Blog

Can Polycarboxylate Superplasticizer be used in underwater concrete?

Concrete pouring is a highly challenging task in underwater engineering, such as bridge piers, dams, underwater tunnels, and port terminals. Underwater concrete needs to have excellent construction performance, resistance to segregation, and a low bleeding rate to resist water erosion during pouring and ensure structural integrity.

As a key component of modern high-performance concrete, can polycarboxylate superplasticizer be used for underwater concrete?

This article provides a detailed overview of the applicability, mechanism of action, and main advantages of polycarboxylate superplasticizer.

Unique challenges faced by underwater concrete

To understand the role of PCE, it is necessary to first understand the difficulties of underwater concrete pouring:

Washout and Segregation: This is the biggest challenge. When ordinary concrete comes into contact with water, the water flow will wash away the cement slurry and fine aggregates, causing the aggregates to separate from the mortar. This will seriously weaken concrete’s strength, compactness, and durability, leading to defects such as “dog holes”.
Flowability requirement: Underwater concrete is usually poured using the Tremie method or the pumping method, which requires the concrete to have excellent fluidity, be able to fill every corner of the formwork by its own weight, and wrap the steel bars without or with vibration.
Complex construction environment: The underwater environment is invisible and has many uncontrollable factors, which require extremely high stability of concrete mixtures.

Therefore, the ideal underwater concrete must have both high fluidity and high cohesion (anti-segregation), which is a contradictory performance in itself.

The role of polycarboxylate superplasticizer used in underwater concrete?

Polycarboxylate high-performance water reducers are currently the most advanced water reducers. Its unique “comb-like” molecular structure can efficiently disperse cement particles via electrostatic repulsion and steric hindrance, thereby endowing concrete with excellent fluidity at extremely low water-cement ratios.

The main contribution of PCE in underwater concrete is:

Achieve high fluidity: PCE can turn concrete mixtures into “fluids” that easily flow through conduits and fill underwater environments, achieving self-compacting effects.

Reducing water-cement ratio: By significantly reducing water usage, PCE can significantly improve the final strength and compactness of concrete, which is crucial for structural durability.

Why is using PCE alone not enough?

What would happen if PCE is only added to underwater concrete?

Although the fluidity of concrete will improve, its internal cohesion will decrease due to excessive dispersion. Such a mixture is like “porridge”. Once it comes into contact with water, the cement paste is very easily washed away by the water flow, resulting in serious erosion and segregation. The high liquidity brought by PCE actually exacerbates the risk of being washed away.

This is precisely the difficulty of underwater concrete preparation: we need both the “flow” provided by PCE and the “dispersion” it brings to resist.

Synergistic effect of PCE and anti-segregation flocculant (AWA)

The key to resolving this contradiction lies in introducing another “expert” – anti-segregation flocculant (AWA), also commonly known as viscosity-modifying admixture (VMA).

Anti-segregation flocculants are usually water-soluble, high-molecular-weight polymers such as cellulose ethers, xanthan gum, and alginates. After dissolving in water, they form a three-dimensional network that envelops cement particles and fine aggregates.

The combination of PCE and AWA is a perfect match:
PCE is responsible for “dispersion”: it breaks up the agglomeration of cement particles and allows the entire system to flow.
AWA is responsible for “wrapping”: it increases the viscosity of the water mixture, like an invisible net, tightly “holding” components such as cement slurry, sand, stone, etc., together, even when flowing, to maintain overall uniformity.

A vivid metaphor:
Imagine honey. The function of PCE is to make viscous honey easier to flow (reducing its yield stress), while the function of AWA is to ensure that even when flowing, honey remains a viscous whole piece and will not disperse in water (increasing its plastic viscosity).

Through this synergistic effect, the concrete mixture not only has high fluidity, but also obtains extremely strong resistance to water erosion, forming the so-called ‘underwater non-dispersing concrete’.

Advantages of the PCE+AWA system in underwater concrete

The combination of polycarboxylate superplasticizer and anti-segregation flocculant can bring a series of significant advantages to underwater concrete:

Excellent self-levelling and self-compaction: Concrete can easily fill complex structures without vibration, ensuring construction quality.

Excellent resistance to segregation and erosion: effectively preventing cement slurry loss, ensuring the integrity and homogeneity of underwater structures.
High strength and durability: The low water-to-cement ratio provided by PCE gives concrete a strong foundation and excellent impermeability.

Improving pumping performance: The high fluidity and cohesiveness of the system make concrete smoother during pumping and less prone to pipe blockage.

Controllable construction window: By adjusting the type and dosage of PCE and AWA, the opening time and flowability of concrete can be precisely controlled to adapt to different underwater construction environments.

Conclusion

Returning to the original question: Can Polycarboxylate Superplasticizer be used in underwater concrete?

The answer is clear: not only can it, but it is also an indispensable key component of modern high-performance underwater concrete. But the prerequisite for its successful application is that it must be scientifically compounded with anti-segregation flocculants (AWA/VMA).

The individual PCE endows concrete with “kinetic energy”, while AWA provides “cohesive force”. It is the strong combination of these two that enables concrete to flow freely in complex underwater environments, while also being able to “remove silt without staining”, ultimately forming a sturdy and durable high-quality underwater structure. Understanding and applying this synergy is the technical core to ensure the success of any project involving underwater concrete.