Earthen Materials Research Articles

Influence of inherent anisotropy on the mechanical properties of normally consolidated clays with a wide range of plasticity indices

Inherent (fabric) anisotropy is one of the most important properties of earthen materials which has a significant influence on their strength and stiffness characteristics. In this study, a comprehensive series of unconfined and constrained compression tests is performed on normally consolidated (NC) clay samples with different plasticity indices to examine the effect of inherent anisotropy on their mechanical characteristics. Accordingly, several cylindrical clay samples with different proportions of kaolinite and bentonite are reconstituted at a wide range of deposition angles and then subjected to both unconfined and constrained compressive loadings. According to the experimental results, for a clay sample with a particular plasticity index, the highest and lowest values of the unconfined compressive strength (UCS), the secant modulus (E50), and the constrained Young's modulus (Eoed) are observed to be associated with the deposition angles of 0o and 90o, respectively. The results also show that at a certain bedding plane angle, the sample containing 30% bentonite (PI = 110%) exhibits the highest UCS, E50, and Eoed values. Several practical empirical correlations are developed to estimate the strength and stiffness properties of NC clays using their plasticity indices and bedding plane directions. Scanning Electron Microscopy (SEM) analysis is also conducted to explore the microstructure of samples containing varying percentages of kaolinite and bentonite.

Geo-based fabrics: using earthen materials for wearables

ABSTRACT Over 50% of synthetic textiles in existence originate from polyester derived from petroleum oil. Synthetic textiles make up over 65% of global circulating textiles and the industry is known for being highly pollutant, resource wasteful, and responsible for nearly 10% of global carbon emissions annually. One prominent solution to the industry’s negative environmental impact is to develop alternative textiles for garment and architectural fabric applications. This paper presents a novel development of earth – and bio-based wearable textiles coined as BioMud Fabric which consists entirely of bio-based materials; 65% of which is clay-rich raw soil. More specifically, the material integrates raw soil with naturally occurring bio-based plastics to create a flexible, lightweight and biodegradable fabric. The research methodology includes a mix-design analysis, using electron microscopy, and a macro-scale structural characterisation using tearing tests. The final demonstrations showcase speculative design applications which serve to expand the possibilities of the material through fashion.

Recovery and Restructuring of Fine and Coarse Soil Fractions as Earthen Construction Materials

Excessive consumption of natural resources to meet the growing demands of building and infrastructure projects has put enormous stress on these resources. On the other hand, a significant quantity of soil is excavated for development activities across the globe and is usually treated as waste material. This study explores the potential of excavated soils in the Brittany region of France for its reuse as earthen construction materials. Characterization of soil recovered from building sites was carried out to classify the soils and observe their suitability for earthen construction materials. These characteristics include mainly Atterberg limits, granulometry, organic matter and optimum moisture content. Soil samples were separated into fine and coarse particles through wet sieving. The percentage of fines (particles smaller than 0.063 mm) in studied soil samples range from 28% to 65%. The methylene blue value (MBV) for Lorient, Bruz and Polama soils is 1, 1.2 and 1.2 g/100 g, and French classification (Guide de terrassements des remblais et des couches de forme; GTR) of soil samples is A1, B5 and A1, respectively. The washing of soils with lower fine content helps to recover excellent-quality sand and gravel, which are a useful and precious resource. However, residual fine particles are a waste material. In this study, three soil formulations were used for manufacturing earth blocks. These formulations include raw soil, fines and restructured soil. In restructured soil, a fine fraction of soil smaller than 0.063 mm was mixed with 15% recycled sand. Restructuring of soil fine particles helps to improve soil matrix composition and suitability for earth bricks. Compressed-earth blocks of 4 × 4 × 16 cm were manufactured at a laboratory scale for flexural strength testing by using optimum molding moisture content and compaction through Proctor normal energy. Compressive strength tests were performed on cubic blocks of size 4 × 4 × 4 cm. Mechanical testing of bricks showed that bricks with raw soil had higher resistance with a maximum of 3.4 MPa for Lorient soil. Removal of coarse particles from soil decreased the strength of bricks considerably. Restructuring of fines with recycled sand improves their granular skeleton and increases the compressive strength and durability of bricks.

