Rammed Earth Buildings Research Articles

Studies on the Ageing of Cement Stabilized Rammed Earth Material in Different Exposure Conditions.

This paper aims to test the deterioration of cement stabilized rammed earth and consider its characteristics during its lifespan in various exposure conditions. Both visual and mechanical properties were tested to determine the impact of long-term exposure to natural weather conditions. Cemented stabilized rammed earth is a variation of the traditional rammed earth building material which has been used since ancient history and is strengthened by the addition of stabilizers in the form of Portland cement. This article analyzes the long-term properties of wall panels made of this material, which were subjected to varying exposure conditions for five years. After this period, compression tests of specimens cut from panels stored in various environmental conditions were carried out. Based on the results and visual properties of the specimens, long-term changes in unconfined compressive strength were observed and primary durability attributes were described. Despite minimal visible wear to the external layers of the wall panels, the natural weather conditions proved to deteriorate material strength characteristics, especially on specimens with high cement content. No correlation between visual characteristics and compressive strength measures were found. The present study is vital in adequately describing cement stabilized rammed earth behavior in natural weather conditions typical of a humid continental climate.

Benefit of Unsaturated Soil Mechanics Approach on the Modeling of Early-Age Behavior of Rammed Earth Building.

Rammed earth has the potential to reduce the carbon footprint and limit the energy consumption in the building sector due to its sustainable characteristics. Still, its use is not generalized due to a lack of understanding of the material behavior, notably its sensitivity to water. The coupled hydro-mechanical behavior has been recently studied in the framework of unsaturated soil mechanics, using suction as the parameter to represent the hydric state. This dependency of the mechanical behavior on the hydric state leads to uncertainty of the drying period required to progress in the construction process. Notably, the drying period before building the next floor is unknown. To determine the drying period, thermo-hydro-mechanical coupled finite element method simulations were carried out on a single wall by using the unsaturated soil mechanics approach and safety criterion recommendations from the practical guide for rammed earth construction in France. It was determined that it takes significant time for the construction of additional floor both in ‘summer-like’ and ‘winter-like’ environmental conditions, whereas the walls were far away from the ultimate failure state. Thus the drying periods were overestimated. It was concluded that the safety criterion from the practical guide is very conservative and drying periods can be reduced without significantly compromising the safety factor.

Determination of the moisture diffusivity of rammed earth from transient capillary absorption moisture content profiles

The determination of the moisture diffusivity in the capillary range is studied for rammed earth building materials, using the X-ray method. To prevent liquefaction and expansion of these materials during the capillary absorption test, a brick wick and paper are added as lower sample parts and a confining sealing is utilised. Since the wick and paper bring about a composite case, the compatibility with the Boltzmann transformation must be redeveloped. It is found that the solution lies in adjusting the Boltzmann transformation through the equivalent height capturing the hydraulic impact of the wick and paper on the capillary absorption process.

Evaluation of seismic performance of rammed earth building and improvement solutions

The present study evaluates the performances of a rammed earth (RE) structure under seismic loading and its reinforcement by using finite element simulations. First, the pertinence of the numerical model was evaluated through the simulation of an experimental test conducted on a 0.5-scale house and presented in the literature. A full 3D model, based on solid elements, and a 3D surface model based on shell elements were conducted. The effects of interface stiffness on the natural frequencies and on the non-linear dynamic behavior were examined. It was found that the interfaces played an important role to well reproduce the experimental results. Reinforcement techniques, such as horizontal reinforced concrete belt beam at the top or/and the middle height, and the internal reinforced concrete columns were also simulated and their benefits under seismic loading were conducted. The results obtained showed that these reinforcements enhanced the seismic capacity of RE house. The Rayleigh damping, which has been rarely addressed in the rammed earth structures, was also investigated.

Research on the factors affecting the development of shrinkage cracks of rammed earth buildings

Rammed earth (RE) buildings have existed all over the world for thousands of years, and have gained increasing attention because of its sustainable advantages, however, the shrinkage cracks reduce its bearing capacity and seriously affect its durability and applicability. In this study, the shrinkage cracks test was carried out to investigate the effects of initial water content, proportion of sand and gravel, compaction degree, thickness and the additives (polypropylene fiber, cement and sodium silicate) of shrinkage cracks in RE buildings, ten groups of RE samples were prepared and dried outdoors to crack. Four quantitative parameters of geometrical structure of crack patterns were used to evaluate the development of cracks. The results show that the specimens cracking behavior and the geometrical structure of crack patterns are significantly influenced by these considered factors. The formation of crack can be accelerated with the increase of initial water content and thickness of specimen, while restricted with the increase of the compaction degree and the proportion of sand and gravel. Moreover, the addition of 1% polypropylene fiber, 10% cement and 0.5 volume ratio sodium silicate can significantly restrain the form and development of cracks. In RE construction, these factors should be considered comprehensively to prevent the harm caused by shrinkage cracks. Further works should be carried out to obtain the optimum dosage of the additives, which can benefit the construction of RE buildings in future.

