Moisture Buffer Value Research Articles

Hygrothermal and mechanical characterization of novel hemp-lime composites with enhanced consistency

Hemp-lime composites have captured attention in the construction industry due to their sustainability and excellent hygrothermal performance. However, variability and inconsistent performance have hindered their widespread adoption. This research introduces a novel approach to improve the uniformity and hygrothermal characteristics, aiming for reproducibility and consistency comparable to traditional insulation materials. This method included (1) reducing hemp particle size to coarse (1.33 mm), medium (0.92 mm), and fine (0.72 mm) particles; (2) maximizing the hemp proportion to 70 % by weight; and (3) standardizing dry density using vibration techniques. The findings indicate dry density variability reduction in all samples, with a coefficient of variation ranging from 0.16 % to 2.36 %. The hygrothermal analysis demonstrates enhanced insulation and moisture-buffering properties, along with reduced directional disparity in thermal conductivity (1.2–6.8 %) compared to the control sample, particularly in samples with fine particle sizes. Thermal conductivity was within the range of 0.0535–0.0667 W/m K, considerably lower than previously reported values. Also, a positive correlation is observed between moisture-buffering and hemp ratio, indicating that higher hemp ratios in the composite lead to increased moisture capacity, with moisture buffer values of 2.47, 2.28, and 2.12 g/m² RH corresponding to the binder-to-hemp ratio of 30:70, 40:60, and 50:50 by weight, respectively.

Assessing the impact of moisture buffering properties of materials on indoor environmental quality: A study on a recycled material plaster

This study examines Moisture Buffer Value (MBV) of interior finishing layers, which impacts buildings internal relative humidity, thus indoor environmental quality. The MBV depends on material's moisture capacity and vapour diffusion resistance factor, both of which depends on relative humidity. The paper aims to (i) characterize a new recycled material plaster that includes construction and food industry waste through laboratory measurements, (ii) use dynamical building simulations to quantify the impact of the MBV of existing and the new interior plaster on relative humidity in real design scenarios, and (iii) evaluate how changing the definition of the MBV to consider its dependence on indoor air relative humidity can improve its accuracy. Results show that the plaster's moisture buffering properties significantly reduce the variations of the relative humidity of interior climates compared to a vapour-tight finishing layer. The performances of the new plaster made with recycled materials are comparable to those of the other plasters. The new MBV definitions (“Dynamical MBV″ and “Summer/Winter MBV”) show a significantly improved correlation with the relative humidity variations of indoor climates of buildings, observed in dynamic simulations, with respect to the typically used practical MBV. The new definitions are therefore promising for practical applications.

Characterization and optimization of desulfurized construction gypsum modified with functionalized nanocellulose

This study focuses on the development and characterization of a novel composite material based on flue gas desulfurization (FGD) gypsum modified with functionalized nanocellulose. The incorporation of 0.1 wt% nanocellulose into the FGD gypsum matrix resulted in significant improvements in mechanical strength, water resistance, and thermal insulation properties. The flexural and compressive strength of the optimized composite increased by 32 % and 27 %, respectively, compared to the control sample. The water absorption decreased by 22 %, and the softening coefficient increased from 0.72 to 0.85, indicating enhanced water resistance. The thermal conductivity of the composite was reduced by 31 %, showcasing its potential as an energy-efficient building material. SEM analysis revealed a refined microstructure with improved interfacial bonding between the nanocellulose and gypsum matrix, while FTIR spectroscopy confirmed the presence of chemical interactions between the components. The moisture buffering capacity of the composite was also superior, with a 38 % higher moisture buffering value than the control sample. These findings highlight the potential of functionalized nanocellulose as a reinforcing agent in FGD gypsum-based composites, offering a promising solution for the development of high-performance, eco-friendly building materials.

Moisture buffer value for hygroscopic materials with different thicknesses

Moisture buffer value (MBV) is a critical parameter for assessing hygroscopic material's ability to moderate indoor humidity variation. The original MBV theory is strictly valid only for a semi-infinite (or “very thick”) material. When the material is thinner than semi-infinite, the material's thickness will affect its moisture buffering ability. The existing MBV theory is inapplicable. This study proposed a new numerical method to calculate a material's MBV at different thicknesses. The proposed model is simple and efficient. The relation between a material's MBV and thickness and the optimal thickness can be obtained without extensive experimental measurement. What's more, the material's adsorption and desorption isotherms, as well as the material's hysteresis loop and scanning isotherms, are incorporated in the proposed model, making it applicable to advanced desiccant materials like Metal-Organic Frameworks (MOFs). MIL-100(Fe), one of the most promising MOF candidates for indoor humidity control, was used to validate the newly developed model. MBVs of MIL-100(Fe) samples with different thicknesses were measured, and the experimental data closely matched the simulated results. Finally, a building energy consumption simulation model was developed based on the proposed numerical model. A MOF panel with its optimal thickness was placed in the BESTEST typical office room located in Copenhagen. The results show that MOF can reduce about 30 % of the energy consumption of air conditioning in a purely passive way.

