Earthen Construction Materials Research Articles

A novel rammed earthen material stabilized with steel slags

Though earthen construction materials are locally available and ecologically friendly, they have some deficiencies, such as the poor compressive strength, water resistance and durability in comparison with the mainstream wall materials. To overcome the drawbacks, a novel rammed earthen material stabilized with slags from a steelwork is prepared in this paper. The mechanical, durability and thermal performance are investigated experimentally. Besides, the mechanism of stabilization is analyzed. The results show that the introduction of the steel slags improves the compressive strength and durability of the earthen materials greatly, but decreases their thermal resistance.

Mechanical properties of biopolymer-stabilised soil-based construction materials

Soil-based construction materials are of interest as structural building materials due to their green credentials, as well as being present in many historical structures. For effective conservation of the latter, and to motivate greater uptake for new construction, understanding of the mechanical and hydraulic properties of these materials is in need of improvement. Earthen construction materials can be considered to be manufactured unsaturated soils, and advances in understanding can be made by considering them from a geotechnical point of view. This paper presents initial results from a major programme of testing, seeking improved properties for earthen construction materials, where unusual organic compounds have been employed as stabilisers. Two gums (guar and xanthan) used as stabilisers for a soil mixture are shown to have significant effects on certain mechanical properties, some of which can be explained, and other aspects which are in need of further investigation.

Fibre reinforcement in earthen construction materials

Earthen construction materials are generally brittle with low tensile strength. To deal with this in practice, it is often proposed that reinforcement be added in the form of fibres of various materials. Construction in earthquake-prone parts of the world is thought to benefit from this form of reinforcement, and indeed fibres (in the form of straw) are a key part of many adobe (unit-based) materials. To remain in harmony with the generally excellent environmental credentials of these materials, the reinforcement should be obtained from a natural material ideally obtained as a waste stream, so natural fibres are often chosen. While some studies have been published on the macroscopic mechanical behaviour of reinforced earthen materials, little is known of what is happening at the interface between the soil matrix and the fibres. In this paper, the authors present laboratory-based studies that attempt to fill this gap, covering pull-out behaviour of natural fibres embedded in earthen construction materials, both stabilised and unstabilised.

Physical, mechanical and hygrothermal properties of lateritic building stones (LBS) from Burkina Faso

Earth is a predominant eco-friendly construction material which provides a good occupational comfort consuming less energy. To improve the durability performance, stabilization is commonly adopted. However the additional costs induced by such process cannot be afforded by the majority of the population in developing countries, and in some circumstances, the environmental side effect may be controversial. Alternatively, laterite stone which is natural available and readily stabilized material that can be used for building construction is studied in this paper. Lateritic building stones (LBS) from Burkina-Faso are studied for their hygroscopic, physical and mechanical characteristics by conducting experimental investigation such as moisture sorption and desorption, moisture buffering, three-point bending, and cyclic unconfined compression test. The analysis is focused on the moisture ingress of the material and its impact on the mechanical strength and also an insight on understanding linear elastic behaviour of LBS is carried out. The experimental results are compared with the stabilized and un-stabilized earthen construction materials. This comparison underlines the good performances of LBS, in both mechanical and hygrothermal properties as a building material.

Challenges in treating earthen construction materials as unsaturated soils

Earthen construction is a loosely defined term covering both the materials and methods for creating structural components from mixtures of subsoil, often with the addition of chemical or mechanical stabilisers. There is evidence of Man creating earthen structures for thousands of years, and there are many world heritage sites containing earthen structures, some of which present issues in terms of conservation. In some parts of the world there is a growing market for new-build earthen structures and a key issue here is the lack of design codes. Since these materials are composed mainly of particulates and water it is natural to regard them as geotechnical in nature, where friction and the presence of water have a key influence on material properties, however until very recently this was not the case, with earthen construction materials regarded as weak concrete or masonry. In this paper we examine these opposing views and discuss the issues associated with regarding these materials as unsaturated soils. The paper is illustrated with outcomes from research at Durham University carried out over the past ten years.

