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The compressed earth block is the modern descendent of the moulded earth block, more commonly known as the adobe block. The idea of compacting earth to improve the quality and performance of moulded earth blocks is, however, far from new, and it was with wooden tamps that the first compressed earth blocks were produced. This process is still used in some parts of the world. The first machines for compressing earth probably date from the 18th century. In France, Francois Cointeraux, inventor and fervent advocate of "new pise" (rammed earth) designed the "crecise", a device derived from a wine-press. But it was not until the beginning of the 20th century that the first mechanical presses, using heavy lids forced down into moulds, were designed. Some examples of this kind of press were even motor-driven. The fired brick industry went on to use static compression presses in which the earth is compressed between two converging plates. But the turning point in the use of presses and in the way in which compressed earth blocks were used for building and architectural purposes came only with effect from 1952, following the invention of the famous little CINVA-RAM press, designed by engineer Raul Ramirez at the CINVA centre in Bogota, Columbia. This was to be used throughout the world. With the '70s and '80s there appeared a new generation of manual, mechanical and motor-driven presses, leading to the emergence today of a genuine market for the production and application of the compressed earth block.
A HIGHLY DEVELOPED TECHNOLOGY
Since its emergence in the '50s, compressed earth block (CEB) production technology and its application in building has continued to progress and to prove its scientific as well as its technical worth.
Research centres, industrialists, entrepreneurs and builders have developed a very sophisticated body of knowledge, making this technology the equal today of competing construction technologies. CEB production meets scientific requirements for product quality control, from identification, selection and extraction of the earth used, to quality assessment of the finished block, thanks to procedures and tests on the materials which are now standardised. This scientific body of knowledge ensures the quality of the material. Simultaneously, the accumulated experience of builders working on a very large number of sites has also enabled architectural design principles and working practices to emerge and today these form practical points of reference for architects and entrepreneurs, as well as for contractors.
ROLE IN DEVELOPMENT
The setting up of compressed earth block production units, whether on a small-scale or at industrial level, in rural or urban contexts, is linked to the creation of employment generating activities at each production stage, from earth extraction in quarries to building work itself. The use of the material for social housing programmes, for educational, cultural or medical facilities, and for administrative buildings, helps to develop societies' economies and well-being. CEB production forms part of development strategies for the public and the private sector which underline the need for training and new enterprise and thus contributes to economic and social development. This was the case in the context of a programme on the island of Mayotte, in the Comoros archipelago, for the construction of housing and public buildings, a programme today regarded as an international reference. The use of CEBs which followed the setting up of an island production industry proved to be pivotal in Mayotte's development, founded on a building economy generating employment and local added value in monetary, economic and social terms.
SOCIAL ACCEPTANCE
CEBs represent a considerable improvement over traditional earth building techniques. When guaranteed by quality control, CEB products can very easily bear comparison with other materials such as the sand-cement block or the fired brick. Hence the allegiance it inspires amongst decision-makers, builders and end-users alike.
1980-1990, industrial units
THE FUTURE OF CEBS
CEB technology has made great progress thanks to scientific research, to experimentation, and to architectural achievements which form the basis of a wide range of technical documents and academic and professional courses. A major effort is now being devoted to the question of norms and this should help to confer ultimate legitimacy upon the technique in the coming years.
The CEB technique has several advantages which deserve mention:
- The production of the material, using mechanical presses varying in design and operation, marks a real improvement over traditional methods of producing earth blocks, whether adobe or hand-compacted, particularly in the consistency of quality of the products obtained. This quality furthers the social acceptance of a renewal of building with earth.- Compressed earth block production is generally linked to the setting up of quality control procedures which can meet requirements for building products standards, or even norms, notably for use in urban contexts.
- In contexts where the building tradition already relies heavily on the use of small masonry elements (fired bricks, stone, sand-cement blocks), the compressed earth block is very easily assimilated and forms an additional technological resource serving the socioeconomic development of the building sector.
