Earthen Buildings Research Articles

Vernacular Earthen Buildings from Leiria, Portugal – Material Characterization

ABSTRACT In Portugal, a large number of vernacular earthen buildings present an advanced state of degradation. These buildings comprise historical, technological, architectonic, cultural and social recognized values and, therefore, efficient interventions are needed for their conservation. The knowledge of the properties that the materials used in their construction show nowadays is one of the bases to support future interventions. Unstabilized earthen samples were collected from the walls of six earthen buildings located in the region of Leiria, Portugal, built with rammed earth and/or adobe masonry. The samples were characterized by particle size distribution and through XRD, density, capillary absorption, drying, dry abrasion, compressive and tensile flexural strength. Mechanical results of rammed earth were lower than adobe’s, contrary to what was commonly found in other studies, and capillary coefficients of adobe were comparable to lime-stabilized adobe from other regions. A surface protection by compatible renders, respectively, earthen-based and air lime-based, is strongly encouraged to extend the walls durability. Although based on a short sampling, this data gives initial support to future compatible, effective and reversible interventions in Leiria vernacular earthen buildings, contributing to the preservation of this earth-built heritage.

Life cycle analysis of environmental impacts of earthen materials in the Portuguese context: Rammed earth and compressed earth blocks

Abstract In the Portuguese context, the life cycle assessment of building materials is still in its infancy. So far, there is only a small number of Environmental Product Declarations (EPDs) available, all target for industrially-based materials. Although vernacular earthen materials are seen as ecological materials, with low potential environmental impacts, there are no studies that allow to quantitatively compare these materials with conventional ones, according to the applicable standards. In the case of Portugal, there are no EPDs or studies for these materials and the studies available worldwide are hard to compare, since they not follow the same life-cycle assessment methodology. This paper aims at contributing to a better understanding about the environmental performance of earthen materials by presenting results from the life cycle assessment of Compressed Earth Blocks (CEBs) and Rammed earth, based on specific life cycle inventory values obtained from a producer company, following the guidance provided by the standard EN15804. Among other conclusions, results show that CEB and Rammed earth have a total Embodied Energy of 3.94 MJ/block and 596 MJ/1 m3 and a Global Warming Potential of 0.39 kg CO2 eq/block and 47.5 kg CO2 eq./1 m3, respectively. In a cradle-to-gate analysis of different walls, the use of earthen building elements can result in reducing the potential environmental impacts in about 50%, when compared to the use of conventional ones. Additionally, the advantages of using earthen materials are also discussed for the different building life-cycle stages, focusing on the possibility to recycle these materials in a closed-loop approach.

Effects of fibre reinforcements on properties of extruded alkali activated earthen building materials

The reaction between clay minerals present in soil and an alkaline solution has the potential to develop in situ binders, which can be harnessed in the development of earth based construction materials. To ascertain the efficacy of this stabilisation mechanism in conjunction with fibres which are commonly used in earthen construction, this study presents a comparative analysis of the reinforcing effect of different fibre types (sisal, Eucalyptus pulp microfibers and polypropylene) in an alkali activated stabilised soil produced using extrusion technique. An evaluation of flexural properties in oven-dry and saturated conditions was conducted to simulate mechanical response in ideal and extreme conditions to evaluate effect of fibre type and content (0–2 vol%). Physical properties were also studied and optimum fibre contents evaluated. Results show that with respect to lignocellulosic fibres, sisal fibre reinforcements yielded the most remarkable result with the highest statistically significant improvement in flexural strength (79% relative to the unreinforced matrix) compared to composites reinforced with Eucalyptus pulp micro-fibres. Improved packing density and attendant reduction in water absorption associated with sisal fibre reinforced composites was attributed to synergistic interactions between sisal fibres and alkali activated matrix. On the other hand, synthetic fibre reinforcement (polypropylene), which had no statistically significant effect on composite flexural strength, transformed brittle unreinforced matrices to deflection hardening composites due to weak fibre-matrix interactions. Sisal fibres have thereby demonstrated a significant reinforcing potential in extruded alkali activated earth-based materials and presents a satisfactory balance of strength, density and ductility for the development of eco-friendly building materials for low cost housing solutions.

