Rammed Earth Research Articles

Experimental testing of the in-plane behavior of bearing modern rammed earth walls

With the introduction of the modern rammed earth technique, a large number of modern rammed earth buildings were constructed in China Mainland. China has a vast territory, which faces the Circum-Pacific seismic belt on the east and the Eurasian seismic belt on the south; earthquake has constantly threatened the safety of people’s lives and property. Consequently, it is necessary to probe in the seismic performance of rammed earth buildings. Two un-stabilized rammed earth specimens, one un-stabilized rammed earth reinforced with geogrid sheets’ specimens, and four stabilized rammed earth specimens were built for obtaining a better insight on the behavior of un-stabilized rammed earth/stabilized rammed earth walls under cyclic in-plane loads. Testing results are discussed in terms of failure mode, shear capacity, hysteretic curve, stiffness degradation, and total energy dissipation to provide comparisons of the seismic performance between un-stabilized rammed earth and stabilized rammed earth specimens. Different failure modes indicated that the cohesion between particles and the bond strength between layers are the two key parameters for the shear capacity of rammed earth buildings. It is also demonstrated that stabilized rammed earth specimens have higher shear and energy dissipation capacity but weaker deformation capacity than un-stabilized rammed earth.

Assessment of out-of-plane behavior of rammed earth walls by pull-down tests

ABSTRACTThis article reports pull-down tests performed on rammed earth construction in Bhutan. The pull–down specimens involved an old rammed earth building component as well as a newly prepared rammed earth wall. Both the wall specimens were tested in out-of-plane direction. Theoretical rigid body formulation and finite element (FE) models were developed to predict the response of the rammed earth structures under out-of-plane loading. The validated FE model was further extended to parametric study of material and physical characteristics of rammed earth construction and their effect on critical response quantities. The change in elastic modulus showed effect in the pre-cracking phase of the wall. Density of rammed earth on the other hand affected the post-peak response of the rammed earth wall. Furthermore, an increase in the physical characteristics, namely, the thickness of wall and the vertical superimposed load on top of the wall, enhanced the rocking resistance capacity of the out-of-plane loaded rammed earth walls.

Using DEM to Simulate the Behavior of Masonry and Rammed Earth Structures

Using DEM to Simulate the Behavior of Masonry and Rammed Earth Structures

Seismic Behavior of Rammed Earth Walls with Precast Concrete Tie Columns

Rammed earth (RE) constructions are widespread in underdeveloped rural areas in developing countries. However, these RE constructions are often susceptible to earthquake damage due to their poor seismic performance. Precast concrete tie columns and ring beam (tie bars) were proposed to improve the seismic behavior of RE constructions. Four RE walls, including a traditional RE wall and three RE walls with precast concrete tie columns and ring beam (tie bars), were tested under reversed cyclic loading, and the seismic behavior of these tested specimens was evaluated in terms of failure pattern, energy dissipation, displacement ductility, and stiffness degradation. The results showed that a significant increase of the load‐bearing and deformation capacity could be achieved with the application of precast concrete tie columns in combination with RE. The load‐bearing capacity and deformation capacity of traditional RE wall were increased by an average of 113% and 417%, respectively. These test results could provide reference to the design and construction of the environmental‐friendly structures in rural areas.

Shear Parameters of Rammed Earth Material: Results from Different Approaches

Rammed earth (RE) is a construction material which is manufactured by compacting the soil in a formwork, in different layers. Several recent studies have investigated this material. The seismic performance of RE buildings is an important topic which needs to be carefully investigated. The complex numerical model seems a performant approach to investigate the seismic performance of a whole building. To correctly establish the model, the shear parameters of the material, which are the cohesion and the friction angle, should be identified. This paper first presents experimental studies on the shear parameters of RE through the direct shear tests, at two different scales. The differences of the results at different scales are analyzed. Then, the obtained experimental values are used in a numerical model to simulate the shear behavior of RE walls which are loaded by a constant vertical stress and pushed horizontally on the top. From the obtained results, the values for numerical models are recommended.

