Raw Earth Material Research Articles

Assessment of hygrothermal performance of raw earth envelope at overall building scale

Environmental challenges in the building sector have made raw earth a significant ecological alternative. The development of sustainable materials and a clear understanding of their behaviour are essential for sustainable construction. This work aims to respond to this societal issue.This investigation uses a HAM-BES cosimulation methodology that integrates dynamic thermal simulation code (TRNSYS) with a hygrothermal transfer model developed by Luikov and solved by Comsol Multiphysics. The study aims to investigate the energy needs of different building envelopes in several climates where there is raw-earth architecture. A comparison between a cob monolayer envelope and a polystyrene insulated polystyrene insulated brick multilayer envelope has been carried out. This study shows that the raw earth monolayer wall has a higher energy need for oceanic and tropical climate with, respectively, 14 and 19%. A decrease in demand has been found for the desert climate. Moreover, it was shown that the coupling of heat and mass transfers results in a notable reduction in energy demand that can reach 11.5% annually and up to 23% quarterly for tropical climate. These findings highlight the efficiency of raw earth materials and stress the importance of thoroughly understanding and incorporating heat and mass transfer dynamics in the evaluation of sustainability for biobased and earth-based construction materials.

Thermal properties of a raw earth-flax fibers building material

The aim of this paper is to investigate the thermal behavior of composite building materials comprised of silt and flax fibers, considering various initial conditions. The experiments were conducted on flax fibers alone, examining factors such as moisture content variation, fibers arrangement, and density. Subsequently, the thermal properties of the earth-flax fiber composite were studied, taking into account the influence of water content and fibers mass content. The thermal properties of both flax fibers and raw earth-flax fibers composite specimens were determined using the experimental unsteady-state method. The results indicate that the thermal conductivity and heat capacity of flax fibers increase with density, temperature, and moisture content. Regardless of fibers density and arrangement of fibers, linear relationships have been established for both thermal conductivity and heat capacity as functions of temperature. Additionally, it was demonstrated that the heat capacity and the thermal conductivity increase with water content, regardless of the percentage of added fibers. Moreover, mixing randomly flax fibers with compacted raw earth material has improved the thermal properties of the composite. This improvement pertains to its insulating capacity, ability to store heat, and, subsequently, its contribution to the thermal comfort provided by such earth composite material when used as a building material.

Thermal Performance, Microstructure Analysis and Strength Characterisation of Agro-Waste Reinforced Soil Materials

The use of raw-earth materials reinforced by natural fibres, i.e., livestock waste in the form of greasy wool, represents an eco-friendly alternative for a variety of construction applications. This proposal is based on the analysis of unfired adobe blocks stabilised with wool fibres for use as both structural and non-structural building materials. The influence of fibre length on the thermophysical and mechanical properties of the tested material was investigated. The thermal conductivity coefficient (λ) of raw-earth samples was assessed by following three different test setting procedures (T = 20 °C, and HR at 30%, 50%, and 70%), with the aim to evaluate the effects of different fibre lengths in the raw-earth mix. Samples reinforced by fibres 20 mm in length exhibited the lowest thermal conductivity coefficient (λ = 0.719 W/mK) obtained by a test reproducing typical indoor conditions within the Mediterranean area, i.e., T = 20 °C, and HR 50%. The best mechanical performance was exhibited by samples reinforced by fibres 40 mm in length, with a flexural and compression strength of 0.88 MPa and 2.97 MPa, respectively. The microstructure of these biocomposites was also examined with a scanning electron microscope (SEM) and an energy dispersive X-ray (EDX) to qualitatively evaluate the variation of thermal and mechanical properties due to the different adhesion among the fibres and the soil. The experimental data show good efficiency and a significant improvement in the behaviour of these materials compared to the control samples. The evaluation of the results, with the length of the fibres being the only variable of the analysed samples, allowed for the identification of the mix suitable for the best mechanical and thermal performances, depending on the final use of the material.

