The recent advent in the field of cementitious composites with the emergence of high and ultra-high performance fiber reinforced concretes (HPFRC and UHPFRC) is considered a great opportunity in infrastructure accelerated construction, strengthening and repair. These materials draw their exceptional mechanical performance from two characteristics: the densely packed microstructure, and the ability of the materials to sustain their tensile resistance after cracking and to strain-harden over a significant range of tensile strain when the appropriate number of fibers is used. In structural design, however, the tensile resilience of these materials can be considered only if it can be characterized by standards and repeatable tests. Four-point bending tests (FPBT) on prism samples are used widely due to their perceived simplicity, particularly for quality control. Although these tests have been introduced in standards as the recommended option, experience shows that in practice they lead to experimental scatter and variability owing to spurious interactions between the specimen and the testing setup. This study explores experimentally, through a round-robin test, the effect of these interactions on the dispersion of the results. Three preblended commercial mixes were considered; identical specimens were tested in three different laboratories using their available hardware to conduct the quality control tests. The variability in the custom details of the FPBT setups and the uncertainties introduced by the operator, as well as the effect of casting methodology on flexural strength were investigated. Bilinear tensile stress–strain and stress-crack mouth opening relationships of the tested materials were derived using the inverse analysis procedures as prescribed in Annex 8.1 of CSA-S6 (Canadian highway bridge design code-annex 8.1 fibre reinforced concrete, Canadian Standards Association, Toronto, 2019) and Annex U of CSA-A23.1 (Ultra-high-performance concrete-UHPC, Canadian Standards Association, Toronto, 2019). Results indicate that cracking strength of HPFRC and UHPFRC derived from inverse analysis was generally higher than the conservative empirical lower bound estimates, whereas a significant difference is evident between results from the three laboratories participating in this round robin testing program. Despite the scatter, in all cases the inverse analysis indicated that the materials exhibited tension hardening behaviour.

随着高性能和超高性能纤维增强混凝土（HPFRC 和 UHPFRC）的出现，水泥复合材料领域的最新出现被认为是基础设施加速建设、加固和修复的绝佳机会。这些材料从两个特性中汲取其卓越的机械性能：密集的微观结构，以及材料在开裂后保持其抗拉性的能力，以及当使用适当数量的纤维时在相当大的拉伸应变范围内应变硬化的能力。然而，在结构设计中，这些材料的拉伸弹性只有在可以通过标准和可重复测试来表征的情况下才能被考虑。棱镜样品的四点弯曲测试 (FPBT) 由于其简单性而被广泛使用，特别是在质量控制方面。尽管这些测试已作为推荐选项在标准中引入，但经验表明，在实践中，由于样本和测试设置之间的虚假相互作用，它们会导致实验分散和可变性。本研究通过循环测试以实验方式探索了这些相互作用对结果分散性的影响。考虑了三种预混的商业混合物；相同的样本在三个不同的实验室进行了测试，使用他们可用的硬件进行质量控制测试。研究了 FPBT 设置的自定义细节的可变性和操作员引入的不确定性，以及铸造方法对弯曲强度的影响。使用 CSA-S6 附件 8.1（加拿大公路桥梁设计规范-附件 8.1 纤维增强混凝土，加拿大标准协会，多伦多）中规定的逆向分析程序推导出受试材料的双线性拉伸应力 - 应变和应力 - 裂纹开口关系, 2019) 和 CSA-A23.1 的附录 U（超高性能混凝土-UHPC，加拿大标准协会，多伦多，2019）。结果表明，从逆向分析得出的 HPFRC 和 UHPFRC 的抗裂强度通常高于保守的经验下限估计，而参与该循环测试计划的三个实验室的结果之间存在显着差异。尽管分散，但在所有情况下，逆向分析表明材料表现出拉伸硬化行为。