Second RILEM International Conference on Earthen Construction

Table of Contents

1. Frontmatter

2. Additive Manufacturing and Rheology

   1. Frontmatter

   2. Additive Manufacturing for Earth-Based Materials: An Experimental Investigation

      Daniel Trento, Flora Faleschini, Maryam Masoomi, Carlo Pellegrino, Mariano Angelo Zanini

      Abstract

      The achievement of sustainable development goals should be driven not only by environmental policies but also considering societal constraints, such as the valorisation of local traditions, especially in emerging countries. In the field of construction engineering, 3D printing can be seen as a modern technique which allows reproducing traditional constructions, such as those made in adobe and cob, using local and natural materials, e.g. soils, and even recycled ones, thus reducing the impacts related to the production and transport of the raw materials. The environmental and economic advantages of additive manufacturing are widely recognized for several applications: 3D printing does not require molds and allows to save material, obtaining complex shapes easily. The main advantages are linked to save money, time, handwork and properly reducing the environmental impact of structures.

      In this paper the results of an experimental campaign aimed at selecting earth-based sustainable mixes for 3D printing are shown. At the beginning of the experimental campaign, 18 mixes were prepared varying the dosage and the components: among them, we selected locally available soil, silica sand, hydraulic lime binder, unaltered rice husk, shredded rice husk, marble waste dust, municipal solid waste incinerator bottom ash and fibres. Each mixture has been evaluated in terms of printability, then mechanical tests were performed at 28 days of curing. Finally, an efficiency evaluation of mixture is carried out considering compressive strength, price and embodied carbon as affecting parameters.

   3. Additive Manufacturing with Earth Based Materials - Minimization of Shrinkage Deformation

      Leonie Gleiser, Robin Pierer, Slava Markin, Marko Butler, Viktor Mechtcherine

      Abstract

      Methods for additive manufacturing in the construction sector have been increasingly developing over the last few years. Consequently, additive manufacturing using sustainable earth-based materials has become feasible. This fusion of traditional circular construction materials with digital production techniques yields a promising construction technology.

      However, components fabricated trough additive manufacturing with earth-based materials still encounter significant shrinkage deformations and cracking, negatively impacting product properties and diminishing overall quality. Therefore, this study investigates methods to mitigate shrinkage in additively manufactured earth-based materials and measures for shrinkage assessment.

      By adjusting the clay, silt and sand content the properties of the earth mixture can be enhanced to minimize shrinkage. Additionally, a strategic deposition or printing path during additive manufacturing can contribute to reducing shrinkage deformations in 3D-printed elements, consequently enhancing their quality. The effects of both measures on the shrinkage of earth materials and printed elements are demonstrated.

      Implementing of the findings from this study enables the 3D-printing of aesthetically earth-made products with reproducible quality in terms of shrinkage and strength.

   4. Comprehensive Investigation into the Influence of Soil Composition and Water Content on Cracking Due to Drying Shrinkage in 3D-Printed Earthen Structures

      Betty Gonzales, Diana Zavaleta, Bruno Bertolotti, Rafael Aguilar, Miguel Pando, Javier Nakamatsu, Suyeon Kim, Guido Silva

      Abstract

      As a raw material for additive construction, earth offers a multitude of benefits, from environmental and economic to social points of view. However, the fresh-state properties of printable materials and the curing conditions of additively manufactured elements make large-scale 3D-printed earthen structures susceptible to suffering severe cracking from shrinkage during drying. This project investigates the effect of soil composition and water content on the development of drying shrinkage cracking in 3D-printed earthen structures. This article presents two strategies for minimizing those cracks: decreasing the clay content of the soil by adding fine sand and decreasing the required water content for printability by using a clay dispersant agent. Earth-based mix designs with different soil/fine-sand ratios and sodium hexametaphosphate (SHMP) contents were subjected to flow table, rotational rheology, and shrinkage cracking tests. The results indicate that the clay and water content are determining factors that minimize the appearance of cracks due to drying shrinkage. Two earthen-based formulations with zero cracks due to shrinkage resulted from replacing 50% wt. of the soil with fine sand and the addition of 0.55 and 2.20% wt. of SHMP. Further research is needed to confirm the validity of these findings across diverse soil types and curing conditions.

