Rammed Earth Samples Research Articles

Microstructural Observations on the Durability of Stabilized Rammed Earth

This study provides a qualitative microstructural investigation of fly ash geopolymers' role in rammed earth's durability against water ingress and contact erosion. A series of SEM (scanning electron microscopy) images were captured on geopolymer-stabilized as well as unstabilized rammed earth samples. These samples were fabricated from predefined amounts of sand and fine materials together with fly ash geopolymers in the laboratory by static compaction to 25 MPa inside rigid molds. Two standardized durability tests were performed, namely, the dip test and the spray (also known as erosion) test. The results of these tests reflected excellent durability properties (practically zero erosion) of the stabilized material. The microscopic investigation provided an insight into the reason behind this improvement, where geopolymer networks inhabited the macro and micro pores and served as a cementing agent interconnecting the earthen materials’ grains. On the contrary, grains of the unstabilized material were weakly bonded by the clay component of the mixture, as observed with the SEM images; therefore, they were more susceptible to erosion by water.

Research on the Effectiveness of Tetraethoxysilane-Reinforced Earthen Site: Influence of Soil Water Content and Curing Humidity

ABSTRACT To investigate the influence of soil water content and curing humidity conditions on the reinforcement effect of tetraethoxysilane on earthen sites, remolded rammed earth samples with 0%, 5%, 10%, and 14.5% water content were prepared and reinforced by tetraethoxysilane and then placed in the relative humidity conditions of 35%, 65%, and 85% for 28 days. The basic physical, mechanical, and durability properties of samples before and after reinforcement were evaluated, and the mechanism was clarified through microscopic analysis. Results showed that tetraethoxysilane strengthened the connection between soil particles and filled the pores by generating Si-O-Si groups mainly through a hydrolysis reaction. Under the same humidity condition, tetraethoxysilane had a better effect on the mechanical and durability properties of samples with low water content (0% and 5% in this paper), while it generated a weak reinforcement effect on the samples with high water content (10% and 14.5% in this paper). For samples with the same water content, too high a curing humidity condition (85% in this paper) was not favorable to the reinforcement effect of tetraethoxysilane. These conclusions were confirmed by microscopic analysis, including scanning electron microscopy, infrared spectroscopy, and X-ray photoelectron spectroscopy.

Influence mechanism of salt erosion on the earthen heritage site wall in Pianguan Bastion

The earthen heritage site wall of Pianguan presented salt crystallization and pulverization in China. In this study, rammed earth samples were collected from the heritage wall, and the salt solution erosion test of samples were carried out. The influence mechanism of salt erosion on the earthen heritage site wall was conducted on the rammed earth samples using portable digital microscope, scanning electron microscope, portable chromatic aberration instrument, strip-shaped adhesive tapes, hardness tester, electronic universal testing machine, X-ray diffractometer (XRD) analysis. The macro and micro observations showed the salt erosion damage of rammed earth goes through three stages roughly. The warping and hollowing were appeared on the surface and salt precipitation in the inner sample at the early stage; The soluble salt precipitation thin salt shell appeared on the surface and the pulverization in the inner sample at the middle stage; Salt particles covered the whole surface, the inner sample was wet and the pulverization was reduced at the later stage. The chromatic aberration analysis showed the chromatic aberration of the surface sample increased with the increase of salt supply time, but the variation decreased when the salt shell covered the surface of the sample. The adhesion analysis showed the number of particles fall off the sample surface increases first and then decreases, and the cohesion of the sample surface is overall decreased. The hardness and compressive strength analysis showed they decreased linearly with the increase of salt supply time. The component analysis of precipitated soluble salts showed sodium chloride in soluble salt mainly migrated and precipitated on the surface during the sample drying process, and the main factor leading to the pulverization of the sample.

Mechanical characterization and elastic stiffness degradation of unstabilized rammed earth

Rammed earth is attracting renewed interest due to its sustainability. In this work, a mechanical characterization of unstabilized rammed earth is presented. Compressive strength, Young's modulus, and Poisson's ratio were determined, with the first of these being the most representative mechanical property of rammed earth. Stress – strain curves were obtained from uniaxial compression tests. Creep is of great importance in the long-term assessment of historical buildings and in the design of new ones. Samples of rammed earth were subjected to a constant load for 15 days to study their creep behavior. In order to simulate the long-term behavior of the material, different rheological models were fitted to the experimental results. The instantaneous deformation of rammed earth samples caused by a sudden additional load (maintaining a previous service load level) was also studied. This is the first time that this phenomenon, called elastic stiffness degradation, has been studied for rammed earth material.

