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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 1 8th 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 ClNVA 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 Comoro islands, 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
CEB represents 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.
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 socio-economic 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 use
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.
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, "craft 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 storage areas.
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 as well as on the skill of the labour-force.
CATEGORIES OF PRESSES
Manual presses
These are manually operated and carry out only the compression and ejection of the block. Light, mechanical and hydraulic presses fall into this category. Production outputs for these presses are in the order of 300 blocks per day. Mechanized manual presses also exist, and are generally heavier and more robust, but their outputs remain hardly any higher than that of light presses (up to 500 blocks per day).
Motorized presses
These are motor-driven and carry out only the compression and ejection of the block. Mechanical and hydraulic presses fall into this category. Motorized mechanical presses form a new generation of presses, sometimes derived from heavy mechanized manual presses. They enable better rates of production and outputs can exceed 800 blocks per day. Hydraulic motorized presses, which are descended from pumping and oil-circuit mechanisms, should only be used in a favourable technological environment. Their viability should be checked.
Mobile production units (light)
These are easily transportable, motorized and sometimes automated. In addition to the compression and ejection of the block, they also carry out raw material preparation operations and/or the removal of the products.
Fixed production units
These are difficult to transport, motorized and sometimes automated. In addition to the compression and ejection of the block, they also carry out raw material preparation operations and/or the removal of the products.
CLASSIFICATION AND CHARACTERISTICS
The types of presses and production units which exist as a whole on the international market today can be classified (see Fig. 4) according to these four main categories and as a function of the systems they use (power source, energy transmission, compressive action) and their main characteristics (compressive force, theoretical output). As far as production output is concerned it should be stressed that the figures supplied by manufacturers fairly often refer to a press's theoretical mechanical cycle, but that on site stated outputs can be lower, as production is very closely linked to the way in which production is located and organized.
|
SYSTEMS USED |
PRESS CATEGORIES |
CHARACTERISTICS | |||
|
POWER SOURCE |
ENERGY TRANSMISSION |
COMPRESSIVE ACTION | |
COMPRESSION PRESSURE |
THEORETICAL SOURCE OUTPUT /8 H |
| |
mechanical |
static | |
very low |
300 to 800 |
|
manual |
mechanical and hydraulic |
static |
manual presses |
hyper |
300 to 400 |
| |
mechanical |
static | |
low |
400 to 1 000 |
| |
mechanical |
static |
motorized presses |
low to medium |
800 to 3 000 |
| |
hydraulic |
static | |
low to medium |
800 to 2 000 |
| |
mechanical |
static | |
low to medium |
800 to 3 000 |
| |
hydraulic |
static |
mobile production units |
low to medium |
800 to 3 000 |
| |
mechanical |
static | |
low |
2 000 to 15 000 |
|
motorized |
hydraulic and mechanical |
static or dynamic |
|
low to hyper |
1 500 to 7 500 |
| |
hydraulic |
static | |
low to mega |
3 000 to 50 000 |
| |
hydraulic and mechanical |
dynamic |
fixed production units | |
1000 000 to 50 000 |
Fig. 4: Classification of presses for the production of compressed earth blocks (29.5 × 14 × 9 cm).
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 presses or moulds used. Two main criteria must, however, be taken into account when determining a compressed earth block's dimensions, which should above all be suited to the great degree of flexibility in use which is one of the great qualities of this building material. These are:
- on the one hand the weight of the block, bearing in mind that they are solid blocks which are principally used in masonry,
- on the other hand the work (or nominal) dimensions of length (1), width (w) and height (h) which will determine bonding patterns. For this reason, as a rule, compressed earth block production has mainly used 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 nominal 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 the way it can be used for many configurations of wall and roof building systems jack-arch flooring, vaults and domes) and of arched openings.
There are 4 main families of blocks:
1. Solid blocks
These are mainly prismatic in shape. They fulfil very widely differing functions.
FIGURE
2. 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).