Cyclic Behavior of Confined Cement‐Stabilized Rammed Earth Walls

Rammed earth is widely utilized in both developed and developing countries due to its low embodied energy and good natural moisture buffering of indoor environments. However, its application in seismic active regions was limited owing to its intrinsically low resistance to dynamic actions. This paper presents the test results of four cement‐stabilized rammed earth walls with confining tie‐column elements under cyclic loading, aiming at assessing the cyclic behavior of proposed rammed earth walls with confining tie‐column elements. The test results revealed that the proposed confining tie‐column elements could significantly improve the cyclic behavior of cement‐stabilized rammed earth wall, exhibiting good strength and ductility.

Measured and simulated thermal behaviour in rammed earth houses in a hot-arid climate. Part A: Structural behaviour

Heating and cooling of residential buildings consumes around ten percent of the world's energy. One approach for reducing these costs is to exploit the high thermal mass of sustainable building materials, for example rammed earth (RE), for intelligent solar passive design. However, there is a lack of scientific evidence about the thermal performance of RE houses in real-world settings.This research investigated to what extent thermal performance in unconditioned RE structures in rural Australia can be captured by current accreditation software. Two custom-designed houses were built in the hot-arid city of Kalgoorlie-Boulder, Western Australia: one comprising traditional solid cement-stabilised rammed earth walls (RE) and the other walls with an insulating polystyrene core (iRE). Otherwise the houses were identical in orientation and design. The houses were instrumented to monitor indoor temperature and humidity conditions prior to and during occupancy. Results were compared to those simulated using cutting-edge assessment software BERS Pro (v4.3) as an example of that used for energy efficiency accreditation in Australia. This first paper in this series discusses the houses' construction and instrumentation and results obtained during the unoccupied period, i.e. those purely demonstrative of the structure's thermal performance. A second paper in the series presents data gathered during occupancy, to contrast occupant thermal comfort with that predicted numerically.Measured data showed that both houses performed nominally-identically: the houses did not receive any relative benefit from including iRE. Simulated data was also similar per house. However, measured performance did not match that simulated: simulated rooms had poorer thermal stability and lag and, consequently, exaggerated internal temperature variations. Collected data has been made publicly available for future analyses.

Assessing the Rebound Hammer Test for Rammed Earth Material

Rammed-earth (RE) is a construction material manufactured from the soil. The soil is compacted at its optimum water content, inside a formwork to build a monolithic wall. RE material is attracting renewed interest throughout the world thanks to its sustainable characteristics: low embodied energy, substantial thermal inertia, and natural regulator of moisture; on the other hand, the existing historic RE buildings is still numerous. This is why several research studies have been carried out recently to study different aspects of this material. However, few investigations have been carried out to explore the possibility of applying the nondestructive techniques on RE walls. This paper presents an assessment of the well-known rebound hammer test on RE walls. The calibration curves of the rebound hammer test have been established for conventional concrete where the rebound number is more than 20. For RE material with lower compressive strengths, a new calibration curve must be established. In the present study, two soils were used and different homogenized specimens with different dry densities were manufactured and tested, to plot a general calibration curve. Then, this calibration curve was applied to RE specimens; different results at different positions in an earthen layer were observed, due to the inhomogeneity of the material. The final results showed an acceptable accuracy of the calibration curve in the prediction of the compressive strength of RE material.

Strength characterisation of soil-based construction materials

Rammed earth (RE) is a venerable construction technique, gaining attention today owing to its environmental and sustainable qualities. A key obstacle to its wider adoption is a lack of strength characterisation methods to aid in design and conservation. Research over the past decade has demonstrated that suction is the key mechanism behind strength and strength gain. As suction changes with the building's environment, being able to predict strength changes with suction is essential for practitioners and conservators alike. This paper presents a method for predicting RE strengths based on the extended Mohr–Coulomb (EMC) framework. Construction of an EMC failure envelope in the residual suction range is discussed and the use of a planar envelope is justified. Unconfined compression and indirect tensile tests on two RE soils are used to construct this envelope and methods to predict strengths from it are derived. Excellent agreement between measured and predicted strengths is also found for available data in the literature. Simplifications are identified to adapt the developed technique to suit RE practice and a suitable experimental procedure is outlined. Finally, the revised experimental procedure is employed at an existing RE construction facility to successfully predict strengths of a compacted Californian sandy loam.