Fernandina Wall of Lisbon: Mineralogical and Chemical Characterization of Rammed Earth and Masonry Mortars

This paper aims to provide information on rammed earth and masonry mortars of the Fernandina defensive Wall of Lisbon, Portugal, which was built in the second half of the 14th century. No previous information exists concerning the materials and construction techniques used in this defensive structure, which is essential to increase knowledge and to define requirements for a reliable conservation. An experimental campaign was carried out on samples extracted in nine different sections of this structure, which were analyzed by X-ray diffraction, thermogravimetry and wet chemical analysis. Calcitic lime was employed as a binder in the stone masonry bedding mortars and was also identified in the rammed earth samples. The results obtained allowed us to verify the use of different binders and aggregates, with heterogeneous binder/aggregate ratios, in different sections of the Wall. To reduce time for lime preparation and to achieve a durable lime matrix, most probably quicklime was used and hydrated together with the moistened earth to produce rammed earth and masonry bedding mortars.

Moisture content and material density affects severity of frost damage in earthen heritage

Successful conservation of earthen heritage requires an understanding of interactions between environmental and climatic conditions, soil-based materials and human interventions. Frost cycling is likely to be an important contributor to the deterioration of earthen heritage, with frost damage known to cause deterioration features such as flaking and granular disintegration. However, it is not clear how important a contribution frost cycling makes in comparison with other agents. Previous earthen heritage studies have focused on other agents of deterioration, such as wind and rain, or investigated the role of freeze-thaw cycles under conditions unrepresentative of many earthen sites. We investigate how density and moisture content affect the severity of frost damage on earthen heritage using materials and conditions informed by those found at earthen sites in NW China. We prepared rammed earth cubes (5 × 5 × 5 cm) at two densities (1.65 and 1.75 g cm−3) and with five moisture content levels between 0.46 and 8%. Samples were subjected to 80 freeze-thaw temperature cycles (+7 to −15 °C) in an environmental cabinet. Deterioration was recorded using visual assessment, measurements of surface roughness, ultrasonic pulse velocities, a Vicat needle test and mass loss. Results showed frost damage was dependent on moisture content and density of rammed earth samples. Samples with <2% moisture content showed no visible frost damage. Samples with higher moisture contents (>6%) and higher densities exhibited the greatest deterioration with surface granulation, salt efflorescence and flakes detaching from the parent cubes. This suggests that frost damage to rammed earth is likely to be focused in periods when rainfall or snowmelt is followed by freeze-thaw temperature cycling. In addition, results suggest that if higher density earthen materials are used for repairs or restoration for sites in dryland environments, these could be more vulnerable to frost damage than lower density materials.

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.

Predicting and evaluating the engineering properties of unstabilized and cement stabilized fibre reinforced rammed earth blocks

This paper investigates the effect of coir percentage, length and cement content on the properties of rammed earth blocks in terms of strength, density and durability followed by predicting the properties using statistical regression analysis. X-Ray Diffraction (XRD) analysis was made on unstabilized (US) and cement stabilized (CS) samples to study the effect of cement stabilization on the phase composition. Scanning electron microscopy (SEM) observations are used to analyze the micro-structural interactions of coconut fibre (coir) with soil and soil-cement matrix. Coir of 1% to 5% and 25 mm to 50 mm lengths was used as reinforcement and 10% of cement as stabilizer. The investigation shows that the characteristic dry compressive strength increases up to 1% coir of 25 mm length and gradually decreases with the increase in coir percentage and length. However, tensile strength increases with the increase in coir percentage and length. CSRE blocks reinforced with 1% and 3% coir of 25 mm and 50 mm lengths respectively meet the durability criteria specified by some standards and researchers. XRD analysis revealed the presence of quartz, calcite, albite and small amounts of other minerals on the other hand cement stabilization increased the calcite peaks. Cement stabilization reduces the microstructure porosity of the material thereby improving the strength and durability properties. Coir reinforcement along with cement stabilization increases the efficiency of rammed earth samples. A series of statistical analysis was also conducted to predict the compressive and tensile strengths correlating coir percentage, length, density and cement content. The equations generated from regression analysis represented a strong correlation between the actual and predicted values, which can be used for accurate prediction of rammed earth strength.

Mineralogical and microstructural characterisation of rammed earth and earthen mortars from 12th century Paderne Castle

