Method for Improving Interfacial Bonding Performance of Functionally Graded Concrete: A Molding Technique Based on Frozen Mortar Transition Layer

Abstract

Existing functionally graded concrete structures are prone to weak interfacial zones due to sequential casting. To address this, this study presents a construction method integrating liquid nitrogen-frozen concrete with normal concrete. The core objective is to investigate the influencing factors and laws of interfacial bonding, and to clarify the interfacial bonding mechanism of the composite system. In this approach, fresh mortar is rapidly frozen into solid blocks via liquid nitrogen to halt cement hydration, and then co-cast with subsequent fresh mortar for molding. The splitting tensile strength, compressive strength and microstructural characteristics of composite specimens under different temperatures were tested. Techniques including scanning electron microscopy, microhardness testing and temperature monitoring were employed to reveal the interfacial hydration mechanism. The results indicate that with appropriate temperature control, the interfacial bonding strength of the pre-frozen composite mortar is comparable to that of monolithic cast mortar. These findings are expected to alleviate the problem of weak interfacial bonding in functionally graded concrete, realize the integral forming of graded structures, and can be applied to practical engineering scenarios such as anti-scouring of functionally graded bridge piers and anti-cracking of concrete graded structures in high-altitude regions in the future.