Modern earth building codes, standards and normative development
Abstract:
This chapter provides an overview of standards and normative documents in the field of building with earth developed in the last 30 years. Building with earth is usually regarded as a ‘non-engineered’ construction technique with roots in a rich tradition of building heritage that needs to be maintained. As a consequence, building standards in the field of earth building have been drawn up in only a few countries. In the last decade, however, the use of earth in construction has become increasingly widespread in many countries. The 33 different standards examined in this chapter come from 19 different countries and provide varying degrees of technical information. With regard to their scope of application, the documents can be classified into three types, each dealing with a particular aspect: soil classification, earth building materials and earth construction systems. Our analysis shows that standard internationally accepted terminology is still lacking. This, however, is an essential general prerequisite for developing standards and normative documents.
4.1 Introduction: a short history of building codes for using earth as a building material
Earth is one of the oldest building materials known to mankind. According to archaeological excavations, the first use of earth as a building material dates back to the Neolithic period in approximately 10 000 BC in the warm and dry climate of the eastern Mediterranean and Mesopotamia in what is today Anatolia (Turkey), Syria, Jordan, Lebanon, Israel (Palestine) and Iraq.
For thousands of years earth was the prevailing building material for house construction in many regions of the world with appropriate soils and climatic conditions. As a result, it became necessary to develop rules for using this material for building purposes. Written or painted documents describing earth building served as early ‘ rules’ for using earth as a building material. Fig. 4.1 34 depicts the process of building with mud blocks in ancient Egypt in about 1500 BC and shows quite some detail including the block sizes, the block bonds in the wall construction and the use of a plumb as an expression of the technical standards and quality control mechanisms of masonry work at the time.
4.1 Technical standard of mud block building in ancient Egypt 1,500 BC34.
In Central Europe the history of technical rules in the field of earth building is closely related to the development of cities in the 14th and 15th centuries. As a result of their rapid growth, the availability of timber as primary building material became scarce. Moreover, timber structures were susceptible to fire damage, and fires were responsible for wiping out entire portions of cities, either by accident or as a result of war.
Both problems led to the drawing up of the first mandatory building codes across several German states. The Ernestine Building Code, introduced in 1556 in the state of Thuringia, did not permit houses to be solely constructed of timber but only as timber frame structures in combination with fired bricks, adobe or natural stone, or alternatively as Weller-structures, the German variant of cob. The Saxony Forester Code drawn up in 1575 permitted the use of timber for new house constructions only when the first floor could not be built of stone or cob. Two hundred years later, other building codes for Saxony (1786) (Fig. 4.2 35), Prussia (1764) and Austria (1753) (called ‘Egyptian stones’) for wall construction. For hundreds of years building codes enforced the use of earth for building purposes by restricting the use of timber for house constructions.
4.2 Decree of the Saxony’s emperor Friedrich August from 1786 concerning the use of cob for ground floors35.
The use of earth was characterised by a high degree of manual work. After around 1850, the Industrial Revolution brought about a fundamental change in the way building materials were produced in many industrialised countries: the mechanisation of production processes meant that building materials such as fired bricks could now be produced in large factories more economically and at better quality than before. Nevertheless, from the end of the 19th century new building materials such as steel, cement, concrete and reinforced concrete began to displace the use of earth until it was only rarely used. In Germany, earth experienced a brief revival after each of the world wars. As a consequence of industrialisation, building standards or regulations for building with earth were developed in just a few countries.
The German Earth Building Code (the Lehmbauordnung), drawn up in 1944, was the first contemporary technical standard in Europe dedicated to earth as a building material. The code summarised the entire technical knowledge of building with earth available at the time. In 1944, a year before the end of the Second World War, the industrial basis had been destroyed along with vast numbers of houses: millions of people were homeless and urgently needed new shelter. Very often earth was the only locally available building material. The German State Building Authority’s intention was to regulate the use of earth as a building material for the period of reconstruction after the war. However, as a result of post-war reorganisation, the code could only be put into effect seven years later in 1951 as DIN 18951. In the five years that followed its issue, a number of further DIN-codes were drafted, dedicated to different fields of building with earth. Of these only the first, DIN 18951, came into force – all the others did not progress beyond draft status.1 By the 1970s, the use of earth as a building material had all but disappeared as a result of industrialisation, and in 1971 the DIN was withdrawn and not replaced.
At the beginning of the 1980s, after the experience of the oil crisis in 1973 and health scandals caused by so-called modern building materials, a new way of thinking arose in some industrialised European countries: alongside ‘traditional’ economic and technical aspects such as durability, strength and so on, consumers started to give greater consideration to ecological aspects such as health, recyclability and low embodied energy as well as aesthetic and ‘soft’ design factors such as indoor climate, colour and surface qualities.
These ‘new’ ecological aspects are now anchored in the European Union framework of building regulations. The principle of ‘life cycle assessment LCA’ as a method for evaluating the sustainability of building materials will lead to a new generation of building standards. In the context of these developments, earth as a building material can be seen in a new light.2,42
4.2 Types of ‘standards’ for earth buildings
The International Standards Organisation (ISO)3 distinguishes between the terms ‘standards’ and ‘normative documents’ as follows:
A standard is a ‘document, established by consensus and approved by a recognised body, that provides, for common and repeated use, rules, guidelines or characteristics of activities or their results, aimed at the achievement of the optimum degree of order in a given context’ and ‘should be based on the consolidated results of science, technology and experience, and aimed at the promotion of optimum community benefits’. In this context ‘consensus’ is a general agreement characterised by ‘the absence of sustained opposition to substantial issues’.
The ‘promotion of optimum community benefits’ means that standards primarily serve economic and social aims, facilitating the exchange of goods and services, protecting the consumer (safety, product quality, etc.) and ensuring a good quality of life (health, hygiene, environment, etc.).
The results of science, technology and experience (the ‘state of the art’) are not static and change continually as new developments arise, which in turn must be reflected in the standards. Standards therefore need to be periodically renewed, revised and updated. This process is the responsibility of the standards writing body.
Technical standards include building standards. The latter are usually established norms or requirements approved and recognised by state building authorities. Building standards can be classified into material standards, which describe the ‘means’ to achieve a ‘result’ (construction) and construction standards that describe the manufacture of materials necessary to achieve a construction with particular performance characteristics. Special topics (building with earth) can also be included as separate chapters of general building standards.
Producers of building materials can apply for a licence from the state building authority for the use of a specific building product. This ‘technical permit’ is a special type of building standard for ‘repeated use’ by the producer. It is not published publicly and is valid only for that manufacturer’s specific building product and for a specified time period. It defines the qualities for production and terms for the ongoing control of the production process for a single building product.
