The most popular material in construction is concrete. Without it, you can neither build a house, nor pave a path. Concrete is a very strong durable material, and if it is reinforced with reinforcement, then the strength and service life increase significantly.
The foundation of any structure is the foundation, which bears not only the weight of the entire building, but also wind and snow loads. The stronger it is, the higher and larger the structure can be.
There are several types of foundations: monolithic reinforced concrete, pile, precast reinforced concrete.
Concrete composition
In individual construction, one of the most popular types of foundations is monolithic tape. It is simple in execution, eliminates the need for special equipment and independently mixes concrete for the foundation. Proportion - the composition of the components included in the mixture and their ratio. Its violation will lead to damage to the material. Instead of strong and durable concrete, you can get a weak structure, prone to rapid destruction.
A special role is played by the composition of concrete for the foundation. The proportions of the constituent components for the mixture must be maintained very accurately.
To get high-quality concrete, you need to use good fillers. The composition of the mixture includes sand, cement, gravel or rubble and water.
Sand
It can be natural or artificial. The particle size varies from 1.2 to 3.5 mm. Sand should not contain any impurities such as clay, silt and others, therefore, in order to achieve the purity of the material, it must be sieved and washed. When working in winter conditions, the sand must be warmed up. Frozen aggregate must not be added to concrete.
Gravel or crushed stone
These inert materials are the main component of the concrete mix. Their amount in concrete should be about 80%. The size of the fraction is used from 5 to 70 mm (depending on the work performed). These aggregates are also washed out of impurities.
Cement
This is the main component that is part of the concrete for the foundation, its proportions in the mixture must be maintained with great care. The quality, strength, and also the brand of concrete depend on this. Typically, for the construction of foundations, Portland cement M300 or M400 is used, characterized by frost resistance and a quick set of strength. A higher brand is more expensive and is used in small critical structures.
In order to obtain high-quality concrete for the foundation, the proportion, composition of the components included in the mixture are kept exactly.
Cement has a short shelf life. When buying, you need to look at the date of manufacture of the material. It is better to take cement made no later than 1-2 months ago. When stored improperly, it has the ability to accumulate moisture and quickly set. But even in a dry room it is not recommended to store it for a long time. The longer the cement lies, the lower its grade becomes, and, accordingly, there will be more consumption and lower strength.
So, storage of material within 6 months will reduce the brand by 25%, per year - by 40%, and in two years the brand will decrease by half. That is,
cement M400 will turn out M200, which is suitable only for paths in the garden.
Water
This is the main binder component that is part of the concrete for the foundation. The proportions of water and other fillers are calculated taking into account the density of concrete. For hard concrete, it needs less, and for plastic - more.
The interaction of water and cement triggers a chemical solidification reaction of concrete. This is a very important process, the strength of the structure directly depends on it. A significant role is played by the quality of water, no impurities such as oil, fat, acids, sulfates are intolerable here. All this will disrupt the setting process of concrete. Do not use swamp or waste water. In work it is better to take drinking.
What and how much is needed
In individual construction, the proportions of concrete for the foundation have long been determined. The optimal composition of the mixture is one part of cement, three parts of sand and four parts of crushed stone (1/3/4). Water is poured individually. If the formwork is heavily reinforced, then for better penetration into the frame, concrete is made more plastic, if not, it can be made rigid, it will freeze faster, its strength will be higher.
It is necessary to immediately determine for what purpose the production of concrete is required. If these are paths in the garden, then
concrete M100 is enough for them
, then cement will need only 1/11 part. If it is a foundation or other critical structures, then the cement in the mixture should be ¼ of the total mass.
When it is necessary to give out a certain amount and composition of concrete for the foundation, the proportions per 1m3 are taken as follows:
- Sand - 0.395 m3.
- Gravel - 0.87 m3.
- Cement - 0.193 m3.
- Water - 0.179 m3.
This is the consumption of inert and binding materials for concrete grade M200, if you need a higher grade, then the amount of cement increases.
There is such a thing as a water-cement ratio, the operational characteristic and quality of the mixture, and, accordingly, the whole structure, depend on it.
If you add more water than normal, then the plasticity of the concrete will increase, it will more easily fit into the formwork, but the grade will decrease, and it will take more time to set.
Adding a smaller volume of water will increase the stiffness of the concrete, this will complicate its laying, and voids can occur in heavily reinforced structures, leading to the weakening of the entire monolithic tape. Therefore, it is necessary to vary the amount of water to yield a better mixture.
In a word, in order to get a good composition of concrete for the foundation, the proportions of water and cement should be such that the mixture is laid into the formwork, and not poured. Stacked concrete must be compacted, this is done either by a special electric vibrator, or improvised means - a shovel, reinforcement.
Production of concrete in a concrete mixer
For the convenience of concreting monolithic structures, there are a large number of types of mixers. They can be a capacity of half a cubic meter, one cubic meter, one and a half meters cubic or more.
How to make concrete for the foundation? The proportions for one batch of vat concrete mixer are approximately the following:
- sand - 650 kg (density - 1400 kg / m3);
- crushed stone - 1300 kg (density - 1350 / m3);
- cement - 300 - 350 kg (about 6-7 bags);
- water - 180 kg.
The output is concrete M300 (the numbers indicate that a sample of a 10x10 cm cube of concrete of this brand withstands a compression force of 300 kg / cm2).
At enterprises for the manufacture of concrete, a sand-gravel mixture is used, in which the ratio of gravel and sand is already maintained in the right proportions.
Since all aggregates have almost the same bulk density, the concrete composition for the foundation can be measured with buckets. The proportions in the buckets will be: cement - 25, sand m 43, crushed stone - 90, water - 18.
25 buckets of cement is about 6-7 bags (calculation per 1 m3 of finished concrete). For a small concrete mixer, a bucket of cementitious material is taken:
- sand - two buckets;
- crushed stone or gravel - four buckets;
- water - half a bucket.
You can choose the proportions of the aggregates so that the concrete of the same grade is obtained, but the cement content in it will be different.
Calculation of the required amount and composition of concrete
In the construction drawings issued for the work, the used volume and weight of all materials are indicated. In individual construction, if there is no project, the calculation is done independently. It is important to choose the right concrete composition for the foundation. How to calculate it so as not to miss?
First you need to determine how much concrete is needed for the entire volume of the structure. It is necessary to measure the length of the entire foundation around the perimeter. Count each side separately. For example: the length of the tape is 10 meters running, the height is 1 m, the width is 0.5 m. Multiply, it turns out that 5 m3 concrete is needed to fill this side of the foundation. We also calculate the volume of the remaining parties. After adding up all the amounts, we get, for example, 20 m3 of the mixture.
Example: for 20 m3 of finished concrete M300 it is necessary:
- cement - 7000 kg;
- sand - 13000 kg;
- crushed stone or gravel - 26000 kg;
- water - 3600 kg.
Some recommendations for concrete laying
When calculating the volume of concrete for pouring the foundation, it is necessary to add another 10-15 percent to the resulting mass for unforeseen expenses, losses during transportation, laying, etc. Concrete should be poured into the formwork in layers of 25-30 centimeters each, with mandatory compaction. The second and subsequent layers are recommended to vibrate or pierce with a shovel, reinforcement with the capture of the previous one so that the structure does not delaminate.
If it was not possible to lay concrete in the whole foundation in a day, then it is necessary to remove the cement film from the previous layer with a metal brush. This is done for better subsequent adhesion of old and new concrete. It is recommended to grout on a fresh surface when the concrete has slightly set, but has not yet completely set. All sludge resulting from grouting of the film must be removed.