Plasticizers for concrete: varieties and technology of use

Recommendation points

• Plasticizers and modifiers – what is the difference
• Plasticizers
• Modifiers
• Targeted and complex additives to mixtures
• Plasticizer technology
• Preparation of high-quality concrete mix with household tools
• Household plasticizers for concrete
• Liquid soap
• Washing powder
• PVA dispersion
• Slaked lime

The most effective method for improving the properties of concrete is various kinds of chemical additives – plasticizers and modifiers. Their use improves the quality of concrete, prolongs the life of the mixture, helps to “set” faster and gain brand strength, reduces construction costs.

Plasticizers and modifiers – what is the difference

To improve the technological properties and obtain higher quality concrete mixtures and mortars based on cement binder, special natural and artificial additives are used. They change the physical and chemical properties of concrete. Several additives can be added to one mixture. Each of them has a basic action, and also has several additional ones. The additional properties of the additive can have positive and negative effects on the properties of the concrete mix. In the Russian Federation, manufacturing enterprises in their manufacture must be guided by GOST 24211-91. Conditionally, additives can be divided into two groups:

1. Plasticizing additives.
2. Modifying additives.

Plasticizers

Plasticizers increase the mobility, elasticity, and viscosity of concrete and maintain long-term mobility of the concrete mixture. By reducing the water-cement ratio (w / c), they reduce the consumption of cement, increase the strength and density of concrete.

According to GOST, 4 groups of plasticizers are distinguished – from weakly plasticizing additives to superplasticizers.

Modifiers

Concrete modifiers allow you to create high-quality mixtures of class B80 (which corresponds to the M1000 brand). Such concrete will work without problems at low temperatures and in aggressive environments, it has increased frost resistance and durability.

Targeted and complex additives to mixtures

Before choosing additives, it is necessary to decide what specific problem needs to be solved or what concrete characteristics need to be improved in this case. Often additives of different purpose do not combine well in the concrete mixture, reacting with each other, they do not improve, but, on the contrary, worsen the quality of the finished concrete.

Often, targeted additives are used only in industrial construction to obtain high-quality concrete or specialized mortars that are used in an aggressive environment. Working with concrete at negative air temperatures requires additional heating costs. The use of anti-freeze additives reduces the freezing point of water with the ability to work with concrete at -25 ° C.

Target additives also include foaming agents for aerated concrete – aerated concrete and aerated concrete.

An individual developer rarely uses targeted additives due to an inappropriate increase in the construction budget.

In private housing construction, complex additives are mainly used. They allow to reduce the consumption of cement, to increase the mobility of the mixture, to reduce the w / c, to increase the “life” of the mortar mixture, to obtain concrete with increased strength characteristics, increased resistance to cracking and moisture resistance.

Plasticizer technology

GOST describes over 80 types of various additives for the manufacture of concrete. Most of them have a limited range of uses or are used for special types of concrete..

Plasticizers, like cement, are introduced at the initial stage of concrete mix preparation. The mass fraction of the additive, depending on its type, is 0.4-5% of the mass of cement.

For example, superplasticizer C3 is added to the solution in the amount of 0.4–0.8% of the cement mass. If we take as a basis the amount of 0.5% plasticizer, this is 200 times less than the required cement. Simply put, 50 kg of cement requires 250 grams of plasticizer..

Preparation of high-quality concrete mix with household tools

Order small amounts of concrete (1–2 m³) for enterprises is impractical, therefore the question arises: is it possible to prepare a high-quality concrete mixture with a household tool?

The main apparatus for preparing mixtures is a concrete mixer – both for an individual developer and on an industrial scale. Concrete mixers are divided into two types:

• gravitational;
• compulsory action.

The preparation of a high-quality concrete mixture in a concrete mixer of gravitational action will require additional costs, since thorough mixing of the components of the mixture can be carried out only by increasing the w / c, which will negatively affect the quality of the mixture. In order to maintain the quality of concrete, it is necessary to increase the amount of cement, as a result, an increase in costs.

Concrete prepared in forced-action concrete mixers is more uniform in composition and has a low w / c.

In a domestic environment, you can prepare a small amount of concrete using a low-speed drill with a mixer. This will be the concrete mixer with forced action, and the use of plasticizers will make the mixture mobile.

Household plasticizers for concrete

No matter how trite it may sound, chemical additives for concrete are used in our everyday life. Among the fixed assets are the following:

• liquid soap;
• washing powder;
• PVA dispersion;
• slaked lime.

Liquid soap

Cement and soap are alkalis, they complement each other perfectly. The concentration of liquid soap should be no more than 1% by weight of the cement. It is necessary to add soap not to the mixture, but directly to the water, and add soapy water to the mixture. Soapy water increases the fluidity of the solution, increases the wetting of large fillers (crushed stone, expanded clay, etc.), the concrete is more homogeneous.

Washing powder

Yes, it is also used as a plasticizer. When using a powder, the positive and negative consequences of its use must be weighed. The concentration should not exceed 1% by weight of the cement. The powder reduces the surface tension of the water, thereby improving the plasticity of the concrete. But the use of powder leads to foaming, as a result – a decrease in the density of concrete, a decrease in its frost resistance. The use of powder leads to intense efflorescence, which degrades the appearance of the structure.

PVA dispersion

It is an organic plasticizer. It is necessary to strictly adhere to the recommended proportions when mixing cement (no more than 15–20%). It is also necessary to buy the “correct” PVA. When buying, you need to pay attention that the word “glue” is not found anywhere on the packaging. Dispersion of PVA as a plasticizer improves the quality of concrete bending.

Slaked lime

Lime has been used since the days of the Roman Empire. It is introduced into the solution at the initial stage of mixing in a concentration of up to 20% of the amount of cement. The main positive feature of lime is its bactericidal properties..