- Policy-makers, investors and entrepreneurs find the flexibility of mode of production of the compressed earth block, whether in the rural or the urban context, small-scale or industrial, a convincing argument.
- Architects and the inhabitants of buildings erected in this material are drawn to the architectural quality of well-designed and well-executed compressed earth block buildings.
TECHNICAL PERFORMANCE
Compacting the soil using a press improves the quality of the material. Builders appreciate the regular shape and sharp edges of the compressed earth block. The higher density obtained thanks to compaction significantly increases the compressive strength of the blocks, as well as their resistance to erosion and to damage from water.
FLEXIBILITY OF USAGE
The wide range of presses and production units available on the current market makes the material very flexible to use. With production ranging from small-scale to medium and large-scale semi-industrial or industrial, CEBs can be used in rural and urban contexts and can meet very widely differing needs, means and objectives.
STANDARDS AND MODELS
Compressed earth blocks are of standard sizes and meet quality requirements which are suitable for carrying out large housing or infrastructure programmes, based on the design of architectural models. These standard block sizes and shapes, as well as the architectural models, can be defined before the programme begins, at the design stage, with great flexibility.
HIGHLY PRACTICAL NATURE OF THE TECHNOLOGY
The common dimensions of CEBs lend themselves to great flexibility of use in various building solutions, as load-bearing masonry or as in-fill. CEBs can also be used for arches, vaults and domes, as well as for jack-arch floors.
GENUINE ARCHITECTURAL MERIT
Very fine masonry work, equal to fired brick building traditions, can be realised thanks to the high quality of compressed earth blocks. The architectural application of CEBs can range from social housing to luxury homes and prestigious public buildings. Since the '50s, the experience of architects and builders has been considerably enriched by widely differing architectural realisations in all areas of application. Experimentation has to a large extent given way to technological and architectural expertise and has enabled CEB technology to evolve to the point where today it can be considered the equal of other construction technologies using small masonry elements.
AN ALTERNATIVE TO IMPORTATION
Whilst meeting the same requirements as other present-day building materials, the CEB also presents a technological alternative to imported materials, the use of which is often justified because of the need for standardisation. CEBs have the advantage of being produced locally, whilst still meeting this need.
SOME CONSTRAINTS
The quality of CEBs depends on good soil selection and preparation and on the correct choice of production material. Architectural use of the material must take account of specific design and application guidelines which must be applied by both architects and builders. This means that professional skills must be ensured by suitable training. From an economical point of view, CEBs can sometimes fail to be competitive with other local materials. A technical-economic survey will enable the feasibility of the technology to be determined in each application context.
When considering embarking on the production or application of compressed earth blocks, particular attention must be paid to various points as follows:
- mastering a new production technique,
- mastering new building principles,
- ensuring that the production process is well organised and managed,
- marketing a building material.
In order to start out without taking unnecessary risks and to check that one has planned sufficiently, one should begin by asking oneself the following questions:
RESOURCES
- Do you have information on the suitability of the local soils for use in the manufacture of CEBs?- Do you already have a building programme and of what size? How many CEBs does that represent (using 33 blocks per m²)?
- If it is intended to sell the blocks, have you already gathered together data on demand for building materials in your region? Do you have favourable indications as far as the attitude of the population towards CEBs is concerned?
- Do you have information on the availability and costs of stabilizers?
SKILLS
- Are you aware that producing good blocks is not enough and that you must also ensure that they are correctly used to obtain strong buildings?- Do you know building entrepreneurs who have a thorough understanding of the basic design and application principles for CEB buildings?
- Do you know where to find technical and training support?
MANAGEMENT/FINANCING
- Have you collected information on the various kind of equipment available and have you started to compare them?- Do you have experience in management and accounting?
- Are you aware that a project of this kind cannot succeed overnight and that it will be some time before your efforts are rewarded?
