应力损伤下玄武岩纤维混凝土内部孔隙结构及能量耗散试验研究

Experimental study on internal pore structure and energy dissipation of basalt fiber reinforced concrete under stress damage

基于试验研究不同应力水平损伤作用下玄武岩纤维混凝土损伤度、孔隙结构及能量耗散规律,采用非金属超声波检测仪测量0σm、0.15σm、0.3σm、0.45σm、0.6σm五种不同应力水平损伤作用下试件纵波波速及损伤因子变化规律,利用核磁共振(NMR)试验方法研究不同应力水平损伤作用下试件T_(2)谱分布、孔径分布及孔隙率变化规律,并结合万能压力机对试件进行单轴压缩试验,分析其应力-应变曲线、峰值应力及能量耗散变化规律。结果表明:应力作用下,玄武岩纤维混凝土试件会发生损伤,试件高度随作用应力水平的增大而减小,纵波波速先小幅度增大后降低,低应力水平作用对试件整体性有增强效果,高应力水平作用对试件造成损伤,且应力越大,损伤程度越高;0.3σm应力水平作用下试件T_(2)图谱峰值最低,0.6σm应力水平作用下试件T2图谱峰值最高,试件孔隙率随应力水平的增大先减小后增加;试件内部孔隙主要以微孔、中孔形式存在,低应力水平作用下试件内部原生裂纹被压缩,试件内部中孔向微孔转化,总孔隙率降低,高应力水平作用时试件在应力作用下发生损伤变形,试件内部裂纹孔径增大,孔隙率增加;玄武岩纤维的掺入增加了混凝土的塑性变形能力,试件峰值应力随作用应力水平的增大而降低,且降幅显著增加;试件单位体积耗散能会随应力水平的增大而减小,机械损伤度S随应力水平的增大存在小幅度增加,应力损伤下试件弹性变形能力减小,能量耗散率增加。

The damage degree, pore structure and energy dissipation of basalt fiber reinforced concrete under different stress levels are studied based on experiments. Non-metallic ultrasonic detector is used to measure 0σm, 0.15σm, 0.3σm, 0.45σm, 0.6σmvariation of longitudinal wave velocity and damage factor under five different stress levels. The T2spectrum distribution, pore size distribution and porosity of specimens under different stress levels were studied by NMR test. Combined with the universal press machine, the uniaxial compression test of the specimen is carried out, and the variation laws of stress-strain curve, peak stress and energy dissipation are analyzed. The results show that the basalt fiber concrete specimen will be damaged under stress, the specimen height decreases with the increase of the applied stress level, and the longitudinal wave velocity first increases slightly and then decreases. The integrity of the specimen is enhanced under the action of low stress level, and the specimen is damaged under the action of high stress level, and the greater the stress, the higher the damage degree. The peak value of T_(2) spectrum of test piece is the lowest under the action of 0.3σ mstress level and the peak value of T_(2) spectrum is the highest under the action of 0.6σmstress level. The porosity of the specimen first decreases and then increases with the increase of stress level. The internal pores of the test piece mainly exist in the form of micropores and mesopores. Under the action of low stress level, the original cracks in the test piece are compressed, the mesopores in the test piece are transformed into micropores, and the total porosity decreases. Under the action of high stress level, the test piece is damaged and deformed under the action of stress, the internal crack pore diameter increases and the porosity increases. The addition of basalt fiber increases the plastic deformation capacity of concrete, and the peak stress decreases with the increase of action stress level, and the decrease amplitude increases significantly. The dissipated energy per unit volume of the specimen decreases with the increase of the stress level, and the mechanical damage degree increases slightly with the increase of the stress level. Under the stress damage, the elastic deformation capacity of the specimen decreases and the energy dissipation rate increases.