Earth-based Materials Research Articles

Machine Learning Approaches for Prediction of the Compressive Strength of Alkali Activated Termite Mound Soil

Earth-based materials have shown promise in the development of ecofriendly and sustainable construction materials. However, their unconventional usage in the construction field makes the estimation of their properties difficult and inaccurate. Often, the determination of their properties is conducted based on a conventional materials procedure. Hence, there is inaccuracy in understanding the properties of the unconventional materials. To obtain more accurate properties, a support vector machine (SVM), artificial neural network (ANN) and linear regression (LR) were used to predict the compressive strength of the alkali-activated termite soil. In this study, factors such as activator concentration, Si/Al, initial curing temperature, water absorption, weight and curing regime were used as input parameters due to their significant effect in the compressive strength. The experimental results depict that SVM outperforms ANN and LR in terms of R2 score and root mean square error (RMSE).

Performance and Durability of Cellulose Pulp-Reinforced Extruded Earth-based Composites

This study aimed to investigate the influence of two alternative cellulosic materials: bamboo organosolv pulp and recycled waste carton pulp, on the flexural strength, fracture toughness, drying shrinkage, and durability of extruded earth-based building materials by varying the reinforcement content at 5, 7.5, and 10 wt%. The results show the flexural strength and fracture toughness achieved by the inclusion of carton pulp were between the range of 2.87–3.20 MPa and 4.22–4.52 MPa.m0.5, respectively, while the introduction of bamboo pulp gave 2.04–2.20 MPa and 3.76–4.05 MPa.m0.5, respectively. Compared with the unreinforced material, composite reinforced with 5 wt% of recycled waste carton pulp significantly enhanced flexural strength (61%), specific energy (416%), and fracture toughness (57%), while increasing the drying shrinkage (81%) and water absorption (38%) and decreasing the bulk density (15%) of earth-based matrix. Although the addition of cellulose pulp in soil matrix increased the drying shrinkage due to the high absorption capacity of pulp fibre, it decreased the wearing percentage and the shrinkage cracking of the composite which contributed to an improvement in the durability of the earth-based material. The repeated drying shrinkage test led to an improvement in the dimension stability at 87%, 83%, 85%, and 82% for 0, 5, 7.5, and 10 wt% of recycled pulp composite, respectively. Cellulose fibre reacts as crack arrester during loading and shrinkage, improves the durability, and provides a lightweight earth wall material for insulation strategies.

Combined and synergic effect of algerian natural fibres and biopolymers on the reinforcement of extruded raw earth

This paper deals with the development of sustainable building earth-based materials. More precisely, it addresses the study of the reinforcement of raw earth with natural fibres originated from Algeria (diss and date palm tree fibres) and their stabilisation with xanthan gum. The aim of this study is the design of extruded earth-based building blocks with improved mechanical properties such as compressive strength and ductility. The effects of separate and simultaneous addition of date palm trees or diss fibres (with length varying between 5 and 15 mm at dosages of 1.5 and 3% in volume) and stabiliser (xanthan gum and HMP at 1 and 2% of the dry earth mass) on the flexural and compressive strength of the stabilised and unstabilised extruded materials are compared. Results show that adding only fibers decreases the compressive strength of the earth in comparison with the unreinforced sample. It is also shown that diss fibres provides better reinforcing efficiency than date palm tree fibres and that a combined addition of xanthan gum and natural fibres create a synergic effect that greatly improved the material mechanical behaviour: higher compressive and tensile strengths and better ductile properties. These results are fully supported by microscopic observations and pull-out tests carried out on single fibres.

Impact of phase change materials on lightened earth hygroscopic, thermal and mechanical properties

Climate change is leading construction engineers and building stakeholders to improve materials thermal insulation and heat storage capacity. The development of energy efficient building materials with a low environmental impact is a real challenge. In this sense, earth-based materials are known worldwide and have been used since thousands of years. These materials present many advantages but their deployment on a large scale, while respecting the operative standards, is still limited.Considering lightened earth, present work aims to improve their thermal properties by using phase change materials (PCM). The incorporation of PCM in construction materials has aroused great interest due to their capacity to store thermal energy.In present study, mechanical, hygrometric and thermal experimental studies were carried out on soil-fiber-PCM mixtures. The PCM incorporation showed an interesting improvement of the lightened earth thermal properties and a deterioration of the hygrometric properties while keeping their mechanical properties relatively unchanged.

