This paper presents the results of an experimental investigation conducted to evaluate the mechanical properties, including strength and flexural toughness of hybrid fiber-reinforced mortar (FRM) containing various combinations of steel and carbon fibers with different material characteristics. The mortar specimens were mixed with steel and carbon fibers in the mix proportions of 100 + 0%, 75 + 25%, 50 + 50%, 25 + 75%, and 0 + 100% by volume at a total volume fraction of 1.0%. The flexural performance (flexural strength and toughness) of the mortar specimens was obtained using the third-point loading arrangement stipulated in the test methods of ASTM C 1609/C 1609/M and KS F 2566. In addition, compressive strength was also measured according to the KS F ISO 679 test method. Their mechanical properties were examined and compared with plain mortar (PM) at the age of 28 days. The test results showed the highest compressive and flexural strengths in the hybrid FRM reinforced with 75% steel fibers + 25% carbon fibers, confirming the synergistic reinforcing effect of the steel and carbon hybrid fibers. However, the hybrid FRM reinforced with 50% steel fibers + 50% carbon fibers has obtained slightly low flexural strength but owned the highest flexural toughness and hence can be judged as the most appropriate combination to be employed in hybrid FRM to improve the flexural toughness. Moreover, the fractured FRM surface was also observed via scanning electron microscopy (SEM) after platinum coating in vacuum. These results would be of great help in establishing the microstructural mechanism of hybrid reinforcing fibers in the cement matrix.

中文翻译：

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钢碳混合纤维增强砂浆强度和弯曲韧性等力学性能的试验研究

本文介绍了一项实验研究的结果，该研究旨在评估包含具有不同材料特性的钢和碳纤维的各种组合的混合纤维增强砂浆 (FRM) 的机械性能，包括强度和弯曲韧性。砂浆试件与钢和碳纤维以100+0%、75+25%、50+50%、25+75%和0+100%的混合比例混合，总体积分数为1.0% . 使用ASTM C 1609/C 1609/M和KS F 2566的测试方法中规定的第三点加载布置获得砂浆试样的弯曲性能（弯曲强度和韧性）。此外，抗压强度还根据KS F ISO 679 测试方法。在 28 天龄时检查它们的机械性能并与普通砂浆 (PM) 进行比较。测试结果表明，75% 钢纤维 + 25% 碳纤维增强的混合 FRM 具有最高的压缩和弯曲强度，证实了钢和碳混合纤维的协同增强效果。然而，50%钢纤维+50%碳纤维增强的混合FRM的弯曲强度略低，但弯曲韧性最高，因此可以判断为混合FRM中最适合用于提高弯曲韧性的组合。此外，在真空中镀铂后，还通过扫描电子显微镜（SEM）观察了断裂的 FRM 表面。