   5. Developing 3D-printed Natural Fiber-Rich Earth Materials in Construction

      EunJin Shin, Olga Beatrice Carcassi, Yierfan Maierdan, Shiho Kawashima, Lola Ben-Alon

      Abstract

      Advanced manufacturing and 3D printing of clay- and earth-based materials have been recently emerging, but have been limited to little or no fiber reinforcement. Enriching 3D printable earthen composites with natural fiber reinforcement may improve durability, thermal resistivity, carbon storage potential, mechanical performance, and ductility. This study continues a line of research by the authors for developing printable fiber-rich earth composites for mixtures, focusing on defining mix-designs. The continued investigation shown in this paper focuses, specifically, on the mechanical performance and ductile behavior through bending tests that comply with ASTM C67. Importantly, the mechanical behavior here aims to comparatively investigate processing parameters – manual vs. machine mixing apparatuses – for the earth-fiber-additive composites, considering a range of agro waste co-products: wheat straw, hemp, banana, and kenaf fibers. The results show the benefits of employing the machine mixing technique for fiber homogenization, resulting in improved performance (with bending strength increased by 29 to 78%) for the 3D printed components.

   6. Keeping the Processability of a Clay Mortar for Extrusion 3D Printing While Decreasing Shrinkage and Increasing the Green Strength

      Evelien Dorresteijn, Sofia Tsiotou, Dirk Lowke

      Abstract

      Growing concern about climate change has spurred the construction industry's exploration of alternative building materials, with particular interest in clay and earth due to its widespread availability and low carbon footprint. Although earth has been used historically, the use of traditional methods in Europe is currently unprofitable and limited to a few pioneering projects due to high labor costs. Recent advances in digital manufacturing techniques have opened up new ways of using earth and clay-based materials. For example, clay mortar can be used in a digitally controlled extrusion 3D printing process to create natural, recyclable building components or formwork for concrete structures.

      However, the mechanical properties of clay mortars fall short of those of materials such as concrete, and the issue of clay shrinkage and low green strength poses a significant challenge. This paper investigates strategies to reduce the shrinkage and increase the green strength of clay mortar while ensuring that its workability for the extrusion 3D printing process is maintained.

      According to the results, it is found that shrinkage can be mitigated, and the green strength can be increased by reducing the water content (water to clay ratio), further reducing the water content by incorporating a deflocculant, incorporating fibers, and increasing the sand content without compromising its suitability for extrusion processes. This research represents a significant step towards realizing the potential of clay-based materials as an environmentally friendly alternative in modern construction practice.

   7. Optimisation of Earth-Based Mixtures in Terms of 3D-Printability and Mechanical Properties: Feasibility Study

      Ivan Markovic, Alexandra Horat, Danilo Pantellini

      Abstract

      This short paper presents the results of the feasibility study on the production and application of 16 different raw-earth mixtures in 3D-earth-printing technology. Mixtures were composed of raw earth with different additional nature-based ingredients such as lime, water glass, oven ash, different natural fibres etc. No cement was added to the mixtures. Our primary goal was to show how the mix design influences the 3D-printing ability (for additive manufacturing, layer-by-layer) in small-scale and large-scale printing test. We also analyzed shrinkage as well as compressive and bending strength in the hardened state.

      In the first part of the paper, mix compositions, testing methods and behavior in the fresh state are shown. Special emphasis is put on pumpability and stability in small- and large-scale printing tests. Subsequently, important properties in the hardening state (shrinkage) and in the hardened state (compressive and bending strength) are presented. Finally, discussion about results and further prospects regarding possible applications for sustainable structures are presented.

