冻融损伤喷射混凝土本构关系及微观结构

Constitutive relation and microstructure on shotcrete after freeze and thaw damage

采用棱柱体试件,通过快速冻融试验方法,对冻融损伤后同配合比普通混凝土、喷射混凝土及钢纤维喷射混凝土单轴受压应力应变全曲线进行研究。对应力应变关系中相关参数进行回归分析,得出冻融循环后试件应力应变全曲线方程。结果表明:随着冻融循环次数增加,受压应力应变曲线趋于扁平;峰值应力降低,峰值应变增大,分别与冻融循环次数呈线性和指数变化。与普通混凝土相比,喷射混凝土峰值应力下降速率小,而钢纤维喷射混凝土的下降速率进一步减小。而后,采用扫描电子显微镜及压汞法,对损伤后试件微观结构和孔结构进行观察分析,发现随着冻融循环次数增加,在渗透压和冻胀压力综合作用下,试件内部微裂纹及气孔增多,孔径增大,试件密实度显著降低;而钢纤维喷射混凝土中仅出现少量连通毛细孔,这与宏观力学性能变化呈现一致性。

Using prismatic specimens of concrete,we examined the uniaxial compression stress-strain curve of ordinary concrete（mixture C43F10）,ordinary shotcrete（mixture S43F10）and steel fiber reinforced shotcrete（mixture S43F10SF50）with the same mixture by using the accelerating freeze-thaw method.By fitting the relationship between parameters and the number of freeze-thaw cycles,the stress-strain curve of specimens under damaging was calculated.The test results show that with the increase of freezing and thawing cycles,the peak stress is low and has a liner relation with the freezing and thawing cycles.However,the peak strain is bigger and demonstrates an exponential relationship.The peak stress of shotcrete decreases more slowly than that of ordinary concrete,and that of shotcrete with steel fiber reduces much more slowly.We also observed and analyzed the microstructure and pores of specimens after damage by using scanning electron microscope and the mercury intrusion method.The result shows thatwith an increase number of freeze-thaw cycles,the amount of micro-creaks and pores and the diameter of pores increase by the effect of osmotic pressure and frost heave pressure while the specimens＇ density decreases.In the same situation,there are only several connected capillary pores in steel fiber reinforced shotcrete,which is consistent with macro-mechanical properties.