A normative document is a ‘document that provides rules, guidelines and characteristics for activities or their results’, and as a result has neither the scope nor the endorsement of a standard, although it can become a ‘ standard’ after adoption by a governmental body. Normative documents are developed by a group of specialists or organisations with proven competence in the respective field and are published for general use.
Technical standards, including those for building, can also be classified into different groups according to the geographic area and corresponding issuing organisation.
4.2.1 International standards
These are issued by the International Organisation for Standardization (ISO) in Geneva with about 150 members represented by the national organisations for standardisation.
4.2.2 Regional standards
These are issued in Europe by the European Committee for Standardization (CEN) in Geneva as European Standards EN. Members of the CEN are all member states of the EU as well as Switzerland and Norway. In addition, there are also European Building Codes (‘Eurocodes EC’) that describe uniform standards for the design, measurement and construction of buildings in the EU, e.g. the ‘measurement and construction of brickwork’ (EC 6). Earth blocks do not feature in this building code.
4.2.3 National standards
These are issued by the National Standards Bodies (NSB), in Germany the Deutsches Institut für Normung e.V. (DIN), which in turn are members of the CEN or ISO. National standards can also be issued by special (building) organisations or associations acting on a national level if they follow a predefined process of approval to acquire ‘legal status’. In order to be recognised as a building standard by the national state building authorities, a draft code has to pass a predefined process of approval:
1. The draft has to be developed by a group of specialists or organisations with proven competence in the respective field (e.g. building with earth). This group is also known as a ‘Technical Committee’.
2. The draft has to be submitted for public discussion to a broad audience of specialists with approved competence (in building with earth) with the aim of reaching a ‘consensus among specialists’.
3. The ‘consensus draft’ is then presented to the national state building authorities for public consultation for a limited time. Comments and suggestions resulting from public enquiries are evaluated and if necessary considered. A revised ‘final draft’ is drawn up and submitted for ratification as a national/regional standard to the relevant authorities.
4. After ratification by the national state building authorities the draft is accorded the status of a building standard and is recommended for implementation.
5. European national standards must be registered with the department of standards at the European Commission in Brussels in order to disseminate the required information to all appropriate departments of the member states.
6. The building standard is published in a state decree and comes into force.
4.2.4 Local standards
In the USA several regional standards bodies exist that are responsible for issuing local building codes for a specific federal state, county or even a city. Each federal state, county or city may join depending on their geographic situation. Building standards issued by State Building Authorities are mandatory for building contracts. Normative documents issued by special national organisations or associations have not passed an approval process and therefore do not have any ‘legal status’, serving instead as a recommendation. Both types of documents must represent the ‘state of the art’ of a process or a technical development.
4.3 Normative documents for earth building
In recent years several studies have undertaken international surveys of standards and normative documents in the field of earth building. These were usually produced as part of financed projects by national technical groups in order to establish a knowledge basis for the development of own (national) standards or normative documents. Examples of such studies include Jiménez and Delgado and Cañas Guerrero, 2005,4 which details various techniques using unstabilised earth, Maniatidis and Walker, 20035 which examines rammed earth codes and Cid et al., 201141 which gives a worldwide, overview about earth-building normative documents. Some handbooks on earth building also include chapters on the state of the art in this field, for example Houben and Guillaud, 19946. McHenry, 19897 provides an overview of regional earth building standards in the USA.
4.3.1 Types of documents
Table 4.1 provides an overview of existing earth building standards and normative documents according to document type. Thirty-three different documents have been identified from 19 countries published by regional, national or local standards bodies over the last 30 years. The technical information they contain varies considerably.
Table 4.1
An overview of the types of earth building standards and normative documents
S Standards issued by national standards bodies (NSBs) or specialised organisations that have passed a predefined procedure approval and are recognised by a state building authority.
BC Building codes issued by NSBs with one or more chapters on building with earth.
ND Normative document issued by specialised organizations that have passed a predefined procedure of approval but are not recognised by a state building authority. L Local
E, ES Earth, earth stabilised with cement
EB Earth block; Adobe; compressed earth block, CEB; compressed stabilised earth block, CSEB; poured earth blocks, PEB
EM Earth mortar; earth plaster, EP; earth masonry mortar, EMM; earth spray mortar, ESM
El Earth infill; wattle and daub, WD; poured earth infill, PEI
RE Rammed earth; cement stabilized rammed earth, CSRE
aConcerns the earthquake resistance of earth construction systems.
bIn 2010 the French national earth building organisation AsTerre began drafting new French earth building standards covering the main earth construction systems prevalent in France, including EB, rammed earth (pisé) (RE) cob (C), light earth (LE) and earth plaster (EP).
cA number of local adobe building codes (L) exist that bear similarity to the NMAC (San Diego/CA, Tucson/AR, Marana/Pima/AR, Boulder/CO).
dDraft of NSB
The ‘Australian earth building handbook HB 195-2002’ was published by the national organization Standards Australia, but ‘the Handbook has not been published under the auspices of the Standards Australia Committee BD-083, and therefore it should not be taken as representative of the views of the committee members’.39 This document has not reached a ‘consensus among specialists’, which is an essential requirement of the approval process. Therefore, it was not included in Table 4.1.
In addition, numerous technical notes have been issued by state building research organisations (Overseas Building Notes and Overseas Information Papers/UK, Commonwealth Experimental Building Station/Australia, etc.) and non-governmental organisations (UNCHS/HABITAT, ILO, CYTED, Gate-BASIN, etc.). These have not been considered in this overview, but could nevertheless contain information that may be valuable for the analysis of existing standards or the development of new earth building standards.
Other national standards have been cited as reference documents for the resolution of specific aspects of earth building. These include standards that address soil classification, soil mechanics, testing procedures, the design of load-bearing earth walls and general codes for the structural design of buildings. Likewise, non-governmental bodies have also drawn up numerous technical notes in the field of conservation of historical earth buildings (cob, earthen infill, etc.). While these are not standards, they could be valuable for the drafting of new standards or normative documents on earth building because the conservation of historic earthen architecture constitutes a significant proportion of earth building activities. In the last few years, standards for the conservation of historic earthen buildings have also been developed by regional and national governmental organisations (Italy 2006,43 Chile draft 2010).
