Water plays a vital role over the entire life cycle of concrete. It is an indispensable constituent for mixing, curing and hardening. Nevertheless, moisture exchange between hardened concrete and the external environment may trigger its shrinkage-expansion behaviour, resulting in cracking defects that directly impair structural service durability. As a novel polymeric functional material, superabsorbent polymer (SAP) offers an internal-curing solution via its unique reversible water-absorbing and water-releasing properties, and has seen increasing adoption in practical engineering.

1. Mechanism of SAP for Concrete Performance Improvement

SAP is a cross-linked polymer that rapidly absorbs water and swells into gel particles upon water contact. When incorporated into a concrete mixture, it absorbs mixing water during batching. Once concrete hardens and internal matrix humidity drops, water stored in SAP gel particles is gradually released, continuously providing moisture for cement hydration to realise the internal-curing effect.

On the one hand, the slowly released moisture preserves internal humidity, mitigates autogenous and drying shrinkage, and restrains early-age cracking. On the other hand, sustained water supply facilitates adequate cement hydration, optimises matrix microstructure and pore characteristics, and improves concrete compactness. Nevertheless, fully dehydrated SAP particles leave micropores inside concrete. Over-dosage introduces excessive voids and causes deterioration in mechanical strength. Hence, rigorous dosage control is required in practical applications.

Note: Although concrete-grade SAP and agricultural water-retention agents are both superabsorbent resins, they differ substantially in cross-linking density, water-absorption capacity and alkali resistance and cannot be directly interchanged. Concrete constitutes a highly alkaline environment; accordingly, alkali-resistant modified SAP shall be selected. Furthermore, additional mixing water should be supplied according to the resin’s water-absorption capacity to guarantee fresh-concrete workability.

2. Outstanding Advantages of SAP in Concrete Engineering

2.1 Simple Construction Operation

SAP can be directly added during mixing, requiring no special equipment or adjustment to existing construction procedures. It barely disturbs conventional workflows. Projects can obtain anti-cracking benefits from internal curing without extra technical inputs, which favours its on-site deployment and popularisation.

2.2 Environmental Compatibility in Line with Sustainable Construction Principles

SAP exhibits favourable environmental performance. Internal curing lowers the demand for external curing water. Meanwhile, it effectively restrains cracking and reduces subsequent repair and re-work, cutting construction waste and conforming to green low-carbon construction trends.

2.3 Robust Environmental Adaptability

SAP-modified concrete shows good tolerance to diverse service conditions such as dry, cold and humid surroundings. Thanks to its unique internal moisture-regulation capacity, it delivers stable performance and mitigates cracking risks induced by environmental fluctuations, even under extreme-climate conditions.

3. Main Application Fields

3.1 Large-Scale Infrastructure

Major infrastructure works including bridges, tunnels and dams impose strict requirements on crack resistance, impermeability and durability. SAP incorporation achieves efficient internal curing, enhances structural anti-cracking performance, prolongs service life and cuts long-term operation-and-maintenance costs.

3.2 Pervious Concrete

As a core material for sponge-city construction, pervious concrete rapidly drains rainwater and mitigates urban waterlogging. The addition of SAP further optimises its water-absorption and permeability properties, rendering it applicable for rainy-region cities and wetland-protection projects.

3.3 Freeze-Thaw-Resistant Building Elements

Concrete in cold zones is vulnerable to freeze-thaw-induced damage. SAP adjusts the internal moisture distribution of building elements, alleviates freeze-thaw-related structural deterioration, and improves the frost resistance of concrete for cold-climate applications.

4. Existing Technical Challenges and Future Development Perspectives

Despite its remarkable merits, SAP still encounters practical technical bottlenecks in concrete engineering. Dosage control constitutes the key challenge: over-dosage lowers early-age strength, whereas under-dosage cannot deliver target internal-curing and anti-cracking performance. Therefore, the optimal dosage shall be determined via mix-proportion tests for real-world engineering.

Moving forward, advances in polymer-materials science will further unlock SAP’s application potential. Combined with other high-performance materials such as fibres and mineral admixtures, SAP is expected to improve multi-dimensional comprehensive properties of concrete and promote innovation in construction functional materials.

5.Conclusion

Superabsorbent polymer (SAP) represents a promising novel functional material for concrete applications. Thanks to its distinctive internal-curing mechanism, it exhibits prominent performance in restraining shrinkage-induced cracking, promoting matrix hydration and boosting structural durability. As relevant research deepens, SAP’s engineering-application system will become increasingly mature, supporting the construction industry toward green, low-carbon, high-efficiency and long-service-life development.