Abstract In many countries, earth was a very common construction material until the middle of the 20th century, being rammed earth one of the most widespread construction techniques. Nowadays, there are still a large number of constructions with this traditional technique, from vernacular dwellings to monuments. Therefore, rammed earth constructions integrate cultural, historical, technical and architectonic recognised value and the constant neglect of this type of constructions, without maintenance and conservations measures over time, or with inadequate interventions, presents a worrying reality. This paper aims to contribute towards increasing the knowledge on materials from 12th century Paderne castle, located in Algarve, south of Portugal. Data from interventions performed on the castle in the 20th and 21st centuries were gathered. Samples from the rammed earth castle tower and walls and mortar from a more recent chapel were collect during the 21st century interventions and characterised, mainly by microstructural and mineralogical techniques. Most of them present calcareous and siliceous aggregates in their composition, except for samples collected from the wall where no siliceous aggregates were detected. Rammed earth samples present a brownish colour being the binder a mixture of clayey earth and lime, and the coarse aggregate mostly limestone. Iron oxide/hydroxide and clay minerals, very common in earth composites, are detected and a lime + clay binder/aggregate ratio of 1:1.5 in volume is the most frequently found. The large amount of calcite in all rammed earth samples is an indication of the use of carbonate gravel mixed with a high content of air lime. The presence of white nodules in the earthen matrix induces that the lime was probably applied as quick lime and, afterwards, hydrated by mixing with the moistened earth. The lime was used as a stabiliser (technique called “military” rammed earth) to promote a hardening process by carbonation and increase durability to weathering. Therefore, characterisation results obtained in this study allow to draw conclusions about the materials and construction techniques used in the past, in order to support future compatible, effective and reversible interventions in this and in similar historic military rammed earth constructions.

The coupling effects of freeze-thaw cycles and salinization due to snowfall on the rammed earth used in historical freeze-thaw cycles relics in northwest China

Rammed earth, a kind of building materials used worldwide because of its straightforward manufacture and low cost, is still used in the construction industry today. Many rammed earth architectural relics are preserved in the arid and semi-arid areas in northwest China. In this area, the winter snowfall process is generally long and may work to degrade the physical and mechanical properties of rammed earth, destroying these relics. Therefore, to protect rammed earth sites, it is very important to understand the mechanisms governing rammed earth deterioration during snowfall. Using real-time monitoring and soluble salt testing of the temperature and water content of the rammed earth at three representative sites in the north-west region, we found that snowfall leads to varying degrees of freeze-thaw cycle and salinization coupling that degrade rammed earth structures. Wind erosion, disintegration, shear and mercury intrusion experiments using remoulded rammed earth samples were performed based on the monitoring results and incorporated different types and concentrations of soluble salts; three freeze-thaw cycles were applied to explore the macro and micro changes in the wind erosion modulus, disintegration speed, cohesion, internal friction angle and pore size of the rammed earth samples. Finally, the joint analysis of the monitoring results, macroscopic property indices and microscopic property indices revealed the mechanisms of rammed earth degradation due to the observed coupling effect.

Mathematical Models of Homogenization for a Rammed Earth Blend Made of Crushed Limestone and Cement in Linear Micro-poro-elasticity

Rammed earth (RE) designates natural building materials that can contain stabilized or non-stabilized soils or crushed stone blends. RE materials are non-homogenous and their performance depends on their compositions, grain size distributions, porosity, and mode of preparation. This category of building materials has recently been subject of extensive studies, due to the increasing interest in sustainable construction, which have highlighted the potential and limits of its large uptake. Although it has been demonstrated that RE can be treated as multi-component materials [1] a full characterization based on micro-structural considerations is still lacking. Full understanding of the role of porosity in the overall material performance has not been addressed. However, extensive literature [2, 3, 4, 5] is available that can describe the overall mechanical behaviour of similar materials, based on the principle continuum micromechanics. This study applies the Mori-Tanaka homogenization scheme to characterize the linear elastic behaviour of cement-stabilized crushed-limestone-based material by treating it as a porous composite. The composite comprises a solid phase consisting of limestone grains bonded together with hydrated cement bridges and a fluid phases consisting of different families of pores. The microstructure of rammed earth samples has been observed using an optical microscope. The obtained images have been collected and processed to obtain the pore sizes and pore size distribution. Finally, these statistics along with the Mori-Tanaka homogenization scheme have been used to determine the overall elastic properties that depend on a damage parameter enclosing the pore sizes, density, and texture

Hydric characterisation of rammed earth samples for different lime concentrations

The rehabilitation of ancient rammed earth houses, as well as the use of earthen materials in modern constructions, are a growing matter of concern, especially in area such as Rhône-Alpes, France, where 40% of old constructions are in rammed earth. A current pathology observed for this type of construction is related to the rising damps, for which the water from the ground is absorbed by the wall. This situation leads to a very saturated state. As it has been proven that the compressive strength is altered by the presence of water in the pores, a better understanding on high relative humidity range is necessary to be able to predict the mechanical behavior of buildings and thus ensure a better risk assessment. The present study describes experimental results of the water uptake experiments and moisture storage at high relative humidities.

The Influence Of Loam Type And Cement Content On The Compressive Strength Of Rammed Earth

AbstractCurrently, 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 Polish Standards from the 1960’s that dealt with earth material.