Integrating Earthen Building Materials and Methods into Mainstream Construction Using Environmental Performance Assessment and Building Policy

Earthen building materials offer an environmentally sustainable alternative to conventional materials because they are locally available, minimally processed, and waste-free. However, they have not been comprehensively implemented because their technical data is highly variable, and they are not fully represented in building codes. To address these hurdles, this paper presents an environmental assessment and a policy repair review, including an environmental embodied impact analysis, and a discussion of the regulatory development required for earthen construction. The results of the environmental assessment show that earthen wall assemblies significantly reduce environmental impacts by 62-99% when compared with conventional assemblies such as timber frame and concrete blocks. Additionally, the policy discussion provides recommendations to overcoming materials variability and regulatory organizational collaboration. Overall, this paper highlights the importance of environmental and policy measures that could be used by policy makers and earthen building advocates in their endeavours to catalyse the representation of earthen building materials and methods in mainstream construction.

Numerical Investigation of the In-Plane seismic Performance of Unstrengthened and TRM-Strengthened Rammed Earth Walls

ABSTRACT The large availability of raw earth around the World led to its extensive use as a building material through history. Thus, earthen materials integrate several historical monuments, but their main use was to build living and working environments for billions of people. On the other hand, past earthquakes revealed their inadequate seismic behavior, which is a matter of concern as a significant percentage of earthen buildings are located in regions with medium to high seismic hazard. Nevertheless, their seismic behavior and the development of efficient strengthening solutions are topics that are not yet sufficiently investigated in the literature. In this context, this study investigates numerically the in-plane seismic behavior of a rammed earth component by means of advanced nonlinear finite element modeling, which included performing nonlinear static (pushover) and nonlinear dynamic analyses. Moreover, the strengthening effectiveness of a low-cost textile-reinforced mortar on such component was also evaluated. The strengthening was observed to increase the load and displacement capacities, to preserve the integrity for higher lateral load levels and to postpone failure without adding significant mass to the system. Furthermore, the pushover analysis was shown to predict reliably the capacities of the models with respect to the incremental dynamic analysis.

Development of unfired earthen building materials using muscovite rich soils and alkali activators

Most studies have focused on the alkali activation of thermally activated kaolinitic clays for the production of innovative building materials. Whilst the widespread use of these minerals may be hindered due to geographical availability; a combination of thermal activation and alkali activator solutions yields a material with high embodied energy with implications on eco-friendliness. This study presents an eco-friendly approach for the development of a low environmental impact building material using a low molarity alkali activator solution for the stabilisation of uncalcined muscovite rich soil. Influence of curing conditions on the physical, mechanical, microstructural and mineralogical properties were evaluated. Results show that alkali activation of uncalcined muscovite in the soil significantly improved the physical and mechanical properties of extruded earthen materials. Samples tested yielded compressive strength values between 9–11 MPa for varying curing regimes. The binding was mainly attributed to the formation of amorphous sodium aluminosilicate gels as a result of the partial dissolution of muscovite. These results show that low environmental impact building materials may be developed with uncalcined muscovite rich soils in developing regions around the world where these minerals are predominant for the provision of sustainable low-cost housing solutions.

Book Review: The Archaeology of Mural Painting at Pañamarca, Peru by Lisa Trever

Lisa Trever. The Archaeology of Mural Painting at Panamarca, Peru . Washington D.C., Dumbarton Oaks Research Library and Collection, 2017. ISBN 9780884024248. xvi + 350 pages, 14 color illustrations, 255 halftones, 67 line illustrations, 1 map. $69.95 (paperback). The north coast of Peru, with a tradition of constructing earthen buildings, was a hub of mural painting. Murals decorated pre-Columbian adobe architecture, including the interior and exterior of monumental architecture, religious centers, plazas, and tombs. Mural painting in the ancient Americas is a practice that extends back thousands of years and, in the absence of a textual record in the pre-Columbian Andes, offers insight to understanding indigenous cosmology and practices. These murals and buildings are rarely encountered intact today, as natural and human forces such as rain, wind, and looting have been detrimental to their preservation. Panamarca, located in the Nepena Valley on the north coast of Peru, is not likely to be a familiar archaeological site to scholars outside of pre-Columbian studies. Vivid, brightly colored murals from the Moche culture, which flourished on the north coast of Peru between 200 and 800 C.E., were discovered and published in the 1950s, bringing the site prominent national and international attention.1 These murals depicted figural imagery of processing priests and warriors, ceremonies, and supernatural beings engaged in battle. At the time, murals such as these were unknown elsewhere. Their figural representations of mythology and ritual have shaped the scholarship of the Moche world and iconography. Mural E, the most well-known of Panamarca’s wall paintings, has been used as an important example of a narrative of human sacrifice and ritual toasting. It features a priestess offering a sacrificial goblet flanked by priests, captured warriors, and human sacrifice. This scene, dubbed the “Presentation Theme” and later “Sacrifice Ceremony,” is believed to be a principal component of Moche religious and political ideology.2 Numerous projects throughout the 20th century …

