Moisture Buffering Research Articles

Building bio-insulation materials based on bamboo powder and bio-binders

Bio-insulating materials are well known to reduce the environmental impact of constructions and are able to regulate the indoor temperature and humidity of buildings. This study investigates the influence of high-absorbing bio-glues based on a protein and lignin compound on moisture transfer and storage as well as on thermal performance of bamboo particleboards. The investigations are based on the moisture buffer value, vapor permeability, isothermal vapor sorption and thermal conductivity. Simultaneously, the mechanical properties and mold growth of these materials, manufactured for the study, are also investigated. The results demonstrate excellent moisture buffer capacity, from 2.13 to 3.26 g/(m2·%RH). The vapor sorption isotherm results exhibit the materials’ high moisture storage, and the vapor permeability behaves like commercial bio-insulating materials. The thermal conductivity of particleboards shows a low value, in accordance with their density and variation in moisture content. In addition, the results indicate mold appearance on the surfaces of specimens after 14 days exposure to 84% relative humidity. Moreover, a comparison of the hygrothermal characterizations between bamboo particleboards and fiberboards (Nguyen et al., 2017) is carefully made to highlight the exceptional features of those bio-boards.

Analysis of moisture buffering effect of straw-based board in civil defence shelters by field measurements and numerical simulations

Moisture problem is one of most serious impediments for the development and sustainable utilisation of civil defence shelters due to poor moisture management. The aim of this study is to develop a passive approach to improve the indoor moisture environment of the shelter, fitting straw-based board on the inner surfaces of walls. The study first conducted long-term field monitoring of room temperature and relative humidity in a typical civil defence shelter in Beijing, and analysed the impact of straw-based board on indoor thermal and moisture environment. The measured results show that straw-based board can dampen the increase in humidity level and improve moisture environment of the shelter significantly, especially in summer. Additionally, a coupling method which combines a well-developed hygrothermal model and dynamic heat transfer in a typical civil defence shelter is used for simulating moisture buffering effect of straw-based board, and the accuracy of the method is validated by the measured data. Finally, using the coupling method, a parametric study is carried out to predict the hygrothermal behaviour of straw-based board for the assessment of its buffering effect in various climate zones of China and for better understanding of its application effect in the civil defence shelter.

Field Investigation of Moisture Buffering Potential of American Clay and Magnesium Oxide Board in a Mild Climate

Field Investigation of Moisture Buffering Potential of American Clay and Magnesium Oxide Board in a Mild Climate

Design and properties of a new sustainable construction material based on date palm fibers and lime

Every year, huge quantities of date palm fibers (DPF) are produced and wasted all over the world. Using this natural fiber as raw material would contribute to the valorization of natural sustainable resources. This paper presents an experimental investigation of a new eco-material based on date palm fiber and lime. The experiments on the elaborated material investigate some mechanical, thermal, acoustic properties and moisture buffering capacity. The influence of the fiber/lime ratio on the behavior of the lightweight aggregate was studied systematically. The results of compressive strength testing indicated that PDF incorporation led to a reduction in resistance limit, however, the recorded average values are still acceptable. Also, it was observed that the thermal conductivity is sensitive to the variation of the fiber/lime composition ratio. The measured thermal conductivity reached a minimum of 0.091 W/m.K for samples of 50% fiber, which indicates that it can be used as a good thermal insulator. With regard to the sound absorption, the new material reveals good absorption capacity based on the measured sound absorption coefficient which is for 50% of fiber: for medium and high frequencies 0.65 and 0.55 respectively. Due to its porous morphology, the proposed material has the ability to absorb water vapor in a high relative humidity environment and to restore it in a dry one. Hence, it could therefore act as a hygric regulator. Measurements of moisture buffer value revealed that the material is classified as good or excellent depending on the percentage of fiber.

