wide variability of results, which reflects the diversity of straw material and of straw construction techniques. It is found that the effective thermal conductivity, density, specific heat, and elastic modulus of straw bales used in construction are in the range 0.033–0.19 W/(m·K), 80–150 kg/m3, 1075–2000 J/(kg·K), and 150–350 kPa respectively. Most straw-based multilayered walls comply with fire resistance regulations, and their U-value and sound reduction index range from 0.11 to 0.28 W/m2 K and 42 to 53 dB respectively, depending on the wall layout. When compared to standard buildings, straw bale buildings do provide yearly reductions in carbon emissions and energy consumption. The reductions often match those obtained after applying energy-saving technologies in standard buildings. The paper ends by discussing the future research needed to foster the dissemination of straw bale construction. [ABSTRACT FROM AUTHOR]

Depending on the data source used, the material hygrothermal properties that are used in the numerical analysis of simultaneous heat and moisture transfer will not be consistent. Differences in measurement methods and the individuality of specimens account for this. It is necessary to choose values from these different physical property sets to conduct a numerical calculation, which can cause the calculated results to differ. The subsequent range of variation in the calculated results should be quantitatively evaluated. In this study, the physical properties of several types of porous building materials were first gathered from four databases. The data were then categorized based on the kind of material and compared in terms of each physical property (density, porosity, specific heat, moisture capacity, thermal conductivity, and vapor permeability). The density, porosity, and specific heat varied by 10% on average, and the moisture capacity, thermal conductivity, and vapor permeability varied by 20% or more for all types of materials. In particular, the vapor permeability of plywood and moisture capacity of gypsum board differed by 50%. The influence that these physical property value variations had on hygrothermal calculation results was then quantitatively demonstrated for moisture and heat flow rate under a step change in the relative humidity or temperature of indoor air for a single layer wall. The moisture and heat flow rate into a single layer wall fluctuated by approximately 10%–40% due to differences in the vapor permeability and moisture capacity of the materials. For all types of materials, moisture was transferred more slowly than heat. Therefore, differences in moisture property values, such as vapor permeability and moisture capacity, influenced the results more significantly. Moreover, the moisture flow was accompanied by a phase change. The differences in moisture property values thus affected the heat flow. [ABSTRACT FROM AUTHOR]

Natural stone is a traditional building material used worldwide for millennia. Its mechanical properties are rather well known, but only a small quantity of data is available regarding its hygrothermal characteristics. However, these characteristics are essential for the design of energy efficient buildings. Stones are in fact associated with insulation materials, which strongly modify the hygrothermal behavior of building walls, thereby impacting their durability and thermal comfort. This study focused on the hygrothermal characterization of a dozen samples of limestone, offering an adequate representation of their use across France. Thermal conductivity and heat capacity, sorption and desorption isotherms, water vapor permeability, and moisture buffer value (MBV) all were determined and analyzed. These data can be used to model heat and mass transfers in building walls. Limestone features extensive physical properties that can vary from one place to another within the same quarry. A statistical classification of the mechanical properties of thousands of French limestones was carried out. This classification allows estimating the hygrothermal properties previously determined for other stones. [ABSTRACT FROM AUTHOR]

The thermal properties of closed-cell foam insulation display a more complex behaviour than other construction materials due to the properties of the blowing agent captured in their cellular structure. Over time, blowing agent diffuses out from and air into the cellular structure resulting in an increase in thermal conductivity, a process that is temperature dependent. Some blowing agents also condense at temperatures within the in-service range of the insulation, resulting in non-linear temperature dependent relationships. Moreover, diffusion of moisture into the cellular structure increases thermal conductivity. Standards exist to quantify the effect of gas diffusion on thermal conductivity, however only at standard laboratory conditions. In this paper a new test procedure is described that includes calculation methods to determine Temperature Dependent Long-Term Thermal Conductivity (LTTC(T)) functions for closed-cell foam insulation using as a test material, a Medium-Density Spray Polyurethane Foam (MDSPF). Tests results are provided to show the validity of the method and to investigate the effects of both conditioning and mean test temperature on change in thermal conductivity. In addition, testing was conducted to produce a moisture dependent thermal conductivity function. The resulting functions were used in hygrothermal simulations to assess the effect of foam aging, in-service temperature and moisture content on the performance of a typical wall assembly incorporating MDSPF located in four Canadian climate zones. Results show that after 1 year, mean thermal conductivity increased 15%–16% and after 5 years 23%–24%, depending on climate zone. Furthermore, the use of the LTTC(T) function to calculate the wall assembly U -value improved accuracy between 3% and 5%. [ABSTRACT FROM AUTHOR]

This research investigated the development of a fast-drying silica-based binder for hemp concrete products with enhanced mechanical and thermal properties. Hemp-silica bio-composites were prepared by mixing hemp shivs with a two-component binder system composed of liquid sodium silicate and tributyl citrate (TBC). Compressive strength, thermal conductivity, moisture buffering value, cyclic moisture resistance and microstructure of hemp-silica composites were analysed, and the results were compared with those of hemp-lime concrete. Hemp-silica blocks with shiv-liquid sodium silicate mass ratio of 1:3.75 and TBC content of 37.5 wt% of sodium silicate dry matter produced a compressive strength of 0.56 MPa only after 3 days of drying and 1.92 MPa after 28 days. These were higher than hemp-lime blocks at the same density range. Hemp-silica panels showed a thermal conductivity of 0.101 W/mK and an excellent moisture buffering value of 3.49. Hemp silica formed an open porosity with large air gaps between the particles and a water-resistance silica-based layer on the shiv surface producing a higher moisture resistance compared to hemp-lime systems. This paper focuses on the development of a novel fast-drying binder system with a potential for use in conjunction with other lingnocellular plant aggregates to form low-carbon and efficient multifunctional building materials. • A novel quick-drying silica-based binder for hempcrete was developed. • Hemp-silica concrete showed enhanced mechanical properties compared to hemp-lime. • Hemp-silica concrete reached 0.56 MPa only after 3 days of drying. • Tributyl citrate improved the water resistance of sodium silicate binder. [ABSTRACT FROM AUTHOR]

