Plasticizer for concrete: what is it, why is it needed in the solution, what is the consumption

One of the most common questions from builders is why a plasticizer is needed for concrete. This is a special additive that improves the quality of the concrete mixture, promotes its hardening even at subzero temperatures, and prevents corrosion of reinforcement and other unfavorable processes. The purpose and rate of consumption of such additives are described in detail in the presented material.

Purpose of plasticizer

First of all, you need to understand what a plasticizer is needed for. It is a special additive based on an organic polymer or inorganic salt, which is always added to the concrete mixture. Based on their composition, there are several types:

• polymer-silicone;
• polycarboxylate;
• lignosulfonate;
• calcium and sodium nitrates.

We can say about a plasticizer that it is an organic or mineral substance that significantly improves the properties of the concrete mixture, for example, it eliminates air bubbles, promotes hardening, and helps prepare the solution even at subzero temperatures.

A plasticizer is added to the composition to solve several problems:

1. Increased fluidity (mobility) for more convenient styling. This allows you to reduce cement consumption (by weight) to 10-15%.
2. Increased ductility by removing air bubbles.This is how additives with hydrophobic properties work, thanks to which the water-repellent properties of the mixture increase.
3. Stabilization of the solution, maintaining its homogeneity for several hours. Additives are necessary so that concrete mixtures can be transported over long distances.
4. Another reason why a plasticizer is needed in concrete is to reduce shrinkage time. During setting and hardening, the mixture loses volume and becomes denser. To make the process go faster, special additives are introduced that speed it up by 2.5 times.
5. Some types of additives increase the frost resistance of the mixture, which allows you to work even in the cold. For this purpose, nitrogen compounds are used, for example, sodium nitrate or urea.
6. When considering why a plasticizer is needed in a solution, it is necessary to mention the increase in strength and other quality indicators.

Plasticizer consumption

Many cement-sand mixtures already contain plasticizers in the required quantities. However, builders often prepare solutions themselves, so they need to correctly determine the plasticizer consumption. Specific values ​​depend on the type of component, but in general the proportion is about 0.3-1%, sometimes up to 4% by weight of cement. Below are some examples:

1. “Superplast” - used to improve the properties of concrete, consumption is 0.2% of the total mass of cement. For example, for 10 kg of cement you should take 20 g of plasticizer.
2. "Polyplast SP-1" is consumed in an amount of 0.5-1% of cement.
3. "SDO" - 0.1-0.3%.
4. “Superplasticizer S-3” – 0.7%.
5. "Mplus" – 1%.

As can be seen from the list, the consumption rate is determined within a certain range, i.e. a slight excess of the amount of plasticizer will not deteriorate the quality of the concrete mixture.At the same time, it is not worth reducing the share, since otherwise the effect of the additive may be weakened.

Universal plasticizer

Different additives perform different functions, so sometimes the question arises of what to add to the screed for strength or better hardening. In order not to consider different components, you can stop at a universal plasticizer. It contains all the essential substances to improve the properties of the concrete mixture and has several advantages:

• reduction of shrinkage;
• prevention of cracks;
• reduction in cement consumption (by weight) by 8%;
• increase in strength up to 10-12%;
• reduction of water consumption up to 15%;
• acceleration of the hardening process in a wide temperature range from -15 to +40°C;
• prevents corrosion of steel reinforcement;
• has no odor of its own;
• characterized by fire safety.

Sometimes, instead of store-bought formulations, folk remedies are added to the mixture, for example, soap, liquid detergent, lime, silicate glue and others. It is not recommended to resort to such measures, since the quality of the final result is not obvious, and the cost of an error increases. It is best to use a universal plasticizer, adding it when mixing the mixture strictly according to the instructions (on average 1%).