GENERAL INTRODUCTION
The production of compressed earth blocks can be regarded as similar to that of fired earth blocks produced by compaction, except that there is no firing stage. Production will be differently organized, depending on whether it takes place in the context of small, "cottage industry" units (or brickworks), or in the context of a semi-industrial or industrial unit. Production, drying and stocking areas will also vary depending on the methods of production selected and the production conditions dictated by the climatic, social, technical and economic environment.
No production period or season is particularly favourable or unfavourable, providing that measures are taken in wet or hot seasons (if any) to protect production areas or areas used for stocking.
Generally speaking, as far as production rates are concerned, these will depend largely on the way production is organised and on the type of equipment used.
PRODUCTION CYCLES
Here we describe a cement or lime-stabilizer compressed earth blocks production corresponding to a small-scale production organisation, using all kinds of presses with the exception of industrialized production units.
FIGURE
- EXTRACTION from the quarry or pit.
- DRYING by spreading in thin layers or passing through a hot-air cyclone.
- PULVERIZING to break up lumps of clay.
- SCREENING to eliminate undesirable elements after general preparation.
- MEASURING OUT the dry soil by weight or by volume with a view to mixing it with water and/or with stabilizer.
- DRY MIXING to maximize the effectiveness of a stabilizer in powder form.
- WET Mixing to add water by spraying after adequate dry mixing, or directly in the form of a liquid stabilizer.
- REACTION during variable hold-back time depending on the nature of the stabilizer; very short for cement, longer for lime.
- MEASURING OUT the amount of mixed material for optimum block density.
- COMPRESSION of the mixed material.
- REMOVING the block from the mould.
- WET CURING, the length of time depending on the climate and the nature of the stabilizer.
- DRYING OUT which should enable the quality required to be achieved.
- STOCKING of the products ready for use.
PRESSES
In compressed earth block production, the presses are used to compact the particles, thus increasing density.
Manual presses
Only the compression and ejection of the block are carried out by the manually operated machine.
Theoretical output: 300 to 1 500.
Motor-driven presses
Only the compression and ejection of the block are carried out by the motor-driven machine.
Theoretical output: 1 000 to 5 000.
Mobile production units
Production units which are easy to transport and where in addition to the compression and ejection of the block, preparation of the material and/or the removal of the products are motorized and sometimes automatic.
Theoretical output: 1 500 to 4 000.
Fixed production units
Products units which can be transported only with difficulty and where, in addition to the compression and ejection of the block, preparation of the material and/or the removal of the products are motorized and sometimes automatic.
Theoretical output: 2 000 to 10 000 and more.
PULVERIZERS
Lumps of soil must be broken up to obtain a homogeneous mix of the constituents.
Grinder
This can also fragment stones or excessively large gravel and thus even out the particle size distribution.
Crusher
This breaks up only the particles which are bound together by clays and is therefore better suited to fine soils.
SCREENS
Screening is indispensable either when the texture is incorrect (excessively large constituents or too much organic material) or when pulverizing is inadequate.
MIXERS
Mixing is particularly important for the ultimate quality of the
product. A homogeneous mix is indispensable. One should preferably proceed first
with dry mixing. For an even distribution of moisture, water should either be
sprinkled on, or added in the form of steam.
TYPES
Various types of production lines can be installed depending on the way the individual pieces of equipment are assembled together. These can be differentiated using the following main criteria: productivity, investment and the quality of the labour-force employed. The table below shows typical examples ranging from a small manual unit to an industrial unit, with medium-scale production units (types 2 to 5) being of most relevance.
FIGURE
* Type of soil and type of machine used for its preparation:
- high proportion of gravel with clay lumps -> grinder
- high proportion of fines with clay lumps -> crusher
- high proportion of stones and gravel with no clay lumps -> screen
** Mechanized transport:
- conveyor belt, dosage system, hopper, pallet transporter or fork-lift truck (see table of types of equipment).
