Fine-grained concrete - a material with a higher density compared to conventional types of concrete. The main condition for its preparation is the use of various fractions in the aggregate mixture and the increased cement content. This material belongs to the category of heavy concrete, but, unlike other types, aggregate with an average fraction of 2.5 mm is present in the composition of such a solution.
Benefits
The use of fine-grained concrete is due to its unique properties. This material has many advantages compared to traditional solutions:
- increased resistance to bending moment at the corresponding load;
- the ability to obtain unique properties using additional additives (for example, acid resistance or water resistance);
- increased resistance to vibration;
- homogeneity of the mixture;
- the possibility of applying various options for pouring complex elements and structures;
- high plasticity of the solution and excellent penetration.
Disadvantages
MB has a number of minuses:
- increased hardness of the material after a full set of strength complicates the processing process;
- to obtain the required qualities, a large amount of cement is used;
- during the set of strength, the material gives noticeable shrinkage;
- high degree of mobility of the solution during application.
Composition and characteristics
Sand, cement and water are the main components. The composition of fine-grained concrete can be supplemented by various additives and plasticizers, based on the purpose of the solution. Regulates fine-grained concrete GOST.
The size of the aggregate, the necessary proportions and the possibility of using plasticizers for heavy concrete are reflected in GOST 26633-2015, as well as in GOST 26633-2012. The production of MB used for the organization of road asphalt concrete pavements is regulated by GOST 9128-97, and GOST 7473-2010 is developed for the production of fine-grained special concrete mixtures.
The main condition for obtaining a high-quality solution is the use of sand with various fractions (up to 5 mm) in the required proportion. It is also possible to use crushed stone with a size of fractions up to 10 mm.
The volume of cement is determined in accordance with the requirements of GOST, since an excess or decrease in the estimated amount can significantly affect the characteristics of the product.
A small proportion of cement leads to insufficient strength of the cast element, and an excess of this material leads to difficulties in the working process, since the setting will take place faster.
Fine concrete has the following characteristics:
- Increased resistance to bending.
- Homogeneity.
- Vibration resistance.
- Frost resistance.
- Water resistant.
- Porosity.
Types, brands and classes
According to the main characteristics and scope of application, MB are divided into two main types:
- MB with traditional component content.
- Fine-grained cement used to fill the forms of structures with fine-mesh reinforcement.
Grades of fine-grained concrete are determined by the quality of the materials used and their ratio in solution. There are five grades for this material:
- M100 (used for repair work);
- M200 (for repair and casting of products not bearing significant loads);
- M300 (for filling molds when casting products with frequent reinforcement);
- M350 and M400 (for casting critical products and structures).
The classiness of the MB reflects its ability to resist compression. This characteristic is measured in MPa and is indicated by the letter "B" with the corresponding figure. For example, fine-grained concrete B25 with the use of M300 grade mortar is used to equip foundations, cast monolithic flights of stairs and floor slabs, which indicates its high strength capabilities. MB class B15 with a solution of grade M200 is used for pouring screeds.
Grading begins with class B3 concrete and reaches class B80.
Scope of application
The use of MB is caused by the absence of open rock deposits in the production area of cement-sand mixtures with the presence of large fractions.
Delivery of crushed stone or gravel to remote areas significantly increases the cost of concrete, which affects the cost of the final product. This reason is the most common when deciding on the production of concrete using fine fractions.
In addition to purely economic reasons, there are many products and structures that cannot be produced using traditional concrete with large fractions. These include:
- asphalt concrete pavement;
- large and small diameter concrete pipes;
- structural elements for the construction of hydraulic structures;
- pipes with special properties for the removal of aggressive waters;
- any thin-walled reinforced structures (for example, spherical products with high strength and, at the same time, low weight) are cast from MB
- floor slabs for equipping canopies in agricultural buildings where large spans are required to be covered;
- bunker structures, large containers for storing bulk and liquid substances and materials;
- products with dense reinforcement;
- arched structures that can cover significant spaces (for example, with the equipment of exhibition pavilions).
How to make
The preparation of fine-grained concrete depends on the purpose of the cast structure and differs in composition by the presence of plasticizers, additives and the number of basic ingredients.
The binder of the mixture is cement. Traditionally, Portland cement M400 is used for standard solutions, but, for special conditions and the nature of the loads, higher grades (M500, M600 and M1100) can be used, as well as cements with special properties: resistant to corrosion, acids and aggressive environments.
The plasticity of the solution is achieved by using a filler selected by the size of the fractions. For the preparation of MB use a filler with fractions of 0.3-5 mm in a certain proportion.
To obtain the filler of the desired quality, a three-stage method of preparing the material is used:
- In the first stage, sand is obtained with a fraction of 1.25 to 5 mm. The proportion of this component in the total volume of the filler is 60%.
- In the second stage, sand with a fraction of 0.3 to 1.25 mm is selected. The share of this material is 20% of the total filler volume.
- And another 20% is sand with a fraction of 0.15 to 0.3 mm.
The proportion of cement in the mixture is due to the nature of the load that the future product will assume and is regulated by regulatory documents, but to prepare a high-quality MB, it is important to pay attention to the quality of the binder material. It is necessary to check the shelf life of cement, the absence of lumps, solid fractions and debris.
The preparation of the solution begins by mixing the dry ingredients. The ratio of the binder material and filler can range from 1 to 1.5 to 1 to 3.5. The addition of water is regulated by the need to obtain a more plastic solution or more viscous. According to the same characteristics, the proportion of plasticizers and additives is regulated.
It must be remembered that the increased content of filler with large fractions leads to a loss of strength characteristics, although it is possible to reduce the consumption of a binder. With a high proportion of small fractions of the filler, the amount of cement will be required more, but the product gets a higher density and strength.
Manufacturers and prices
The most famous manufacturers of MB include domestic companies:
- "Stromat";
- Apogee Story ";
- "Alliance".
Prices for one cubic meter of this material range from 2500 rubles.