The documents analyzed are almost always national standards (S) or normative documents (ND). Sometimes these take the form of individual chapters on earth building within broader national building codes (BC). In the USA, building standards are issued by the regional standards bodies, federal states, counties or even cities (L). One of the standards listed has been developed at a continental level (African Regional Standard ARS). The documents can be classified into three types with regard to their scope of application (see page 82):
This classification relates to the life cycle assessment (LCA) of earth as a building material (Fig. 4.3 2). Each section of this cycle has its own specific requirements that guarantee the usability of the material or product in that section. Usability requirements are defined in standards by corresponding parameters. Typical parameters include:
4.3 Building with earth presented as self-sustaining life cycle2.
4.3.2 Classification of earthen materials and construction systems
In the standards listed in Table 4.1, the terminology used to describe earthen building materials and earth construction systems reflects the differing levels of technological development in different parts of the world. The definitions used are often derived from local building traditions and are not always appropriate for use as contemporary technical terminology. Nevertheless, the existing building stock of traditional earth buildings must also be considered in standards concerning conservation work. On the other hand, 12 of the 33 standards and normative documents are less than 5 years old, demonstrating an increasing acceptance of earth as a viable contemporary building material. At present, there is no common internationally accepted terminology for earth building. This, however, is an essential prerequisite for establishing earthen building materials alongside other conventional building products for contemporary building. In this chapter we recommend the following terminology based primarily on recent standards documents and guidelines.8’9’10’13’18’29 The recommended terminology encompasses all earthen building materials and earth construction systems commonly used today and detailed in (earth) building standards. In some cases it was necessary to modify regional definitions in order to avoid misunderstandings.
Soil
A granular material derived from weathered parent rock, often transported and sedimented by natural processes. It can contain natural constituents (organic content/humus, soluble salts). A soil that is already suitable for building purposes is classified as ‘earth’.
Earth (E)
A soil suitable for building purposes, which contains an appropriate mixture of silty, sandy and/or gravelly particles, together with clay minerals as a natural binder and water. Earth does not set chemically but hardens in the air. The specific properties of clay minerals mean that hardened earth can be softened again to a plastic mass through the addition of water (re-plasticisation). As a result, it can be recycled as often as required, which is one of the ecological qualities of the material. Other natural constituents of soils (e.g. lime, iron oxides) can also function as a natural binder but cannot be re-plasticised. Earth for building purposes must be prepared to a homogeneous mass, shaped and dried in order to produce an earth-building material or product.
Earth building materials
These can be produced in situ for individual constructions or manufactured industrially according to standardised reproducible procedures as defined in standards or norms. Unstabilised earth-building materials harden in the air with clay minerals acting as a natural binder. Stabilised earth-building materials contain artificial tempering admixtures (e.g. granular or fibrous particles), which are added during the preparation process. Stabilising admixtures can also constitute artificial binders (lime, cement) that change the clay minerals chemically (i.e. chemical stabilisation) in order to improve the mechanical properties of the earth building materials. A chemically stabilised earth material cannot generally be re-plasticised by adding water, and when possible only slightly. Unshaped earthen building materials are dry or moist ready mixtures for specific uses such as rammed earth (RE), cob walling (C), light clay (LC), earthen infill (EI), wall linings (WL), earthen mortars (EM), etc. Shaped earthen building materials are manufactured from moist unshaped earthen building materials by moulding in conjunction with different types of compaction (i.e. mechanical stabilisation), for example, earth blocks (EBs) or clay panels (CPs). In a dry state they are used for a specific purpose such as earth block masonry (EBM), EI, wall linings (WL), etc.
Earth mortars (EM)
These are earthen building materials containing appropriate tempering admixtures. They are delivered as unshaped dry or moist ready mixtures and are mixed to serve a specific type of application, which must be declared:
• Earth plaster mortar (EPM) is applied to the surfaces of (earth) building constructions and usually contains sand and/or natural fibrous tempering materials. A large number of different types of EPMs exist with coarse/fine aggregates, particular colours or stabilised with artificial binders or tempering admixtures for special granularity or colour effects, etc.
• Earth masonry mortar (EMM) is used for constructing EBM and usually contains sand as a natural tempering material
• Earth spray mortar is used for manufacturing EBs or parts of a building by spraying into or against formwork. They contain appropriate tempering admixtures and in many cases artificial binders.
Earth blocks (EB)
A shaped earth building product manufactured from moist unshaped earth building materials with appropriate admixtures in a moulding process. The mechanical properties of earth blocks are influenced significantly by the type of compaction (manual/mechanized) and the amount of mixing water. Unlike conventional bricks (ceramic bricks), EBs are air-dried and not fired.
• Adobe: air-dried masonry block without any specific type of moulding or compaction. Adobe blocks made of a wet earth mixture are sometimes called ‘mud’ blocks
• Compressed: EBs formed in a block mould with the addition of (static) mechanical compression (CEB) or (dynamic) compaction. The use of compressed stabilised earth blocks (CSEB)/cement stabilised compressed earth blocks (CSCEB) is widespread in many countries
• Extruded: EBs formed by a process of extrusion
• Cast: EBs manufactured by pouring or spraying a slurry of (chemically) stabilised earthen materials into forms.
Clay panels (CP)
These differ from EBs in size and thickness as well as in their method of manufacture. They are typically used for non-load-bearing partitioning interior walls. Thin CPs are usually up to 30 mm thick and of a similar size to conventional plasterboard panels. They are mounted on a supporting construction of wood or metal studs. Thick CPs are large-format EBs that are self-supporting and can be laid with mortar or glued.
Earth construction systems
A variety of construction systems exist that employ earthen building materials either entirely or in part for load-bearing and non-load-bearing elements in different parts of a building. Common earth construction systems include earth block masonry (EBM), rammed earth (RE), cob (C) and earthen infill (EI).
Earth block masonry (EBM)
A construction system using earth blocks (EB)/compressed earth blocks (CEB)/cement stabilised compressed earth blocks (CSCEB) and earth mortars (EM) for building structures as well as for the earthen infill (EI) of framed or half-timbered constructions.
Cob (C)
A construction system in which a moist unshaped cob mixture (straw clay) is lightly tamped into place without formwork to form monolithic walls.
Rammed earth (RE)
A construction system that uses a slightly moist unshaped rammed earth mixture. The earth mixture is filled into prepared formwork in layers that are individually compacted (rammed). The series of compacted layers produces the desired shape of the final structure. The formwork can be removed before the compacted material has fully dried. Special decorative effects can be achieved by using earth mixtures of different granularity or colour.
Poured earth (PE)
A construction system in which a slurry containing earth mortar and artificial binders is sprayed against or poured into formwork similar to those used for in situ concrete.
Earth plaster (EP)
Earth plasters are made of earth plaster mortars (EPM). They are applied manually or mechanically in one or more layers to the interior surfaces of buildings or to exterior walls protected against exposure to water. The overall thickness of all earth plaster layers is usually no more than 20 mm for a new application. EPs help to improve the indoor climate by regulating humidity.