The growing concern about the environmental impact of contemporary construction has posed emphasis on the possibilities offered by bio-based and raw earth construction. The front challenge for the establishment of earth-based technologies in contemporary building markets is the guarantee of high structural and energy performances, while maintaining a low environmental impact. This work focuses on the performance analysis of compressed earth blocks (from now on CEBs) which are currently commercialized for the construction of massive vertical envelopes, with high thermal inertia. However, to obtain an acceptable comfort and an optimized thermal behavior, CEBs walls must also reach a high thermal resistance. This issue can be overcame by the design of insulated CEB stratigraphies using bio-based thermal insulations presenting hygrothermal properties compatible with raw earth-based materials. In this way, the thermal performance of CEBs walls can be increased, while preserving their hygroscopic behavior. In this spirit, this work reports the results of the experimental characterization of three materials: CEB, lime hemp and sugarcane bagasse bio-based insulation panels. It includes their composition, their main physical (dry density, porosity, capillary water absorption), thermal (specific heat capacity, thermal conductivity) and hygrometric (sorption isotherm, water vapor permeability) properties. Finally, these experimental data are used for the implementation of several numerical simulations at a wall scale in a reference climate to estimate the hygrothermal performances of both uninsulated and bio-insulated CEB walls. The simulations allow for a better comprehension of CEBs' behavior in view of their combination with the chosen bio-based thermal insulations, and give insights into possible moisture-related issues as mold growth or increase of U-value. • Compressed earth blocks (CEBs) are innovative building products with good hygrothermal properties. • Lime hemp and sugarcane bagasse panels have compatible hygrothermal properties with earth-based materials. • Adding bio-based thermal insulations to CEBs walls enhance their thermal resistance and maintain their hygroscopicity. • Hygrothermal behavior and mold growth risk in CEBs walls can be estimated by numerical simulation at a wall scale. [ABSTRACT FROM AUTHOR]

The results of calculated research of steam flow in the block of stop and control valves, thermal and thermal stress state, creep, cyclic fatigue and resource assessment of the steam distribution system body of the K-325-23.5 steam turbine are given. The non-uniformity of steam flow and areas where vorticity of steam flow appear are shown. The temperature distribution in the valves body, steam pressure on its walls, and thermal stress in the stationary operation modes are determined. It is established that the highest equivalent stresses in the valves body are observed when the turbine power is 180 MW, whereas they do not reach the yield stress of material. The maximum equivalent stresses and creep deformations are observed in areas of the body with damages during operation. The resource of valves body by low-cycle fatigue and creep is estimated. [ABSTRACT FROM AUTHOR]

In order to improve the comfort of the living environment, the thermal performance and temperature–humidity regulation of the exterior walls of two timber-framed structure buildings is theoretically calculated and experimentally studied in this study. Both of the two buildings are located in Nanjing, China, the hot-summer and cold-winter zone. Then WUFI is used to simulate and predict the changes of temperature, relative humidity, and water content of the two timber-framed structure buildings, to strengthen the theoretical analysis of the thermal and humidity coupling of the external walls, and to propose an optimal design scheme for the insulation and temperature and humidity regulation of the external walls. The main results show that the tested thermal conductivity is basically consistent with the predicted value, which prove that WUFI simulation can effectively predict the thermal insulation performance of the external wall. The two timber-framed structure buildings are both suitable for the cold areas, and the reasonable optimization of the design of the structure is the key to the insulation of the building wall. Timber-framed structure is proved to have good temperature–humidity regulation effect. The moisture content of the two timber-framed structure buildings is stable, and the annual temperature and winter humidity are within the appropriate humidity range, which indicates that the wall design is suitable for Nanjing hot-summer and cold-winter climate zone. Four types of wall structure indoor mold spore germinations are less likely, which is not easy to produce the mold. The above research aims to optimize the design of the energy-saving wall of the timber-framed structure and create a comfortable and healthy living environment. [ABSTRACT FROM AUTHOR]

[Display omitted] • Capric acid phase change microcapsules was prepared by in-situ polymerization. • The microcapsule was doped into matrix to prepare humidity control matrix@CAM. • Temperature fluctuation range is reduced by 2 °C ~ 3 °C. • Sepiolite-zeolite powder has capillary condensation and surface absorption. A composite material with temperature-humidity control functions was prepared by using sepiolite-zeolite powder as humidity control matrix and capric acid phase change microcapsules as temperature control material. The micromorphology, thermal conductivity, compressive strength, hygrothermal effect were studied by environmental scanning electron microscope (ESEM), thermal conductivity test, strength test and hygrothermal effect test, respectively. The results showed that the phase change temperature of capric acid phase change microcapsule is between 31 °C ~ 32 °C, the phase change enthalpy is 123.91 J/g, and it has good thermal stability. The humidity control performance is the best and the maximum humidity absorption rate is 6.28% when sepiolite-zeolite powder ratio is 9:1. The humidity control matrix@CAM (Capric acid microcapsules) can control the relative humidity of the environment at 51.74 ~ 58.54% and reduce the temperature fluctuation range by 2 °C ~ 3 °C. Capric acid phase change microcapsules are embedded in the interlaced sepiolite and zeolite powder to form a frame space body which produce capillary condensation adsorption and surface adsorption, absorb and desorb heat through phase changes, thus giving humidity control matrix@CAM a good temperature-humidity control performance. [ABSTRACT FROM AUTHOR]

[Display omitted] • Effects of cementitious stabilizers on thermal and hygroscopic properties of rammed earth materials were investigated. • The hygrothermal experiments were conducted on the unstabilized specimens with different water masses ranging 5 to 15% and on the stabilized specimens with different cement content ranging from 5 to 20%. • The main hygroscopic parameters were sorption isotherms, moisture buffering capacity and water vapor diffusion resistance factor and the thermal parameter was thermal conductivity. • Three mathematical models of Halsey, modified Chung-Pfost and Oswin were applied to simulate the sorption isotherm data and the results were satisfactory in comparison with the experimental results. The increasing interest in earthen materials is primarily driven by their hygroscopic and thermo-buffering capabilities, which contribute to their superior indoor air quality. Stabilization is the commonly used solution to enhance their mechanical and hygrothermal properties. The current study uses an experimental approach to investigate the impact of cementitious stabilizers on the hygroscopic properties and thermal conductivity of rammed earth materials. Measured hygroscopic parameters included sorption isotherms, moisture buffering capacity, and water vapor diffusion resistance factor. The hygrothermal experiments were conducted on the unstabilized specimens with different water masses ranging from 5 to 15% and on the stabilized specimens with different cement content ranging from 5 to 20%. Finally, three mathematical models of Halsey, modified Chung-Pfost and Oswin were applied to the sorption isotherm data. The results showed that stabilization positively impacted decreasing the heat conduction and improving the hygroscopic properties of rammed earth materials. Among the three models, the modified Chung-Pfost model was the best fit for sorption isotherms. [ABSTRACT FROM AUTHOR]

