超高性能混凝土韧性提升的作用机理研究

Compared with ordinary cementitious materials, ultra-high performance concrete (UHPC) has been considered a promising material in many engineering fields such as construction and national defense industry due to its remarkable toughness. Some research reveals that the toughness of UHPC can be effectively enhanced through measures like using deformed steel fibers, fiber hybridization or adding nano materials. However, there has been lack of research on the underlying mechanisms that contributes to the improved toughness. Taking the toughening mechanisms as the objective of this study, the proportions of consumed energy through fiber bridging, fiber pullout, fiber deformation and matrix multiple cracking to toughness are quantitatively studied when different toughening measures are adopted. Meanwhile, the relationship between toughness and fiber distribution and orientation as well as the influence of fiber─matrix bonding property on toughness are investigated, which help to further elucidate the toughening mechanisms. The result of the project is expected to provide guidance for scientific design and regulation of toughness as well as the engineering application of UHPC.

相比于普通水泥基材料，超高性能混凝土（ultra-high performance concrete，UHPC）因其优异的韧性而在建筑和国防工程等领域具有广阔的应用前景。一些研究表明，通过采用异型钢纤维、纤维混杂以及掺加纳米材料等措施能够有效提高UHPC的韧性。然而，对于上述增韧措施的潜在作用机理，目前缺乏系统研究。本课题围绕UHPC韧性提升的作用机理展开研究，探讨采用不同增韧措施时纤维桥接、纤维拔出、纤维变形以及基体多缝开裂对UHPC韧性的贡献比重，实现增韧机理的定量分析，同时通过系统研究纤维的空间分布和取向与韧性的关系以及纤维─基体的界面粘结性能对韧性的影响，进一步明晰不同宏观韧性行为的产生机理。本课题的预期研究成果对于UHPC韧性的科学设计与调控以及UHPC的工程应用具有重要的指导意义。

提升工程材料的韧性对于提高工程结构服役寿命以及确保工程结构的安全性具有重要意义。超高性能混凝土作为一种新型土木工程材料，提高其韧性能够进一步推动其在建筑和国防工程等领域的应用。本项目探索了钢纤维种类及混杂、掺加氧化石墨烯以及成型时浇筑位置对UHPC韧性的影响，定量研究了UHPC在三点弯曲断裂过程中基体开裂和纤维拔出所消耗的能量。研究结果表明：（1）长直和端勾纤维相比短直纤维制备的UHPC具有更高的韧性，蒸汽养护相比标准养护有利于提升掺大尺寸纤维试样的韧性，而对掺小尺寸纤维试样的韧性有不利影响；（2）纤维混杂试样的韧性基本介于单掺试样的性能之间，未发现明显的混杂协同效应；（3）掺加适量的氧化石墨烯能略微提升UHPC的韧性，氧化石墨烯粒径大小对提升效果有一定影响；（4）纤维拔出对韧性的贡献较大，而基体开裂的贡献较小。本项目的研究成果对于UHPC的设计调控、试验开展以及工程应用具有一定的指导意义。