Preparation of concrete technology and proportions

Construction almost always involves the use of concrete, namely a concrete mixture, which is an artificial stone. When erecting a house, a garden greenhouse, fences, a foundation is necessarily poured. Also, concrete is used to make blind areas, farm blocks and even pedestrian paths in suburban areas. A wide range of applications speaks of the universality of concrete as a building material.

Concrete is manufactured in the manufacturing process or self-mixing the main constituent components. Mixing is done in wooden or metal boxes, baths, mobile concrete mixers. The latter provide the greatest productivity and quality mixing of the components of the mixture( crushed stone, sand, cement, water).When making concrete by oneself, it is extremely important to exclude foreign substances from entering the mixture, and also to observe the technology and take into account the proportions( dosage).

Concrete, classification

Classification	Weight, kg / m3	Scope of use
Heavy	Over 2500	Power plant
Heavy	From 1800 to 2500	Manufacture of foundations, reinforced concrete structures, other construction work
Light	500 to 1800	Production of ceilings, panels, wall blocks
Particularly light	Less than 500	Thermal insulation of facades of buildings

In addition, specialized concrete has been developed, characterized by the presence of special impurities in themth, improving these or other characteristics( thermal conductivity, strength, density, etc.).For example:

• is heat resistant( resistant to heating up to 1000 degrees);
• road( especially strong in bending and frost-resistant);
• hydraulic( has a high resistance to corrosion, water resistance, high density);
• aerodrome and other types of concrete special purpose.

Basic components of the concrete mix

If you are thinking about hand-made concrete preparation, it is necessary to take into account not only the quantity of "ingredients" used for the mixture, but also their quality, which will affect the characteristics of the finished basement.

Sand

To prepare a concrete mix, use sand with fraction from 1,2 to 3,5 mm. Too fine sand is not suitable for making concrete. When choosing sand, pay attention to its purity - the presence of clay inclusions, sludge no more than 5%.Otherwise, the concrete will lose its strength because of the high fat content that clay gives, and will quickly crumble accordingly.

How to check the quality of sand? Enough to pour a little into a container of running water and shake. A clean or slightly muddy water will tell you about the high quality. If the liquid instantly stains in the color of the clay or there is a deposit - sand is unsuitable for the manufacture of concrete.

Crushed stone, gravel

The next component of the concrete mix is ​​gravel( gravel, granite screening, scrap of bricks, expanded clay, etc.).It is chosen with a particle size of 1 to 8 centimeters( for self-manufacturing of concrete - from 1 to 2 centimeters), checking for the cleanliness and absence of debris, clay impurities. The use of a larger fraction of rubble will lead to the loss of the foundation due to the strength and at the same time to the inconvenience of the work.

Cement

In addition to crushed stone and sand, concrete is added with cement. At the same time, cement consumption depends on its brand. The amount of cement is calculated strictly by proportions, the rule "the more, the better" does not affect the quality of the future concrete.

Cement can be:

• portland cement - used for all types of construction, as well as for foundation pouring, is optimal for self-preparation of concrete;
• slag Portland cement - differs from the previous reduced frost resistance and increased moisture resistance;
• pozzolan portland cement - used in the construction of underground and underwater structures due to high moisture resistance;
• other types of cement with special additives that allow the mixture to harden faster, which shortens the maturation of concrete for up to 14 days.

Water

Water must be used warm and clean, free from impurities of oils, petroleum products, paints, enamels.

Of course, absolute cleanliness is difficult to guarantee, especially when self-preparing concrete. It is also quite difficult in practice to check absolutely accurate proportions of crushed stone, cement and sand to a liter or kilogram. In addition, it is worth considering that cement loses some of its properties over time. After a month of storage, it will lose a tenth of its properties, respectively, the cement of maar will drop. For 6 months of storage, cement loses up to one-third of all its properties.

Marking of concrete and cement

The cement grade characterizes its compressive strength( kilogram per square centimeter of a concrete cube with a side of 20 cm 28 days after its manufacture).If additional impurities are present in the cement, additional letters are indicated in the marking( for example, M( PC) 400 - D20).

The most commonly used cement grades in the preparation of concrete are the M350 and M500 .

The concrete grade( M50 - M1000) also reflects its averaged characteristics. In this case, the marking of concrete depends on the amount of cement used in the manufacture of the mixture. In the marking of concrete also indicate its class - B1 - B60, which is an indicator of strength.

How to calculate and know the volume of concrete

Directly the amount of concrete used is measured in cubic meters. Calculate the amount of concrete for the foundation of the is not difficult.

To calculate the volume of concrete and formwork, we multiply its depth by the width and by the length. This result is the amount of concrete needed for pouring.

For to calculate the proportions of components( cement, sand, crushed stone, water) for the preparation of concrete, the following "recipe" should be consulted.

If it is necessary to prepare 10 cubic meters of concrete, and for its manufacture cement M500 is used, then it is necessary to take 1 part of cement, 2 parts of water, 4 parts of rubble. From the received seven parts will be made 10 meters of cubic ready-made concrete, that means 10 ÷ 7 = 1,42 m3.This volume falls on each of the parts of concrete components. Respectively:

1. of sand 1,42 m3 × 2 parts = 2,84 m3;
2. cement one part, 1.42 m3;
3. rubble 4 parts 1.42 m3 × 4 = 5.68 m3.

Approximate weight of materials ( kg / 1 m3): cement - 1500, sand - 1800, gravel - 1400.

Optimal amount of water - half of the volume used for the preparation of concrete cement( in this case ½ part).A greater amount of water will lead to a deterioration in the consistency of the mixture.

Concrete preparation proportions

When using M400 and M500 cement for the preparation of concrete mortar, the proportions of crushed stone, cement and sand will be as follows.

Concrete, grade	Proportions of cement M400 ( Ц), sand( П), rubble( Щ), kg - Ц: П: Щ	Proportions of cement М500 ( Ц), sand( П), rubble( Щ), kg- Ц: П: Щ	Quantity of the obtained concrete from 10 l of cement of grade М400, l	Quantity of the received concrete from 10 l of cement of mark М500, l
M100	1: 4,6: 7,0	1: 5,8: 8, 1	78	90
M150	1: 3.5: 5.7	1: 4.5: 6.6	78	73
M200	1: 2.8: 4.8	1: 3.5: 5.6	54	62
M250	1: 2.1: 3.9	1: 2.6: 4.5	43	50
M300	1: 1.9: 3.7	1: 2.4: 4.3	41	47
M400	1: 1.9: 3, 7	1: 1.6: 3.2	31	36
M450	1: 1.1: 2.5	1: 1.4: 2, 9	29	32

After the amount of crushed stone, sand, cement and water have become known and prepared, it is necessary to prepare the mixture. To do this, add a small amount of water to the concrete mixer, then cover the cement, mix it, add sand, mix again, achieving homogeneity of the mass without lumps. And only now you can add rubble and the remaining amount of water. The mixture is immediately used for construction work.

Maturing of concrete and its proper strength

Traditionally, all work with concrete is carried out in the warm season with positive air temperatures. In this case, water reacts with cement and the composition qualitatively solidifies. When pouring concrete in cold weather, water can turn into ice, which will cause damage to the bud and strength of its destruction from the inside.

"Concretes" the concrete for 12 hours, solidifies within the first week, after two weeks concrete gets almost 80% of its strength, and fully ready for operation becomes only a month( assuming an ambient temperature of about 20 ° C).If you have used special types of fast-hardening concrete for pouring, the maturation period may be shorter.

Video - Concrete preparation