• Hygrothermal properties of packed straw vary strongly with manufacturing process. • Conductivity is the lowest for low-density short-fiber samples with 0.0468 W/mK. • Water vapor diffusion resistance factor ranges from 3.34 to 11.20 among samples. • Moisture buffer value is higher for low-density short-fiber sample with 2.95 g/m2%RH. • Hysteresis of sorption isotherms is smaller for crushed straw particle samples. Biosourced materials are increasingly considered to replace traditional insulators to reduce environmental impacts and benefit from better hygrothermal buffering characteristics. Barley straw is cheap and abundant and can be manufactured into insulation material. However, it is necessary to understand their hygrothermal properties as a function of manufacturing to design proper assemblies. The present work aims to determine experimentally and analyze sorption–desorption curves, thermal conductivity, water vapor permeability, and moisture buffer value (MBV) of barley straw as a function of density, fiber size, and relative humidity. Expressions were developed to correlate hygrothermal properties with the characteristics of the samples. Results revealed thermal conductivity values from 0.0468 W/mK (low-density short-fiber dry samples) to 0.0799 W/mK (low-density short-fiber 90 % RH samples) and MBV from 2.12 g/(m2 %RH) for high-density long-fiber samples to 2.95 g/(m2 %RH) for low-density short-fiber samples. The water vapor diffusion resistance factors ranged from 3.34 to 11.20 depending on the method used (wet versus dry) and the sample characteristics. These results indicate that straw offers a good potential as an insulator and indoor climate regulator in buildings. [ABSTRACT FROM AUTHOR]

• Extended hygrothermal characterization of unstabilized rammed earth. • Low influence of density and grain size distribution on sorption isotherm. • High influence of density on thermal conductivity and vapor resistance factor. • Same linear dependency of thermal conductivity on moisture content for different soil compositions. • Vapor transfer resistance factor for a large span of relative humidity. Although hygrothermal properties of rammed earth represent great potential for improving thermal comfort during hot summers, still little knowledge is available about this topic. The literature lacks complete sets of hygrothermal characteristics of rammed earth, although they are fundamental for heat and moisture transfer modeling necessary to predict earthen building performances. The present work reports the results of a large collaboration between four academic laboratories in order to obtain an extended hygrothermal characterization of rammed earth, focusing on the material used in a modern construction in Lyon, France. The aim of the article is to provide for the same kind of soil an extend characterization on a large span of relative humidity to provide complete set of material properties for heat and moisture transfer simulation. The hygrothermal measurements cover adsorption and desorption isotherm, intermediate isotherm loop, specific heat capacity, dry thermal conductivity, moisture-dependent thermal conductivity and water vapor resistance factor for a large span of relative humidity. In addition, the capillary rise test was performed to estimate the liquid transport coefficient for suction and redistribution. The results show that variations in the density of the samples have a low impact on sorption isotherm, while they have a non-negligible impact on thermal conductivity and water vapor permeability. Surprisingly, variations in the grain size distribution do not produce a significant modification in the sorption isotherm, while hysteresis slightly reduces when bigger grains are added to the soil composition. Approximation of empirical model coefficients for the determination of moisture-dependent thermal conductivity is proposed for rammed earth materials. [ABSTRACT FROM AUTHOR]

Polyimide (PI)-silica aerogel composite aerogels with low shrinkage (3.7%), low density (0.061 g/cm3), low thermal conductivity (0.0216 W m−1 K−1), high hydrophobicity (146°) and good fire resistance were prepared by incorporating silica aerogel powders into PI matrix. The properties of the aerogels are affected by the type and content of silica aerogel powders. The samples show high compressibility, and the stress at 80% strain increases with the increase of silica aerogel powder content. The addition of inorganic silica aerogel powders (ISAp) can improve the thermal stability of the aerogel and the fire resistance and structural integrity of the sample under flame, but has adverse effect on moisture resistance. While the addition of polyvinylpolymethylsiloxane aerogel powders (PAp) improves the moisture resistance of the aerogel but weakens the thermal stability and fire resistance. The introduction of both ISAp and PAp can reduce the thermal conductivity of the aerogel, and the samples exhibit good thermal insulation performance. Furthermore, ground equivalent simulation tests were carried out to verify the adaptability of these aerogels in the space environment. The sample meets the standard requirements and shows stable structure and performance during the tests, which proves its potential application in the aerospace field. [Display omitted] • Reduced shrinkage and increased hydrophobicity of PI aerogel were achieved by using two diamines simultaneously. • Physically mixing of silica aerogel powders into PI matrix reduces the shrinkage and thermal conductivity of PI aerogel. • The adaptability of PI aerogel in space environment was verified by ground equivalent simulation tests. [ABSTRACT FROM AUTHOR]

This study aims to produce sandwich-structured composite boards with flame retardance, far-infrared emissivity, and electromagnetic shielding effectiveness using nonwoven, weaving processes, and heat treatment. Needle punching and roller-type hot pressing are used to improve their tensile strength, tensile elongation, puncture strength, and burst strength. The limiting oxygen index is 30 regardless of whether the flame retardance/far-infrared emissivity/electromagnetic shielding effectiveness composite board is stainless steel (SS), SS+Ni–Cu (nickel-coated copper), or SS+Ni–Cu+Cu (copper) composite fabrics. SS+Ni–Cu and SS+Ni–Cu+Cu composite boards both have optimal thermal conductivity at the eighth test hour. SS–B composite board exhibit far-infrared emissivity of 0.81; moreover, they have optimal electromagnetic shielding effectiveness of −41dB at 2450 MHz when they are laminated into three layers at a 90° lamination. [ABSTRACT FROM AUTHOR]