FIGURE
3. Perforated blocks
These are light but require fairly sophisticated moulds and greater compressive force. They are suitable for reinforced masonry (in earthquake areas).
FIGURE
4. 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
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, 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 situ.
ASPECTS OF UTILISATION
The position of the compressed earth block relative to other masonry materials can be established according to aspects of use of the material.
Technical aspects
Its mechanical, static, hydrous, physical
etc. characteristics.
Economic aspects
Unit production cost, capital investment,
etc.
Health and safety aspects
The emission of dangerous fumes,
radioactivity etc.
Psychological aspects
The nature of the material, surface
texture, colour, shape, luminosity, etc.
Ecological aspects
Deforestation, the hollowing out of
hillsides as a result of quarrying, use of water and energy sources, production
of pollution and waste material etc.
Social aspects
Economic and social spin-offs resulting from
job creation, socio-cultural acceptability, etc.
Institutional aspects
Legislation, insurance, norms,
development policies linked to the setting up of productive industries, etc.
Taking these various aspects into account leads directly back to the need to carry out a preliminary technico-economic feasibility study before setting up a production system, for these considerations weigh heavily in the choice of system. The table (Fig. 7) shows simple points of comparison, but these should not overshadow the importance of these various aspects of utilization of the material.
FIGURE
The very distant origins of the contemporary compressed earth block technique must be traced back to thousand year-old traditions of brick-making, first hand-shaped and then moulded. Building with the "thob" or "otoub" in Egypt as early as pre-dynastic epoches (3rd century B.C.), or in Mesopotamia, on the bountiful banks of the Tigris and the Euphrates, or again in the Indus valley, laid the foundations of "adobe" construction which is still to be found in these regions and which has radiated out to many countries.
The use of the moulded earth brick remains linked to the fantastic evolution of mankind which took place between the agricultural revolution of the neolithic age and the urban revolution and corresponds to an advanced stage in the evolution of societies, and in the organisation of materials production and the building of dwellings. With the building of cities, the use of the earth brick was to be very quickly associated with architectural prowess. Building using small masonry elements indeed liberated man from the most rudimentary building technologies, such as waffle-and-daub or cob, which had restricted building and architectural performance. The advent of the earth brick enabled the most prestigious palaces, sanctuaries and religious temples of the great river civilizations (of the Nile, the Tigris and Euphrates, the Indus and the Huanghe) to be erected, multiplying the number of towns on fertile banks favourable to the installation of human settlements. Modern and contemporary archeological studies bear witness to the architectural genius of the builder of ancient times.
The progression from the moulded earth brick technique to the compacted earth block corresponds to a logical improvement in the material. The increased density and reduced porosity resulting from compression improve the behaviour of the earth block in the face of the harmful effects of water. This compression technique was first practised manually using a tamp and always inside moulds' a painstaking technique giving poor quality blocks from the point of view of both appearance and mechanical performance. It was therefore logical that the technique should gradually evolve towards the development of machinery. The first presses emerged recently and were derived from the ceramic and calcium-silicate industries; there then appeared a new generation of presses specific to compressed earth block technology. This evolution from adobe, to compacted block and then to compressed earth block remains a logical progression in many regions, although very often the technological leap occurs directly between the adobe and the compressed earth block.
With the "modern movement" of the '20s end '30s, and then the "international style" of the '70s end '80s, came an architectural language which used precise shapes, sharp edges, and white facades made from industrialized building materials which demanded precise and regular assembly. This form of architectural language clearly revealed the predominance of the industrial machine over craftsmanship. With concrete, the modern material par excellence, anything was possible, both good and bad, but its use did not necessarily demand very high skills. In many cases, it must be admitted, the use of concrete is not linked to very sophisticated skills. Some very attractive architectural uses of concrete cannot disguise the overall mediocrity of contemporary architectural structures. At the same time, this modern and international architectural style has never really eclipsed the tradition of building using small exposed masonry elements which has remained common throughout the industrialized countries of Latin or Anglo-saxon origin. This latter architectural style is still perfectly contemporary and many architects are today once again giving pride of place to the brick in their work. Those who come across the compressed earth block generally find that it presents the same interest and flexibility in use, and that it links back to a traditional architectural language.