Earthen construction materials: Assessing the feasibility of improving strength and deformability of compressed earth blocks using polypropylene fibers

Abstract Earthen construction materials are often ecologically friendly and locally available. They are however weaker and poor in damage resilience compared to mainstream walling materials like fired bricks and concrete masonry units (CMU). Compressed earth blocks (CEB), a modern form of the adobe brick, are gaining popularity as a construction material globally because they are stronger and more dimensionally stable compared to earlier forms of earthen construction methods/techniques. Despite the strength improvement achieved through using CEBs over other traditional forms of earthen construction, they are still more brittle and weaker in bending and compression in comparison to CMU and fired bricks. This research investigated the potential of addressing some of the shortcomings of earthen construction materials by assessing the influence of polypropylene fibers on the strength, ductility, and deformability of CEBs. CEBs were produced using different fiber weight fractions and tested in both compression and bending. Overall, performance in bending and ductility were improved by the addition of fibers. The quantity of fibers present was found to have an influence on block strength, post-crack response, and deformability. The findings presented in this paper suggest that polypropylene fibers are a feasible fiber option for CEB production.

Geochemical Characterization of Bolivian Formative Earthen Architecture by Wavelength‐Dispersive X‐ray Fluorescence

In this study, we employ wavelength‐dispersive X‐ray fluorescence (WDXRF) to characterize construction materials from Formative civic architecture (1000 B.C.E.–C.E. 400), ethnographic mudbricks, and off‐site controls from the Taraco Peninsula, Bolivia. The preparation of earthen construction materials for civic buildings can shed light on aspects of community development such as labor organization, resource management, and architectural technologies. We apply geochemical results to reconstructing how public buildings were made as communities moved toward socio‐political complexity in this region. However, there are few geochemical studies in the Andes, and little prior scientific analysis of earthen architecture. We therefore tested the efficacy of WDXRF for this region, and developed control materials. Our archaeological samples were selected from two Formative villages, Chiripa and Kala Uyuni. In this study, we performed WDXRF analyses on 63 archaeological and control samples including archaeological floors, walling, plasters, and mortars, as well as contemporary ethnographic walling and topsoils. Elemental signatures for 28 elements clearly distinguished the archaeological flooring, walling, plaster, and mortars from ethnographic and off‐site controls. More subtle variations were detected that distinguish study sites and the different material types. Laboratory‐calibrated multi‐element XRF effectively supports efforts to reconstruct the pathways to social complexity in the Titicaca Basin.

Optimum water content tests for earthen construction materials

There is considerable interest in earthen construction materials, owing to their inherent sustainability, and also in the conservation of heritage structures. For new-build in situ construction a key aspect of quality control is the achievement of full compaction to maximum dry density. At present the guidance available in this area to those using these materials varies from British Standard tests to heuristic-based methods developed by practitioners. In this paper, the various tests are compared for different soil mixes and also to judge the influence of the test operator. The study demonstrates shortcomings in the heuristic methods and indicates that, for modern standards of quality control to be achieved, alternative tests should be used.

An Integrated Geoarchaeology of a Late Woodland Sand Mound

AbstractThe Graveline Mound (22JA503) is a sand platform mound in Jackson County, Mississippi, built on a low, late Pleistocene terrace on the Mississippi Sound. The Late Woodland mound (A.D. 590–780) is composed of local soils, and its presence today is a testament to the ancient builders’ knowledge of earthen construction materials and methods. Central to the study of the mound is an integrated geoarchaeological approach that uses stratigraphy and micromorphology to decipher material source and selection, construction techniques, and periodicity, in combination with more traditional artifacts, revealing the activities that created this ultimately monumental space. The mound was built in three rapid stages beginning with a low earthwork demarcating a ritual precinct used during late spring/early summer. Stage II quickly followed with a series of alternating zoned fills, sealing the space that was then subsequently covered by Stage III, a massive hard red surface that marked the location with a platform mound.

Macrostructural changes in compacted earthen construction materials under loading

There is increasing interest in the use of earthen materials for modern construction. The mechanical behaviour of these materials is strongly controlled by their internal macrostructures. Rammed earth (RE) is one example of these materials, created by in situ compaction of a wet soil mixture. Changes to the material structure occur on loading and during compaction; therefore, the nature of these changes needs to be understood if the effect on the material behaviour can be predicted. Here, the change in the macrostructure of RE on the application of compressive loading is investigated by using X-ray computed tomography and fractal analysis to monitor the changes in loaded RE specimens. The macrostructures of specimens comprising different layer thicknesses are also investigated in order to determine how layer thickness affects the compaction of the material. Results are used to recommend procedures for manufacturing specimens that are representative of the material found in full-scale RE structures.

