Moisture Buffer Value Research Articles

Development of methods to measure the potential of a plaster to regulate indoor humidity

Moisture buffering utilises hygroscopic construction materials as a more sustainable approach to passively moderate indoor humidity. This study seeks to develop a reproducible test method to obtain a moisture buffering value of common building materials under conditions that reflect typical indoor environmental conditions. Temperature and humidity variations in sinusoidal profiles for two different materials, typically used to finish internal surfaces, have been studied to identify their potential moisture regulation behaviour. Outcomes were then combined and ranked indicating the potential of materials to passively regulate the indoor humidity and the need for robust methods of investigation. Practical application: In response to current practice and materials’ testing procedures, a reproducible test method is considered to enable comprehensive understanding of a hydroscopic materials’ behaviour, where subsequent interpretation of their performance can be quantified. The practicality to consider the use of passive regulation using hygroscopic materials can then be justified to bring indoor RH closer to the optimal range without heavy reliance on mechanical solutions, achieving a more effective passive indoor climate monitoring. It is expected that the outcome of this investigation can potentially form the basis of further improvement on a standardised test method to obtain moisture buffering value of hygroscopic non-structural elements for pragmatic application during design integration process.

Impact of Temperature on the Moisture Buffering Performance of Palm and Sunflower Concretes

The use of bio-based materials (BBM) in buildings is an interesting solution as they are eco-friendly materials and have low embodied energy. This article aims to investigate the hygric performance of two bio-based materials: palm and sunflower concretes. The moisture buffering value (MBV) characterizes the ability of a material or multilayer component to moderate the variation in the indoor relative humidity (RH). In the literature, the moisture buffer values of bio-based concretes were measured at a constant temperature of 23 °C. However, in reality, the indoor temperature of the buildings is variable. The originality of this article is found in studying the influence of the temperature on the moisture buffer performance of BBM. A study at wall scale on its impact on the indoor RH at room level will be carried out. First, the physical models are presented. Second, the numerical models are implemented in the Simulation Problem Analysis and Research Kernel (SPARK) suited to complex problems. Then, the numerical model validated with the experimental results found in the literature is used to investigate the moisture buffering capacity of BBM as a function of the temperature and its application in buildings. The results show that the temperature has a significant impact on the moisture buffering capacity of bio-based building materials and its capacity to dampen indoor RH variation. Using the numerical model presented in this paper can predict and optimize the hygric performance of BBM designed for building application.

Thermal and hygroscopic study of hemp concrete in real ambient conditions

Most building materials, and more particularly bio-based materials, are subject to hygrothermal transfers in the environment in which they are disposed. These transfers depend on their thermophysical characteristics as well as the ambient humidity and temperature conditions. In such environment, and despite these variations, the material must be able to ensure in a sustainable manner, the functions for which it was implemented (thermal, mechanical, acoustic …). Among these materials, hemp concrete, which is a bio-based material, is widely considered in building construction for its superior thermal and hygroscopic performance. The hygrothermal modelling of such materials in real conditions is essential for a better understanding of buildings’ energy performances. Several works targeted the numerical hygrothermal modelling of hemp concrete; however most of them are done in controlled laboratory conditions, which may be different from the real buildings scenarios. In this paper, heat and mass transfer are investigated both numerically and experimentally in real conditions. The hygrothermal properties of hemp concrete were first determined through laboratory experiments; then, an experimental wall segment made of hemp concrete was instrumented in real ambient conditions in order to validate the Philip and De Vries model describing heat and mass transfer. The comparison of the numerical results to the experimental data leads to interesting results regarding local temperature and relative humidity variations. Moreover, numerical investigation of the moisture buffer values of hemp concrete was performed and the results were validated by bibliographic data. The hemp concrete was found to be a very interesting potential hygrothermal regulation material in terms of thermal conductivity, decrement factor, time lag, and humidity regulation.