Hierarchical organization and skilled workforces for constructing the Tartessic earthen building at Casas del Turuñuelo (Guareña, Spain)

This article presents the results of the geoarchaeological study of earthen building materials used in a Tartessic public building at Casas del Turuñuelo. The construction dates back to the fifth century BCE and is one of the monumental buildings of Tartessic culture, characterized by its complex architecture, prestige goods, and intentional destruction after a feast and animal sacrifice. We applied an integrated methodology combining macro and micro approaches to investigate earthen construction processes, such as techniques, labour organization, workers’ specialization, and environmental exploitation. The sample mainly consists of mudbricks, but we also include other forms of earthen materials such as mud plasters, mud mortars, and geological soils for comparison. In total, 64 samples from different building parts were studied through X-ray fluorescence, X-ray diffraction, thin-section petrography, and CHN analyses. The results reveal that the workforce involved in the construction process used different resources and presented different skill levels, but was centrally planned and organized. This study reflects on the communities’ knowledge of the environment, the logistic effort and technical skill employed in the building process, and the existence of strong political structures capable of managing the erection of the complex Tartessic buildings.

Three-Dimensional Printing with Earthen Materials: A Settlement-Scale Design Experience

This case study originates as a design experiment for a sustainable housing system built on-site. The context is Niamey, the capital of Niger. The study takes into account the environmental issues in the construction sector and aims to find a solution capable of meeting housing, environmental, and economic needs. In the field of earthen construction, the most important developments have been achieved in manufacturing methods. In particular, the use of an additive digital manufacturing system, such as large-scale 3D printing, allows the construction of complex shapes derived from structural and thermal studies, maintaining a high degree of automation in the construction process, reducing construction times and labor costs. This paper investigates the possibility of responding to housing and environmental needs with a settlement system made almost entirely of printed earth, maintaining the highest possible degree of automation. Starting from a study on the state of the art of 3D printing in architecture and printable earthen compounds, the design choices of similar cases are analyzed to understand the construction techniques, potentials, and limitations of the medium. Finally, a design proposal is developed based on the definition of a fully printable functional module, which, upon aggregation, determines the characteristics of the final settlement. This implies a radical change of approach compared to previous prototyping of 3D-printed earthen buildings, as the design of the single functional module is not an exercise that finds completion in itself, but is oriented to the scale of the settlement right from the definition of its basic geometric characteristics. In other words, the settlement is no longer the result of the serial aggregation of independent basic units, but arises spontaneously from the juxtaposition of functional modules designed to interact with each other and merge into a single residential complex. The settlement is, therefore, the large-scale replication of the alternation between full and empty spaces, that characterizes the single functional module and, even more importantly, the replication can take multiple forms. In fact, the full and empty spaces of the functional module are planned to allow multiple combinations of aggregation. This introduces a certain degree of customization into the growth dynamics of the settlement, a factor that is entirely new compared to previous proposals by repeatable modules. No less important are the environmental implications, as designing for the scale of the settlement allows the low carbon footprint typical of earth-based construction to be extended from the single building to the entire settlement.

Snapshot on 3D printing with alternative binders and materials: Earth, geopolymers, gypsum and low carbon concrete

The rapid development of 3D concrete printing now offers mechanical efficiency and freedom to push the limits of construction design. The digital manufacturing process holds potential for reducing carbon footprints through design optimization. Printable concrete, which is a mix of cement (based on ordinary Portland cement), aggregates, and admixtures, is attractive due to widespread and cost-effective constituents. However, many common formulations omit gravel, requiring higher cement paste volumes and inducing significant embodied carbon. Assessing the potential of low-carbon cements like Limestone Calcined Clay Cement (LC3), calcium aluminate cement (CAC), or magnesium-based cement for 3D printing is a current challenge that can address this issue. Tailoring these construction materials to printing applications and environmental needs now drives scientific exploration. This paper comprehensively reviews alternative materials and binders such as earthen materials, geopolymers, low carbon binders or gypsum-based materials, addressing fresh and hardened properties, developed digital processes, targeted applications, and discussing advantages and drawbacks of each alternative.

