This paper presents the effect of incorporating wollastonite microfibers and cellulose nanofibers on mechanical properties and microstructure of ultra-high-performance mortar (UHPM). Cellulose nanofibers of 0.005%, 0.015%, and 0.030% are combined with 4.8% wollastonite microfiber by weight of binder, which consists of 10% silica fume and 90% cement. Compressive and flexural strengths of the UHPM specimens are measured at 7 days. The microstructure is characterized in terms of SEM/EDX, XRD, FTIR, and nanoindentation. The results show the effectiveness of the fiber hybridization in enhancing the compressive and flexural strength of ultra-high-performance mortar with the improvement in flexural toughness and fracture energy by as much as 10% than control mortar. Moreover, hybrid fiber-reinforcement based on the microstructural analysis provided more synergic effect and uniform distribution of the fibers, thus developing an efficient micro crack bridging mechanism as well as resulting in enhanced toughening properties and an increased load carrying capacity. Additionally, the combination of wollastonite microfibers and cellulose nanofibers promoted the hydration reaction products and contributed a denser matrix between the fibers and cement matrix, resulting in an increase of the microstructure and interface area between the fibers and cement matrix. Nano indentation analysis also confirmed the increase of UHD C-S-H from 65% to 84% and lower percentage of anhydrous phase in ultra-high-performance matrix after combining wollastonite microfibers and cellulose nanofibers.

中文翻译：

---

硅灰石和纤维素纳米纤维混合纤维增强对超高性能砂浆强度和微观结构表征的影响

本文介绍了掺入硅灰石微纤维和纤维素纳米纤维对超高性能砂浆（UHPM）力学性能和微观结构的影响。 0.005%、0.015%、0.030%的纤维素纳米纤维与按重量计4.8%的硅灰石微纤维相结合，粘合剂由10%硅粉和90%水泥组成。 7 天后测量 UHPM 样品的压缩和弯曲强度。通过 SEM/EDX、XRD、FTIR 和纳米压痕对微观结构进行表征。结果表明，纤维杂化可有效提高超高性能砂浆的抗压和抗折强度，其弯曲韧性和断裂能比对照砂浆提高了 10%。此外，基于微观结构分析的混合纤维增强材料提供了更多的协同效应和纤维的均匀分布，从而开发出有效的微裂纹桥接机制，并提高了增韧性能和承载能力。此外，硅灰石微纤维和纤维素纳米纤维的结合促进了水化反应产物，并在纤维和水泥基体之间形成了更致密的基体，导致纤维和水泥基体之间的微观结构和界面面积增加。纳米压痕分析还证实，硅灰石微纤维与纤维素纳米纤维结合后，超高性能基质中的UHD CSH从65%增加到84%，并且无水相的百分比降低。