加载速率对钢纤维与超高性能混凝土黏结性能的影响

Effect of loading rate on bond properties of steel fiber and ultra-high performance concrete

为深入了解超高性能混凝土(UHPC)的黏结性能,进一步明确钢纤维与UHPC基体黏结界面在不同加载速率下的破坏方式,以及影响纤维速率敏感性的因素,分析不同加载速率下UHPC基体中嵌入高强度钢纤维的单纤维拉拔性能,以更深入了解UHPC的黏结性能。试验变量为纤维类型(直圆形、端钩形、波纹形)、加载速率(0.5~5 mm/min)和基体强度(77.10、90.50、111.33 MPa),共制作27组试件。在不同加载速率下,对纤维的最大拉应力、拉拔能、等效黏结强度和平均黏结强度等参数进行表征和分析,并在扫描电子显微镜(SEM)下对纤维拔出后的表观形态以及基体隧洞形貌进行观察和探讨。试验结果表明:不同纤维的拉拔性能从大到小依次为直圆形纤维、端钩形纤维、波纹形纤维;在SEM中观察到所有拔出纤维的表面上有不同程度的刮伤,附着微小的基体颗粒,基体隧洞产生了不同程度的微裂纹,端钩形纤维的拔出会造成拔出口附近的基体剥落;纤维的速率敏感性与基体强度有关,随着基体强度增加,直圆形纤维的速率敏感性先减小后增大,最大拔出荷载、拉拔功、等效黏结强度、材料的强度利用率分别提升了42.9%、160.7%、160.8%、21%;端钩形纤维的速率敏感性减小,但最大拔出荷载达到了226.71 MPa,材料的强度利用率高达134%;波纹形纤维的速率敏感性增大,最大断裂荷载增加了8.9%,最大材料强度利用率达到68%;纤维的速率敏感性还与纤维种类有关,其速率敏感性从大到小依次为波纹形纤维、端钩形纤维、直圆形纤维。此外,UHPC基体具有速率敏感性,其速率敏感性与直圆形纤维和端钩形纤维呈正相关,与波纹形纤维呈负相关。该研究可为深入了解钢纤维增强超高性能混凝土的力学性能提供参考。

In order to gain a deeper understanding of the bonding properties of UHPC, further define the failure mode of the bonding interface between the steel fiber and the UHPC matrix under different loading rates, and the factors effecting the fiber rate sensitivity. Single-fiber drawing performance of ultra-high performance concrete(UHPC) matrix embedded with high-strength steel fibers under different loading rates were studied. The test variables were fiber type(straight round, end-hooked, corrugated), loading rate(from 0.5 to 5 mm/min) and matrix strength(77.10, 90.50, 111.33 MPa). A total of 27 sets of samples were made. Under different loading rates, the maximum tensile stress, pull-out energy, equivalent bond strength and average bond strength of the fiber were characterized and analyzed. The apparent morphology of the fiber and the morphology of the matrix tunnel after fiber being pulled out were observed and discussed with the aid of the scanning electron microscope(SEM). The results show that the drawing performance of different fiber types is sorted from large to small as follows, straight round fiber, end-hooked fiber, corrugated fiber. And it is observed in SEM that all the pulled-out fibers have different degrees of scratches on the surface, and tiny matrix particles are attached. The matrix tunnels appear different degrees of micro-cracks, and the pull-out of the end-hooked fibers also cause matrix spalling near the pull-out exit. The speed sensitivity of the fiber is found to be related to matrix strength. With the increase of matrix strength, the speed sensitivity of the straight round fiber first decreases and then increases, the maximum pull-out load, pull-out work, the equivalent bond strength and strength utilization rate increase by 42.9%, 160.7%, 160.8% and 21%, respectively. The rate sensitivity of the end-hooked fiber reduces but the maximum pull-out load reaches 226.71 MPa, and the strength utilization rate of the material is as high as 134%. The rate sensitivity of the corrugated fiber increases, the maximum breaking load increases by 8.9%, and the maximum material strength utilization rate reaches 68%. The speed sensitivity of the fiber is also related to the type of fiber, the order from large to small of rate sensitivity of fibers is corrugated fiber, end-hooked fiber, straight round fiber. In addition, the UHPC matrix itself is rate-sensitive, and has a positive correlation with straight round and end-hooked fibers, and a negative correlation with corrugated fibers. A reference for further understanding the mechanical properties of steel fiber reinforced ultra-high performance concrete can be provided. 5 tabs, 13 figs, 25 refs.