Profiling of Tayammum Clay Product in Malaysia by Spectroscopic-Chemometric Approach

Tayammum is a dry purifying method that uses earthen materials, mostly clay. The technique is applied when there is no access to water or in specific circumstances, such as when a person has susceptible skin on water. In tayammum, Islamic law describes clay as pure dust or soil used as a cleansing agent. Nevertheless, no scientific report examined the components of clay present in tayammum clay. Therefore, this study aimed to characterise and profile the mineral composition of tayammum clay, which is a commercially available product in Malaysia. Twelve commercial clay samples and one representative sample were analysed by ATR-FTIR spectroscopy in the range of 4000 to 600 cm-1. PCA exploratory analysis clearly demonstrated the differentiation of the tayammum clay product into seven groups according to its functional group. Following the FTIR analysis, the samples underwent examination using X-ray diffraction (XRD) and X-ray fluorescence (XRF) spectrometers further to identify the mineral and element composition of the clay, respectively. The XRD analysis indicated that there were possibly four types of mineral powder commonly distributed in the market for Tayammum purposes which are three types of clay: palygorskite, kaolinite, and phengite, and another one is zeolite-type: Na-heulandite. All four of them are common materials used for adsorbent and cleansing purposes.

Construction materials and building techniques – Comparing anthropogenic sediments of three Middle Bronze Age sites from Hungary

This paper compares various ‘earthen’ construction materials and building techniques from three Middle Bronze Age tell (multi-layered settlement) sites in Hungary: Százhalombatta-Földvár, Kakucs-Turján (Vatya material culture) and Borsodivánka-Marhajárás-Nagyhalom (Otomani-Füzesabony Cultural Circle (OFCC)). It employs microscopic analyses – archaeological soil micromorphology and phytolith analysis within thin sections – to examine floor, wall and fire installation materials at a high resolution. The term ‘earthen construction materials’ is used in archaeology extensively to refer to anything from soils to sediments that sometimes lack proper classification or terminology. Through a closer look at the types of materials used at the three analysed sites, we describe more clearly what comprises ‘earthen’ construction materials. Using this data, we then employ a chaîne opératoire approach to think through various stages in the sourcing and preparation of building materials. In analysing this, the paper makes visible the decisions by Bronze Age builders and discusses their possible reasons, which include environmental conditions and socially learned practices. Further, by comparing three contemporary sites within a micro-landscape, our analysis highlights that even small variations in the environment and therefore the available raw materials impact building materials and techniques, and that different groups of people can make different decisions even when facing similar environments.

Experimental investigation of Catalan vault structures based on earthen materials

The Catalan vaulting have succeeded in reducing reliance on support centers, resulting in lowered costs and expedited construction processes. This research advances the study of Catalan vaulting by exploring innovative, environmentally friendly earth-based materials. The study conducts a comprehensive comparative analysis of load-bearing behaviors across distinct vault elements: those fabricated from terracotta, raw-earth tiles, and shot-earth. Constructed and tested at a 4-meter span, full-scale vault specimens are subjected to varying distributed load configuration, followed by rupture testing employing a linear load at a quarter of the span. Experimental evidence, corroborated by FE results, indicates that both terracotta and raw earth tile vaults offer commendable performance, yet their failure loads are surpassed by vaults constructed using shot-earth. Therefore, shot-earth emerges as a sustainable alternative for constructing vault elements. Furthermore, the study demonstrates that incorporating reinforcement within shot-earth vaults increases their strength and ductility.