Improvement of Water Resistance of Hemp Woody Substrates through Deposition of Functionalized Silica Hydrophobic Coating, While Retaining Excellent Moisture Buffering Properties

This paper reports on the development of a novel treatment for hemp shiv that improves resistance to liquid water and protects hemp shiv from biodegradation without impacting the natural ability of the shiv to buffer moisture vapor. The hydrophobic surface was produced by depositing silica nanoparticles, which were prepared by the functionalization of silica nanoparticles with hexamethyldisilazane (HMDS). The surface chemical composition was determined showing replacement of surface silanols on the silica nanoparticles with trimethyl groups. The specific surface area of silica nanoparticles decreased after the trimethylsilyl treatment. The surface modifications reduced the level of hysteresis between absorption and desorption isotherms and also the total amount of moisture absorbed by the silica nanoparticles. The surface of the hemp shiv was initially hydrophilic but became hydrophobic once the material was treated, demonstrating contact angle with water of 120°. The results show the coating layer of fun...

Rammed Earth incorporating Recycled Concrete Aggregate: a sustainable, resistant and breathable construction solution

Construction and demolition debris, mainly concrete and masonry rubble, represent a significant share of municipal waste. Recycling crushed concrete aggregates and using them as substitutes for natural ones might therefore be determinant in reducing landfilling and mineral resource depletion. An innovative way to give new value to Recycled Concrete Aggregates (RCAs) is to ram them in layers to form load-bearing walls for stabilised Rammed Earth (RE) applications. However, the success of those few existing RE projects using RCA is mainly due to the knowledge and experience of the contractors rather than official standards or guidelines or scientific literature. The objective of this study was to further the knowledge of this building technique by determining the effect of different RCA replacements on the material’s mechanical resistance, sustainability and hygroscopic properties: indicative of the structure’s structural, environmental and hygrothermal performance. Mechanical resistance was assessed by means of the Unconfined Compressive Strength (UCS, commonly used for rammed earth-like materials), hygroscopic properties via Moisture Buffer Value (MBV) and sorption isotherms while the sustainability was assessed via consequential Life Cycle Assessment (LCA). Microstructural investigations via mercury intrusion porosimetry, nitrogen adsorption-desorption isotherms, scanning electron microscopy and X-ray diffraction were performed to understand and explain material mechanical and hygroscopic behaviour. The building technique, already proven to be durable, was demonstrated to be resistant (from 4 to 12 MPa at 28 days depending on the RCA replacement and cement content), sustainable (down to 25 kg CO2-eq. of embodied carbon per square meter of load-bearing wall) and to have good moisture buffering abilities (0.88 g/(m2%RH) for mixtures containing only RCA). Strength appeared to be more related to the particle size distribution of the mix rather than to the percentage of RCA added. The amount and type of stabiliser added to the mix and the distance covered by the RCA during its lifetime strongly affected the environmental sustainability of the mixture; to maximise the potential of this building technique, reducing the amount of cement in the mixture by using alternative stabilisers should be the main priority.

Chemical and multi-physical characterization of agro-resources’ by-product as a possible raw building material

The aim of this paper is to find out the best valuation of agro-resources’ by-products as new alternative raw building materials that meet to sustainable development requirement. Five agro-resources are considered: flax, hemp, corn, rape and wheat. In the present work, the chemical characteristics of bio-aggregates are studied by FTIR, Van soest method and Phenol sulfuric method to identify their composition. The investigated physical properties are particle size distribution, density, porosity, water absorption, thermal conductivity and moisture buffer value. The studied materials differ on a chemical and a thermal point of view while they all are excellent hygric regulators. These results suggest that agro-resources can be used as a raw building materials for several types of use: as lightweight aggregates or as binder.

Experimental and numerical evaluation of the hygrothermal performance of a hemp lime concrete building: A long term case study

Hemp-lime concrete (HLC) is a bio-based material which is currently undergoing a growing development. HLC is a low embodied energy material and an excellent hygrothermal regulator. Its thermal, hygric and mechanical properties are well known, and its capacity to reduce energy needs and to improve hygrothermal comfort is demonstrated across many laboratory and numerical studies. However, there are few works about its hygrothermal performance in real climatic conditions on the scale of a building. In order to address this issue, a long term in-situ measurement is carried out to analyze the hygrothermal performance of a HLC individual dwelling-house during 4 years. The analysis of the hygrothermal behavior of a wall is achieved by comparing measurements and numerical simulations results. In this study, two simulation tools are used and compared. The first tool is based on the well-known Wufi software. In the second simulation tool, hysteresis phenomenon and temperature-dependence of moisture content are considered in a heat and moisture transfer model. In-situ monitoring of walls temperatures shows the ability of HLC to almost completely dampen variations of external temperature with about 12 h time-shift. The evolution of indoor relative humidity confirms that HLC has an excellent moisture buffer performance. Comparisons between numerical and experimental results highlight the interest to consider the effect of temperature on sorption process in the simulation of the hygrothermal response of a HLC wall in real climatic conditions.

