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<p>To reduce the shrinkage of ultra-high-performance concrete (UHPC) and achieve efficient bonding with steel tubes, this study systematically investigated the effects of incorporating expansion agents and internal curing agents—both individually and in combination—on shrinkage and mechanical properties of UHPC, while also exploring optimized design methods. The experiments employed a calcium oxide–magnesium oxide composite expansive agent, a high-performance calcium sulfoaluminate (HCSA), a superabsorbent polymer internal curing agent, and a lightweight aggregate (LWA) internal curing agent. Optimal dosages were determined through single-factor and combined tests, and the coupled effects of the composite expansion agent and internal curing agent on the volumetric stability and mechanical properties of UHPC were systematically evaluated. The results show that 10% HCSA and 60% LWA can effectively reduce the concrete shrinkage. To further optimize shrinkage reduction, both 10% HCSA and 60% LWA were simultaneously incorporated into UHPC, and an external curing control group was established (in which water was periodically added to the specimen surface to maintain moisture). Experimental results indicate that, after additional external curing, the UHPC specimens exhibited a slight expansion effect at 28&#xa0;days, with expansion strains exceeding 200&#xa0;με. Subsequently, composite specimens were prepared by combining the micro-expansion UHPC with Q345 steel tubes, and the interfacial bond strength was evaluated using push-out tests. The bond strength reached 2.456&#xa0;MPa—nearly three times higher than that of conventional UHPC (0.817&#xa0;MPa) and superior to that of C50 steel tube concrete (1.043&#xa0;MPa). Based on the experimental results, the influence mechanisms of chemical bonding, micro-interlocking, and macro-interlocking on the bond strength were discussed. This study provides a theoretical basis and optimized design methods for the integrated application of UHPC and steel tubes.</p>

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Optimized design of micro-expansive ultra-high-performance concrete and interfacial bonding properties with steel tube

  • 期刊论文

  • 发表日期：

    2025年6月22日

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  • Shuling Gao,
  • Yuyang Zhang,
  • Chengyang Liu

摘要

To reduce the shrinkage of ultra-high-performance concrete (UHPC) and achieve efficient bonding with steel tubes, this study systematically investigated the effects of incorporating expansion agents and internal curing agents—both individually and in combination—on shrinkage and mechanical properties of UHPC, while also exploring optimized design methods. The experiments employed a calcium oxide–magnesium oxide composite expansive agent, a high-performance calcium sulfoaluminate (HCSA), a superabsorbent polymer internal curing agent, and a lightweight aggregate (LWA) internal curing agent. Optimal dosages were determined through single-factor and combined tests, and the coupled effects of the composite expansion agent and internal curing agent on the volumetric stability and mechanical properties of UHPC were systematically evaluated. The results show that 10% HCSA and 60% LWA can effectively reduce the concrete shrinkage. To further optimize shrinkage reduction, both 10% HCSA and 60% LWA were simultaneously incorporated into UHPC, and an external curing control group was established (in which water was periodically added to the specimen surface to maintain moisture). Experimental results indicate that, after additional external curing, the UHPC specimens exhibited a slight expansion effect at 28 days, with expansion strains exceeding 200 με. Subsequently, composite specimens were prepared by combining the micro-expansion UHPC with Q345 steel tubes, and the interfacial bond strength was evaluated using push-out tests. The bond strength reached 2.456 MPa—nearly three times higher than that of conventional UHPC (0.817 MPa) and superior to that of C50 steel tube concrete (1.043 MPa). Based on the experimental results, the influence mechanisms of chemical bonding, micro-interlocking, and macro-interlocking on the bond strength were discussed. This study provides a theoretical basis and optimized design methods for the integrated application of UHPC and steel tubes.