Manufacture of the concrete

The Béton is one of principal construction materials. To carry out a floor, a flagstone or walls built S which require great quantities of concrete one in general calls upon a concrete batching and mixing plant who delivers this last in “spinning top”, with proportioning and consistency adapted to work to realize. For more modest work, like the foundations of a low wall, a staircase of garden or a small terrace, one Trowel oneself his concrete with the Concrete-mixer.

Necessary products

The necessary tools

Concrete-mixer
round Shovel
Bucket of mason

Before starting

Préparer a zone of mixing planes to install the concrete-mixer and easy access to bring sand and the gravel
Installer the concrete-mixer near the gravel and sand heaps in order to be able to charge it with the shovel
Prévoir a pipe with water supply provided with a stop valve

The principle

The concrete is a mixture of cement, sand, gravel and water, proportioned according to the type of realization to carry out.

Components

The two basic components of the concrete are the same ones as those of the mortar (cement and dry sand) and they must have same qualities. He is necessary to add to it the gravel, which can be of river (smooth) or crushed (resulting from career). The gravel exists in various sizes (one speaks about granulometry):

the fine fine gravel (5 mm) gets busy for dampings and small the Coffrage S
the average fine gravel (8 mm) for the alleys and the terraces like for the formwork and sealings
the large gauge (12 mm) is reserved for the reinforced concretes and the large Coffrage S.

One usually uses a mixture of several granulometry, symbolized by two digits, for example 8/15.

Additives

Different Adjuvant S can be used to improve the characteristics of the concrete:

Antifreeze for a use at temperatures lower than 0 Accelerating °C, or S of catch
Plasticizer S to facilitate the implementation of lintel X, narrow and major trenches, Formwork S of complex forms, etc
Superplastifiants to reduce the quantity of water (harmful with the quality of the concrete in overdose) and to increase the mechanical resistance by maintaining a great workability (better implemented).
Retarding S of catch to have a longer time of implementation.
Colorant S powders some for exposed concretes.
Agents air-entraining to create a network of bubbles of air in the concrete and to allow him to better resist the attacks gel

Proportionings

The table gives indicative proportionings:

These proportionings are given for dry sand (to add 15 to 20% if sand is wet), and the water proportioning is indicative.

More the aggregates (sand and gravels) are wet, less one needs water for the Gâchage.

proportioning out of water is important, but there remains approximate and left with the judgment of each one by knowing that:

a too wet concrete is porous and has an important withdrawal with drying;
a too dry concrete misses homogeneity and of compactness, and it is less resistant.

For a flagstone of mortar (cement and sand only), it is necessary to count for a Brouette approximately:

ten sand shovels;
four cement shovels;
a water half-bucket (approximately 5 L); to adjust according to the moisture of sand (for example, ¼ of bucket for a very wet sand), in order to have a consistent mixture.

Cement bags making 35 KG now Formula for a " Courant" concrete; : volume 100 liters;

1 Bag of 35 kg;
5 Buckets of 10 liters sand;
8 Buckets of 10 liters Fine gravels;
17 liters of water;

Method

To start the concrete-mixer. While it is turning, to pour 1/2 to 2/3 of water necessary to the batch
Verser the gravel and to let turn a few seconds so that it is well wet
Verser cement which will be watered in water and will uniformly be distributed around the grains of gravel
Verser sand with the bucket or the shovel, after having located the volume of a shovelful
By supervising the mixture, to pour a little water in complement, without exceeding proportioning envisaged.
One can also in order to have an extremely malleable concrete and preserving all its resistance, to add a little liquid soap crockery. That avoids putting too much water in the concrete and to have a too important water cement ratio.
There exist also plasticizing additives allowing implementation an easy of a concrete " sec" for formwork of complex geometry.
the concrete must be consistent but never soft, and wet on the surface. If a concrete handle is taken, this one must keep its form and, if the hand is tightened, the concrete must remain wet surfaces some without losing water
Verser the concrete in a Brouette, a vat or on the surface of Gâchage cleaned as a preliminary

Time of mixing

A concrete-mixer spends a time very runs to waste concrete: 2 to 3 min only. A time of too long Malaxage can harm the homogeneity of the concrete.

The Councils

At the end it work, to pour a gravel bucket and water in the concrete-mixer, and to make turn a few minutes to clean the tank. It is advised to wash rather quickly the tools (shovels, trowels…) in order to avoid the strong adherence of cement on metal.

See too

To make a traditional coating smoothed

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