This paper describes the effect of inorganic adsorbents on the hygrothermal performance of insulating materials. The addition of the inorganic adsorbents leads to significant effect to the microstructure and mechanical properties of these materials. The thermal conductivity rang of the materials containing adsorbents from 0.095 to 0.116 (W/m−1 K−1) is lower than that of those without adsorbents (0.121 (W.m−1 K−1)), resulting in reducing the heat consumption of these insulation materials. The kinetics and isotherms water vapor adsorption confirm an increase in moisture uptake capacity at low relative humidity (33%) and small variation of moisture adsorption capacity at high relative humidity (75%) in the presence of the adsorbents. The moisture buffering of the boards containing different adsorbent contents is improved with an excellent moisture buffer value up to 2.7 g/(m2.%RH). [ABSTRACT FROM AUTHOR]

The thermal conductivity of construction materials is among the main factors influencing the thermal performance of buildings. This property is, thus, extensively demanded for design purposes. The thermal conductivity is especially related to the pore system and the composition of cement-based composites, the same factors that affect their Ultrasonic Pulse Velocity (UPV). In this sense, the present work evaluates the correlation between thermal conductivity and UPV. To this purpose, mortar specimens were investigated, with varying mix proportions, fine aggregate types, and dosages of air-entraining admixture. A satisfactory determination coefficient (R2 > 0.9) was obtained between thermal conductivity and UPV of the mortars when they were grouped under similar components and pore structure. It was observed that the pore system of the mortars tested is more influential to the UPV than their overall porosity. In this sense, a better correlation was found between UPV and thermal conductivity than between thermal conductivity and specific gravity. Additionally, the fine aggregate type presents a significant impact—not only due to its chemical and mineralogical properties but also as a result of the morphology that each aggregate generates within the matrix. In conclusion, this technique potentially presents high applicability to the thermal characterisation of cement-based composites. [ABSTRACT FROM AUTHOR]

This work presents an extensive experimental characterization of two different ceramic brick blocks with hydraulic contact interface (cement mortar or lime mortar), at different heights, during the drying process. First, a laboratory characterization of the building material used (ceramic bricks and different mortars) was carried out to determine their hygrothermal, mechanical and thermal properties, namely, bulk porosity and density, water vapor permeability, capillary absorption, retention curve, moisture diffusivity as a function of moisture content and thermal conductivity. Finally, the moisture transfer in multi-layered systems was analyzed in detail taking into account the hydraulic contact between the building elements. The results showed an increase of the drying time constant for the materials with cement mortar interface compared to the lime mortars materials, and that as further away from the base the interface is located, higher is the drying time constant. The hydraulic interface (imperfect contact) could significantly retard the flow of moisture transport. i.e., the assumption of perfect hydraulic contact may result in significant error in predicting moisture transport in building materials. [ABSTRACT FROM AUTHOR]

The paper aims to present a new insulating material based on cork aggregates and cement designed for building applications. Samples are prepared by mixing natural cork aggregates, sand, cement and water. Four cork volume dosages are considered, 0, 25, 50 and 75% (relative to the sand). Samples are characterised in terms of hardened density, compressive and flexural strength, as well as thermal conductivity and hydric properties (moisture content, vapour permeability, moisture buffering value and absorption by partial immersion). Results show that increasing cork granule amount tends to increase moisture retention and buffering value but decreases density, thermal conductivity and mechanical properties. Depending on the cork content, cork concrete mixture can be used as thermal insulator or as a structural component. [ABSTRACT FROM AUTHOR]

The 2010/31/CE directive has highlighted the necessity to improve the energy efficiency in buildings, since they are responsible for 40% of energy consumption and 36% of CO2 emissions in the EU. In situ measurements of envelope components are needed for estimating the thermal transmittance of existing buildings in order to perform the energy certification. The instruments devoted to this aim, the heat flux meters (HFMs), are unfortunately not always provided with metrological traceability, and the appropriate reference standards are not available. The calibration systems currently adopted present different limits related to low performances at low and constant heat fluxes, non-uniformity of the heat flux in the measurement section and impossibility to control the heat flux at different temperatures. In this paper, the authors discuss the metrological behaviour of an existing HFM reference standard. A numerical model is employed to analyse the calibration system in different operating conditions (low and moderate heat fluxes), to improve it and to design a new prototype presenting high performances also in the presence of the HFM under calibration. In particular, the numerical tool is applied to investigate the heat flux uniformity and the metrological performances in a specific sub-region of the measuring section where the HFM under calibration is applied. A detailed experimental analysis is also conducted with the objective to validate the adopted numerical tool. Moreover, a metrological characterization of the system affords a combined standard uncertainty of better than 6% at low heat flows. [ABSTRACT FROM AUTHOR]

• Bio-based materials are examined in terms of 2D image analysis. • Influence of casting on biofibres dispersion in bio-based insulation materials. • Bio-composites made with barley straw, hemp shiv and rice husk fibres were produced. • Production variables have a significant impact on the physical properties. Wetting of bio-based mortars — the affinity of the biofibres and earth to the water — can have a strong impact on the flow, but the microscale physics and macroscopic consequences remain poorly understood, not helping in the material optimisation. This research analyses the influence of casting on biofibres dispersion in bio-based insulation materials at the macro-level and evaluate changes on hygrothermal behaviour if fibres and casting change. Earth-based blocks reinforced with 3% weight content of barley straw, hemp shiv and rice husk fibres were produced with 5 and 4 cm thickness using two casting methods. The 5 cm blocks were unstabilised and compacted; the 4 cm blocks were moulded and stabilised with gypsum and air lime. The approach is to implement a developed method of image analysis to elucidate the inherently 2D pore-scale mechanisms and help explain the striking macroscopic displacement patterns that emerge. The results indicate that production variables have a significant directionally dependent impact on the physical properties of cast bio-based materials. This means that the Image analysis can be used for quality control towards the optimisation of the bio-composites. Thermal conductivity and ultra sound velocity are affected by fibres distribution inside bio-based materials. The shape of ultra sound distribution from direct and indirect methods enhance the anisotropy of the bio-based materials with different composition and casting methods. [ABSTRACT FROM AUTHOR]

