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PTDC/EPH-PAT/4684/2014 With the aim of developing economic and ecological bio-based composite panels to be used on indoor wall or ceiling coating systems, contributing to hygrothermal comfort and health, three different composite formulations were produced, differing on the content and pre-treatment of rice husk: 15% and 30%, only dried or previously boiled. Composite samples were tested for biological development and several physic-mechanical characteristics. Increasing on rice husk content decreases thermal conductivity due to bulk density decrease, decreasing ultrasound velocity, flexural strength, abrasion and fire resistance, but improving the moisture buffering capacity at least in 20%. For high rice husk-content composites, its pre-boiling decreases biological susceptibility although decreasing resistance to fire, most probably due to destruction of the cellulose wall, but significantly increases abrasion resistance and compressive strength, probably because of a better bond between the rice husk and the earthen matrix, quicker reaching a high water vapour adsorption limit. authorsversion published

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.

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 c...

International audience; 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 functionalized silica on the hemp shiv reduced water absorption from 400% (untreated shiv) to 250%. However, the moisture buffer value results showed that the coating films do not limit the access of moisture to adjacent pores in the hemp shiv, and the functionalized silica coating layer retains the moisture buffering ability of hemp shiv.

To investigate the influence of plastering on the moisture buffering behavior of hemp concrete, experiments are performed on two samples, one uncoated and one coated with less hygroscopic lime-based plasters. Global mass variations were monitored and results indicate in this case that coating reduces the MBV of hemp concrete. In addition, local temperatures and relative humidities are also measured at several depths within the samples in the view of validating a heat and mass transfer model. Results show that including the hysteretic behavior of each layer (hemp concrete and plasters) leads to a better agreement between numerical and experimental results, but also plays a significant role in the prediction of stored energy.

One of the acknowledged qualities of rammed earth (RE) is its moisture buffering capacity. Recently, stabilisation of RE has become a common practice to improve the mechanical resistance but very little is known about the effect that stabilisation has on hygroscopic properties. The present study aims to fill this gap by understanding the role that stabilisation plays in the buffering and sorption capacity of RE. The use of alternative stabilisers such as fly ash and calcium carbide residue and a comparison with traditional unstabilised RE (URE) have also been investigated. Moreover, the effect of weathering, simulated by cyclic wetting-drying, on hygroscopic performance has been analysed. Moisture Buffer Value (MBV) testing, moisture and nitrogen adsorption-desorption isotherms and mercury intrusion porosimetry were performed on stabilised samples to examine microstructural phenomena responsible for behavioural changes. URE was confirmed to be a good-to-excellent passive air conditioner according to the MBV scale but its performance seemed to be highly influenced by the soil particle size distribution and mineralogy. Based on the experimental outcomes of the mixtures investigated, stabilisation had a detrimental effect on the moisture buffer capacity of rammed earth, likely due to the inhibition of the physico-chemical interactivity between moisture and clays. Weathering had a variable effect on the buffering capacity, depending on the availability of unreacted particles in the matrix. (C) 2017 Elsevier Ltd. All rights reserved.

This paper presents an inverse modelling approach for parameter estimation of a model dedicated to the description of moisture mass transfer in porous hygroscopic building materials. The hygric behaviour of unfired clay-based masonry samples is specifically studied here and the Moisture Buffer Value (MBV) protocol is proposed as a data source from which it is possible to estimate several parameters at once. Those include materials properties and experimental parameters. For this purpose, the mass of two clay samples with different compositions is continuously monitored during several consecutive humidity cycles in isothermal conditions. Independently of these dynamic experimental tests, their moisture storage and transport parameters are measured with standard steady-state methods.A simple moisture transfer model developed in COMSOL Multiphysics is used to predict the moisture uptake/release behaviour during the MBV tests. The set of model parameters values that minimizes the difference between simulated and experimental results is then automatically estimated using an inverse modelling algorithm based on Bayesian techniques. For materials properties, the optimized parameters values are compared to values that were experimentally measured in steady state. And because a precise understanding of parameters is needed to assess the confidence in the inverse modelling results, a sensitivity analysis of the model is also provided.

International audience; The main objective of this chapter is to present the important link between a material’s physical properties and its durability. First, the influence of pore structure and the material composition is considered. The diffusion coefficient evolution of cementitious material is also studied taking into consideration the influence of the W/C ratio. The permeability and the effective thermal conductivity of such material are also evaluated in conjunction with the function of porosity, where different correlations are presented. Finally, the liquid vapor interaction inside porous building material is evaluated through the moisture buffer value parameter.

International audience; Effects of compaction stress on the physical, hygroscopic and mechanical properties of an earthen construction material

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)).

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))

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.