   8. Robotic Rammed Earth-Concrete (RREC): A Novel Additive Manufacturing Technology to Strengthen Rammed Earth Structures by Integrated Rammed Concrete Parts

      Harald Kloft, Ali Salamatian, Joschua Gosslar, Evelien Dorresteijn, Dirk Lowke

      Abstract

      Rammed earth is part of our building culture and is a suitable solid construction method for load-bearing structures. The advantages are its global availability, low ecological footprint, and complete reusability. However, challenges arise from the manual construction processes, which makes manufacturing time intense and leads to significant scatter in the compressive strengths. The robotic rammed earth process (RRE) developed at the Institute of Structural Design at TU Braunschweig (ITE) unifies formwork and compaction in one process step and enables the automated manufacturing of rammed earth components with consistent material properties. Nevertheless, even robotically rammed earth components have a significantly lower load-bearing capacity compared to concrete structures and are, therefore, very limited in their application. In order to increase the structural performance of rammed earth elements, a new additive manufacturing method has been developed at the ITE that combines rammed earth and rammed concrete in one-step automated process and enables the manufacturing of structural components with hybrid materiality. The so-called robotic rammed earth-concrete technology (RREC) makes it possible to utilise the different performance capabilities of the two materials, earth and concrete, in a customised way. RREC can be used for structural or architectural purposes, e.g. structural optimisation or erosion reinforcement, and ensures material-specific separation and recycling of materials at the end of their service life. The paper presents initial research results on material-process interactions in automated processing material studies, tool developments and structural design.

   9. Workflow for Earth-Based 3D-Printing

      Inka Mai, Joschua Gosslar, Noor Khader, Dirk Lowke, Norman Hack

      Abstract

      There is the need to improve the ecological footprint of modern construction; accordingly, earth as a sustainable building material is increasingly coming into focus. Besides the material itself, digital fabrication of earth-based materials offers additional ecological potential, as it is possible to create individualized components without using formwork and at the same time save resources due to a form-follows-force approach. However, the material must be adjusted for being suitable for additive manufacturing, i.e. material needs to be pumpable, extrudable and subsequently buildable. In this paper, a workflow is presented that shows the possibilities for engineering an earth-based mixture. Therefore, a systematic characterization of mixtures is carried out. For this purpose, loam to water ratio and volumetric aggregate content are systematically varied and the addition of natural fibers is investigated. For the evaluation of pumpability and buildability, the yield stress is evaluated. Mechanical strength as well as drying shrinkage are assessed as solid properties for these earth-based mixtures. The results are discussed and the developed workflow is prototypically demonstrated by the successful fabrication of a demonstrator. Therefore, six stackable 3D printed elements are fabricated with extrusion and then assembled in a 2 m high column.

   10. Monitoring and Modeling of Formwork Pressure Exerted by Castable Earthen Materials

       Simon Guihéneuf, Mathieu Audren, Nathan Lely, Tangi Le Borgne, Damien Rangeard, Arnaud Perrot

       Abstract

       Castable earth appears to be a promising solution for an efficient modern earthen construction method. In this construction technique, a setting agent is added to the earthen material (biopolymer or hydraulic binder), induces a material hardening and allows for the formwork removal. However, and contrarily to castable concrete, there is no available study dealing with the monitoring and the modeling of the pressure exerted by the earth at fresh state on the formwork. Nevertheless, it is critical to be able to predict the formwork pressure and its evolution with time after casting in order to design the formwork structure and to schedule its removal.

       In this study, a formwork mock-up equipped with interstitial pressure sensor is used to monitor the formwork pressure and the ability of theories developed for the prediction of pressure exerted by cement-based materials are tested and adapted to self-compacting earthen materials, one using alginate as a setting agent and the other incorporating 5% of CEM IIIA cement.

   11. Viscosity Control of Kaolinites Dispersion via Addition of Tannin and Ferric Chloride

       Charlotte Lovage, Elodie Prud’homme, Yves Jorand

       Abstract

       Traditional recipes from around the world show that various organic additives can affect the properties of clay-based materials. Tannins, which are polyphenols derived from plants, have the ability to interact with clay particles in both attractive and repulsive ways due to their surface properties. The study investigates the effect of complex formation between tannin, clay, and metal ions on the apparent viscosity of mixtures. Rheological measurements were conducted on several slurry formulations based on kaolinites, ferric chloride, and three types of tannin representing the main typological families of polyphenols. The results indicate that the inclusion of tannins of any kind decreases the apparent viscosity of pastes across all pH ranges. However, the dispersing capacity of the substance is particularly effective at natural pH value between 3 and 5. The addition of iron can be used to neutralise the dispersant effect. Controlling the viscosity and the creation of tannin-iron bridges between the clays is a promising approach to stabilisation.