Water Dams: From Ancient to Present Times and into the Future

Since ancient times, dams have been built to store water, control rivers, and irrigate agricultural land to meet human needs. By the end of the 19th century, hydroelectric power stations arose and extended the purposes of dams. Today, dams can be seen as part of the renewable energy supply infrastructure. The word dam comes from French and is defined in dictionaries using words like strange, dike, and obstacle. In other words, a dam is a structure that stores water and directs it to the desired location, with a dam being built in front of river valleys. Dams built on rivers serve various purposes such as the supply of drinking water, agricultural irrigation, flood control, the supply of industrial water, power generation, recreation, the movement control of solids, and fisheries. Dams can also be built in a catchment area to capture and store the rainwater in arid and semi-arid areas. Dams can be built from concrete or natural materials such as earth and rock. There are various types of dams: embankment dams (earth-fill dams, rock-fill dams, and rock-fill dams with concrete faces) and rigid dams (gravity dams, rolled compacted concrete dams, arch dams, and buttress dams). A gravity dam is a straight wall of stone masonry or earthen material that can withstand the full force of the water pressure. In other words, the pressure of the water transfers the vertical compressive forces and horizontal shear forces to the foundations beneath the dam. The strength of a gravity dam ultimately depends on its weight and the strength of its foundations. Most dams built in ancient times were constructed as gravity dams. An arch dam, on the other hand, has a convex curved surface that faces the water. The forces generated by the water pressure are transferred to the sides of the structure by horizontal lines. The horizontal, normal, and shear forces resist the weight at the edges. When viewed in a horizontal section, an arch dam has a curved shape. This type of dam can also resist water pressure due to its particular shape that allows the transfer of the forces generated by the stored water to the rock foundations. This article takes a detailed look at hydraulic engineering in dams over the millennia. Lessons should be learned from the successful and unsuccessful applications and operations of dams. Water resource managers, policymakers, and stakeholders can use these lessons to achieve sustainable development goals in times of climate change and water crisis.

Surface characterization of consolidated earthen substrates using an innovative multi-analytical strategy

This study evaluates the combined use of innovative non-destructive methods and standard laboratory techniques for assessing the surface effects of various consolidation treatments (i.e., bacterial biomineralization, alkaline activation, colloidal dispersions containing nanolime or nanosilica, and ethyl silicate as a standard) on earthen building materials. It demonstrates that novel portable equipment (i.e., portable digital microscope, air permeameter, and mobile surface (contact angle) analyzer) and advanced strategies for the application and data interpretation of conventional analytical and testing methods (i.e., scanning electron and confocal microscopy, Leeb hardness testing, and visible light spectrophotometry) can yield complementary and extremely valuable quantitative results for the evaluation of consolidation treatments on such complex substrates. Our multi-analytical approach allows a detailed characterization of surface and near-surface features of treated earthen mock-ups. It is possible to disclose significant differences in the film-forming propensity and in-depth distributions of consolidants and their effect on key properties such as surface roughness and appearance, permeability, water behavior, and mechanical properties. Even though, the substrate's inhomogeneity and surface texture has proven to be especially challenging, this methodology offers a promising strategy for long-term in-situ monitoring of treatment performance and weathering behavior of built heritage materials.

Research Progress of Superhydrophobic Coatings in the Protection of Earthen Sites

As an important part of human cultural heritage, earthen sites are subject to damage caused by a variety of environmental factors, such as cracking, weathering, and flooding. Due to the low mechanical strength of earthen site materials, especially in humid environments, they are susceptible to hazards like moisture penetration, freeze–thaw cycles, and biological invasion. Superhydrophobic coatings show promising potential in the protection of earthen sites, with key properties that include waterproof performance, breathability, robustness, and transparency. By exploring various material systems and preparation methods, the current state of research on the protection of building materials with superhydrophobic materials has been demonstrated, highlighting advantages in the corrosion resistance, self-cleaning, frost prevention, anti-scaling, and other aspects. At the same time, it also points out the challenges faced in the practical application of earthen site protection and the prospects for future research. These include enhancing the bonding strength between the coating and soil particles, improving durability and breathability, and developing large-scale, low-cost, and efficient coating construction techniques.