Indoor air quality, occupant’s comfort, durability of building parts, and energy consumption are highly related to the variations in indoor relative humidity. Since interior finishes and objects assist in dampening the peaks in relative humidity, the knowledge of the moisture buffer potential of room enclosures is necessary to include its effect in whole-building simulations. In this article, a method for the in situ determination of the moisture buffer potential of room enclosures is presented. During a period of some days, a humidifier is placed in a room and a moisture production scheme is implemented. Based on the measured RH-increase and decrease during loading and unloading steps, the ventilation rate and moisture buffer potential of the room are determined inversely by solving the moisture balance of the room using the effective capacitance and effective moisture penetration depth models. The methodology is validated by well controlled experiments in a large climatic chamber with known hygric inertia, and afterwards applied to real room enclosures. Main advantage of the proposed method is that a simple and fast experiment allows obtaining a comprehensive characterization of the hygric inertia of the whole building enclosure – including all interior finishes and multidimensional interior objects such as furniture, carpets, drapes, books, etc. ispartof: Journal of Building Physics vol:34 issue:3 pages:223-246 status: published

This study investigates the effect of temperature on thermal properties (conductivity and thermal diffusivity) and on Moisture Buffer Value (MBV) of two types of hemp-lime plasters. These plasters differ from their kind of hemp shiv: one is made of Chanvribat defibered hemp shiv (CHLP) and the other one is made of Terrachanvre defibered hemp shiv (THLP). The investigations are based on experimental measurements and are performed at 14°C, 17°C, 20°C and 23°C for thermal properties and at 11°C, 14°C, 17°C, 20°C and 23°C for MBV. The measurements of thermal properties are made at 50% Relative Humidity (RH). To limit the problems of water migration, the measurements are performed with transient state methods. Hot disk is used at all temperatures; it provides both thermal conductivity and diffusivity. Hot wire is used at 23°C, it provides thermal conductivity only. Over the considered temperature range (14- 23°C), the impact of temperature on thermal properties is very low while it is more sensitive on moisture buffer value. It is shown that the moisture buffer value decreases by about 54 % for Terrachanvre Hemp Lime Plaster (THLP) and by about 59 % for Chanvribat Hemp Lime Plaster (CHLP) when the temperature decreases from 23°C to 11°C., Academic Journal of Civil Engineering, Vol 33 No 2 (2015): Special Issue - ICBBM 2015

International audience; Hemp concrete is a bio-based building material made of hemp shiv and lime. This material is not used as load-bearing due to low mechanical properties. Hemp concrete is thus mainly used as filling material associated to a wooden structure. The indoor side of the wall can be coated or not. On hygrothermal point of view, hemp concrete shows low thermal conductivity, about 0.1 W/m/K, and can be used without added insulation layer in buildings. The hydric characterization of hemp concrete shows high transfer and storage capacities. Thus, this study deals with hydric characterization of hemp concrete under dynamic conditions. The experimental method is based on the NORDTEST protocol where specimens are exposed to daily cyclic variation of relative humidity. Generally, hygrothermal characterization is held at 23°C. This study deals with the impact of temperature on moisture buffer value of hemp concrete. Several temperatures are investigated from 11°C to 23°C. The results show that moisture buffer value increases with the temperature according an exponential law.

International audience; This study deals with dynamic characterization of hygric behaviour of precast hemp concrete. In a first time, the study is held on the material itself. Then, the study considers systems made of plastered precast hemp concrete for two kinds of plaster. The measurement of moisture buffer value (MBV) is held according to the NORDTEST protocol. Results show that precast hemp concrete has a good, nearly excellent, moisture buffer capacity (MBV=1.94 g/(m².%RH). So, it is an excellent hygric regulator that improves hygrothermal comfort and reduces energy needs. Once plastered, hemp concrete remains good hygric regulator (for closed plaster) and nearly excellent hygric regulator (with open plaster).

In their recent paper in Building Simulation (Trabelsi et al. (2012), Building Simulation, 5: 107–115), “Assessment of temperature gradient effects on moisture transfer through thermogradient coefficient”, Trabelsi et al. introduce their assertions on “the occurrence of significant thermal diffusion”. In this comment, the premises and outcomes of their analysis are challenged, based on my own recent paper on that same topic (Janssen (2011), “Thermal diffusion of water vapour in porous materials: Fact or fiction?” International Journal of Heat and Mass Transfer, 54: 1548–1562). Firstly Trabelsi et al.’s physical model and measurement methodology are critiqued, partially based on their own measured results. Reinterpretation of their data indicates that no consistent nor significant thermal diffusion can be found, confirming vapour pressure as sole significant transport potential for diffusion. This suggests that their physical model, built upon vapour density and temperature, is physically confusing and needlessly complicated. The model additionally requires a thermogradient coefficient, the measurement of which is complex and unreliable. A physical model for vapour diffusion based on vapour pressure, making use of the easy to measure vapour permeability, is thus pragmatically and fundamentally preferable. The comment finally ends by disputing Trabelsi et al.’s findings on the impact of thermal diffusion on moisture buffering: it is argued that they are practically and fundamentally faulty.