Structural behaviour of unstabilized rammed earth constructions submitted to hygroscopic conditions

Rammed earth constructions exhibit strength and deformation properties that evolve as a function of the relative humidity of the air in contact with the walls. This effect must be considered in the structural design of the construction. This work studies, through finite element simulation, the impact of the hygroscopic transfers through the wall on the structural response of a classical two-storey rammed earth building. The coupling between the mechanical and the hygroscopic behaviour is considered by the concept of effective stress for unsaturated soils, in order to reproduce the effect of suction on the strength, the stiffness and the volumetric variations of the rammed earth. The simulations show classical deformation of the structure due to distributed load on the floors while the hygroscopic changes in the rammed earth (essentially drying) induce additional displacements of the walls that remain in a very acceptable range. Finally, an extreme case is envisaged in which the loads on the floors are increased excessively in order to study the plastic response of the wall.

Measured and simulated thermal behaviour in rammed earth houses in a hot-arid climate. Part B: Comfort

Heating and cooling of residential buildings consumes around ten percent of the world's energy. One approach for reducing these costs is solar passive design using building materials with high thermal mass such as Rammed Earth (RE). Several studies have examined the performance of small RE structures or individual rooms within RE dwellings and have demonstrated the material's capacity to provide comfortable internal conditions passively. However, there is a lack of scientific evidence about the performance of full RE houses in real-world settings spanning several seasons. This research investigated the thermal performance of RE structures prior to occupancy and over the course of an occupied year. Two custom-designed houses were built in the hot-arid city of Kalgoorlie-Boulder, Western Australia: one with traditional solid RE walls and the other with walls with an insulating polystyrene core (iRE). Otherwise the houses were identical in orientation and design.This study is presented in two Parts. Part A examined the houses' performance without occupants: This Part examines their occupied behaviour in terms of the occupants' thermal comfort. Comfort was examined using qualitative and quantitative data from sensor measurements as well as occupant surveys and simulated results using state-of-the-art assessment software BERS Pro. Comfort scores for measured and simulated data were determined using rules built into BERS Pro's engine Chenath and a modified version of the ANSI/ASHRAE Standard 55-2010 SET* method.Real-world thermal comfort of both houses outperformed their simulated behaviours: occupants reported comfortable conditions throughout Summer (outdoor maxima 45°C) and Winter (minima 1°C) with no artificial cooling and with minimal heating. The Chenath and SET* methods agreed with comfort performance in Summer but scored Winter performance poorly. Similarly, simulations predicted poor performance in Winter. Consequently, predicted energy demands due to heating were likely far higher than those needed in reality. This paper therefore argues from measured evidence of RE and iRE houses for the suitability of RE as a sustainable building material able to curb domestic energy demands. Collected data has been made publicly available for future analyses.

Characterization of a Compatible Low Cost Strengthening Solution Based on the TRM Technique for Rammed Earth

Rammed earth constructions are widely found worldwide, but they are endangered by their recognised high seismic vulnerability. As compatible and affordable reinforcement approaches are important requirements for these constructions, a strengthening solution based on low cost textile reinforced mortars (LC-TRM) is proposed here, within the framework of a large research project. This paper presents the results of an experimental program aimed at characterising low cost meshes available in the market (glass fibre, plastic, metallic and nylon) and at assessing possible mortars (unstabilised earth, stabilised earth, commercial earth and cement-based) capable of integrating the LC-TRM strengthening system. In general, the results obtained seem to indicate that the glass fibre meshes and the earth mortar are good options.