Research on the Hygroscopicity of a Composite Hygroscopic Material and its Influence on Indoor Thermal and Humidity Environment

Indoor air humidity is closely related to daily life and productivity. It is necessary to develop new materials which can maintain the indoor humidity environment steady within an acceptable range of 40–70%. In this paper a new composite hygroscopic material composed of wood fibre and sepiolite with expanded perlite (CHM-WSE) is used in a building envelope to evaluate its moisture buffering performance. A series of experiments assessing the microstructure, hygroscopicity, mechanical and thermodynamic properties of the new composite hygroscropic material have been executed. Furthermore, a numerical model for predicting the influence of humidity environment and energy consumption on composite hygroscopic mortar in different climatic regions has been established. The experiments show that the indoor moisture buffering performance in late spring is better than that in winter, when the practical moisture buffering performance can reach at 0.89 g/(m2%RH)@8/16h; and the non-uniformity coefficient of indoor relative humidity is about 0.006. The simulation results show that a room with CHM-WSE is more comfortable than a common mortar (CM) room, and it has better energy-saving performance in the hot summer and cold winter (HSCW) region in China. The experiments and simulations show that the developed hygroscopic material could be feasible for application in buildings.

Wood waste as an alternative thermal insulation for buildings

Current insulation materials in the construction market, which are predominantly inorganic materials, have a high performance in relation to heat transfer, i.e. high R-values, but the environmental impacts in their production processes are significant. The use of bio-based natural fibre materials such as cork, cotton, wood fibre, hemp, etc. with their lower embodied energy, moisture buffering capacity and, consequently, improved Indoor Environmental Quality have received increasing focus in both research and application, particularly amongst environmentally-conscious clients and designers.In this study a natural fibre material in the form of wood waste is examined experimentally to assess its suitability for use as a thermal insulation material, without the addition of any binder, within a timber frame wall construction. The wood waste is from primary production sources using untreated material. According to our experimental results, the thermal conductivity values of wood waste with different densities, ranged from 0.048 to 0.055 W/mK. These values are slightly higher than commonly used inorganic based insulation materials, although comparable to other natural insulation materials in the market, but have the economic advantage of being a low-cost by-product. The values relating to the material hygric performance including the water vapour diffusion resistance factor, water vapour permeability, and water absorption coefficient were also determined and presented, which will help facilitate future hygrothermal modelling.

Measurement of the dynamic moisture buffering potential of fabrics

In non-stationary wear conditions, characterized by intermittent pulses of moderate or heavy sweating, a garment with a good moisture buffering action can improve comfort. This is consistent with the common consumer belief that clothing manufactured from hygroscopic natural fibers (e.g., wool or cotton) provides better breathability. The current work describes a new approach for measuring dynamic moisture buffering potential using the sweating guarded hotplate instrument in a novel mode of operation. A fabric test sample is placed on the hotplate following the normal procedure for dry mode testing but with the relative humidity of the surrounding environment set to a low value (45%). After equilibration, the relative humidity is rapidly increased to a high value (85%). In the case of hygroscopic samples, a transient reduction in the heat required to maintain the hotplate at its fixed temperature is observed. It is demonstrated that the area of this transient peak is a measure of the water vapor absorbed during this transition, that is, the moisture buffering potential of the test specimen. A key to this new approach is that the heat of sorption per gram of water vapor absorbed is approximately the same for a wide range of natural and synthetic fibers commonly used in clothing. Using matched knitted fabrics manufactured from wool, cotton or polyester, the technique detected the heat released from light weight fabrics and the performance of the different fiber types is clearly distinguished.