Reuse of livestock waste for the reinforcement of rammed-earth materials: investigation on mechanical performances

Agricultural wastes as additive within raw earth materials could both improve mechanical and physical properties of new sustainable construction materials and enhance waste management in a circular economy perspective. This study intends to fill the lack of knowledge considering the mechanical effects of animal fibers on rammed earth materials. The effects of a livestock waste, i.e., sheep wool fiber (SWF), as reinforcing element in building components produced by using raw earth and lime-free mortars, have been evaluated. Linear shrinkage, flexural strength, and compressive strength were evaluated on samples incorporating SWF, with the aim of assessing the effects of this waste addition on the mechanical performances of a new bio-composite material. The samples were made by varying the content of wool (0.25 % or 0.50%weight) and the length of the fibers (from 10 mm to 40 mm). The best result of the flexural strength was 1.06 MPa, exhibited by samples made with the longest and highest percentage of fibers, 40 mm and 0.50%, respectively. The addition of SWF to adobe bricks changed their failure mode, from fragile to ductile, reduced dry density and shrinkage rate.

Water vapor permeability of flax fibers reinforced raw earth: Experimental and micro-macro modeling

The expected impact of this study is to propose a bio-sourced composite material coupling mechanical and hygrothermal performances. This paper deals with the prediction of hygric properties of compacted raw-earth material reinforced with the flax fibers. New experiments have been performed on fibers and earth composite specimens. Then two modeling approaches have been applied using mixing theory and asymptotic homogenization. It was showed, that besides adding flax fibers improves the mechanical behavior of raw earth as strength and shrinkage reduction, their impact on the hygric property as water vapor permeability was also proved. For longitudinal arrangement of flax fibers with different fibers contents, experimental and modeling results are in good agreement.

Research on Weibull Distribution Theory for Cubic Compressive Strength Test Method of Raw Earth Materials with Different Curing Methods and Time

Cube compressive strength of raw-soil based mater is an important index of mechanical property. Because the test results vary by different curing modes and trial curing time, compressive strength test on 160 cubic raw-soil test-pieces which were made by 4 curing modes (natural curing, indoor curing, indoor+ preservative film curing, curing in standard curing chamber) and 4 Curing period (4d, 14d, 21d, 28d) was designed.In this study,the failure mechanism, failure mode, force mechanism of test were analyzed.Using Weibull distribution theory, the influence of different environmental factors on material strength is discussed.The research revealed that the different curing methods and curing time had remarkable effect on failure mode of material, but the load displacement curves had not affected. The compressive strength with 21d and 28d ‘s indoor curing and standard curing method were same in the test.The strength of raw soil increases with time, and the curing temperature had a significant effect on the early strength of raw soil materials, but had little effect on the later strength. The humidity had a great influence on the later growth of material strength. Constant temperature and humidity could effectively ensure the full response of internal water loss hardening of raw soil-based materials, and the strength of specimens increases obviously.The recommended curing mode and standard curing time for standard test of raw-soil test-pieces were temperature of 25-30oC, humidity of 50%-55%, and 28day, respectively.

Mechanical Characterization And Water Resistance Of Raw Earth Materials Made According To Malagasy Traditional Technique

This study aims to contribute to a more responsible world, by stimulating the applications of natural building materials and the enhancement of the prestige of the Malagasy traditional building technique, more respectful of the environment. To this end, preliminary investigations were carried out to formulate the tested samples and to study the preparation processes of the earthen pastes. Three different lateritic soils were studied and stabilized with cow dung and rice straw. The results show that the soils used are rich in SiO 2 , Al 2 O 3 and Fe 2 O 3 . Introducing cow dung and rice straw with fermentation improves sample characteristics. Consequently, the sample density increases from 1728 to 1913 Kg/m 3 . It also increases the dry and wet compressive strengths of our samples. From the 2nd week of the paste maturation time, the dry compressive strength increases from 0.64 MPa to 1.2 MPa and at the 24th week, it is 9 times higher than that of the beginning of the tests (5.4 to 6.5 MPa). Regarding water resistance, the results show that from the 4th week of the maturation time, the samples withstand more than 24 hours of immersion in water and this resistance increases until the 24th week, becoming comparable to that of the Malagasy ancestral walls aged more than 100 years, which is equivalent to 7 days.

