Earthen materials, one of the oldest known building materials, are also one of the most sustainable materials with promising properties to meet the environmental and economic challenges currently ...facing the construction industry. For its use in buildings and structures, this material has been studied in almost all of its thermo-hygro-mechanical aspects. However, the fire behavior of such materials is not well known and poorly documented. For this reason, the present study focuses on the fire behavior of compressed earth bricks compacted with variable compaction pressure in order to evaluate the risk of thermal instabilities during fire exposure. Different bricks were made from a mixture of earth and water with compaction pressures of 5, 15, 30 and 50 MPa. The bricks were set to an equilibration period at 75% RH until they were stable. According to previous research, this chosen relative humidity level corresponds to an unfavorable configuration with regard to the risk of thermal instabilities of compressed earth bricks. Each material configuration was subjected to two fire tests of 30 min. The results obtained showed that the risk of instability increased as the level of compaction increased. Further residual nitrogen permeability tests were performed to analyze the results obtained. It was found that the microstructure of the material upon its compaction plays an important role in the build-up vapor pore pressure during heating. This pore pressure was certainly responsible for the thermal instabilities observed.
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EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, KILJ, KISLJ, MFDPS, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
Cement is a common candidate for soil treatment when stabilization is required. Its employment in compacted earth blocks requests curing the product as efficiently as possible to obtain satisfactory ...performances. In this context, many practitioners’ recommendations exist. However, no studies have stated clearly optimum curing method required to achieve best possible strength for cement stabilized compacted earth. In this study, an exploratory analysis was used to assess the influence of moist curing duration on strength development in cement stabilized compacted earth. For this investigation, two natural earths stabilized with different types of cement were considered. The main differences between the chosen cements are their clinker content and strength class. The applied moist curing method consists of conditioning samples in moist environment (99.8% ± 0.2%RH) at ambient temperature (21 °C). Curing duration was varied between 0 (no curing) and 21 days. The uniaxial compressive strength was used as a practical indicator to inspect strength development in dry and wet conditions. Results demonstrate that moist curing is profitable until 7 days regardless of the formulation. In addition, results show that efficiency of cement stabilization depends on earth characteristics rather than cement composition. To discuss moist curing in more detail, accelerated curing conditions performed at 60 °C in ambient and moist environment were analyzed. In conclusion, some recommendations on the optimization of cement usage in compacted earth were provided.
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EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, KILJ, KISLJ, MFDPS, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
Earthen building materials, with their hygroscopic properties conferred by clay minerals, interact with the indoor environment, regulating factors such as relative humidity. While their moisture ...buffering capacity is well documented, there is limited data on their potential for CO
2
buffering. Whilst previous research has investigated the CO
2
retention mechanism in dry air conditions, this study focuses on the effect of relative humidity (RH) and temperature on the CO
2
retention process. Experimental comparisons were carried out at 0%, 51% and 71% RH with a CO
2
concentration of 20,000 ppm at a temperature of 25
∘
C and 35
∘
C using a TG-DSC instrument. The results show that the presence of water reduces CO
2
retention and slows down the kinetics of mass uptake. However, CO
2
is still retained in the presence of water, indicating the availability of adsorption sites and potential CO
2
–water interactions. Furthermore, the study shows that the effect of temperature is less pronounced at 51% than at 0% RH, and higher CO
2
retention is observed at 71% than at 51% RH, indicating the possibility of CO
2
dissolution in water. This paper presents the first analysis of the complex interactions between CO
2
earth and water, elucidating their dependence on relative humidity and ambient temperature conditions.
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EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, KILJ, KISLJ, MFDPS, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
•Strong hysteresis is observed between total sorption and desorption curves.•No hysteresis is observed during moderate cycles of relative humidity.•Significant hygrothermal processes are underlined ...on hemp concrete wall.•Sorption-desorption curves should be determined form cycles of relative humidity.