Effect of cellulose pulp fibres on the physical, mechanical, and thermal performance of extruded earth-based materials

Due to the growing concerns of deforestation, renewable materials as recycled cellulosic waste and non-wood fibres provide an alternative solution for partial replacement of wood resources as a reinforcement agent in building material. This study examined the effect of cellulose pulp inclusion on the physical, mechanical, and thermal performance of extruded cement stabilized earth-based matrices. Laboratory experiments of earth-based matrices reinforced with two types of fibres (bamboo pulp and recycled waste carton pulp) at varying fibre contents (0, 5, 7.5 and 10 %wt.) were performed. The results show that the inclusion of recycled waste carton pulp fibre in the soil matrix significantly improved the performance of the composites compared to matrices reinforced with bamboo pulp fibre. Addition of recycled waste carton pulp displayed improvement in flexural strength (56%), in toughness (733%), and in thermal insulation (36.35%) compared to the control sample. Inclusion of recycled waste carton pulp in earth-based matrix increases the moisture loss, the drying shrinkage and behaves as a water reservoir for earth-based materials. It has been concluded from this study that recycled waste carton pulp has the potential as a suitable reinforcement for the promotion of lightweight earthen wall block materials (reduction of bulk density up to 21% after the inclusion of 10% of recycled waste carton pulp), where flexural strength, ductility, and thermal insulation performance are the primary requirements. In addition, the successful replacement of virgin bamboo pulp fibres with recycled waste carton pulp fibres reduces the environmental footprint of the building material. Therefore, the use of this recycled waste carton pulp in the construction industry will be an attractive alternative as it will solve both energy and environmental concerns.

Invasive alien plants as an alternative resource for concrete production – multi-scale optimization including carbon compensation, cleared land and saved water runoff in South Africa

Today's cities are ever-growing, especially in the Global South, inducing massive construction activity. To satisfy these needs we need feasible and environmentally sustainable construction materials, the use of local solutions and, if possible, to enable synergies between sectors for maximum environmental benefit.In South Africa and beyond, invasive alien plants are threatening the indigenous ecosystem while exacerbating water security by affecting water surface runoff and fueling wildfires that release carbon to the atmosphere. The literature suggests that bio-based construction materials can turn buildings into carbon pools. However, the dynamics of using bio-based materials at the urban scale are not yet well known. This paper tests a new type of non-structural bio-concrete, using invasive alien wood chips as a substitute for sand and gravel as aggregates, for future residential construction in Cape Town, comparing this new material to conventional and to earth-based materials, and benchmarking different policy scenarios. Firstly, the material is optimized within technical possibilities achieving the capture of 897 kg of CO2 equivalents per m3. Secondly, a reverse-engineered approach is employed to uncover the limitations of the material. Additionally, C02 emissions from cradle to gate and additional land and water use benefits are analyzed, considering spatial dynamics for transportation impacts.The optimized mix design using invasive alien plants as an alternative resource, combined with a policy that promotes multi-story buildings, offers great potential to achieve near carbon neutral cities, clearing land of invasive alien plants and thus saving annual water surface runoff.

Development and Applications of Transition Metal or Rare Earth-Based Luminescent Inorganic Materials

This Special Issue is dedicated to luminescent inorganic materials, an extremely vast topic that often and willingly crosses over into other important fields of chemistry and physics [...]

Processing methods for optimising the mechanical strength of raw earth-based materials

In the last few years, raw earth construction has recovered much consideration due to its low environmental impact, local characteristics and recyclability. However, the strength of this material fluctuates in reality due to the variability of soils and the different methods used in vernacular earth construction. The aim of this study was to identify the mechanisms that increase the strength of this material. Optimisation of the processing method of raw earth blocks was sought in order to obtain better strength for different sorts of soils systematically. Soils were extracted from the same region, Brittany, France, in order to keep the local character of this material. The soils were mixed with water only or water and a dispersant (sodium hexametaphosphate or tannins). The rheological behaviour of each soil changed with different processing methods. Thus, the processing method and the use of dispersant can be efficient ways to enhance the mechanical properties of the selected soils. This study highlights that some of these methods could be used in the near future at a semi-industrial scale to produce a structural material that can achieve compliance with modern standards without hydraulic binders.

Enablers supporting acceptance of earth-based material in UK urban housing sector

ABSTRACT Earth is not widely used in the UK and a vast majority of local construction professionals are unaware of the potential of contemporary earthen architecture and construction. A number of interrelated factors (inhibitors) render earth globally unpopular, and, in the UK in particular, earth is not readily exploited. Certain factors (enablers), no doubt, may increase the acceptance level of earthen construction and technology, and a key aim of this article is to deliver an in-depth investigation and present a clear understanding of how certain enablers may support the widespread acceptance of earth-based material in the context of UK urban housing. In order to achieve this aim, an Interpretivist research philosophy was employed. It comprises a detailed review of the current literature and Delphi method (designed to identify generic enablers that may support acceptance of earth); in-depth interviews employed to validate and contribute to an extensive list of drivers that may promote the widespread acceptance of earth in the background of UK urban housing. A number of interrelated enablers such as offering earth-based material courses in universities, organizing training programmes for all stakeholders, promoting earth building via British media, increased funding on earth construction innovation and exhibiting exemplar earth architecture are found to be the key enablers of acceptance of earth in the UK urban housing. However, this study recommends that implementing all these enablers along with constructing exemplar earth structures in all local areas of the UK would increase public acceptance of earth.