Mechanical and hygrothermal properties of hemp-silica bio-composites

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.

Super-stable modified wood for enhanced autonomous indoor humidity regulation

The crucial development of materials that automatically adjust indoor humidity, a significant factor in human health and daily life, has gained importance due to the emphasis on energy conservation. Wood, with its natural hygroscopic properties, is effective in this regard but faces challenges of deformation and cracking due to moisture content changes. Herein, we introduced an innovative in-situ wood modification strategy, which integrated deep eutectic solvent (DES) impregnation with heat treatment, producing dimensionally super-stable modified wood for enhanced autonomous indoor humidity regulation. This modification process focused on creating more robust cross-linking structures within the amorphous regions of the wood cell wall. As a result, water-induced deformation of natural wood was significantly reduced, as evidenced by an anti-swelling efficiency exceeding 80%, ensuring the long-term reliability of DES-modified wood in varying humidity environments. Additionally, the introduction of additional pores and hygroscopic sites in the cell wall enhanced the natural wood’s moisture buffering value by 2.5 times, showcasing the superior ability of DES-modified wood to control indoor humidity effectively. Moreover, the DES-modified wood also exhibited commendable flame retardancy and antibacterial properties. Consequently, this novel modified wood emerges as a reliable material for indoor humidity regulation, promoting healthier indoor conditions and offering a sustainable alternative for energy-efficient construction practices.

Hygroscopicity and Morphology of Bio-Based Boards—The Influence of the Formulation

The internal structures and the hygroscopicity of bio-based boards consisting of giant reed (Arundo donax L.) and hazelnut shells as bio-aggregates, and a sodium silicate solution as the adhesive, were investigated. The aim was to evaluate the influence of each material (the bio-aggregates and adhesive) and their distributions in the boards on the final performance. By carrying out X-ray computed tomography, the internal structures and the porosities of the boards were determined, allowing important considerations of their hygroscopicity. The voids’ percentages were between 26% and 36% of the total volume of the composites. Both the materials and the composites demonstrated high hygroscopicity. In particular, the mixtures of the bio-aggregates and the sodium silicate allowed reaching a moisture buffering value of 7.44 g/(m2%RH) for the A. donax-based composite, 3.86 g/(m2%RH) for the hazelnut-shell-based composite, and 4.65 g/(m2%RH) for the mixture-based composite. Besides the identification of the contributions of the materials, a detailed discussion of the assessed properties was carried out to use these bio-based boards in vernacular historic construction. The results show how the aggregate type and the adhesive content affected the final behavior, demonstrating the importance of a conscious material choice. Furthermore, helpful information for the future development of these types of bio-based boards and their possible optimization was provided.

Effect of Posidonia oceanica on the hygrothermal characterization of compacted earth blocks

A hygrothermal characterization of new construction materials, namely unstabilized and Posidonia oceanica fiber stabilized compressed earth blocks, were studied in this work. In the first part, the sorption-desorption isotherms of unstabilized blocks were compared with others stabilized with raw and treated fibers to detect the effect of adding fibers. The results revealed an improvement in hygric properties after the addition of raw fibers. Moreover, the Guggenheim-Anderson-de Boer (GAB), the Oswin, and Brunauer, Emmet, and Teller (BET) models successfully fitted experimental sorption-desorption isotherms curves. In the second step, the moisture buffer value and water vapor permeability were evaluated under dynamic conditions. According to the classification of the NORDTEST project, the innovative and new compacted earth blocks studied in this paper seem to be excellent moisture regulators because they have an MBV greater than 2 g/ (m2. %RH). In fact, BAFBB samples (block with crushed Posidonia oceanica) achieved the best results. These formulations recorded an ideal water buffer coefficient equal to 2.66 g/ (m2.%RH)

A feasible re-use of an agro-industrial by-product: Hazelnut shells as high-mass bio-aggregate in boards for indoor applications

