Mechanisms underlying the strength enhancement of UHPC modified with nano-SiO2 and nano-CaCO3
Mechanisms underlying the strength enhancement of UHPC modified with nano-SiO2 and nano-CaCO3
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DOI：
10.1016/j.cemconcomp.2021.103992
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发表时间：
2021-02
影响因子：
10.5
通讯作者：
Zemei Wu;K. Khayat;C. Shi;B. Tutikian;Qing Chen
中科院分区：
文献类型：
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作者：
Zemei Wu;K. Khayat;C. Shi;B. Tutikian;Qing Chen
纳米颗粒独特的物理和化学性质可以在微米和纳米尺度上增强水泥基材料的性质，从而改善其性能。为揭示不同类型纳米颗粒的增强机理，通过室内试验研究了纳米SiO2和纳米CaCO 3对掺2%钢纤维超高性能混凝土（UHPC）力学性能的影响。每种类型的纳米颗粒以四种含量掺入，并且UHPC的微坍落流动度保持在240-260 mm。采用电子显微镜（SEM）、X射线衍射（XRD）、差示热重（DTG）分析、3D显微成像等先进技术对超高性能混凝土基质和纤维-基质界面的微观结构以及水化产物的特征进行了表征。和压汞孔隙率仪（MIP）。试验结果表明，随着纳米SiO2和纳米CaCO 3掺量的增加，UHPC的纤维基体强度和力学强度均有所提高，并分别达到1%和3.2%的临界值。用3.2%的纳米碳酸钙制成的最佳UHPC混合物的28-d纤维-基质粘结、压缩和弯曲强度分别比参考混合物的高约40%、10%和20%。这些强度值高于用1%纳米SiO2制成的UHPC。SEM观察和DTG分析表明，在低于最佳纳米材料掺量时，纳米SiO2和纳米CaCO 3的填充和成核效应通过提高水泥的密度和均匀性以及优化水化产物结构促进了水泥的强度发展。超过这些限制，纳米材料的额外使用导致空气空隙和毛细孔的体积增加，以及由于纳米颗粒的团聚而导致的弱界面区，这阻碍了强度的发展。
The unique physical and chemical properties of nano-particles can enhance the nature of cement-based materials at the micro-scale and nano-scale levels, leading to improved properties. To uncover the strengthening mechanism associated with various types of nano-particles, a laboratory investigation was undertaken to evaluate and compare the influence of nano-SiO2and nano-CaCO3on mechanical properties of ultra-high performance concrete (UHPC) made with 2% steel fibers. Each type of nano-particle was incorporated at four contents, and the mini-slump flow of the UHPC was maintained at 240–260 mm. The microstructure of the matrix and the fiber-matrix interface of UHPC, as well as the features of hydration products were characterized using advanced techniques, such as electron microscopy (SEM), X-ray diffraction (XRD), differential thermal gravimetric (DTG) analyses, 3D micro-tomography, and mercury intrusion porosimetry (MIP). Test results indicate that both the fiber-matrix strength and mechanical strength of UHPC increased with the increase of nano-SiO2and nano-CaCO3until threshold limits of 1% and 3.2%, respectively. The 28-d fiber-matrix bond, compressive, and flexural strengths of the optimal UHPC mixtures made with 3.2% nano-CaCO3were approximately 40%, 10%, and 20%, respectively, greater than those of the reference mixture. These strength values were higher than those of UHPC made with 1% nano-SiO2. When used below these optimal nano-material contents, the filler and nucleation effects related of the nano-SiO2and nano-CaCO3promoted the strength development through improved density and homogeneity with optimized structure of hydration products, as indicated by SEM observation and DTG analysis. Beyond these limits, additional use of nano-materials resulted in increased volume of air voids and capillary pores and weak interfacial zones due to the agglomeration of nano-particles, which hindered strength development.