The influence law of concrete aggregate particle size on acoustic emission wave attenuation

Elastic waves have different attenuation laws when propagating in various materials, which is one of the important challenges in the application of non-destructive testing methods, such as acoustic emission (AE) technology in geotechnical engineering. The study presented in this paper investigated the influence mechanism of concrete composition materials and parameters on the propagation law of elastic waves using concrete specimens produced in six different particle sizes of sand or gravel. The burst AE signal was generated through the lead-breaking experiment, and ceramic piezoelectric sensors were used to record the signal waveform at different propagation distances. Through parameter analysis, spectrum analysis, and pattern recognition techniques, the influence of the concrete aggregate particle size on AE wave propagation and attenuation was revealed. The results show that the attenuation of elastic wave amplitude, energy spectral density, and frequency all were positively correlated with the aggregate particle size, and the elastic wave spectrum center of gravity generally decreased with the propagation distance. The ring count gradually decreased with the propagation distance, and the specimens with a larger aggregate particle size underwent a relatively faster ring count attenuation rate. The rise time increased rapidly with the propagation of the elastic wave, and the specimens with a larger aggregate particle size experienced a relatively rapid increase in rise time. In addition, in the feature spaces of ring count-amplitude and rise time–amplitude, the size of aggregate has an obvious influence on the distribution of these feature vector.

EFFECT OF RECYCLED CONCRETE AGGREGATE, AIR ENTRAINING ADMIXTURE AND MAXIMUM AGGREGATE PARTICLE SIZE ON THE BEHAVIOR OF CONCRETE UNDER FREEZE-THAW CYCLES

ABSTRACT This article presents freeze-thaw (F/T) resistance of concrete containing recycled concrete aggregate (RCA). RCA percentages of 15%, 30%, 45%, and 60% were replaced by natural aggregate. Air entraining admixture (AEA) with three different ratios (0.06%, 0.13%, and 0.20%) were used and three different maximum aggregate particle sizes (dmax = 16 mm, 22.4 mm and 31.5 mm) were selected. F/T resistances of the concretes were determined through the measurement of scaling on the surfaces of the samples placed in 3% NaCl solution in pursuance of TS CEN/TS 12390-9. It was observed that the compressive strength of the concretes decreased by 20% on average compared to the control samples with the increase in the amount of RCA. However, it was determined from the experiments that the use of RCA increases the F/T resistances of the concretes as it provides extra voids in the concrete and decreases capillary permeability. Within the limits of this study, dmax = 22.4 mm, RCA = 45% and AEA = 0.13% are recommended as the optimum values for F/T resistance of the concrete. It is also recommended to use RCA in pavement applications including roadways, highways, parking facilities, and other non-structural concrete elements subjected to severe winter conditions.