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When pouring the foundation of a private house of almost any type, it is recommended to use concrete M300 B22.5. Its properties are optimal for the conditions of our country.
Characteristics of concrete M300 B22.5
According to the standard classification, concrete mortar M300 is classified as heavy concrete. In general, the classification using the strength grade (type M300) is outdated. It is more correct to apply new standards, according to which the properties of concrete are described by compressive strength. This parameter is displayed with the Latin letter B and numbers, which indicate the load limit that this type of concrete can withstand in compression. For M300 concrete, the closest match is B22,5. Until they get used to the new terminology, many try to use both. So they often say “concrete M300 B22.5”, given both classifications.
Concrete M300 B22.5 can be on granite and lime aggregate. Depending on the type of filler, the mass of a cubic meter is 1,83-2,5 t / m³. This parameter is also called specific gravity or simply density. On crushed limestone, the weight of one cube of the solution will be in the region of 1850 kg / cubic meter. The minimum allowable value is 1800 kg/m3. Less weight can only be in violation of technology or when using low-quality aggregate. When using granite aggregate, the weight of a cube of M300 concrete will be about 2300-2500 kg / m³. The specific figure depends on the mobility of this solution. The higher the mobility, the lower the mass. A solution with granite filler is also called granite concrete, on limestone – limestone.
Characteristics and technical indicators
Concrete M300 B22.5 has the following characteristics:
- Frost resistance – F150-F200. That is, it can withstand from 150 to 200 defrosting / freezing cycles without loss of properties.
- Water resistance – W5 – W8. If necessary, the parameter can be increased by using special additives.
- Mobility / ease of installation – from P1 to P5. Often this characteristic is called rigidity or fluidity. Rigid concrete is more difficult to lay, but it cracks less when it shrinks. Fluid is used in reinforced elements so that the solution can fill all the cavities around the reinforcement.
Evenly mixed components of concrete M300 – the main sign of the quality of the solution - Consumption at a layer thickness of 10 mm – 20-25 kg / m². That is, in order to fill a square meter of area with a layer 1 cm thick, 20-25 kg of solution is needed (depending on the filler and the stiffness of the solution).
- The minimum layer thickness is 16-18 mm. The specific figure depends on the fluidity of the composition.
- You can walk after 7-8 hours, provided that the work was carried out at a temperature of +20°C.
As in the production of any concrete, in order for the mortar to gain normalized strength, it is important to choose high-quality components. If you are going to prepare it yourself, pay attention to the purity of the components, the freshness of the cement (not older than 3 months from the date of production). It is also very important to keep the proportions exactly. More cement, water, additives can not be introduced. In most cases, this leads to a decrease in strength. So we keep the proportions as accurate as possible. If we talk about GOST, then it allows deviations in the amount of 3-5% of the mass fraction. No more.
Application area
As can be seen from the technical characteristics, M300 B22.5 concrete has high strength, water resistance, and excellent frost tolerance. All this determined the scope of its use. It is applied:
- When pouring the foundations of private houses and cottages.
- For blind areas around the house.
- For garden paths, making homemade slabs for paths.
M300 B22.5 concrete is widely used both in private and multi-storey construction - In the manufacture of concrete stairs.
- For concreting of a platform under a car.
- For monolithic walls and ceilings in multi-storey buildings.
- During the construction of the pool.
As you can see, concrete M300 B22.5 is also used in frequent housing construction. It is especially popular when pouring the foundation, but for this purpose it is better to order a ready-made solution. Especially when pouring a slab foundation. Then it will definitely turn out to fill the entire area without cold seams. In other cases, the volumes will not be so significant and you can prepare M300 concrete with your own hands.
Proportions of concrete grade 300
Concrete M300 B22,5 consists of crushed stone, sand and water. To improve the properties (frost resistance and water resistance), additives can be introduced to increase the fluidity. The rest of the composition is stable.
Cement grade PC 400 is suitable for mixing – this is the recommended grade. Permissible – PC 500. It is advisable to buy cement produced no more than two months ago. After three months, it loses 20% of its strength, then even more. So the freshness of the binder is critical. Water is usually taken in relation to the proportion of cement and is 0,45-0,56 of its amount. The exact flow rate can only be selected in relation to specific materials and especially the moisture content of the sand.
To make it easier to navigate, the proportions in the table are given in kilograms and volume fractions. When purchasing materials, kilograms are often needed; when kneading, volume fractions are usually used – buckets or shovels. Such a measure, of course, does not give accuracy. If you are going to prepare a mortar for the foundation of a house, it is still better to accurately measure the components. Otherwise, no one knows what strength you will get.
Components of concrete M300
We have already talked about cement. In order for self-made concrete M300 B22.5 to have the desired strength, it must be fresh. The norm of stale must be increased by 2-4 times, but the result can be guaranteed only after the test. And this is a long time and hardly anyone will mess with it. So we are looking for cement from a good manufacturer, packaged at the factory, indicating the release date.
Crushed stone
The use of lime and crushed granite is allowed. When using lime, see that its strength is not lower than M600. In granite, it will already be higher, so there is no need to worry. Crushed stone should be at least two fractions, but it is better to mix all three: large, medium and small. Large about 30-35%, the rest in equal shares (medium and small). This will allow the infill to be more evenly distributed. A well-chosen composition of crushed stone allows you to increase the strength of concrete up to B25 with the same proportions.
Regardless of the type of gravel, it must be clean, free of dust and foreign inclusions. The presence of dust and clay reduces the strength of concrete, and seriously. So we unload either on a clean site, or on a piece of tarpaulin, other clean cloth or film. If the gravel is dirty, it is better to wash and dry it. But this takes time, and if it is not there, look for a clean one.
Sand
To prepare concrete M300 B22.5, washed river sand is needed. You can also use quarry, but definitely washed, so that there is a minimum amount of impurities. The presence of lumps of clay is generally not allowed. If there is such a problem, the sand is preliminarily sifted through a sieve. Hold the sand in your hands and rub it, if dust remains on the palm of your hand, then it is better to rinse and dry it.
In the manufacture of concrete, it is impossible to replace sand with fine granotsev. Not the same will be strength. For a guaranteed result, it is better to take sand of several fractions: large and medium. Dusty (very fine) is not needed.
How to prepare concrete grade 300
Mixing concrete – it just seems that it’s easy. In fact, even the order in which the components are bookmarked matters. Uniformity is also important. So you need to mix the ingredients thoroughly. Most often, the following order of bookmarking materials is used:
- Throw half the norm of rubble.
- Pour in half the amount of water.
- Stir until evenly moistened.
- Add sand and cement, achieving uniform distribution.
- Throw the remaining half of the rubble. Mix again.
- Add water.
This option is good if the sand is seeded (without lumps), but it usually takes more time. If the sand has not been sifted, dry crushed stone and sand are first thrown into the pear and mixed well. In this case, the rubble will break all the existing sand lumps. Then add cement and mix until a uniform gray color. After that they pour water.
In general, to obtain normal strength, it is important to mix all the components very carefully. You can check the readiness of the solution if you throw out some of it and inspect the aggregate. Each pebble should be wrapped in a creamy mixture of sand, cement and water. And this mixture should be homogeneous, one consistency and one color. By changing the bookmark order a couple of times, the mixing time will be able to determine the best algorithm for yourself, because the only and correct one simply does not exist. The components are different for everyone, with different humidity. So we choose how to prepare the solution ourselves.