• Pore structure of bio-based materials is investigated combining WIP, MIP and X-ray CT. • X-ray CT is a promising tool for the exploration of inner porosity of plant particles. • Hygrothermal properties and compressive strength are measured on bio-based concretes. • Types of binder and aggregate impact the use performances of vegetal concretes. Bio-aggregate based building materials offer promising perspectives thanks to their low environmental impact and interesting hygrothermal behaviour. In this paper, different formulations of bio-aggregate concrete are proposed and analysed. We focus on two types of locally available bio-aggregates, namely maize and sunflower bark chips, and two types of binder matrices, based on respectively metakaolin and lime. The study specifically focuses on the pore structure of the composite material, as this quantity has a decisive impact on the insulating properties (thermal conductivity), the hygric behaviour (sorption isotherms, water vapour permeability and moisture buffer value) as well as on the mechanical performance (compressive strength). The results underline the impact of the constituents' porosity on the complex porous structure of the bio-concrete and the influence of porosity on its performance. The findings demonstrate that metakaolin and sunflower are high-potential raw materials for the design of a bio-aggregate based concrete. [ABSTRACT FROM AUTHOR]

• Bio-based composites based on rice husk (RH) and an earthen matrix are evaluated. • RH content improves thermal conductivity and contribute to hygrothermal comfort. • RH increase at least 20% the composites MBV and their ability to adsorb-desorb indoor moisture. • Pre-boiling of RH reduces biological susceptibility and improves mechanical behaviour. • Optimised composite panels can be applied in coatings systems of massive walls and ceilings. With the aim of developing economic and ecological bio-based composite panels to be used on indoor wall or ceiling coating systems, contributing to hygrothermal comfort and health, three different composite formulations were produced, differing on the content and pre-treatment of rice husk: 15% and 30%, only dried or previously boiled. Composite samples were tested for biological development and several physic-mechanical characteristics. Increasing on rice husk content decreases thermal conductivity due to bulk density decrease, decreasing ultrasound velocity, flexural strength, abrasion and fire resistance, but improving the moisture buffering capacity at least in 20%. For high rice husk-content composites, its pre-boiling decreases biological susceptibility although decreasing resistance to fire, most probably due to destruction of the cellulose wall, but significantly increases abrasion resistance and compressive strength, probably because of a better bond between the rice husk and the earthen matrix, quicker reaching a high water vapour adsorption limit. [ABSTRACT FROM AUTHOR]

Due to increasingly stringent requirements in building energy performance, further development of fired clay masonry blocks are essential nowadays for the manufacturers. One of the possible directions for improving thermal performance of the masonry blocks is to fill them with insulating materials. The currently developed bricks are most commonly containing mineral wool thermal insulation filler. The main criteria for manufacturers to develop their products are thermal performance and manufacturability, which leads to unsolved hygrothermal questions. While the filler materials have low thermal conductivities, they may deteriorate in high humidity environment and due to freeze-thaw cycles. The aim of this research is to test existing filled building blocks, to prevent hygrothermal deterioration. The study compares one-dimensional monthly based steady state Glaser method with steady state two-dimensional hygrothermal simulations and dynamic multi-dimensional conjugated heat and moisture transfer simulations. The calculations were made considering Central European Budapest climate. Hygrothermal material properties were measured in laboratory. After the calculations, results show that effective thermal transmittance, maximum freezing depth from the external surface of the plastered masonry blocks and the number of freeze-thaw cycles during a year vary depending on the facade's orientation. The possible freezing zone can reach one third of the masonry block from the external side, and affect the thermal performance of the bricks. The outermost insulation layers of the masonry blocks therefore must selected to bear freeze-thaw cycles and high humidity because of protection aspects. The new aspects of this study can be used to extend the application limits of insulation filled masonry blocks and design these type of masonry blocks against hygrothermal deteroriation. • U value shows up to 30% difference between catalogue and hygrothermal simulations. • HAM simulated U value could differ up to 18% considering facade orientation. • Thermal conductivity of outermost MW layer showed 1.6–4% lower performance. • One third of the external side of a 44 cm thick filled masonry could freeze. • MW filler have to withstand up to 20 freeze-thaw cycles each winter. [ABSTRACT FROM AUTHOR]

The thermal conductivity, a fundamental property for insulating materials, is often advertised using a single value implied to be constant. However, research shows that the effective thermal conductivity changes as a result of material aging and the environmental parameters, including temperature and moisture content levels. In recent years, linear temperature-dependent laws have been occasionally proposed for inorganic fibrous materials, although there is increasing awareness of the fact that foam insulating materials have less regular temperature-dependent behaviours. This depends on the fact that the equilibrium among the different gasses in the material changes over time. In this paper, several polyurethane and polyisocyanurate foams are analysed in order to determine how the effective thermal conductivity is altered after accelerated aging obtained by exposing them to high temperature, high relative humidity levels, and freeze-thaw cycling. For each material, and after each aging exposure condition, measurements of the thermal conductivity were collected over a large temperature range from −20 °C to +40 °C using a Heat Flux Meter. These experimental results allow to build 3-D plots showing the effective thermal conductivity as a function of temperature and moisture content for both pristine and aged materials. Then, the measured results are used in hygrothermal simulations performed inputting the measured temperature- and moisture-dependent thermal conductivity in order to determine the effective performance of the considered insulating materials in both pristine and aged conditions. Results show that the aging of the foams and the operating temperatures have higher impacts on the insulating performance of polyisocyanurates than on polyurethanes. Additionally, high moisture levels contribute to lower performance in all foam materials, with open cell foams experiencing the greatest thermal resistance reduction. The increase in the energy fluxes across the insulating layer with respect to the constant thermal conductivity assumption was significantly higher once the effective thermal conductivity of aged materials was considered, especially when polyisocyanurate foams were modelled in cold and humid conditions. • Foam materials experience aging which results in a deterioration of their properties with time. • Thermal conductivity of porous materials depends on the temperature and moisture content. • Some foams show higher thermal conductivity at low temperature. • Several aging (high temperature, high relative humidity, and freeze-thaw cycling) are done. • Simulations considering aging, temperature and moisture content reveal large deviations. [ABSTRACT FROM AUTHOR]

