How to make concrete

Posted by: monty - 23/03/2010 22:34:06

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Concrete
A building material composed of cement, sand, and crushed stone or gravel, mixed in varying pro¬portions so that when dry there results a solid stone-like substance of very great durability.
Concrete was used by the Romans before 500 BC, and many examples of Roman work nearly 2,000 years old still exist. In medieval times it was used for the foundations, etc., of Westminster Abbey, Salisbury and York Cathedrals, etc. concrete of the type known today was not used until the middle of the last century, following the discovery of Portland cement by Aspdin in 1824.
The life of concrete is almost unlimited, and it is not affected by extremes of weather conditions, but durability may be affected by chemical additives to achieve faster setting. Additional strength is imparted by the use of steel rein¬forcement in the form of rods. Owing to its fireproofing qualities concrete is frequently used as a coating for steel structural bars.
Pre-cast concrete units such as paving slabs, lamp posts, drain¬pipes, walling blocks, etc., are now common, but the more recent development of larger units not only speeds the con¬struction time of tunnels, blocks of flats and offices, etc., but minimizes interruptions due to bad weather. Concrete can be applied to other substances by means of a cement coating, and coloured concrete is decoratively effective.

Concrete is a mixture of cement, sand (fine aggregate), small stone or gravel (coarse aggregate) and water. It has many applications, from fence posts to motorway bases and, because of this; there are many different ratios for the constituents to be mixed. Bags of ready mixed aggregate can be bought in most builders merchants or is can be bought loose and delivered to you by lorry.

Try a 1:2:3 mix for general applications, say a concrete base for a shed or greenhouse, or a pathway.

This is 1 part cement, 2 parts sand and 3 parts gravel. Suggest a bucket rather than a shovel to potion these out as you will see a shovel of gravel due to the way it heaps is more than a shovel of cement so the quantities will be wrong to start with.

Mix them on a smooth concrete base or mixing board (have plenty of water and a stiff broom to clean up later). Once mixed hollow out the centre and add water slowly to form a small lake trying not to overflow. Gradually fold in the mix until the water is absorbed. Form a hollow again and repeat the lake procedure until a heavy paste like consistency is reached. A small trowel should be able to stand up and not fall over in this.
You have now made concrete and can wheel barrow it to where needed.

Posted by: Prof Ro - 23/03/2010 22:34:49

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