Relation between activator ratio, hydration products and mechanical properties of alkali-activated slag

The use of cement substitute, such as alkali-activated slag, is of great interest in the field of earth-based construction materials to preserve their environmental benefit. Nonetheless, the cationic activity of clayey particles of earth-based materials induces new issues by affecting the alkaline conditions in which slag is activated. This work aims to present how alkaline conditions modify the nature and the amount of hydrates formed, the kinetics for reaction and the resulting mechanical properties. A minimum of 5 wt% of activator with respect to the slag was needed to trigger consolidation of the samples within the first 24 h, while an activator content of 15% led to an excess of sodium, especially remarkable at early age. Besides, hydration kinetics were followed in situ during the first 3 days by infrared spectroscopy. The formation of portlandite and hydrotalcite-like hydrates were only observable from 10% of activator and the presence of hydrotalcite is correlated with an increase in mechanical properties. Finally, these results are of interest for the formulation of earth-based materials by predicting hydrated phases formed during slag activation depending on alkaline conditions.

Environmental assessment of large-scale 3D printing in construction: A comparative study between cob and concrete

This paper explores the environmental impacts of large-scale 3D printing (3DP) construction in comparison to conventional construction methods using two different types of construction material: concrete and cob (a sustainable earth-based material). The study uses a standard Life Cycle Assessment (LCA) method, from cradle to site, to assess the environmental impacts of the construction materials and processes, with a focus on load-bearing walls in small/medium size houses. As expected, cob-based methods (conventional followed by 3DP) show lower overall environmental impacts and global warming potentials than the concrete-based methods. The study also shows that while the overall environmental impacts of 3DP concrete is higher than that of 3DP cob due to higher global warming potential, stratospheric ozone depletion and fine particulate matter formation, it has less impact on marine eutrophication, land use, and mineral resources scarcity. The environmental issues that remain to be overcome in relation to 3DP concrete is its high-cement content, while the issue in 3DP cob rises from the use of electricity for the 3D printing operation. The study indicates that the use of renewable energy resources and innovative material science can greatly increase the potentials of both 3DP cob and 3DP concrete respectively for future construction.

Petrography and Micromorphology Face-to-Face: the Potential of Multivocality in the Study of Earth-Based Archaeological Materials

Soils and sediments are among the most commonly found materials in archaeological contexts, occurring in a myriad of forms. We need only think of pottery, which is a manipulated and fired sediment, or the different earthen deposits that compose the bulk of many sites. Traditionally, the study of the microscopic and compositional characteristics of pottery has been the focus of ceramic archaeometry, while the microstratigraphic analysis of archaeological sediments was always the main task of geoarchaeology. In this paper, the authors explore the potential of a closer collaboration between researchers dealing with the same type of raw material and often using the same methods (optical microscopy), who rarely confront the approaches and expertise of the other field. For this purpose, two samples belonging to the pre-historic and early historic site of Arslantepe were selected for a methodological exercise: a fragment of an andiron and a piece of a double-vaulted oven. Ultimately, the results of this work demonstrate that researchers from both fields can profit from a more intense exchange: one that takes advantage of the expertise developed in answering distinct but complementary research questions, and calls for the blurring of strict inter-disciplinary boundaries.

The path from geology to indoor radon

It is generally accepted that radon emission is strongly influenced by the geological characteristics of the bedrock. However, transport in-soil and entry paths indoors are defined by other factors such as permeability, building and architectural features, ventilation, occupation patterns, etc. The purpose of this paper is to analyze the contribution of each parameter, from natural to man-made, on the radon accumulation indoors and to assess potential patterns, based on 100 case studies in Romania. The study pointed out that the geological foundation can provide a reasonable explanation for the majority of the values recorded in both soil and indoor air. Results also showed that older houses, built with earth-based materials, are highly permeable to soil radon. Energy-efficient houses, on the other hand, have a tendency to disregard the radon potential of the geological foundation, causing a higher predisposition to radon accumulation indoors and decreasing the general indoor air quality.