Structure creation in earthen construction materials: information from dry soil mixtures

There is increasing interest in the use of earthen construction materials, such as rammed earth, due to their inherent sustainability. These materials have been used by man for thousands of years and some of the earliest examples can be found in China. Features of the structures of these materials arise from the means of production. In particular, in situ earthen construction materials exhibit strong anisotropy due to their layered nature. A more subtle structure effect arises from the way that the earth mixture is deposited. This paper reviews and discusses stratification effects in dry soil mixtures, including some original experimental work, and indicates some links between the features of the dry mixtures and earthen construction materials. Improved understanding of the physical processes in play will allow more accurate specification of these materials in the future, and hence spread their use.

The DaVincis of dirt: Geoarchaeological perspectives on Native American mound building in the Mississippi River basin

The complexity of mound construction, as revealed through geoarchaeological analyses, indicates the cultural significance of mounds may be as well reflected in the earthen construction materials and their arrangement, as it is in the artifacts abandoned on their summits. We use geoarchaeological examples from three sites in the Mississippi River basin, Shiloh Mounds, Cahokia, and Poverty Point, to advocate a geoarchaeological approach that considers multiple scales from the regional soils and geomorphology, field observation of lithostratigraphic units, to the micro-scale identification of the mineralogy and soil development in order to decipher the source and processing of the soils and sediments. We focus on the use of five types of construction referred to here as: sod blocks, soil blocks, loaded fills, zoned fills and veneers. Also we address the selection and transportation of soils and sediments used in mound building and what these types of deposits reveal about the methods used to build mounds. These data can be used to evaluate and understand organization of labor, pace of construction, and mound appearance. We hold there is a considerable (although unquantified) difference between earth moving and mound building and that the construction of these important monuments required considerable knowledge, skill, planning, hard work, and attention to symbolic and ritual meaning.

Another (mud)brick in the wall: scientific analysis of Bronze Age earthen construction materials from East Crete

Mudbricks appear to have been one of the most common building materials used in domestic architecture in Bronze Age Crete. Well-preserved earthen construction materials from the sites of Vasiliki, Makrygialos and Mochlos in East Crete have been examined with regard to their macromorphological characteristics and their mineralogical and chemical composition in order to investigate the nature of the raw materials used, the technology of manufacture and the potential use of specific recipes. The methods applied include a combination of mineralogical and chemical analytical techniques, namely petrography, neutron activation (NAA), X-ray fluorescence (XRF), and X-ray diffraction (XRD) analysis. Finally, a range of raw materials from the immediate vicinity of each site were sampled and analyzed in order to compare with the archaeological data and identify potential sources. The analyses suggested that there is a degree of standardization in the recipes and the manufacturing process and that the selection of the raw materials depends on availability.

Microscopic physical basis of the poromechanical behavior of cement-based materials

Contrary to other porous materials such as sandstones, bricks or porous glas, the inter-atomic bonding continuity of cement-based materials is far from obvious. When scrutinized at very microscopic level, continuity of the ionic-covalent bonding in the solid phase is almost everywhere interrupted by water molecules or liquid water films of variable thickness. Yet, concrete and cement pastes are able to withstand stresses of the same magnitude as rocks. The purpose of this paper to explore the possible reasons for such a high cohesion, in terms of inter-particle forces using general arguments and molecular simulation computations includingab initio quantum chemical methods applied toC-S-H. As it will be discussed, molecular simulation studies provide strong arguments for predicting that short-and medium-range attractive electrostatic forces are the essential components of the cohesion, ofC-S-H with, at short distance (sub-nm), a significant iono-covalent contribution involving strongly localized calcium ions and water molecules and, at larger distance (a few nm), ionic correlation forces involving hydrated and mobile calcium ions in liquid water films. Only a marginal contribution is expected from van der Waals attraction whereas capillary forces might contribute at a level comparable to that of correlation forces in unsaturated conditions. The parallel with clay-based earthen construction materials is part of the clue of this rationale.