Simple and effective route to tailor the thermal, acoustic and hygrothermal properties of cork-containing waste derived inorganic polymer composites

Future generation building materials produced using sustainable precursors and exhibiting multifunctional properties are in huge demand, as they might be a key tool to tackle the carbon dioxide emissions from the building sector. This study provides new insights regarding the impact of the cork particle size on the hardened-state properties of inorganic polymer composites derived from fly ash waste. The composites were characterised regarding their mechanical, thermal, acoustic and hygrothermal properties. The use of smaller sized particles favours the specimens' sound insulation and moisture regulation capacity, while larger granules enhance the specimens’ mechanical performance. The best performing composite containing 80 vol% of small size cork granules shows an excellent moisture buffer value (2.22 g/m2 Δ%RH), low thermal conductivity (79 mW/m K) coupled with high sound insulation ability. In addition, the cork-composites show sound absorption frequency selectivity according to the thickness of the samples or the size of the cork granules used in their production, and this allows tuning the specimens according to the frequency of the sound pollution source. This study reduces the knowledge gap regarding the production cork-containing inorganic polymers which might foster the technology deployment.

Mechanical, Thermal, and Moisture Buffering Properties of Novel Insulating Hemp-Lime Composite Building Materials.

Hempcrete is a sustainable biocomposite that can reduce buildings’ embodied energy while improving energy performance and indoor environmental quality. This research aims to develop novel insulating hemp-lime composites using innovative binder mixes made of recycled and low-embodied energy pozzolans. The characterization of composites’ mechanical and hygrothermal properties includes measuring compressive strength, splitting tensile strength, thermal conductivity, specific heat capacity, and moisture buffer capacities. This study also investigates the impact of sample densities and water content on compressive strength at different ages. The findings suggest that mixes with a 1:1 binder to hemp ratio and 300−400 kg/m3 density have hygrothermal and mechanical properties suitable for insulating infill wall applications. Hence, compressive strengths, thermal conductivity, and specific heat capacity values range from 0.09 to 0.57 MPa, 0.087 to 0.10 W/m K, and 1250 to 1557 J/kg K, respectively. The average moisture buffer value for all hempcrete samples of 2.78 (gm/m2 RH%) indicates excellent moisture buffering capacity. Recycled crushed brick pozzolan can enhance the hygrothermal performance of the hemp-lime composites. Thus, samples with 10% crushed brick have the lowest thermal conductivity considering their density and the highest moisture buffer capacity. The new formulas of hydrated lime and crushed brick have mechanical properties comparable to metakaolin and hydraulic lime formulas.

Moisture Buffer Value of Composite Material Made of Clay- Sand Plaster and Wastepaper

The scope of the Nordtest method is to evaluate the moisture buffer value (MBV) for materials exposed to indoor air. The test is intended to simulate daily variations with relative humidity (RH) of 75% during 8 hours and 33% during 16 hours.Many authors have noted that clay plaster has a very good MBV (Altmäe et al. 2019). Our previous tests have shown that the MBV of clay plaster can be increased by adding paper plaster mixture (Nutt et al. 2020a). The specimen made according to a recipe contains the following: waste paper, glue, clay plaster mixture and water. Eleven paper plaster mixtures with different percentages were used.Test results showed that a large percentage of paper in the plaster increases the MBV. An impressive result, which needs to be studied further, was that the MBV was the highest in the mixture that consisted of 80% paper.

The Effects of Natural Paint on the Moisture Buffering Ability of Paper Plaster

Abstract The scope of the Nordtest method is to evaluate the moisture buffer value (MBV) of materials exposed to indoor air. The test is intended to simulate daily variations with relative humidity (RH) between 75 % during 8 hours and 33 % during 16 hours. The specimens follow a recipe that consists of waste paper, glue and water. Specimens made of paper plaster were covered with different colours. The results of the experiment showed that the type of paint used and the number of layers applied affected the MBV. Natural colours have a better moisture permeability than chemical paints, but the number of natural colour layers affects the MBV. The higher the number of layers, the lower the MBV.