The Biophilic Power and Environmental Urgency of Earthen Construction

The built environment must meet the highest demands of human habitation, resource management and community enrichment. To achieve these goals, modern built environments should adopt restorative environmental and biophilic design principles which seek to reconnect the human built environment with nature. In this paper, the biophilic aspects and environmental benefits of earthen construction are assessed and compared to conventional construction in order to demonstrate the tangible and intangible benefits of earthen materials. Specifically, the synergies between biophilic design attributes and earthen construction are elaborated, characterizing the ecological, health, and community collaboration advantages that earthen structures provide. Subsequently, the results of an environmental Life Cycle Assessment (LCA) of earthen building materials from cradle to gate enumerate the environmental preferability of earthen materials over conventional materials.

Cradle to site Life Cycle Assessment (LCA) of natural vs conventional building materials: A case study on cob earthen material

Cob is an earthen building material that offers a minimally processed, low carbon, and locally available alternative to conventional building materials and methods. This paper provides a framework for a comparative Life Cycle Assessment (LCA) from an embodied perspective of energy and air emissions, using cob earthen wall construction as well as benchmark wall assemblies of concrete masonry and wood frame. The results of the study show that cob production requires only 18–38% energy and reduces 75–82% of global climate change impacts when compared to conventional materials. Significantly, the embodied environmental impacts of cob were shown to be lower than conventional materials in all aspects. Further, sensitivity analysis shows that impacts can be further reduced by maximizing the use of local materials.

Numerical modeling of the seismic out-of-plane response of a plain and TRM-strengthened rammed earth subassembly

The importance of raw earth is highlighted by the millions of persons living in earthen buildings around the World and by numerous historical monuments made of this material. Its widely availability led to the development of a variety of building techniques, including rammed earth, which is the main focus of this study. Similarly to unreinforced masonry structures, rammed earth buildings acceptably withstand gravity loads, but are significantly vulnerable to earthquakes. In this regard, great attention has been put on the proposal of efficient, compatible, affordable and reversible strengthening solutions. However, very limited studies address either the experimental testing or modeling of the seismic response of such buildings. The current study investigates the seismic out-of-plane performance of a plain and subsequently strengthened rammed earth subassembly (U-shape) using an advanced finite element modeling approach calibrated based on previously conducted small-scale experiments. Here, failure mechanisms, corresponding capacity and efficiency of the adopted strengthening solution (low-cost textile-reinforced mortar) are evaluated by means of pushover analyses. Then, the reliability of the pushover analyses is assessed by comparing its outcomes with that of the incremental dynamic analyses. In general, the failure was found to be governed by overturning of the web wall due to its detachment from the wing walls, while the strengthening was found to increase the capacity and delay the damage development.

Chemico-microstructural changes in earthen building materials containing calcium carbide residue and rice husk ash

Clay earthen materials can essentially be stabilized with calcium carbide residue (CCR) and rice husk ash (RHA) to produce compressed earth block (CEBs) with improved mechanical performances for application in building construction. Nevertheless, the curing process in mixtures of these materials needs to be monitored in order to assess the maturation of the reaction among these materials and their reactivity. This study investigated the curing process in mix solutions and microstructural changes in the cured mixtures made of kaolinite-rich earthen material, portlandite-rich CCR, and silica (amorphous)-rich RHA. Dry mixtures were prepared by adding 0–25% CCR and 10–25% CCR:RHA (various ratios) to the earthen material (5 g). The mix solutions were prepared by addition of 100 mL of deionized water to the dry mixtures. Stabilized CEBs were also produced by manually compressing moisturized mixtures in 295 × 140 × 95 mm3 mold. The curing process was undertaken between 1 and 90 days at 40 ± 2 °C. Throughout the curing, the chemical changes in mix solutions were monitored by measuring the pH, electrical conductivity (EC) and concentration of unconsumed calcium ions [Ca2+]. The microstructural changes in cured mixtures were characterized using X-Ray diffraction (XRD), thermogravimetric analysis (TGA) and scanning electron microscopy (SEM). The EC and [Ca2+] decreased over the curing time mainly due to the consumption of calcium ions through pozzolanic reaction involving the earthen material with CCR and CCR with RHA. The minimum values of EC and [Ca2+] were reached after 45 days of curing in the mix solutions containing the earthen material and CCR alone and 28 days in those containing the earthen material and CCR:RHA. This was related to the end of the reaction and occurrence of optimum maturity in the respective mixtures. The XRD analyses revealed the consumption of kaolinite and portlandite from the raw materials and formation of calcium silicate hydrates (CSH) and calcium aluminate hydrates (CAH) in the cured mixtures. The SEM micrographs showed the formation of porridge-like products forming an interlocking network which densely cemented the matrix of stabilized CEBs.