A microstructural insight into the hygro-mechanical behaviour of a stabilised hypercompacted earth

The use of raw earth as construction material can save embodied and operational energy because of low processing costs and passive regulation of indoor ambient conditions. Raw earth must however be mechanically and/or chemically stabilised to enhance stiffness, strength and water durability. In this work, stiffness and strength are enhanced by compacting raw earth to very high pressures up to 100 MPa while water durability is improved by using alkaline solutions and silicon based admixtures. The effect of these stabilisation methods on hygro-mechanical behaviour is explored and interpreted in terms of the microstructural features of the material. Stiffness and strength are defined at different humidity levels by unconfined compression tests while the moisture buffering capacity is measured by humidification/desiccation cycles as prescribed by the norm ISO 24353 (Hygrothermal performance of building materials and products determination of moisture adsorption/desorption properties in response to humidity variation. International Organization for Standardization, Geneva, 2008). As for the microstructural characterisation, different tests (i.e. X-ray diffractometry, Infrared Spectroscopy, Mercury Intrusion Porosimetry, Nitrogen Adsorption) are performed to analyse the effect of stabilisation on material fabric and mineralogy. Results indicate that the use of alkaline activators and silicon based admixtures significantly improves water durability while preserving good mechanical and moisture buffering properties. Similarly, the compaction to very high pressures results in high levels of stiffness and strength, which are comparable to those of standard masonry bricks. This macroscopic behaviour is then linked to the microscopic observations to clarify the mechanisms through which stabilisation affects the properties of raw earth at different scales.

Effective moisture penetration depth model for residential buildings: Sensitivity analysis and guidance on model inputs

Moisture buffering of building materials has a significant impact on the building's indoor humidity, and building energy simulations need to model this buffering to accurately predict the humidity. Researchers requiring a simple moisture-buffering approach typically rely on the effective-capacitance model, which has been shown to be a poor predictor of actual indoor humidity. This paper describes an alternative two-layer effective moisture penetration depth (EMPD) model and its inputs. While this model has been used previously, there is a need to understand the sensitivity of this model to uncertain inputs. In this paper, we use the moisture-adsorbent materials exposed to the interior air: drywall, wood, and carpet. We use a global sensitivity analysis to determine which inputs are most influential and how the model's prediction capability degrades due to uncertainty in these inputs. We then compare the model's humidity prediction with measured data from five houses, which shows that this model, and a set of simple inputs, can give reasonable prediction of the indoor humidity.

Cyclic Behavior of Confined Cement‐Stabilized Rammed Earth Walls

Rammed earth is widely utilized in both developed and developing countries due to its low embodied energy and good natural moisture buffering of indoor environments. However, its application in seismic active regions was limited owing to its intrinsically low resistance to dynamic actions. This paper presents the test results of four cement‐stabilized rammed earth walls with confining tie‐column elements under cyclic loading, aiming at assessing the cyclic behavior of proposed rammed earth walls with confining tie‐column elements. The test results revealed that the proposed confining tie‐column elements could significantly improve the cyclic behavior of cement‐stabilized rammed earth wall, exhibiting good strength and ductility.

Determination of optimal plaster thickness for moisture buffering of indoor air

The relative humidity of indoor air influences the health and wellbeing of building occupants and the integrity of the building fabric. One potential solution for regulating relative humidity is provided by the plaster used for finishing internal spaces if it has the ability to passively buffer moisture through adsorption and desorption of vapour. During the adsorption and desorption, the water vapour will only penetrate to a certain depth of the plaster. Therefore, it is important to know the minimum thickness of plaster required for the maximum buffering effect. Uniquely, this paper presents a method for determining the optimal thickness from experimental measurements on specimens of varying thickness. In this paper it is demonstrated through a novel method, that there is a thickness of material beyond which there is no increase in moisture buffering capacity. Below the optimal thickness moisture sorption increases linearly as a product of the density and specific moisture capacity. Significantly, existing numerical methods were found to overestimate the performance when compared to empirical measurements. The expected impact of this work is the increased knowledge of surrounding material performance and use, that will ultimately improve the indoor environment quality of buildings and occupant health.