The use of pith in the formulation of lightweight bio-based composites: Impact on mechanical and hygrothermal properties

The use of bio-based concretes or renders is rapidly developing. These sustainable materials present many advantages such as their acoustical and hygrothermal properties. These bio-sourced composites are made of vegetable aggregates, associated with a hydraulic binder. One of the most common aggregates is hemp shiv, which is an agricultural waste. However, hemp shiv is not available in big quantities nor in all geographical areas, so it seems interesting to introduce other bio-sourced aggregates in order to increase the availability. Sunflower and maize pith are unexploited agricultural by-products which can have a great potential as insulation materials. To use these aggregates, it is essential to assess first their interactions with different binders. In the present paper, the impact of density and type of aggregate (either hemp shiv or pith) on several key physical parameters was evaluated. These parameters were the uniaxial compressive strength test, the thermal conductivity, the sorption isotherms and the water vapor permeability, as well as the moisture buffering value (MBV). The use of pith shows promising results in terms of thermal and hygroscopic performances, the results also indicate that specific precautions should be taken to preserve the porosity of the soft pith material to optimize the hygrothermal performances.

Modeling of hygrothermal transfers through a bio-based multilayered wall tested in a bi-climatic room

A bio-based multilayered wall has been developed in the framework of the European ISOBIO project. A key point was to be able to perform proper simulations of the hygrothermal transfers occurring through the wall: local predictions are of first importance to characterize the behavior of the wall and thereafter its ability to ensure comfortable hygrothermal conditions inside buildings. A previous study proved that the conventional assumption of an instantaneous equilibrium between local relative humidity and water content according to the sorption isotherm is not relevant for bio-based porous materials, where in practice slow sorption kinetics occur. In the present study, an improved expression of the local kinetics is proposed and validated by sorption experiments. Then, Moisture Buffer Value tests are performed (Nordtest project's protocol). The simulations are adjusted to these measurements by using the inverse method in order to refine the knowledge of some critical parameters. Depending on the studied materials, the local kinetics constants are between 0.15 and 14 day-1/(kg.m-3). Finally, the ISOBIO wall is studied in a bi-climate room under a wide range of operating conditions. Simulations carried out with the conventional approach (TMC) and the local kinetics approach (TMCKIN) are compared to measurements: this clearly shows that the latter is able to predict well the relative humidity dynamics while the former underestimates it by a factor up to 66%. These results highlight the relevance of the new expression of the local kinetics and its ability to describe well the local hygric dynamics is certainly an achievement.

Characterization of hygrothermal insulating biomaterials modified by inorganic adsorbents

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).

Preliminary approach to bio-based surface healing of structural repair cement mortars

Mitigating the maintenance and repair costs of structures and infrastructures is a major problem in all countries. The aim of this research work is to analyse the performance of surface healing technique for crack control of cement-based mortars for structural repair in maritime environments. Microbiologically induced calcite precipitation (MICP) with ureolytic bacteria Sporosarcina pasteuri DSM 33 was introduced for crack-healing. Only main cracks were filled with the bioagent (bacterial cells and nutrients) for cost-saving purpose. It is intended to analyse the effectiveness of this technique for structural application in areas exposed to cyclic moisture changes. Hygric properties and their relation to durability increase were analysed through moisture buffering tests, capillary, porosity, compressive strength, SEM and microscopy analysis before and after bio-agent application to evaluate the evolution of the precipitation. For the first time, moisture buffering value (MBV) was used to evaluate the performance of the self-healed mortar and time needed for bacterial precipitation. The treated material can be classified as good in terms of MBV, and there was a general increasing trend of moisture buffering behaviour in self-healed samples. SEM analysis showed distinctive differences between the treated and non-treated cracks. The results show that bio-agent had remarkable effect on compressive strength recovery (over 87% of original value) after 21 days of healing and positively affected the initial stage of capillary absorption.