Earthen infill (EI)
A construction method used in conjunction with framed or half-timbered constructions that serve as the load-bearing system. The panels between the timber studs, rails and braces are filled with a non-structural ‘infill’ or ‘nogging’ in a variety of different techniques:
• Wattle and daub (WD): There are numerous different regional variants. The wattle and daub technique typical in Europe employs wooden struts jammed between the timber members that are interwoven with a wickerwork of split willow branches. This supporting ‘wattle’ is then daubed from both sides with a straw clay mixture
Wall linings (WL)
This technique, sometimes called an ‘inner leaf, is often used in renovation work to improve the thermal insulation, wind-proofing and noise insulation of existing thin (historical) exterior walls, in particular where external insulation is not an option because the half-timbered elevations must remain visible. WLs can be executed as masonry wall linings using earth blocks (EB), as light clay wall linings using moist unshaped light earth or earth spray mortar/poured earth (PE) or as a lining of dry stacked earth blocks to create a suitably massive heat retentive thermal mass. Clay panels (CP) can also be used.
4.4 Selecting the parameters for earth building standards
Historically, earth construction techniques were ‘non-engineered’ building systems. Earth building materials were produced in-situ, quality tests were carried out according to quick and simple field tests in the form of macroscopic visual observations and manual handling. The equipment required was inexpensive and easily accessible, but the test conditions were not exactly reproducible. As such, the results could be classified as ‘estimated values’ and depended on the subjective observation of the tester. For non-engineered building systems field tests were entirely sufficient.
Since the late 20th century, the increased interest in building with earth has resulted in a change in the character of production methods from predominantly ‘hand-made’ to large-scale industrial production. The corresponding building techniques have now become ‘engineered’ and standardised construction systems. As a result, the character of test procedures also changed from field tests to laboratory tests. ‘Engineered’ construction systems require industrially produced building materials with defined parameters that are arrived at using standardised and reproducible testing procedures and quality controlled by authorised laboratories with qualified personnel using standardised test equipment.
An analysis of the standards and normative documents listed in Table 4.1 shows that uniform test procedures for determining the mechanical parameters of earth building materials as well as common design criteria for earthen construction systems do not currently exist. Instead, test procedures from other disciplines are often used, e.g. from soil mechanics for soil classification or from concrete testing for determining compressive strength. The applicability of these ‘adopted’ procedures for earth building materials has as yet not been proven.
It is, therefore, necessary to bring the test procedures for earth building products up to the same level as for other ‘ standardised’ building materials in order to improve their range of use and competitiveness in the building sector. While field tests can support the results of laboratory tests, they cannot replace them. As such, they can be included as non-mandatory information in the appendices of standards and normative documents (e.g. ASTM, 201013). A central reason for establishing proper standardised testing and quality control procedures is to ensure the quality of industrially manufactured earth building materials so that producers have a legal status for their products.
The differences between the analysed standards can be demonstrated using three examples of laboratory testing procedures and design criteria covering key areas of earth building:
1. soil classification and selection: granular composition and plasticity
2. compressive strength and optimum compaction for rammed earth
4.4.1 Soil classification and selection
The primary parameters for selecting soils suitable for earth building purposes are the granular composition, which serves as the ‘load-bearing skeleton’, and the plasticity or cohesion caused by the type and amount of clay particles (d ≤ 0.002 mm). These particles act as a natural binder holding together the coarse grains. The plasticity can also be influenced by natural admixtures such as humus and soluble salts. The nature of the binding properties of clay minerals mean that soil can be prepared, including mixing with admixtures, in a wet state but also retains its shape and stability, e.g. as a block or panel, during desiccation and when dry. Some natural soils exist that exhibit a nearly ‘ideal’ combination of plastic properties and grain composition for specific uses, e.g. loess-type soils for use as earth plaster. Secondary soil parameters, such as shrinkage, can be derived from the primary parameters. The interaction between these physical and chemical – mineralogical parameters is very complex and cannot be analysed independently of one another.
Industrially produced earth building materials consist of different ingredients which are exactly dosed and prepared according to defined recipes. Soil as a natural binder characterised by its plastic properties is only one part of this mixture. It is often replaced by industrially produced clay powder or other artificial binders. The importance of natural soil as a binding agent in the mixture therefore depends on the specific composition of a particular earth building material. Discussions concerning the definition of general or specified limits of plastic soil properties and soil grading in earth building standards does not lead to satisfactory and reliable results.
The new German Technical Recommendation DVL TM 05 ‘Quality control of soil as an ingredient of industrially produced earth building materials’36 defines controls for the soil ‘quality’ in the form of a series of appropriate test procedures for determining typical soil parameters including plasticity, grain composition and soluble salt content level. A producer of such soils can declare these parameters to aid earth building product manufacturers in sourcing appropriate soils. The control of mechanical properties (compressive strength, shrinkage, etc.) that influence the usability of the resulting earth building product, e.g. earth mortar EM and earth blocks EB, including the definition of permissible limits, will be defined in ‘product standards’.32’10’40
Grain composition and plasticity
Two approaches are used in earth building standards to quantify the parameters ‘grain composition’ and ‘plasticity’ for soils suitable for building:
The first approach defines numerical ranges for each of the soil parameters ‘grading’ and ‘plasticity’. This approach was developed by Houben and Guillaud, 1989, 19946 on the basis of standard geotechnical testing procedures used by the Unified Soil Classification System (USCS). The American ASTM standards use other maximum grain diameters: silt 0.002–0.075mm; sand 0.075–4.75mm; gravel > 4.75mm. They propose two separate diagrams for the ranges of granular composition and plasticity with respect to their different uses: rammed earth (RE), adobe, compressed earth blocks (CEB) and cement stabilised earth blocks CSEB. ‘The limits of the zones recommended are approximate, the permitted tolerances vary considerably. Present knowledge does not justify the application of narrow limits. The zones are intended to provide guidance and are not intended to be applied as a rigid specification.’6
Nevertheless, these diagrams were adopted by different earth building standards and normative documents as given in Table 4.1: ARS 680-681 (1996)16 for CEB and earth masonry mortar EMM, AFNOR (2001)27 for CEB, MOPT (1992)28 for RE and the Swiss earth building guidelines 0(1994)12 for RE and adobe (plasticity diagrams only). Figure 4.5 on page 92 shows the respective diagrams according to a study by Jiménez Delgado and Cañas Guerrero, 20054
Table 4.2 shows the following recommendations for unstabilised and cement stabilised rammed earth and earth blocks respectively with regard to soil gradation and plasticity.
