Internal curing using modified superabsorbent polymers: Dual optimization of shrinkage mitigation and mechanical performance

Superabsorbent polymers (SAP) show significant promise in mitigating autogenous shrinkage in high-performance concrete (HPC), although their tendency to reduce compressive strength remains a persistent challenge. This study investigates SAPs synthesized from distinct monomer types (acrylic acid, acrylamide, and an acrylic acid-acrylamide copolymer), varying cross-linking density, and the incorporation of active additives, to quantitatively assess their performance characteristics. The study further examines the impact of SAP on autogenous shrinkage, microstructural evolution, and the mechanical properties of cement pastes internally cured by SAP. Results indicate that polyacrylamide-based SAPs exhibited superior water retention compared to both polyacrylic acid-based SAP and acrylamide-co-acrylate SAP, with enhanced retention capacity corresponding to the cross-linking density. This property improved the efficient use of internal curing water, thereby reducing autogenous shrinkage in the cement paste. Additionally, the active additives were found to effectively reduce residual pore size following SAP water release, thereby enhancing the mechanical performance of the paste. A positive correlation was observed between the concentration of active additives in SAP and improvements in the structural integrity of the cement paste. The polyacrylamide-based SAP with 9 wt% cross-linking and 50 wt% Nano-SiO₂ loading (SAP-NS c ) exhibited the best overall performance. Compared to polyacrylic acid-based SAP and acrylamide-co-acrylic acid SAP, SAP-NS c demonstrated superior suppression of autogenous shrinkage while significantly mitigating the adverse effects of SAP on the mechanical properties of cement pastes. Relative to SAP-free cement pastes, the SAP-NS c modified formulations achieved reductions in 7-day autogenous shrinkage of 96.5 % and 89.7 %, respectively, with compressive strength variations of −8.7 % and + 12.6 % after 91 days. These results highlight the promising potential of SAP-NS c as an advanced internal curing material for HPC applications. • SAP-M demonstrated superior water retention capacity, enabling effective implementation of internal curing functionality. • Increased cross-linking density enhanced spatial distribution of SAPs and improved moisture regulation efficiency. • SAP-NS effectively promoted cement hydration reactions and optimized microstructural development in cement matrices. • SAPs containing nano-SiO₂ inhibits autogenous shrinkage and avoids severe damage to mechanical properties.