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Concrete. How to mix cement ratio

Concrete is one of our finest building materials. Millions of tons are used every year in all forms of construction work from laying paths and building brick walls in the garden to building skyscrapers, dams and bridges, and roads.

Concrete is made by adding water to a mixture of cement, sand, and gravel or stone. The cement and water form a paste which binds the sand and gravel or stone together. The sand, called the fine aggregate, fills in the gaps between the gravel or stone, called the coarse aggregate, to form a solid mass.

The most common kind of cement used is Portland cement. This is a fine gray powder made by heating a crushed mixture of limestone, clay, and iron ore in a rotating kiln.

When concrete is first mixed, it is a pasty mass which can be molded into any shape. But it quickly sets rock-hard. It can be used under water, too. It is cheap, easy to make and is waterproof and fireproof.

Cement may be cast into its final position in wooden molds. Or it may be precast into shape in, say, a factory and then assembled on the building site.

For large construction projects, concrete is usually mixed on site in concrete mixers. Sometimes, however, concrete is supplied ready mixed in huge trucks and poured directly into place.
Concrete has great strength when it is squeezed, or compressed, but is weak when it is stretched, or under tension. A concrete beam supported only at it sends may crack and collapse if the load on it is too great. To prevent this happening, concrete can be strengthened, or reinforced, with steel bars or wires to give it strength under load. The strength of reinforced concrete can be further improved by stretching, or tensioning, the wires or rods before or after concreting. The tension in the wires compresses the concrete and therefore makes it stronger. Concrete made in this way is called pre-stressed.

How to mix cement ratio. Small amounts of concrete you can mix in any capacity by a spade. Cement parity to sand approximately at a ratio of three to one (or four to one if it is not necessary for very big stability). At the same time larger amounts might require a concrete mixer.

How to mix cement ratio

A reinforced concrete (cement) arch bridge. As compressive forces only are set up in the arch, the maximum use is made of the mechanical strength of the reinforced concrete

Concrete. How to mix cement ratio

Concrete has strength when compressed, but is weak under tension (1). Reinforcing the concrete by embedding steel bars in it transfers the tension to the bars (2). In prestressed concrete, steel bars are threaded through holies cast in the concrete (3) and put under tension. This action produces compression throughout the concrete, making it very strong (4) and (5)

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