Analysis of Microwave-Induced Damage in Granite Aggregates Influenced by Mineral Texture

Abstract

The use of microwave energy to recycle high-quality coarse aggregates from waste concrete or assist hard rock breakage in underground building engineering is promising. Controlling or promoting the damage of coarse aggregates, i.e., hard rocks, under microwave irradiation is a crucial issue faced by these techniques. Understanding the damage mechanisms of hard rocks exposed to microwaves is thus urgent. Fracture toughness is a significant mechanical parameter of rocks that reflects their ability to resist crack propagation and damage evolution. In this study, the fracture toughness degradation of microwave-heated granite was investigated by combining experimental investigations and numerical simulations. A three-point-bending (TPB) experiment was conducted on granite specimens after microwave irradiation. A coupled electromagnetic–thermal–mechanical model considering the actual mineral texture of the granite specimen was established. The evolution of the temperature gradient and stress field near the initial notch tip were investigated. The results suggest that the microwave-induced maximum temperature gradient and stress in granite are at the plagioclase–quartz (Pl–Qtz) interfaces or inside the Pl near the boundary. The region of cracking initiation was defined as the damage zone, which could be obtained by comparing the microwave-induced thermal stress with the critical value. The fracture toughness degradation, which corresponds to the evolution of the damage zones, can be divided into two stages. A relatively rapid decrease in fracture toughness in the first stage is primarily caused by the spread of the scattered damage zones along the Pl–Qtz interfaces; subsequently, a gentler fracture toughness degradation results mainly from the extension of the previous damage zones.

Analysis of the Effect of Loading Rate on Mechanical Properties of Fissured Rock Materials and Acoustic Emission Characteristic Parameters

“…From Figure 4, it is evident that the stress-strain curve distribution pattern of the prefabricated fissure specimens is similar to that of the intact specimens. Both exhibit four distinct stages: (I) initial crack closure stage, (II) elastic deformation to micro-elastic crack stability development stage, (III) unstable crack propagation stage, and (IV) post-peak failure stage [1,17].…”

“…In order to investigate the loading rate and the crack incli men crack initiation stress and penetration stress, the initiatio stress corresponding to the appearance of the first crack in the s tion stress is the stress corresponding to the penetration betw cracks [17], which is located in the distribution of the stress-str…”

“…In order to investigate the loading rate and the crack inclination angle on the specimen crack initiation stress and penetration stress, the initiation stress is defined as the stress corresponding to the appearance of the first crack in the specimen, and the penetration stress is the stress corresponding to the penetration between the two prefabricated cracks [17], which is located in the distribution of the stress-strain curve shown in Figure 8. Figure 9a shows the effect of loading rate v on the peak stress σC, crack σCi, and penetration stress σCC of the prefabricated slit specimen (α = 45°).…”