Fibre reinforced concrete (FRC) increases shear capacity mainly by providing post-cracking residual strengths and by improving the aggregate interlock mechanism on the two crack faces. Hence, direct shear tests can be adopted to study the shear transfer mechanisms across a crack. Several researches studied the behaviour of steel fibre reinforced concrete by means of shear tests initially developed for plain concrete (PC). Due to an increased heterogeneity of material (caused by a random fibre distribution) and the need to carry out the test up to a higher crack width (Mode I) and slip (Mode II), tests on FRC are more difficult as compared to PC and the issue related to the rotation of the cracking plane is more likely to develop. In addition, other fibre types or materials different than ordinary concrete have not been studied in depth so far. In this context, the present study firstly evaluates the influence of rigid (steel) and non-rigid (polypropylene) fibres on the direct shear behaviour of ordinary concrete (considering a broad range of FRC toughness). To do this, the modified JSCE SF6 test was improved by avoiding friction and by providing a steel system to control rotations. Secondly, the direct shear behaviour of alkali activated concrete (AAC) reinforced by steel fibres was compared against ordinary FRC in order to underline possible differences. Experimental results showed that, under direct shear tests, the fibre influence on the shear stresses transferred across a crack is only related to FRC toughness and not to fibre type (rigid or non-rigid). AAC also showed to have a shear behaviour comparable to ordinary concrete.

中文翻译：

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不同纤维类型增强的普通混凝土和碱活化混凝土中裂缝的剪切传递

纤维增强混凝土 (FRC) 主要通过提供开裂后残余强度和改善两个裂缝面上的骨料互锁机制来提高抗剪能力。因此，可以采用直剪试验来研究跨裂纹的剪切传递机制。多项研究通过最初为素混凝土 (PC) 开发的剪切试验研究了钢纤维混凝土的性能。由于材料的不均匀性增加（由随机纤维分布引起）以及需要进行更高裂纹宽度（模式 I）和滑移（模式 II）的测试，与 PC 相比，FRC 测试更加困难与裂纹平面旋转相关的问题更容易发展。此外，与普通混凝土不同的其他纤维类型或材料目前尚未深入研究。在此背景下，本研究首先评估刚性（钢）和非刚性（聚丙烯）纤维对普通混凝土直接剪切行为的影响（考虑到广泛的 FRC 韧性）。为此，改进的 JSCE SF6 测试通过避免摩擦和提供钢制系统来控制旋转进行了改进。其次，将钢纤维增强的碱活化混凝土 (AAC) 的直接剪切行为与普通 FRC 进行比较，以强调可能的差异。实验结果表明，在直接剪切试验下，纤维对跨裂纹传递的剪切应力的影响仅与 FRC 韧性有关，与纤维类型（刚性或非刚性）无关。AAC 还显示出与普通混凝土相当的剪切性能。本研究首先评估刚性（钢）和非刚性（聚丙烯）纤维对普通混凝土直接剪切行为的影响（考虑到广泛的 FRC 韧性）。为此，改进的 JSCE SF6 测试通过避免摩擦和提供钢制系统来控制旋转进行了改进。其次，将钢纤维增强的碱活化混凝土 (AAC) 的直接剪切行为与普通 FRC 进行比较，以强调可能的差异。实验结果表明，在直接剪切试验下，纤维对跨裂纹传递的剪切应力的影响仅与 FRC 韧性有关，与纤维类型（刚性或非刚性）无关。AAC 还显示出与普通混凝土相当的剪切性能。本研究首先评估刚性（钢）和非刚性（聚丙烯）纤维对普通混凝土直接剪切行为的影响（考虑到广泛的 FRC 韧性）。为此，改进的 JSCE SF6 测试通过避免摩擦和提供钢制系统来控制旋转进行了改进。其次，将钢纤维增强的碱活化混凝土 (AAC) 的直接剪切行为与普通 FRC 进行比较，以强调可能的差异。实验结果表明，在直接剪切试验下，纤维对跨裂纹传递的剪切应力的影响仅与 FRC 韧性有关，与纤维类型（刚性或非刚性）无关。AAC 还显示出与普通混凝土相当的剪切性能。