Earth Mortars Research Articles

Analysis of dynamic moisture movement within bio-based earth mortars

Understanding moisture movement within building materials is critical for the understanding of how they dynamically respond to their hygrothermal environment. Utilising low embodied energy, hygrothermal materials such as bio-fibers and earth will enable a ‘green solution’ to the current climate change issues surrounding carbon intensive materials such as concrete. Within this research an earth mortar with bio-fibres of 2 types of sheep wool: Wool 1 (W1), Wool 2 (W2) and a Saw Mill Residue (SMR) in addition to a plain, control sample (PL) were cast. Experimentation was completed on these materials to identify Water Vapour Permeability (WVP), Sorption Isotherms and latent heat of sorption. Results demonstrated that for WVP, SMR has the greatest value of WVP (2.2 x10−11 kg.m−1.s−1.Pa−1). PL also had the lowest value (1.4 x10−11 kg.m−1.s−1.Pa−1). For sorption isotherm, over the course of the experiment it can be demonstrated that the incorporation of fibres increases the rate in which the mortars adsorb water molecules. This is particularly highlighted as above 30% RH sample begin to increase in moisture content with this rapidly increasing from approximately 65% RH. Finally, latent heat of sorption analysis demonstrated that a dynamic change in latent heat under differing hygorthermal conditions can be indentified; for all samples, even after 21, 24 h cycles. However, SMR had the lowest quantity of latent heat even by comparison to the PL sample as there is a sustained difference of approximately only 0.5 °C between samples. This establishes that the SMR sample requires less heat energy in order for the water to change to and from vapour and liquid state.

Hygrothermal simulation of building performance: data for Scottish masonry materials

Retrofitting thermal insulation to solid masonry walls alters their hygrothermal behaviour, which can be modelled by hygrothermal simulation software. However, such software needs values of key material properties to ensure satisfactory results and until now data has not been available for Scottish masonry buildings. This work aims to contribute to a Scotland-specific dataset of material properties for use by designers working on such buildings. Thermal conductivity, water vapour permeability, sorptivity, water absorption coefficient, hygroscopic sorption, density and porosity were all determined experimentally for selected historic and contemporary masonry materials. Within the range of materials tested three groups of materials properties emerge. Natural hydraulic lime mortars, hot-mixed quicklime mortar and earth mortar all show comparatively low density, high porosity, low thermal conductivity, high water vapour permeability and variable but generally high hygroscopic sorption. Craigleith, Hailes and Giffnock sandstones, no longer available but obtained from conservation works on historic buildings, and Locharbriggs and Hazeldean sandstones, obtained from current production, all show intermediate values of these properties. Crathes granodiorite and Scottish whinstone (from current production) show high density, low porosity, high thermal conductivity, low water vapour permeability and low hygroscopic sorption. It is shown that these materials are all relevant to Scottish buildings constructed in traditional masonry and this paper presents the first comprehensive set of hygrothermal property data for them.

Determination of specific heat capacity of bio-fibre earth mortars stabilised at different relative humidities using Differential Scanning Calorimetry

Understanding the relationship that earth-based mortars have with both water and temperature is imperative to optimise moisture buffering properties. Specific Heat Capacity (Cp) is a key factor to understand the benefits in terms of thermal mass and latent heat. This paper presents the results of bio-based earth mortars (with fibres consisting of two varieties of sheep wool: Wool 1 (W1), Wool 2(W2) and Saw Mill Residue (SMR)) stabilised at 53% and 75% Relative Humidity (RH). Differential Scanning Calorimetry (DSC) according to ISO 11357–4 was used to calculate Cp of the aforementioned mortars. The temperature range of this experiment was that of 0–50 °C with a particular focus on values at 20 °C as this best represented a suitable indoor temperature. From these experiments, the results demonstrate that when stabilised at different RH, the difference in Cp was bio-fibre dependant and had a range between 0.71– 1.01 kJ/kg.K at 53% RH and 0.85–1.14 kJ/kg.K at 75% RH. These differences could potentially be attributed to the materials ability to readily accept water molecules. This emphasised that incorporating bio-fibres to a plain mixture (PL) can increase the Cp by up to 60%; significantly improving the thermal inertia of the building material. By reducing this temperature differential, it will reduce the heating requirements of a building which as consequential carbon reduction and thermal comfort benefits. Overall, SMR has the largest Cp for 75% at 20 °C was 1.141 kJ/kg.K, therefore specifically, this fibre would be the most effective to implement within a building. It also demonstrates the differences of the samples adsorption and absorption of water in differing hygrothermal environments.