Table 4.2
Numerical ranges of recommended soil gradation and plasticity for stabilised rammed earth and earth blocks
agrain fractions according to US standard systems.
baccording to Russian standard system CHиΠ (SNiP) the maximal particle diameter of clay is 0.005 mm.
The second approach used by the German Lehmbau Regeln (2009)8 issued by the Dachverband Lehm e.V. also employs the geotechnical parameter ‘soil plasticity’ in conjunction with a second recommended parameter, ‘binding force’, which summarises the physical-chemical effects of ‘grading’ and ‘plasticity’ including the influence of possible natural admixtures in a single parameter (DIN 18952-21). The respective testing procedure is known as the ‘8-shaped’ test in which the ultimate tensile strength (i.e. binding force or cohesion) of an 8-shaped specimen made of a ‘normative’ test consistency is determined (Fig. 4.4). The tested soils are classified numerically according to their binding force on a scale ranging from ‘lean/poor’ to ‘rich/clayey’.
The ‘binding force’ classes correlate numerically to ‘linear shrinkage’ classes. A soil suitable for a specific use, e.g. rammed earth, earth blocks, etc., should exhibit a defined binding force classification, which is given in the general requirements of soil selection for a specific earth building product8.
Table 4.3 shows the numerical correlation between binding force and linear shrinkage according to DIN 18952-21 and their limits of suitability for a specific use.8 Soils with a binding force < 0.005 N/mm2 cannot be analysed exactly using the 8-shaped test but these are unsuitable for many earth building purposes. A numerical correlation between the parameters ‘soil plasticity’ (first approach) and ‘binding force’ is recommended in Schroeder, 20102 as a first approach. Further research is needed in this area. The permissible maximum grain diameter and minimum percentage of clay and recommended plasticity parameters for a specific use can be derived from Fig. 4.5.4
4.5 Recommended limits of grain composition and soil plasticity in earth building standards4.
The ASTM E2329 201013 also contains an appendix with ‘non-mandatory information’. This part recommends two field tests (‘ribbon’ and ball test) in order to estimate the plasticity and the cohesion of a test soil.
Permissible salt content levels
Naturally occurring soils exhibit a ‘three-phased’ system consisting of soil solids, water and air. The solid phase is formed by the ‘mineral skeleton’ as well as other natural ingredients such as lime, soluble salts and organic matter. The soluble salt content in natural soils is considerably higher in dry regions with low precipitation and where the ground water is between 2 and 3 m beneath the soil surface. The soluble salts usually consist of sulfates, chlorides and nitrates of calcium, sodium, potassium and magnesium.
If water is present in the structure, soluble salts can lead to typical damage patterns in buildings structures. Possible water sources include rain ingress or vapour or moisture penetration (rising damp) from the ground where a damp proof course is lacking. Moisture from the surrounding ground rises through capillary action transporting additional salts into the wall. The moisture eventually evaporates from the wall surfaces leaving behind salts in concentrated quantities, which appear as crystalline efflorescence on the wall surface. The salts additionally absorb water hygroscopically, reducing the strength of the earth building materials.
Only very few earth building standards define permissible levels of soluble salts in soils for use as a raw material for the production of earth building products as shown in Table 4.4. The permissible levels also differ considerably. Sulfates will damage cement and can, therefore, be a special problem for cement stabilised earth constructions. In this case, the use of sulfate-resistant Portland cement is recommended.
4.4.2 Compressive strength and optimal compaction
The mechanical strength of a soil or earth building material is one of the most fundamental items of information for earth construction design, especially for load-bearing wall constructions. The prepared soil or earth mixture must be compacted into a dense state of optimal compaction to minimise the void content. In this state the strength increases as it dries to a maximum while volumetric changes are minimal. The mechanical strength of a soil or earth building material is normally determined by the unconfined compressive strength (UCS) of test specimens as a result of uni-axial compression.
The maximum compaction of a given soil sample (maximum dry density MDD) is usually determined by heavy manual compaction, internationally known as the PROCTOR test and standardised in national norms in the field of soil mechanics (e.g. BS 1377-4, 1990). This general approach is also used in several earth building standards and normative documents for determining the UCS of soil specimens. For most practical earth building purposes an MDD ≥ 0.90% will be accepted.
The soil preparation process usually involves the addition of water to cover the particle surfaces with a thin film of water. During compaction these films allow the soil particles to slide over each other more easily. Finer particles fill voids created by the coarser ones. This process works well for coarse-grained soils because the water film is extremely thin in comparison to the grain diameter. Up to a certain point the addition of water replaces air in the voids in the soil. After a relatively high degree of water content has been reached, the amount of entrapped air remains essentially constant. This ‘optimum moisture content’ (OMC) for a given soil and a defined compaction energy allows one to derive a maximum weight of soil per volumetric unit.
This process only works to a limited degree with fine-grained soils. The smaller particles are likewise covered with thin coatings of clay minerals, which also adsorb films of water. Due to the higher overall proportion of clay minerals and water in fine-grained clayey soils, the films of water are correspondingly ‘thicker’ compared with coarse-grained soils and resist significant compaction. The MDD is therefore lowest for fine-grained soils using the same compaction energy. The density can be increased for all soil types by using a greater compaction energy. In the case of fine-grained soils, a water content level higher than the OMC according to PROCTOR during compaction results in a higher compressive strength as a result of systematic laboratory tests.2
When considering strength properties, one should be aware that laboratory test conditions (size of test specimen, compaction energy, defined loading rate per time unit) cannot easily be transferred to real construction site conditions. ‘ Engineered’ earth building structures require comparable design parameters determined by reproducible uniform test procedures. One laboratory test sample includes a series of a minimum of three and more individual specimens from which the arithmetic average value is determined for the UCS. The characteristic value denotes the standard deviation of the test sample. The design value (permissible working stress) also incorporates a safety factor to take into account likely worst-case ambient conditions that may affect the earth construction during use, in particular with regard to moisture.
Table 4.5 provides an overview of the recommended design values and specimen details/characteristic UCS values for rammed earth (RE) in the earth building standards and normative documents listed in Table 4.1.
Table 4.5
Recommended design values and specimen details/characteristic UCS values for rammed earth (RE)
a‘Design’ and ‘characteristic’ values not distinguished.
bCement-stabilised.
cE/I: Exterior/interior walls.
