Sand for concrete: purpose and characteristics

The quality of concrete depends on its components, one of which is sand. Often there are dilemmas - career or river sand for concrete to choose, large or small, dry or wet? We will tell which sand is better for concrete according to standards and practical experience.

Fine aggregate for concrete mortar

Purpose

Concrete is an artificial stone that is obtained by mixing several components with water in a certain proportion. The main ingredients of the concrete mix and their purpose:

During cement hydration, a sufficiently active stone formation occurs, as a result of which an intensive redistribution of the volume and structure of the substance is observed. This inevitably leads to the appearance of internal stresses, which exert on the material such loads that its structure cannot withstand due to the low strength of concrete and immaturity. As a result, the material cracks, seeking to compensate for the current efforts.

Note! The inclusion of sand avoids cracking of the cement stone, since its granules are rather strong and able to absorb the loads that arise, as well as distribute them more evenly throughout the entire volume of the mixture.

In addition to the physical and technical function, fine aggregate also has an economic function. As is well known thanks to Karl Marx, any human activity, in one way or another, is based on economics, without taking it into account no serious production is possible, and it is difficult to disagree.

Sand replaces cement, the price of which most significantly affects the cost of the finished mixture, and a decrease in its consumption largely determined the economic feasibility of using concrete in mass construction.

Note! Fine aggregate is necessary for two reasons: technical and economic, and we can state that without it, the production of traditional construction cement concrete is impossible.

Properties and specifications

For the manufacture of building concrete use natural sand - a mixture of small grains of various minerals that are part of the rocks of volcanic (less often - sedimentary) origin. Grains are obtained as a result of the process of weathering rock particles..

To determine the variety of sand, depending on its quality and technical characteristics, a special standard GOST 10268-80 was introduced. According to this document, the main characteristic for the classification of varieties is considered to be the particle size and material composition of the sand mixture.

It is also important to take into account such factors as the surface area of ​​the grains, the voidness and density of the material, the shape of the grains and the amount of impurities.

As a rule, the natural material contains grains of various sizes, so after extraction it is divided into fractions of different particle size.

To do this, use a set of sieves with cell sizes of 0.14 mm, 0.315 mm, 0.63 mm, 1.25 mm, 2.5 mm, 5 mm and 10 mm.

The fraction with grains larger than 10 mm is not used.

The composition of the sand mixture fraction of 5 - 10 mm should not exceed 5% by weight, and the content of the granules passing through a sieve of 0.14 mm, should not exceed 10% by weight. The remaining fractions in the quality material must be present together in various proportions determined by the purpose of the raw materials.

As for impurities, the picture is as follows: powdered, clay and silt substances should not be more than 3% by weight of the mixture. At the same time, it is clay that is most harmful, since it envelops grains of sand and prevents their adhesion with cement.

Organic impurities and decomposition products of plants should be minimized, only very small amounts of them are allowed, as humus and organic acids react and alter the cement, which leads to its destruction.

Sand для пенобетона выбирают на основании тех же критериев, что и для традиционного цементобетона. Количество песка в растворе для приготовления этого материала может достигать 40% по массе, поэтому он должен быть тщательно отобран и подготовлен.

As practice shows, sand of one fractional composition has a greater voidness than a mixture of large and small particles. Therefore, the most high-quality raw materials are obtained by mixing different fractions in specially calculated ratios. The shape of sand grains is also important: it is more rounded in river sand than in open-cast sand, therefore it is better distributed and compacted in a concrete solution.

Note! For the production of high-quality cement concrete, the river sand of mixed fractional composition, well washed from clay and organic matter, should be used, but the content of coarse (more than 5 mm) and smallest (less than 0.14 mm) fractions should not exceed 5 and 10%, respectively.

Quantity calculation

Production of ready-mixed concrete and special-purpose concrete in the conditions of a construction site is difficult, since in order to achieve the required qualities, special preparation, accurate dosing and proper mixing of all components are required.

There are different recipes, for example, here’s a small table for calculating the number of components for different grades of cement concrete:

In the manufacture of their own hands to follow these proportions is very difficult, because it applies a simplified instruction or dosing scheme for a volume of 1: 3: 5 (cement / sand / gravel). Water should be added about 50 - 70% by weight of cement, if you express it in volume, taking into account the difference in densities of these substances, you get about 90% of the volume of cement. That is, the full proportion will look like this: 1: 3: 5: 0.9 (cement / sand / gravel / water).

Conclusion

Its quality and the possibility of using such operations as cutting reinforced concrete with diamond circles, diamond drilling of holes in concrete, as well as its grinding and a number of other types of processing depend on the component composition of concrete. Fine aggregate plays an important role in the concrete solution, and the video in this article will tell about its features.