Hemp concrete is a sustainable material with low embodied energy. However, its development as a building material requires a better evaluation of its moisture-thermal buffering abilities behavior, which are known to strongly depend on the amount of water contained in wall pores and its evolution. In this context, the aim of this paper is to study the experimental determination of sorption-desorption curves of hemp concretes following two methods and at two temperatures (23°C and 40°C). The former considers the total sorption-desorption loop, from the dried state to a relative humidity of 85%, while the second one is based on partial relative humidity cycles between 23% and 85%. At first, the difference between the curves obtained through these two methods were analysed. They were then implemented in a simple hygrothermal model to simulate dynamic hygroscopic and hygrothermal loadings. The comparison between the theoretical calculations and the experimental results eventually allows to scan which of these relations is more representative of the real dynamic behaviour of the tested hemp concretes.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
Due to the environmental impact of building materials, researches on sustainable materials, such as bio-based and earth materials, are now widespread. These materials offer numerous qualities such as ...their availability, recyclability and their ability to dampen the indoor relative humidity variations due to their hygroscopicity. As these materials can absorb large amount of humidity, numerical and experimental studies of their hygrothermal behaviour are crucial to assess their durability.
To validate a hygrothermal model, numerical and experimental data have to be confronted. Such confrontation must take into consideration the uncertainties related to the experimental protocol, but also to the model. Statistical tools such as uncertainty and global sensitivity analysis are essential for this task. The uncertainty analysis estimates the robustness of the model, while the global sensitivity analysis identifies the most influential input(s) responsible for this robustness. However, these methods are not commonly used because of the complexity of hygrothermal models, and therefore the prohibitive simulation cost.
This study presents a methodology for comparing the numerical and experimental data of a rammed earth wall subjected to varying temperature and relative humidity conditions. The main objectives are the investigation of the uncertainties impact, the estimation of the model robustness, and finally the identification of the input(s) responsible for the discrepancies between numerical and experimental data. To do so, a recent and low-cost global variance-based sensitivity method, named RBD-FAST, is applied. First, the uncertainty propagation through the model is calculated, then the sensitivity indices are estimated. They represent the part of the output variability related to each input variability. The output of interest is the vapour pressure in the middle of the wall to confront it to the experimental measurement. Good agreement is obtained between the experimental and numerical results. It is also highlighted that the sorption isotherm is the main factor influencing the vapour pressure in the material.
In this paper, the results of static and dynamic hygric tests on 114 unfired clay masonry samples are presented. Samples were prepared as Compressed Earth Blocks (CEB) or plasters. The variability of ...soils, the soil density and the preparation methods were investigated to determine their influence on the moisture buffering capacity, water vapour permeability and sorption isotherms. The Moisture buffering Value (MBV) was measured according to the Nordtest protocol and the results could therefore be compared to conventional materials. The results indicate unfired clay masonry has a much higher potential to regulate the indoor humidity than conventional construction materials previously reported in the literature. Because of the benefits of humidity buffering, using unfired clay masonry could reduce health risk for inhabitants, reduce mould growth, reduce energy consumption of air conditioning and ventilation systems and increase the durability of building materials. The presented results show that the soil selection (mineralogy and particle size distribution) is more important for humidity buffering than changes than can be made to a particular soil (density, preparation methods or stabilisation) and the information presented will therefore allow designers to maximise the buffering capacity of buildings.
•Hygric properties of over 100 samples of unfired clay masonry were measured.•Soil variability and its influence on moisture buffering performance.•Soil variability and its influence on sorption isotherms and water vapour permeability.•DVS equipment used to investigate the dynamic adsorption properties.•Comparison between static and dynamic properties.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
•There is no common agreement on how to assess soil suitability for earth building.•A large sampling campaign was achieved on rammed earth heritage buildings in France.•The samples were analysed ...through laboratory tests.•The tests included water content, dry density, sieving, hydrometer tests, MBV, PI.•Current classification systems relying only on granularity appeared inappropriate.•A classification system based on granularity and clay activity is recommended.