The present work investigates the feasibility of producing boards, with unconventional materials, namely hazelnut shells as a high-mass bio-aggregate and a sodium silicate solution as a no-toxic adhesive, and discusses possible applications based on an extensive characterization. The aim is to define a feasible reuse of a largely produced agro-industrial by-product to reduce the high environmental impact caused by both the construction and the agriculture sectors, by proposing a building composite that improves indoor comfort. The presented combination of aggregate-adhesive generated a product with characteristics interesting to explore. The thermal conductivity is moderated, and the composite achieved values of σmax = 0.39 N/mm² for flexural strength and σmax = 2.1 N/mm² for compressive strength, but it showed high sorption capacity with a moisture buffering value of about 3.45 g/(m² %RH), and a peak of sound absorption between 700 and 900 Hz. Therefore, the boards' most promising performance parameters seem to be their high hygroscopicity and acoustic absorption behaviour, namely in the frequency range of the human voice. Hence, the proposed composite could improve indoor comfort if applied as an internal coating board.

Moisture buffer value for hygroscopic materials with different thickness

Moisture buffering is the capacity of hygroscopic building materials or adsorbents to mitigate the humidity fluctuations in the indoor environment through the adsorption/desorption phenomenon. NORDTEST proposed the moisture buffer value to quantitively characterize the moisture buffering capacity of porous materials. Materials with high moisture buffer values have a higher ability to passively control indoor humidity conditions and thus reduce building energy consumption and improve indoor thermal comfort. However, the ideal moisture buffer value theory is based on the assumption that the thickness of the studied materials should exceed the penetration depth of that material. This assumption significantly limits the application of moisture buffer value theory to thin-layer materials, such as textiles, desiccant coating, wallpaper, wood wall panels, etc, which represent a large proportion of moisture buffering in the built environment. In this study, we developed a new numerical model to calculate moisture buffer values for hygroscopic materials with different thicknesses. Experimental measurements were also carried out to validate the solutions. The moisture buffer value of a new kind of desiccant (metal-organic frameworks) under different thicknesses were measured by climatic chamber tests. Simulated results showed agreement with both the measurements and theory. The results indicate that the new moisture buffer value model can be used to find the optimal thickness of desiccant coating or hygroscopic materials for autonomous indoor humidity control.

Development of a fast moisture prediction model based on the moisture buffer value theory

Moisture transfer in buildings significantly affects indoor thermal comfort, energy consumption, and durability of construction materials. It is crucial to predict the moisture storage and transfer in building simulations accurately. However, moisture transfer was neglected in many simulation tools for building performance analysis. In those calculation tools, including a moisture model, moisture transfer has been either estimated by simple approximations or calculated by complex combined heat, air, and moisture transfer (HAMT) models that require orders of magnitude more computing time than simple calculations. In this study, a new moisture prediction model with fast solution time and reasonable accuracy was developed based on the moisture buffer value (MBV) theory. The moisture buffer value was initially designed to quantify the moisture buffering ability of porous building materials. Very little research has been conducted to use MBV for calculating building energy performance directly. This paper first studied the MBVs under different boundary conditions (i.e., square wave and harmonic wave variation of vapour content), and then a time-average MBV was proposed. Experiments were carried out to get the parameters for the new FMBM model. Finally, simulation tests were conducted to compare the FMBM model with other moisture prediction models (e.g. EC, EMPD and HAMT models). The results indicate that the FMBM can provide a fast and reasonably accurate solution for indoor moisture prediction.

Super adsorbent bio-polymer additive to improve hygroscopic and acoustic properties of a conventional lime plaster

The paper introduces a new lime plaster composition, with a Super Bio-Polymeric Adsorbent (SABP), for interior applications to improve hygrothermal and acoustic comfort. Alginate SABP is added to a conventional lime plaster to improve hygroscopic and acoustic performance. The hygrothermal and acoustic properties of the modified plaster are compared with the ones of the original plaster with a preliminary moisture uptake test, the evaluation of the sorption isotherm, the moisture buffering value (MBV), and the acoustic absorption. The results show a significant increase in the equilibrium moisture contents and the MBV (from 0.7 to 6.2 g/(m2⋅%RH)). At the same time, the sound absorption coefficient is slightly improved, increasing 0.1-0.2 at frequencies higher than 500 Hz compared to the reference conventional lime plaster. The paper describes the material characterization: the sorption isotherm and the MBV are obtained using a dynamic vapor sorption (DVS) analyzer. The acoustic absorption is measured using the impedance tube method.

