Carbon Fiber Reinforced Polymers (CFRPs) have been increasingly employed for structural strengthening, and are attached to structures using bonding adhesives. The aim of this work is to characterize ...defects in the bond between CFRP and concrete (after they are located by pulse infrared thermography), and assign the defects a “numerical value” (ranging from 0 for a complete air–gap to 1 for a fully glued bond). Quantitative characterization is performed by measuring the thermal impedance, and then identifying the thermophysical parameters of the system through fitting the measured impedance to a theoretical model. An inversion procedure is carried out to estimate the unknown parameters, without prior knowledge of sample properties. In particular, it is possible to estimate more accurately both the amount of glue within a defect and the thermal contact resistance.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
The objective of this study is to demonstrate and to study the sustainability and the qualities of the earthen construction in real conditions. A demonstrative building was designed and built with ...unfired clay bricks, were industrially produced by the factory “Briqueteries du Nord” (BdN). This industrial plant is located in the north of France. This project aims to create conditions for the development of earthen construction techniques in the north of France. Moreover, it aims to prove the benefits of this material on the sanitary quality of the building.
This article is composed of three parts. Firstly, the identification of raw materials was performed in order to study the mains properties of these building materials. The second part of this work presented an experimental study conducted to investigate the dynamic thermal performance of unfired clay bricks.
To complete the tests already carried out in laboratory, an experimental investigation was carried out in situ on a demonstrative building. The hygrothermal performance of building is monitored for two consecutive years. The first analysis of the obtained data proved clearly that the earthen wall reduces the fluctuations of the outside temperature.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
The reliable estimation of buildings energy needs for cooling and heating is essential for any eventual thermal improvement of the envelope or the HVAC equipment. This paper presents an interesting ...method to evaluate the thermal performance of a massive wall by using the frequency-domain regression (FDR) method to calculate CTF coefficients by means of the Fourier transform. The method is based on the EN ISO 13786 (2007) procedure by using the Taylor expansion for the elements of the heat matrix. Numerical results were validated through an experimental heating box with stochastic boundary conditions on one side of the wall representing real weather conditions and constant temperature profile on the other side representing the inside ambiance in real cases. Finally, a frequency analysis was performed in order to assess the validity and accuracy of the method used. The results show that development to the second order is sufficient to predict the thermal behavior of the studied massive wall in the range of frequencies encountered in the building applications (one hour time step). This method is useful for thermal transfer analysis in real weather conditions where the outside temperature is stochastic; it also allows the evaluation of the thermal performance of a wall through a frequency analysis.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Western Europe area is one of the world regions where traditionally flax is grown. Whether in France or Belgium, flax is mainly used for the production of fabrics. When separating the different ...components of the plant, small woody elements called shives which represented about 50% of the production, are recovered. This work aims to study the behavior of flax shives used as insulation material in an attic of a French Flanders traditional house. Main scientific issues related to the study of heat and mass transfer is to determine the evolution of the thermal characteristics of the material and its durability. First, we propose a laboratory analysis of the hygrothermal behavior of shives by conventional thermal methods for characterizing thermal conductivity and volumetric heat (heat flux method), sorption curve is also determined. Then we focus on an experimental site which is an independent house where the old insulation of the attic in glass wool was replaced by flax shives. The hygrothermal behavior of this new insulation was monitored with humidity and temperature sensors for ten months. The thermal performances determined for a raw form of the shives in the laboratory are encouraging and hygrometric results show advantageous behavior whatever the season.
AbstractNatural stone is a traditional building material used worldwide for millennia. Its mechanical properties are rather well known, but only a small quantity of data is available regarding its ...hygrothermal characteristics. However, these characteristics are essential for the design of energy efficient buildings. Stones are in fact associated with insulation materials, which strongly modify the hygrothermal behavior of building walls, thereby impacting their durability and thermal comfort. This study focused on the hygrothermal characterization of a dozen samples of limestone, offering an adequate representation of their use across France. Thermal conductivity and heat capacity, sorption and desorption isotherms, water vapor permeability, and moisture buffer value (MBV) all were determined and analyzed. These data can be used to model heat and mass transfers in building walls. Limestone features extensive physical properties that can vary from one place to another within the same quarry. A statistical classification of the mechanical properties of thousands of French limestones was carried out. This classification allows estimating the hygrothermal properties previously determined for other stones.