Rammed Earth with Straw Fibers and Earth Mortar: Mix Design and Mechanical Characteristics Determination

Raw earth is one of the oldest building materials, which is suitable for various uses: from the construction of load-bearing walls to use for plasters and finishes. The presence of straw fibers can give different behavior to this material. The present paper illustrates preliminary sensory and qualitative analyses, and subsequent laboratory tests that allow the characterization of the raw earth material with straw fibers for rammed earth constructions through mechanized compaction and the identification of a compatible earth mortar. The raw material considered in this study is mainly clayey; for this reason, a mix design usable with the pisé (or clay) technique has been developed. Cylindrical samples have been made through a press and subject to unconfined compression and indirect tensile tests. The results of the tests showed consistent tensile and compressive strength values in the context of earth materials. At the same time, a study for the realization of a mortar with the same base soil was carried out considering four mixtures, in order to investigate the best compromise between workability, shrinkage and compressive strengths. The purpose of the study was to investigate the mechanical characteristics of the local material through preliminary and laboratory tests, to classify it according to the Unified Soil Classification System (USCS) and to verify its suitability for a possible use in the construction field.

Research on application and thermal performance of raw earth material in building envelope

Mainstream green has recently swept the construction industry throughout the world. Building envelope and material are two important aspects of green building evaluation. As the growing development of new green building concept “human-orientation design”, raw earth, as a natural, locally sourced, minimally processed, and recyclable material that is very different from concrete, becomes one of the most attractive options. Most architects pay attention to the aesthetic design of the raw earth wall, while other researchers like civil engineers focus on the physical properties of raw earth material itself. Few studies discussed the effect of the raw earth wall in building a thermal environment. This paper firstly conducts a parametric study on the thermal performance of raw earth wall with the consideration of thermophysical properties of materials, application of thermal insulation layer in the wall, and design parameters, i.e. thickness, of each layer of the wall. A naturally ventilated public building in Shanghai is then simulated to discuss the feasibility and the most optimum strategy of raw earth wall applications as building envelope in the sub-tropical high-density cities. Based on comprehensive data analysis, four findings are identified: (1) Compared with common building materials like concrete, raw earth materials have significant advantages in two thermophysical parameters - thermal transmittance and thermal effusivity which directly influence the indoor air temperature; (2) Thickness and structure of both raw earth layer and insulation layer are two important design parameters to meet the requirements of the indoor thermal environment; (3) Raw earth wall performs better than the standardized “Green Wall” based on local green building standards; (4) In terms of thermal performance, “Raw Earth Wall with External Insulation” is more suitable in subtropics. However, “Raw Earth Wall with Sandwich Insulation” is more recommended if pursuing the beauty of raw earth materials, because the thermal performances of “Raw Earth Wall with Sandwich Insulation” and Raw Earth Wall with External Insulation” are almost the same in summer, and very close in winter.

A unified compaction curve for raw earth material based on both static and dynamic compaction tests

This paper investigates the compaction characteristics of raw earth via a double-faced static compaction and the traditional Proctor test (dynamic process). The corresponding compaction energies are estimated for each individual sample, while the matric suctions are measured by a simple method using filter papers. The obtained results allow to draw the following observations and conclusions. Firstly, similar to classic Proctor tests, a family of iso-energy curves (i.e. tests with identical compaction energy) are identified for the set of static compaction tests. With increasing compaction energy, the iso-energy curve shifts leftwards and upwards, leading to a reduction of optimum moisture content and an increase of maximum dry density. Secondly, a new term called the optimum saturation degree (Sr)opt is introduced, defined as the degree of saturation Sr where (ρd)max is obtained for a given value of compaction energy and for a particular compaction method. For a specific earth type, and a given compaction energy, our experimental results indicate this (Sr)opt value is constant and that, a unique compression curve linking the degree of compaction Dc = ρd/(ρd)max to Sr−(Sr)opt exists regardless of the compaction method (static compaction, dynamic Proctor etc.) and compaction energy. Thirdly, the matric suction of specimen subject to static compaction tests is slightly higher than that in dynamic Proctor tests at the same moisture content, whereas the dry density has hardly any correlation with the variation of matric suction. Finally, a new method of earth compaction control is proposed here. This new protocol is organized to compact the earth to a target dry density ρd, by taking advantage of practically achievable compaction energies and meeting the design requirement, while keeping the Sr = (Sr)opt condition.

