Water Kinetics and Performance of Concrete Internally Cured Using Waste Soda Residue

To mitigate early-age shrinkage cracking and enhance the durability of concrete, this study explores the valorization of soda residue, an industrial byproduct, as an internal curing agent. A novel soda residue-based internal curing agent material was synthesized via water washing and fly ash-assisted grinding. Concrete mixtures with varying soda residue contents were evaluated, revealing that the incorporation of 10% soda residue yielded optimal performance, characterized by significantly reduced autogenous shrinkage, superior frost resistance, and enhanced later-age compressive strength. The transition from macro performance to underlying mechanisms was elucidated through low-field nuclear magnetic resonance and calorimetry. The results demonstrate that the performance of soda residue-modified concrete is governed by a competition between the beneficial internal curing effect and the introduction of weak interfaces. At the optimal 10% dosage, the positive internal curing effect predominates. Specifically, the water kinetics-as evidenced by a distinct internal curing peak and the evolution of the T₂ spectrum-indicate that soda residue facilitates a dynamic water absorption desorption process. This behavior effectively alleviates internal drying, promotes further cement hydration, collectively improving the mechanical and durability properties. This work not only validates the high-value utilization of soda residue but also provides a mechanistic understanding of its dual role in concrete.