Evaluating shear test methods for stabilised rammed earth

Géotechnique, 59(5): 487- 490, 2009

Rammed earth is a manufactured material comprising sand, gravel and clay, which is compacted between forms to build walls. Primarily a historic method of construction, it is now receiving considerable interest worldwide owing to its zero reliance on materials such as cement, and its potential for recycling. Despite its longevity, the source of its shear strength is poorly understood. This paper presents initial laboratory test results that point to the main source of strength in rammed earth being suction, and indicating that recent advances in unsaturated soil mechanics may also be applied to this material.

Rammed Earth Construction, 2015

There is currently little scientific understanding of stabilised rammed earth (RE) and the relationship between water-cement ratio and compressive strength. For traditional (unstabilised) RE materials, it is standard practice to compact the soil mix at its optimum water content to achieve maximum dry density and hence maximum strength. However, this may not also apply to cement-stabilised rammed earth (CSRE). A recent investigation (Beckett and Ciancio 2014) showed that CSRE samples stabilised with 5% cement and compacted at a water content lower than optimum performed better than samples compacted at optimum or higher. This seems to be in agreement with the well-known effect in concrete materials, according to which the lower the water-cement ratio, the stronger the cementitious products hence the higher the compressive strength. This paper investigates the effect of water cement ratio in CSRE samples. Results of an experimental programme are presented and used to discuss the appropriateness of the water-cement ratio for RE materials.

Rammed earth is an ancient building technique used in many regions of the world. Due to the low embodied energy of the material and diminished transportation costs, rammed earth offers an economical and sustainable alternative to concrete. Along with other advantages like sustainable construction, architectural quality & flexibility, contribution to building health and performance, ease & speed of construction etc. The main weakness of earth as a building material lies in its low resistance to water. Overhanging eaves and verandas help considerably, but tropical rains of any intensity can damage unprotected walls. Because of the clay fraction, which is necessary for cohesion, walls built of unstabilised soil will swell on taking up water and shrink on drying. This may lead to severe cracking and difficulty in getting protective renderings to adhere to the wall. There are some issues which needs to be addressed like shrinkage, proper soil selection, low compressive strength, cracking, durability aspects etc for rammed earth construction. From the available literatures and research works done earlier, it is evident that one way to address these problems is to stabilize rammed earth with cement.

Archives of Civil Engineering, 2015

Currently, a worldwide dynamic rise of interest in using soil as a construction material can be observed. This trend is evident in the rapid rise of the amount of standards that deal with soil techniques. In 2012 the number of standards was larger by one third than five years prior. To create a full standardization of the rammed earth technique it is necessary to take into account the diversity of used soil and stabilizing additives. The proportion of the components, the process of element production and the research methods must also be made uniform. The article describes the results of research on the compressive strength of rammed earth samples that differed from each other with regards to the type of loam used for the mixture and the amount of the stabilizer. The stabilizer used was Portland cement CEM I 42.5R. The research and the analysis of the results were based on foreign publications, the New Zealand standard NZS 4298:1998, the American Standard NMAC14.7.4 and archival Pol...

Australian Journal of Civil Engineering

Cement-stabilised rammed earth (CSRE) is a popular building material in Australia due to its natural aesthetic, good thermal properties and environmental appeal. However, little work has been done investigating the effect of long term exposure to environmental conditions on its durability. This paper presents a case study investigating the aged properties of material obtained from a 32-year old CSRE wall in Perth, WA. Core samples were obtained for unconfined compressive strength (UCS) testing and compared to results found for 28-day old specimens, manufactured using the same material and nominal compaction regime, to investigate changes in material strength over time. Sample wall sections were also obtained to determine material volume losses due to erosion. Results found for 32-year and 28-day old material are compared taking into account local climate conditions to comment on the suitability of current laboratory methods for predicting degradation of CSRE materials. Loss of strength due to exposure is found to be significant in this study. This result suggests that, when designing for the longevity of exposed CSRE materials, aging strength is an important factor that should not be neglected.

