EFFECT OF FREEZE-THAW ACTION ON ACOUSTIC EMISSION CHARACTERISTICS OF SELF-COMPACTING LIGHTWEIGHT AGGREGATE CONCRETE
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摘要: 为研究冻融后自密实轻骨料混凝土单轴压缩下的声发射(AE)特性，对未掺引气剂的自密实轻骨料混凝土试件进行0次、50次、100次快速冻融试验。结果表明：随着冻融次数增加，试件轴压应力-应变曲线趋于完整，峰值应力有明显降低；声发射峰值频率主要位于15 kHz~45 kHz, 85 kHz~105 kHz, 235 kHz~255 kHz和285 kHz~320 kHz 这4个“优势频段”区间，对应于混凝土内部预存裂纹或孔隙压密，骨料/砂浆界面增强层的开裂，粗骨料断裂破坏以及砂浆的开裂。受冻后的试件在轴压作用经历拉伸裂缝与剪切裂缝之间的交替转化，最终形成主裂缝导致破坏。冻融作用以及应力水平变化对AE信号源分布有较大影响，随着应力水平的增加，AE信号源趋于活跃，且在试样断裂面有聚集趋势。Abstract: To study the acoustic emission (AE) characteristics of self-compacting lightweight aggregate concrete (SCLC) under uniaxial compression after freeze-thaw action, 0, 50 and 100 rapid freeze-thaw tests are carried out on self-compacting lightweight aggregate concrete specimens without air entraining agent. The results show that: with the increase of freeze-thaw cycles, the uniaxial compressive stress-strain curves of the specimen tend to be complete, and the peak stress decreases significantly. The peak frequency of AE is mainly located in the four 'dominant frequency bands' of 15 kHz-45 kHz, of 85 kHz-105 kHz, of 235 kHz-255 kHz and of 285 kHz-320 kHz, corresponding to the compression of pre-existing cracks or pore in concrete, the cracking of aggregate/paste interface reinforcement layer, the penetration fracture of coarse aggregate and the cracking of mortar, respectively. Under the action of uniaxial compression, the freeze-thawed specimens undergo the alternating transformation between tensile cracks and shear cracks, and finally form the main crack which leads to failure. Freeze-thaw action and the variation of stress level have a great influence on the distribution of AE signal source. With the increase of stress level, AE signal tends to be active and gathers on the fracture surface of the sample.
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图 2 质量损失率和相对动弹性模量的变化
Figure 2. Variation of mass loss rate and relative dynamic modulus of elasticity
图 3 AE特征参数与加载时间的关系图(左: 振铃计数-时间关系图，右: 能量-时间关系图)
Figure 3. Relationship between AE characteristic parameters and loading time (left: the ringing count-time diagram; right: the energy-time diagram)
表 1 自密实轻骨料混凝土配合比
Table 1. Mix proportion of self-compacting lightweight aggregate concrete
/(kg/m3) 水泥 粉煤灰 硅灰 水 砂 粗骨料 减水剂/(wt.%) 358 108 46 179 665 613 0.3 
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表 2 自密实轻骨料混凝土性能指标
Table 2. Performance index of self-compacting lightweight aggregate concrete
抗压强度/
MPa干表观密度/
(kg/m3)自密实性能 扩展度/
mm扩展时间
T500/sJ环扩展度/
mm离析率/
(%)54.2 1891 700 2.6 700 3.9
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表 3 声发射系统参数
Table 3. Parameters of AE system
参数类型 参数值 数据传输速度/(MB/s) 132 触发器处理能力/Mflops 150 最低噪声阈值/dB 18 频率范围/kHz 10.0~2.1×103 高速处理速度/(hits/s) 20 000 PDT/μs 35 HDT/μs 150 HLT/μs 300
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