Building materials

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Building Materials - A wide range of building material options can be used for low cost school construction. The main factor in the choice would depend on what is locally available or produced in the area and the relative cost of the materials available locally. Cost and availability of materials varies from place to place, so what is cheap and available in one area might not be so in another.Climate is another important factor determining material choice and building design. Whereas, for example, the use of earthen-based flat roofs as well as earth-based arches, vaults and domes would be completely suitable for relatively dry climates, these constructions would be less suitable in wetter climates unless they would be built and finished by highly skilled labour. It also needs to be notedthat in areas with night frosts, or with very high daytime temperatures, a more massive type of construction would be better for reducing the effect of temperature change as a more heavy building heats up and cools down slower than a light one. This would imply the use of more massive materials such as rammed earth, stabilised earth blocks, or ashlar stone or rubble for walls and clay or concretetiles or thatch for roofs, rather than a lightweight walling materials such as ferrocement or timber panels, or galvanised corrugated iron sheets for roofs. Although researchers and designers have sometimes devised innovative designs and use of materials for building, generally to reduce costs, make more use of waste materials, or to make more efficient use of space, there would also be greaterrisks with aiming to use particularly innovative or experimental materials and techniques. It would generally usually be better to choose materials which have already been well proven, and particularly if they are also well known about and used in the local area. Some relatively common materials used for construction are described briefly below, though they would not all be suitable for use inevery case.

• Stone - rough hewn (rubble) or worked smooth (ashlar) blocks; the former being cheaper to produce while much less mortar is needed with the latter if they are well-finished • Stabilised soil blocks - now a proven low cost technology, especially in areas where soil of low shrinkage - which requires less use of costly stabiliser, is available locally • Rammed earth or pisé - alow cost material, though stabiliser might need to be added to control cracking, but labour-intensive and heavy to work with. The earth wall is built up between shutters or formwork that are progressively moved up the wall as construction proceeds. Use of internal and external plastering preferred with rammed earth buildings to reduce the need for maintenance, which is otherwise high, and theharbouring of insects and other pests. • Fired clay bricks - requires a higher level of skill for laying than the larger blocks, also in some cases field bricks might be warped and of variable size, so relatively large quantities of mortar are required • Concrete blocks - usually hollow rather than completely solid blocks are used as this allows some saving on the material for the blockmaker with thesame level of structural stability as solid blocks. Blocks can be used structural or loadbearing, or used for infill. The strength and durability requirements of blocks for structural use need to be considerably higher than those for infill • Precast concrete panels - panels are inserted within a structural frame and bolted with each other and the frame. Panels contain steel reinforcement, whichincreases the cost. However costs can be reduced by mass fabrication, so the application of pre-fabrication would be likely to be most relevant to very large building programmes with many identical or modular constructions. Prefabricated components do not require high levels of skill to erect, and erection can be relatively fast so having a low labour requirement - rarely a priority in many...
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