Fabrication, microstructure, and properties of fired clay bricks using construction and demolition waste sludge as the main additive

Green routes to prepare or manufacture sustainable building materials have been attracting much attention over the years targeting sustainability issues. In this investigation, for the first time, sludge from the inert mineral part of the construction and demolition waste (RA-S) is used as a primary raw material in the fabrication of fired bricks for building purposes. Fired bricks fabricated with different dosages of RA-S and earth material (i.e., 0%, 30%, 50%, 70%, and 100% by weight) were prepared and evaluated in terms of their physical-chemical properties. The RA-S was characterized, and the results showed that it could be classified as a clayey material and richly graded silty sand according to the French Standards. XRD analysis revealed that the addition of the RA sludge into raw earth material provoked changes slightly in the fired bricks. The compressive strength (CS) results indicated that the CS of the fired bricks increased with the addition of the RA-S from 30% to 70%. The highest CS was attained at the firing temperature of 800 °C. The density of the fired brick slightly reduced with the RA-S addition. The thermal conductivity results suggest that RA-S has better insulation properties compared to earth material. The RA-S sludge can be used in combination with earth material to fabricate fired bricks, which can meet the requirements of many Standards all over the World.In the light of these results, it is possible to say that the RA-S generated from recycling inert mineral part of construction and demolition waste plant is an excellent raw material to prepare efficient fired bricks that can be successfully employed in the real construction sector. Also, the highlighted results suggest that brickwork factories have the opportunity to improve production quality while significantly reducing manufacturing time, energy consumption, resource depletion, and environmental impact.

Characterization of the microbiome associated with in situ earthen materials

BackgroundThe current increase in public awareness of environmental risks is giving rise to a growth of interest in the microbiological safety of buildings. In particular, microbial proliferation on construction materials can be responsible for the degradation of indoor air quality that can increase health-risk to occupants. Raw earth materials are still widely used throughout the world and, in some cases, are linked to heritage habitats, as in the southwest of France. Moreover, these building materials are currently the subject of renewed interest for ecological and economic reasons. However, the microbial status of earthen materials raises major concerns: could the microbiome associated with such natural materials cause disease in building occupants? Very few analyses have been performed on the microbial communities present on these supports. Characterizing the raw earth material microbiome is also important for a better evaluation and understanding of the susceptibility of such materials to microbial development. This study presents the distribution of in situ bacterial and fungal communities on different raw earth materials used in construction. Various buildings were sampled in France and the microbial communities present were characterized by amplicon high-throughput sequencing (bacterial 16S rRNA gene and fungal ITS1 region). Bacterial culture isolates were identified at the species level by MALDI-TOF mass spectrometry.ResultsThe major fungal and bacterial genera identified were mainly associated with conventional outdoor and indoor environmental communities, and no specific harmful bacterial species were detected on earthen materials. However, contrary to expectations, few human-associated genera were detected in dwellings. We found lower microbial alpha-diversity in earthen material than is usually found in soil, suggesting a loss of diversity during the use of these materials in buildings. Interestingly enough, the main features influencing microbial communities were building history and room use, rather than material composition.ConclusionsThese results constitute a first in-depth analysis of microbial communities present on earthen materials in situ and may be considered as a first referential to investigate microbial communities on such materials according to environmental conditions and their potential health impact. The bacterial and fungal flora detected were similar to those found in conventional habitats and are thought to be mainly impacted by specific events in the building’s life, such as water damage.

