Despite the variety of modern building materials, concrete continues to maintain a leading position among competing options, as it has such important characteristics as strength, reliability and durability. It is an integral component of mortars for creating foundations, masonry walls, plaster and other construction operations.
Water resistance of concrete, as well as its ability to withstand harsh weather conditions, are the main qualities that ensure the long service life of finished products. These criteria are the main ones when choosing the brand of this building material.
Concrete, whose frost resistance and water resistance are at a high level, is the key to quality and excellent performance indicators of any design. These properties mean the ability of concrete products to withstand the negative effects of such natural phenomena as moisture, water and freezing temperatures.
Currently, there are various types of concrete in terms of frost resistance and water resistance, characterized by quality, price and technological capabilities. Such a classification helps to select the most suitable material for the creation of structures designed for operation in certain conditions.
Concrete waterproof grades
Depending on the degree of water resistance, concrete is divided into ten major grades (GOST 26633). They are indicated by the Latin letter W with a certain digital value indicating the maximum water pressure that a test concrete specimen with a cylindrical shape 15 cm high can withstand during special tests.
Determination of water resistance of concrete is carried out by direct and indirect indicators of its interaction with water. Direct indicators are the concrete grade and its filtration coefficient, while indirect indicators are indicators of the water-cement ratio and water absorption by weight.
In private and commercial construction practice, in order to find out the waterproofness of concrete, they pay attention to its brand, and the rest of the criteria are important mainly in the production of this building material.
Characteristic features of concrete grades in terms of water resistance
When choosing the necessary concrete grade for a certain type of construction work, they are guided by digital indices standing after the letter W, characterizing the degree of interaction of the material with moisture and water. So, for example, the lowest water resistance of concrete and, consequently, the low quality of the brand W2. Solutions based on this basis are categorically not recommended for use in environments with even a slight level of humidity.
The normal degree of permeability of concrete brand W4. This means that this composition has the ability to absorb a normal amount of water, so its use is possible only if good waterproofing is provided.
The next position in the quality scale is W6, which is characterized by low permeability. This concrete belongs to the composition of medium quality and low price category, which is due to the popularity of its use in construction.
Concrete brand W8 has a low permeability, as it absorbs moisture in an amount of only about 4.2% of its mass. It is a better and more expensive option compared to the W6 brand.
This is followed by concrete grades with indices 10, 12, 14, 16, 18 and 20. The higher the digital indicator, the lower the permeability of the material. According to this classification, W20 concrete is the most waterproof, but it is not often used because of the rather high price.
The practical use of certain brands of concrete for water resistance
A variety of concrete should be selected depending on the operating conditions of the objects. For example, the W8 brand is quite suitable for pouring the foundation, provided that additional waterproofing is provided. Wall plastering is carried out with W8-W14 concrete. However, for equipping sufficiently damp and cold rooms, the waterproofness of concrete should be maximum, therefore it is recommended to use the highest quality mortars, and additional processing of the walls with special soil compositions will be required.
For high-quality and durable exterior wall decoration, pouring personal plots and walkways, concrete with maximum waterproof performance should also be used, since these areas will be systematically exposed to the negative effects of external weather factors.
DIY concrete additives for waterproofing
The need to use high-class concrete mixtures in the production of various objects or their elements is obvious, however, this requires significant financial investments due to the high cost of such materials. But what to do if the construction budget is limited, and the violation of the technological process is unacceptable? The answer is simple: you can use a compromise option, namely to increase the water resistance of concrete yourself.
Today, there are several effective ways to increase the resistance of concrete mixtures to water, but two of them have gained the most popularity: by eliminating concrete shrinkage and by temporarily influencing the concrete composition.
Elimination of concrete shrinkage
Concretes of low and medium grades are quite porous materials that easily absorb moisture. This negative property is enhanced during the shrinkage of the solution during solidification. Thus, it is possible to improve the quality and waterproofness of the concrete mixture by reducing its shrinkage.
An integrated approach will help to achieve the desired result:
- It is necessary to use special additives in concrete for waterproofing. The principle of their action is that when the solution solidifies, they form a protective film that prevents its shrinkage. Today, various additives for concrete are presented on the market for waterproofing, and although they have one task, each individual option has its own characteristics, so you should carefully read the manufacturer's instructions before buying.
- In addition to adding special additives to the concrete for waterproofing, it is also recommended to water it. This procedure is performed during the first four days with an interval of 4 hours. Further, the concrete structure must dry in natural conditions.
- With the rapid evaporation of moisture from the solution during solidification, unwanted shrinkage also occurs. To slow down this process, after pouring the concrete structure, it is immediately necessary to cover it with a special film under which condensate will form, which prevents shrinkage and helps to increase the strength of concrete. The coating is positioned so that it does not touch the fill. At the edges leave small gaps for air ventilation.
Temporary exposure to concrete
This method consists in allowing the dry solution to “mature” for a certain time. The main requirement in this case is the observance of the correct storage conditions. The mixture should be in a warm, dark room and subject to constant moisture. Thus, after six months, its water resistance can increase several times.
Concrete frost resistance
This indicator refers to the ability of concrete mixtures to maintain their physical and mechanical properties under conditions of repeated freezing and thawing. This characteristic plays a priority role in the selection of concrete for the construction of bridge supports, airdrome and road surfaces,
hydraulic structures, buildings and other facilities operating in the middle and northern latitudes.
Determination of frost resistance of concrete is carried out by laboratory tests using two methods: basic and accelerated. If the research results diverge, the final option will be considered data obtained using the basic method.
Study of the resistance of concrete to low temperatures
The tests are carried out using basic and control samples, which are made of concrete of various grades for water resistance for serial testing. Test concrete blanks are used to determine their compressive strength. This procedure is carried out before testing the main samples, which will be subjected to alternate freezing and thawing in different modes of water saturation, which take place in natural climatic conditions.
For instance:
- in the presence of the highest possible level of groundwater;
- with seasonal thawing of permafrost;
- when exposed to precipitation;
- in the complete absence of periodic water saturation, when concrete is reliably protected from groundwater and precipitation.
Classification of the level of frost resistance of concrete by grades
According to the latest edition of GOST, frost resistance concrete grades are indicated by the Latin letter F. This value characterizes the maximum number of freeze / thaw cycles maintained by specimens of a certain design age, taking into account a decrease in the tensile strength and a decrease in the weight of the material by its value provided for by the standards in force.
To determine the level of frost resistance of concrete, digital indicators from 25 to 1000 are used. The higher this value, the higher the quality and reliability of the material.
Rules for the selection of concrete mixtures
The choice of the necessary brand of concrete mixtures for frost-resistant properties should be carried out taking into account the climatic features of the area, as well as the number of freezing and thawing cycles during the cold season. It should be noted that the most frost-resistant concrete have high density indices.