Hygric Regulators Research Articles

Effect of Air Velocity and Initial Conditioning on the Moisture Buffer Value of Four Different Building Materials.

Porous materials are able to exchange moisture with the surrounding air. The more hygroscopic they are, the more they contribute to regulate ambient humidity. This ability is characterized by the moisture buffer value (MBV) which is measured under dynamic solicitations according to different protocols. The NORDTEST protocol is the most commonly-used. It gives recommendations regarding the air velocity and the ambient conditions for initial stabilization. The purpose of this article is to measure the MBV according to the NORDTEST protocol and to study the effect of air velocity and of initial conditioning on the MBV results for different materials. Two mineral and two bio-based materials are considered: gypsum (GY), cellular concrete (CC), thermo-hemp (TH) and fine-hemp (FH). Following the NORDTEST classification, GY is a moderate hygric regulator, CC is good, TH and FH are excellent. When the air velocity ranges from 0.1 to 2.6 m/s, the MBV of GY and CC materials remains constant, but the MBV of TH and FH materials is highly affected. The initial conditioning has no effect on the MBV, but has an effect on the water content of the material, whatever the material.

Effect of hemp content and clay stabilization on hygric and thermal properties of hemp-clay composites

The objective of this paper is to investigate the effect of clay stabilization and hemp content on hygric and thermal performances. This experimental study is based on the measurement of sorption isotherm, moisture buffer value and thermal properties. The effect of water content on thermal conductivity is also investigated. The results show that Hemp Clay Composites (HCC) and Hemp Stabilized Clay Composites (HSCC) are hygroscopic and moisture buffering materials. The correlations between hemp content and water content are identified for sorption curves. An innovative analysis of the contribution of hemp and binder to water sorption is performed. The moisture buffer values classify the designed composites as excellent hygric regulators according to the Nordtest classification. The thermal conductivity ranges from 0.089 to 0.120 W/(m.K) at dry state, making them suitable for distributed insulation. The thermal conductivity increases linearly with density, for the two binders investigated in this study. Besides, the thermal conductivity increases linearly with water content too. Finally, this study underlines that the designed composites show high hygrothermal qualities.

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.

Trilemma of historic buildings: Smart district heating systems, bioeconomy and energy efficiency

Today buildings become part of Smart Energy Systems. 4th generation district heating network requires buildings with low energy consumption. In Europe, historic buildings account for around 30% from total buildings stock with high energy consumption which has to be reduced. Many of them have heritage value and external insulation of walls is not possible. If internal insulation is applied, careful hygrothermal assessment has to be carried out to avoid critical moisture conditions in the wall leading to failure modes. Insulation material market is dominated by petrochemicals or non-renewable natural materials. Yet development of bio-based thermal insulation materials is increasing and some of them successfully entered the market. EU Bioeconomy Strategy enhances use of bioresources to increase their added value. The main goal of this research is to assess applicability of innovative bio-based pine needles insulation material that is produced based on bioeconomy principles as internal insulation material for historic massive walls. Results show that studied material is highly porous, has high moisture transfer, storage capacity, and is good hygric regulator. Lime treated material has no mold growth at relative humidity 85%. Even if insulation material is treated with lime, heat savings have to be sacrificed to reduce critical conditions for mold growth.

Development of a sustainable and innovant hygrothermal bio-composite featuring the enhanced mechanical properties

In this study, machine controlled high compaction force was used to produce an innovant, sustainable and energy efficient bio-composite based on magnesium phosphate cement (MPC) as binder and corn stalk as bio-aggregate. Characterization of corn stalk was investigated by water absorption, image processing, scanning electron microscopy (SEM), x-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR) analysis. Mechanical, hygrothermal, aging and microstructural properties of bio-composites were examined. Compressive strength of bio-composites compacted by the machine was considerably higher than the manually compacted bio-composites. Capillary absorption and water absorption of bio-composites were lowered due to high compaction force. Increase in the temperature slightly affected the thermal properties of bio-composites. All the bio-composites were rated from good to excellent hygric regulators based on their moisture buffer performance. Influence of high compaction on the thermal, hygric and moisture buffer properties of bio-composites was discernible. Development of molds was detected on the specimens subjected to higher relative humidity level. Finally, formulated energy-efficient and sustainable bio-composites were classified into structural and insulation grade concrete.

