Concrete hollow block walls
• The use of concrete hollow blocks has several advantages:
• they can be made much larger than solid bricks, and if lightweight aggregate is used, can be very light, without forfeiting much of their load-bearing capacity;
• they can be made to any shape and size, and remain dimensionally stable;
• they require far less mortar than solid bricks (because of the cavities and less proportion of joints, due to the large size), and construction of walls is easier and quicker;
• the cavities can be filled with reinforcement and concrete, achieving high earthquake resistance;
• the air-space provides good thermal insulation, which is of advantage in highland and cooler regions (alternatively, the cavities can be filled with thermal insulation material);
• the cavities can also be used as ducts for electrical installation and plumbing.
• The concrete hollow blocks can be made in simple hand moulds and vibrator (for production on the building site) or in expensive, stationary or "egg-laying" machines (for mass production). Further information: Bibl. 22.07, 22.08.
Standard Hollow Blocks
• Concrete hollow blocks generally have two cavities and the length is twice the width plus l cm (thickness of joint).
• In order to be able to divide the block into two identical halves, a narrow cavity in the centre is needed. Division of blocks is done with a few knocks along the centre line with the edge of a hammer.
The Zipbloc System (Bibl. 22.08)
• This system is based on a special type of hollow block (53 x 25 x 14 cm), which can be used for different types of walls, as well as for ceiling and roof construction.
• For wall constructions, the blocks are assembled vertically with a little mortar. The gaps between these vertical units are filled with concrete 1: 3: 6 (1 cement: 3 sand: 6 aggregate). Reinforcing steel is placed in the vertical cavities and also filled with concrete. In most cases, it is sufficient to fill only one cavity. Door and window frames are eliminated, as the shape of the block provides the necessary jamb for fixing shutters.
• For ceilings and roofs, inverted T-beams of required length are precast and placed on the walls at 60 cm centres and propped at mid-span. The concrete hollow blocks are placed to span two beams (as illustrated). On top of this a welded steel mat is provided (for temperature stresses) and screed is cast in-situ.
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