N.B. All prices are given only as indications and to allow broad comparison. For more details, consult the manufactures and GATE’s Product Information sheets. The productivity rates quoted are calculated assumption of normal usage of the machines, but can vary significantly.
FIGURE
Comment
The ratio of type 1 to type 6 is approximately nine to one as far as the number of lines of production and of workers are concerned. The capital invested sheds light on the table (next fig: Changes in productivity according to the level of investment) with type 5 requiring a major investment, i.e. more fixed capital than type 6, and this for virtually the same productivity as type 4.
FIGURE
Comment
As can be seen, productivity stagnates wheras the investment required increases significantly between production lines 4 and 5, i.e. with effect from the mechanization of the transport systems (daily production in the order of 2000 blocks measuring 29.5 × 14 × 9 cm)
Given the nature of the equipment currently available, it seems vital to move on mechanized transport only in conjuction with higher (type 6) productivity if the investment is to be viable (see picture above: suggested productivity/labour/investment ratios for fixed capital assets)
FIGURE
Comment
The consupmtion of raw materials between the various work stations must be calculated in the light of the projected target productivity. High consumptions will require:
- sufficient natural resources (large soil deposits)- a large cash flow provision to cover the purchase of materials, overheads and wages, particulary at the start of production.
The figures given on the left are approximate indications only and should be accurately calculated for each given context. They do, however, provide a base for an initial evaluation.
Compressed earth blocks are small masonry elements, parallelepiped in shape, but the common dimensions of which differ from those of hand-moulded earth blocks or of fired bricks and vary depending on the type of specially developed press and mould used.
For masonry constructions, solid blocks are most commonly used.
For this reason, compressed earth block production has typically used block dimensions consistent with a unit weight in the order of 6 to 8 kg and with the possibility of building walls 15, 30 or 45 cm thick. The most common (or nominal) work dimensions in use today are 29.5 × 14 × 9 cm (I × w × h), which gives a material which is very easy to handle and very flexible in its use for many configurations of wall and roof building systems (jack-arch floors, vaults and domes) and of arched openings.
There are 4 main families of blocks:
Solid blocks
These are mainly prismatic in shape. They fulfil very widely differing functions.
FIGURE (Standard block; ¾
block; ½ block)
Hollow blocks
Generally the voids of hollow blocks account for a total of 5 to 10%, and up to 30% using sophisticated techniques. Voids can improve the adherence of the mortar and reduce the weight of the block. Certain hollow blocks can be used to build ring-beams (lost formwork).
Perforated blocks
These are light but require fairly sophisticated moulds and greater compressive force. They are suitable for reinforced masonry (in earthquake areas).
Interlocking blocks
These can be assembled without mortar, but they require sophisticated moulds and high compressive force. They are often used for non-loadbearing structures.
FIGURE
Comparisons between the characteristics and performances of the compressed earth block and those of other classic masonry materials, should not be restricted solely to taking account of their compressive strength or differences in production costs. The issue is a more complex one and any comparison should rather be based on a wide register of parameters, including: the shape and dimensions of the material, its appearance (surface, texture, attractiveness,) as well as a full range of measures of performance, such as - indeed - dry and wet compressive strength, but also thermal insulation, apparent density, and durability. But over and above this aspects linked to the production and use of the material highlight all the complexity of such comparisons by taking account of such factors as the nature of the soil deposits supplying the raw material, the means by which this raw material is processed into a building material, the energy involved in this processing or production, the nature of the material when considered as a building component or element, and its state in the finished building, taking account of questions of durability and maintenance. This "intelligent" way of comparing materials with each other, over and above scientific considerations intended to compare materials in laboratory conditions, takes account of the architectural and practical application of materials. In the same way, cost comparisons should not be made between equal volumes of materials, but by comparing the m² of habitable surface area built using various materials, each of them with their own design requirements.
FIGURE
GENERAL SPECIFICATIONS (given as for a standard block)
Tolerance on dimensions
- length: +1, -3 mm,
- width: +1, -2 mm,
- height: +2, -1 mm.
