Cement Stabilized Rammed Earth Research Articles

Compressive Strengths of Cube vs. Cored Specimens of Cement Stabilized Rammed Earth Compared with ANOVA

Cement-stabilized rammed earth (CSRE) is a variation of the traditional rammed earth building material, which has been used since ancient times, strengthened by the addition of a stabilizer in the form of Portland cement. This article compares the compressive strength of CSRE determined from specimens cored from structural walls and those molded in the laboratory. Both types of specimens underwent a 120-day curing period. The tests were conducted on specimens with various grain sizes and cement content. An analysis of variance (ANOVA) was performed on the obtained results to determine whether it is possible to establish a conversion factor between the compressive strength values obtained from laboratory-molded cubic samples and those from cored samples extracted from the CSRE structure. The study revealed that the compressive strength of CSRE increases significantly over the curing period, with substantial strength gains observed up to 120 days. The results indicated no statistically significant difference in the mean unconfined compressive strength (UCS) between cubic and cored specimens for certain mixtures, suggesting that a shape coefficient factor may not be necessary for calculating CSRE compressive strength in laboratory settings. However, for other mixtures, normal distribution was not confirmed. These findings have implications for the standardization and practical application of CSRE in construction, highlighting the need for longer curing periods to achieve optimal strength and the potential to simplify testing protocols.

INFLUENCE OF CEMENT AND COIR FIBER ON THE MECHANICAL PROPERTIES OF RAMMED EARTH

Rammed earth, a construction is widely used globally due to its ease of availability of materials and mechanical performance. Stabilization is necessary in rammed earth construction to enhance the binding of the soil particles which in turn increases the mechanical and durability properties of rammed earth. The purpose of this research is to determine the optimum percentage of chemically treated Coir fiber dust and cement for rammed earth. Fibers and cement can be easily integrated into the soil mixture, increasing the wall's strength and durability. Compressive, flexural, and tensile strength tests were performed on the samples, and failure patterns were studied. Cement is varied in percentages of 6%, 9% and 12% and coir fiber dust (0.1, 0.2, 0.3, and 0.4 percent by weight of soil) were added as stabilizer and reinforcement. To assess the optimum strength and durability, it is recommended to utilize 0.2 percent fiber content Coir fiber dust, along with 9 percent cement by weight of soil. It is observed that with the cement and fiber dust incorporation there has been increase in the mechanical properties of rammed earth. Keywords- Cement Stabilized Rammed Earth (CSRE), Coir Fiber Dust, wet compressive strength, flexural strength.

Chemo-thermo-hydro-mechanical behavior of a cement-stabilized rammed earth wall in interaction with the environment and underground soil

This work presents a numerical investigation into the structural behavior of a newly built cement-stabilized rammed earth (CSRE) wall and its interaction with the underground soil and environment. Finite element simulations were used to obtain the results, which show that the average degree of cement hydration of the wall increases annually, with the rate of increment decreasing over time. Even after five years of curing, the cement is not completely hydrated. In the first year after construction, the degree of cement hydration is higher near the indoor side of the wall compared to the parts near the outside and underneath the ground due to the higher indoor temperature. The upper and indoor sides of the wall are generally drier than the lower and outdoor sides. Rising damp water that does not evaporate in time stores as a water source in the wall, making the wet areas expand in the following days. The average wall temperature first increases due to the hydration heat and later varies seasonally with the environment. Water has a significant impact on the thermal insulation qualities of the wall. The thermal insulation of the wall decreases due to rising damp but increases owing to water evaporation. The compressive strength of the wall is mainly controlled by cement hydration at an early age but is also impacted in the later four years by the humidity of the environment and the underground soil. The higher portion of the wall loses its strength later than the lower part since it takes longer for water to reach the upper side from the ground soil. This delay is dissipated on the wall surface owing to sufficient contact with the air. The shortage of water on the upper side of the wall leads to the hydration process in this area being governed chiefly by temperature.

Compressive strength of rammed earth filled steel tubular stub columns

Rammed earth (RE) is a potential sustainable building material applicable for modern composite construction. To expand its potential application scenarios, this paper proposes RE-filled steel tubular (REFST) columns: using RE as the infill confined by external steel tubes. Uniaxial compression tests on both material and member levels are conducted. At the material level, cement-stabilized RE cylinder samples with two RE compositions and four levels of cement content are designed. Addition of cement significantly enhances the axial capacity of RE. A method to estimate the compressive strength of RE with considering the added cement content is proposed. Following the same RE composition and cement content at the member level, 15 REFST columns are axially compressed. The comparative study results show that confinement effect needs to considered in estimating maximum axial compressive strength of REFST columns and the strength ratio between the steel tube and infill RE is suggested to be no larger than 10 to fulfill the confinement effect. Finally, a method is proposed to predict the maximum compressive strength of REFST columns.

