How Concrete Admixtures Help in Your Construction?
Preparing to pour the foundation, you need to get as much information as possible about concrete - the basis of any monolithic structure. Additives will improve the properties of concrete. Use it while choosing the ratios of the components of the initial mixture.
The list of Construction chemicals, concrete admixtures has been increasing in the market day by day. So, one should have a proper understanding of the types of concrete admixtures and their properties like sustainability to different weather conditions, strength and the quality of the admixtures.
Varieties of additives
The need to change the properties of concrete is due to the following factors:
- Climatic
- Technological.
- Operational.
- Chemical aggression of the environment.
The use of admixtures for concrete allows changing its properties in a wide range, improving the quality of the structures being built.
The classifier of modifying compositions includes several groups:
- plasticizing additives;
- air-entraining and gas-generating;
- accelerating (retarding) concrete hardening;
- sealing;
- anti-frost;
- waterproofing;
- colouring (pigmented).
Why are plasticizers needed?
It may seem to a beginner in construction that the concrete mix does not need to increase its plasticity. Pour in plenty of water, and the concrete without any additives will become liquid and convenient for laying. In fact, excess water is not good for the concrete mixture. The water:concrete:cement ratio has to be followed strictly. It is called the water-cement ratio. For instance, if you want to make high-quality concrete, then it is allowed to add no more than 14 litres of water to 20 kg of cement. By pouring more liquid, you will sharply reduce the strength of the structure.
The denser the concrete, the better it resists stress. This is what plasticizing additives are for. They make concretely flowable without adding excess water. Plasticizers for concrete are the most popular types of additives. By reducing the cohesion force of the particles of the initial mixture, they protect it from delamination. Using such additives, it is possible to fill the mould and thin-walled formwork of the foundation without a vibrator.
Why does concrete need air?
The action of air-entraining additives is clear from their name. Air pockets in concrete reduce its strength. However, in small quantities, they are useful, since they increase the frost resistance of a monolithic structure. The mechanism of action of air-entraining substances is very simple. Water, freezing, tears concrete like paper. By creating air cavities in the material, we give the water room to expand and reduce its destructive force. This task is performed by air-entraining compositions. Their percentage should be minimal so as not to reduce the strength of the structure. Gas-forming additives are similar in action to air-entraining ones. They also create microcavities in concrete, but their main task is different: to reduce the weight of concrete and increase its heat-insulating properties.
Retardation and hardening accelerators
Considering the modifying additives, a few words must be said about compositions that increase the rate of hydration of cement stone. In cold weather, the concrete mix hardens very slowly, but in frost, this process stops. If you do not add a hardening accelerator to the water used for mixing, then it will be impossible to work with concrete at sub-zero temperatures. Alternatively, the electric heating of the mixture is rather complicated and costly.
Slowing down the rate of maturation of the concrete mix is necessary when transporting it over long distances. In addition, retarders are required when concreting massive and extended structures (foundations and floors). In this case, the technology requires that until the end of pouring all the concrete is in a liquid state. Without the use of retarders, the sections of the foundation that were poured earlier than others begin to harden, forming joints that weaken the structure.
We don't care about frost.
There are two ways to combat the destructive power of frost. We have already said about the first, considering hardening accelerators. The second method is antifreeze additives, which give the water antifreeze properties. Freezing not at 0С, but at sub-zero temperatures (up to -25С), the water has time to fully react with cement.
It should be noted that many types of hardening accelerators have an antifreeze effect on cement mortar (sodium nitrite, a mixture of sodium chloride with calcium chloride, urea in combination with nitrite and calcium nitrate). This fact must be taken into account when choosing.
Waterproofing additives
Concrete is very often used for pouring foundations. Therefore, protecting basements and building walls from water penetration is a very important task. Without additives, concrete slowly, but still passes water through micropores. Waterproofing additives give it hydrophobic properties (repelling water molecules). Using them, it is possible to block access to the body of the structure for groundwater without roofing material or bitumen coating.
Pigments
Considering the types of additives for concrete and their purpose, one should not forget about pigments. They are used for surface painting and tinting in the bulk of paving slabs, self-levelling floors, wall blocks and figured casting.
Giving concrete the desired colour is not an easy task. This material has a strongly alkaline reaction and quickly discolours common dyes. Therefore, for colouring concrete products, iron and chromium oxides are used, which are resistant to alkalis and solar ultraviolet radiation.
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