In what cases it is necessary to use additives for concrete

Liquid concrete mix is ​​a versatile building material, without which no building site can do. However, its use has some limitations, which may be due to low ambient temperature or constrained styling conditions, as well as poor quality of the mixture itself.

In order to reduce the negative impact of various external factors, special plasticizing agents for concrete are used, which can change the physical properties of the liquid mixture.

The complex use of such additives allows one to achieve those or other necessary qualities that a concrete concrete product must meet under certain operating conditions.

Variety of Concrete Admixtures

In order to substantively answer the question of what is added to concrete for strength, this article will discuss various types of modifying additives that are introduced into the mortar during its manufacture.

Also, the reader will be presented with detailed instructions, which describe the basic properties, the principle of operation and recommendations for the use of various additives used to give the finished concrete the necessary performance characteristics.

Purpose of modifying additives

To have a complete understanding of the application of a particular type of auxiliary components of mortar, first of all, you need to understand for what purpose it will be used.

The introduction of certain modifying additives may have the following effect on the liquid concrete mix:

1. Reducing the minimum temperature of the hydration reactionthat contributes to the normal setting and hardening of the cement stone without significant loss of strength, in low or negative temperatures.
2. Giving antifreeze properties to water cement-sand mortarthat prevents the formation of ice crystals and the transformation of water into a solid state at temperatures below 0 ° C.
3. Acceleration of the hydration process and reduction of the time to set critical strengththat provides normal further hardening of the concrete, even after freezing and subsequent defrosting.
4. Reducing the specific viscosity and increasing the plasticity of the liquid mortar, which increases its workability, and also reduces the likelihood of voids and cavities in the cast form or formwork.
5. Increasing the density, water resistance and frost resistance of a solid block after it hardens, which generally has a positive effect on the strength and durability of the entire concrete structure.

Tip! Immediately it should be noted that the price of modifying additives on the scale of the entire construction is very insignificant, therefore, if necessary, the use should not be neglected.

Conditional classification

Depending on the purpose, principle of operation, and conditions of use, it is common to divide all chemical modifying additives into several different groups.

1. Winter or antifreeze substances allow you to perform concrete work without loss of quality at ambient temperatures of up to -20 ° C.
2. Superplasticizers, or in other words, additives to concrete for plasticity, provide the dense mortar with the necessary mobility, increase its density, and, accordingly, strength, frost resistance and water resistance.
3. Accelerators of curing, which reduce the time of hardening of the cement stone to a set of critical strength, thereby ensuring its curing before the freezing of the mortar.

1. Additives for self-compacting concrete solutions, which are used in monolithic and frame construction for pouring thin-walled or densely reinforced building structures into the formwork.
2. Corrosion-resistant substances, which have a neutral or passive reaction with iron, increase the ductility and workability of the mixture, as well as provide corrosion protection for steel elements of the reinforcing strapping.
3. The latter group includes the so-called universal or complex additives, which have several modifying properties at once.

Tip! Complex additives have a balanced set of certain functions, therefore they are recommended for use in the case of self-preparation of concrete with their own hands directly at the construction site.

Change of plasticity and mobility of concrete solution

One of the most important parameters of a liquid concrete mix is ​​its workability and plasticity, since the final result and the quality of the finished solid product largely depend on these properties.

To improve these indicators, three types of modifying additives are used, which differ from each other in the principle of operation and application technology.

1. Surface-active plasticizers, which are designed to improve the physical properties of concrete solutions of thick consistency. Their action is based on the reduction of the surface tension of water, which ensures a good slip of the particles of the solution among themselves and increases its mobility with reduced water consumption. Due to this, the solution becomes more homogeneous and plastic, is better pumped by concrete pumps and fills the form or formwork tightly.

1. Wetting agents allow you to make a solution of a more liquid consistency with a normal amount of water. Due to this, the concrete is easy to fit into the form, but at the same time does not stratify and has a constant density.
2. For the manufacture of lightweight concrete, special air entraining additives are used, which form a large number of small closed pores in the monolithic structure. The air in this case acts as a lubricant, the volume of the solution slightly increases, its density decreases, but at the same time the plasticity and workability increase.

Pore-forming additives also increase the frost resistance of concrete, since closed pores take up the main part of the load that occurs in its structure when capillary water freezes.

Note! Light and ultralight grades of concrete should not be confused, since the manufacture of the latter uses special gas-forming additives for foam concrete, which provide it with very low density and large porous structure.

Improving the frost resistance of the liquid mixture

Reducing the minimum temperature of solidification of mortar is of particular relevance in the cold season, since the use of conventional concrete at temperatures below + 5 ° C is difficult, and at negative temperatures it becomes impossible at all.

The main task of concreting in the winter time is to reach the mortar with a value of critical strength before it begins to freeze and turn water into ice.

In order to ensure the fulfillment of this condition, two types of modifying additives are used.

1. Hardening accelerators, such as an additive for concrete, calcium nitrate, which reduces the setting time of the mortar and accelerates the formation of cement stone, allowing it to achieve critical strength at an early stage of solidification. It is used when casting monolithic structures in winter, as well as in the manufacture of repair solutions for embedding cracks and eliminating defects.
2. Antifreeze substances allow the water in the composition of the concrete solution to be in a liquid state even at very low negative temperatures. Thus, in the hardening structure of the monolith, no foci of local stress are created due to the formation of an ice crystal lattice, and free water remains in the interior of the solution for the normal course of the hydration reaction of the cement.

Note! As a rule, any anti-freezing additive for concrete has a high corrosive activity, therefore such compositions are not recommended for the manufacture of reinforced concrete structures with steel reinforcement.

Improving the waterproofing ability of concrete

For the construction of artificial reservoirs, pools, fountains, as well as the construction of cellars or buried objects for the installation and operation of utilities, water-repellent and waterproofing properties of the building material are very important.

In principle, concrete itself has a certain watertightness limit, however, with increasing water pressure, the threshold value can be exceeded, which ultimately will lead to flooding or leakage.

It is also possible to increase the water resistance of concrete with the help of certain chemicals added to the mortar.

1. Sealing substances that increase the density of the solution by reducing its porosity and weakening the capillary effect, which ultimately leads to a decrease in water absorption of the monolithic array. Such a tool can also be considered as an additive in concrete for strength and frost resistance, since its use increases the brand density of monolithic concrete.
2. Elastic swelling substances that slightly increase in volume during solidification and thus fill all the pores and voids of the monolithic massif, ensuring absolute tightness and impermeability to it.

Table 1 shows the comparative indicators of water resistance and frost resistance, various brands of concrete.

Conclusion

After reading this article, it becomes clear that there is a huge amount of all sorts of modifying additives, the use of which makes it possible to impart the necessary operational qualities to the mortar.

For a more visual presentation of this topic, we suggest watching the video in this article, where there is still a lot of useful information.