Hygro-thermal coupling in earth building materials (original) (raw)
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Hygrothermal Behavior of Earth-Based Materials: Experimental and Numerical Analysis
MATEC Web of Conferences, 2020
Bio-based building materials such as earth bricks are attracting renewed interest throughout the world due to their thermal and environmental properties. In this work, a numerical study of the hygrothermal behavior of building walls consist of compressed earth bricks (CEB) and stabilized earth bricks (SEB) was performed. A two-dimensional Luikov model for evaluating the temperature and the moisture migration in porous building materials was proposed. The coupled heat and moisture transfer problem was modeled. The governing equations of a mathematical model were solved numerically with the finite difference method. Input parameters in the model and their dependency on stabilizers content were determined by laboratory experiments. In order to specify the effect of chemical stabilization on the heat and mass transfer within studied materials, average moisture content and temperature were presented as a function of time. Results show that the addition of chemical stabilizers enhances th...
Experimental Characterization of Raw Earth Properties for Modeling Their Hygrothermal Behavior
Buildings
Raw earth is one of the oldest building materials of mankind. Almost a third of the world’s population is living in an earth-based house. However, their use remains low compared to conventional materials such as concrete, steel, and wood. Although these geosourced materials are abundant, recyclable, and have a low environmental footprint, their use is very limited in the construction sector. This can be explained by the lack of data regarding their hygrothermal behavior. In this context, the present work aims to highlight the properties of cob construction material with straw addition. An experimental characterization of hygrothermal and microstructural properties has been carried out. Thermal conductivity, specific heat, sorption isotherms, moisture storage capacity, moisture buffer value (MBV), and water vapor permeability are obtained experimentally. Then, the collected data are used as input parameters of a numerical prediction model to numerically assess the thermal and hygric ...
Journal of Engineering Science and Technology, 2016
This work is focused on the behaviour of a block of cement mortar, subjected to variable external temperature and humidity conditions. The porous building material sample is fitted inside a box, in which a heat exchanger is connected to a thermostatic bath. Three sequences of measurement are considered: (i) the response of the sample, when variations of temperature are applied; (ii) the air ranging between the exchanger and the non-isolated face of the mortar is continuously humidified, by injecting of sprayed water; (iii) the effect of simultaneously variation on temperature and humidity. A mathematical model representative of heat and mass transfer, in multiphasic medium (cement mortar), is developed in order to confront experimental and numerical results. Displacements of moisture and temperature fronts are observed and discussed. This study would enable us to understand the hygro-thermal behaviour of construction walls, to make an adequate design according to the climatic parame...
Hygrothermal Properties of Raw Earth Materials: A Literature Review
Sustainability, 11, 5342, 2019
Raw earth historic and contemporary architectures are renowned for their good environmental properties of recyclability and low embodied energy along the production process. Earth massive walls are universally known to be able to regulate indoor thermal and hygroscopic conditions containing energy consumptions, creating comfortable interior spaces with a low carbon footprint. Therefore, earth buildings are de facto green buildings. As a result of this, some earthen technologies have been rediscovered and implemented to be adapted to the contemporary building production sector. Nevertheless, the di↵usion of contemporary earthen architecture is decelerated by the lack of broadly accepted standards on its anti-seismic and thermal performance. Indeed, the former issue has been solved using high-tensile materials inside the walls or surface reinforcements on their sides to improve their flexural strength. The latter issue is related to the penalization of earth walls thermal behavior in current regulations, which tent to evaluate only the steady-state performance of building components, neglecting the benefit of heat storage and hygrothermal bu↵ering e↵ect provided by massive and porous envelopes as raw earth ones. In this paper, we show the results of a paper review concerning the hygrothermal performance of earthen materials for contemporary housing: great attention is given to the base materials which are used (inorganic soils, natural fibers, and mineral or recycled aggregates, chemical stabilizers), manufacturing procedures (when described), performed tests and final performances. Di↵erent earth techniques (adobe, cob, extruded bricks, rammed earth, compressed earth blocks, light earth) have been considered in order to highlight that earth material can act both as a conductive and insulating meterial depending on how it is implemented, adapting to several climate contests. The paper aims to summarize current progress in the improvement of thermal performance of raw earth traditional mixes, discuss the suitability of existing measurement protocols for hygroscopic and natural materials and provide guidance for further researches.
