Often there are questions about the concept of lean concrete - what is it, what are its characteristics and composition, for which it is used. Taking into account the popularity of this building material and high sales volumes, we want to tell what lean concrete is, what properties are characteristic of it, and what area of its application.
Concrete with low binder content
In order to fully understand the properties and characteristics of lean concrete, you should know the basic principles of concrete preparation as such and keep in mind the dependence of its characteristics on the composition and quality of components, their proportions and properties.
As we all know, concrete is called artificial stone, which is obtained by mixing with water a dry mixture of cement, sand and rubble. There are other types of concrete mix with the use of asphalt, resin, polymer compositions and slags, but we will talk about cement concrete.
So, in the table you can study the composition of construction cement concrete:
|Cement||Today, in the manufacture of a concrete solution, Portland cement of the grades M400 or M500 are used, sometimes slag and pozzolanic cements are used. It is the main binder that provides strong adhesion of all other components and a homogeneous stone-like structure of the material.|
|Sand||For the manufacture of concrete solution used river or quarry sand of fine and medium fractional composition, washed from clay and dust impurities. Sometimes coarse sand is used, which is obtained by crushing rock in the sand solution plays the role of fine aggregate and fills the voids between large components, and also ensures the normal hardening of the mixture|
|Rubble||As a part of concrete, various rubble can be used - stone, slag, limestone, gravel, etc. For lean concrete, stone, gravel and mixed aggregate of both small and coarse grain is used; Water. It is a reagent for the cement hydration reaction, which leads to solidification of the solution. For an optimal course of this reaction, it is important to observe the correct proportion of reagents (cement and water), which is commonly called the water-cement ratio or W / C module.|
|Water||It is a reagent for the cement hydration reaction, which leads to solidification of the solution. For an optimal course of this reaction, it is important to observe the correct proportion of reagents (cement and water), which is commonly called the water-cement ratio or W / C module.|
|Additives||To improve the quality or give the material certain properties, special and targeted additives are introduced into its composition - plasticizers, water repellents, antiseptics, compactors, surfactants, air-entraining agents, retarders or hardening accelerators, etc.|
The dosage and quantitative ratio of the components determines the properties and quality of concrete. For various purposes, a material is prepared with different indicators of strength, density, mobility, frost resistance, water resistance, etc.
From the point of view of the theory, the water-cement module (W / C) has the most significant influence on the characteristics of the stone produced.
The estimated proportion of water sufficient to hydrate the cement is 0.2, whereas in practice such a solution would be too dense and unsuitable for laying. Therefore, the practical ratio of water to cement is assumed to be 0.3 - 0.7.
Note! Based on the above, it can be concluded that the amount of water in the solution is rigidly tied to the amount of cement in it by the W / C module.
The amount of sand is usually at least 30% of the total amount of aggregate. The proportion of rubble can vary within fairly wide limits, depending on the required strength, stiffness, oiliness and workability of the solution.
Modern design of mixtures is aimed at increasing the share of aggregate and reducing the proportion of cement while maintaining the required strength parameters. Based on the foregoing, it is possible to distinguish a typology of solutions according to the ratio of cement and aggregate.
There are three main types:
- Commodity. Here, the ratio of all components is selected for optimum strength, fluidity, cold resistance and water resistance of concrete, which is characteristic of general building requirements and needs. It is the main material for the construction of monolithic structures and reinforced concrete products;
- Fatty. The ratio is biased towards a higher cement content. This leads to higher prices and increased mobility of the mixture;
- Honey. The proportions of the components are shifted towards a lower cement content and a higher content of crushed stone, which entails a reduction in the mixture and an increase in its rigidity.
The main characteristics of concrete are its class, brand, frost resistance class, mobility and density, which are governed by GOST and SNiP, and are determined by experimental design. These parameters will be discussed in the next section of the article.
Composition and brand
We gave the definition of lean concrete, now let's talk about its properties, labeling and class affiliation.