AbstractHollow concrete blocks can be thermally improved either by modifying their cavities shapes or by adding insulation materials into these cavities. It is also possible to improve the thermal ...conductivity of solid concrete matrix by incorporating some materials to its composition like recycled solid wastes for example. This paper offers a solid and comprehensive study for thermally improved hollow blocks through a case study from the Lebanese context and provides a scientific basis for improving the thermal performance of these blocks. The effect of adding expanded polystyrene (EPS) beads to the concrete solid mixture was investigated in this study through numerical and experimental approaches. The experimental and numerical results were in good agreement and the potential thermal improvement by adding EPS beads to concrete mixture was examined on both numerical and experimental levels. The numerical results for the three-dimensional (3D) model allow the visualization of the heat flux and temperature distribution in the block as well as the air velocity and convective heat exchanges inside the cavities of the block. The results showed that the block thermal resistance can almost double by adding 18 g of polystyrene beads to the concrete mixture.
The use of bio-based insulation materials is widely spreading in buildings. Due to their organic load, they can be an important source of Volatile Organic Compounds (VOCs). This study is among the ...first that evaluates the spatial and seasonal in-field VOC surface emissions from bio-based and conventional building structures as a whole, in a French public building insulated with wood wool. In addition to surface emissions, measurements of VOC concentrations in indoor air were taken. Results showed that a spatial difference (up to 5 times) in VOC emissions was observed due to the inhomogeneity of the surface. Moreover, the cardinal orientation of building structures with the same constitution induced a difference (up to a factor 30) in emission rates due to the exposure to different hygrothermal conditions. The variation in temperature and relative humidity between seasons led to higher summer VOC emissions and indoor air concentrations. In addition, indoor VOC concentrations were shown to be higher at night compared to daytime due to the decreased ventilation rate. Furthermore, an interesting approach was developed in this study to have a primary overview of the impact of surface emissions on indoor VOC levels. Results confirmed that the three bio-based walls have no significant specific VOC emissions at high rates compared to the floor and the ceiling. Bio-based insulations showed no impact on microbial indoor air concentrations during the two seasons. Moreover, no detected VOCs could be attributed to microbial development as they were also emitted from building materials.
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•Spatial, temporal, and seasonal variations affect in-field measured VOC emissions.•VOC emissions rates from bio-based and conventional structures are comparable.•No specific VOCs are exclusively emitted from bio-based surfaces.•Emissions from building structures contribute moderately to VOC indoor air levels.•No direct link between VOCs and microbial development could be evidenced.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
The objective of this work is to improve the knowledge on the thermophysical characterization of opaque walls by determining the thermophysical properties of an experimental massive brick wall ...identical to old buildings walls in the North of Europe.
This method allows the determination of equivalent dynamic thermal properties of existing building walls λ and ρCp by simple measurement records of the inner (Twi) and outer (Two) wall temperatures as well as heat flux at the inner (or outer) face of the wall Fi.
The approach developed here consists in carrying out a parametric identification of the thermophysical properties of the wall in question (namely the thermal conductivity λ and the heat capacity ρCp), by comparing and minimizing the difference between the results resulting from the experimental tests and those resulting from the numerical model.
The optimization of the identified parameters is based on the Levenberg-Marquardt algorithm via the Comsol tool. The validation of the algorithm was carried out as well as its use in different ambient conditions (harmonic and random temperature profiles).
The investigated method shows satisfactory results for both λ (0.877, 0.880, and 0.935 W/(m.K)) and ρCp (1,012,400, 944,710, and 1,057,100 J/(m3.K)). The inner heat exchange coefficient hi was also successfully determined for the three tests with similar values (6.13, 6.53, and 6.03 W/m2.K). The results were also confirmed by comparing measured and numerical outer heat fluxes for the optimized values. The second part of this article is devoted to the study of the sensitivity of the results with respect to various parameters: the optimization algorithm, the total simulation time, the simulation time step, and the meshing element size.
•A parametric identification of wall thermo physical properties (λ and ρCp) was carried out.•The investigated method shows satisfactory results for both λ and ρCp.•The inner heat exchange coefficient hi was also successfully determined for the three tests.•The results were also confirmed by comparing measured and numerical outer heat fluxes for the optimized values.•A sensitivity analysis with respect to various simulation parameters was carried out.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
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