The most demanded material in construction is concrete. Without it, it is impossible to build a house or lay a path. Concrete is a very strong durable material, and if it is reinforced with reinforcement, then its strength and service life increase significantly.
The basis 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 taller and larger the structure can be.
There are several types of foundations: monolithic reinforced concrete, pile, prefabricated reinforced concrete.
Concrete mix composition
In individual construction, one of the most popular types of foundation is tape monolithic. It is simple in execution, allows you to do without special equipment and independently knead 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 that is subject to rapiddestruction.
The composition of concrete for the foundation plays a special role. The proportions of the constituent components for the mixture must be maintained very accurately.
To get high-quality concrete, it is necessary to use good fillers. The mixture consists of sand, cement, gravel or crushed stone 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 purity of the material, it must be sieved and washed. When working in winter conditions, the sand must be warmed up. Adding frozen aggregate to concrete is unacceptable.
Gravel or crushed stone
These inert materials are the main constituent 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 from 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, as well as the grade of concrete depend on this. Usually, Portland cement M300 or M400 is used for foundations, which is characterized by frost resistance and fast curing. A higher grade is more expensive and is used in small, critical designs.
To get high-quality concrete for the foundation, the proportion, composition of the components included in the mixture are maintained 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. If stored improperly, it has the ability to absorb moisture and set quickly. But it is not recommended to store it in a dry room for a long time. The longer the cement lies, the lower its brand becomes, and, accordingly, there will be more consumption and lower strength.
Thus, storing material for 6 months will reduce the brand by 25%, for a year - by 40%, and in two years the brand will decrease by half. That is, from cement M400 you get M200, which is only suitable for paths in the garden.
Water
This is the main binding 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 rigid concrete it needs less, and for plastic concrete it needs more.
The interaction of water and cement triggers the chemical reaction of concrete hardening. This is a very important process, the strength of the structure directly depends on it. Water quality plays a significant role, no impurities such as oil, fat, acids, sulfates are allowed here. All this will disrupt the concrete setting process. Do not use swamp or waste water. It is better to take drinking water to work.
What and how much you need
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, the concrete becomes more plastic, if not, then it can be made rigid, it will harden faster, its strength will be higher.
We must immediately decide for what purposes the production of concrete is required. If these are paths in the garden, then concrete M100 is enough for them, then only 1/11 of the cement is needed. If this 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 issue 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 binder materials for M200 concrete, if a higher grade is needed, then the amount of cement increases.
There is such a thing as the water-cement ratio, the performance and quality of the mixture depend on it, and, accordingly, the entire structure.
If you add more water than the norm, then the plasticity of concrete will increase, it will be easier to fit into the formwork, but the brand will decrease, it will take more time to set.
Adding less water will increase the stiffness of the concrete, making it more difficult to lay, and voids can occur in heavily reinforced structures, leading to a weakening of the entire monolithic tape. Therefore, it is necessary to vary the amount of water to produce better qualitymixes.
In a word, in order to get a good concrete composition for the foundation, the proportions of water and cement must be such that the mixture fits into the formwork, and not poured. The laid concrete must be compacted, this is done either with a special electric vibrator, or with improvised means - a shovel, fittings.
Concrete production in a concrete mixer
For the convenience of concreting monolithic structures, there are a large number of types of mixers. They can be half a cubic meter, one cubic meter, one and a half meters cubic and more.
How to make concrete for the foundation? The proportions for one batch of cubic concrete mixer are approximately as follows:
- 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 made of concrete of this brand withstands a compressive force of 300 kg/cm2).
At the enterprises for the production of concrete, a sand-gravel mixture is used, in which the ratio of gravel and sand is already maintained in the required proportions.
Since all aggregates have almost the same bulk density, it is possible to measure the composition of the concrete for the foundation 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 (calculated for 1 m3 of finished concrete). For littleconcrete mixer on a bucket of binder is taken:
- sand - two buckets;
- rubble or gravel - four buckets;
- water - half a bucket.
You can choose the proportions of aggregates so that you get concrete of the same grade, but the cement content in it will be different.
Calculation of the required amount and composition of concrete
In the construction drawings issued for work, the volume and weight of all materials used are indicated. In individual construction, if there is no project, the calculation is made independently. Here it is important to choose the right composition of concrete for the foundation. How to calculate it so as not to miss?
First you need to determine how much concrete will be 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 linear meters, the height is 1 m, the width is 0.5 m. We multiply, it turns out that 5 m3 of concrete is needed to fill this side of the foundation. We also calculate the volume of the remaining sides. After adding up all the sums, we get, for example, 20 m3 of the mixture.
Example: for 20 m3 of finished concrete M300 you need:
- cement - 7000 kg;
- sand - 13000 kg;
- crushed stone or gravel - 26000 kg;
- water - 3600 kg.
Some recommendations for concrete placement
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. Pouring concrete intoformwork should be in layers of 25-30 centimeters each, with obligatory tamping. The second and subsequent layers are recommended to be vibrated or pierced with a shovel, reinforcement with the capture of the previous one in order to prevent delamination of the structure.
If it was not possible to lay concrete in the entire 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. Grouting is recommended to be done on a fresh surface, when the concrete has slightly set, but not yet completely frozen. All sludge resulting from the grouting of the film must be removed.