Certain so-called "brick" countries (Great Britain, Belgium, Holland, etc.) have greatly developed the art of the large exposed masonry wall. Very great architects have used brick for their most beautiful works, both for housing and public buildings. The architectural language of the brick, with its multitude of formal variations in expression, has always been considered to be one of unparalleled flexibility and richness. In an inaugural speech in 1938 in Chicago, Mies Van der Rohe declared: «Take a brick, how practical its small' convenient size, so handy for any use. What logic in its bonding and in the resulting texture. What richness in the most simple surface of a wall, and yet what a discipline this material imposes». Who better than Louis Khan has given expression to the seductiveness, the delight and harmony to be found in the contemporary architectural style of exposed bricks in which he finds a search for "romanity" and continuity? How impossible to dissociate the harmony of the exposed wall from the delight and pleasure of observing it. Present day compressed earth block architecture follows on in the succession of brick architecture and is its direct descendant. It plays its part in the continuity of the harmony of the exposed wall and the skills which unite architect and contractor. It is the link woven with history.
Since the 1950s, which marked the emergence of the contemporary technology of compressed earth block construction, the scope of activity in terms of architectural realisations has continued to grow, both in industrialized and in developing countries. The compressed earth block provides a complete response to demands for modernity linked to the improvement of well-being and lifestyle in a comfortable, agreeable, and aesthetic built environment, which is in harmony with the environment. It also meets economic concerns, by enabling the most favourable socio-economic conditions of production, and, notably in countries which are dependent on an outward-looking construction economy based on the importation of materials, gives access to high quality housing at competitive costs. When the technique has been fully mastered in the context of a production industry which creates employment opportunities and skills, it gives rise to a "stock" of high quality architecture which can then become a reference programme. Such is the case with the compressed earth block architecture of the social housing and public facilities programme which was implemented in the Comoro islands, on the island of Mayotte. In France, the "romaine de la Terre" ("Earth Domain") project, which was completed in 1985 near Lyon, was a flagship operation for the renewal of earth architecture. The demonstrative value of this operation, from a technological and architectural point of view, opened the way for a renewal of earth architecture.
IN FRANCE, THE "DOMAINE DE LA TERRE"
The "romaine de la Terre" project was the physical embodiment of the idea, which had been advanced towards the end of the '70s, of once again using unbaked earth in the organized building sector. By succeeding in mobilizing all the normal actors involved in building production (planners and contractors, architects and entrepreneurs, technical standards offices and insurance companies, research centres, production equipment and building materials manufacturers), the project led the way for a new approach to building with earth, based on actual implementation. It also resolved a number of problems to which solutions had up till then not been found. Located in the Rhone-Alpes region, itself rich in rammed earth architecture, it forms a link between vernacular traditions and modernity. The "romaine de la Terre" operation, which provided local authority accommodation at modest rents, consists of 65 housing units, grouped into 12 lots of 5 to 10 semi-detached or terraced units. The earth block was one of the earth building techniques most used, with more then half of the buildings being built in vibration compacted Barth blocks, the remainder being built from rammed earth (compacted between shuttering) or taking the form of straw-clay (covering a wooden framework). The architectural quality of the built estate and the demonstration of the economic feasibility of this project, despite its experimental character, subsequently stimulated, both in France and abroad, through the value as an exemplary operation, a significant development in the realization of earth housing in general and using compressed earth blocks in particular.
