Various materials are used for constructing buildings (Fig. 20.3). Wood is simple to work with and simple to join together. Normally it is cheap, at least in smaller buildings and in areas with timber. It is used in walls, roofs and load-carrying constructions. To increase the strength and the length, glued beams can be used. Wood may also be part of constructions, for example in chipboard panels.
Metals such as steel or aluminium are also quite easy to work with; pieces are either welded or screwed together. Metals are much used in load-carrying constructions, such as beams or frame-work. Metal plates are used for covering interior and exterior surfaces on walls and roofs.
Concrete is a widely used building material. It is made of a mixture of sand and gravel with cement that functions as a glue, and water. After mixing followed by some hardening time this makes a permanent construction. The method of mixing and proportions of materials used will give concrete of different strengths.
Concrete has good compressive strength but poor tensile strength. Therefore iron is used, either as rods or mats, as reinforcement in concrete to enable it to withstand tension, while the concrete can withstand compressive forces. In small constructions, concrete is quite simple to handle and work with, and in addition it is fairly cheap. It can either be mixed on site or in a factory and delivered in special trucks ready mixed but not hardened. This latter method is most normal in larger constructions.
Concrete can also be delivered as prefabricated elements which are finished and hardened. Elements, such as beams, may also be pre-stressed to increase tolerance to higher forces without increasing the weight too much. Sizes of components vary from small blocks to bars to complete parts of buildings, such as wall elements or roof elements. Concrete may also be used for beams in load-carrying constructions.
A lightweight version of concrete is also avail-able as blocks and bars. Here the gravel is replaced with a light material, for example, expanded clay products
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