Moisture Buffering Properties 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.

Experimental investigation on hygrothermal behaviour of cement and lime plaster

Traditional buildings since many centuries have used lime as a binder and finishing material. However, in contemporary construction practices, lime mortar and lime plaster have been replaced by cement mortar and cement plaster. Lime is a sustainable and self-healing material whose strength increases with time. In addition to its pleasing appearance, lime has excellent moisture buffering properties. Buildings with lime mortar and lime plaster are also breathable due to moisture transfer across the envelope. The objective of this work is to compare the hygrothermal performance of lime and cement plaster. For this purpose, two identical test cells of 1 m3 volume were constructed with brick as masonry material. One of the test cells was built with cement mortar and cement plaster, while the other cell was made with lime mortar and lime plaster. Environmental variables such as indoor air temperature, indoor relative humidity, globe temperature, surface temperatures, surface moisture content were monitored for a period of 74 days. It was found that the lime test cell was cooler by 3–5 °C and the indoor conditions were comfortable for 40% more time. The moisture buffering capacity of lime also helped to moderate the indoor relative humidity. The above differences were observed when the test cells passively responded to the changing outdoor conditions without internal loads. Further investigation of real-sized spaces would be necessary to endorse the advantages of lime plaster found in this study.

Determination of specific heat capacity of bio-fibre earth mortars stabilised at different relative humidities using Differential Scanning Calorimetry

Understanding the relationship that earth-based mortars have with both water and temperature is imperative to optimise moisture buffering properties. Specific Heat Capacity (Cp) is a key factor to understand the benefits in terms of thermal mass and latent heat. This paper presents the results of bio-based earth mortars (with fibres consisting of two varieties of sheep wool: Wool 1 (W1), Wool 2(W2) and Saw Mill Residue (SMR)) stabilised at 53% and 75% Relative Humidity (RH). Differential Scanning Calorimetry (DSC) according to ISO 11357–4 was used to calculate Cp of the aforementioned mortars. The temperature range of this experiment was that of 0–50 °C with a particular focus on values at 20 °C as this best represented a suitable indoor temperature. From these experiments, the results demonstrate that when stabilised at different RH, the difference in Cp was bio-fibre dependant and had a range between 0.71– 1.01 kJ/kg.K at 53% RH and 0.85–1.14 kJ/kg.K at 75% RH. These differences could potentially be attributed to the materials ability to readily accept water molecules. This emphasised that incorporating bio-fibres to a plain mixture (PL) can increase the Cp by up to 60%; significantly improving the thermal inertia of the building material. By reducing this temperature differential, it will reduce the heating requirements of a building which as consequential carbon reduction and thermal comfort benefits. Overall, SMR has the largest Cp for 75% at 20 °C was 1.141 kJ/kg.K, therefore specifically, this fibre would be the most effective to implement within a building. It also demonstrates the differences of the samples adsorption and absorption of water in differing hygrothermal environments.

Hygrothermal performance of temperature-humidity controlling materials with different compositions

In this paper, gypsum, zeolite, expanded vermiculite, and shell powder were used as substrates respectively, and phase change microcapsules were mixed into different substrates at a certain mass ratio to prepare phase change microcapsule composites with different substrates. Through the moisture absorption and desorption performance experiments, water vapor permeability coefficient experiments, and isothermal equilibrium moisture content experiments, the moisture buffering properties of composite phase change materials with different substrates were compared. Differential scanning method, specific surface area and pore analysis, and scanning electron microscope were used to study their thermal performance, apparent morphology, and pore distribution characteristics. The moisture buffering performance index of zeolite-based phase change microcapsule composites is 1.5 times that of pure zeolite materials and 2 to 10 times that of other materials. The zeolite-based composites with good stability, large phase latent heat, and the best humidity controlling performance in all substrates have the phase transition temperature range (20 ~ 25℃) closed to the ideal room temperature, which are the most suitable for use as temperature-humidity controlling building materials.

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.

Determination of paper plaster hygrothermal performance: Influence of different types of paper on sorption and moisture buffering

The study focuses on the moisture buffering properties of paper plaster. Two questions are under consideration in this article. Firstly, how the paper used influences the properties (dry density, drying shrinkage) of paper plaster, and secondly, what the material sorption and moisture buffering properties of paper plaster are.Two different dry density sized groups of densities approx. 140–150 kg/m3 (glossy paper and egg cartons) and 240–250 kg/m3 (printer paper and newsprint). Shrinkage properties were 10–14% (in diameter) for printer paper, 3–4% for glossy paper and egg carton, and 5.6% for newsprint.The results of the tests carried out in a climate chamber show that paper plaster adsorbs water vapour well - more than clay plaster, which is often used as a good moisture buffering material. The maximum moisture content was 961 g/m2 and as a minimum of 726 g/m2. The moisture uptake rate was higher on the first day of RH change than on other days.Paper plaster is an outstanding water buffering material [2.11–2.99 g/(m2·%RH)] belonging to the moisture buffering class presented by Nordtest method as “excellent".The results demonstrate that the moisture buffering properties of paper plaster when different papers are used do not differ significantly. It means that all the paper materials used in the study can be used to make paper plaster. Therefore, sorting paper before making paper plaster is not necessary.

