The concrete is a generic name which indicates(appoints) a material made from three main constituents(components):

Some sand and bits of gravel agglomerated by a sociable disposition. The sand-coloured and sociable mixture is called mortar.
The coulis is a very fluid mortar. In the ordinary language, this sociable disposition is a cement which makes taken by hydration, it is a hydraulic sociable disposition.
The chemical reaction which allows the concrete of cement to make grip is slow: hardly 50 % of the final resistance at the end of 7 days.
The value taken as reference in the calculations that is obtained in 28 days (80 % of the final resistance).
It is possible to improve the speed of grip of the concrete or to delay her(it) thanks to additives (additives).
It exists of numerous other there, for example to increase the flow of the concrete and facilitate its implementation ( plastifiants ).
These "improvements" are generally obtained to the detriment of the final resistance.

The cement plays the role of sociable disposition of the hydraulic concrete.
The cement consists of a mixture in powder of lime and of clayey limestone which hardens with the water.
To make some concrete Or some mortar, we use some common grey cement said about Portland. There is generally in bag of 25, 35 even 50 kg.

We use generally some sand of river or career freed(cleared) of the impurities, never the maritime sand or the sand of Elevation.
These last ones contain fatal elements for the quality of the concrete and the mortar.
The dosages are given most of the time in volume of dry sand.

Quite as the other constituents(components) of the mixture, the water must be appropriate(clean).
The dosage has to give evidence of a particular attention: too much water in the concrete entails(pulls) the birth of cracks and a loss of resistance at the time of the drying.

The little stone consists of smoother(smooth) rocky particles when they arise from a river (it is the most popular little stone) or crushed when they result from a career.
The little stone has necessarily to be freed(cleared) of some mud and of dirts which he could contain before making the concrete.
There are various calibres of little stone.
The biggest calibres are generally used for the foundations and the big person(main part) opens.
The resistance of the concrete will be all the bigger as you will mix various calibres of little stones.

Additives (additives) are incorporated into the concrete in small quantity (less than 10 kg / m3).