3. Biostabilisation

   1. Frontmatter

   2. Challenges for Bio-Stabilised Earth-Based Construction

      Céline Perlot, Agostino Walter Bruno, Magda Posani, Guillaume Habert, Snežana Vučetić

      Abstract

      The RILEM technical committee TC BEC is considering the development of alternative stabilisation methods for earthen materials based on natural stabilisers with low environmental impact. An in-depth review of the state of the art has been carried out to identify the advances made and the main challenges to be addressed to democratise this practice. It appears that a rigorous classification of methods needs to be drawn up to support the draft of guidelines, among other things. The effects on mechanical and hygrothermal performance are beginning to be studied, but to better describe the mechanisms and guide the choice of methods, a link between the effects on the microstructural scale and performance needs to be established. This requires new experimental protocols adapted to bio-stabilised clayey matrices. The development of a performance-based approach is presented to take into account the environment in which the structural component is used. Finally, elements are presented for assessing climate change adaptation.

   3. Mechanical and Durability Properties of GGBS- Based Geopolymer Stabilized Earth

      Diana Chami, Victor Schmitz, Pierre Gerard, Alessia Cuccurullo

      Abstract

      The use of geopolymer binders has attracted increasing interest in the construction industry, especially due to the promising results it has provided as a substitution for cement in the production of concrete. Recently, the use of geopolymers for soil stabilization started emerging, allowing the enhancement of the mechanical properties of clayey or sandy soils for geotechnical applications. However, very few research studies exist addressing the use of geopolymers to stabilize compressed earth bricks for construction purposes. This paper aims to investigate the use of a geopolymer binder, manufactured using ground granulated blast furnace slag as a precursor and a solution of sodium hydroxide as an activator, for the stabilization of a clayey silty soil for use as earthen materials in construction applications. The mechanical properties of the stabilized earth are assessed in terms of unconfined compressive strength on compacted cylindrical samples (7.2x3.6 cm) cured under wrapped and unwrapped conditions for 7 and 28 days. In addition, the durability against water is assessed using immersion, drip, and contact tests on compacted unwrapped bricks (4x4x16 cm) cured for 7 and 28 days. The findings suggest a noticeable improvement in the stabilized earth's strength and durability, though exposure to air has a negative influence on the strength caused possibly by carbonation.

   4. Mechanical and Thermal Characterisation of Compressed Earth Blocks Made of Termite Mound Soil (Macrotermes Sp.) Stabilised with Corn Starch Gel

      Berthia Malonga, Philippe Poullain, Fateh Bendahmane, Stéphanie Bonnet, Nabil Issaadi, Louis Ahouet

      Abstract

      This work focuses on the feasibility of improving the mechanical strength of Compressed Earth Blocks (CEBs) made from Macrotermes termite mound soil with corn starch gel to provide an ecological and sustainable building material.

      The results demonstrate the suitability of raw earth collected from termite mounds for the production of compressed earth blocks (CEB) at the Proctor optimum. Mechanical tests on 4 × 4 ×16 cm³ specimens showed an increase in the compressive strength with decreasing water content (0%, 2%, 4%, 6%, 8%, 10% and 13.6%).

      In addition, unstabilised CEB and CEB stabilised with corn gel (5%, 10% and 15%) concentrated at 10% in water are compared in the dry state. Our results show that corn gel improves the mechanical properties by more than 50% and has a negligible effect on the thermal conductivity of compressed earth blocks. In short, starch seems to give CEBs improved thermal properties. This new family of composite materials - termite mound soil and starch - would be ideal for the construction of modern, sustainable, renewable buildings with a low carbon footprint.