A Critical Review on the Advancement of the Development of Low-Cost Membranes to Be Utilized in Microbial Fuel Cells

Microbial fuel cells provide a promising solution for both generating electricity and treating wastewater at the same time. This review evaluated the effectiveness of using readily available earthen membranes, such as clayware and ceramics, in MFC systems. By conducting a comprehensive search of the Scopus database from 2015 to 2024, the study analyzed the performance of various earthen membranes, particularly in terms of wastewater treatment and energy production. Ceramic membranes were found to be the most effective, exhibiting superior power density, COD removal, and current density, with values of 229.12 ± 18.5 mW/m2, 98.41%, and 1535.0 ± 29 mW/m2, respectively. The review emphasizes the use of affordable resources like red soil, bentonite clay, CHI/MMT nanocomposites, and Kalporgan soil, which have proven to be effective in MFC applications. Incorporating earthen materials into the membrane construction of MFCs makes them more cost-effective and accessible.

Microstructural Observations on the Durability of Stabilized Rammed Earth

This study provides a qualitative microstructural investigation of fly ash geopolymers' role in rammed earth's durability against water ingress and contact erosion. A series of SEM (scanning electron microscopy) images were captured on geopolymer-stabilized as well as unstabilized rammed earth samples. These samples were fabricated from predefined amounts of sand and fine materials together with fly ash geopolymers in the laboratory by static compaction to 25 MPa inside rigid molds. Two standardized durability tests were performed, namely, the dip test and the spray (also known as erosion) test. The results of these tests reflected excellent durability properties (practically zero erosion) of the stabilized material. The microscopic investigation provided an insight into the reason behind this improvement, where geopolymer networks inhabited the macro and micro pores and served as a cementing agent interconnecting the earthen materials’ grains. On the contrary, grains of the unstabilized material were weakly bonded by the clay component of the mixture, as observed with the SEM images; therefore, they were more susceptible to erosion by water.

Influence of bacterial cellulose stabilization on strength characteristics of construction earthen materials

Influence of bacterial cellulose stabilization on strength characteristics of construction earthen materials

Experimental assessment of yarns and coatings for mesh production to strengthen earthen elements

Earthen construction has gained attention during the last decade because of its sustainability. Nevertheless, increasing its strength properties is still a challenge that is faced herein by including vegetal meshes with different coatings as internal reinforcement. An experimental campaign oriented to characterise the bending response of little scale earth beams in simply supported configuration was carried out including three different mesh materials (jute, hemp and cotton) and three different coatings (arabic gum, colophony and white glue). The results as failure mode, maximum load/stress and absorbed energy are presented and discussed. Results indicated that it is feasible to strengthen earthen materials with vegetal meshes. Colophony was too stiff to be combined with the chosen vegetal meshes with the goal of strengthening deformable earth. In addition, greater yarn thickness and smaller yarn separation were associated to premature debonding failure. Using cotton meshes with arabic gum coating brought the more promising results. In this case, the strength was slightly increased by 6 % but the absorbed energy was increased by 25 times respect to the control case.