Stress-Strain Relationships and Failure Load Analysis of Cement-Stabilized Rammed Earth under Concentric and Eccentric Loading Using Finite Element Modelling

Among many alternative building materials, soil in the form of rammed Earth is the most ancient construction material and technology. Large-scale application of the rammed Earth technology in the construction industry requires the assessment of its strength and failure behaviour. Therefore, this study focused on performing a nonlinear stability analysis of cement-stabilized rammed Earth (CSRE) specimens having a height-to-thickness (H/T) ratios—3 and 4 and loaded under varying degrees of eccentricities 0, 1/3, 1/6, and 1/12. The maximum compressive strength and the stress-strain behaviour of the CSRE specimens were determined through finite element (FE) modeling. The experimental results of the cement-stabilized rammed Earth (CSRE) have been obtained from literature for validation by FE simulation. As the H/T ratio was increased from 3 to 4, the load-bearing capacity of the CSRE specimens increased by 2.91% under concentric loading condition; however, when the eccentricity of load application was swapped from 0 to 1/12, 1/6, and 1/3, the load-bearing capacity decreased incrementally. The results of the FE analysis of the specimens showed that the compressive strength and elastic properties of the CSRE specimens did not differ significantly. The stress-strain relationships were nonlinear and elastic properties were affected by soil textural composition and density.

Behaviour of plain and fibre reinforced cement stabilised rammed earth under compression, tension and shear

Cement stabilised rammed earth (CSRE) is used for load-bearing walls in buildings and other structures. There is an upsurge in interest for using CSRE constructions worldwide in the last six to seven decades. The CSRE wall elements in a structure undergo sudden catastrophic shear failures under the compression and shear loadings and exhibit brittle flexure failures under out of plane bending. The brittle failures should be avoided in the structural wall elements. The limited studies on the fibre reinforced CSRE reveal that the addition of fibres can enhance the material's mechanical properties and help prevent sudden catastrophic failures. However, the studies on the fibre reinforced CSRE are still in nascent stage. The behaviour of fibre reinforced CSRE under different loading conditions remains an unexplored area. The present study attempted to understand the behaviour of fibre reinforced CSRE under compression, tension, and shear. The investigations revealed that the addition of short coir fibres significantly increases the failure strains and the energy absorption capacity of CSRE under compression and in-plane shear, eliminating the sudden catastrophic shear failures observed in the plain CSRE. The coir fibre inclusion, although partially increases the compression and the shear strength of CSRE, it significantly enhances the splitting tensile strength and post peak response.

Influence of interlayer shear studs on the behaviour of cement stabilised rammed earth under compression, tension and shear

Cement stabilised rammed earth (CSRE) has been used for the construction buildings since the last 6–7 decades across the world (Australia, Europe, Asia, Africa, and countries such as New Zealand and the United States). The rammed earth is a monolithic construction, where the processed earth is compacted in layers. The interfacial bond strength between the compacted layers is weak, and hence there is a weak link among the compacted layers of CSRE. The major issues with CSRE walls are (1) catastrophic shear failures under compression and shear and (2) poor flexure and shear strength. Introducing short shear studs at the interfaces of the compacted rammed earth layers is one possibility to enhance the shear and the flexure strength of the CSRE. The paper focuses on evaluating the compressive strength, interface shear strength, shear stress-shear strain relationships, and the flexural strength of steel studs embedded CSRE for the first time. The results reveal that due to the introduction of shear studs, (a) the interfacial shear strength and diagonal shear strength of CSRE improved significantly, (b) The ultimate moment-resisting capacity doubles and (c) the steel studs embedded CSRE wallette showed ductile failure. The results clearly demonstrated that introducing steel studs among the compacted layers of CSRE could help avoid sudden catastrophic failures of CSRE walls under out of plane bending.

Designing the Composition of Cement-Stabilized Rammed Earth with the Association Analysis Application.

