高强混凝土的高脆性及其在冲击作用下的破坏机理

High Brittleness of High Strength Concrete and FailureMechanism Under Impact Loading

通过试验对比了高强混凝土(C60)和中低强混凝土(C30)抗压强度、抗折强度、折压比随龄期的变化规律,并采用微计算机断层扫描技术(Micro Computed Tomography,Micro-CT)分析高强混凝土在冲击作用力下的破坏机理。结果表明:与C30混凝土相比,3、7、28、56 d龄期时,C60混凝土抗压强度分别增长57.5%、53.7%、54.3%和52.8%,C60混凝土抗折强度分别增长51.2%、39.6%、32.4%和21.7%,C60混凝土抗折强度的增幅低于抗压强度,说明其脆性特征明显;C60混凝土折压比小于C30混凝土,说明C60混凝土韧性较差,脆性较大;在外部冲击荷载作用下首先在C60混凝土薄弱界面过渡区出现微裂缝,然后向粗骨料内部扩展形成骨料微裂缝,骨料微裂缝继续扩展连通,与水泥石微裂缝连接,最终导致混凝土试件开裂破坏。

The changes in compressive strength,flexural strength,and flexural compression ratio of high strength concrete(C60)and medium-low strength concrete(C30)with age were compared through experiments,and the failure mechanism of high strength concrete under impact loading was studied using micro computed tomography(Micro-CT)analysis technology.The results showed that compared with C30 concrete,at 3,7,28,56 d of age,the compressive strength of C60 concrete increased by 57.5%,53.7%,54.3%,and 52.8%,and the flexural strength of C60 concrete increased by 51.2%,39.6%,32.4%,and 21.7%,respectively.The increase in flexural strength of high strength concrete is lower than that of compressive strength,indicating that their brittle characteristics are obvious.The flexural compression ratio of C60 concrete is lower than that of C30 concrete,indicating poor toughness and high brittleness of C60 concrete.Under external impact loading,microcracks first appear in the weak interface transition zone of high strength concrete,and then expand into the interior of coarse aggregate to form aggregate microcracks.The aggregate microcracks continue to expand and connect with cement stone microcracks,ultimately leading to cracking and failure of concrete specimens.