Rammed Earth with Straw Fibers and Earth Mortar: Mix Design and Mechanical Characteristics Determination

Raw earth is one of the oldest building materials, which is suitable for various uses: from the construction of load-bearing walls to use for plasters and finishes. The presence of straw fibers can give different behavior to this material. The present paper illustrates preliminary sensory and qualitative analyses, and subsequent laboratory tests that allow the characterization of the raw earth material with straw fibers for rammed earth constructions through mechanized compaction and the identification of a compatible earth mortar. The raw material considered in this study is mainly clayey; for this reason, a mix design usable with the pisé (or clay) technique has been developed. Cylindrical samples have been made through a press and subject to unconfined compression and indirect tensile tests. The results of the tests showed consistent tensile and compressive strength values in the context of earth materials. At the same time, a study for the realization of a mortar with the same base soil was carried out considering four mixtures, in order to investigate the best compromise between workability, shrinkage and compressive strengths. The purpose of the study was to investigate the mechanical characteristics of the local material through preliminary and laboratory tests, to classify it according to the Unified Soil Classification System (USCS) and to verify its suitability for a possible use in the construction field.

Earth mortars in the “Castro de Santa Trega” (A Guarda, Pontevedra, Spain)

Among many other issues, characterisation of construction techniques is very interesting for understanding protohistoric societies. In the case of Iron Age sites in the Iberian Peninsula, knowledge about materials and construction techniques is minimal. This work explores the challenges of the characterisation of earth mortars in Iron Age sites in the N.W. of the Iberian Peninsula, focusing the study on the archaeological site of Castro de Santa Trega (Galicia, Spain). Samples of mortars, renders and plasters were taken from walls, and mineral composition, texture and micromorphological features were obtained. The results, which are discussed taking into account the particular historiographic framework of this site, confirmed the absence of lime mortars and the widespread use of local raw materials for the production of complex construction materials.

Effect of innovative bioproducts on the performance of bioformulated earthen plasters

Biotechnologies mainly based on precipitation of chemical compounds produced by microbial metabolism can be used as biotreatment or bioformulation of construction materials. Bioformulation of cement-based materials has been a common research practice, though its application to earthen-based building materials is still limited. Although earth mortars are vulnerable to water damage, they are nowadays often used as plasters on new constructions but also for the retrofitting of existent buildings. Their reversibility and compatibility with old substrates make them also interesting for conservation interventions, namely when applied to protect archaeological structures as sacrificial renders. In this study, an innovative bioproduct based on cellular extracts of Escherichia coli, cultured in Lysogeny broth (LB) medium and supplemented with iron, was developed and used as a component for earth mortars’ bioformulation. The Escherichia coli strain used is classified as not hazardous. An additional earth mortar bioformulated with LB medium as mixing liquid was also tested to assess the influence of the culture medium. The iron supplement was chosen to infer about iron oxide biomineral formation, a less toxic mineral than calcite, since no toxic by-products are produced, and iron oxide minerals have a longer lifetime when compared with calcite crystals. Bioformulated mortars presented a very distinct porous structure, with a significant decrease on mechanical properties. Nevertheless, they also showed a decrease on thermal conductivity, a slight consolidative effect, and a significant decrease on vulnerability towards water. Apart from the possible use as mortar air entraining agents, the obtained results show the interest on further studies on the use of nontoxic iron-based bioproducts for earthen mortars optimization.

Estabilização de argamassas de terra: Uma revisão

Earth as a building material has been gaining a renewed interest due to current environmental and eco-efficiency concerns. Indeed, earth is an ecological and economically efficient material that can also contribute to increase indoor comfort. However, earth mortars have a limitation: their susceptibility to water. In order to implement a more comprehensive use in indoor and outdoor environments, where there may be contact with water, the inclusion of stabilizing agents has been studied. This article presents a critical literature review of the effect of the most common stabilizers used in earth mortars, specifically: vegetable fibres; binders such as calcium sulfates, air limes and limes with hydraulic properties, cement; and oils. It appears that some of these stabilizers seem to improve the earth mortars resistance to liquid water. However, in most cases, this improvement occurs at the expense of other important properties, which are also discussed.

