Improving Concrete Sustainability With Slow-Absorbing N-SAPs

Sustainability in the construction industry is a critical concern, particularly in the context of concrete production and usage. Concrete, being one of the most widely used construction materials, has a significant environmental footprint, primarily due to its cement component.

Super Absorbent Polymers (SAPs), specifically Nippon Shokubai's novel SAPs (N-SAPs), offer promising advancements in enhancing concrete sustainability thanks to their many benefits, including enhanced durability, reduced environmental impact and improved freeze-thaw resistance.

Slow Absorption Rate

One of the primary distinctions between conventional SAPs and N-SAPs lies in their absorption behavior. Conventional SAPs are known for their rapid absorption rates, which can be beneficial in applications requiring quick water uptake. However, this rapid absorption can be detrimental in concrete applications, where slower absorption is preferred to maintain the material's workability and structural integrity.

Addressing these issues, Nippon Shokubai has specifically designed N-SAPs to exhibit slow absorption behaviors, which is achieved by adjusting the amounts of nonionic groups and stimuli-responsive units within the polymer structure. The slower absorption rate maintains fresh properties and allows for better control over the hydration process in concrete, improving internal curing and reducing shrinkage.

Internal Curing and Compatiblity With Alternative Mixes

In addition to slower absorption, N-SAPs facilitate internal curing by gradually desorbing water as the internal humidity of the concrete drops. This process enhances the hydration of cement, improving the concrete’s mechanical properties. This internal curing effect addresses issues related to autogenous shrinkage and cracking.

The versatility of N-SAPs extends to their compatibility with alternative cement mixes, such as those incorporating Ground Granulated Blast Furnace Slag (GGBS) and Limestone Calcined Clay Cement (LC3). The internal curing effect of N-SAPs has been confirmed in these alternative mixes, contributing to enhanced compressive strength and reduced clinker content.

Other Key Features and Their Impact on Concrete Properties

Flowability. Flowability is a critical property in concrete applications, as it affects the ease of mixing, transporting and placing the concrete. Conventional SAPs, when added to concrete, can significantly reduce flowability due to their rapid water absorption, leading to poor workability and challenges in achieving the desired concrete consistency.

In contrast, N-SAPs are shown to have a minimal impact on the initial slump of fresh concrete. N-SAPs will minimize the impact on initial workability but will not improve slump retention. In fact, they tend to reduce slump retention after 30 minutes or more, as they gradually begin to absorb water. To maintain slump life, we recommend using a slump-retaining admixture.

On the other hand, conventional SAPs absorb water rapidly at the initial stage, making it difficult to maintain slump even with a slump retainer. In such cases, the only effective solution is to add additional water, but this comes at a cost: reduced strength.

Compressive Strength. Compressive strength is an important parameter when assessing the structural integrity of concrete. Traditional SAPs also provide internal curing benefits, improving strength and reducing autogenous shrinkage. However, they negatively affect initial workability, requiring the addition of extra water. This additional water alters the mix design and ultimately reduces the final strength.

N-SAPs, on the other hand, enhance the compressive strength of concrete through their internal curing effect. By gradually releasing water as the internal humidity drops, N-SAPs promote greater hydration of the cement, improving strength and reducing autogenous shrinkage. Concrete test results indicate that N-SAPs can increase compressive strength by up to 38% compared to mixes without SAPs.

N-SAPs enhance the strength of concrete via their internal curing effect.

Freeze-Thaw Resistance. Concrete structures are often exposed to freeze-thaw (FT) cycles, which can cause significant damage over time. Conventional SAPs can also enhance FT resistance through the same mechanism as N-SAPs. However, achieving this effect requires an appropriate SAP particle size — meaning that not all N-SAPs will necessarily improve FT resistance.

N-SAPs have demonstrated an ability to improve freeze-thaw resistance by forming smaller, more evenly distributed air voids within the concrete matrix. This property enhances the concrete’s durability and longevity, making N-SAPs a more reliable choice for structures exposed to harsh environmental conditions.

Reduction in Environmental Impact. Clinker production is a major source of CO2 emissions in the cement industry, and N-SAPs contribute to sustainability by reducing the clinker content of cement. Using N-SAPs can reduce the clinker factor by more than 10%, thereby lowering the carbon footprint of concrete production.

Additionally, the compatibility of N-SAPs with alternative cementitious materials further supports the shift towards more sustainable concrete solutions.

Learn More As the construction industry continues to prioritize sustainability, the adoption of NSAPs could play a pivotal role in reducing the carbon footprint and enhancing the performance of concrete structures. To learn more, please contact us.