Effects of the pre-absorption of superabsorbent polymers and the water-cement ratio of paste on the adsorption-desorption of superabsorbent polymers: an NMR study

As an internal curing material, superabsorbent polymers (SAPs) can effectively reduce the risk of volume shrinkage of cement-based materials. By preparing the cement paste mixed with SAPs, the amount of pre-absorbed water and the water-cement ratio of paste on the water absorption-release behavior in the fresh cement paste were studied by using 1H low-field NMR. The results showed that when the water-cement ratio was 0.30, the SAPs without pre-absorption could absorb the mixing water from the fresh paste and stored the mixing water in the SAPs relatively stable, while the pre-absorbed SAPs released the absorbed water into the paste rapidly, and the more pre-absorbed water, the faster the water released after mixing. When the watercement ratio was increased to 0.40, the mixing water absorbed by SAPs without pre-absorption was more than that absorbed by SAPs when the water-cement ratio was 0.30, but in the system with super high water-cement ratio of 0.50, the SAPs cannot absorb mixing water from the paste after mixing