Recycled aggregates from construction and demolition wastes as alternative filling materials for highway subgrades in China

With the rapid advancement of urbanization in China, a huge amount of construction and demolition wastes (CDW) are generated. Recycling CDW into subgrade materials is a promising way to process these wastes, with significant environmental and economic benefits. But very little work has been done in this field. Therefore, based on a CDW subgrade construction case in Beijing, the physical and chemical properties of the CDW materials were analyzed. Then the construction procedures of the CDW subgrade were presented, and a series of tests (compaction degree test, settlement observation, Portable Falling Weight Deflectometer test) were carried out. At the same time, the effects of different loose paving thicknesses, cycles of strong vibration on the subgrade performances were assayed. Subsequently, grading analysis of the CDW particles, plate load test and Beckman beam deflection test were performed to evaluate the construction quality. According to the test results, the construction technologies of the CDW subgrade, such as the optimum loose paving thicknesses and cycles of strong vibration, were determined. And then, the post-construction settlement monitor and radar survey were conducted for subgrades filled with CDW and soil to further analyze the applicability of CDW. The results show that recycled CDW aggregates with proper grading and strict construction technologies perform well. The subgrade filled with recycled CDW has a smaller deformation than that of the soil subgrade. Finally, the life cycle assessments (LCA) of two treating schemes of CDW were conducted to analyze the environmental benifits: recycling utilization as subgrade materials and directly landfilling. If the subgrade is filled with the recycled CDW aggregates, CDW will be consumed in large quantities and the environmental impactions of eutrophication and ecotoxicity can be reduced obviously.