Failure analysis of earthen, masonry and concrete buildings during the 2017 Tripura earthquake

This paper reports on an evaluation of failures of non-engineered earthen buildings, timber-framed buildings with bamboo matting, unreinforced load-bearing masonry buildings and framed reinforced-concrete structures with brick infill during the 5·7 magnitude 2017 Tripura earthquake in India. Field observations showed that some of the concrete and masonry buildings, and many of the non-engineered earthen buildings in the Dhalai and Unokoti districts, suffered damage due to this moderate earthquake. Out-of-plane failure, corner cracks, shear cracks and damage of infill wall materials were among the predominant forms of seismic damage. On the basis of the analysis, some remedial measures are proposed in this paper, which will require future research and testing.

Passive strategies used in Southern Portugal vernacular rammed earth buildings and their influence in thermal performance

In Portugal, there is a lack of quantitative studies on the thermal performance of earthen buildings. This paper aims at contributing to this research context by studying site-specific strategies, and the thermal performance and comfort conditions of a rammed earth building located in southern Portugal. The study is based on objective and subjective assessments and consists of assessing the hygrothermal conditions, thermal comfort levels and analysing the occupants' perception regarding thermal sensation. The results showed that the strategies used are closely related to local conditions, mitigating the effects of high summer temperatures and ensuring a good summer thermal performance by passive means alone. During the summer monitoring, results showed that the building stayed most of the time (80%) in Category I (high level of expectation) and the remaining time in Category II, according to the classification method defined by the standard EN15251. During the winter period, the building had the worst performance, being necessary a heating system to guarantee comfort conditions. Additionally, the results showed that the good thermal performance of the case study depended more on the high thermal inertia than on the U-value of the envelope. Limitations and advantages of the use of earthen construction elements are discussed.

Susceptibility of earth-based construction materials to fungal proliferation: laboratory and in situ assessment

The impact of building materials on the environment and the health of occupants is nowadays a priority issue. Ecological construction materials such as earthen materials are currently experiencing a regain of interest due to both ecological and economic factors. The microbial proliferation on indoor materials can induce a deterioration of the building air quality and lead to an increase of health risks for the occupants. The issue of indoor air quality raises questions about the use of earthen building materials and their possible susceptibility to fungal development. The microflora of earthen materials and their ability to grow on such support are indeed poorly studied. This study focused on the quantification of both bacterial and fungal microflora along the manufacturing process. The impact of extreme humidity, simulating a hydric accident, on microflora development was analyzed on the surface and inside earthen bricks. The initial microflora of these materials was dramatically reduced during the manufacturing process, especially after heat treatment for drying. Proliferation of remaining microorganisms was only observed under high humidity condition, in particular for earthen materials with vegetal aggregates. Moreover, in situ samplings were performed on naturally dried earthen materials used in buildings. The characterization of the microbial density revealed a higher microbial density than on manufactured specimens, while microbial concentration and detected taxa seemed mainly related to the room use and building history. These results provide a better understanding of microbial proliferation on these materials.

Consolidation of earthen building materials: a comparative study

The consolidation and protection of mud bricks are a challenge in the field of conservation of archeological sites. One of the solutions is represented by the coverage of the entire excavation that assures a protection against mud dissolution. Unfortunately, this is not always feasible, both for economical and practical issues. For these reasons, alternative solutions are needed. In this work, laboratory experimentation has been carried out in order to test the efficacy of some products to slow down the dissolution process and increase the brick toughness. Three typologies of raw materials taken from different outcrops (one from the Republic of Azerbaijan and two from Calabria region, Italy) have been characterized and used to build mud brick specimens. Four consolidation treatments were tested (ethyl silicate, potassium silicate, potassium hydroxide, sodium hydroxide) and different investigations have been performed to check their efficiency against the dissolution in water. Results suggested that the efficacy of each treatment is related to the main intrinsic characteristics of the raw material employed for the mud bricks manufacture. Among the tested products, nanolime and NaOH solution showed very poor performance, while ethyl silicate and KOH could be very promising compounds for successful conservation.