Compressed earth block architecture for housing progressed significantly during the 1980s, both in European and in developing countries. Progress in scientific, technical and architectural research on mastering the means of production of the material as well as its application, the implementation of numerous pilot or experimental programmes, and the dissemination of technical data amongst field operators, all contributed to the expansion of a building market specific to this material. The building industry was right, if one is to judge by the regular appearance on the market of new presses and other production equipment (mixers, grinders, etc.). Simultaneously, the increasing importance attached to training, at academic and at professional levels, and the development of sites linking production, construction and training, have helped to set up a network of skills favourable to the blossoming of a genuine body of knowledge. Finally, mention must be made of the support given by large international organizations, and notably the role played by UNIDO (United Nations Industrial Development Organization), and CID (Centre for Industrial Development) or UNCHS-Habitat (United Nations Centre for Human Settlements), linked to a cooperation effort on the part of European countries (France, Germany) in the promotion of this material and the support given to the setting up of compressed earth block production industries, notably in African countries. The example of the social housing programme in Mayotte (Comoro) remains most impressive: 6,000 low-cost houses and nearly 1,000 public buildings (primary and secondary schools, state offices) have been built in the space of 10 years on an island which in 1978 was still using wattle-and-daub and raffia.
LOW-COST AND RENTED HOUSING
Marrakesh, Morocco
There has been renewed interest in building with compressed earth blocks since the 1980s. Between the traditional rammed earth and abobe of the "ksour" of southern Morocco and the modern use of compressed earth blocks rendered with "taddelakt" (a coloured and smoothed lime render), the architect Elie Mouyal is a fervent promoter of this technique which he has exploited to build luxury homes framed by the greenery of palm groves (figs. 16 and 18).
Mayotte, a Comores island
The compressed earth block industry was developed on Mayotte from 1980-81 onwards, atthe initiative of the state public facilities department (Direction de l'Equipement) and the Mayotte Housing Company (SIM). The SIM design team and the architects settled on the island, desirous to make full use of local materials, very quickly become interested in this material, the technical qualities and architectural potential of which were to be very soon demonstrated in the first housing and public facilities buildings. These first projects were to pave the wayfor Mayotte's own architectural language, which was rapidly placed at the service of a new-born genuine housing stock. The use of compressed earth blocks was linked with other local materials (wood, raffia, basalt and phonolitic stone) as a real building skill developed founded on a knowledge of the characteristics and potentialities of these. Historic lever of development of a local architecture, the compressed earth block has become a local material introducing new skills to Mayotte's small contractors and craftsmen (figs. 19, 20 and 21).
Promoting the compressed earth block, from the perspective of setting up a local production and construction industry, is an indispensable stage. Notably to overcome psychological barriers, as the compressed earth block remains a construction material which is linked in the minds not only of the people but also of professionals to the rustic nature of traditional materials, as opposed to sand-cement blocks. In this initial phase, the construction of public facilities buildings, as experience in a number of areas has shown, is a major asset with great political and social impact.
On Mayotte, officials and locally-elected representatives, together with building professionals, from the outset realized the importance of the demonstrative value of built examples. The first pilot housing programmes were immediately linked to the construction of primary schools in the vicinity of the largest built-up areas of the island and in rural areas. Over an interval of ten years, all the administrative offices previously located together at "Petite Terre", Pamandzi, were to be transferred to Mamoudzou, the administrative capital of the island at "Grande Terre". The "Prefecture" (or main administrative building), and the offices of the departments of health and social affairs, of public facilities, and of education are of remarkable architectural quality and elegance and display their architects' intention to highlight the value of using the compressed earth block combined with other local materials and with the skills acquired by the island's craftsmen and contractors.
ADMINISTRATIVE BUILDINGS, SCHOOLS, HOTELS
Burkina Faso and Morocco
Many countries have adopted the approach of promoting the compressed earth block through the construction of public facilities in the context of implementing local materials construction strategies. In Burkina Faso and in Morocco, the compressed earth block has been used for building schools, university accommodation, or luxury tourist hotels which provide an opportunity to demonstrate/he quality of the material and the part it can play in high quality architecture. Such projects are the spear-head of a new confidence and interest in building with earth which is emerging in present-day architectural production (figs. 25, 26 and 27).
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