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内掺硅烷和纳米SiO2对不同养护条件下UHPC力学与吸水性能的影响

Influence of incorporating silane and nano-SiO2 on mechanical and water absorption properties of UHPC under different curing conditions

    摘要
  • 摘要: 超高性能混凝土(Ultra-high performance concrete, UHPC)在既有混凝土结构修复和防护领域有着广阔的应用前景。本文通过内掺硅烷和纳米SiO2对UHPC进行改性，以提升其修复和防护性能。首先，系统研究了内掺硅烷和纳米SiO2对标准、蒸汽和密封养护条件下UHPC抗压和抗折强度及其与不同饱和度混凝土基体间粘结性能的影响规律。之后，通过称重法、表面接触角测试研究了其吸水性能演化机理。最后，分别利用压汞法和低场核磁共振技术研究了内掺硅烷和纳米SiO2对UHPC孔结构和凝结硬化过程的影响。结果表明：单掺硅烷会使UHPC的抗压强度降低13.3%~29.7%，而复掺硅烷和纳米SiO2试件的抗压强度较单掺硅烷试件高2.9%~11.3%。单掺硅烷可使标准和密封养护时UHPC与基体间的界面剪切强度提高3.5%~34.8%，而单掺纳米SiO2或增加基体饱和度可使3种养护条件下UHPC与基体间的界面剪切强度提高8.3%~31.9%。单掺硅烷组UHPC的毛细吸水系数较空白组降低了38.7%~76.2%，而其表面接触角升高为130.3°。单掺纳米SiO2组UHPC的毛细吸水系数较空白组试件低5.2%~12.6%。密封养护试件的毛细吸水系数是标准和蒸汽养护试件的1.8~3.7倍。标准条件养护下，内掺硅烷和纳米SiO2使UHPC的孔隙率较空白组试件增长5.0%~22.2%，单掺或复掺硅烷和纳米SiO2未显著改变UHPC的平均孔径。

     

    Abstract: Ultra-high performance concrete (UHPC) has broad application prospects in the field of the repair and protection of existing concrete structure. In this paper, UHPC was modified by incorporating silane and nano-SiO2 to enhance its repair and protection performance. Firstly, the influence of incorporating silane and nano-SiO2 on the compressive and flexural strengths of UHPC under standard, steam, and sealed curing conditions, as well as the bonding performance between UHPC and concrete with different saturations, were systematically investigated. Additionally, the evolution mechanism of water absorption properties was investigated through the weighing method and surface contact angle test. Finally, the effects of incorporating silane and nano-SiO2 on the pore structure and setting-hardening process of UHPC were studied by Mercury Intrusion Porosimetry and low-field nuclear magnetic resonance techniques, respectively. The results show that the incorporation of silane can reduce the compressive strength of UHPC by 13.3%~29.7%, while the compressive strength of the specimens with combined incorporation of silane and nano-SiO2 is 2.9%~11.3% higher than that of the specimens with silane incorporated.The incorporation of silane can increase the interfacial shear strength between UHPC and substrates by 3.5% to 34.8% under standard and sealed curing conditions, while incorporating nano-SiO2 or increasing the concrete saturation can enhance the interfacial shear strength between UHPC and substrates by 8.3% to 31.9% under three curing conditions. The capillary water absorption coefficient of UHPC with silane is 38.7%~76.2% lower than that of the blank group, and its surface contact angle can be increased to 130.3°. The capillary water absorption coefficient of UHPC with the incorporation of nano-SiO2 is 5.2%~12.6% lower than that of the specimens in the blank group. The capillary water absorption coefficient of the sealed curing specimens is 1.8 to 3.7 times that of standard and steam curing specimens. Under standard curing conditions, the incorporation of silane and nano-SiO2 increases the porosity of UHPC by 5.0% to 22.2% compared with the specimens in the blank group, but the average pore size of UHPC is not changed significantly by the incorporation of silane or nano-SiO2.

     

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