Table 4.5 shows that uniform test procedures for determining the UCS of soils or earth building materials do not exist. The test specimens alone have different shapes and dimensions (cube, prism, cylinder). The UCS of unstabilised soils is in the range 0.7–4.0 N/mm2 and for (cement) stabilised soils it is significantly higher. In this case the UCS is determined after 28 days (additionally 3 and 7 days) along with the ‘wet’ UCS.
Only very few documents distinguish between ‘design’ and ‘characteristic’ values of the UCS. The German standards8 and Swiss normative documents12 recommend design values for UCS which include safety factors of 6.7–8.0. The smallest ‘design’ value is 0.3 N/mm2, the largest permissible 0.5 N/mm2.
The Spanish normative document28 recommends ‘approximate but safe values of permissible stresses’ (design values) for ‘low risk projects’,31 for interior walls not exposed to wet environments and for exterior walls. For ‘important projects’ the characteristic UCS should be determined in a laboratory using 30-cm3 cubes and then divided by a recommended safety factor of 6.0 for exterior walls exposed to the weather, or 3.0 for interior walls in order to obtain the design strength. For ‘most cases’ a ‘low/medium/high crushing strength’ can be chosen for the respective actual situation and than compared with the real situation from in-situ testing of 5-cm3 samples cut from test units by simple means.31
Walker et al., 200530 recommend partial safety factors ranging between 3.0 and 6.0 to account for variations in materials and the quality of work. The selection of the partial safety factor is a matter discretion for the designer, who needs to consider the possible consequences of failure and likelihood of accidental damage.
The SLS 1382: Part 321 recommends the determination of characteristic compressive strength for CSEB masonry on the base of BS 5628: Part 1.
4.4.3 Wall thickness
Limits for wall thickness and slenderness are key parameters required in building standards in order to limit the likelihood of excessive cracking and compression buckling under service load. The slenderness of a wall h/t is the ratio of wall height to thickness. In traditional building this ratio is usually 10 for freestanding walls and 18 for walls laterally restrained at the top and bottom. In seismic regions13’14’17’18 these values are significantly lower and special reinforcement of the walls is required. Most standards limit earth constructions to buildings with a maximum of two-storeys. The SLS 138221 is applicable for load-bearing CSEB masonry construction up to three stories. Table 4.6 provides an overview of the limits for wall thickness and slenderness of laterally restrained load-bearing earth walls in different construction techniques.
Table 4.6
Recommended values for wall thickness and slenderness of earth walls
aE/I: Exterior/interior wall; L/NL: load-bearing/non-load-bearing.
bSingle storey/bottom wall of a 2-storey house.
cEarthquake zone factor Z > 0.6 (10 and 24 at Z < 0.6 resp.)
dMaximum length of the wall: 12 
t
eEmpirical design recommendation: h ≤ 8 t for medium seismic risk; h ≤ 6 t for high seismic risk
fLimits of heights for adobe buildings: seismic zones (SZ) V + IV one storey; SZ III two-storey buildings. Important buildings should not be constructed in SZ IV + V, in SZ III only one storey
4.5 New developments in earth building standards
4.5.1 Ecological aspects
Global climate change, excessive consumption of energy and resources and sustainable development are aspects of considerable concern to modern society. Sustainability means that our generation shall make careful and economic use of the available resources in order to guarantee appropriate living conditions for future generations. The building industry can make a major contribution to this aim. Construction systems with a smaller environmental impact over their life cycle and building materials with low primary energy consumption are becoming increasingly significant. In this respect, earthen building materials and construction systems are particularly favourable. This new development is also reflected by an increasing number of earth building standards in recent years that focus on industrially produced earthen building materials.
The assessment of the environmental impact of building materials, buildings and other necessary services throughout their lifetimes is known as Life Cycle Assessment (LCA). The assessment analyses the entire life cycle of a building product from raw material excavation (soil), through the processing of raw materials (soil and additives), manufacturing of the (earthen) building materials, the construction, utilisation and maintenance (of earth buildings), as well as recycling and final disposal. A model LCA for earthen building materials is described in Fig. 4.3.2
Energy impact
A simplification of the LCA is the life cycle energy analysis (LCEA), which focuses only on the measure of energy as environmental impact. The energy consumption employed by a building can be classified in:
• energy for production of (earthen) building materials incl. transport to the site (Primary Energy Impact, PEI or ‘embodied energy’, Tables 4.7 and 4.82
Table 4.7
Primary energy impact values (PEI) of typical building materials comparing with earth building materials
| Building material | PEI (kWh/m3) |
| Earth | 0–30 |
| Straw insulation panels | 5 |
| Timber, home | 300 |
| Timber materials | 800–1,500 |
| Fired bricks | 500–900 |
| Cement | 1700 |
| Concrete, ‘normal’ | 450–500 |
| Lime sandstone | 350 |
| Glass panes | 15,000 |
| Steel | 63,000 |
| Aluminium | 195,000 |
| Polyethylene (PE) | 7600–13,100 |
| Polyvinylchloride (PVC) | 13,000 |
• energy consumed during the building process
• energy used for maintenance and repair of the building
• energy used in demolition of the building at the end of its useful lifetime.
The PEI is a criterion commonly used to ascertain a rough estimation of the ecological balance of a building material, allowing one to compare the energy efficiency of production processes in terms of ‘embodied’ energy. In the case of earth building materials, the PEI is a favourable parameter because it is extremely low: comparing the PEI of earth with that of typical building materials such as concrete, reinforced concrete or steel shows just how much difference this makes. This is a further reason why the use of earth for construction purposes has become increasingly significant in many countries, and this new development is also reflected by a rising number of earth building standards.
The PEI of building materials is just one aspect of energy consumption over the entire life cycle of a building. In most countries with cold and temperate climates, buildings that are in regular use have to be heated during the winter period. Building standards in these countries define limits for the heat energy demand (e.g. in Germany, DIN 4108, EnEV 2009), particularly for residential buildings, and require appropriate heat insulation. The reduction of energy consumption achieved by thermal insulation over the lifetime of a construction (e.g. ~ 100 years for a residential house) outweighs the ‘embodied’ energy of the building materials significantly.
Earth building materials are not good thermal insulators (λ – values, Table 4.9). They generally do not fulfil the thermal insulation requirements for exterior walls in new buildings as stipulated in the respective national building codes in regions with cold and temperate climates. Earth building materials can comply with building code requirements for thermal insulation in two general ways.
Table 4.9
Thermal conductivity values for earth building materials2,8
Earth building materials in comparison to: polyurethane, 0.02 W/mK, aluminium, 200 W/mK.
