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鋼纖維混凝土動態力學特性及損傷規律研究

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

  • 摘要: 以云南某礦山超深井襯砌支護為工程背景,對不同摻配方案、不同標號的鋼纖維混凝土試樣進行動態沖擊試驗,并采用數字圖像相關技術分析了沖擊荷載下試樣表面的應變場演化. 試驗結果表明:三摻鋼纖維混凝土動態抗壓強度和耗散能占比大于單摻和雙摻鋼纖維混凝土;素混凝土的動態強度越小,摻配鋼纖維后混凝土試樣的動態強度提升越顯著. 采用高速攝像機記錄了鋼纖維混凝土試樣的破壞全過程,試樣破壞模式受混凝土標號和鋼纖維摻配方案控制,可分為剪切、劈裂和剪切–劈裂復合型破壞. 與素混凝土試樣相比,鋼纖維混凝土試樣在沖擊荷載下的裂紋數量減少,反射能占比更低,透射能和耗散能占比更高,表明鋼纖維能有效抑制裂紋萌生擴展,增強井壁混凝土的穩定性. 鋼纖維混凝土試樣的非破壞性沖擊試驗結果顯示三摻鋼纖維方案能夠最大程度抑制混凝土在沖擊荷載下的損傷. 最終建議該礦山深部豎井襯砌支護采用混凝土標號為C50,鋼纖維的摻配方案為每立方素混凝土摻配端鉤型長纖維40 kg、鍍銅平直型中長纖維5 kg以及短鍍銅平直型短纖維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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