For the last decades, new reparation or fabrication processes have been studied to replace traditional rebar by roving of different mineral or organic fibres to avoid corrosion issues. Such materials refer to the family of cementitious composite. Their tensile strength would directly depend on the proportion of reinforcement and strongly on the interfacial mechanical properties between fibres and cementitious matrix. From now, evaluation of interfacial properties was mostly limited to the use of force–displacement curves obtained from mechanical experiments. This work presents a new methodology using micromechanical tension stiffening tests combined with X‐ray computed tomography (XRCT) observations, performed at the Anatomix beamline at Synchrotron SOLEIL, and specific image processing procedures. Multi‐XRCT acquisitions with suitable scanning strategy are used to image the whole fibre‐matrix interface along centimetric samples at four to five different levels of loading magnitude. Intensive image processing is then performed on tomographic images including digital volume correlation (DVC), image subtraction and Hessian‐based filtering. This experiment allows to study damage mechanisms at small scale. The proposed methodology shows great potential to provide both qualitative and quantitative elements on interfacial mechanical behaviour such as crack growth and crack orientation. The interface between mortar and sufficiently small multi‐fibre yarn used in this paper is shown to behave in certain condition as traditional rebar interface producing conical cracks in the surrounding matrix rather than debonding in mode 2, permitting a much higher energy dissipation during debonding. According to this study, conical cracks repartition and geometry are mostly influenced by the cementitious matrix. The spacing between cracks goes from 50 to 100 μm, and the angle between crack normal vector and yarn orientation goes from 35° to 50°.

中文翻译：

---

X射线断层扫描观察纤维增强砂浆中的微裂纹图案

在过去的几十年中，已经研究了新的修复或制造工艺，通过粗纱不同的矿物或有机纤维来替代传统的钢筋，以避免腐蚀问题。此类材料是指水泥基复合材料系列。它们的抗张强度将直接取决于增强材料的比例，并强烈取决于纤维与水泥基体之间的界面机械性能。从现在开始，界面特性的评估主要限于使用从机械实验获得的力-位移曲线。这项工作提出了一种新的方法，该方法结合了在Synchrotron SOLEIL的Anatomix束线处执行的微机械抗拉刚度测试与X射线计算机断层扫描（XRCT）观察以及特定的图像处理程序相结合。使用具有适当扫描策略的Multi-XRCT采集，可以在4到5个不同的加载大小级别上，沿集中样本对整个纤维-基质界面进行成像。然后对断层图像进行密集图像处理，包括数字体积相关性（DVC），图像减法和基于Hessian的滤波。该实验允许小规模研究破坏机理。所提出的方法显示出在界面力学行为（如裂纹扩展和裂纹取向）上提供定性和定量元素的巨大潜力。研究表明，砂浆和足够细的多纤维纱之间的界面在一定条件下表现出一定的性能，因为传统的钢筋界面在周围的基体中产生圆锥形裂纹，而不是在模式2下脱胶。在剥离过程中允许更高的能量耗散。根据这项研究，圆锥形裂缝的重新分配和几何形状主要受胶凝基体的影响。裂纹之间的间距为50至100μm，裂纹法向矢量与纱线方向之间的夹角为35°至50°。