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Concrete is strong in compression but weak in tension, and where tension occurs it is usual to introduce steel bars to provide the tensile strength which the concrete lacks. For example, with a concrete beam or lintel, compression occurs at the top and tension at the bottom of the beam and the ends are often hooked to provide a grip. The 25 mm cover prevents rusting of the reinforcement. The steel must be free from loose mill scale, loose rust, grease, oil, paint, mud and other deleterious substances which impair the bond between the steel and concrete. The most common form of reinforcement is the mild steel bar to Bs 4449 or Bs 4482. Medium and high tensile bars are also available, and deformed bars which are twisted and/or ribbed provide a better bond and greater frictional resistance than round bars and obviate the need for hooked ends. It is important that the reinforcement is fixed securely to avoid displacement during the placing of the concrete. The bars are tied together with soft wire at intersections, and spacers of small precast concrete blocks, concrete rings or plastic fittings ensure the correct cover of concrete. In raft foundations, reinforcement may take the form of steel fabric to Bs 4483, and this consists of a grid of small diameter bars, closely spaced and welded at the joints. Contact us for your building projects or other enquiries through this e-mail, michaeltony29@yahoo.com

Concrete is simply a mixture of cement and aggregates in an appropriate proportion. It is mixed with clean water to ensure quality concrete. Concrete production consist of 6 main stages which are batching, mixing, transportation, placing, compaction and curing. (1) batching: Prior to use, the cement needs to be stored in a damp-proof and draught-proof structure while aggregates should be measured stored on a clean, hard surfaces. For very small jobs the aggregates may be measured by volume using a timber gauge box with its size related to quantity of aggregate required for a bag of cement. (2) Mixing: concrete can be mixed by hand or machine on the job or purchased ready-mixed. Hand mixing should only be used for small quantities of concrete. (3) Transportation: The type of plant used to transport concrete depends on the size of of the job and the height above ground at which the concrete will be placed. Barrows, lorries, dumpers and mechanical skips are used for this purpose, and on very large jobs pumping may prove to be easier, quicker and cheaper.
(4) Placing: All formwork should be checked, cleaned and oiled before concrete is poured into it. Concrete should not be permitted to fall freely more than one metre to prevent air pockets forming and segregation of the materials.
(5) Compaction: The concrete must be adequately compacted to secure maximum density. It can be done by hand or by using vibrators. Care must be taken to ensure that concrete is well compacted against forms and at corners and junctions. In large areas of concrete expansion joints should be incorporated to permit movement of the concrete with differences in temperature.
(6)Curing: The chemical reaction which accompanies the setting of cement and hardening of concrete is dependent on the presence of water, so exposed concrete should be covered with plastics or waterproofed sheets or building paper to protect it from the sun and drying Error
Timeoutwinds for at least seven days.
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