In the European Union, most of the wastes from the building sector are composed of earths. Earth construction may be an interesting outlet for the re-use of these wastes, while meeting the challenge of circular economy: in particular, it involves low-embodied energy processes and earth material can be re-used for building by end-of-life. Nonetheless, the identification of suitable earths for construction remains an issue. To overcome this problem, an option may be to analyse earth building heritage, which is at least one-century old in Europe: indeed, earth employed in these buildings can be regarded as “time-tested”, and thus suitable for construction. In this paper, more than 20 different earths collected in rammed earth heritage building in France are presented. The results are confronted both to literature and to several classifications employed in soil sciences. A classification system based on granularity and clay activity will be relevant to address the convenience of earth for building purposes.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
In the global will of reducing fossil energy consumption and greenhouse gas emission in the building sector, the use of bio-based insulating materials is gaining interest thanks to their profitable ...properties and their suitability for the renovation of ancient buildings made out of unconventional materials. However, such materials are still lacking of characterization, and more precisely of on-site evaluation, as no complete measurement protocol is available. The starting point to fill this gap would be to set-up a protocol for whole building instrumentation, and this paper is investigating questions arisen in that goal, and more precisely regarding the impact of sensor locations on the assessment of key parameters. For that purpose, instrumented polystyrene and hemp concrete wallets of dimensions 0.9 × 0.9 × 0.1 m3 with well-known thermal and hydric characteristics are tested within a double climatic chamber. The impact of temperature sensor locations and implementations are tested through indirect estimation of the thermal conductivities of the materials composing the wallets. The effect of the hygrothermal processes on the measurement of thermal performance is also investigated through the analysis of the wall global transmittance. These results finally allow to provide some recommendations concerning the on-site instrumentation of hemp concrete walls.
Unfired clay masonry has a high potential to regulate indoor humidity and therefore create healthier living environments. The measurement of such potential on various building materials has received ...increasing attention and has generated the Moisture Buffering Value (MBV) concept. This work experimentally explored various conditions affecting the measurement and calculation of the buffering potential. Measurements of MBV and steady state properties (water vapour permeability and sorption isotherms) were performed on 18 samples, Compressed Earth Blocks (CEB) and Stabilised Compressed Earth Blocks (SCEB). It is quantitatively shown how the variability of experimental conditions in the dynamic measurement can change the obtained MBV (MBVpractical). The calculated buffering potential (MBVideal) is equally affected by the variability of the steady state properties measurements. A good agreement between calculated and measured MBV was observed for most samples when reducing this variability which was shown by using a DVS (Dynamic Vapour System) system to obtain the sorption isotherms of the material.
•Capacity of compressed earth blocks to regulate indoor humidity.•Experimental measurements of moisture buffering values (MBV) are provided.•Conditions affecting these measurements are presented.•Steady state properties are measured and used to calculate theoretical MBVs.•On 3 out of 6 cases good agreement between experimental and theoretical values was found.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
•Pith composites’ hygrothermal performance is comparable to hemp composites’.•Hygrothermal properties are affected by the interaction between aggregate and binder.•MBV is more accurate when ...calculated from RH cycles rather than sorption isotherms.•A new device has been developed for measuring thermal conductivity of wall samples.
The use of bio-based concretes or renders is rapidly developing. These sustainable materials present many advantages such as their acoustical and hygrothermal properties. These bio-sourced composites are made of vegetable aggregates, associated with a hydraulic binder. One of the most common aggregates is hemp shiv, which is an agricultural waste. However, hemp shiv is not available in big quantities nor in all geographical areas, so it seems interesting to introduce other bio-sourced aggregates in order to increase the availability. Sunflower and maize pith are unexploited agricultural by-products which can have a great potential as insulation materials. To use these aggregates, it is essential to assess first their interactions with different binders. In the present paper, the impact of density and type of aggregate (either hemp shiv or pith) on several key physical parameters was evaluated. These parameters were the uniaxial compressive strength test, the thermal conductivity, the sorption isotherms and the water vapor permeability, as well as the moisture buffering value (MBV). The use of pith shows promising results in terms of thermal and hygroscopic performances, the results also indicate that specific precautions should be taken to preserve the porosity of the soft pith material to optimize the hygrothermal performances.
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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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