冻融作用对自密实轻骨料混凝土声发射特性影响

EFFECT OF FREEZE-THAW ACTION ON ACOUSTIC EMISSION CHARACTERISTICS OF SELF-COMPACTING LIGHTWEIGHT AGGREGATE CONCRETE

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。

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.