The main advantage of the structural composite material known as cement-stabilized rammed earth (CSRE) is that it can be formulated as a sustainable and cost-saving solution. The use of the aggregates collected very close to a construction site allows economizing on transportation costs. Another factor that makes sustainability higher and the costs lower is a small addition of cement to the CSRE in comparison to the regular concrete. However, the low cement content makes the compressive strength of this structural material sensitive to other factors. One of them is the composition of the aggregates. Considering the fact that they are obtained locally, without full laboratory control of their composition, achieving the required compressive strength of CSRE is a challenge. To assess the possibility of achieving a certain compressive strength of CSRE, based on its core properties, the innovative algorithm of designing CSRE is proposed. Based on 582 crash-test of CSRE samples of different composition and compaction levels, along with the use of association analysis, the spreadsheet application is created. Applying the algorithm and the spreadsheet, it is possible to design the composition of CSRE with high confidence of achieving the required compressive strength. The algorithm considers a random character of aggregates locally collected and proposes multiple possible ways of increasing the confidence. They are verified through innovatively applied association analyses in the enclosed spreadsheet.

Strength and stress–strain characteristics of fibre reinforced cement stabilised rammed earth

Cement stabilised rammed earth (CSRE) is used in the construction of load bearing walls. CSRE elements under compressive loads experience sudden catastrophic shear failures. Such brittle failures shall be avoided in the CSRE structures. The addition of short discrete randomly oriented fibres to CSRE can help avoid such catastrophe failures, where the fibres can bridge across the crack and help inhibit the crack propagation. The paper deals with studies on the effect of coir fibre reinforcement on the behaviour of CSRE under compression. The influence of fibre volume fraction, cement content and moisture content on the strength and stress–strain characteristics of CSRE has been investigated. Five fibre volume fractions (VF), 0.0, 0.5, 1.0, 1.5 and, 2.0%, two cement contents (7 and 10%), and two moisture conditions were considered. The compressive strength of fibre reinforced CSRE increased by 10–30% for 1% VF. The strain at peak stress and the failure strains have significantly increased with the addition of fibres indicating the improved ductility and the post peak response of the material. The energy absorption capacity of CSRE increased by 2–5 times for an increase in the fibre volume fraction from 0 to 2%. The sudden catastrophic shear failures observed in the cement stabilised rammed earth under compression can be eliminated by the addition of short randomly oriented coir fibres. The fibre volume fraction of 1% is the optimum.

Alternative stabilised rammed earth materials incorporating recycled waste and industrial by-products: Durability with and without water repellent

Rammed earth (RE) materials with low greenhouse gas emissions have been developed as replacements for conventional construction materials. In this series, we examine the strength development, durability and sustainability, via life cycle assessment, of these new materials.In this paper, we present findings for material durability with and without the addition of the water repellent admixture, Tech-Dry ‘Plasticure’. Understanding of durability properties is essential to verify the suitability of the RE materials for building. The study assessed four distinct RE materials, all based on a substrate of crushed limestone: a control mix, cement-stabilised RE (the industry standard in Western Australia) and three alternative stabilisers, i) alkali-, ii) lime-, and iii) self-activated RE. The alternative RE stabilisers incorporated industrial by-products fly ash, ground granulated blast furnace slag and silica fume, in combination with sodium hydroxide, hydrated lime or no activator (respectively, by mix). Durability was assessed using initial rate of absorption, immersion and wire brush testing. Both with and without Plasticure, all materials either passed these tests or, where pass/fail criteria were unavailable, were found to be comparable to conventional building materials. Scanning electron microscopy and energy dispersive spectroscopy showed that greater maturity in terms of reaction of raw materials was associated with lower absorption. Those materials with Plasticure had lower initial rate of absorption than those without, especially in the case of lime- and self-activated RE. Plasticure was shown to improve durability properties of all tested RE mixes.

Experimental investigation of non-stabilized and cement-stabilized rammed earth reinforcement by Waste Tire Textile Fibers (WTTFs)

Waste Tire Textile Fibers (WTTFs), waste materials derived from scrap tires, have been used to enhance the mechanical properties of Rammed Earth (RE) and Cement-Stabilized Rammed Earth (CSRE) structures. To do so, standard compaction, Unconfined Compressive Strength (UCS), Split Tensile Strength (STS), and Flexural Bending Strength (FBS) tests were conducted on plain, Cement-Stabilized (CS), Fiber-Reinforced (FR), and Cement-stabilized Fiber-reinforced (CSFR) RE elements. Both FR and CSFR samples have shown favorable behavior. Therefore, based on the project specifications, it is concluded that WTTFs can be used with and without cement-stabilization to improve the brittle and relatively weak behavior of RE structures.