Hygro-thermo-mechanical properties of earthen materials for construction : a literature review
2012
Although earth has been used for construction for millennia and is still one of the most widely used building materials in the world, it is still difficult to find reliable values for the hygro-thermal and mechanical properties of earthen materials. Only little scientific research has been conducted on this material compared to the huge literature available concerning cementitious materials. Considering the literature available on earthen materials, a majority of studies deal with cement or lime stabilized earth for compressed earth blocks or rammed earth, and less has been done about natural unstabilized earth. The only existing comprehensive overview on the hydro-thermal and mechanical properties of earthen materials was authored by CRAterre-ENSAG and published 25 years ago. Now, for the second time in its thirty years of existence, CRAterre-ENSAG has undertaken the task of reactualizing this synthetic knowledge by writing a comprehensive review of the existing literature on the s...
1 Hygro-Thermo-Mechanical Properties of Earthen Materials for Construction: A Literature Review
2015
Although earth has been used for construction for millennia and is still one of the most widely used building materials in the world, it is still difficult to find reliable values for the hygro-thermal and mechanical properties of earthen materials. Only little scientific research has been conducted on this material compared to the huge literature available concerning cementitious materials. Considering the literature available on earthen materials, a majority of studies deal with cement or lime stabilized earth for compressed earth blocks or rammed earth, and less has been done about natural unstabilized earth. The only existing comprehensive overview on the hydro-thermal and mechanical properties of earthen materials was authored by CRAterre-ENSAG and published 25 years ago. Now, for the second time in its thirty years of existence, CRAterre-ENSAG has undertaken the task of re-actualizing this synthetic knowledge by writing a comprehensive review of the existing literature on the ...
Hygrothermal properties of light-earth building materials
Journal of Building Engineering
This experimental study provides complete datasets of hygrothermal properties of numerous hemp-clay with density ranging from 200 to 350 kg.m-3 for building thermal insulation. In addition, attention is also paid on protocols and methods, on the measurements repeatability and on the influence of conditioning temperature and relative humidity: mean uncertainties do not exceed 10 % for all measurements, while initial conditioning influences at most the results, particularly for the sorption isotherm. Heat and moisture storage properties depend obviously of the constituent (hemp or clay). Furthermore, they can be estimated with a good accuracy with a mixing law. Thermal conductivity of the composites ranges between 0.06 and 0.12 W.m-1 .K-1 and clearly depends on the density. Water vapor diffusion resistance factor ranges between 2.24 and 4.14, while capillary absorption coefficient ranges between 0.027 and 0.135 kg.m-2 .s-0.5 .
Simultaneous heat and moisture transfer in soils combined with building simulation
Energy and Buildings, 2006
In order to precisely predict ground heat transfer, room air temperature and humidity, a combined model has been developed and conceived to calculate both the coupled heat and moisture transfer in soil and floor and the psychrometrics condition of indoor air. The present methodology for the soil is based on the theory of Philip and De Vries, using variable thermophysical properties for different materials. The governing equations were discretized using the finite-volume method and a three-dimensional model for describing the physical phenomena of heat and mass transfer in unsaturated moist porous soils and floor. Additionally, a lumped transient approach for a building room and a finite-volume multi-layer model for the building envelope have been developed to integrate with the soil model. Results are presented in terms of temperature, humidity and heat flux at the interface between room air and the floor, showing the importance of the approach presented and the model robustness for long-term simulations with a high time step. #
The hygrothermal transfer is very important for the design of a building envelope for thermal comfort and economic and energy analysis of the building envelope. The applications of various materials in building envelope have been studied extensively. The study presents several models for the hygrothermal transfer for various building walls. Several energy and mass conservation equations with different boundary conditions and input considerations were presented in this paper for concrete, bricks and wooden walls. The effect of hysteresis was ignored in developing most model equations, while few considered flow pattern of fluid through the wall surfaces. Due to the flexibility of Luikov models, it formed the basis for modelling the coupled heat and mass transfer for porous material independent of hygroscopic nature with different boundary conditions defined according to the geometry and orientations. The influence of type of wall, orientation, thickness, the density of the material an...