Energy dissipation of rammed earth-timber joints under cyclic loading

Rammed earth-timber joints without enlarged ends have been used in rammed earth buildings for several hundreds of years. Due to the embedment nature, the joint has a certain degree of flexibility, allowing the floor and roof beams to slide without damaging the rammed earth, enabling dissipating energy during earthquakes. The energy dissipation mechanism of rammed earth-timber joint has not yet been fully understood. This study studied the energy dissipation characteristic of eight rammed earth-timber joint specimens via cyclic pull-out/push-in experiments, investigating the effects of compressive loading, embedment length, and surface roughness on joint performance. Results show that the joint stiffness under cyclic loading was reduced nonlinearly with the increase of pull-out displacement until the occurrence of slippage. The high vertical compression from the upper level, the deformability of timber frames, and the plasticity of rammed earth were found to be the primary energy dissipators. A linear frictional and nonlinear geotechnical hysteretic model, combining frictional and soil mechanics theories, was established to represent the joint behavior. In addition, a simplified multi-linear hysteretic model was developed for the same purpose. The predictions and the measurements had good agreement, suggesting that geotechnical methods should be employed to analyze the joint, maintaining the assumption that both the timber frame and the rammed earth are linear-elastic.

Experimental study on the capillary absorption characteristics of rammed earth

The capillary absorption test is redeveloped for rammed earth building materials. Since these materials liquefy and expand upon contact with water, the standard method must be modified to tackle this material evolution during the test. Firstly, a thin permeable wick and paper are applied as lower sample parts, to counter the liquefaction. It is shown that their influence on the resulting absorption properties is limited. In addition, a confining sealing is utilised against the expansion. It is shown that this confined way of testing offers crucial advantages as a result of the material remaining stable throughout the test.

Design Optimisation Strategies for Solid Rammed Earth Walls in Mediterranean Climates

The renewed attention paid to raw earth construction in recent decades is linked to its undoubted sustainability, cost-effectiveness, and low embodied energy. In Italy, the use of raw earth as a construction material is limited by the lack of a technical reference standard and is penalised by the current energy legislation for its massive behaviour. Research experiences, especially transoceanic, on highly performative contemporary buildings made with natural materials show that raw earth can be used, together with different types of reinforcements, to create safe, earthquake-resistant, and thermally efficient buildings. On the basis of experimental data of an innovative fibre-reinforced rammed earth material, energy analyses are developed on a rammed earth building designed for a Mediterranean climate. The paper focuses on the influences that different design solutions, inspired by traditional bioclimatic strategies, and various optimised wall constructions have in the improvement of the energy performance of the abovementioned building. These considerations are furthermore compared with different design criteria aiming at minimising embodied carbon in base material choice, costs, and discomfort hours. Results have shown the effectiveness of using the combination of massive rammed earth walls, night cross ventilation, and overhangs for the reduction of energy demand for space cooling and the improvement of wellbeing. Finally, the parametric analysis of thermal insulation has highlighted the economic, environmental, and thermophysical optimal solutions for the rammed earth envelope.

Material characterization and structural response under earthquake loads of hakka rammed earth buildings

Hakka Tulou are rammed earth buildings that have survived material aging, natural weathering and earthquakes for hundreds of years. Previous paper has reported our observations and findings from nondestructive evaluations in field with focus on the integrity of the rammed earth outer walls and inner timber structures as well as the thermal comfort of living in these buildings. This paper presents the structural response of Tulou buildings under earthquake loads using material data from field and employing finite element (FE) analysis program. The material characterization included scanning electron microscopy and compression strength/modulus of rammed earth samples and wall reinforcements, revealing their high strength and durability. The FE analyses were conducted on unreinforced Huanji Tulou as per the simplified lateral force analysis procedure defined by the Code ASCE-7 under three types of wall conditions: 1) unreinforced rammed earth outer wall only, 2) reinforced rammed earth outer wall without inner wooden structures, and 3) unreinforced rammed earth outer wall with inner wooden structures. The FE modeling revealed that the existing large crack in the outer earth wall of Huanji Tulou would not have developed under a strong earthquake load if the earth walls were reinforced. Furthermore, the high volume rammed earth wall integrated with inner timber structures would have offered the building unique earthquake resistance.

