What roles do superplasticizers play in concrete materials?

What roles do superplasticizers play in concrete materials?

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Superplasticizer performance
The performance of water reducer mainly includes dispersing and lubricating, improving strength, reducing slump loss and improving concrete durability.

Lubricating effect, the polar hydrophilic groups in high-efficiency water reducer are directional adsorbed on the surface of cement particles, and are easy to associate with water molecules in the form of hydrogen bonds. The force of this hydrogen bond is much greater than the molecular attraction between water molecules and cement particles. When cement particles absorb enough water reducer, a stable solvated water film is formed on the surface of cement particles, which plays a three-dimensional protective role, prevents direct contact between cement particles, and plays a lubricating role between particles.

Improve the fluidity of concrete and improve construction efficiency. Concrete water reducer can improve the fluidity of concrete, making it easier to pour, vibrate and maintain concrete at the construction site, and improve construction efficiency.

Reduce the amount of cement in concrete
Reduce the amount of cement in concrete and reduce costs.  Concrete water reducer can significantly reduce the amount of cement in concrete without affecting the strength of concrete, thereby reducing the cost of concrete.

Reduce the shrinkage of concrete
The use of water reducer has another important benefit, which is to reduce the shrinkage of concrete, making the shrinkage of concrete much smaller than that without water reducer, thus making the building more stable.

Improve strength
Adding superplasticizer to concrete can significantly improve its strength. At the same time, due to the presence of polycarboxylate superplasticizer, a good interface bonding state is formed between cement stone and aggregate, thereby improving the performance of cement-based materials. During the hydration process, the effect of water reducer on the hydration rate is slightly delayed. In the middle and late stages, it inhibits the transformation of gel into crystals, thereby promoting the growth of petal-shaped crystals, including C-S-H gel, tetracalcium aluminoferrite and tobermorite. The above crystalline substances reduce the number of capillary pores of hardened cement stone, with more contact points, interweaving together to form a dense spatial network structure, and then dividing and filling the pores in cement stone to be finer, significantly enhancing the strength of cement stone.

Improve the plasticity of concrete and reduce slump loss. After adding water reducer to concrete, the fluidity can be increased while keeping the water-cement ratio unchanged. Ordinary water reducer can increase the slump of fresh commercial concrete by more than 10cm while keeping the cement dosage unchanged. High-performance water reducer can prepare commercial concrete with a slump of 25cm.

Due to the dispersibility of water reducer, the water and water-cement ratio required during mixing are significantly reduced, while the water required during blending is significantly reduced, so that the pores of hardened cement stone are reduced, and the pore size shifts toward small pores; enhance the density of cement. The test results show that the pore size of concrete with water reducer added can be reduced from 100 nanometers to less than 10 nanometers. At the same time, by reducing the evaporation and release of excess water in cement paste, the capillary channels remaining in cement paste are reduced, the transfer rate of chloride salts in cement paste is slowed down, the resistance of cement paste to chloride salt penetration is enhanced, and its strength and durability are improved.
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