Experimental Strength of Earth-Based Construction Materials in Different Regions of China

According to the latest UN statistics, more than 2 billion people in the world still live in various forms of earthen buildings, including some in China. The variety of earth-based constructional materials is significant among different regions, with each region influencing the selection of local earth construction materials. In this study, earth materials from four regions of China were collected and sorted, with 10 samples from each source, and cube compressive strength tests were performed to analyze the composition and mechanical properties of the four materials, including northeast black earth, southeast red earth, northwest loess, and Xinjiang yellow sand earth. The results showed that significant differences existed in the composition of earth-based constructional materials from different regions, which have influence on the materials’ compressive strength. The order from large to small of compressive strengths was loess, black earth, yellow sandy earth, and red earth. Material load-displacement curves were influenced significantly by the plasticity index, but the overall failure processes of the various samples were basically the same.

Reconstruction of Wooden and Earthen Buildings in 17th to 18th-Century Russian Forts in Siberia: The Case of the Sayansky Ostrog

On the basis of the materials of the Sayansky Ostrog (fort), built in the Northern Sayan in 1718, we reconstruct the type of building that was common during the initial stage of the Russian colonization (1600s and 1700s). This is one of the few well preserved Russian forts. While its buildings, their function, and location are known from written sources and from the findings of a complete archaeological excavation, their construction has been hitherto unknown. To reconstruct their size and appearance, we collated archaeological and ethnographic findings, museum materials, and written evidence about the layout of buildings and construction techniques. Judging from the totality of data, we suggest the reconstructions of buildings, such as powder magazine, supply depot, barn with cellar, forge, and commandant’s house. We describe traditions and innovations in construction techniques, choice of building materials, details and blocks, layout of floors, ceilings, and roofs. The commandant’s house reproduces the architectural standards of that time, set by Domenico Trezzini, who designed buildings in the capital and in provincial Russian towns.

Semi-fortified Palatial Complexes in Central Asia: New Work at the Great Kyz Kala, Merv, Turkmenistan

Within Central Asia there is an unusual group of earthen buildings (köshks), usually constructed on raised platforms, with vertical engaged columns forming iconic ‘corrugations’ on the exterior walls. The complexes are semi-fortified, with a second storey entrance, and often with asymmetrical ranges of rooms around an internal courtyard. Little systematic archaeological work has taken place on these monuments, which have mainly been studied as relatively eroded standing structures. However, recent work at the Great Kyz Kala at Merv, Turkmenistan, the largest surviving monumental köshk in Central Asia, has provided more details of construction and use. The excavations suggest that this complex was constructed in the 8th/9thcentury CE, with well-appointed rooms on the second storey, including a large hall, and functional rooms and storage spaces around a courtyard on the lower floor. The complex was set within an enclosure, containing gardens and possibly ancillary buildings. This particular köshk may have acted as an elite palatial suburban residence, perhaps for the governor of Merv.

The Palaepaphos-Laona rampart. A pilot study on earthen architecture and construction technology in Cyprus

Excavations conducted in the context of the Palaepaphos Urban Landscape Project (PULP) have revealed a defensive monument of the Cypro-Classical period (fifth and fourth centuries BCE), which had been preserved under an anthropogenic mound (tumulus) of the 3rd century BCE. Besides stone-work, the construction of the monumental rampart made extensive use of mudbricks. In 2016–2017, PULP introduced a pilot study based on analytical techniques (pXRF, SEM-EDS, granulometric and petrographic analysis) to address issues relating to the manufacture and construction of the earthen architecture of the rampart. The paper presents a description of the geoarchaeological analyses and their results, which have highlighted specific manufacturing practices in relation to the construction of the monument. Given that the rampart constituted a major investment of the royal authorities of ancient Paphos, the results provide new information on the production of earthen building materials and also on environmental choices with respect to raw material selection in the context of a public project carried out by a central authority circa the mid first millennium BCE.

Modeling of Coupled Heat and Mass Transfers in a Stabilized Earthen Building Envelope with Thatched Fibers

In order to reduce the heat and mass transfers in buildings, which increase energy bills, the development of composites materials such as earth bricks stabilized with thatch fibers is important for their construction. This paper aims to study a one-dimensional model of heat and moisture transfer through porous building materials. The coupled phenomena of heat and mass transfer are described by the Luikov model. Equations and boundary conditions are discretized using the finite difference method. The results obtained illustrate the temporal evolutions of the temperature and the moisture content, as well as the distributions of the temperature and moisture content inside the wall. The profile of the temperature and water content that are obtained are compared with the other numerical solutions that are available in the literature.