Improving rammed earth wall thermal performance with added expanded granulated cork

Most construction materials require large amounts of energy for production and transportation purposes and are also associated with high levels of greenhouse gas emissions. One such material, rammed earth, has the advantage of being reusable and extremely durable, while it can also be locally sourced. However, rammed earth walls have a low thermal resistance. The aim of this study is to improve the thermal performance of rammed earth walls by increasing their thermal resistance. To this end, a range of different percentages and particle sizes of expanded granulated cork were added to rammed earth samples. The thermal conductivity of the samples was then determined in the laboratory and the data obtained were used to calculate heat transfer coefficients for a model rammed earth wall. Finally, the samples were subjected to uniaxial compression tests to determine whether the added cork led to a reduction in compressive strength. It was found that adding 10% granulated cork produced a reduction of about 12% in the heat transfer coefficient of a rammed earth wall with a thickness of 0.60 m, while the 28% reduction in compressive strength recorded is within the limits set out in the relevant standards.

Effect of moisture content on the mechanical characteristics of rammed earth

In this paper, influence of moisture content on the mechanical characteristics of rammed-earth has been studied. Samples from different soils (sandy, clayey, stabilised) were manufactured and tested in unconfined compression at several moisture contents. Compressive strength, elastic modulus and Poisson's ratio were determined. A simplified method to measure the suction within rammed earth samples has been developed and validated. The variation of mechanical characteristics related to moisture content and suction are presented. This paper shows that a slight increase in the moisture content of dry rammed-earth is not followed by sudden drop in wall strength. Qualitative explanations at the nano-scale are presented.

Unstabilized Rammed Earth: Characterization of Material Collected from Old Constructions in South Portugal and Comparison to Normative Requirements

Unstabilized rammed earth is a recyclable, economical, and eco-friendly building material, used in the past and still applied today. Traditionally, its use was based on a long empirical knowledge of the local materials. Because this knowledge was mostly lost or is no longer sufficient, in many countries normative documents have been produced to allow the assessment of rammed earth soils. With the aim of contributing for a refining of these normative requirements, this article presents a research work that included: (i) collection of Unstabilized rammed earth samples from six constructions in Portugal; (ii) a literature survey of normative and complementary documents to identify the most mentioned key-properties, the test procedures and the corresponding threshold limits; and (iii) a discussion of the test procedures and of the thresholds limits in the light of the experimental results. The analyzed properties are the particle size distribution, maximum particle size, plasticity, compaction, linear shrinkage, organic content, and salt content. The work highlights the advantages of taking into account the characteristics of existing constructions as a basis for the establishment and further refining of consistent threshold values. In particular, it shows that it is essential to adjust the requirements to the specificities of local materials.

Influence of Water Contents on Shear Strength of Rammed Earth Wall of Earth-Building

As the "Fujian earth-building" have been inscribed by UNESCO in 2008 as World Heritage Site, attentions of protection about the "Fujian earth-building" has getting more and more. This article takes samples of a rammed-earth wall from Yongding earth-buildings and determines the shear strength of the samples with different water content through triaxial compression tests. The influence on shear strength of water content of rammed-earth samples is analyzed. Test results show that the shear strength of rammed-earth has much to do with the water content of the soil, the greater the water content is，the smaller the shear strength is. With water content increasing, cohesion and internal friction angle of rammed-earth were decreases, and its changing trend is of marked characteristic of stage. When water contents of rammed-earth is under some value, its cohesion changes in small ranges; when water contents of rammed-earth is over the value, its cohesion decreases with water content increasing.

Experimental investigation on the compressive strength of cored and molded cement-stabilized rammed earth samples

This research aims to improve the insufficient and inadequate quality control techniques currently available on cement-stabilized rammed earth construction sites. To achieve this goal, the comparison between the compressive strength of cored and molded cylindrical samples have been experimentally investigated. In order to gain a deeper understanding of the additional causes influencing the strength of rammed earth samples, investigations on specimen slenderness, size, shape and capping methods have been also conducted. This study shows that in certain cases the mechanical behavior of concrete and cement-stabilized rammed earth are similar. The obtained results also indicate that the strength of cored specimens is always lower than that of molded specimens. A list of recommendations for the assessment of cement-stabilized rammed earth strength is proposed.

Rammed earth sample production: context, recommendations and consistency

A novel approach to specifying and creating rammed earth soil recipes, through a process of blending graded quarry material, has been presented. The soil recipes are highly consistent and reproducible, allowing the accurate control of parameters such as particle-size distribution. A novel technique for the consistent production of rammed earth cube samples has been presented that satisfies NZS 4298: 1998, and is in good agreement with the established Proctor standard for compaction. Under the proposed method for rammed earth sample production, the level of energy input used for compaction can be varied depending upon soil type. For a given compactive effort, the variation in dry density due to soil type did not appear to be directly related to the characteristic unconfined compressive strength of the rammed earth samples. Experimental data have been included.