   5. Strength and Durability of Biostabilised Ghanaian Mud Bricks

      Christopher T. S. Beckett, Irene Appeaning Addo, Frederick Owusu-Nimo, Ibrahim Yakubu, Yalin Gulen, Oscar Ukwizagira, Yuner Huang, Alexandre S. Gagnon, Ana Margarida Armada Brás

      Abstract

      Communities in northern Ghana (Tamale and Wa) rely on earthen materials to construct affordable houses. However, these traditional practices are threatened by climate change: repeated flooding is triggering a transition to using cement-based building materials, and urban expansion and loss of biodiversity threaten the source of biostabilisers traditionally used to protect structures from water damage. Local builders currently rely on cementitious or bituminous renders to protect earthen houses, but these can trap water within the walls and so increase the likelihood of failure instead of protecting the buildings from harm. Such materials are, however, viewed as being prestigious and local people race to be able to apply them to their homes, creating a vicious cycle of earthen building degradation.

      This paper explores the possibility of using traditional Ghanaian biostabilisers dawadawa and beini in communities in northern Ghana to create water-resistant earth renders, to stabilise earth bricks and avoid the need for cement or bitumen. Methods used in Tamale and Wa to manufacture mud bricks were identified through field studies and used to recreate specimens in UK laboratories. The compressive strength and resistance to water (from immersion or dripping water) were tested for unstabilised bricks and bricks stabilised with a solution of dawadawa or beini. The results indicate that dawadawa can quadruple the resistance of mud bricks to water damage for no loss in mechanical properties, creating a strong incentive to protect and manage this resource.

   6. Sustainable Poured Earth Construction Using Tropical Soil and Local Wood Residue Extracts

      Lily Walter, Yannick Estevez, Gildas Medjigbodo, Adeline Armougom, Baptiste Roux, Laureline Lespinasse, Laurent Linguet, Ouahcène Nait-Rabah

      Abstract

      French Guiana faces high population growth and requires affordable local building materials. Poured earth construction primarily uses local soils and could offer a cost-effective and eco-friendly solution. However, achieving easy casting and fast hardening requires additives, which can increase the economic and environmental costs when using imported industrial chemicals. Recent advancements highlight the promise of combining tannin, a polyphenolic wood extract, with sodium hydroxide (NaOH) and ferric oxides for easy pouring and fast hardening. Importantly, the tannin-iron interaction enhances water resistance, addressing a major drawback of earth-based materials. This study evaluated five local wood residue extracts and compared them to commercial Chestnut tannin to fluidify and improve the water resistance of a local soil. Extracts were obtained through microwave-assisted water extraction and analyzed by infrared spectroscopy and total phenolic content. Results revealed that each wood extract showed different structures and amounts of phenolic content, resulting in different effects on the soil's fluidity and water resistance. Notably, the extract from Wapa, abundant in the forests of northern South America, showed the highest phenolic content and could improve soil fluidity similar to Chestnut. Additionally, Wapa significantly improved water resistance, resulting in a 79% reduction in mass loss, compared to only a 43% reduction achieved with Chestnut. This study underscores the potential of locally sourced tannin extract for sustainable poured earth construction with tropical soils.

   7. Use of Organic Residues for the Mechanical Enhancement of Sustainable Rammed Earth

      Vania Calle, Rosario Rojas, Kevin Guillen, Bartolomeo Pantò, Javier Nakamatsu, Guido Silva, César Chácara

      Abstract

      This research focuses on defining a sustainable rammed earth (RE) material using organic residues. Based on the wide availability and the positive effects on earthen materials, it was decided to incorporate used cooking oil as an organic stabilizer and rice husk as fiber reinforcement to enhance the mechanical properties of RE. Considering these residues, six mix-designs were evaluated with different concentrations of used cooking oil and rice husk. Two additional mix-designs based on unstabilized and cement-based stabilized RE were evaluated for comparison purposes. The optimum water content was defined based on compaction curves obtained with standard proctor tests. The compressive strength of the sustainable RE at different curing conditions was assessed by uniaxial compression tests on cubic samples extracted from the RE walls, and the results were compared with those of an unstabilized and cement-based stabilized RE. Results indicated that using rice husk residue could enhance the compressive strength of RE, obtaining similar strength values to traditional cement-based stabilized RE. On the contrary, used cooking oil samples were characterized by a substantial reduction in compressive strength at ambient curing conditions. However, this negative effect was overcome when oven-induced drying was applied.