Characterization of earthen plasters Influence of formulation and experimental methods

All over the world there is a vast heritage of earth construction where earth plasters were applied. Nowadays, due to environmental but also technical reasons, new earth plasters are also applied on common new masonries. That is why its characterization, in the laboratory but also in situ, is very important. In the present study, a pre-mixed earth plastering mortar (as control) and nine earth-based plastering mortars formulated in laboratory with different compositions were characterized. These mortars were formulated with 1:3 (illitic clayish earth:aggregate) volumetric ratio. The aggregate comprises a variation of fine and coarse sand and the partial replacement of the fine sand by a phase change material (PCM). The influence of the addition of a low amount of oat fibers is also evaluated. The mortars were characterized by different methods in laboratory and on an experimental all exposed outdoors by destructive and nondestructive methods: dry bulk density, dynamic modulus of elasticity, flexural and compressive strengths, adhesive and shear strengths, dry abrasion resistance, surface cohesion, ultrasonic pulse velocity and hardness. Results were discussed and some were correlated. Most mortars present good mechanical strengths. However, the addition of PCM significantly decrease the mechanical strength of mortars. In terms of mechanical properties, the addition of oat fibers only promotes an improvement on adhesive strength. The simple surface hardness by durometer presents laboratory and in situ results well correlated for earth mortars without PCM.

Eco-efficient earth plasters: The effect of sand grading and additions on fresh and mechanical properties

Earth-based plasters can be very eco-efficient both in terms of embodied energy and technical efficiency, although they are vulnerable to water when unstabilized. An experimental campaign was developed to assess the workability and the mechanical properties of formulated earth-based plastering mortars with a 1:3 (illitic clayish earth:aggregate) volumetric ratio. The aggregate components include different proportions of coarse and fine siliceous sands and the partial replacement of fine sand by a phase change material (PCM) or the addition of a low content of oat fibers. A pre-mixed earth mortar produced with clayish earth picked from the same pit was assessed as control. Mortars were tested to evaluate workability and density in the fresh state, and results were compared to dry bulk density, dynamic modulus of elasticity, flexural, compressive and adhesive strengths and dry abrasion resistance. Results show that even 15% replacement of the fine sand by the PCM significantly changes the workability, apart from decreasing the shrinkage and dry bulk density and reducing the mechanical strength of the mortars. Therefore, the addition of this type of PCM, that most probably have advantages in terms of thermal behavior of the plasters, may have important drawbacks in the fresh and hardened state of earth plasters that should also be considered. The addition of oat fibers does not show any improvement on the workability and mechanical characteristics of the earth mortars. In these mixed sand mortars, higher coarse sand content promotes a decrease in mechanical performance, showing the advantage of using sand with a well graded particle size distribution.

Efficacy of iron-based bioproducts as surface biotreatment for earth-based plastering mortars

Abstract The use of bacteria for the enhancement of construction materials has been a focus of study in the past few years. Microbial cells have been applied to consolidate the surface of different materials. Earthen plasters are eco-efficient building products that can be applied on new buildings but also used to protect cultural heritage structures, with several advantages. They are based on abundant, affordable and easy to obtain materials, but are vulnerable to water. New eco-efficient bioproducts were developed based on E. coli cultures supplemented with iron, that can be obtained as an industrial by-product. They were applied in laboratory on an earth plaster surface and the biotreatment efficacy was assessed. The main objective was to improve the durability of the plastering mortar when exposed to water. An optimized E. coli-iron based surface biotreatment strongly increased the plaster resistance to water with the application of only 0.0625 mL/cm2 of E. coli++Fe leading to a significant increase of water absorption time in comparison with similar plasters where the same amount of water was applied. Moreover, all biotreatments produced an increase of resistance to water absorption creating a slight waterproofing effect, ensuring compatibility. Their loss of efficacy with time guarantees reversibility of the intervention. The results show the interest to perform an in-depth study on the microstructure of biotreated earth mortars to understand the biotreatment effect.

Cation Exchange Capacity (CEC), texture, consistency and organic matter in soil assessment for earth construction: The case of earth mortars

There is a rapid development of earth construction the last few decades followed by an increased interest in scientific research in this field. One of the issues that have arisen is which soils are suitable for construction and can be designated as construction soils and which are not. Thus, the main objective of this paper is to investigate the relation between physical soil properties and mechanical properties of the dried building material. In this context, the Cation Exchange Capacity (CEC) of the soil is investigated in this research as an innovative tool in soil assessment for earth building. The distinct advantage of CEC is its dependence on clay type and organic matter apart from clay content, which is the soil property most frequently used in soil assessment for building purposes. This study focuses on earth mortars, on which little experimental research has been carried out despite their widespread use. In order to overcome the issues often mentioned in literature of using a certain soil and then generalizing the results, it was decided to use a wide range of soils with different textures from various regions of Greece. So, 26 soils were collected and a total of 49 earth mortar mixes were fabricated in two phases. The soil properties assessed were texture, Atterberg limits, CEC, mineralogy and organic matter content, while the hardened mortar properties assessed were compressive strength, flexural strength, dry density and linear shrinkage. It was found that CEC provides stronger correlation with compressive strength and linear shrinkage than clay content and Plasticity Index. A linear correlation between linear shrinkage and compressive strength was also established. Finally, it is shown that the soils with high organic matter content used in this research, are unsuitable for earth building despite having sufficient compressive strength.