Durability of Japanese-earth cob walls subjected to accelerated rain simulation

Earthen materials are increasingly being recognized in architecture for their low embodied energy, recyclability, and hygrothermal properties. However, the common use of manufactured stabilizers, while enhancing weathering resistance, compromises these merits. Japan, known for its typhoons, has used unstabilized earth in construction for centuries, suggesting the viability of this construction material. While architecture around the world attests to its resilience, in-depth research into unstabilized earthen material is limited. This study examines unstabilized earth durability through 90-min accelerated rain simulation tests, totaling over 6500 mm of “rain” exposure on each of twelve test surfaces (eight representing rural Japanese cob-ball construction and four, monolithic cob walls). Surface changes were monitored by 3D scans performed at seven intervals. The test walls were built using two common materials in Japanese earthen wall craft, sourced from the areas of Kashiba and Fukakusa. It was clear from 3D-scan analysis that the base-layer material, Kashiba, is remarkably resistant to weathering. The four monolithic Kashiba test surfaces, constructed on four different foundation types, respectively eroded just 1 mm, 2.6 mm, 3.8 mm, and 3.9 mm. These results corroborate traditional building practices. Thus, our study also underscores the value of incorporating knowledge from vernacular earthen architecture professionals in expediting academic research. Additionally, our results suggest the potential of hose-showerhead tool use for research, and for on-site testing of earthen material erosion levels for material adequacy.

Sorption mechanisms of CO$$_{2}$$ in earthen materials under variable hygric states

Sorption mechanisms of CO$$_{2}$$ in earthen materials under variable hygric states

Advancing Earth-Based Construction: A Comprehensive Review of Stabilization and Reinforcement Techniques for Adobe and Compressed Earth Blocks

This comprehensive literature review investigates the impact of stabilization and reinforcement techniques on the mechanical, hygrothermal properties, and durability of adobe and compressed earth blocks (CEBs). Recent advancements in understanding these properties have spurred a burgeoning body of research, prompting a meticulous analysis of 70 journal articles and conference proceedings. The selection criteria focused on key parameters including construction method (block type), incorporation of natural fibers or powders, partial or complete cement replacement, pressing techniques, and block preparation methods (adobe or CEB). The findings unearth several significant trends. Foremost, there is a prevailing interest in utilizing waste materials, such as plant matter, construction and demolition waste, and mining by-products, to fortify or stabilize earth blocks. Additionally, the incorporation of natural fibers manifests in a discernible reduction in crack size attributable to shrinkage, accompanied by enhancements in durability, mechanical strength, and thermal resistance. Moreover, this review underscores the imperative of methodological coherence among researchers to facilitate scalable and transposable results. Challenges emerge from the variability in base soil granulometry and disparate research standards, necessitating concerted efforts to harness findings effectively. Furthermore, this review illuminates a gap in complete lifecycle analyses of earthen structures, underscoring the critical necessity for further research to address this shortfall. It emphasizes the urgent need for deeper exploration of properties and sustainability indicators, recognizing the inherent potential and enduring relevance of earthen materials in fostering sustainable development. This synthesis significantly contributes to the advancement of knowledge in the field and underscores the continued importance of earth-based construction methodologies in contemporary sustainable practices.

Upscaling earth formworks: 3D printing strategies for material optimised reinforced concrete structures

There is a growing need to understand how locally sourced earthen materials can be processed to build more efficiently and sustainably. Earthen formworks combined with 3D printing technologies present a unique opportunity for the concrete construction sector to address the wastefulness and complexity of custom formworks. The current state-of-the-art projects in academia and industry demonstrate that earthen formwork strategies effectively address this challenge, but remain burdened by upscaling issues such as production speed. This research bridges the gap by exploring strategies for 3D Printed earth formworks to efficiently produce structural elements using custom self-compacting and set-on-demand concrete mixtures. A first base earth mix is developed for reduced shrinkage and later modified via a plasticizer for increased green strength, forming the final mix. Two mix iterations are deployed in two corresponding strategies where concrete is cast into the earth formwork in a dry or plastic state. The methods highlighting the setups for 3D printing and procedures for appropriate material processing such as slump flow, shrinkage and rheology are presented. The results are explored via two column prototypes leading to a final demonstrator for a 2 m high reinforced concrete column. Conclusions are drawn on the implications of the two casting strategies, the current persisting challenges and the crucial next steps for development. Thus, the research provides a foundation for how clay formworks can be upscaled effectively for more sustainable production of complex concrete structures.