Characterization of an Arundo donax-based composite: A solution to improve indoor comfort

Arundo donax (giant reed or giant cane) is a widely available, perennial, invasive, non-food crop, present worldwide and employed for several uses, including building practices. Considering the increasing demand for sustainable building materials, A. donax can be an efficient solution. This study investigated its properties as a bio-aggregate mixed with a sodium silicate solution as an adhesive. A horizontal analysis that provided a general characterization of the composite was carried out. The results showed that the A. donax-based composite had an apparent density of 517 kg/m³, thermal conductivity of 0.128 W/(m.K), and high hygroscopicity, with a moisture buffering value of 4.33 g/(m² %RH), property that could be both an advantage for indoor comfort and a drawback. The uncommon sound absorption behaviour can be comparable to granular materials, with the highest sound absorption coefficient values, α, between 600 Hz and 700 Hz. Due to the range and the shape of the acoustic absorption property, this material may be helpful in acoustic treatments for speech noise. The mechanical tests defined flexural and compressive strength, respectively, 0.35 N/mm² and 0.9 N/mm², ensuring applicability. Above all, these tests opened new possible solutions for A. donax-based composite production either alone or in combination with other agro-industrial wastes and justified further tests, such as fire resistance and bio-susceptibility.

Impact of Density, relative Humidity, and fiber size on hygrothermal properties of barley straw for building envelopes

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.

Experimental Study of the Dimensional and Hygrothermal Properties of Hemp Concrete under Accelerated Aging

In this article, the functional properties of hemp concrete are studied. Hemp concrete stands to reduce the carbon impact and improve the energy consumption of houses. Hence, numerous properties are measured: mass and dimension (volume) variations are found, as is the variability in hygrothermal properties (density, thermal conductivity, heat capacity, moisture buffer value, and water vapor permeability). This entry proposes three different characterization campaigns. The first is a short introduction to the spatial variability in thermal conductivity; the second is dedicated to the study of univariate variations in the mass, volume, and hygrothermal properties of hemp concrete samples. The last one tackles the aging evolution of the properties characterized during the second campaign, in which the samples follow several aging protocols, including exposure to outdoor conditions, the application of immersion-drying cycles, and the application of freeze–thaw cycles. A set of samples is kept under control conditions to allow for comparison. As the main result, spatial variability was found in the material. This is related to the random manufacturing variability or the spatial position regarding the height of the manufactured element. A high univariate variability is found across hemp concrete samples. Moreover, the storage of samples under stable reference conditions implies very little change in the studied materials’ properties, whereas all accelerated aging protocols implied major changes of properties. In particular, we observed an evolution of the thermal conductivity of the samples kept under control conditions for 4 months, with the thermal conductivity ranging from −2.7% to +6.3% with a mean evolution of +1.22%. We observed an increase in the same property, ranging from +2.7% to +18.3%, with a mean of +9.0% for samples kept for 4 months under natural outdoor conditions, an increase ranging from +7.3% to +23.6% with a mean of +15.2% for samples that had undergone 20 cycles of immersion-drying, and an evolution of this property ranging from −5.6% to +12.3% for samples that had undergone 20 freeze–thaw cycles.

Gypsum plastering mortars with Acacia dealbata biowaste additions: Effect of different fractions and contents on the relative humidity dependent properties

Hemihydrate gypsum is a very eco-efficient binder. Gypsum plasters were commonly used in the past and should be still chosen nowadays for being an eco-efficient choice. However, their hygroscopicity and contribution to act as moisture buffer are not very high. The present study analyses the hygrothermal behaviour of mortars based on gypsum and modified with the addition of residual biomass of A. dealbata, an invasive species in Portugal. Five different fractions of the plant were tested as additions for mortars, at incorporation levels of 5% and 10% by volume, with the purpose of enhancing the moisture buffering of the plasters without jeopardizing other properties. The study found that the addition of A. dealbata increases their hygroscopic behaviour. In some cases (bark fraction) the Moisture Buffering Value of the reference mortar is triplicated, and the behaviour is comparable with high hygroscopic plasters as clay-based ones. However, biological colonization must be controlled.