• The temperature and humidity inside the mass concrete were measured. • The results of numerical simulation and field tests are compared. • A model was proposed and solved for coupled heat – moisture-force transport in concrete. • Changes in temperature, humidity and stress can be predicted by establishing a coupled numerical analysis model. Hydraulic mass concrete has been in a temperature and humidity cycle environment for a long time, reducing the performance and service life of its structure. Under the premise of temperature control, we use the Soret effect as the basis of heat- humidity coupling, and then use thermal conductivity, diffusion coefficient and elastic modulus to evaluate the coupling effect between temperature, relative humidity, and stress of mass concrete, and establish a thermal – humidity -force coupling model. Using the embedded temperature and humidity sensor to conduct experiments on mass concrete, this study explores the temperature control pipeline's influence on the temperature and relative humidity distribution inside the concrete and the feasibility of the coupling model. Through experimental results and model analysis, this study found that, under temperature control, the prediction results of the coupled model are more consistent with the experimental results, and its accuracy is higher than that of the uncoupled model. In the process of temperature control, temperature has a significant effect on surface water diffusion, whereas humidity has little effect on temperature conduction, and temperature conduction is mainly affected by temperature gradient. Temperature control can effectively reduce the temperature amplitude inside the concrete, reducing the stress inside the concrete. Moreover, the coupled thermal-moisture-force model can accurately predict the variation trend of temperature, relative humidity, and stress with time at each point inside the concrete under temperature control. The theoretical results of this study can provide a reference for the design, construction, and maintenance of hydraulic engineering structures in the future and better grasp the internal temperature, relative humidity, and stress of hydraulic concrete in different environments and the change law. [ABSTRACT FROM AUTHOR]

• Development of novel hemp shiv based composites with low thermal conductivity of 0.05 W/mK. • Enhanced vapour permeability and excellent moisture buffering value up to 3.6 g/m2 RH. • Pre-treatment of hemp shiv leads to high water resistance reducing water absorption by 123%. • The composites have low density (175–240 kg/m3) and show good mechanical performance. This study focuses on the development of advanced water resistant bio-based composites with enhanced hygrothermal performance for building applications. The highly porous structure of hemp shiv is responsible for low thermal conductivity and allows the material to adapt to varying humidity conditions providing comfortable indoor environment. However, the pore network and the hydrophilic nature of hemp shiv affects the compatibility and durability of the material in presence of excess moisture conditions. In this work, novel hemp shiv composites were prepared in a starch based or silica based matrix and characterised for their hygroscopic, thermal and mechanical properties. The hemp shiv based composites were resistant to water yet permeable to vapour and showed excellent moisture buffering capacity when compared to conventional hemp-lime composites. The composites prepared were light weight with low thermal conductivity values of 0.051–0.058 W/mK and showed good mechanical performance. Hemp shiv composites with superior hygrothermal characteristics have immense potential as robust thermal insulation building materials. [ABSTRACT FROM AUTHOR]

This paper is focused on the problems of moisture reduction in old buildings. Wet walls are very common problem of old buildings, but it can appears also in new buildings as well. The moisture in the wall influence the insulation quality; bigger heat losses continuously cause problems of worse heat balance, higher consumption of energy for heating and it can result in not sufficient indoor conditions in such a room or building. Old rural residential buildings and also agricultural buildings for housing of animals, storage of different materials, workshops etc. could be repaired and reconstructed by the used of some special methods. The application of special plaster can reduce the walls moisture as well as improve the thermal properties of the buildings by reduction of thermal conductivity. This paper includes the results of laboratory experiments focused on research of plaster properties (temperature, moisture and thermal conductivity) and tests provided in the real building. Different measuring principles, enabling mutual comparison of results were used for this research. The measurement results showed a significant effect of high wall moisture on the heat losses. Differences between the walls improved by new tested plaster and old untreated walls are discussed in this paper. Obtained results from this measurements and findings may be useful for further research in this issue as well as for the practical solutions for similar problems in many old buildings. [ABSTRACT FROM AUTHOR]

Highlights • Bio-based materials are examined in terms of MBV, microstructure and latent heat. • 11 bio-based insulation materials and thermoplastic recycled polymer were analysed. • Only half the samples revealed equivalent efficient moisture transfer. • Latent heat tests highlight the good performance of wool and saw mill residue. Abstract UK construction industry contributes 120 Mt of waste every year. Bio-based building materials may be a solution for this problem, as they combine re-use and recycling abilities together with hygroscopic characteristics, leading to buildings energy savings. For the first time, the dynamic response to hygrothermal changes of bio-based materials is examined in terms of Moisture Buffering Value (MBV), dry/wet thermal conductivity, microstructure, density and latent heat through daily cycles. It is shown that MBV is a useful tool for characterisation but needs to be combined with the shape of the change in mass of the final hygrothermal cycle. Mastering this is required to obtain significant improved indoor environment quality in buildings. Ten samples of bio-based insulation materials and one thermoplastic recycled polymer were analysed (wool, hemp, saw mill residue, wood, straw, cork and polyethylene terephthalate). Saw and wool are the most promising, as materials exhibit dynamic response to hygrothermal changes. Only half the amount of samples revealed equivalent efficient moisture transfer to be able to desorb the adsorbed quantity of water. Latent heat of vaporisation and condensation tests led to the conclusion that samples of wool and saw mill residue can qualify as bio-based materials for 'green' panels. [ABSTRACT FROM AUTHOR]

Heat and moisture transfer models are increasingly used in building thermal and energy simulation tools. These phenomenological transfer models are based on experimentally evaluated input data. Therefore, to ensure a better prediction of the hygrothermal behavior of the building envelope, a correct and reliable experimental evaluation of these parameters is required. Indeed, these input data are the thermal and hygric properties of the materials constituting the wall. However, the hygrothermal properties available in the databases are far from complete, particularly regarding the evolution of these properties with changes in the water content and temperature of the material. In this paper, an experimental characterization campaign of the main transfer and storage hygrothermal properties is conducted, with particular interest in the variation of these properties as a function of the temperature and the water content of the material. In this work, different materials are analyzed: cinderblock, plaster, chipboard and red brick. This study includes analysis of the thermal conductivity, the specific heat capacity, the water vapor permeability, and the moisture storage capacity. The obtained results confirmed that the water content and the temperature of the material have considerable effects on the values of its hygric and thermophysical properties. Indeed, the thermal conductivity and the specific heat capacity of a hygroscopic material as plaster can reach an increase of 2 times between dry and saturated states. Concerning water vapor permeability, a relative gap of 30% is observed between the values obtained at 20 °C and 30 °C. Therefore, enriching existing databases with this type of information is essential to ensure a reliable prediction of the hygrothermal behavior of the whole building. [ABSTRACT FROM AUTHOR]

