Abstract Ultra-high-performance fibre reinforced concrete (UHPC) is a class of advanced cementitious composites characterized by its high compressive and flexural strengths, toughness and enhanced durability. The mechanical properties of the UHPC are to a great extent dependent on fibre volume fraction, orientation and distribution within the cementitious matrix. However, determination of the true three-dimensional fibre orientation and distribution is challenging. In this paper micro-computed tomography (micro-CT) is used to determine these parameters. Cylindrical samples of UHPC were extracted from a dogbone tension test specimen and from a pretensioned bridge girder, and high-resolution micro-CT images were then acquired. Using the scanned data, and following three-dimensional image reconstruction and image processing, quantitative fibre information was obtained via a novel image post-processing technique based on local-intensity gradient significantly improving cross-fibre detection compared to existing techniques. The estimated fibre volume fraction is close to design and experimentally measured values. Straight and hooked end fibres in UHPC sample were successfully identified and segmented using this novel technique. The test results show the fibre arrangement to be highly anisotropic with fibres aligned predominantly in one direction, which is attributed to the casting processes and flow.

中文翻译：

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基于梯度的 3D 显微 CT 断层图像纤维检测方法用于定义超高性能混凝土中的纤维取向偏差

摘要 超高性能纤维增强混凝土（UHPC）是一类先进的水泥基复合材料，具有较高的抗压和抗弯强度、韧性和增强的耐久性。UHPC 的机械性能在很大程度上取决于水泥基体中的纤维体积分数、取向和分布。然而，真正的三维纤维取向和分布的确定是具有挑战性的。在本文中，微型计算机断层扫描 (micro-CT) 用于确定这些参数。UHPC 的圆柱形样品是从狗骨拉力试样和预张紧桥梁中提取的，然后获取高分辨率显微 CT 图像。利用扫描数据，经过三维图像重建和图像处理，定量纤维信息是通过一种基于局部强度梯度的新型图像后处理技术获得的，与现有技术相比，显着改善了交叉纤维检测。估计的纤维体积分数接近设计和实验测量值。使用这种新技术成功识别和分割 UHPC 样品中的直端和钩端纤维。测试结果表明纤维排列高度各向异性，纤维主要在一个方向上排列，这归因于铸造工艺和流动。使用这种新技术成功识别和分割 UHPC 样品中的直端和钩端纤维。测试结果表明纤维排列高度各向异性，纤维主要在一个方向上排列，这归因于铸造工艺和流动。使用这种新技术成功识别和分割 UHPC 样品中的直端和钩端纤维。测试结果表明纤维排列高度各向异性，纤维主要在一个方向上排列，这归因于铸造工艺和流动。