Characterization of beet-pulp fiber reinforced potato starch biopolymer composites for building applications

This work deals with the making of a new renewable green material for building insulation from sugar beet pulp and potato starch. The material is both lightweight and ecofriendly. The influence of starch/extruded sugar beet pulp mass ratio (S/EBP) is studied. Four mass ratios are considered, 10, 20, 30 and 40% (relative to the starch). Samples are characterized in terms of absolute and bulk density, sound absorption coefficient, compressive and flexural strength, as well as and hygrothermal properties (the moisture buffering value and thermal conductivity). The sound absorption coefficient shows that this material is a good sound absorber, especially in medium and high frequencies. The sound absorption capacity depends on the fiber content and the humidity content. The best values are between 0.6 and 0.8. The compressive strength increases linearly with the S/EBP weight ratio to reach 0.52 MPa and the compressive strain is 30%. The elasticity modulus and the Poisson’s ratios were also studied. The transversal and vertical strain were measured using ARAMIS optical system. The moisture buffering value was measured according to Nordtest Protocol. The recorded moisture buffering value was between 2.6 and 2.8 g/(%RH.m2) and shows that the sugar beet pulp-starch composite is an excellent hygric regulator. The thermal conductivity is to around 0.070 W/(m·K). The results obtained shows that increasing starch amount tends to decrease composite porosity but increases thermal conductivity and mechanical properties. Depending on the starch content, beet pulp composites have a good thermal and acoustical performance and can be used as building materials.

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.

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.

Hemp-Straw Composites: Thermal And Hygric Performances

The European ISOBIO project aims to develop new bio-based building insulating materials which contribute to reduce environmental impacts of buildings. The developed materials shall have low embodied energy and low carbon footprint and shall contribute to reduce energy needs of buildings and to ensure high hygrothermal comfort of users. This study investigates the valuation of agro resources as bio-based aggregates and as binding material to produce wholly bio-based composites. The developed composites are made of hemp shiv glued with wheat straw. After a feasibility study which investigates several ways to use wheat straw as a gluing material and several hemp to wheat straw ratio, three hemp-straw composites are selected. Specimens are produced to characterize thermal and hygric properties of developed composites. They show interesting thermal and hygric properties as they have low thermal conductivity (0.071 to 0.076 W/(m.K)) and they are excellent hygric regulators (MBV > 2 W/(m².%RH)).

Thermal insulation materials from renewable resources: thermal and hygric performances

The European ISOBIO project aims to develop new bio-based building insulating materials which contribute to reduce environmental impacts of buildings. The developed materials shall have low embodied energy and low carbon footprint and shall contribute to reduce energy needs of buildings ant to ensure high hygrothermal comfort of users. This study investigates the valuation of agro-resources as bio-based aggregates and as binding material to produce wholly bio-based composites. Two types of aggregates: hemp shiv and corn cob residues (obtained after alkali treatment on the corn cob), and five types of green binders are investigated. Specimens are produced to characterize thermal and hygric properties of developed composites and to identify the best mixture between aggregate and binder. They show interesting thermal and hygric properties. They have low thermal conductivity ranging from 0.067 to 0.148 W/(m.K) and depending on the mix (aggregate with binder). They are excellent hygric regulators (MBV >2 g/(m².%RH)). These results suggest that developed composites can be used as building materials but not for the same types of use. In fact, some composites would be more suitable for thermal insulating products and others would be better suited to indoor facing panels.

