Synthesis of a chitosan-based superabsorbent polymer and its influence on cement paste.

To address the challenge of adaptability between cement-based materials and conventional superabsorbent polymers (sodium polyacrylate, Na-PA), a chitosan-based superabsorbent polymer (CSP) with high salt and alkaline resistance was synthesized, and the optimal synthesis process was determined by a single-factor method. The macroscopic performance and microstructure of CSP and Na-PA were compared, and their influences on cement paste were studied. The results show that CSP exhibits a gradual swelling process during water absorption, which is independent of the solution environment. The poriferous structure of CSP allows it to form a network composed of gel membranes. The introduction of amide group enhances the resistance of CSP to salt and alkaline conditions. The autogenous shrinkage of cement paste is mitigated by CSP, with a superior effect compared to Na-PA. The longer desorption time of CSP allows it to promote cement hydration for a longer period, reducing the loss of compressive strength. The heat release, chemically bound water and hydration products (portlandite and amorphous substances) of CSP pastes are higher than those of Na-PA pastes. The water desorption from CSP fills some middle capillary pores and mesopores, leading to the pores in the hardened cement paste being more concentrated in smaller sizes.