Reuse of construction and demolition waste (CDW) fines as plant-growing substrate

The reuse of construction and demolition waste (CDW) is of great significance for the reasonable treatment of urban waste and the protection of soil. CDW fines less than 10 mm in size were used to explore the application in improving clay loam soil and as plant-growing media. Four sizes of CDW were mixed with clay loam soil in three mass proportions to plant 1-year-old Duranta repens seedlings with clay loam soil (C1) and 100% CDW fines (C2) as the controls. CDW fines application increased net carbon assimilation, leaf size, leaf nutrients, and plant growth with the best addition of 3–6 mm size and 35% mass proportion (T5) for clay loam. The branch number and leaf area in 3–6 mm group were 32.8% and 263.9% higher than those in C1, and 110.8% and 374.2% higher than those in C2. On average, the assimilation rate in T5 was 43.8% higher than that in the controls, while the respiration rate was 44.6% lower, indicating that plants in the T5 fixed more carbon. We suggest that CDW fines have the potential to be plant cultivation substrate and the addition ratio depends on the soil property. Our research provides an effective solution for the disposal of CDW fines.