Nowadays a building’s framework is made of reinforced concrete and of structural steel. Concrete is made by mixing together small stones, sand, cement and water. The coarse stones used in the mix give the concrete its strength. The sand is needed to fill the gaps between the stones. The cement, mixed with just enough water to make it into a paste, covers the surface of all solids, and binds the entire mixture into single mass. It is used less water to make mixing concrete denser and stronger. It is a difficulty here. Dry mixing concrete is not so easy to stir as one that is fairly wet and sloppy. When it is really strong concrete, it is mixed with the necessary minimum of water and placed in the forms. After this it is vibrated with electrically vibrated bars. The mixture is tipped or piped into forms (wooden mold) of the shape required.
Основной идеей текста является …
To make really strong concrete, you must fill the gaps between the stones.
To make really strong concrete, you must place it in the forms.
To make really strong concrete, you must mix it with water.
To make really strong concrete, you must mix it with the necessary minimum of water.