Construction and Building Materials, 2020

h i g h l i g h t s Shear strength of rammed earth is inadequately explored. Examined the shear behaviour of cement stabilised rammed earth (CSRE) under tri-axial state of stress. Shear strength parameters and Mohr-Coulomb failure envelopes were generated. Cement content influenced the shear strength and cohesion of CSRE in both dry and wet conditions.

Procedia Materials Science, 2014

Unstabilised rammed earth (RE) is the name given to both a construction method and a material that has been used by Man for thousands of years. Recently, it has received renewed interest as the desire for sustainable construction methods has increased, as it commonly uses subsoil from the construction site, hence reducing waste and transport costs. It has been established that the addition of stabilisers, such as cement or lime, increases the ultimate compressive strength (UCS) of RE, while the addition of fibrous material, such as straw or wool, has been shown to improve flexural strength. This paper describes experimental work investigating the fracture properties of RE, an area in which little research has been conducted to date, despite the brittleness of most variants of these materials. The effect of both stabilisation and fibre reinforcement are reported here from samples with 0 -12% by mass of cement and different amounts (0%, 1%, 2% by mass) of waste fibres. Fracture energies were determined using a modified wedge splitting test (WST) and results are presented that demonstrate the clear effect of fibrous reinforcement on specific fracture energy.

The rammed earth technique has a significant presence in the earthen built heritage, where was used to build from simple dwellings to fortresses. However, the high vulnerability of rammed earth construction to decay agents and to seismic events puts at risk their further existence and the lives of millions of people. With respect to the seismic behaviour of rammed earth walls, the understanding and modelling of their shear behaviour are topics rarely approached in literature. Nevertheless, these topics are of significant importance in the preservation and strengthening of rammed earth constructions. This paper presents experimental and numerical work where the shear behaviour of unstabilised rammed earth is analysed. The experimental program consisted in the testing of several unstabilised rammed earth wallets subject to diagonal compression, which allowed a better understanding of the shear behaviour of unstabilised rammed earth. The numerical work consists of the modelling, of the previous tests, using the finite element method and by considering both the macroand micro-modelling approaches. In general, the numerical models showed a good agreement with the experimental results.

Civil Engineering and Architecture, 2023

The world's willingness to reduce the ecological footprint of construction materials is the main engine of the development and reuse of earth-based materials. With its availability, low cost, and simplicity of implementation, the rammed earth material presents a good alternative for ecological construction. However, this material remains less resistant than conventional construction materials, especially cement-based ones. To enhance the mechanical characteristics of rammed earth, several stabilization and reinforcement techniques were adopted. Among these techniques, the use of natural fibers shows an increasing trend. This review is based on studies carried out on the reinforcement of rammed earth with natural fibers. The types of fibers used, their treatment methods, and their physical and mechanical properties are presented. The impact of natural fiber reinforcement on the physical and mechanical properties of rammed earth is also reviewed and discussed. The results of the studies carried out, prove the effectiveness of the fiber reinforcement technique. Indeed, an increase in the compressive, flexural, and tensile strengths of the rammed earth was reported. This improvement depends on the type of fibers used, their contents, and their dimensions. At the end of the study, perspectives for future research are given, especially regarding the durability of the reinforced rammed earth and the impact of the fiber reinforcement on its hygrothermal properties. To improve the adhesion strength between the fibers and the earth matrix, the use of chemically treated fibers for reinforcement is suggested.

2011

Rammed earth is a sustainable construction material, especially in remote areas where utilising the locally available soil means reduction of costs and environmental impact of construction. Before the soil could be used in construction, testing is required to determine whether it is suitable for rammed earth. Past research studies and current earth building technical documents provide some guidelines for the suitability of soils for rammed earth. Nevertheless, these guidelines are sometimes broad and vague making assessment of the soil difficult. This paper shows the limits of the currently available guidelines and determines whether the recommended assessment criteria are appropriate. From this study, it is evident that more research is needed to understand the effect of water suction, water-cement ratio and mineralogy of clay in the mechanical behavior of rammed earth. Furthermore, suitable tests to assess durability properties (such as erodibility) need to be implemented.