Recently, improvements in energy efficiency have become a worldwide strategy for limiting global CO₂ emissions and energy consumption. In the fields of civil and construction engineering, effort is being made to reduce energy consumption, as well as environmental pollution by recycling construction waste. Among these efforts over the last decade, engineers have conducted several investigations of insulating materials in order to reduce energy consumption in the production of construction materials. Insulating concrete is a type of material designed to reduce thermal conductivity in order to save operational energy. Insulating material generally contains numerous voids inside the specimen, and lightweight aggregates or air-entraining admixtures are used to secure the voids inside the materials. The voids and aggregates within insulating material play a particularly important role in determining the heat conduction and strength of the specimen.

Insulating concrete is designed to reduce heat conduction through entrained voids in the material. An insulating concrete specimen contains numerous voids, the spatial distribution of which strongly affects the physical properties of the material such as its thermal conductivity and strength. As the void ratio increases, the thermal performance of the material improves and the strength of the material decreases. Therefore, an appropriate method for examining the void distribution is necessary for better understanding the material behavior of insulating concrete specimens (Figure 1).

In this study, the effects of different types of recycled aggregates on the material properties of insulating concrete are investigated. Several types of recycled aggregates from removal concrete elements are utilized to generate a series of eco-friendly insulating concrete specimens. In addition, the effect of bio-based (organic) fibers on the concrete specimens is also examined. To investigate the inner structure of aggregates and concrete specimens, a micro-CT is utilized as a nondestructive method. The spatial distributions of the voids and aggregates within each specimen are characterized using probabilistic methods, and the thermal and mechanical properties of the specimens are also evaluated through real and numerical experiments in micro- and macro-scales. The obtained results demonstrate the effect of recycled, eco-friendly components on insulating concrete, and the systematic tools developed in this research can be utilized as an approach to developing high-performance insulating materials in the future.