Hybrid effect of macro and micro steel fibers on the pullout and tensile behaviors of ultra-high-performance concrete
Hybrid effect of macro and micro steel fibers on the pullout and tensile behaviors of ultra-high-performance concrete
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DOI：
10.1016/j.compositesb.2018.11.026
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发表时间：
2019-04-01
影响因子：
13.1
通讯作者：
Yoo, Doo-Yeol
中科院分区：
文献类型：
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作者：
Chun, Booki;Yoo, Doo-Yeol
本研究旨在探讨宏微观钢纤维混合使用对超高性能混凝土(UHPC)拉伸性能的影响。为此，使用三种不同的宏观钢纤维(即，直纤维、钩状纤维和扭曲纤维)和单一的微直钢纤维，其中以2%的恒定总体积分数用微纤维取代部分宏观纤维。为了制备超高性能混杂纤维混凝土(UHP-HFRC)，分别采用0、0.5、1.0、1.5和2.0%5种不同掺量的超细纤维对超高性能混杂纤维混凝土进行改性。同时，将多根取向纤维埋入超高性能混凝土中的拔出行为与超高强度纤维混凝土的拉伸行为进行了对比，分析了两者之间的相关性。试验结果表明，超高性能混凝土中粗直纤维的平均粘结强度和归一化拔出能随取代率的增加而提高，而钩状和加捻大纤维的平均粘结强度和归一化拔出能随取代率的增加而降低。在钩状纤维和加捻纤维的情况下，用微细纤维替换大纤维后得到较低的纤维效率比，而在大直纤维的情况下，得到大约0.3-0.4的纤维效率比。与普通纤维相比，宏观直纤维增强超高性能混凝土的开裂后拉伸强度和吸能能力降低，而钩状和扭曲纤维增强的超高性能混凝土被微纤维取代后，其开裂后的拉伸强度和吸能能力有所提高。由于在纤维拔出试验中没有考虑纤维在复合材料中的实际取向和粘结面积，导致纤维拔出与所有UHP-HFRC的拉伸行为呈负相关。因此，不能根据定向纤维的拔出试验结果来预测混杂钢纤维对超高性能混凝土复合材料拉伸性能的影响。
This study aims to investigate the effect of hybrid use of macro and micro steel fibers on the pullout and tensile behaviors of ultra-high-performance concrete (UHPC). To this end, three different macro steel fibers (i.e., straight, hooked, and twisted fibers) and a single micro straight steel fiber were used, whereby a portion of the macro fibers was replaced with the micro fibers at the constant total volume fraction of 2%. In order to fabricate ultra-high-performance hybrid fiber-reinforced concrete (UHP-HFRC), five different replacement ratios of the macro fibers with the micro fiber were employed, including 0, 0.5, 1.0, 1.5, and 2.0%. The pullout behaviors of multiple aligned fibers embedded in UHPC were also compared with the tensile behaviors of UHP-HFRC to analyze their correlations. The test results indicated that the average bond strength and normalized pullout energy of the macro straight fibers in UHPC were improved after their replacement with micro fibers, whereas those of the hooked and twisted macro fibers were reduced according to the replacement ratio. Lower fiber efficiency ratios were obtained after the replacement of the macro fibers with the micro fibers in the hooked and twisted fiber cases, while similar ratios of approximately 0.3-0.4 were obtained in the cases of the macro straight fibers. In comparison, the post cracking tensile strength and energy absorption capacity of UHPC reinforced with macro straight fibers decreased, whereas those of UHPCs with hooked and twisted fibers increased when they were replaced by the micro fibers. The negative correlation between fiber pullout and tensile behaviors of all UHP-HFRCs occurred because the actual fiber orientation and bonding area in the composites could not be considered in the fiber pullout tests. Thus, it is concluded that the effects of the use of hybrid steel fibers on the tensile performance of the UHPC composites could not be predicted based on the pullout test results of the aligned fibers.