Can an earth plaster be efficient when applied on different masonries?

Earth mortars are known for being ecological but also reversible, contributing to comfort and aesthetic. Nevertheless, compatibility with different masonries is scarcely assessed. A commercial unstabilised ready-mixed earth mortar was produced with an ilitic earth with addition of sand and oat straw fibres. It was used to plaster different experimental masonry walls, at protected outdoors environmental conditions. The plasters applied on the masonries were visually monitored and characterized in situ by non-destructive techniques and in laboratory by bulk density and microstructure. The same mortar used for the plasters was characterized in laboratory in fresh state and, after drying, on prismatic specimens and specimens composed by a mortar layer applied on hollow bricks. Some variation of results occurs when the same unstabilised ready-mixed earth mortar is used to plaster different masonries, what may be related to the water absorption of the masonry materials. However, after six months the earth plaster presented durability on the different masonries when protected from rain. It proves that this ecological mortar is technically efficient to plaster different types of masonry, historical or contemporary.

Strength of Hollow Compressed Stabilized Earth‐Block Masonry Prisms

Earth represents an ecological building material that is thought to reduce the carbon footprint at a point in its life cycle. However, it is very important to eliminate the undesirable properties of soil in an environmentally friendly way. Cement‐stabilized rammed earth, as a building material, has gradually gained popularity due to its higher and faster strength gain, durability, and availability with a low percentage of cement. This paper covers a detailed study of hollow compressed cement‐stabilized earth‐block masonry prisms to establish the strength properties of hollow compressed cement‐stabilized earth‐block masonry. The test results for masonry prisms constructed with hollow compressed cement‐stabilized blocks with two different strength grades and two earth mortars with different strengths are discussed.

Sustainable bio-based earth mortar with self-healing capacity

This paper describes the hygrothermal and mechanical properties and self-healing capacity of a sustainable bio-based mortar repair system for earth construction. There is currently limited characterisation of materials that directly compare earth, bio-fibres and self-healing behaviour. Additionally, the thermal performance of self-healing materials has been under-researched. Both prismatic and 0.1 m × 0.1 m samples were cast with plain mixes, saw mill residue (SMR), straw, wool and wood pellets. Executing both structural and hygrothermal experimentation provided an indication of the performance and durability of the samples. The bio-based agent added to the bio-based composite consisted of bacteria. Adding the bio-based agent to an earth matrix with (wheat) straw, (sheep) wool, SMR and wood pellets showed promising results for the hygric properties, as the initial water adsorption and absorption were lessened. The thermal conductivity was reduced from 0.32 to 0.23 W/m.K when bio-based agents were combined into the earth-based mix design with SMR. Overall, it is evident that out of all ten mix designs, bio-SMR provided the best environmental conditions for the bio-agent.

Eco-efficient earth plasters: influence of clay content, sand particle size and support

Earth construction, including the use of earth mortars, has been extensively used in the past. However, with the appearance of hydraulic binders, the use of earth strongly decreased for new construction and even to repair old earth buildings, whose best solution would be the use of compatible materials such as earth mortars.Due to the innumerable advantages of earth and with the growing concern on eco-efficient construction, the interest on earth construction has resurfaced, namely on earth mortars.In order to optimize the composition of an earth plastering mortar made with a defined clayish earth and two siliceous sands with different particle size, six compositions were assessed. Mortars with different volumetric ratios were applied in two different supports (on the back of a tile and on a brick) and planar specimens were also produced. Distinct characteristics were assessed, such as their visual appearance, shrinkage, surface cohesion, surface hardness, dry abrasion resistance, ultrasonic velocity, adhesive strength and thermal conductivity.It is possible to conclude that a higher clay content in the earth mortar composition increases the shrinkage and occurrence of cracking, the use of fine sand promotes high mass loss by abrasion, and the same mortar applied in different supports behave differently in terms of durability.

Grouts for strengthening two- and three-leaf stone masonry, made with earthen mortars

ABSTRACTEarth was used in the past to produce mortars either on its own or in combination with other materials (such as lime and sand). Earth mortars were used both in adobe and in stone masonry structures. This article aims to study stone masonries made with earth mortar and their strengthening by grouting. Six wallettes were constructed, in order to study the mechanical properties of the two- and three-leaf stone masonry before and after grouting. In parallel, several compositions of grouts, having different ratios of hydraulic lime (NHL5), earth and water, were designed and evaluated regarding their injectability properties (fluidity-penetrability, stability tests). Moreover, flexural and compressive strength tests were performed. Thus, this project led to the development of a number of suitable mixes that satisfy the performance criteria set for their design. The suitability of those mixes from the mechanical point of view was checked by injecting them to wallettes, subsequently tested in compression.