Roughness of external sides
- External faces of the block which are to be rendered or faces which will not be visible within the masonry should preferably have a rough finish.- External faces of the block which are not to be rendered should have a smooth finish.
Pitting, holes, punctures, scratches
- For rough finish faces, these should not exceed 15% of the surface.
- For smooth finish faces, these should not exceed 1% of the surface.
Density
- Dry: minimum: 1,700 kg/m³ or 6.319 kg/block; recommended: 2,000 kg/m³ or 7.434 kg/block.
- Freshly moulded: minimum: 1,870 kg/m³ or 6.950 kg/block; recommended: 2,200 kg/m³ or 8.177 kg/block.
Surface flatness
- Sides: any deviation should not exceed 1 mm.
- Compression surfaces: any deviation should not exceed 3 mm.
Edge straightness
- Any deviation should not exceed 2 mm.
- Some roughness of the edges is tolerated, as long as it is due to turning out and not due to faulty manipulation.
Obliqueness of surfaces
- The external faces, shape and size tolerances must be respected.
- The internal faces of voids must be oblique and should have no acute angles.
1. First check on the local availability of sufficient suitable soil and on how easy it is to organize its extraction.
2. Once a soil supply has been established, a feasibility study should be carried out to prepare the project. This feasibility study should comprise a technical study including an analysis of the local soils, a description of the best production methods in the local context, a description of the equipment needed and where it would be available, and a study of production costs. A market survey should complement the technical study, including figures about the demand for building materials and the opportunities for using CEBs, the size and shape of the product and the maximum price for the CEB to be more attractive than other building materials.
3. Local building regulations, and if they allow the use of CEBs, must be checked, as must requirements about technical performance.
4. Securing the capital to cover the investment required and the first few months' expenditure is the next step before preparing the production area.
5. Ordering the equipment can be done simultaneously with the preparation of the production area and the construction of the few buildings necessary: storerooms, office, etc.
6. A training course on production and workshop management must be carried out by an experienced organization during the installation of the production equipment. Production tests can then be undertaken.
7. As soon as the results of the production tests on the production process are available, commercial production can start. Quality control procedures must be set up as soon as commercial production is underway.
8. Before or as soon as production starts, the entrepreneur or the manager must become suitably qualified in marketing, accounting and production monitoring.
9. The manager or a qualified technician must check how the CEBs are used and give technical advice if anything goes wrong.
10. During the first months, a producer would be wise to keep in touch with one or more competent associates from whom he can get technical or marketing advice.
ENTERPRISE PROJECT
CEB production is not merely a technical activity. It is first and foremost an enterprise project. An enterprise can be defined as a human, material and financial investment. To set up an enterprise project is to mobilize all of these. This means that the entrepreneur must above all be able to convince the professional colleagues who are to provide financial and technical support. It is therefore very important to have a clear statement of the entrepreneur's project before embarking on the actual start-up of the project.
START-UP OF THE PROJECT
Once the preliminary phase is complete, the following phase, the start-up of the project, can begin. This consists in reviewing all the ways and means which will be used to achieve the production and marketing of the volume of blocks determined during the previous phase. This means drawing up first a technical dossier and then a financial dossier covering each aspect of the enterprise project.
FIGURE
PARAMETERS
When setting-up a brickworks, a certain number of factors have to be taken into consideration at various stages of production. The table below presents in simplified form a list of the factors which should not be neglected.
Setting-up of the brickworks
- Land costs (distinguish between purchase and rent, and state duration).
- Infrastructure costs.
- Building costs.
- Miscellaneous expenses.
Preparation of the material
- Extraction, loading and transportation of the earth (running costs of the quarry).
- Unloading and screening the earth.
- Loading, transporting and unloading the reject material after screening.
- Measuring out and mixing in the various elements making up the material (soil/sand/stabilizer/water).
Block production
- Loading the press and compressing the blocks.