Condensation retardation performance of metal-organic framework-based composite humidity-control materials in a radiation cooling room

The use of radiant cooling systems in humid regions is limited by surface condensation. Promising advancements have been made in the field of humidity regulation through the utilization of novel high-capacity adsorption materials, known as porous metal-organic frameworks (MOF), which possess expansive surface areas. This study investigated the condensation retardation performance of MOF-based composite humidity-control materials used as surface coatings in a typical radiation cooling room. A total of 16 working conditions in summer were tested, including extreme and typical climates, open windows, and fresh air supply. The influence of two types of MOF-based coating materials and two types of ceiling constructions (with or without a desiccant interlayer) on humidity was analyzed. The results showed that the coating materials and desiccant interlayer construction significantly affected condensation retardation and indoor humidity ratio variation. The better the moisture regulation performance of the material, the lower the risk of condensation. Under extremely high-humidity conditions, the MOF-based coating delayed the critical condensation time by up to 4.5 times that under no-coating conditions. The risk of condensation decreased with improvement of ideal Moisture Buffer Value (MBVideal) of the material, and with the addition of desiccant interlayer during ceiling construction. A coating material with a higher MBVideal can increase the average values of the difference between the surface and dew point temperatures by as much as 181.0%, compared with an uncoated ceiling. The average difference between the surface and dew point temperatures was found to increase by up to 2.11 °C, compared with that for the desiccant-free construction.

Enhancement of the hygroscopic and acoustic properties of indoor plasters with a Super Adsorbent Calcium Alginate BioPolymer

The present study introduces a novel-composition lime plaster that contains a Super Adsorbent BioPolymer (SABP) based on Calcium Alginate (CaAlg) for indoor applications, to improve hygrothermal and acoustic comfort. The sorption isotherm of the plaster, the moisture buffering value (MBV), the acoustic absorption, and the thermal conductivity have been assessed. The hygrothermal and acoustic properties of the modified plaster have been compared with those of the original composition to evaluate its performance under different concentrations of CaAlg (between 10 and 30% wt). Adding the CaAlg SABP to a conventional lime plaster consistently enhanced its hygroscopic properties. The results show a substantial increase in the equilibrium moisture uptake (between 10 and 23 fold) and MBV, from 0.9 to 9.3 g/(m2⋅%RH). The sound absorption coefficient improved by 0.1–0.2 at higher frequencies than 500 Hz. This paper provides detailed information on the characterization of the material. It includes details about using a dynamic vapor sorption (DVS) analyzer to evaluate the sorption isotherm and MBV. It also contains information on the impedance tube method used to measure the acoustic absorption of the material.

A Review of Sustainable Bio‐Based Insulation Materials for Energy‐Efficient Buildings

AbstractThe surge towards a sustainable future in the construction industry requires the use of bio‐based insulation materials as an alternative to conventional ones for improving energy efficiency in structures. In this article, the features of bio‐based insulation materials, including their thermal conductivities, moisture buffering value, fire performance, and life cycle evaluations are examined. It is clear from the review that pre‐ and post‐treatment of the bio‐based materials used for insulation materials optimize their properties. The life cycle analysis reveals a significant reduction in global warming potential (GWP) compared to conventional foams. In addition, it is envisaged that producing bio‐based insulation materials on a larger scale will further decrease the net GWP. The article, therefore, proposes the implementation of policies that will promote the commercialization of bio‐based insulation materials.

New hybrid bio-composite based on epoxidized linseed oil and wood particles hosting ethyl palmitate for energy storage in buildings

In this study, the incorporation of ethyl palmitate (EP) as a bio-based phase change material (BPCM) in wood particles, the preparation and properties of the novel biocomposite for building applications were investigated. The wood particle-based composites hosting BPCM were produced by cold compression moulding. The EP impregnation step was optimized in terms of uptake and its ratio by post-addition of non-impregnated fibers. The optimized wood particles/EP ratio were combined with 37.5% epoxidized linseed oil (ELO) as a binder to produce a composite with energy storage function containing more than 99% bio-ingredients. The optimum BPCM content in the composite was 25%. The produced biocomposites were characterized by T-hystory, DSC, TGA, and a moisture buffer test. The results revealed excellent moisture buffer values (2.07 g/m2 RH%) according to the Nordtest protocol, significant thermal mass, ability to store excessive energy in terms of latent heat and maintain the temperature constant for longer time, good thermal stability and improved specific heat capacity when compared to a reference composite without BPCM. The effect of incorporating BPCM into biocomposite for regulating temperature fluctuations was confirmed by comparing test prototype cubes, with and without BPCM, subjected to temperature fluctuation between 0 and 40 °C.