Comparison of moisture buffering properties of plasters in full scale simulations and laboratory testing

The regulation of indoor relative humidity is a key factor for the provision of occupant health and comfort. Passive humidity regulation is possible if porous materials, for example clay and gypsum plasters, are exposed to the indoor environment. Materials that are highly hygroscopic can help regulate relative humidity levels through their capacity to adsorb and release water vapour from and to the indoor air via a dynamic process referred to as moisture buffering. Laboratory test methods have been developed to measure this moisture buffering capacity, which are well-suited for comparative testing of relatively small material samples under controlled conditions. However, quantification of the impact of hygroscopic materials in real buildings requires additional evaluation, like field testing and the support of simulation models, which can successively be used for the development of new protocols capable of giving information about materials’ moisture buffering performances indoors.

Hygrothermal performance of paper plaster: influence of different types of paper and production methods on moisture buffering

Paper as a material needs a lot of input energy. Many measures have been suggested to recycle paper, but still a huge amount of it ends in landfills. Hereby, one possibility for recycling paper - making paper plaster and putting it into service in indoor environment - is introduced. The study focuses on the moisture buffering properties of paper plaster. Two questions are under consideration in this article. Firstly, how paper type and production method influence the properties (dry density, drying shrinkage) of paper plaster, and secondly, what the material moisture buffering properties of paper plaster are. The plasters for testing were made from four types of paper (printer paper, glossy paper, newsprint and book paper). The production methods used were rumpling, grinding with a shredder or special crusher (prepared for the study) and soaking the paper after that. The dry density of groups varied from approx. 240 kg/m3 to 400 kg/m3. The shrinkage properties were from 3% to 10% in diameter. To evaluate the moisture buffering ability of paper plaster, the methodology introduced in the Nordtest protocol was used. Paper plaster is an outstanding water vapour buffering material [MBV=2.23-3.91 g/(m2·%RH)] belonging to the moisture buffering class "excellent" defined by Rode [15]. From the production methods rumpling gave the best value while printer paper showed the best values from the chosen materials. The tests with glossy paper resulted in modest values. To conclude, all the paper materials and preparation methods introduced in this study can be used to make paper plaster

The response of clay plaster to temperature and RH sinusoidal variations

Hygroscopic finishing materials can be used to moderate indoor humidity levels; they have the capacity to adsorb and release moisture from and to the surrounding air, depending on the indoor relative humidity levels. To determine the moisture buffering properties of materials several protocols have been introduced. However, testing procedures are based on a time-response method, where humidity variations are under a square wave function and temperature remains constant. Therefore, the ability of these methods to simulate material behaviour under real conditions, where cyclical humidity variations are more gradual, and temperature is variable, has been called into question. The aim of this study is to perform a standard moisture buffering test, by substituting the step-variation method, with a sinusoidal humidity function at different temperatures. Clay has been used to perform the tests in a climatic chamber, where a small increase of relative humidity have been set, in order to obtain a quasi-sinusoidal curve. The relative humidity variation are limited by low humidity (33% RH) and high humidity (75% RH) and temperature variation between 18 °C and 28 °C. Materials tested present a lag in the response to the peak relative humidity to peak mass gain, which suggests an alternative way to consider the rate of sorption and the moisture storage function. The significance of the paper is to develop a laboratory test that can be more readily compared with the behaviour real buildings, which operate under more of a sine waveform

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...

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.

Layer-by-layer assembled hydrophobic coatings for cellulose nanofibril films and textiles, made of polylysine and natural wax particles

Herein we present a simple method to render cellulosic materials highly hydrophobic while retaining their breathability and moisture buffering properties, thus allowing for their use as functional textiles. The surfaces are coated via layer-by-layer deposition of two natural components, cationic poly-l-lysine and anionic carnauba wax particles. The combination of multiscale roughness, open film structure, and low surface energy of wax colloids, resulted in long-lasting superhydrophobicity on cotton surface already after two bilayers. Atomic force microscopy, interference microscopy, scanning electron microscopy and X-ray photoelectron spectroscopy were used to decouple structural effects from changes in surface energy. Furthermore, the effect of thermal annealing on the coating was evaluated. The potential of this simple and green approach to enhance the use of natural cellulosic materials is discussed.

Hygrothermal Assessment of a Prefabricated Timber-frame Construction Based in Hemp

In this paper, an assessment is made on a pre-fabricated timber framed hemp-based building envelope system. The hemp-lime mixture within the envelope is produced by mixing the hemp shiv with a lime formulated solution, which acts as a binder, and provides thermal insulating and moisture buffering capacity to the resulting construction.Hemp, by its natural origin, is a fixative of CO2 and can result in a negative carbon footprint helping to reduce the global impact of a building. In addition the hemp-lime layer absorbs and expels heat and humidity in relation to the environment and acts as a thermal storage by reducing the flow of energy through the wall. The presented system targets at the generation of an innovative building system focused on the expansion of the market for structural products, sustainable, ecological and low carbon footprint.As part of its development its thermal insulation and moisture buffering properties have been assessed, and case studies and outcomes of full scale experimental studies are presented.