In the modern classification used in our country, the main indicator of the quality of concrete is its compressive strength, which is reflected in the marking after the letter M. Thus, the M300 concrete grade indicates that we have material that can withstand a compressive load of 300 kgf / cm2.
At the same time, the global classification practice operates on such a concept as the class of concrete. The main difference here is that in order to determine the class, it is not the averages that are taken, but the test results, in which the prototype showed compliance with the stated strength in 95% of cases.
According to the rules adopted in SNiP 2.03.01-84, the class is designated by the letter “B”, followed by an indication of the compressive strength in megapascals. There are classes from B3.5 to B80, when determining they also take into account many factors and other quality indicators.
Thus, if we are confronted with material of class B10, this means that in 95 cases out of a hundred, a prototype of this concrete withstood a pressure of 10 MPa.
Lean concretes, most often, are grade B7.5, sometimes B10 and B15. These classes correspond to the brand of lean concrete M100 - M200. To obtain more durable grades, a more fatty recipe or highly active cement is used.
As already mentioned, the composition of lean concrete has a high content of rubble with a low proportion of cement. At the same time on 1 m3 of concrete class B7.5 have the number of components: 160 kg of portland cement M400-D0, 800 kg of sand, 1300 kg of rubble and 75 - 90 liters of water.
Note! The reduced content of cement in the solution leads to the fact that its price becomes noticeably lower than other brands. This is the main motive for the creation and use of lean concretes.
Due to the low cement content, and, consequently, of water, the lean type solution is relatively hard. It has a norm in hardness of 31 - 60 s and there is practically no shrinkage of the cone, which corresponds to the grade in terms of workability G4.
Frost resistance, as a rule, corresponds to class F50 - F100, which indicates the number of freeze-thaw cycles that the material can withstand without significant loss of quality and strength. Water resistance is within the grades W4 - W8, and W4 is characteristic of the material of class B7.5. The increase in this indicator is achieved by the introduction of pozzolan and other special additives.
One of the advantages of lean concrete is the ability to do it yourself at the site. This distinguishes this material from analogues of higher grades, for the manufacture of which requires a more accurate dosing of components and the use of additives, which is difficult to implement in terms of construction.
Cooking instructions do not differ from the conventional one: the components are mixed in the desired proportion, shut with water and thoroughly mixed to a uniform consistency with the most evenly distributed ingredients. To facilitate labor and speed up the process, it is better to use an electric concrete mixer with a gravitational effect.
So, to prepare one batch in a 0.25 m3 drum, we will need:
- 1 bag of Portland Cement M400-D0 (25 kg);
- 10 buckets of crushed stone fraction 20 - 40 mm;
- 7 sand sand;
- 5 - 2 buckets of water.
Measure should be 10-liter buckets without a slide, compact and ram concrete components can not be.
Note! When laying such concrete in the form of a horizontal sole, it is imperative to use a vibrating plate, and when pouring it into the formwork, a powerful vibrating rod.
Spheres of application
The main applications of lean concrete are bulk constructions that do not require high strength and high quality stone.
- Road works on the construction of a concrete base for roadbeds;
- Construction of the lower plates and the soles of the foundations of buildings;
- The construction of the lower parts of the walls of the foundations;
- Construction of sites, paths and other elements of land improvement;
- Filling screed floors and terraces.
Casting of lean concrete in narrow formwork, as well as structures with a high frequency of reinforcement is considered undesirable, since high rigidity interferes with the normal distribution and compaction of the material in the formwork.
Due to the low yield strength, the material is perfectly rolled by a road roller and due to this it is considered especially acceptable for building bases under the carriageway of highways and highways.
Due to the use of increased amounts of stone and gravel rubble, cutting of reinforced concrete with diamond circles and diamond drilling of holes in concrete are the only acceptable ways of processing frozen material.
Honey бетон – это разновидность бетонного раствора с низким содержанием цемента и высоким содержанием щебня или гравия. Главное преимущество этого материала – невысокая стоимость и простота изготовления, что делает его популярным в ряде областей. Для более полного впечатления смотрите видео в этой статье.