The Water Absorption-release of Superabsorbent Polymers in Fresh Cement Paste: An NMR Study
Jingbin Yang, Zhenping Sun, Yihe Zhao, Yanliang Ji, Biyun Li
Abstract
Superabsorbent polymers (SAPs) can effectively reduce the risk of concrete cracks by acting as an internal curing material. In this study, 1H low-field NMR was used to investigate the influence of the pre-absorbed water amount and the water-cement ratio of paste on the water absorption-release behavior of SAPs in fresh cement paste. Results show that when the water-cement ratio was 0.30, the SAPs without pre-absorption absorbed water from fresh cement paste and retained them with relative stability. The SAPs with pre-absorption would rapidly release the pre-absorbed water into a paste, and the water releasing speed increased with the amount of pre-absorbed water. Additionally, the water amount absorbed by the SAPs without pre-absorption increased with the water-cement ratio from 0.30 to 0.40. However, the water absorption of SAPs from the paste was also found to be severely inhibited when the water-cement ratio reached 0.50. SAP swelling in fresh cement paste is affected by the synergistic effects of multiple ions.