The Water Absorption-release of Superabsorbent Polymers in Fresh Cement Paste: An NMR Study

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.