Dissertação para obtenção do Grau de Mestre em Engenharia Civil – Perfil de Construção As variações de humidade relativa (HR) afectam a salubridade e as características higrotérmicas dos ambientes interiores e, consequentemente, a saúde e o conforto dos ocupantes. Os materiais de construção utilizados nos paramentos interiores podem ter um contributo activo na regulação da HR dos ambientes interiores desde que possuam características higroscópicas, ou seja, que tenham a capacidade de adsorver e desadsorver vapor de água. Neste trabalho estudou-se o comportamento de várias argamassas que podem ser utilizadas em sistemas de reboco, desde argamassas de terra a argamassas de ligantes aéreos e hidráulicos, de forma a analisar a influência dos diferentes tipos de constituintes no seu comportamento higroscópico. Conhecendo-se as propriedades higroscópicas que muitos sais apresentam analisaram-se também argamassas contaminadas com sulfatos para apurar a influência que estes têm. Para além disso analisaram-se provetes de argamassas com uma camada de acabamento ou aplicadas sobre suporte de tijolo, de forma a fazer uma primeira abordagem acerca da influência dos acabamentos e suportes no comportamento higroscópico dos conjuntos, comparativamente apenas a uma análise independente de cada material. Durante a campanha experimental os provetes das diferentes argamassas foram sujeitos a ciclos de variação de HR; cada ciclo é composto por 8 horas a 75% HR seguidas de 16 horas a 33% HR. Estes ciclos pretendem simular as alterações verificadas dentro de uma divisão de uma habitação de um país do Norte da Europa, por exemplo um quarto que durante a noite está ocupado e com aquecimento e durante o dia está vazio. Este procedimento permite a classificação das argamassas segundo uma escala que traduz a sua capacidade de regulação da HR dos ambientes. Verifica-se que, de uma forma geral, as argamassas que utilizam terra como ligante apresentam resultados superiores, incluindo-se sempre nas classes de higroscopicidade elevada quanto à capacidade de regulação da HR interior. O traço das argamassas revelou-se também decisivo no moisture buffer value (MBV) das argamassas, sendo que as argamassas com menor quantidade de agregado obtiveram sistematicamente resultados mais elevados. Em adição foi também possível verificar que o tipo de cura, agregados e ligantes utilizados afecta o MBV obtido. Confirma-se que a análise de soluções de sistema, constituídas por argamassas associadas a suportes, conduz a resultados distintos daqueles que se obtêm quando se analisam os materiais individualmente, o que incentiva o estudo futuro de soluções deste tipo por serem as que mais se aproximam da realidade.

International audience; In a context of sustainable development, the choice of materials for building envelop shall take into account the environmental impact of the material, the energy consumption of building (for heating, cooling), the indoor environmental quality (safety and comfort), etc... The so-called "environmentally friendly" materials are more and more used. Hemp concrete is told to have a low impact on environment as it is made of hemp shiv (renewable raw) and of lime (lower embedded energy than cement). This material is not used as load-bearing due to low mechanical properties. Hemp concrete is thus mainly used as filling material associated to a wooden structure. On hygrothermal point of view, hemp concrete shows low thermal conductivity, about 0.1 W/m/K, and can be used without added insulation layer in buildings. The hydric characterization of hemp concrete shows high transfer and storage capacities. Numerical studies have shown that the transient hygrothermal behavior allows reducing energy demand of building while maintaining indoor relative humidity. However, these studies are based on experimental data of sorption curve and water vapour permeability; it was shown that the uncertainty on this kind of data hampers reliable simulations of hygroscopic buffering. Thus, this study deals with hydric characterization of hemp concrete under dynamic conditions looking for more realistic characterization. The experimental method is based on the NORDTEST protocol where specimens are exposed to daily cyclic variation of relative humidity. This measure leads to moisture buffer value. The study is held, firstly, on uncoated specimens of hemp concrete and then on coated ones. Six specimens are tested. Only one side is exposed to the ambient condition while the other sides are sealed with aluminum tape. Their thickness is chosen to be higher than the predicted penetration depth. The steady state is reached after two days and the measures are performed during five steady cycles. The mean value of moisture buffer value of uncoated hemp concrete is 2.14 g/(m².%RH). This induces that hemp concrete is an excellent hydric regulator according to the MBV classification given in the NORDTEST project. By comparison, the moisture buffer value given in the NORDTEST project are : 1.04 g/(m².%RH) for cellular concrete (good hydric regulator), 0.64 g/(m².%RH) for gypsum (moderate hydric regulator) and 0.38 g/(m².%RH) for concrete (limited hydric regulator). The coating reduces moisture buffer value of hemp concrete. For closed coating (sand-lime coating), the value is nearly half the previous one (1.08 g/(m².%RH)). For open coating (hemp-lime coating), the value is much less reduced (1.82 g/(m².%RH)). This capacity would allow energy saving while maintaining adequate air quality and hygrothermal comfort. Also, this experimental method is very relevant to characterize dynamic behavior of building material. The experimental data set can be used for benchmarking buffering models.