Ductility analysis of vegetal-fiber reinforced raw earth concrete by mixture design

Building construction technology by raw earth materials is already known and used since ancient times. The raw earth material is abundant, low cost, requires very low energy to manufacture and does not generate waste. Ductility is required for earth building materials in the areas of seismic risks where the earth buildings are particularly vulnerable to earthquakes. Hence, a raw earth treatment by binders and vegetal fibers is one of the techniques applied to improve its strength and ductility. This paper presents the use of mixture design as a tool to evaluate and analyze the plastic behavior of the raw earth material. The ductility is quantified through two ductility indices. The results indicate that an alternative ductility index based on the post-peak behavior of the material could be used to define a ductility criterion to meet specific requirements of the seismic regions.

Hygrothermal Properties of Raw Earth Materials: A Literature Review

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 diffusion 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 buffering effect 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. Different 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.

Numerical Constitutive Models of Low Tensile Strength Materials for the Description of Mechanical Behavior of Rammed Earth Masonry

The preservation and enhancement of traditional earthen masonry structures as well as the practice of new construction with raw earth material is nowadays matter of investigation. At this stage of research, experimental analysis needs to be supported by numerical analysis to corroborate and interpret results and, successively, to extend the analysis to more complex load conditions, tune design methods and define quick verification formulas for simple structures. For this reason, constitutive models provided by engineering simulation software for mechanical analysis, to describe low tensile strength materials, have been used to reproduce mechanical tests and have been compared. The arch was selected as the best case study to test the response of constitutive models suitable for a low tensile strength material and, in a successive stage of research, the efficiency and the modelling of reinforcement techniques.

Laboratory test to assess sensitivity of bio-based earth materials to fungal growth

The effect of molds present in buildings on the health of the occupants is a major issue hence, when a building material is developed, its sensitivity to microbial growth should be assessed. However, few studies have investigated fungal growth on bio-based building materials with the resources available in a laboratory specializing in materials. The objective of this paper is thus to propose a simple and efficient experimental method useful for construction materials laboratories, adapted from methods proposed in the literature. For this purpose, fungal growth was investigated under different environmental conditions on earth-based material with or without the addition of straw or hemp shiv. Samples were inoculated with a strain of Aspergillus brasiliensis and were incubated for 12 weeks at 76, 84 or 93% RH, and 30 °C or 20 °C. Reproducible results showed that earth-based materials were more sensitive to fungi when they were enriched in plant aggregates. Fungal development was observed on earth material containing plant aggregates after 4 weeks of exposure at 93% RH and 30 °C, whereas it was observed after 8 weeks on raw earth material under the same conditions. Additionally, the possibility of quantifying fungal development with increased sensitivity by using image analysis is proposed. Due to the growth of fungal species other than A. brasiliensis, a natural inoculation approach is recommended. One of the conclusions is that liquid water is more favorable to mold growth than relative humidity alone. The addition of liquid water is thus recommended to accelerate the test.

The Economics of Geomedical Resources

In Europe and around the globe, geomedical resources have contributed enormously to natoinal GDPs. Anual reciepts for bottled mineral water sometimes rises in excess of $10billion for many countries exporting same. Beside mineral waters, are peloids, medicinal rocks, clays, minerals and waters whose exploration, exploitation, processing, marketing, and applications have serious economic outcomes. This paper looks at the different economic outlooks associated with geomedical resources, as raw earth materials to finished, processed products for use in the cosmetic and health industry.

Linking rheological and geotechnical properties of kaolinite materials for earthen construction

Due to its low environmental impact, earth construction has received much consideration in recent years. However, its development is limited by construction time as the strength of the material results from a slow drying stage and not by chemical setting. This means that using conventional rammed earth construction, it is not possible to strike the formwork the day after casting. In order to find another construction technique, many researchers have studied the behaviour of freshly made earth material using different types of admixtures that change the material’s rheology. Conventional dispersants used in the ceramic industry (such as sodium hexametaphosphate) or superplasticizers used in concrete are used to modify the fresh raw earth material. Moreover, earth materials are often described using empirical geotechnical parameters such as Proctor water content or plasticity index that are not directly linked to the material intrinsic behaviour. This paper has two simultaneous goals: the first one is to describe the rheology of kaolinite paste with and without dispersants and the second one is to link the “engineering” geotechnical parameters to the material’s rheology.