Among the ingredients of the concrete mixture, which are used to create the foundation, is not only an inorganic binder in the form of cement and sand, but also crushed stone. Its characteristics determine the strength of the structure. For this reason, before construction, you should decide what kind of rubble is needed for the foundation.
Gravel classification
It is possible to subdivide crushed stone into several types, among them material should be distinguished by
- used in the production process of rock;
- strength;
- frost resistance.
As for raw materials, the material is obtained by crushing the rock. As a result, crushed stone with different strength is obtained. Slag has the smallest, then secondary and limestone. Gravel and granite varieties of crushed stone have higher strength. Granite is the most durable, so it acts as the best option for the foundation.
If you decide what crushed stone is needed for the foundation, then you can choose its gravel variety, since it has an ideal ratio of economy and strength. By crushing concrete waste, secondary material is obtained. A brick battle can also serve as raw material. Before using it, remove the old fittings.
When deciding what kind of crushed stone is needed for the foundation, you should also pay attention to its strength. The material is divided into grades that determine the compressive strength. The M200 brand is characterized by weakness, so it is not recommended to use it to create concrete structures that will undergo significant loads. The highest brand is M1600. In this case, we are talking about high-strength material, in which the content of grains from low-strength rocks is low, their volume should not exceed 5%.
Crushed stone is also classified by frost resistance. For the construction of structures in a temperate climate, this factor is of great importance. The higher the frost resistance, the more cycles of freezing and thawing will be able to withstand the material without compromising performance. In this regard, brands are allocated in the range from F15 to F400. The best in this regard is crushed granite.
When deciding on what kind of crushed stone is needed for the foundation, you should first of all pay attention to the above indicators. However, the described filler can also be classified according to some auxiliary indicators, among them the degree of adhesion and the level of radioactivity should be distinguished.
Selection recommendations
The requirements for concrete and gravel are determined by the type of concrete structure. For example, the foundation of the building will undergo constant and temporary loads from the building throughout the life of the building. Therefore, the most stringent requirements are imposed on concrete and gravel.
If you will be fulfilling the foundation of crushed stone and cement, you must determine the brand of aggregate. As practice shows, for the most commonly used crushed stone grade M1200. However, for the construction of a small country house, you can buy less durable crushed stone.
Experts advise to pay attention also to the geometric characteristics of the grains that are part of the composition. In this case, we are talking about the fraction and the permissible degree of flakiness. Under the fractional composition of the elements mean the average grain size. A crushed stone fraction in the range of 5 to 40 mm is used to form the foundation. A fraction from 10 to 20 mm acts as an intermediate value.
The shape of the grains is also of great importance. For ideal binder consumption and ease of compaction, it is better to use cube-shaped crushed stone. In this case, the grain size should be the same. In the composition there are also flaky grains that have a needle or plate shape. The use of material with a high content of such grains becomes the reason for the binder overuse for the preparation of the same volume of the mixture. Among other things, vibration compaction is complicated.
Flask grains are also bad in that they can cause voids in the mixture, which distinguishes them from cuboid grains. Their adhesion to the material is worse, and the frame is not so rigid. Depending on the content of flaky grains, some types of crushed stone are distinguished , among them:
- cubiform;
- improved;
- normal.
Cube-shaped crushed stone has flaky grains in volume up to 10%. In the improved material, the number of such grains is limited to 25%. Ordinary gravel can contain flaky grains up to 50% of the volume. Given the fact that the foundation is a critical structure that is undergoing stresses, it should use improved or cube-shaped crushed stone.
Recommendations for choosing crushed stone for additional characteristics
Choosing crushed stone under the strip foundation, you should pay attention to a number of other properties of the material. For example, high-strength crushed stone is more radioactive in comparison with crushed stone of the M600 brand. For this reason, it is desirable that the batch of aggregate is subjected to radiometric monitoring.
You should not try to save money by buying crushed stone. On the market you can find offers of secondary crushed stone, which is represented by crushed concrete and brick. This option has only one advantage - low cost. However, it is not necessary to talk about the strength of such building materials, because after operation brick and concrete could change the initial properties.
The choice of crushed stone in appearance and method of extraction
Experts advise paying attention also to the surface of the elements. It is better to use cuboid grains with a rough surface, which have well-defined edges. Quite often, the mistake of builders is the use of river gravel, which they try to replace crushed stone. Although it is notable for its good strength and low content of flaky grains, it has one important drawback, which is expressed in a smooth surface polished with water. Therefore, to achieve the desired contact between the grains is impossible. But the use of mountain gravel, which has sufficient roughness, is acceptable.
How to get a reliable foundation?
In the mixture for the foundation, crushed stone elements form a macro frame, and operational loads fall on it. Cement and sand act as bonding agents and filling the voids. For this reason, gravel should be chosen that will not collapse under stress, while the grains must be firmly bonded to each other.
If this condition is met, then the foundation will be truly reliable, and it will stand idle for more than a dozen years.
The proportions of the mortar for the foundation
In order to get high-quality concrete and a reliable foundation, it is necessary not only to choose the right components that will meet all the requirements, but also to observe the proportions for the foundation. Sand, cement and gravel are added in the following ratio: 2: 1: 4. Water is taken in a volume of 0.5 parts.
It is with this composition that the plants supply mortar to construction sites. If you are building the foundation yourself, then the proportions will depend on the brand of concrete. Usually M200 or M300 is enough for the foundation of the house.
How to avoid mistakes?
Choosing the proportion for the foundation, sand, cement and gravel must be added in the right amount. If there is more cement in the mixture, then the solution will be tough, and it will not be very convenient to lay it.
With an excess of crushed stone or sand, concrete will not grab well. But with a rather impressive amount of water, you get porous concrete.
How to determine the fraction and the amount of crushed stone?
When choosing a fraction of crushed stone for the foundation, you should pay attention to the material, the sizes of the elements of which vary from 20 to 40 mm. Crushed stone should have a cuboid shape. It is most suitable for housing. This will achieve high performance compaction of the filler and the lack of air in the composition.
If you have a question about how much crushed stone is needed for the foundation, then you can use the following proportion, which is most often used by developers: 3 parts of sand, part of cement and 1.5 parts of water. For this ratio, you need 5 parts of gravel.
Conclusion
Granite crushed stone, although it is the best material in terms of strength, has the highest cost. When erecting foundations, its characteristics guarantee high structural strength.
At the same time, the material may be unprofitable for light buildings for economic purposes. Therefore, granite gravel is often replaced by gravel.