International audience; This study deals with dynamic characterization of hydric behaviour of sprayed hemp concrete. The measurement of moisture buffer value (MBV) is held according to the NORDTEST protocol (Rode, 2005). Specimen are exposed to daily cyclic variation of relative humidity: 8 h at 75%RH and 16 h at 33%RH the test is held under isothermal conditions (23 °C). The experimental set-up is validated by comparison of moisture buffer value measured on cellular concrete with values given in the NORDTEST project for the same kind of material. Results show that sprayed hemp concrete has an excellent moisture buffer capacity (MBV = 2.15 g/(m2 %RH)). So, it is an excellent hydric regulator that improves hygrothermal comfort and reduces energy needs. Moisture effusivity is then calculated from sorption and water vapour permeability value and from dynamic test of MBV. The results (respectively 5.8 * 10^-07 and 4.8 * 10^-07 kg/ (m2 Pa s1/2) show a slight discrepancy between values obtained from steady-state and from dynamic conditions. Finally, the penetration depth for daily cyclic variation is estimated about 5.8 cm for sprayed hemp concrete. Also, the experimental data set can be used for benchmarking buffering models.

Two test methods, one worked out in a Nordtest project and the other available as a Japanese Industrial Standard, both developed to characterize building materials with respect to moisture buffering performance, are analyzed in detail by a numerical study on four different materials. Both test methods are based on a similar kind of dynamic loading, but the specifications of each test protocol vary. Therefore, the sensitivity of the test protocols is investigated by varying different protocol parameters. Subsequently, the practical applicability of the obtained values is investigated by confronting the values obtained for the four materials with the dynamic response of a small room with each of the materials used in turns as finishing material. Finally, the results determined according to the dynamic test protocol are compared with values calculated from steady-state material data. ispartof: Journal of building physics vol:30 issue:2 pages:137-161 status: published

Experiments were carried out according to the Nordtest protocol to study the moisture buffer potential of hemp-lime walls with a range of different internal linings and surface treatments. It was observed that the moisture buffer value was ‘Excellent’ when the inner surface of hemp-lime was exposed. ‘Excellent’ moisture buffer values were also obtained for hemp-lime with lime plaster. All other assemblies demonstrated ‘Good’ moisture buffer value. Moisture buffer values of the assemblies, after application of paint on the upper surfaces, were also determined. It was observed that application of synthetic pigment based trade paint could reduce the moisture buffer performance of the assembly consisting of hemp-lime and lime-plaster from ‘Excellent’ to ‘Good’ while between 61 and 69% reduction of moisture buffer value was observed for the other assemblies. However, the reduced buffer values of the assemblies are still comparable with other moisture buffering building materials. It was further observed that moisture buffer performance was improved when clay based organic paint was used instead of trade paint.

Hemp concrete is a bio-based material generally made of lime-based binder and hemp shiv currently used for building envelop. This lightweight material shows a thermal conductivity about 100 mW/(m.K). On hygric point of view, hemp concrete is strongly hygroscopic, with high moisture transfer and storage capacities. These properties allow hemp concrete to moderate ambient relative humidity variations. It is an excellent hygric regulator with moisture buffer values globally higher than 2 g/(m².%RH).On mechanical point of view, hemp concrete is a non-load bearing material. It gains mechanical resistance over the first few weeks after manufacturing. These mechanical performances depend, among other factors, on the properties of components and on the mix proportioning. In order to improve the mechanical resistance of hemp concrete at early stage, this study investigates new formulations starting from reference formulation. The binder composition varies by increasing the substitution rate of lime-based binder for selected calcium sulfate-based binder. This binder leads to interesting hardening at early stage. The effect on mechanical performances at long term appears effective, without large influences on thermal and hygric properties (maximal variation about 20% and 15%). Effective proportioning tool is then available., Academic Journal of Civil Engineering, Vol 33 No 2 (2015): Special Issue - ICBBM 2015