Characterization of biomass-based materials for building applications: The case of straw and olive tree waste

Vegetable fibers are more and more frequently used in building materials because of their low carbon footprint and their suitability as hygrothermal panels and acoustic absorbers. In particular, as vegetable materials have high carbon sequestration capacity, any use that prevents their incineration (e.g. the natural end-of-life for most pruning wastes), represents an essential contribution to reduction of CO2 emissions. For the above reasons, several researches promote the revival of sustainable building materials made of biomass. In this study, the hygrothermal and acoustical properties of materials suitable for buildings, made with vegetable fibers, are investigated. Straw fibers and olive tree-pruning residues were mixed with sodium silicate solution binders to create high performance insulating panels. Tests carried out in the laboratory allow a correlation between physical and microstructural properties. They evaluated thermal properties, such as thermal conductivity and thermal diffusivity, as well as the hygric performances of the materials, such as sorption isotherm and water vapor permeability. Moisture diffusivity and moisture buffer value were also estimated. Furthermore, sound absorption measurements were carried out. A final comparison between the new panels and one insulating material (EPS) on the market was discussed based on a numerical simulation using Wufi® software.

Development of a moisture buffer value model (MBM) for indoor moisture prediction

Hygroscopic materials could be used to passively regulate indoor moisture fluctuations, and thus reduce building energy consumption. It is essential to accurately calculate the moisture buffering effect in building energy simulations. However, in many building simulation tools, moisture buffering has been neglected. In those building tools that include moisture model, moisture buffering either has been estimated by very simple approximations or has been calculated by complex coupled heat-air-moisture transfer models that require orders of magnitude more computing time than simple energy prediction. Here, we have developed a new moisture prediction model with fast solution time and reasonable accuracy based on the moisture buffer value (MBV) theory. The MBV was originally designed to evaluate the moisture buffering capacity of building materials. Little research has been carried out to directly use MBV for building energy simulations. This paper first investigates MBVs under different boundary conditions. Secondly, a time-average MBV has been proposed, and its parameters can be obtained from the practical MBV test. Finally, comparison tests between the new moisture buffer value model (MBM) and other moisture prediction models have been carried out. The results indicate that the MBM can provide a fast and reasonably accurate prediction for indoor moisture variation.

Moisture buffer, fire resistance and insulation potential of novel bio-clay plaster

The novel bio-clay plaster was formulated by adding hemp powder to clay plaster to improve the performance of buildings by moisture buffering the indoor climate, providing a fire insulation layer to encapsulate inflammable bio-based substrates and enhancing air tightness within the system by closing joints. The results showed the plaster formulation influences drying shrinkage, thermal conductivity, density and the moisture buffer value of the plaster. The thermal conductivity of the novel bio-clay plaster decreased with a decreasing proportion of Earthen Clay. The proportion of hemp powder had little effect on the thermal conductivity of the plaster, whereas the amount of hemp powder had a slightly effect on the moisture buffering property. The novel bio-clay plaster exhibited improved fire resistance. The detailed hygrothermal characterization using the measurement of moisture buffer value and thermal conductivity analysis indicated that the novel bio-clay plaster showed a good moisture buffering capability, even for small thicknesses, and low thermal conductivity, with the potential to develop industrially viable products.

Effect of compaction on multi-physical properties of hemp-black liquor composites

This study aims to develop fully agro-based insulating building materials. Previous studies investigated several types of aggregates and binders to develop composites. The thermal conductivity of such composite appears mainly impacted by the density. This paper aims to investigate the effect of density on various multi-physical properties of composites, using the same formulation and adjusting the forming step. Thus, specimens are produced with the same hemp shiv to black liquor ratio but different compaction stress. The effect of compaction on bulk density, porosity, mechanical resistance, thermal conductivity and Moisture Buffer Value (MBV) is analyzed. It is shown that it is possible to reach thermal conductivity that is low enough to be considered as building insulating material. Thanks to this study, the required compaction stress to ensure targeted values of density, then thermal conductivity and MBV, is identified.

