钢纤维混凝土动态力学特性及损伤规律研究

Experimental study on dynamic mechanical properties and damage law of steel fiber concrete

  • 摘要: 以云南某矿山超深井衬砌支护为工程背景,对不同掺配方案、不同标号的钢纤维混凝土试样进行动态冲击试验,并采用数字图像相关技术分析了冲击荷载下试样表面的应变场演化. 试验结果表明:三掺钢纤维混凝土动态抗压强度和耗散能占比大于单掺和双掺钢纤维混凝土;素混凝土的动态强度越小,掺配钢纤维后混凝土试样的动态强度提升越显著. 采用高速摄像机记录了钢纤维混凝土试样的破坏全过程,试样破坏模式受混凝土标号和钢纤维掺配方案控制,可分为剪切、劈裂和剪切–劈裂复合型破坏. 与素混凝土试样相比,钢纤维混凝土试样在冲击荷载下的裂纹数量减少,反射能占比更低,透射能和耗散能占比更高,表明钢纤维能有效抑制裂纹萌生扩展,增强井壁混凝土的稳定性. 钢纤维混凝土试样的非破坏性冲击试验结果显示三掺钢纤维方案能够最大程度抑制混凝土在冲击荷载下的损伤. 最终建议该矿山深部竖井衬砌支护采用混凝土标号为C50,钢纤维的掺配方案为每立方素混凝土掺配端钩型长纤维40 kg、镀铜平直型中长纤维5 kg以及短镀铜平直型短纤维10 kg.

     

    Abstract: Investigating the effect of steel fiber blending schemes on the dynamic mechanical properties and damage evolution of concrete is crucial for deep-shaft construction projects. Dynamic impact tests were conducted on steel fiber concrete specimens with varying mixing schemes and grades, according to the settings of the ultra-deep shaft-lining support project of a mine in Yunnan Province. The evolution of strain fields on the specimen surfaces under impact loads was analyzed using digital image correlation techniques. The steel fiber mixing schemes were as follows: single mixing, in which 55 kg of end-hook long fibers were added per cubic meter of concrete; double mixing, which involved the addition of 15 kg of end-hook long fibers and 40 kg of short copper-plated straight fibers per cubic meter of concrete; and triple mixing, which involved the addition of 40 kg of end-hook long fibers, 5 kg of copper-plated straight medium-length fibers, and 10 kg of short copper-plated straight fibers per cubic meter of concrete. The test results indicated that the dynamic compressive strength and dissipated energy ratio of the triple-mixed steel fiber concrete specimens were greater than those of the single- and double-mixed steel fiber concrete specimens. The smaller dynamic strength of plain concrete, the more pronounced the enhancement in the dynamic strength observed in concrete specimens with a steel fiber admixture. A high-speed camera was used to record the complete failure process of the steel fiber concrete specimens. The camera revealed that the failure mode was influenced by the concrete grade and steel fiber mixing scheme. The observed failure modes included shear, splitting, and shear-splitting failures. Compared with plain concrete specimens, steel fiber concrete specimens exhibited fewer cracks, a lower percentage of reflected energy, and higher percentages of transmitted and dissipated energy under impact loading. This indicates that the steel fibers effectively inhibited crack initiation and propagation, thereby enhancing the stability of the shaft wall concrete. Non-destructive impact tests on steel fiber concrete specimens showed that the triple-mixed steel fiber scheme inhibited concrete damage under impact loading to the maximum extent. It is recommended that the lining support for the deep shaft of the mine be constructed using grade C50 concrete with steel fibers mixed with 40 kg of end-hooked long fibers, 5 kg of copper-plated straight medium-length fibers, and 10 kg of short copper-plated straight fibers per cubic meter of concrete.

     

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