Exploring the micro-indentation behavior of mortar and aggregate samples exposed to low-power microwave energy

Abstract

Microwave heating presents a promising approach for repurposing waste concrete aggregates, leveraging its time efficiency and selective heating capabilities for complex materials. This study employs a micro-indentation test to investigate how low-power microwave radiation affects the micromechanical characteristics of recycled mortar-aggregate samples. The changes in properties, such as modulus and hardness under varying microwave exposure times, along with the influence of creep, are examined. The results indicate that with prolonged microwave exposure, the aggregate surface becomes stiffer and harder, a stark contrast to the mortar's weakening, attributed to the increased surface crystallinity of the aggregates as confirmed by X-ray diffraction (XRD) analysis. The mortar's softening is linked to the formation of micro-pores due to moisture evaporation. Additionally, while the aggregate surface showed improved creep modulus post-microwave treatment, the mortar samples displayed the opposite trend. However, both materials maintained a consistent creep recovery rate of about 50 % under different microwave heating conditions. These findings suggest that low-power microwave irradiation can selectively enhance the micromechanical properties of the aggregate surface while diminishing those of mortar, offering valuable insights into the micro-scale constitutive modeling of these materials with potential applications in separating aggregate from mortar in an industrial setting.