Using Raw Earth Construction Systems on Contemporary Buildings: Reflections on Sustainability and Thermal Efficiency

Although the existence of building energy efficiency policies for several years, studies show that up to 74% of the participant consider their house uncomfortable. European policies favored construction solutions focused on insulating materials rather than other solutions which traditionally were used and proved to be effective. Construction system that uses earth as construction material showed for centuries that it can offer high levels of thermal comfort in a passive way, with a highly sustainable and quasi-neutral environmental impact. With this paper, a study on the thermal performance of three contemporany rammed earth buildings is presented. The aim is to analyze thermal comfort over a critical period of time. It is expected that earth construction proves to be a good choice, creating a sustainable and better integration with the local environment, with almost zero energy incorporation, promoting the local work craftmen and with a construction range price below the common construction systems.

Experimental assessment of freezing-thawing resistance of rammed earth buildings

The use of earth as a building material is worldwide encouraged thanks to its low environmental impact and its high hygrothermal performances. In wet and cold regions, the durability of earthen constructions is a major preoccupation because of water attack and frost damage. The variety of raw earth, compaction method and exposition to water increases the complexity to agree on a representative testing protocol to assess the frost resistance of earthen buildings. In this context, various molding and testing configurations are proposed to evaluate the impact of repeated freezing and thawing (F-T) cycles on earthen compacted samples. The experimental protocol is adapted from ASTM D560 standard which recommends 12 F-T cycles of −23 °C/+23 °C. A series of cylindrical samples were made from two types of earths (unstabilized and cement-stabilized) compacted following two compaction methods (dynamically and statically). They were experimentally investigated under two kinds of freezing-thawing cycles that can affect earthen buildings. One with water absorption aimed at reproducing the combined effect of capillary rise and frost action. The other one consisted in testing samples at their manufacture saturation ratio in a moist environment in order to analyze the frost resistance at early age. After each cycle, frost damage was evaluated through the amount of mass lost by scaling, as well as water content and the volume changes. The results indicated that surface scaling affected all samples exposed to freezing and thawing, even if cement stabilization upgraded frost resistance. The impact of the freeze-thaw cycles on water uptake within the samples was analyzed, and some considerations were given in order to develop a dedicated test to assess freezing-thawing resistance of earthen building materials in milder conditions.

Seismic performance test of rammed earth wall with different structural columns

Rammed earth wall load-bearing dwellings are widely distributed in western China. Rammed earth has the advantages of warm in winter and cool in summer, and it is a kind of sustainable construction material. In recent years, in previous earthquakes, the collapse of rammed earth buildings is serious, resulting in huge losses of personnel and property. To improve the seismic performance of rammed earth buildings and retain the characteristics of local buildings, a reinforcement measure with additional structural columns is proposed in this article. Three kinds of structural columns are designed, which are cast-in-place concrete, square steel tube, and concrete-filled square steel tube core column. Through the quasi-static experimental study on the rammed earth wall, the effects of different structural columns on the failure shape, bearing capacity, deformation capacity, and energy dissipation capacity of the wall are compared. The test results show that adding structural columns on both sides of the wall can effectively restrain the rammed earth wall, restrain its brittle failure, significantly improve the energy dissipation capacity of the wall, and obviously improve the seismic performance of the wall. This measure is applicable to rammed earth buildings and provides theoretical support for improving the seismic performance of traditional dwellings.

TOOLS FOR LOCAL GOVERNMENTS TO PROTECT AND FAVOR SUSTAINABLE CONSERVATION AND (RE-) USE OF EARTHEN HERITAGE IN AUVERGNE RHÔNE ALPES REGION, FRANCE

Abstract. In 2018, a guide to the attention of the local governments has been published by CRAterre, entitled « Guide à destination des collectivités territoriales pour la réhabilitation et la valorisation du bâti en pisé ». It is one of the main results of a four years projects funded by the Auvergne-Rhône-Alpes Region on traditional rammed earth buildings that included researches on the geographical repartition, the variety of typologies, the state of conservation and the potential for sustainable development in the Region. It contains an organised series of recommendations and tools that could be implemented for the identification and revitalisation of rammed-earth vernacular heritage at a local level. These have been prepared as a response to the overall assessment made which revealed high potential and responsibility on the part of local governments to protect this heritage, promote continuity of its uses and to disseminate good rehabilitation practices. This paper presents the participative approach adopted for both the research process and the elaboration of the guide. That resulted in developing some original contents to the attention of the variety of groups of stakeholders. These were tested in the field and gradually improved taking into account the interactions with the local politicians and actors. The paper also covers a reflection on further dissemination of the knowledge developed for applications at a wider scale.

TULOU: THE RAMMED EARTH DWELLINGS OF FUJIAN (CHINA). FUNCTIONAL, TYPOLOGICAL AND CONSTRUCTIVE FEATURES

Abstract. This research is focused on different aspects concerning two types of Tulou: Minnan and Hakka Tulou. Through the analysis of eight case studies, we managed to highlight the relation between typological-functional features and constructive ones aiming to offer a more orderly analysis of distinct models, divided into two substantially different families. Future studies will further analyse the knowledge of these rammed earth buildings by studying the phases of the construction site, conducting architectural surveys on the most important details and investigating the mechanical behaviour of both types. The future goal is the creation of a “Manuale del recupero dei Tulou” (Manual on Tulou restoration) in order to provide a guide for restoration and spread the knowledge about original materials and techniques applied in the construction of these unique rammed earth architectures. The research, which is currently ongoing, has been carried out by the Architecture Department of Roma Tre University in cooperation with Fuzhou University.

