Behavior of Acoustic Emission of Mortar Degraded by Mixing with Expanded Polystyrene Beads
Kiyohito YAMAMOTO, Akira KOBAYASHI and Shigeyasu AOYAMA
Abstract:Degraded specimens were prepared by mixing expanded polystyrene (EPS) beads with mortar, and sound specimens include no beads. Measurements of compressional elastic wave velocity (Vp) and acoustic emission (AE) were performed using an AE transducer. The relationships between air content and AE parameters were investigated based on the Vp measurements. The changes in AE behavior with increase in strain were measured by a uniaxial compression test and a splitting test. The AE parameters-rise time, count, frequency, average signal level, and event count rate-were evaluated, on average, every ten seconds. The following results were obtained. (1) In the uniaxial compression test, the volumetric contraction of the degraded specimens was small. This is because large volumetric expansion of the degraded specimens occurs with increase in axial strain. (2) It is difficult to measure the degree of degradation due to increase in porosity using only one AE transducer. The degree of degradation can be evaluated qualitatively using two AE parameters (mean value of count and standard deviation of rise time). (3) It is inferred that the area of observation can be recognized as degraded by increase in cracks when the behavior of average signal level and event count rate for monotonic load is similar to that for cyclic load. (4) It is also inferred that the failure type can be determined as either extensive compression or local tension by long-term observation of reverberation frequency and rise time. Key Words:Mortar, acoustic emission, EPS beads, degradation, uniaxial compression test, splitting test, cyclic loading