Analysis of the pore-forming mechanism of SAP and its influence mechanism on cement paste performance based on fluorescence impregnation method

Understanding the porosity characteristics and mechanisms of superabsorbent polymers (SAPs) in cement-based materials is crucial for evaluating their effects on autogenous shrinkage and compressive strength in cement-based materials. In this study, SAPs with different chemical compositions were synthesized by copolymerization of acrylic acid (AA) and acrylamide (AM). Absorption and release behaviors were analyzed, while pore formation parameters were assessed using ultraviolet fluorescence impregnation and digital image processing. Combined with FTIR, TG/DTA, and performance tests, water release characteristics, pore formation mechanisms, and regulatory effects on cement paste were evaluated. Key findings include in terms of absorption behavior, the equilibrium absorption capacity in cement filtrate decreases as AA content in SAP increases. Pore-forming absorption capacity in actual cement paste is higher than that obtained in cement filtrate. The ability of SAP to reduce autogenous shrinkage depends on its water storage and release properties. The optimal composition for minimizing shrinkage is m AA : m AM = 25 %:75 %. For compressive strength, SAP-induced porosity ( η pf ) is the primary factor. Similar η pf values for certain compositions lead to lower strengths. When SAP contains only −CONH groups, the compressive strength is highest. This study provides a theoretical basis for optimizing SAP composition to reduce autogenous shrinkage and enhance concrete strength.