Unraveling multi-scale synergistic mechanisms in SiC whiskers-reinforced UHPC: insights from systematic aspect ratio comparisons

This study systematically quantifies how the dosage and aspect ratio of silicon carbide whiskers (SiCws) regulate the coupled mechanical–electrical performance of ultra-high performance concrete (UHPC) under standard and microwave curing, and proposes a nano–micro–macro multi-scale synergistic modification mechanism. Under standard curing, SiCws exhibit a previously unreported “early-stage inhibition–late-stage promotion” hydration mode, which is governed by the interfacial interaction between Ca 2+ ions and the amorphous SiO 2 protective film on pyrolysis-derived SiCws. The Ca 2+ capture at early ages retards clinker dissolution, leading to a 5.9% decrease in the 8-h flexural strength of UHPC incorporated with 0.15% SiCw1. In contrast, at the late hydration stage, SiCws serve as effective nucleation sites to facilitate the formation of C-(A)-S-H gels and the densification of the UHPC matrix. Furthermore, microwave curing is demonstrated as an effective activation strategy that disrupts the early Ca 2+ adsorption equilibrium and accelerates whisker-enabled nucleation, thereby significantly improving the early hydration degree of UHPC. Notably, the aspect ratio of SiCws plays a decisive role in the overall modification efficiency. High-aspect-ratio SiCw1 enables “3D interweaving–in situ nucleation” to construct a micro-scale reinforcing skeleton, refine the pore structure, and form a percolated conductive framework. Specifically, at the optimal dosage of 0.15%, UHPC incorporated with SiCw1 achieves a 53.8% increase in ultimate tensile strain, an 80.3% increase in energy dissipation capacity, and a 23.5% reduction in 7-d electrical resistivity. Meanwhile, excessive SiCws induce agglomeration and disrupt the continuity of the reinforcing/conductive skeleton, thus leading to a significant degradation of both mechanical and electrical properties of UHPC.