International audienc

Summary As an essential preliminary to understand the hydration of wood-cement composites, the effects of some additives on the delayed setting due to wood of an Ordinary Portland Cement have been investigated by isothermal calorimetry. With the addition of calcium chloride and activated charcoal, an increase of 50% of the total enthalpy is observed in wood-cement composites hydration, because calcium chloride mostly influences aluminate phases and activated charcoal silicate phases.

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Building and furniture materials are known to be major sources of volatile organic compounds (VOCs) indoors. During the construction process, an introduced material can have a more or less long-term impact on the indoor air quality according to the building characteristics. In this study, field measurements were carried out at six construction stages in three energy-efficient timber-frame houses. Data analysis focused on the ten most abundant compounds found among an initial list of fifteen target VOCs, namely formaldehyde, acetaldehyde, hexanal, toluene, m/p-xylenes, ethylbenzene, styrene, α-pinene, 3-carene and d-limonene. The chemical compositions and concentration variation patterns were recorded. The results showed a high pollution count, with m/p-xylenes and ethylbenzene concentrations ranging from 1900 to 5100 μg m occurring at the time of the structural work (representing more than 88% of the sum of the target VOCs). Emission tests done on a large number of materials used in the construction revealed that this pollution is due to the emissions from the polyurethane adhesive mastic used as a sealing material. The emission kinetics of polyurethane adhesive mastic was assessed alone and also within a material assembly reconstituting a room wall. The results showed that the superposition of materials led to a slowing down of the VOC emission process from polyurethane adhesive mastic, which explains the concentration decays recorded in houses during the construction process. At the final construction stage, the concentration levels were low for all compounds (the sums of the target VOCs were between 18 and 32 μg m), with the aldehydes (formaldehyde, acetaldehyde and hexanal) now becoming the major fraction in the chemical composition in the last stages of construction (representing 50-70% of the sum of the target VOCs). This is in agreement with the fact that the sources of aldehydes are the most numerous among the materials and have rather slow emission kinetics.

International audienceThis paper deals with a finite element implementation concerning the shape memory behavior. Shape memory behavior is usually driven by temperature changes. This model allows the simulation of problems integrating complex mechanical loading effects under random temperature variations. According to the relationship between stress and strain, the shape fixation during cooling phases and the memory effect during heating phase are modelised through a hereditary behavior needing incremental formulation developments. The step by step process introduces an additional fixed stress. Simulations request, for complex geometries including boundary conditions, a finite element approach. Thermodynamic developments are presented in order to define energetic balance and dissipations. In this paper, we propose to generalize this dependence of elastic modulus variations. A formulation for random mechanical loading and temperature variations is proposed. An experimental validation is proposed about shape memory alloy polymer DP5

For in situ timber structures applications, heat and mass transfer are strongly dependent on temperature. This work focuses on a parametrical modeling to evaluate and quantify temperature effect at each stage. The model is classically based on a coupling between Fourier's Law, which establishes the temporal and spatial distribution of temperature, and Fick's Law dealing specifically with the water field distribution. Several hypotheses are proposed and discussed in this work as regards thermal coupling. In particular, it is shown how to integrate temperature into a permeability correction. Also proposed herein is an interaction between temperature and the sorption isotherm. The model incorporates partial adsorption and desorption isotherms. Implementation in a finite element software allows highlighting the various couplings, in comparison with more standard calculus approaches.

Basing on the material emission data obtained in a test chamber, chemical mass balance (CMB) was used to assess the source apportionment of volatile organic compound (VOC) concentrations in three newly built timber frame houses. CMB has been proven to be able to discriminate the source contributions for two contrasted environmental conditions (with and without ventilation). The shutdown of the ventilation system caused an increase in the VOC concentrations due to the increased contribution of indoor surface materials like the door material and furniture explaining together over 65% of total VOCs. While the increase in formaldehyde concentration is mainly due to furniture (contribution of 70%), the increase in α-pinene concentration is almost exclusively attributable to the emission of door material (up to 84%). The apportionment of VOC source contributions appears as highly dependent on the position of source materials in the building (surface materials or internal materials) and the ventilation conditions explaining that the concentrations of compounds after the shutdown of ventilation system do not increase in equivalent proportion. Knowledge of indoor sources and its contributions in real conditions may help in the selection of materials and in the improvement of construction operations to reduce the indoor air pollution.