Synthesis and characteristics of composite phase change humidity control materials

A new kind of phase change humidity control material (PCHCM) was prepared by using PCM microcapsules and different hygroscopic porous materials. The PCHCM composite can regulate the indoor hygrothermal environment by absorbing or releasing both heat and moisture. The PCM microcapsules were synthesized with methyl triethoxysilane by the sol–gel method. The vesuvianite, sepiolite and zeolite were used as hygroscopic materials. The scanning electron microscopy (SEM) was used to measure the morphology profiles of the microcapsules and PCHCM. The differential scanning calorimetry (DSC) and the thermal gravimetric analysis (TGA) were used to determine the thermal properties and thermal stability. Both the moisture transfer coefficient and moisture buffer value (MBV) of different PCHCMs were measured by the improved cup method. The DSC results showed that the SiO2 shell can reduce the super-cooling degree of PCM. The super-cooling degrees of microcapsules and PCHCM are lower than that of the pure PCM. The onset temperature of thermal degradation of the microcapsules and PCHCMs is higher than that of pure PCM. Both the moisture transfer coefficient and MBV of PCHCMs are higher than that of the pure hygroscopic materials. The results indicated the PCHCMs have better thermal properties and moisture buffer ability.

Elaboration and Characterization Of Eco-Materials Made From Recycled Or Bio-Based Raw Materials

This work test the feasibility and characterize the thermohygric properties of composite materials, realized with eco-friendly raw materials and designed to make suspended ceilings or interior partition walls. Several raw materials are considered: recycled paper (granules or cellulose wadding) and wood fibers. Aggregates or fibers are bonded with organic or mineral binder. One of the binder considered is starch, due to its availability in Ivory Coast (cassava flour). The calcium sulfate hemihydrate is also used for comparison.The density of the produced composites ranges from 400 to 1200 kg/m3 depending on formulation. The thermal conductivity increases proportionally with the density and ranges from 0.09 to 0.5 W/(m.K). The characterization of hygric behavior is based on the measurement of moisture buffer value (MBV) [1]. The hydric performances of the composites made of mineral binder goes from moderate (MBV around 1 g/(m².%RH)) to excellent (MBV > 2 g/(m².%RH)). The moisture buffer value of the paper granules -starch composite is also excellent (MBV > 2 g/(m².%RH))

Improving the Impact of Commercial Paint on Indoor Air Quality by Using Highly Porous Fillers

In the current paper, the effect on Indoor Air Quality (IAQ) of two commercial acrylic-based paints were compared: one (Paint A) for indoor applications, the other (Paint B) for indoor/outdoor applications. Both were applied on an inert and on a real mortar substrate. The possibility of Paint B to passively improve IAQ was also investigated when adding highly porous adsorbent fillers, both as addition or as total replacement of a conventional siliceous one. The obtained results show that all paints have high capacity to inhibit biological growth. Paint A is more breathable and it has a higher moisture buffering capacity. Paint B negatively modifies the beneficial properties of the mortar substrate for IAQ. However, the use of unconventional fillers, especially as addition to the formulation, allows the recovery of the same properties of the substrate or even the enhancement of about 20% of the ability to adsorb volatile organic compounds (VOCs) under the current test conditions.

Hygrothermal properties of clayey plasters with olive fibers

This research deals with how to use agricultural waste materials in constructions considering that the development of innovative materials has to respond to both environmental and energy issues. The leaves and the small branches derived from the pruning of olive trees were incorporated, after drying, into a clay-sand mixture to obtain a bio-based plaster. Earthen samples, containing different percentages of olive fibers, were prepared and tested to investigate their hygrothermal behaviour. Thermal conductivity and the effects of several parameters on thermal performance were analyzed. The evaluation of the hygric behaviour was based on the measurement of the water vapour diffusion resistance factor and of the isothermal sorption curves. Results showed that the addition of olive fibers in the earth matrix enhances the insulating and hygric performances. The ability of the material to exchange moisture was studied by calculating the ideal Moisture Buffering Value (MBVideal). Results showed that the effects of moisture adsorption/desorption improved with the increase of the fibers content.

Mechanical and hygrothermal characterisation of cork concrete composite: experimental and modelling study

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.