Superabsorbent polymer in alkali-activated slag paste: Swelling-deswelling behaviour and effects on surrounding matrix

Superabsorbent polymer (SAP) has been applied in alkali-activated slag (AAS) for internal curing, but its interaction mechanism remains unclear. This study employed SAP of a large size (∼2 mm) to achieve in-situ and continuous observation of SAP behaviors in AAS paste and their impacts on the reaction kinetics, reaction products, and microstructure of surrounding matrix for 90 days. Results showed that the behaviors of SAP in AAS changed over time: swelling (0–10 h), fast deswelling (10 h–48 h), and slow deswelling (48 h-90 d). SAP swelling in AAS paste is subjected to the additional physical restriction by surrounding matrix. SAP postponed the hydration of AAS but hardly affected the long-term reaction degree due to the ion release during deswelling. Some Ca ions were retained in SAP, altering the reaction products of AAS by forming N-A-S-H gels. The effects of SAP on AAS diminish over distance, ultimately forming an hollow, annular affected zone with a dense microstructure.