In new buildings earth materials can be used in exterior walls in combination with additional thermal insulation materials e.g. straw insulation panels. In addition, the capacity of constructions with a heavy mass (e.g. rammed earth) to absorb and re-radiate heat can be used to even out the degree of air temperature fluctuation in rooms in buildings made of lightweight constructions. Earth plasters also have good sorption properties: airborne moisture is absorbed through the pores of the earth building material, and as the interior room climate becomes drier the earth plaster releases moisture back into the air. As such, earth materials help regulate and filter the interior room climate.
Today, the improvement of the Indoor Environmental Quality (IEQ) is becoming an increasingly important criteria for the selection of building materials. Growing consumer awareness of hazardous emissions from building products has given rise to a new class of discerning consumers seeking building materials with few to no negative emissions (formaldehyde, volatile organic compounds, pesticides, radiation, etc.). Clay and earth building products are able to meet such criteria for healthy living. Producers of earth building materials declare the product constituents on their product labels, and ecocertificates11 also underline their zero-emissions credentials.
Historical buildings, including those that use earth building materials in external walls, are not required to fulfil the same level of thermal insulation as new buildings. In Germany, light clay (LC) is often used for lightweight earth wall linings applied to the inside of the external walls of historical buildings, particularly half-timbered constructions with earth infill panels. In this way, earth building materials can contribute significiantly to improving the thermal performance of historical constructions. Not all ‘modern’ thermal insulation materials are appropriate for use with earth constructions and there have been many cases where damage resulting from such ‘repairs’ has itself needed repairing, particularly of half-timbered constructions.
Environmental impact
A comprehensive evaluation of a building material’s life cycle (LCA) analyses the energy consumption of all processes, including maintenance and repair, over its entire ‘lifetime’ (Fig. 4.3). It also considers the environmental effect of related energy production and consumption. Descriptive parameters are used to quantify the environmental impact (e.g. global warming potential GWP = ‘CO2-equivalent’).
In the last ten to twenty years, assessment methodologies for evaluating the environmental impact (‘ecological footprint’) of technological (building) processes have been developed. The LCA methodology is generally defined in ISO 14044: 2006 ‘Environmental management, life cycle assessment, requirements and guidelines’ and ISO 14040: 2009 ‘Environmental management, life cycle assessment, principles and frameworks’.38 It consists of four stages:
• balancing (definition of goal and scope, inventory analyses, impact assessment, improvement analyses)
Based on the parameters calculated, the final evaluation can provide a variety of different information:
• an analysis of construction alternatives with a view to identifying preferred variants (e.g. earth building materials)
• an estimation of ecological effects
• identification of effects relating to existing environmental impacts.
The quality of a LCA depends to a large degree on the quality of the inventory analysis data. LCA studies are directly related to the availability and quality of these data. These can consist of direct measurements, industrial reports, laboratory measurements and other documents and reports. There are numerous public LCA databases developed by academic, industrial, institutional, commercial and governmental organisations.33
This new ‘way of thinking’ will gradually be reflected in all (building) standards. At present, however, only very few earth building standards consider ecological criteria for the planning of building processes today. On the other hand, in comparison to other building materials, earth building products exhibit considerable advantages with regard to PEI and Indoor Environmental Quality (IEQ). This is an important factor for the promotion of earth building products, although it is currently still not reflected in the respective standards.
The ASTM 239213 and SLS 138221 include a verbal description of aspects of sustainable development, such as the PEI, the IEQ and the energy efficiency of earth building systems. But there is no reference to ISO 14040 and LCA procedures.
The DVL TM 02 and TM 0310,32 detail procedures for determining the global warming potential (GWP) on the basis of (DIN EN) ISO 14040 and in TM 0332 for the vapour adsorption of earth plaster (EP) on interior wall and ceiling surfaces in order to evaluate the IEQ.
4.5.2 Production process
In future, all European national standards will be replaced by European EN norms in response to the process of convergence in regulations. In the context of building products this will be achieved by the Construction Products Directive (CPD) of the European Economic Commission from 1989 (89/106/EEC). In March 2011, the European Commission replaced this document with a new ‘Regulation of the European Parliament and the Council laying down harmonised conditions for the marketing of construction products’.42
The aim of this document is to foster the free movement and use of construction products in the internal European market. The emphasis of the revised proposal includes the use of a common technical language and clear terms for applying the CE mark. The CE mark guarantees defined qualities and reproducible testing procedures for the quality control of the production process of building products.
The Dachverband Lehm e.V. (DVL) has developed three standard drafts for approval by the German NSB DIN which will be issued in advance of the approval process as Technical Recommendations: DVL TM 02 ‘Earth blocks’ (EB),10 DVL TM 03 ‘Earth masonry mortars’ (EMM)32 and DVL TM 04 ‘Earth plaster mortars’ (EPM).40 A fourth document – DVL TM 05 ‘Quality control of soil as an ingredient of industrially produced earth building materials’36 – will also be issued but is not currently part of the DIN approval process. The future DIN standards will have the following designations: DIN 18945 ‘Earth blocks’; DIN 18946 ‘Earth masonry mortar’; DIN 18947 ‘Earth plaster mortar’.
The DIN standard drafts comply with the requirements of the Building Products Act, the German national version of the European CPD. Earth building materials defined by DIN earth building standards will be classified as ‘regulated building products’. They will receive the ‘Ü mark’ (conformity mark), the national version of the European CE mark which guarantees requirements for the quality control of the production process. The transition from this to a CE mark is subject to a special procedure and will be a future project for the DVL.
Today, earth building materials can be produced in two ways: manual ‘handmade’ production and ‘industrialised’ factory fabrication using appropriate technical equipment. The manual production of earth building materials characterises the traditional way of building with earth in many parts of the world. The industrialised production of earth building materials changes the traditional, non-engineered into an engineered construction system. This shift means that the material is subject to the same quality standards for testing material parameters and for quality control of the production process as other industrially produced building materials such as lime, cement, concrete, etc. It also requires uniform standards for the design, measurement and construction of buildings with earth building materials.
4.6 Conclusions
In the last decade the use of earth for construction purposes has become increasingly significant in many countries because of its favourable ecological properties and its contribution to sustainable development. This new ‘way of thinking’ is also reflected by an increasing number of earth building standards that have arisen in the same period. Nevertheless, in absolute terms, the number is still very small compared with other building materials and systems. The earth building standards analysed were published by regional, national and local standards bodies over the last 30 years.
There is no common and internationally accepted terminology for earth building materials and systems. This, however, is an essential prerequisite for developing standards and normative documents and for the establishment of earthen building materials in contemporary building alongside other conventional building products and systems. This chapter describes recommended terminology for relevant earthen building materials and earth construction systems commonly used today and which are covered in (earth) building standards.
