Enhancement mechanisms of the UHPC-NC interface under fresh-on-fresh casting: A multiscale perspective study

• Published in: Journal of Building Engineering Vol. 111; p. 113249
• Main Authors: Liu, Shaoyan, Hu, Lingling, Kai, Mingfeng, Yao, Yingkang, Sun, Jinshan, Wang, Mingxin, A, Hubao
• Format: Journal Article
• Language: English
• Published: Elsevier Ltd 01.10.2025
• Subjects: A multiscale perspective; Fresh-on-fresh cast method; Interfacial bonding strength; UHPC-NC composite structure; UHPC-NC composite structure; A multiscale perspective; Fresh-on-fresh cast method; Interfacial bonding strength
• ISSN: 2352-7102; 2352-7102
• DOI: 10.1016/j.jobe.2025.113249

For UHPC-NC composite structures, the newly proposed fresh-on-fresh (FF) cast method holds promise for effectively addressing the discontinuity issues in the interfacial region and enhancing the interfacial mechanical properties. In this work, we explore the enhancement mechanism of the UHPC-NC interface under FF casting from a multi-scale perspective, the effects of cast interval and ambient humidity are determined as well. Macroscopically, we find that the interfacial bonding strength of specimens prepared by the FF cast method are significantly superior to those prepared by the fresh-on-harden (FH) cast method. Macroscopically, the FF casting method yields specimens with markedly superior interfacial bonding strength compared to those produced by the traditional fresh-on-hardened (FH) method, with interfacial splitting tensile strength and direct shear strength increased by approximately 60 % and 292 %, respectively. At the mesoscopic level, FF casting significantly reduces interfacial porosity and weak zones, alleviates discontinuities in composition and microstructure, and leads to a more continuous distribution of mechanical properties aligned with hydration products. At the nanoscale, molecular dynamics simulations based on a simplified interfacial models reveal that the continuous distribution of C-S-H gel across the interface under FF casting results in enhanced tensile strength and toughness. Furthermore, optimization of the casting interval and ambient humidity further improves interface continuity and overall mechanical performance. These findings deepen our understanding of interfacial bonding mechanisms and provide valuable guidance for the design and fabrication of high-performance UHPC-NC composites and other multi-material structures. •Characterized the microstructural features of the UHPC-NC interface zone.•Developed a simplified molecular model of the UHPC-NC interface.•Revealed the multi-scale enhancement mechanism of the UHPC-NC interface.