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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 19 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 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.
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 s, both in European and in developing countries.
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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.
The example of the social housing programme in Mayotte Comoro remains most impressive: 6, low-cost houses and nearly 1, public buildings primary and secondary schools, state offices have been built in the space of 10 years on an island which in was still using wattle-and-daub and raffia. 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.
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.
Architecture for public buildings 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.
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. Masonry principles A compressed earth block masonry structure consists of small building elements placed one on top of the other following a particular bonding pattern and bound together with mortar. The earth blocks therefore form a building system - whether it be a wall or a partition, a post or a pillar, an arch, a vault or a dome - which has compressive strength. This characteristic of compressive strength is indeed essential as, by contrast, masonry structures using small elements have very little tensile strength.
The good strength and good stability of a masonry structure using small elements is dependent on the interaction of several factors: the quality of the block itself, the quality of the masonry i. Com pressed e arth bl oc k mason ry is a system in which sm all elements are placed one on top of the other in an onganlzed way. Definition A mortar is a mixture of aggregates sand and fine gravel with a binding agent generally cement or lime , to which water is added in previously determined proportions.
Used in a plastic state, mortar ensures good mechanical bonding between the masonry elements making up a wall, a pillar, or other building systems. Role In compressed earth block construction, as in construction using other masonry elements such as stones, fired bricks, sand-cement blocks , mortar plays a threefold role: It bonds the masonry elements together in all directions vertical and horizontal joints.
It allows forces to be transmitted between the elements and notably vertical forces i. It enables these forces to be distributed across the whole surface of the masonry elements. It compensates for any defects in horizontality in the execution of the masonry work. Properties and characteristics When freshly mixed, mortar should be easily "worked".
Apart from having a suitable consistency, it should display good cohesion, as well as the capacity to retain water against the suction of the masonry elements on which it is applied. Allow good permeability to humidity. Have mechanical performances which are compatible with that of the compressed earth blocks.
Composition The composition of the mortar should in each case take account of the actual requirements of the masonry structure. A good mortar should have good mechanical strength and should have the same compressive strength and resistance to erosion as the compressed earth blocks. Too low a strength mortar carries the risk of erosion, water infiltration and the deterioration of the compressed earth blocks. Erosion and cracking of the mortar, in addition to tensile forces, results in a risk of rupture.
Too high a strength mortar carries the risk of water stagnating on parts of the visible mortar matrix standing proud of the surface which in turn causes the erosion of the blocks; this can result in the blocks cracking and in lowering their strength. The texture of a good mortar is generally more sandy than that of compressed earth blocks, with a maximum particle diameter of 2 to 5 mm.
What is Compressed Earth Block (C.E.B) or Ecological Brick?
Stabilized mortar must always be used with stabilized compressed earth blocks. In this event, the proportion of cement or lime used should be increased by a factor of 1. It could be possible to use a non-stabilized earth mortar if one is sure that the walls which are to be built with this mortar are well sheltered from exposure to rain or to water in general. But even so, it will still be necessary to ensure that the non-stabilized mortar has the same compressive strength and resistance to erosion as the earth blocks.
Compressed Earth Blocks
Disadvantages Mortars have certain weaknesses: they shrink as they dry out, they can be chemically unstable, they can present a lower strength surface at the point of contact between the mortar and the block in a solid state. The main disadvantage is due to the hardening through drying out with a significant risk of shrinkage occurring.
This shrinkage can cause the masonry to settle.
This danger can be avoided by not making joints too wide, by using a fairly sandy mortar, or by wedging the joint apart by adding small stones. Good practice The mixing water of the mortar should be clean i. The surface to which it is to be applied should be prepared and clean. The bonding of the blocks should be correct in both directions of the bonding pattern, using vertical and horizontal joints.
Vertical joints should be well filled. Care should be taken to prevent the mortar drying out too quickly e. The width of the mortar joints, both horizontal and vertical, should be even and a maximum of 1 to 1. For stabilized compressed earth blocks, blocks should be pre-soaked, and the surface on which they are to be placed should also be moistened. The block should be "spread" with the right quantities of mortar on the sides to be bonded.
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Once the block has been laid, it should be pushed firmly into place, but above all it should never be tapped or hit as this could destroy the adherence between the block and the mortar. Joints can be finished in three ways, giving different appearances: 1 - flush with the wall 2 - slightly hollowed out concave and rounded 3 - hollowed out concave and chamfered FIGURE FIG. Bonding patterns The term "bonding pattern" refers to the way in which compressed earth blocks are arranged, assembled and therefore bonded together in all directions of a masonry structure horizontally and vertically, and in the thickness of the wall.
The bonding pattern determines the position of each earth block from one course to another and notably prevents vertical joints occurring one immediately above the other, which would entail the risk of cracks spreading through the structure.
Bonding patterns play an essential part in ensuring the cohesion, the stability and the strength of masonry structures built from small elements bonded together with mortar. Deciding which bonding pattern to use should be done before the masonry work begins will depend on five interrelated factors which should be considered together: 1 - the type of structure wall, partition, pillar, other , 2 - the size of the structure, 3 - the dimensions of the compressed earth blocks, 4 - the skill of the masons appropriate level of complexity , 5 - the aesthetic effect required of the finished appearance of the external faces of the structure.
C;D Generally, the minimum distance between two blocks in two successive courses should be equal to a quarter of the logest side of the block its length. To build simple earth block masonry structures, such as walls, the most common bonding patterns require the use of half and three-quarter dimension blocks, as well as of full blocks Fig.