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<p>In coastal bridge widening projects, the interfacial transition zone (ITZ) between new and old concrete represents a critical durability vulnerability—it is highly susceptible to chloride ion ingress, which poses a severe threat to the long-term serviceability of the structure. To mitigate this hazard, this study employed a multi-scale experimental approach to systematically elucidate the inhibition mechanism of silica fume (SF)-polypropylene fiber (PPF) composite interface agents on chloride ion transport in the ITZ, with a specific focus on delineating the pivotal role of high-density calcium silicate hydrate (HD C-S-H) gel. The results demonstrate that the pozzolanic reaction of SF effectively drives the transformation of C-S-H gel from the low-polymerization state to high-polymerization states. This transformation elevates the volume fraction of HD C-S-H to approximately 53% while enhancing its intrinsic stiffness. The densified nanostructure of HD C-S-H imparts a robust steric hindrance effect, which substantially elongates the diffusion pathway of chloride ions. Additionally, the physical bridging effect of PPF efficiently suppresses the propagation of microcracks in the ITZ, thereby preserving the structural integrity of the dense HD C-S-H barrier. This work provides a critical theoretical foundation for improving the durability and extending the service life of widening structures in coastal environments.</p>

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Mechanism of inhibiting chloride ion transport by high-density calcium silicate hydrate (C-S-H) gel at the concrete widening interface

  • 期刊论文

  • 发表日期：

    2026年6月21日

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  • Kun Wang,
  • Chenxu Fu,
  • Jinjun Guo,
  • Zedi Zhang,
  • Qingxin Meng,
  • Jinlong Zhang

摘要

In coastal bridge widening projects, the interfacial transition zone (ITZ) between new and old concrete represents a critical durability vulnerability—it is highly susceptible to chloride ion ingress, which poses a severe threat to the long-term serviceability of the structure. To mitigate this hazard, this study employed a multi-scale experimental approach to systematically elucidate the inhibition mechanism of silica fume (SF)-polypropylene fiber (PPF) composite interface agents on chloride ion transport in the ITZ, with a specific focus on delineating the pivotal role of high-density calcium silicate hydrate (HD C-S-H) gel. The results demonstrate that the pozzolanic reaction of SF effectively drives the transformation of C-S-H gel from the low-polymerization state to high-polymerization states. This transformation elevates the volume fraction of HD C-S-H to approximately 53% while enhancing its intrinsic stiffness. The densified nanostructure of HD C-S-H imparts a robust steric hindrance effect, which substantially elongates the diffusion pathway of chloride ions. Additionally, the physical bridging effect of PPF efficiently suppresses the propagation of microcracks in the ITZ, thereby preserving the structural integrity of the dense HD C-S-H barrier. This work provides a critical theoretical foundation for improving the durability and extending the service life of widening structures in coastal environments.