Late Medieval Castles Built with Rammed Earth in Castile, Spain

Late Medieval Castles Built with Rammed Earth in Castile, Spain

A multi-criteria study on rammed earth for low carbon buildings using a novel ANP-GA approach

Nowadays, the growth of energy consumption in buildings is an important topic. Rammed earth (RE) structures have attracted the attention of engineers and contractors in recent years due to their advantages such as sustainability, availability and low embodied energy content. These advantages result in less energy consumption in the life cycle of the RE structures. However, there is a lack of research on the mixture composition of RE materials containing admixtures. This research introduced integrated analytic network process (ANP) and genetic algorithm (GA) methodology to select the optimum mixture of RE material containing cement, expanded polystyrene(EPS), and phase change materials(PCM) with different moisture content. The five criteria for evaluations were cost, building weight, carbon footprint, mechanical strength and thermal performance. Thermal and mechanical experiments were performed on the different mixtures of RE. Based on the results of the ANP-GA approach, a RE mixture with mass ratios of 78% soil, 12% moisture, and 10% cement was found to be the most suitable RE mixture. ANP-GA eliminated EPS and PCM due to the low strength of EPS-RE and the high cost of PCM; however, they made RE perform well in thermal characteristic. This proposed the model can be used to select the ideal mixture of other engineering materials.

Assessing the in-plane seismic performance of rammed earth walls by using horizontal loading tests

Abstract Rammed earth (RE) construction is attracting renewed interest throughout the world thanks to its sustainable characteristics: very low embodied energy, advantageous living comfort due to substantial thermal inertia, good natural moisture buffering and an attractive appearance. This is why several studies have recently been conducted to investigate RE. However, there have not yet been sufficient studies on the seismic performance of RE buildings. This paper presents an experimental study on the static nonlinear pushover method and its application to the seismic performance of RE structures. Several walls with different height/length ratios were built and tested to obtain nonlinear shear force–displacement curves. By transposing these shear force-displacement curves to an acceleration–displacement system and using the standard spectra presented in Eurocode 8, the performance points were determined, making it possible to assess the seismic performance of the walls studied in different conditions (seismicity zones and soil types).

Life cycle analysis of environmental impact vs. durability of stabilised rammed earth

Rammed earth (RE) has enjoyed a revival in recent decades due to the increasing awareness of environmental issues surrounding the building industry. Although RE in its traditional form is deemed a highly environmentally-friendly material, the same cannot be said for its modern stabilised counterpart. Comprehensive experimental procedures exist to estimate mechanical strength properties of stabilised RE (SRE). However, tests for material durability are far less common. Engineers and practitioners therefore assume that strength and durability are interchangeable properties, i.e. the stronger the material, the more durable. Inflated strengths are recommended to ensure adequate durability, leading to high environmental costs through excessive use of stabilisers.This paper rates the relevance of two acknowledged durability tests (accelerated erosion due to sprayed water and mass loss due to wire brushing) and relates outcomes to the strength and the environmental impact of several SRE mixes. The environmental impact of each mix was estimated using attributional and consequential life cycle assessment (LCA) approaches as well as an assessment of cumulative energy demand. Results demonstrated that it is possible to have durable SRE mixes without paying the cost of using environmentally-expensive stabilisers.

Weathering’s beneficial effect on waste-stabilised rammed earth: a chemical and microstructural investigation

The most common method to improve the mechanical properties of a rammed earth mix is to add chemical stabilisers like cement and/or lime. Varying the stabiliser type will affect strength gain but also the environmental impact. In this paper, the effect of wetting-drying cycles on the long-term unconfined compressive strength of stabilised rammed earth (SRE) mixes was investigated through the chemical characterisation of the soil components and microstructural analyses. The mixes were stabilised using different agents characterised by distinct environmental impacts, such as cement, calcium carbide residue and fly ash. These last two are considered waste materials, significantly affecting their use’s associated environmental implications. The results of this experimental campaign support others in this series of work and showed an improvement of the mechanical properties after cyclic wetting-drying due to the formation of new hydration products which bound particles together. The use of waste materials proved to be an effective solution to stabilise RE.

