Synthesis of a high-performance semi-interpenetrating network SAP and its effects on microstructure and hydration of cementitious materials

High neutralization and semi-interpenetrating structure increase PVA/AA-SAP water absorption in cement by over five times. • PVA/PAA-SAP can significantly improve the compressive strength and mitigate autogenous shrinkage of cement paste at the same total w/c ratio. • PVA/PAA-SAP releases water slowly, promotes hydration, and has more obvious water enrichment area and internal curing area. This study develops a novel synthesis strategy for superabsorbent polymers (SAPs) tailored for cementitious materials, achieving high-performance properties without the conventional incorporation of non-ionic monomers. A high-performance semi-interpenetrating network (sIPN) SAP (PVA/AA-SAP) composed of polyvinyl alcohol (PVA) and polyacrylic acid (PAA) was synthesized. The effects of PVA content and neutralization degree on the performance of SAPs were investigated. The water absorption-desorption characteristics and mechanisms in cement pore solution were systematically examined. Results demonstrate that the sIPN structure, coupled with the shielding effect of sodium ions at high neutralization degrees, significantly suppresses the complexation of calcium ions. Consequently, the water absorption of SAPs in cementitious environments is substantially enhanced. Notably, the water absorption of the PVA/AA-SAP in cement filtrate is more than five times higher than that of conventional PAA-SAP. Incorporation of PVA/AA-SAP into cement reduced the hydration heat release during the acceleration stage and maintained higher internal relative humidity compared to conventional PAA-SAP. The sustained water release from PVA/AA-SAP promoted the later hydration, refined the pore structure, and established a distinct internal curing zone. Under the same total water-to-cement (w/c) ratio, adding 0.35% PVA/AA-SAP enhanced the 28-day compressive strength of cement paste by 19.56% and mitigated autogenous shrinkage by 99.8% within 24 h. This design strategy of combining sIPN structure with a high neutralization degree eliminates the demand for acrylamide, improves the compressive strength under the same total w/c ratio and effectively mitigates the autogenous shrinkage of cement pastes.