The Influence of the Type of Lime on the Hygric Behaviour and Bio-Receptivity of Hemp Lime Composites Used for Rendering Applications in Sustainable New Construction and Repair Works

The benefits of using sustainable building materials are linked not only to the adoption of manufacturing processes that entail reduced pollution, CO2 emissions and energy consumption, but also to the onset of improved performance in the building. In particular, hemp-lime composite shows low shrinkage and high thermal and acoustic insulating properties. However, this material also shows a great ability to absorb water, an aspect that can turn out to be negative for the long-term durability of the building. For this reason, the hygric properties of hemp-based composites need to be studied to ensure the correct use of this material in construction and repair works. The water absorption, drying and transpirability of hemp composites made with aerial (in the form of dry powder and putty) and hydraulic limes were investigated here and related to the microbial growth induced by the water movements within the material. Results show that hemp-natural hydraulic lime mixes exhibit the highest transpirability and drying rate, the lowest water absorption by immersion and capillary uptake and the least intense microbial attack and chromatic change. A microscopical study of the hemp shives also related their great ability to absorb water to the near-irreversible swelling of their structure under dry-wet conditions.The research leading to these results has received funding from the European Union's Seventh Framework Programme (FP7/2007-2013) under grant agreement n° 326983 (NaturALiMe), and the Spanish project MAT-2012-34473 of the Ministerio de Ciencia y Competitividad. Author MB, owner of the CANNABRIC company, had some role in the design and preparation of mortar samples and in the preparation of this manuscript, but did not have any additional role in data collection and analysis

Degradation aspects of water formation and transport in Proton Exchange Membrane Fuel Cell: A review

This review paper summarises the key aspects of Proton Exchange Membrane Fuel Cell (PEMFC) degradation that are associated with water formation, retention, accumulation, and transport mechanisms within the cell. Issues related to loss of active surface area of the catalyst, ionomer dissolution, membrane swelling, ice formation, corrosion, and contamination are also addressed and discussed. The impact of each of these water mechanisms on cell performance and durability was found to be different and to vary according to the design of the cell and its operating conditions. For example, the presence of liquid water within Membrane Electrode Assembly (MEA), as a result of water accumulation, can be detrimental if the operating temperature of the cell drops to sub-freezing. The volume expansion of liquid water due to ice formation can damage the morphology of different parts of the cell and may shorten its life-time. This can be more serious, for example, during the water transport mechanism where migration of Pt particles from the catalyst may take place after detachment from the carbon support. Furthermore, the effect of transport mechanism could be augmented if humid reactant gases containing impurities poison the membrane, leading to the same outcome as water retention or accumulation. Overall, the impact of water mechanisms can be classified as aging or catastrophic. Aging has a long-term impact over the duration of the PEMFC life-time whereas in the catastrophic mechanism the impact is immediate. The conversion of cell residual water into ice at sub-freezing temperatures by the water retention/ accumulation mechanism and the access of poisoning contaminants through the water transport mechanism are considered to fall into the catastrophic category. The effect of water mechanisms on PEMFC degradation can be reduced or even eliminated by (a) using advanced materials for improving the electrical, chemical and mechanical stability of the cell components against deterioration, and (b) implementing effective strategies for water management in the cell

Caractérisation thermo-hydrique d'agro-matériaux à base de chanvre

Actes du colloques SFT, Perpignan, 24 - 27 mai 2011

Caractérisation thermo-hydrique d'agro-matériaux à base de chanvre

Actes du colloques SFT, Perpignan, 24 - 27 mai 2011

Temperature dependence of sorption isotherm of hygroscopic building materials. Part 1: Experimental evidence and modeling

International audienceThe knowledge of sorption isotherm is of high importance when evaluating the performance and the durability of building envelope. Whereas the influence of hysteresis was often investigated, less attention has been paid to the influence of temperature. In the present paper, a specific experimental protocol is defined to investigate the influence of temperature on relative humidity variations within three building materials (Autoclaved Aerated Concrete, wood fiber insulation and hemp concrete). The measurements are analyzed in terms of a hygrometric coefficient K [%r.h./degrees C], defined as the maximal relative humidity amplitude against the maximal temperature amplitude, and are compared to three modeling approaches: temperature dependent sorption model, Kelvin equation and Clausius-Clapeyrbn equation. Discussions show that the third approach is relevant and that it can be used to evaluate effortless the isosteric heat of sorption and the temperature dependence of the sorption isotherm. (C)2017 Elsevier B.V. All rights reserved

Prise en compte des transferts de masse dans la détermination de la conductivité thermique de matériaux bio-sourcés

International audienc

Prise en compte des transferts de masse dans la détermination de la conductivité thermique de matériaux bio-sourcés

International audienc