Salt-alkali resistant semi-interpenetrating network SAP for internal curing of concrete: A combined experimental and molecular dynamics study

To address the low salt-alkali resistance and poor sustained-release performance of conventional superabsorbent polymers (SAPs) in marine concretes, this study developed a semi-interpenetrating network SAP by integrating 2-acrylamido-2-methylpropane sulfonic acid (AMPS) and polyvinyl alcohol (PVA) into polyacrylic acid networks. Laboratory tests, molecular dynamics (MD) simulations, and marine field test were combined to clarify the salt-alkali resistance mechanisms of SAPs and the macro-micro performance of SAP-modified concrete. Experimental results demonstrated that PVA/(AA-co-AMPS) achieved an outstanding absorption of 22.79–30.13 g/g (3–5 times higher than that of commercial SAPs) and slowly released water in cement filtrates. This is attributed to the weak interaction between -SO 3 H groups in PVA/(AA-co-AMPS) and Ca 2 + , which mitigates the Ca bridging effect and thereby inhibits the water diffusion within the SAP network. In SAP-modified concrete, the PVA/(AA-co-AMPS) improved the internal relative humidity, reduced the autogenous shrinkage of concrete by 58.8 %, and improved the concrete durability. Furthermore, MD simulations revealed the H-bonds network formed by -SO 3 H (from AMPS) and -OH (from PVA) groups in PVA/(AA-co-AMPS) with water molecules, leading to a 61 % increase in SAP-water interaction energy. This enhanced interaction explains the exceptional water retention and salt-alkali resistance of PVA/(AA-co-AMPS), offering a theoretical basis of SAPs design for high-salinity and high-alkalinity environments.