Hygrothermal Behavior of Earth-Based Materials: Experimental and Numerical Analysis

Bio-based building materials such as earth bricks are attracting renewed interest throughout the world due to their thermal and environmental properties. In this work, a numerical study of the hygrothermal behavior of building walls consist of compressed earth bricks (CEB) and stabilized earth bricks (SEB) was performed. A two-dimensional Luikov model for evaluating the temperature and the moisture migration in porous building materials was proposed. The coupled heat and moisture transfer problem was modeled. The governing equations of a mathematical model were solved numerically with the finite difference method. Input parameters in the model and their dependency on stabilizers content were determined by laboratory experiments. In order to specify the effect of chemical stabilization on the heat and mass transfer within studied materials, average moisture content and temperature were presented as a function of time. Results show that the addition of chemical stabilizers enhances the heat transfer through the earthen materials and reduces their water vapor permeability.

Lime stabilization for compressed stabilized earth blocks with reduced clay and silt

Compressed stabilized earth blocks (CSEBs) are comparatively new earth-based materials similar to rammed earth, adobe, and bricks. Additionally, CSEBs can overcome the problems of fired bricks. The most common stabilizers used for CSEB production are cement and lime. Lime is environmentally friendlier than cement. This study was performed with the aim of finding the suitability of lime and lime-cement combinations as the stabilizer for CSEB production with reduced clay and silt contents. The soil selected for this study was modified to obtain clay and silt contents of 5 %, 10 %, and 15 %. River sand was used to change the clay and silt contents of the soil. Lime percentages of 5 %, 10 %, and 15 % by weight as the stabilizer were selected. The stabilized blocks were tested for dry density, water absorption, and 28-day wet and dry compressive strengths and were compared with the SLS 1382 standards. Cement-stabilized blocks with 10 % and 8 % cement by weight were prepared for comparison purposes. The study showed that lime alone did not give sufficient properties as specified in SLS 1382. From the percentages tested, 10 % lime showed the maximum performance; hence, this optimum percentage of lime was replaced by cement contents of 3 %, 5 %, and 7 %. Lime-stabilized blocks can be used for single-story buildings, while the combination of lime and cement stabilizers helped to obtain higher compressive strengths than that of lime alone. The other properties of the CSEB also meet all the specification values. Grade 2 block strength was achieved with the contents of 15 % and 10 % clay and silt with 5 % lime: 5 % cement combined stabilizer and 5 % clay and silt contents with 3 % lime: 7 % cement combined stabilizer.

Influence of coconut fibres and lime on the properties of soil-cement mortar

Stabilisation of earth-based materials continues to gain attention among researchers in the field of construction. This study investigates the influence of coconut fibres and lime on the properties of soil-cement mortar. Fibres of 0.2–0.8 %; the lime of 0–15 %; cement of 5 % by weight of soil were used and tested for density, water absorption, compressive strength, tensile strength and SEM/EDS. There were improved density, water-resistance and erosion of the specimen. The optimum strength was recorded at 0.2 % fibre and 5 % lime addition of the specimen. The study concludes that coconut fibres and lime positively influences soil-cement mortar properties for construction application.

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.

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.

3D printing of earth-based materials: Processing aspects

Due to its low environmental impact, earth construction has received much consideration in recent years. Nevertheless, its development remains limited due to low production rate. Recent developments have been made to improve earth-based materials mix-design and processing methods. Simultaneously, digitally based construction methods have been introduced in the field of construction especially for cement-based materials application. Among these new techniques, the so-called 3D printing by extrusion deposit has been the most intensively studied. In this study, we assess the possibility of adapting this technique to earth-based material. After making the earth’s rheological behaviour suitable for 3D printing, a laboratory-scale printing has been carried out and the printed samples have been mechanically tested.

Earth-based construction material field tests characterization in the Alto Douro Wine Region

AbstractThe Alto Douro Wine Region, located in the northeast of Portugal, a UNESCO World Heritage Site, presents an abundant vernacular building heritage. This building technology is based on a timber framed structure filled with a composite earth-based material. A lack of scientific studies related to this technology is evident, furthermore, principally in rural areas, this traditional building stock is highly deteriorated and damaged because of the rareness of conservation and strengthening works, which is partly related to the non-engineered character of this technology and to the knowledge loosed on that technique. Those aspects motivated the writing of this paper, whose main purpose is the physical and chemical characterization of the earth-based material applied in the tabique buildings of that region through field tests. Consequently, experimental work was conducted and the results obtained allowed, among others, the proposal of a series of adequate field tests. At our knowledge, this is the first time field tests are undertaken for tabique technology. This information will provide the means to assess the suitability of a given earth-based material with regards to this technology. The knowledge from this study could also be very useful for the development of future normative documents and as a reference for architects and engineers that work with this technology to guide and regulate future conservation, rehabilitation or construction processes helping to preserve this important legacy.