The 33 standards from 19 different countries provide widely differing technical information. With regard to their scope of application, the documents can be classified into three types dealing with typical parameters:
Soil: grading, plasticity, natural constituents content, linear shrinkage
Earth building material: strength/deformation characteristics
Earth construction system: strength/deformation characteristics, aspect ratio, earthquake resistance.
There are no uniform and internationally accepted laboratory testing procedures for determining material properties and design values for earth building construction. The test procedures currently in use were often originally developed for testing soils (soil mechanics) or concrete and did not take into account the specific properties of earthen materials. The suitability of these ‘ adopted’ procedures for earthen building materials and systems is still to be proven. It is necessary to bring testing procedures for earth building products up to the same level as other ‘ standardised’ building materials in order to improve their scope and competitiveness in the building sector.
Three examples of laboratory testing procedures and design criteria covering important aspects of earth building were discussed that demonstrate some of the differences in the standards documents:
1. Soil classification and selection: granular composition and plasticity, content of soluble salts
2. Earth building material: compressive strength and optimum compaction for rammed earth
3. Earth construction system: slenderness of wall structures.
In terms of the granular composition and plasticity of soils suitable for building purposes, it is impossible to justify the application of narrow limits on the basis of existing earth building standards. The new German earth building standards include a recommendation for the quality control of soil as an ingredient of industrially produced earth building products.
With regard to the strength characteristics of earth building materials (unconfined compressive strength UCS) there are no uniform and internationally accepted testing procedures. As a consequence, this makes comparability very difficult if not impossible. Very few of the standards documents examined distinguished between ‘design’ and ‘characteristic’ UCS values. There is practically no information on partial safety factors. The new German building standard for earth blocks defines ‘strength’ classes for different kinds of application.
The slenderness or aspect ratio of wall structures is a factor depending on the degree of regional seismic activity. There are very few countries subject to seismic activity that permit the use of earth building materials in construction systems and regulate their use through building standards. In many such countries, the use of earth as a building material for new building is excluded.
A new generation of building standards will be developed that take sustainable development into account by assessing the entire life cycle of a building product. Traditional evaluation systems that currently address material properties, construction systems, durability and economic features will be augmented by parameters that provide an indication of the ‘ecological footprint’ of a building material or system. The LCA is an appropriate methodology for analysing and evaluating the environmental impact of building materials, buildings and other necessary services throughout their lifetimes. In this respect, earth building materials compete very favourably. At present, however, such methodologies are rarely part of statutory standards.
Building with earth can contribute to sustainable development by reducing environmental impact when compared with other building materials and systems. This aim can only be achieved by developing earth building into an ‘engineered’ building system on the basis of building standards issued by national standards organisations.
4.7 References
1. DIN 1169 Earth mortars for masonry and plaster (06/47) DIN 18951 Earth buildings (01/51)01: Construction02: CommentsDIN VN 18952 Earth01: Designations, Types (05/56)02: Tests (10/56)DIN VN 18953 Earth, earth construction elements01: Use of earth (05/56)02: Adobe walls (05/56)03: Rammed earth walls (05/56)04: Cob walls (05/56)05: Light-clay walls in timber-framed structures (05/56)06: Earth floors (05/56)DIN VN 18954 Construction of earth buildings, design (05/56)DIN VN 18955 Earth, earth construction elements, waterproofing (08/56)DIN VN 18956 Building with earth, plaster on earth constructions (08/56)DIN VN 18957 Building with earth, earth roofing tiles (08/56).(VN = draft)
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27. AFNOR. Compressed Earth Blocks for Walls and Partitions: Definitions – Specifications – Test Methods – Delivery Acceptance Conditions, AFNOR XP.P13-901. St Denis de la Plaine, France: AFNOR; 2001.
28. Ministerio de Obras Públicas y Transportes (MOPT). Bases para el diseño y construcción con tapial. Madrid, Spain: Secretaría General Técnica; 1992.
29. Dachverband Lehm e.V. Building with Earth – Consumer Information. Weimar, Germany: Dachverband Lehm e.V; 2004.
30. Walker, P., Keable, R., Martin, J., Maniatidis, V. Rammed Earth – Design and Construction Guidelines. Watford, UK: BRE Bookshop; 2005.
31. Jiménez Delgado, M.C., Cañas Guerrero, I. Earth building in Spain’. Construction and Building Materials. 2006; 20:679–690.
32. Dachverband Lehm e.V. Lehm-Mauermörtel – Begriffe, Baustoffe, Anforderungen, Prüfverfahren. Weimar, Germany: Technische Merkblätter Lehmbau – Blatt 03; 2011.
33. Menzies, G.F., Turan, S., Banfill, P.F.G. LCA methodologies, inventories, and embodied energy: A review. Proceedings – Institution of Civil Engineers Construction Materials. 2007; 160:135–143.
34. Fathy, H. Architecture for the Poor – An Experiment in Rural Egypt. Chicago and London: The University of Chicago Press; 1973.
35. Güntzel, J. Zur Geschichte des Lehmbaus in Deutschland. Kassel: Gesamthochschule; 1986. [Dissertation Band 1].
36. Dachverband Lehm e.V. Qualitätsüberwachung von Baulehm als Ausgangsstoff für industriell hergestellte Lehm-Bauprodukte – Richtlinie. Weimar, Germany: Technische Merkblätter Lehmbau – Blatt; 2011. [05].
37. Bureau of Indian Standards (BIS). Indian Standard Code of Practice for Manufacture and Use of Stabilised Soil Blocks for Masonry. In: indian Standards IS 1725, Part I: Specifications for stabilized soil blocks for masonry; Part II: Code of practice for manufacture and construction using stabilized soil blocks. New Delhi: BIS; 2011.
38. International Standards Organisation (ISO) (2006–2009), ‘Environmental Management, Life Cycle Assessment. ISO 14040: Principles and frameworks (2009)ISO 14044: Requirements and guidelines (2006)Brussels, Belgium.
39. Walker, P., Standards Australia. The Australian Earth Building Handbook, HB 195-2002. Sydney, Australia: Standards Australia International; 2002.
40. Dachverband Lehm e.V. Lehm-Putzmörtel – Begriffe, Baustoffe, Anforderungen, Prüfverfahren. Weimar, Germany: Technische Merkblätter Lehmbau – Blatt; 2011. [04].
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45. Instituto Colombiano de Normas Técnicas y Certificación (ICONTEC). Bloques de suelo cemento para muros y divisiones. Definiciones. Especificaciones. Métodos de ensayo. Bogotá: Condiciones de entrega. NTC 5324; 2004.
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