In pursuit of carbon neutrality by 2050, the utilization of natural materials in construction has become indispensable. Among such resources, soil is ubiquitous, requires minimal maintenance, and can be molded into various forms. Historically, it has been widely used as a building material owing to its moisture-buffering capacity, thermal mass, insulation, recyclability, and fire resistance. Construction-generated soil has attracted attention as both a sustainable resource and a solution to problems associated with improper landfilling. Since 2021, our company has undertaken initiatives to reincorporate construction-generated soil into building materials, focusing on earthen wall applications.
This study aimed to clarify how soil origin, construction method, stabilizer type, and fiber reinforcement influence the physical properties and recyclability of earthen wall materials. Seven types of construction-generated soil collected from sites across Japan were characterized through particle size and loss-on-ignition tests. Specimens were then fabricated using two water-content-based methods: adobe, representing higher water content, and rammed earth, representing lower water content. Stabilizers examined included MgO, lime, and bittern, while fiber additives comprised straw, sawdust, bamboo fiber, and recycled paper. Greenhouse gas (GHG) emissions associated with each mixture were also estimated based on emission factors.
The results revealed that particle size distribution and construction method strongly affected compressive strength and shrinkage behavior. Adobe specimens generally exhibited higher water content, shrinkage, and strength compared to rammed earth, though the suitability of each method depended on soil fineness. Stabilizers enhanced durability but showed distinct trade-offs in shrinkage and thermal conductivity. Straw fibers improved both compressive and flexural strength while enhancing insulation, whereas recycled paper achieved the highest compressive strength but decomposed more slowly.
Overall, the findings suggest that appropriate matching of soil properties, construction method, and admixtures can enable effective utilization of construction-generated soil, contributing to sustainable building practices.