Accurate determination of the thermal conductivity of building material is key to calculating its heating/cooling loads and energy consumption. The thermal conductivity of building material is not only related to the pore structure characteristics but also the internal static moisture distribution and moisture transfer characteristics, and the mechanisms of both differ in how they affect the internal heat transfer performance. This paper analyzed the influential quantitative relations between the static moisture distribution and moisture transfer with respect to the thermal conductivity of building materials in different hygrothermal environments. The analysis is based on the additional thermal conductivity calculation method derived from static moisture distribution and moisture transfer proposed by us. The results show that the static moisture distribution has a notable influence on the thermal conductivity under the heating conditions in winter, whereas the influence of moisture transfer is negligible. Nonetheless, the influence of both factors on the thermal conductivity should be considered during air-conditioning in summer. The comprehensive correction rate of the thermal conductivity of building materials in typically hot and humid areas in China are determined, and the influence of the thermal conductivity of moist building materials on the heat transfer coefficient of enclosure structures is analyzed. • Thermal conductivity calculation methods of moist building materials were proposed. • Effect of hygrothermal environment on thermal conductivity of materials was studied. • Thermal conductivity correction of moist porous building materials were given. [ABSTRACT FROM AUTHOR]

In recent years, thermal insulation filled masonry blocks have become widespread in Central-Europe. These blocks can satisfy thermal performance requirements without the need of additional insulation. However, these requirements in the building regulations only consider thermal, but neglect moisture aspects. This paper presents a comparative analysis of steady-state numerical conjugated heat- and moisture transport FEM simulations of masonry walls. The hygrothermal material properties of the insulation filled masonry blocks were measured in laboratory. In the paper, besides a wall section, a wall corner joint is presented, both modeled in 2D from complex building elements, such as insulation filled blocks, and were tested using different fillers (aerogel, expanded perlite, expanded polystyrene, mineral wool and PUR foam), respectively. Monthly variation of the fillers' thermal conductivity, thermal and moisture transmittance and effective water vapor diffusion resistance of the walls, as well as linear thermal and moisture transmittance of the wall corner joints were examined in details. A comparison between detailed and simplified modeling were also carried out. The evaluation of the results shows that there are noticeable differences in trends between thermal and moisture transmittances, latter show significantly greater variation and depends mainly on the hygrothermal behavior of the filler. Based on effective water vapor resistance factors, we showed that assuming the same vapor transmission properties for all type of filled masonry blocks is a mistake. [ABSTRACT FROM AUTHOR]

Abstract Cross Laminated Timber (CLT) is attracting worldwide attention, due to its durability, usability, and many other advantages. However, since CLT is made of timber, analysis of the hygrothermal performance is essential. In this study, the basic hygrothermal values are measured to obtain the exact hygrothermal performances. The values are put into the simulation with various assemblies which has hygroscopic effects. The effectors are the type of insulation, the presence of the vapor retarder, the climate condition and the type of standards. The final goal of this paper is to find the optimal CLT assemblies. The thermal conductivity, thermal transmittance coefficient, and water vapor resistance factor were measured. The thermal transmittance coefficient of the wall system was measured by using TCi and facing thermo-hygrostat, and applied in the simulation. The water vapor resistance was measured by conducting dry-cup test. In addition, the various conditions that affect the thermal moisture behavior were applied to the simulation for getting stable hygrothermal results. As a result, the standard of Passive house and Domestic wooden house, the climate condition, the presence of breathable water proofing paper, and the insulation alternatives of Expended Polystyrene (EPS) and Extruded Polystyrene (XPS) were applied. It was concluded that breathable waterproofing paper should be installed inside, and the applications of both XPS and EPS made no difference to moisture but the application of Mineral Wool was adversely affect to hygrothermal performance of the CLT wall system. The thickness of insulation should be designed according to the Passive house standard (0.15 W/m2K) rather than the Domestic (Korea) Wooden house standard (0.21 W/m2K). [ABSTRACT FROM AUTHOR]

Highlights • An experimental assessment of the impact of the perlite content on the thermal performance of plaster is here presented. • Analyses have been carried out through laboratory, in-situ measurements and heat and moisture transfer simulations on a real case study. • The embodied energy and embodied carbon have been assessed for different percentages of perlite content. Abstract In the last few years, thermal insulating plasters have started to be an attractive solution for the insulation of already existing wall structures, especially old masonry ones, where refurbishment interventions can involve the replacement of damaged plasters. Intensive research efforts are being made to reduce the thermal conductivity and the environmental impact of these materials by optimizing their mixtures (combination of lightweight aggregates, binders and additives). In the present study, the hygrothermal performance and environmental impact of the different perlite-based plasters that are currently being developed have been investigated. A series of analyses has been carried out, at a material scale, by means of heat flow meter apparatus, to determine the relationship between the perlite content and the thermal properties. Moreover, the effect of the moisture content on λ has been analyzed, and the embodied energy and embodied carbon of the four mixtures have been assessed using both the cradle-to-gate and the cradle-to-site approaches. Furthermore, in-situ measurements have been conducted at a demonstration site, at a component scale, and a series of heat and moisture transfer simulations has been carried out to evaluate the actual thermal behaviour of the plaster under real operating conditions. The thermal conductivity values of the four plaster mixtures ranged from between 0.118 W/mK and 0.059 W/mK, thus demonstrating that the perlite concentration had a significant impact on the reduction of thermal conductivity and that the embodied energy of the applied material (5 cm thickness) decreased as the perlite content increased. Moreover, the results of the measurements on the demonstration building and the hygrothermal simulations have revealed that the thermal insulating plaster is able to reduce the U-value of the wall. However, an increase of 26–30% of the actual thermal conductivity should be considered when the material is exposed to real operating conditions. [ABSTRACT FROM AUTHOR]