The development of EMPD model for identifying and predicting the materials' moisture performances

Moisture excess or lack in buildings has many adverse effects on human health, structural durability and building energy consumption, and moisture design for building materials is an important and efficient measurement for creating a stable indoor climate. However, the current quick test method (e.g., moisture buffer value test) can only evaluate the materials' moisture buffering abilities roughly, and the advanced numerical prediction method (e.g., using HAM models) is hardly applicable in practices due to insufficient materials’ hygrothermal properties and its long computing time. EMPD model can calculate with less input parameters and short time without sacrificing accuracy. While this paper found existing EMPD has limited application conditions, and further proposed modified multilayer EMPD model. A new approach can be applied to identify and predict the moisture performances of building materials. In this paper, two typical building materials with diverse hygric properties were simulated. Their key parameters of the modified model was easily inversed by a 24h standard box test instead of several months of material hygrothermal properties tests, based on which, the materials' actual performances under various conditions can be predicted. The presented approach was validated by comparing the numerical predictions with HAM results in the corresponding conditions. This study provides an easy and fast way to test and predict the moisture performances of building materials and indoor moisture in practices.

Building incorporated bio-based materials: Experimental and numerical study

In building environments, several research on dynamic moisture storage in hygroscopic building materials has improved interest in moisture buffering capacity of bio-based materials and demonstrated the potential of these materials to improve thermal comfort and buildings energy consumption. This paper presents an investigation, which aims to compare the hygroscopic behavior of different bio-based materials to identify their hygric proprieties. For this, an experimental facility is used to measure the moisture buffer value (MBV) for different categories of building materials. Thereafter, a dynamic simulation has been carried out by using TRNSYS software in order to evaluate heating and cooling loads. The results showed that the wood-cement composite still has excellent moisture regulator when compared to wood panels or fibrous materials. It has a buffer capacity superior to 3 [g/m2.% RH] very close to that of wood fiber panels. The simulation results of the different cases showed that the insulation reduces significantly total energy demand, but it does not lead heat evacuation in the summer season. Thus, from this study, it can be concluded that a natural ventilation mechanism is recommended to improve energy efficiency in the building.

Is stabilization of earth bricks using low cement or lime contents relevant?

The starting premise of this article is that it is not environmentally consistent to stabilize earth by using more than 4% of mineral binder (cement or lime). Thus, this paper presents a study of the effects of low mineral binder contents (2 and 4%) on the properties of earth bricks. The results obtained on two different soils show that the effects are not observable for dry compressive strengths or for dry thermal conductivities but the addition of small amounts of mineral binders significantly modifies the resistance to water and the Moisture Buffer Value.

Modelling the hygrothermal behaviour of cement-bonded wood composite panels as permanent formwork

This paper reports on the hygrothermal behaviour of a new bio-based composite building material, based on recycled wood fibres used as eco-aggregate within a cementitious matrix. A coupled heat and moisture transfer was established through the material and resolved numerically with a model developed herein. Relative humidity and temperature were chosen as driving potentials. The hygric and thermal properties of the material were analysed and then used as input parameters in the model. The accuracy of the latter was verified by comparing the simulation results with experimental hygrothermal tests, from which the moisture buffering value (MBV) could be determined. The MBV showed that the wood-cement composite material might contribute to improve the indoor thermal comfort and be relevant for low-energy building design.

Development of a high clay content earth plaster

Earth, as a building material, offers many advantages: on an ecological point of view, it is a natural, abundant, recyclable material with low energy used for production and transportation. Moreover, earth is known to be a natural humidity regulator and to improve comfort inside buildings, making it a good choice for indoor plastering. The clayey phase gives the global cohesion of the material by acting as a binder for the sand grain skeleton. The finest grain soil fraction is responsible for the dry strength, the water vapour permeability and the sorption capacity of earthen plasters. However, clay also induces the drying shrinkage of the mortar leading to the cracking of the plaster. The objective of this work is to improve the moisture buffer capacity of earthen plaster by increasing its clay content without jeopardizing the general behaviour of plasters. Based on consistency, shrinkage and shear tests, the characteristics of mortars in fresh and hardened states were evaluated. The hygric regulator potential of earthen materials were measured through the Moisture Buffer Value (MBV) test. As expected, results have shown that, to maintain a standard level of consistency, an increase in the clay content leads to a greater amount of mixing water. Moreover, to enhance the MBV, the highest possible earth content must be used. Addition of organic admixtures can be considered to improve the high-clay content plaster behaviour without jeopardizing the aesthetic and mechanical aspects of plaster.