Reduction of rammed earth's hygroscopic performance under stabilisation: an experimental investigation

One of the acknowledged qualities of rammed earth (RE) is its moisture buffering capacity. Recently, stabilisation of RE has become a common practice to improve the mechanical resistance but very little is known about the effect that stabilisation has on hygroscopic properties. The present study aims to fill this gap by understanding the role that stabilisation plays in the buffering and sorption capacity of RE. The use of alternative stabilisers such as fly ash and calcium carbide residue and a comparison with traditional unstabilised RE (URE) have also been investigated. Moreover, the effect of weathering, simulated by cyclic wetting-drying, on hygroscopic performance has been analysed. Moisture Buffer Value (MBV) testing, moisture and nitrogen adsorption-desorption isotherms and mercury intrusion porosimetry were performed on stabilised samples to examine microstructural phenomena responsible for behavioural changes. URE was confirmed to be a good-to-excellent passive air conditioner according to the MBV scale but its performance seemed to be highly influenced by the soil particle size distribution and mineralogy. Based on the experimental outcomes of the mixtures investigated, stabilisation had a detrimental effect on the moisture buffer capacity of rammed earth, likely due to the inhibition of the physico-chemical interactivity between moisture and clays. Weathering had a variable effect on the buffering capacity, depending on the availability of unreacted particles in the matrix.

A Collaborative Engineering and Archaeology Project to Investigate Decay in Historic Rammed Earth Structures: The Case of the Medieval Preceptory in Ambel

ABSTRACTThis study assesses the structural vulnerability of part of a later medieval earthen building at Ambel (near Zaragoza, Spain), once a preceptory or monastic house belonging to the Military Orders. An inspection of its morphology and materials coupled with the results of an extensive campaign of static monitoring reveals marked structural inhomogeneities, the product of more than a thousand years of construction, failure, and repair from the 10th century to the present day. Building materials are inappropriately juxtaposed, there are discontinuities between construction phases and fundamental concerns remain over the long-term stability of the structure. The current condition of the structure is mainly influenced by structural discontinuities introduced at the time of construction, the unintended consequences of repair and modification and the material decay that has affected the base of the rammed earth walls. The overall findings of the static monitoring show that there is no related damage, variations in crack widths are related to the building seasonal cycle. While static analysis is an essential prerequisite before a suitable maintenance program can be fully defined, this study argues that no evaluation of the structural behavior of any historic building can afford to ignore its archaeological “biography” of modification and repair.

Reliability analysis of rammed earth structures

Rammed earth (RE) structures are widely used for more sustainable and environment-friendly buildings. Due to lack of design standards, the engineering decisions often rely on rule-of-thumb method which may lead to quite conservative or unsafe designs. In this study, load and resistance parameters were treated as random variables in reliability analysis. The reliability index and failure probability of RE structures were evaluated using First-Order-Reliability-Method (FORM) and then compared with Second-Order-Reliability-Method (SORM) and Monte Carlo Sampling method. The analysis was performed based on the different a) load combinations, b) wall geometry, c) material type (unstabilized or cement stabilized) and d) mechanical properties of the materials. Based on the results, the RE wall under moderate loading conditions require smaller wall thickness than recommended wall thickness by various guidelines such as New Mexico-USA, New Zealand and Zimbabwe Codes. However, larger wall thickness is needed under severe loadings conditions, especially when unstabilized materials are used. The compressive strength of unstabilized materials under severe loading conditions should be more than minimum recommended. The sensitivity analysis was performed by calculating different importance and sensitivity vectors. The results show that the compressive strength and the environmental loads factors are the most important random variables that contribute to reliability of the structures. The recommended wall thickness and compressive strength for different conditions are presented.