Acoustic emission characteristics of Pykrete under uniaxial compression

Highlights

• The acoustic emission characteristics of various Pykrete were evaluated first in the process of uniaxial compression failure.

• The differences of acoustic emission characteristics between Pykretes and matrix were compared.

• The mechanism for the different acoustic emission features between Pykretes and matrix were analyzed.

Abstract

Pykrete is a special building material suitable for cold regions. It has attracted extensive attention in recent years owing to its high strength and toughness. However, for structures constructed using Pykrete, appropriate damage detection and evaluation methods have rarely been investigated. As with most materials, the destruction of the Pykrete structure releases energy as stress waves and produces acoustic emission (AE) signals, which help understand the damage process and evaluate the degree of damage to the Pykrete. In this study, the AE technique was employed to monitor and evaluate the damage to different types of Pykretes and matrix subjected to uniaxial compression. Combined with the load-time curve, the conventional parameters of AE signals obtained from Pykretes and matrix were analyzed first. Furthermore, the failure modes of Pykretes and the matrix were investigated via the relationship between the ratio of the rise time to the waveform amplitude and the average frequency. The b-value was also calculated using the least-squares method to evaluate the failure process of Pykretes and matrix. The results show that the AE technique can qualitatively assess the damage process of Pykretes and has the potential to detect damage to actual Pykrete structures in situ.

Introduction

Researchers have recently been looking into Pykrete, a reinforced ice material, due to its reported higher strength and ductility than ice. Structures built with Pykrete are light and strong and can significantly prolong the operation period of structures (Vasiliev et al., 2015). In high-latitude or cold regions, it has been used for transportation roads, ice runway, hotels, working spaces, and outdoor decorative structures. Pronk et al. (2016) constructed a 30 m-span ice dome with Pykrete, which was the world's largest igloo at that time. Wu et al., 2019a, Wu et al., 2019b built a shell structure with ice composites and analyzed the effects of ambient temperature and solar radiation on the shell structure.

Pykrete is composed of a matrix of different reinforcement materials. The former is usually a water or snow-water mixture, and the latter can be sawdust, wood shavings, and pulp fiber (Vasiliev et al., 2015; Wu et al., 2020). Pykrete structures have been built by pouring or spraying the Pykrete mixture (Millar et al., 2019). These construction methods result in many initial internal defects such as pores and micro-cracks. Under the influence of load intensity, ambient temperature, solar radiation, and freeze-thaw cycles, the defects inside the Pykrete mixture gradually develop and form cracks, causing structural slips and dislocations. Thus, it is necessary to monitor and evaluate the damage inside Pykrete to provide decision-making suggestions for the maintenance and management of Pykrete structures. However, for structures constructed using Pykrete (Pronk et al., 2022; Pronk et al., 2020; Thompson Towell et al., 2022), appropriate damage detection and evaluation methods have rarely been investigated.

For ice and snow structures, which are similar to Pykrete structures, some basic monitoring methods have been studied, such as displacement transducers (Vallero et al., 2022), strain gauges (Määttänen et al., 2011), leveling (Wu et al., 2019a, Wu et al., 2019b), Fiber Bragg Grating sensors (Marchenko et al., 2016), and Distributed Fiber Optic Sensors (Zhou et al., 2010). However, these methods only monitor and present the apparent information of ice and snow structures and are unable to evaluate structural damage, which is of great significance for the safety assessment of ice and snow structures.

The acoustic emission (AE) technique can effectively solve this problem. By detecting the stresses waves, AE can be used to monitor the internal damage of structures (Du et al., 2020; Verstrynge et al., 2021). It has been applied to many civil structures because of its high sensitivity and dynamic monitoring performance (Ghaib et al., 2018; Chen et al., 2020; Li et al., 2021). Some studies have shown that waveform-based analysis methods (Bhuiyan and Giurgiutiu, 2018; Barile et al., 2019a, Barile et al., 2019b; Das et al., 2019; Karimian et al., 2020; Yang et al., 2020) and parameter-based analysis methods (Moradian and Li, 2017; Al-Jumaili et al., 2018; Chai et al., 2018; Barile et al., 2019a, Barile et al., 2019b; Qiu et al., 2019; Wu et al., 2019a, Wu et al., 2019b; Ma and Du, 2020) of AE signals can effectively assess the damage state of different structures. The effectiveness of the AE technique has also been demonstrated for ice and snow structures. Datt et al. (2015) evaluated the damage process of snow samples using the b-value estimation and AE parameters. Li and Du (2016) monitored and evaluated the damage behavior of ice structures using the AE technique. The results indicate that AE parameters can be used to describe the damage and failure processes of ice structures and to distinguish between the various failure modes. Datt et al. (2020) evaluated the failure mode of ice beams using the AE technique and found that the failure of an ice beam under the bending load is dominated by a tensile crack. Lishman et al. (2020) analyzed the acoustic emission of sea ice in-situ compression and indentation experiments. The results show that AE can be used to evaluate the damage and healing process of natural sea ice in situ.

However, for Pykrete structures, owing to Pykrete's reinforcement components, there may be a gap between the AE characteristics of Pykrete and those of ice and snow. This study aimed to investigate the internal damage evolution of Pykrete under the most basic loading mode, uniaxial compression, using the AE technique, and compared the AE characteristics of Pykrete with those of its matrix. For the remainder of the paper, the experimental setup and data analysis method are presented first. Subsequently, the conventional AE parameters were analyzed and compared for both types of materials. Finally, further AE signal analysis methods were employed to evaluate the damage patterns of Pykretes and their matrices.