Micromechanics modelling of cement stabilised rammed earth

Rammed earth (RE) is a generic term for a number of construction materials that contain stabilised or non-stabilised earthen materials. RE materials are heterogeneous and their bulk performance depends on their mineralogical composition, physical texture, water content and mode of preparation. This category of building materials has recently been the subject of extensive studies, given the increasing interest in sustainable construction. This trend has highlighted not only the potential of RE, but also the lack of standards and guidelines that can promote its adoption by architects and builders. Predictive modelling techniques that faithfully forecast the mechanical behaviour of RE are also scarce. This study introduces a micromechanics approach and proposes a multi-scaling model to predict the mechanical behaviour of cement stabilised rammed earth (CSRE) in linear elasticity. The RE heterogeneity is addressed hierarchically at different scales separated by the sizes of their representative volume elements (RVE). Homogenisation procedures are applied to predict the material properties at each scale and investigate the overall macroscopic behaviour of earthen mixtures. The Mori-Tanaka homogenisation scheme is used to predict the linear elastic behaviour of CSRE by treating it as a porous composite. The theoretical results obtained by the application of various micro-mechanics-based models (Reuss-Voigt, Hashin-Strickman, Mori-Tanaka and Self-consistency) are assessed by comparison with the experimental data. The Mori-Tanaka homogenisation scheme proved to predict the material's macroscopic linear elastic behaviour fairly accurately while taking into account local heterogeneities.

Interfacial behavior of cement stabilized rammed earth: Experimental and numerical study

Cement stabilised rammed earth (CSRE) is a modern earth construction technology witnessing renewed interest by researchers worldwide due to its improved strength and durability vis-a-vis un-stabilised rammed earth (URE). Rammed earth walls are predominantly subjected to compressive loading and occasionally to lateral loads. Strength and deformation ability of interface in rammed earth plays a vital role in case of in-plane lateral loads. The present study focuses on assessing the performance of interface layers in cement stabilized rammed earth elements. Triplet test is conducted on CSRE specimens under dry and saturated condition. Three types of bonding techniques are considered for the interface in CSRE triplets, namely, (i) formation of dents (ii) coating cement slurry across interfacial area (iii) combination of dents and slurry. The influence of stresses normal to the interface of CSRE triplet is also explored in this study. Further, a finite element simulation of the CSRE triplet test is performed. A finite element model of the CSRE triplet is developed by using ABAQUS software. Eight node brick elements are adopted to model the CSRE material and interface. Linear elastic material model is adopted for the CSRE material whereas a PPR-potential based cohesive model is adopted for the interface. Shear stress-displacement curve obtained from the finite element model and experiment are compared with each other and were found to be in reasonable agreement.

Feature Importance of Stabilised Rammed Earth Components Affecting the Compressive Strength Calculated with Explainable Artificial Intelligence Tools.

Cement-stabilized rammed earth (CSRE) is a sustainable construction material. The use of it allows for economizing on the cost of a structure. These two properties of CSRE are based on the fact that the soil used for the rammed mixture is usually dug close to the construction site, so it has random characteristics. That is the reason for the lack of widely accepted prescriptions for CSRE mixture, which could ascertain high enough compressive strength. Therefore, assessing which components of CSRE have the highest impact on its compressive strength becomes an important issue. There are three machine learning regression tools, i.e., artificial neural networks, decision tree, and random forest, used for predicting the compressive strength based on the relative content of CSRE composites (clay, silt, sand, gravel, cement, and water content). The database consisted of 434 samples of CSRE, which were prepared and crushed for testing purposes. Relatively low prediction errors of aforementioned models allowed for the use of explainable artificial intelligence tools (drop-out loss, mean squared error reduction, accumulated local effect) to rank the influence of the ingredients on the dependent variable—the compressive strength. Consistent results from all above-mentioned methods are discussed and compared to some statistical analysis of selected features. This innovative approach, helpful in designing the construction material is a solid base for reliable conclusions.

Bond strength of rebars in cement stabilised rammed earth

Rammed earth construction involves compacting processed soil in progressive layers inside a rigid formwork. Rammed earth structural elements experience bending stresses under lateral loads such as wind and earthquake loads. The flexural strength of cement stabilised rammed earth (CSRE) walls is low. Reinforcing the rammed earth will improve the flexural strength of rammed earth to resist lateral loads. There is hardly any information on the bond strength of rebars embedded in CSRE matrix. There is a need to examine the bond developed between rebar and CSRE matrix. This paper focuses on determining the bond strength between rebar and CSRE; establish bond force – slip relationships for reinforced CSRE. The variables considered in the study included two dry densities (1800 and 1900 kg/m3), two cement contents (7% and 10%) and three types of rebars. The CSRE cubes embedded with different types of rebars were tested for pullout loading under two testing conditions (dry and wet). The bond strength of rebars in CSRE matrix was found to be greatly influenced by the dry density of the CSRE and the type of reinforcement. The bond strength of deformed rebars is higher than the plain rebars irrespective of the specimen density.

