Optimization in water absorption and desorption of bentonite modified superabsorbent polymer for improving internal curing effect of cement mortar

• Introducing organic modified expansive bentonite to prevent water premature release of SAP. • Optimizing the water absorption release behavior of bentonite modified SAP through synthetic parameters. • An improvement of internal curing properties is attributed to secondary hydration and internal curing effect. Cracks induced by autogenous shrinkage in high performance concrete showed significant impact on its durability. Designing composite superabsorbent polymers (SAPs) with different chemical structures and optimization of water absorption and release can effectively enhance the internal curing efficiency of cement-based materials. Herein, a series of composite SAPs with high water absorption and water retention properties, compose of bentonite and acrylamide (AM) and methacrylic acid (MAA), were synthesized through intercalation polymerization. Chemical composition and surface morphology of the composite SAP were characterized using Fourier transform infrared spectroscopy (FT-IR) and scanning electron microscopy (SEM). The effects of different synthesis parameters on the water absorption and release performance of the composite SAPs were evaluated. Furthermore, the influence of the composite SAPs on the mechanical properties, frost resistance, chloride ion penetration resistance, and microstructure of mortar was investigated. By optimizing the synthesis parameters, the modified bentonite P (AM- co -MAA) exert best water absorption and release behavior. A lowest decrease in compressive strength of cement mortar modified by composite SAP with dosage of 0.2% and a particle size of 200 mesh can be observed. The frost resistance and chloride ion permeability of modified mortar can be significantly improved by composite SAP. Bentonite in composite SAP promoted the secondary hydration reaction of cement and refined the microstructure. This new type of bentonite modified composite SAP will effectively enhance durability of concrete and providing theoretical guidance for internal curing.