Highlights • Thermal conductivity decreases with the addition of plant aggregates. • Earth material is highly water vapour permeable. • Sorption–desorption isotherms are assessed with DVS and saturated salt solution methods. • MBV of earth-based materials is excellent. Abstract Earth is a material presenting good hygric properties, which is an important point as comfort and indoor air quality have become major issues. Nowadays, the energy efficiency of a construction is also crucial, but the thermal insulation provided by an earth brick is quite low. Therefore, some plant aggregates were added to lighten the material, thus decreasing its thermal conductivity. The hygrothermal properties of seven formulations made of earth with 0, 3 or 6% by weight content of barley straw, hemp shiv or corn cob were assessed. The properties determined were thermal conductivity, specific heat capacity, water vapour permeability, and sorption–desorption isotherms measured with the saturated salt solution and DVS methods. The theoretical MBV was also calculated. The study showed a large decrease in thermal conductivity when a large volume of plant aggregates was added while plant aggregates incorporation conversely affected the thermal inertia parameters. Concerning water vapour permeability, as earth is a very permeable material, the addition of plant aggregates did not improve this property. The sorption capacity of bio-based earth materials was slightly increased in comparison with earth alone. Finally, the calculated MBV showed the excellent buffering capacity of this kind of material, with and without plant aggregates. [ABSTRACT FROM AUTHOR]

Because of their complex hygromorphic shape, microstructural study of wooden materials behavior has recently been the point of interest of researchers. The purpose of this study, in a first part, consists in characterizing by high resolution X-ray tomography the microstructural properties of spruce wood. In a second part, the subresulting geometrical parameters will be incorporated when evaluating the wooden hygrothermal transfers behavior. To do so, volume reconstructions of 3 Dimensional images (3D), obtained with a voxel size of 0.5 μm were achieved. The post-treatment of the corresponding volumes has given access to averages and standard deviations of lumens’ diameters and cell walls’ thicknesses. These results were performed for both early wood and latewood. Further, a segmentation approach for individualizing wood lumens was developed, which presents an important challenge in understanding localized physical properties. In this context, 3D heat and mass transfers within the real reconstructed geometries took place in order to highlight the effect of wood directions on the equivalent conductivity and moisture diffusion coefficients. Results confirm that the softwood cellular structure has a critical impact on the reliability of the studied physical parameters. [ABSTRACT FROM AUTHOR]

Thermal insulation and renovation plasters are in still greater demand for the insulation and renovation of existing as well as new buildings. The main reason is the need for thermal protection with the purpose of reducing the energy consumption of existing buildings and the construction of near zero energy buildings. Suitable thermal insulation brings considerable savings in terms of energy costs and reduction of pollutants and emissions generated during heating. Protection of the environment and human health is also very important. Another reason is the need for the materials to be able to withstand increased humidity, which is a problem in older buildings. Research is aimed at developing materials which would be ecological, exhibit capillary activity, have an optimal ratio of thermal insulation and mechanical properties, high porosity, and low diffusion resistance. This paper describes the results of the development of plasters useable for thermal insulation and renovation of buildings and the study of their hygrothermal behaviour including a simulation of thermal and humidity conditions of a selected construction detail. Measurements and simulations showed that the newly developed mixtures had similar or better properties than the reference lime-cement plaster. The optimal mixture in terms of physical, thermal insulation, and mechanical properties was mixture 7 made with lime hydrate and fly ash 2. Simulations were run in the software THERM and WUFI so as to calculate the lowest surface temperatures for 3 different implementations of a jamb. The results showed that the newly developed plasters delivered markedly higher surface temperatures than the reference plaster, i.e. Mixture 1. All the new plasters tested in jamb detail 3 showed a surface temperature above 12.94 °C based on a determination of the dew point according to ČSN 73 0540–2 at a temperature of +21 °C and relative humidity of 60%. [ABSTRACT FROM AUTHOR]

• The interconnections distribution in fibers determines the heat transfer model. • The development of a thermal conductivity equation considers the radiative heat transfer. • The bale's thermal conductivity varies according to the fiber orientation. • Thermal conductivity depends on the chemical composition of the straw. Straw fibers are natural fibers that have a strong insulating property and a minimal environmental effect, making them suitable construction materials. In the construction sector, to predict the building energy consumption, the thermal conductivity of the materials composing the envelopes must be precisely known, which is not the case for the straw material. The properties of a straw bale are variable and mainly depend on its density, fibers orientation, chemical composition, temperature and relative humidity. Consequently, this study consists of determining a mathematical equation to predict the effective thermal conductivity of straw bales that can be applied to all straw types, in different circumstances. For this purpose, the size, distribution, and morphology of straw fibers are first determined from microscopic images. Second, a mathematical model for estimating the thermal conductivity is suggested using the heat transfer models of porous and fibrous materials. The numerical model is validated by an experimental study that measures the thermal conductivity of straw bales by altering their density between 80 and 120 kg/m3, their relative humidity between 15 % and 95 %, and their temperature between 15 ˚C and 55 ˚C. The experimental results show that the thermal conductivity increases from a minimum of 0.047 W/(m∙K) to a maximum of 0.09 W/(m∙K) when increasing the three altered factors. For a straw fiber having 40% cellulose content, the thermal conductivity increased from a minimum of 0.05 W/(m∙K) to a maximum of 0.0832 W/(m∙K). This behavior is found the same for the numerical findings. The comparison of numerical and experimental values shows a good agreement, with a root mean square error of 0.005 W/(m∙K) and a scatter index of 5.5 %. [ABSTRACT FROM AUTHOR]

Three wall panels of identical calculated U-value were simultaneously assessed in a large dual environmental chamber under a number of steady state and dynamic hygrothermal boundary conditions. This study used large-scale wall elements under identical controlled conditions in order to eliminate uncontrollable variables normally encountered in full-scale studies. The following panels were tested: Mineral Wool Panel, Wood Fibre Panel and the Biond Panel (an assembly of wood fibre and hemp-lime). Within the limits of the error range of the calculation, the measured U-value was same for all test panels when assessed under steady state and dynamic hygrothermal boundary conditions. It was however observed that in a boundary condition simulating intermittent heating, the Biond panel showed the highest heat storing and releasing capability whereas the Mineral Wool Panel showed the lowest. In terms of moisture management, the Biond panel exhibited the highest moisture dampening ability within the panel structure. Higher thermal and hygric inertia of the Biond panel may be useful in mitigating overheating of dwellings and reducing interstitial condensation. [ABSTRACT FROM AUTHOR]