Influence of Traditional Building Practices in Seismic Vulnerability of Bhutanese Vernacular Rammed Earth Architecture

ABSTRACT Rammed earth architecture is still widespread and alive in Bhutan, especially in rural villages, where dwellings are built by the local community. The country recently suffered two intense earthquakes that put traditional architecture at risk. Rammed earth building techniques show high seismic vulnerability by nature, whose degree strongly depends on good building practices. Within the framework of SATREPS, a research project led by Nagoya University in collaboration with the Royal Government of Bhutan and the Politecnico di Torino, this article aims to investigate the role of local building practice in fostering the most frequently occurring seismic failure mechanisms in unreinforced masonry such as rammed earth. Those mechanisms have been cross-checked with damage-assessment-related studies carried out by the Bhutanese government. Traditional building practices, potential weaknesses, and the influence on seismic failure mechanisms have been analyzed through definite parameters. Outcomes have been verified through a full-scale static test conducted on a rammed earth mock-up building.

Evolving Vernacular: Reinventing Rammed Earth in the Context of Twenty-First Century Seismic Regulation

The vernacular architecture of the Auvergne-Rhône-Alpes region in southeast France is dominated by unstabilized rammed earth buildings. Despite a plentiful source of raw material, cultural anchorage, and low carbon footprint, the use of rammed earth in new building projects is severely constrained by contemporary building codes and norms which have been developed around industrial building products, to the detriment of natural building materials. In particular, stringent seismic regulations have rendered monolithic earth masonry difficult to justify structurally. The Maison Pour Tous design/build project identifies and demonstrates a replicable path for new rammed earth buildings within the existing regulatory framework. While cost remains a challenge, the successful realization of the Maison Pour Tous illustrates that rammed earth is no longer relegated to the region's past.

Assessment of Heritage Rammed-Earth Buildings: Alcázar of King Don Pedro I, Spain

Abstract The conservation and maintenance of earthen buildings is crucial, especially when dealing with heritage sites. This normally involves considerable effort in preliminary studies, which must...

Effect of adding insulation on the energy performances of rammed earth buildings in hot and arid climates

In a world context focused on energy efficiency and sustainable construction, returning to the use of raw earth in construction constitutes a good alternative to concrete construction, a system more energy consuming and yet more used nowadays. This return is justified by the excellent energy performance and the high level of thermal comfort provided by earth constructions in different climates. In cold climates, adding an insulation on earth walls has proven to be effective in improving their thermal performances. However, the influence of adding an insulation on the energy performance of rammed earth buildings in hot and arid climates remains to this day little explored. The present work comes in this order of ideas; it is based on a comparative study of the energetic performances of a mud building before and after the addition of the insulation. In order to compare between their performances, we have performed a simulation of the thermal behaviour of each by the dynamic thermal simulation software Design Builder.

An overview on contemporary rammed earth buildings: technological advances in production, construction and material characterization

Raw earth is a traditional material used worldwide in vernacular architectures. For its wide availability, recyclability and low embodied energy in its life cycle, earth is acknowledged as one of the most environmentally sustainable material. Earth construction diffusion has been slowed by the lack of broadly accepted standards. Due to it, earth has been used as an artisanal material or adapted to existing technologies in combination with high embodied energy materials as steel, concrete and EPS or PU insulations (as in rammed earth technique, from now on RE). Aim of the research is to propose an innovative RE constructive technology, more coherent with the sustainable features of the base material, which can reach the high performances and the quality target required by the constructions sector using a low-tech prefabrication process. Prefabrication of RE elements can also reduce the construction times and the risks of technological faults, enhancing the quality of the entire building. The basic idea is to create manageable and transportable rammed earth panels with superior mechanical and thermal performances. The prefabrication under controlled conditions ensures a high-quality product which can be combined, on site, with a reinforcing timber structure with anti-seismic function. A characterization campaign on different local soils has been performed in order to implement the desired RE elements. The soils have been analysed with a set of geotechnical tests and qualitative assessments in order to detect their suitability for constructions. Once a suitable soil has been identified, a physical and / or chemical stabilization is needed to improve the physical features, mechanical characteristics and thermal properties of the natural soil. In the last section of the paper, the first results on natural local soil and engineered soil (an optimized mix of soil, sand and gravel) are presented and compared to identify a suitable material for the RE panel.

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.