Characterization of Neutral Versus Anionic Superabsorbent Polymers (SAPs) in Ion-Rich Solutions for Their Use as Internal Curing Agents
Predominant SAPs used for internal curing are anionic gels, such as polyacrylamide, polyacrylic acid, and polyacrylate. They contain or can be hydrolyzed to form carboxylate functional groups. This allows them to retain water up to a few hundred times their dry weight, especially in a high pH environment. SAPs’ swelling behavior is desirable, but other characteristics of SAPs are important for their application as internal curing agents. These anionic SAPs are not only sensitive to the pH environment but also the types of ions. SAPs show less swelling in a calcium-rich solution than in a sodium-rich solution at the same pH. This has direct implications for internal curing because the cement pore solution is rich in various kinds of cations.
In this study, two types of SAPs are developed. One is a neutral SAP in which its swelling ability is independent of its ionic environment, and the other is a semi-anionic SAP, which contains an anionic moiety (polyacrylamide). As expected, the SAPs with anionic moieties show a higher degree of swelling in all environments. The cement pastes dosed with the semi-anionic SAP show a lower calcium concentration in the pore solution. These cement pastes show a lower initial rate of hydration, observed from isothermal calorimetry. The results suggest that the lower calcium content in the pore solution due to calcium absorption into the semi-anionic SAPs may interfere with the initial cement hydration.
KeywordsNeutral SAPs Anionic SAPs Hydrogels Cement pore solution Cement hydration
- Siramanont, J., et al.: The impact of SAP structure on the effectiveness of internal curing. In: International RILEM Conference on Use of Superabsorbent Polymers and Other New Additives in Concrete, Lynby, Denmark, RILEM Publications SARL (2010)Google Scholar
- Siriwatwechakul, W., et al.: Superabsorbent polymer structures. In: International RILEM Conference on Use of Superabsorbent Polymers and Other New Additives in Concrete, RILEM Publications SARL (2010)Google Scholar