- Transportation and storage of the blocks.
- Delivery of the blocks on site.
FIGURE
FIGURE
ECONOMICS
Improved housing is part of any development strategy. One must therefore consider the effect of this on the local economy. These effects are reflected both in reduced imports and in the setting up of small businesses, resulting in the creation of jobs and in increased skills.
In more global terms, one should also bear in mind the reduction in energy consumed, as well as the emergence of a contemporary role, following on in a continuous building tradition.
NORMS AND QUALITY STANDARDS
Very often technical documents which have been devised for other materials are applied to building with earth and this places CEBs at an unfair disadvantage. Reference texts suited to this particular building method are therefore of prime importance. The definition of norms aims at promoting quality standards and opening up the market to clients who will have greater confidence thanks to the credibility of the producers and the viability of the materials.
FLEXIBILITY
One of the characteristics of CEB production is the degree of flexibility in conditions for creating production units. The possibility of investing in stages, both in terms of equipment and technical capacity (training, skills) makes it very easy to adapt to a given context by modifying the approach selected in the light of market needs and constraints.
PARTNERSHIP
National development strategies often make it easier to find the capital for setting up small production units than for large building materials factories. For this reason, the efforts of small businesses are more and more supported by national or international institutions, notably by promoting partnerships with technical organisations or equipment manufacturers. Such partnerships can provide assistance not only with the production process, but also with preparatory studies, with marketing, and with the financial and technical management of production units.
INFORMATION
Ensuring that the product, its performance and potential are well understood is of vital importance. There are several ways of approaching this: the products must be described, and their cost and uses or performance, endorsed by technical organisations, clearly stated. One should also be able to point out buildings which have been erected using CEBs and seek opportunities to use CEBs in such a way as to be able to demonstrate a real improvement in existing housing.
DIVERSIFICATION
There must be a readiness to consider new production methods as well as the production of new products, both compressed earth products and other building elements suited to the particular design requirements of CEBs. This means keeping in touch with users and partners in order to keep abreast of needs and techniques and to be able to offer useful services (suggestions for technical production and implementation, production and building costs, etc.).
FIGURE
A VERY ANCIENT BUILDING TRADITION
The distant origins of the compressed earth block technique can be traced back thousands of years to the moulded sun-dried earth brick, better known by the name of "adobe". The sun-dried earth brick marks historical stages in the evolution of the human race. Linked to the emergence of an architectural tradition and urban settlements which laid the foundations for the urban revolution, with sun-dried earth bricks came social and economic organisation, the production of building materials and the use of these for building. This use, which was to radiate further and further afield, liberated man from rudimentary materials and techniques of limited architectural potential. The way was now open for a durable and monumental form of architecture, in Mesopotamia (present-day Iraq), in the Indus valley (India), along the banks of the Huanghe (China) and the Nile (Egypt), the main cradles of civilisation.
AN INEVITABLE HISTORICAL PROGRESSION
The recent progression towards the compressed earth block is a logical extension of the benefits of the industrial revolution which brought the significant development of the fired brick. With the need to improve the quality of materials and the durability of buildings, linked to better productivity, came compaction. CEB press technology is inherited directly from the ceramics or calcium silicate industries. The need to save energy and notably that used for firing in times of shortage (after the second world war, and later during the petrol crisis), accelerated the development of the compressed earth block and encouraged a broadening of its architectural application in regions faced by high energy costs.
THE CONTEMPORARY ROLE OF COMPRESSED EARTH BLOCKS
In Mayotte, an island in the Comoros, for example, a large
programme for the construction of several thousand homes and public buildings
(schools, offices etc.), launched over ten years ago has proved beyond doubt not
only the contemporary role of the CEB, but also its architectural merit.
Demonstrating this contemporary role means putting it into practice, developing
a market for business skills, spreading a genuine building and architectural
culture, evidenced by skills, and ensuring the social and economic secondary
benefits for the population, thus furthering the development of societies.
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