Hygric buffer and acoustic absorption of new building insulation materials based on date palm fibers

In this work, we focus on new insulation materials based on date palm fiber. The developed lightweight composites are eco-friendly building materials from a renewable source and are less polluting than synthetic materials having harmful impacts on the environment. For manufacturing the composites, we used two different binders which are: lime and corn starch. The parts of date palm that are used for producing fibers are trunk and petioles (rachis). The proposed biobased materials could provide both thermal insulation and acoustic absorption; they could also act as a moisture buffering material to regulate indoor relative humidity variations.The sound absorption coefficients recorded show that these materials are good sound absorber, especially in medium and high frequencies. The acoustic absorption depends on the type of binder and the fiber content. The best value observed is around 0.7 when testing samples containing 20% trunk fiber and 80% starch. From the measurements of the Moisture Buffer Value (MBV), the composite made from 50% of trunk fiber and lime has an average MBV of 3.73g/(m2%RH). For samples based on petioles fiber and lime, the greatest MBV measured is 2.58g/(m2%RH) for samples of 50% of fibers. Using starch as a binder, we recorded a moisture buffer value of 4.05 (g/m2%RH) with only 20% of trunk fibers. The results obviously show that the use of date palm fiber-based materials for noise reduction presents a smart choice and on the other hand all MBV measured classify these new materials as an excellent hygric regulator.

Development and hygric and thermal characterization of hemp-clay composite

This study investigates the use of clay as binder in hemp composite and compares hemp–clay composite to hemp–lime concrete. The clay is produced from washing mud from gravels production site. Two clay drying temperature are used. The thermal properties are measured with a hot wire method and the hygric characterization is based on the measurement of Moisture Buffer Value. Performances obtained on clay blocks, hemp–clay composite and hemp–lime composite are compared. The results show that the two clay drying temperatures do not impact on the thermal conductivity nor on the moisture buffer value of clay blocks. Hygric and thermal performances of hemp–clay and hemp–lime composites with the same density are close. These materials act as excellent hygric regulators. Performances measured separately on hemp and clay underline an interesting synergetic effect in the case of hemp–clay composite leading to a higher ability to the moisture buffering. Such material can be advantageously used in buildings to moderate indoor humidity variations.

Hygric and thermal properties of hemp-lime plasters

Hemp-lime mortars are generally used as indoor insulating plasters of building envelopes. They can be applied in thick coat to allow high enough hygrothermal performances to be reached in retrofit case. This study investigates hygric and thermal properties of two hemp-lime plasters. These plasters are made with the same lime-based binder and differ from their kind of hemp shiv. The two kinds of hemp shiv are defibered but one is smaller than the other. This experimental study is based on the measurement of sorption isotherm, water vapour permeability, moisture buffer value and thermal properties (conductivity and diffusivity). The effect of temperature on moisture buffer value and on thermal properties is also investigated. It is shown that hemp-lime plasters are hygroscopic and breathable materials. They are good hygric regulators according to the Nordtest classification and their moisture buffering ability is slightly impacted by temperature in the range from 11° to 23 °C. The hemp-lime plaster with the smallest hemp shiv is a better hygric regulator than the one with the biggest hemp shiv. Hemp-lime plasters show a quite low thermal conductivity, around 0.2 W/(m.K). The hemp-lime plaster with the smallest hemp shiv is slightly more conductive than the one with the biggest hemp shiv. The temperature does not impact thermal conductivity at dry state. At wet state, for a given relative humidity, when the temperature increases the thermal conductivity decreases simultaneously with water content. This study underlines that hemp-lime plasters show high hygrothermal qualities.

Comparison of the hygric behaviour of three hemp concretes

Hemp concrete is a bio-based building material the main qualities of which are its low environmental impact and its hygrothermal behaviour. Even for one kind of application (for example: wall), several compositions and manufacturing methods are encountered in the market. This study compares the hygroscopic behaviour of three hemp concretes used for building walls to identify whether composition and manufacturing have an impact on hygric properties. The investigations are based on the measurement of the sorption curve, of the water vapour permeability versus humidity and of the moisture buffer value. Moisture diffusivity is calculated from the sorption curve and from the water vapour permeability. The results underline the high transfer and storage capacities of these materials; they are classified as excellent (or nearly excellent) hygric regulators. A slight effect of porosity, connected with composition and manufacturing method, is observed.