Shear strength parameters and Mohr-Coulomb failure envelopes for cement stabilised rammed earth

Cement stabilised rammed earth (CSRE) is a stratified layered construction. The technology is predominantly used in the construction of structural walls in buildings, retaining walls, foundations etc. across the world. There is inadequacy in the study on the shear strength parameters of CSRE and there is hardly any information on Mohr-Coulomb failure envelopes for CSRE. Determining the shear strength parameters of CSRE assumes importance in the analysis of CSRE behaviour under compression and in determining the in-plane shear strength walls. The paper presents the experimental studies on characterising the shear strength parameters and generating the Mohr-Coulomb failure envelopes for CSRE. Triaxial compression tests were performed and the shear strength parameters, cohesion and angle of internal friction were determined in dry and wet conditions. Cohesion of CSRE was found to be a function of cement content. Mohr-Coulomb failure envelopes of the form τcsre=c+σtanϕ were generated.

Flexural strength and failure trend of bamboo and coir reinforced cement stabilized rammed earth wallettes

Present study investigates the flexural strength and failure trend of unstabilized and cement stabilized rammed earth (CSRE) wallette with and without bamboo and coconut fiber reinforcement. Twenty four wallettes were prepared and tested under lateral load applied parallel and perpendicular to the compacted layers. Test results shows that the wallette loaded perpendicular to compacted layers/bed joints possesses higher flexural strength. CSRE wallette reinforced with bamboo and fiber shows 139% to 167% higher flexural strength than that of unstabilized rammed earth and shows improved ductility property. Flexural strength obtained in the current study ranges from 0.54 MPa to 2.11 MPa which is comparable to good quality burnt clay bricks masonry wallette strength. Initial failure cracks was observed at bed joint and mid-span for unreinforced samples and shear cracks was observed for bamboo and fiber reinforced samples. Lastly, the reinforced walls can be used for strengthening single leaf internal and external load bearing walls of single or two storey houses depending upon area seismicity.

The Effect of Soil Mineral Composition on the Compressive Strength of Cement Stabilized Rammed Earth.

Cemented stabilized rammed earth (CSRE) is a building material used to build load bearing walls from locally available soil. The article analyzes the influence of soil mineral composition on CSRE compressive strength. Compression tests of CSRE samples of various mineral compositions, but the same particle size distribution, water content, and cement content were conducted. Based on the compression strength results and analyzed SEM images, it was observed that even small changes in the mineral composition significantly affected the CSRE compressive strength. From the comparison of CSRE compressive strength result sets, one can draw general qualitative conclusions that montmorillonite lowered the compressive strength the most; beidellite also lowered it, but to a lesser extent. Kaolinite lightly increased the compressive strength.

Predicting Compressive Strength of Cement-Stabilized Rammed Earth Based on SEM Images Using Computer Vision and Deep Learning

Predicting the compressive strength of cement-stabilized rammed earth (CSRE) using current testing machines is time-consuming and costly and may harm the environment due to the samples’ waste. This paper presents an automatic method using computer vision and deep learning to solve the problem. For this purpose, a deep convolutional neural network (DCNN) model is proposed, which was evaluated on a new in-house scanning electron microscope (SEM) image database containing 4284 images of materials with different compressive strengths. The experimental results show reasonable prediction results compared to other traditional methods, achieving 84% prediction accuracy and a small (1.5) oot Mean Square Error (RMSE). This indicates that the proposed method (with some enhancements) can be used in practice for predicting the compressive strength of CSRE samples.

Hydro-thermal Analysis of Building Envelope Walls with Cement-Stabilized Rammed Earth Structural Layer and Different Thermal Insulators and Their Positioning in Humid Continental Climate

The objective of the work is to analyse thermal insulation positioning in a building envelope wall with a load-bearing layer made of cement stabilized rammed earth (CSRE) in a humid continental climate. In the article CSRE is described and recommendations regarding the wall thickness of this material are presented. The results of the CSRE coefficient of thermal conductivity and current standard values of the heat transfer coefficient for external walls in various countries of a humid continental climate are also presented. On this basis, the thickness of the necessary thermal insulation in building envelope partitions with a load-bearing layer of CSRE is estimated. In the latter part of the article, the results of the simulation of hydro-thermal conditions occurring in partitions with a load-bearing layer of CSRE insulated with different types of thermal insulation placed in different parts in the partition are presented. The simulations have shown that in a humid continental climate the best solution is the use of thermal insulation on the external side of the building envelope.