Strategies for optimizing the mechanical strengths of raw earth-based mortars

Earth-based mortars are commonly reinforced with bio-based materials such as straw or biopolymers. The aim of this work is to identify reinforcements that are able to improve the mechanical strengths and the ductility of an earth-based matrix. We have also attempted to describe the mechanisms of reinforcement involved in such materials. Firstly, a kaolinite-based clay soil was mixed with sand to achieve earth-based mortars with the highest density at the dry state. For this material (kaolinite-based mortar), we have shown that, at the same water content, the compressive strength at the dry state only depends on the dry density of the sample whatever the forming process. Various quantities of fibers, fabrics and alginate were then used to reinforce the studied mortars (a kaolinite based mortar and a natural soil containing swelling clay sieved at 4 mm). We found that these reinforcements significantly increase the compressive strength of all tested samples containing kaolinite. A comparison between the two materials helps us to understand the reinforcement mechanisms for various fibers; it also demonstrates that natural fibers and woven fabrics enhance the mechanical behavior of earth mortars notably under a compressive load.

Experimental investigations on the initial shear strength of masonry with earth mortars

In this paper, a comparative study on the initial shear strength of masonry with earth mortars is presented. Triplet tests were carried out to characterise the shear bond strength of five different types of earth mortar, three purely mineral and two with vegetable additives (wood and straw chaff), using calcium silicate blocks. In spite of their lower bulk densities, mortars with chaffs reached a value of compressive strength comparable to the values shown by the purely mineral mortars. The characteristic initial shear strengths of all the tested earth mortars were between two and five times higher than the minimum values for initial shear strengths required by standards. To assess the influence of blocks pre-wetting, a comparison between calcium silicate blocks and earth blocks was performed to evaluate the results obtained from the standard test procedure compared to the more common practice of using earth mortars in combination with earthen blocks.

Experimental investigations on the initial shear strength of masonry with earth mortars

In this paper, a comparative study on the initial shear strength of masonry with earth mortars is presented. Triplet tests were carried out to characterise the shear bond strength of five different types of earth mortar, three purely mineral and two with vegetable additives (wood and straw chaff), using calcium silicate blocks. In spite of their lower bulk densities, mortars with chaffs reached a value of compressive strength comparable to the values shown by the purely mineral mortars. The characteristic initial shear strengths of all the tested earth mortars were between two and five times higher than the minimum values for initial shear strengths required by standards. To assess the influence of blocks pre-wetting, a comparison between calcium silicate blocks and earth blocks was performed to evaluate the results obtained from the standard test procedure compared to the more common practice of using earth mortars in combination with earthen blocks.

Durability of the earth mortar: Physico-chemical and mineralogical characterization for the reduction of the capillary rise

The stabilization of the earth material in the fields related to the earthen construction, in compliance with the standards in force, allows strong results of strength and durability. The chemical and mineralogical elements play an important role, in the presence of an 'optimum' cement dosage, to strengthen the ties between the clays and the grains of the earth.. This approach targets the search for better performances in the use of natural materials resource in an eco-responsible habitat. This study presents the experimental results of the four techniques of mineralogical and chemical analysis on mortar specimens obtained from earth of the city of Fez. The results of the uni-axial compressive tests of the cylindrical specimens for this earth, associated by various percentages 0%, 4%, 7% and 10% by weight of cement, make it possible to analyze the effect of the mineralogical and chemical elements on the mechanical properties, namely Young's modulus, compressive strength and limiting deformation. However, we determine the water absorption coefficient of the mortar for different cement dosages in order to optimize the durability of the mortar against bad weather, rain and / or very wet climates. In the earth mortar of Fez, the strong presence of calcite (CaCO3), quartz SiO2 and dolomite CaMg (CO3)2 amplifies the improvement of the behavior of the material by the addition of cement. In fact, this strong presence of calcite stabilized the clay by cementing quartz and the cement matrix to strengthen the ties between the grains of the earth. In addition, with respect to the capillary rise, the water absorption decreases with the addition of cement. We also note that the evolution of the mechanical properties is of no importance except in the interval [4 to 7%] which represents the zone of effect for cement stabilization and which houses the optimum technicoeconomic cement dosing.