Design, synthesis and characterization of a starch-based superabsorbent polymer and its impact on autogenous shrinkage of cement paste

The commercial sodium polyacrylate (PAA) and poly acrylic acid-co-acrylamide (PAM) are commonly used superabsorbent polymers (SAPs) that act as internal curing agents of cement pastes. However, their adaptability relatively low to the alkaline environment hinders their practical application in concrete. Based on the application and compositions of SAPs, a starch-based superabsorbent polymer (SSP) was designed and synthesized using corn starch by modulating charge density and hydrophilic group. SSP exhibited water absorption of 1305 g/g in deionized water and 86 g/g in cement filtrate. The water absorption and water desorption processes of SSP follow the second-order kinetics model. Increasing the hydrophilicity of the ionic groups and the proportion of non-ionic groups can enhance the water absorption and salt resistance of SSP. The SSP containing -SO3H and -CONH2 groups has low crystallinity and high thermal stability, forming thin gel membranes in solutions. Compared to PAA and PAM, SSP shows faster water absorption, higher water storage and slower water desorption. Its mitigating effect on autogenous shrinkage of cement paste is significantly higher than that of PAA and PAM, with less compressive strength loss.